U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2010–5042

Prepared in cooperation with the

Massachusetts Executive Office of Environmental Affairs

Department of Conservation and Recreation

Effects of Water Use and Land Use on Streamflow and 

Aquatic Habitat in the Sudbury and 

Assabet River Basins, Massachusetts

Effects of Water Use and Land Use on 

Streamflow and Aquatic Habitat in the 

Sudbury and Assabet River Basins, 

Massachusetts

By Phillip J. Zarriello, Gene W. Parker, David S. Armstrong, and Carl S. Carlson

Prepared in cooperation with the 

Massachusetts Executive Office of Environmental Affairs 

Department of Conservation and Recreation

Scientific Investigations Report 2010–5042

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, 

natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod

To order this and other USGS information products, visit http://store.usgs.gov

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Zarriello, P.J., Parker, G.W., Armstrong, D.S., and Carlson, C.S., 2010, Effects of water use and land use on streamflow 

and aquatic habitat in the Sudbury and Assabet River Basins, Massachusetts: U.S. Geological Survey Scientific Investigations Report 2010–5042, 160 p.

ISBN 978 1 4113 2944 7
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................2

Purpose and Scope ..............................................................................................................................2

Description of the Sudbury and Assabet River Basins ..................................................................2

Population .....................................................................................................................................4

Climate...........................................................................................................................................4

Surface-Water Resources and Streamflow............................................................................4

Topography ...................................................................................................................................7

Surficial Geology..........................................................................................................................7

Wetlands .......................................................................................................................................7

Land use ........................................................................................................................................7

Water Withdrawals and Wastewater Returns .....................................................................11

 Stream Habitat ..........................................................................................................................11

Previous Studies .................................................................................................................................11

Acknowledgments.......................................................................................................................................14

References Cited..........................................................................................................................................14

Chapter 1—Simulated Effects of Water Use, and Projected Water-Use and 

Land-Use Change on Streamflow with a Precipitation-Runoff Model .................................17

Purpose and Scope ............................................................................................................................17

Time-Series Data ................................................................................................................................17

Climate.........................................................................................................................................18

Water Withdrawals and Wastewater Returns .....................................................................18

Streamflow .................................................................................................................................19

Precipitation-Runoff Model...............................................................................................................20

Functional Description of the HSPF Model ....................................................................................20

Representation of the Basin .............................................................................................................22

Development of Hydrologic Response Units ........................................................................24

Impervious Areas (IMPLNDs).........................................................................................24

Pervious Areas (PERLNDs) .............................................................................................24

Stream Reaches (RCHRES) ......................................................................................................29

Hydraulic Characteristics (FTABLEs).............................................................................29

Lakes and Impoundments ..............................................................................................29

Wetlands ............................................................................................................................29

Water Withdrawals and Wastewater Returns ............................................................32

Model Calibration................................................................................................................................32

Sudbury River at Ashland ........................................................................................................33

Sudbury River at Saxonville ....................................................................................................37

Assabet River at Maynard........................................................................................................37

Nashoba Brook near Acton ............................................................................................37

Hydrologic Flow Components and Water Budgets .......................................................................41

Sensitivity Analysis.............................................................................................................................44

Model Uncertainty and Limitations..................................................................................................46
iv

Simulated Effects of Water Use and Land Use on Streamflow...................................................47

Effects of Current Water Use on Streamflow .......................................................................48

Effects of Groundwater and Surface-Water Withdrawals on Streamflow......................53

Effects of Potential Water- and Land-Use Change on Streamflow...................................53

Potential Effects of Reactivating Production Wells near Lake Cochituate......................65

Summary...............................................................................................................................................70

References Cited.................................................................................................................................74

Chapter 2—Fish Communities, Stream Temperature, and Assessment of Minimum Streamflow 

Targets for Aquatic Habitat at Selected Sites in the Sudbury and Assabet River Basins, 

Massachusetts ...............................................................................................................................76

Purpose and Scope ............................................................................................................................76

Fish Communities................................................................................................................................76

Main-Stem River Fish Communities .......................................................................................77

Cold-Water Fishery Resources ...............................................................................................80

Stream Temperature...........................................................................................................................80

Determination and Assessment of Target Streamflows for Aquatic Habitat at 10 Riffle 

Sites.........................................................................................................................................84

Physically Based Streamflow Targets....................................................................................84

Whitehall Brook near Hopkinton....................................................................................87

Sudbury River near Hopkinton........................................................................................87

Sudbury River near Ashland ....................................................................................................90

Indian Brook near Hopkinton..........................................................................................91

Indian Brook near Ashland .............................................................................................91

Baiting Brook near Framingham ....................................................................................92

Assabet River near Westborough..................................................................................93

Danforth Brook at Hudson...............................................................................................93

Fort Meadow Brook near Hudson..................................................................................94

Elizabeth Brook near Stow.......................................................................................................95

Statistically Based Streamflow Targets.................................................................................96

Tennant Method................................................................................................................96

New England Aquatic Base Flow Method (ABF).........................................................96

Range of Variability Approach (RVA).............................................................................98

Comparison of Computed Target Flows .................................................................................99

Frequency and Duration Streamflows were below Target Flows ..................................101

Summary.............................................................................................................................................104

References Cited...............................................................................................................................108

Appendix 1. Partial Listing of the Hydrologic Simulation Program–FORTRAN (HSPF) 

Model Run File (uci).....................................................................................................................111

Appendix 2. Calibration of a One-Dimensional Channel Hydraulic Model (HEC-RAS) used to 

Determine Physically Based Target Flows at Six Riffle Reaches in the Sudbury River

Basin ..............................................................................................................................................123

Water-Surface-Profile Model ........................................................................................................124

Whitehall Brook near Hopkinton...........................................................................................125

Sudbury River near Hopkinton...............................................................................................127

Sudbury River near Ashland ..................................................................................................128

Indian Brook near Hopkinton.................................................................................................132
v

Indian Brook near Ashland ....................................................................................................135

Baiting Brook near Framingham ...........................................................................................136

Appendix 3. Indicators of Hydrologic Alterations (IHA) Computed from Long-Term (1960–2004) 

Daily Streamflows Simulated with the Hydrologic Simulation Program–FORTRAN (HSPF) 

without Withdrawals (NOWU) at 10 Riffle Reaches in the Sudbury and Assabet River 

Basins.............................................................................................................................................139

Indicators of Hydrologic Alteration (IHA) Statistics ...................................................................140

References Cited...............................................................................................................................140

Appendix 4. Duration and Frequency Long-Term (1960–2004) Daily Streamflow Simulated 

with the Hydrologic Simulation Program–FORTRAN (HSPF) with (AVGWU) and without 

(NOWU) Withdrawals were below Target Flows Determined by Six Standard-Setting 

Methods at 10 Riffle Sites in the Sudbury and Assabet River Basins .................................153

Frequency and Duration Simulated Streamflows were below Target Flows .........................154

References Cited...............................................................................................................................154

Figures

1. Map showing towns, streamgages, and climate stations in and near the Sudbury

and Assabet River Basins, Massachusetts..............................................................................3

2. Graph showing mean annual streamflow, water years 1942–2006, Assabet River at

Maynard, Massachusetts ...........................................................................................................6

3. Map showing elevation, simplified surficial geology, and major water withdrawals

and return flows in the Sudbury and Assabet River Basins, Massachusetts ....................8

4. Map showing forested and nonforested wetlands in the Sudbury and Assabet 

River Basins, Massachusetts .....................................................................................................9

5. Map showing land use classified from 1997 aerial photography in the Sudbury and

Assabet River Basins, Massachusetts ...................................................................................10

6. Simplified schematic representation of the Hydrologic Simulation

Program–FORTRAN inflows and outflows to a stream ........................................................23

7. Graph showing distribution of general Hydrologic Response Unit types for pervious 

area and impervious area used to develop the Hydrologic Simulation Program–

FORTRAN for the Sudbury and Assabet River Basins, Massachusetts ............................26

8. Map showing public water and sewer infrastructure in the Sudbury and Assabet

River Basins, Massachusetts. ..................................................................................................27

9. Map showing discretization of the stream reaches used in the Hydrologic

Simulation Program–FORTRAN model of the Sudbury and Assabet River Basins, 

Massachusetts............................................................................................................................30

10. Graphs showing annual (A) and monthly (B) precipitation variability in relation to

model error at streamgages on the Sudbury River at Ashland and Saxonville,

Assabet River at Maynard, and Nashoba Brook near Acton, Massachusetts, 

1993 to 2003..................................................................................................................................34

11. Graphs showing simulated flow in relation to observed and estimated flow for 

(A) daily mean, (B) mean monthly, (C) mean annual, (D) daily mean flow-duration 

curves, and (E) daily mean hydrographs, at Sudbury River at Ashland, 

Massachusetts, 1993 to 2003 ....................................................................................................36
vi

12. Graphs showing simulated flow in relation to observed flow for (A) daily mean, 

(B) mean monthly, (C) mean annual, (D) daily mean flow-duration curves, 

and (E) daily mean hydrographs, at Sudbury River at Saxonville, Massachusetts, 

1993 to 2003..................................................................................................................................38

13. Graphs showing simulated flow in relation to observed flow for (A) daily mean, 

(B) mean monthly, (C) mean annual, (D) daily mean flow-duration curves, 

and (E) daily mean hydrographs, at Assabet River at Maynard, Massachusetts, 

1993 to 2003..................................................................................................................................39

14. Graphs showing simulated flow in relation to observed flow for (A) daily mean, 

(B) mean monthly, (C) mean annual, (D) daily mean flow-duration curves, 

and (E) daily mean hydrographs, at Nashoba Brook near Acton, Massachusetts, 

1993 to 2003..................................................................................................................................40

15. Graphs showing mean annual 1993–2003 water-budget outflow components (A) in 

inches per acre and (B) in inches over the basin from each Hydrologic Response 

Unit simulated by the Hydrological Simulation Program–FORTRAN model of the 

Sudbury and Assabet River Basins, Massachusetts............................................................42

16. Graphs showing mean 1993–2003 March water-budget outflow components 

(A) in inches per acre and (B) in inches over the basin from each Hydrologic 

Response Unit simulated by the Hydrological Simulation Program–FORTRAN 

model of the Sudbury and Assabet River Basins, Massachusetts ....................................43

17. Graphs showing mean 1993–2003 August water-budget outflow components 

(A) in inches per acre and (B) in inches over the basin from each Hydrologic 

Response Unit simulated by the Hydrological Simulation Program–FORTRAN 

model of the Sudbury and Assabet River Basins, Massachusetts ....................................45

18. Graphs showing summary of 1993–2003 mean (A) annual, (B) March, 

and (C) August water-budget outflow components simulated by the Hydrological

Simulation Program–FORTRAN (HSPF) model of the Sudbury and Assabet River

Basins, Massachusetts. ...........................................................................................................46

19. Graphs showing daily mean flow-duration curves from long-term simulations 

with no withdrawals, average 1993–2003 withdrawals, groundwater-only 

withdrawals, and surface-water-only withdrawals at (A) Jackstraw Brook, 

(B) Piccadilly Brook, (C) Ashland Reservoir Outle, and (D) Lake Cochituate outlet, 

upper Sudbury River Basin, Massachusetts..........................................................................50

20. Map showing percent change in the simulated long-term mean annual

streamflows with average 1993–2003 withdrawals relative to no withdrawals 

in the upper Sudbury River Basin, Massachusetts...............................................................52

21. Map showing percent change in the simulated long-term median of the August

mean streamflows with average 1993–2003 withdrawals relative to no withdrawals

in the upper Sudbury River Basin, Massachusetts...............................................................53

22. Graph showing daily mean flow-duration curves from long-term simulations with

no withdrawals and average 1993–2003 withdrawals, at Indian Brook, upper

Sudbury River Basin, Massachusetts .....................................................................................54

23. Map showing percent change in the simulated long-term median of the August

mean flows with average 1993–2003 groundwater withdrawals relative to no

withdrawals in the upper Sudbury River Basin, Massachusetts .......................................55

24. Map showing percent change in the simulated long-term median of the August

mean flows with average 1993–2003 surface-water withdrawals relative to no

withdrawals in the upper Sudbury River Basin, Massachusetts .......................................56

25. Maps showing generalized land use as (A) classified from 1997 interpreted 1:25,000

aerial photographs, and (B) projected 2030 buildout analysis by the Metropolitan

Area Planning Council, upper Sudbury River Basin, Massachusetts................................58
vii

26. Map showing percent change in the simulated long-term median of the August

mean flows with estimated 2030 water withdrawals distributed among existing

supply sources relative to no withdrawals in the upper Sudbury River Basin,

Massachusetts............................................................................................................................61

27. Map showing percent change in the simulated long-term median of the August

mean flows with estimated 2030 water withdrawals dispersed among self-supply

sources and a 20-percent consumptive use relative to no withdrawals in the upper

Sudbury River Basin, Massachusetts .....................................................................................62

28. Map showing percent change in the simulated long-term median of the August

mean flows with estimated 2030 land use and water withdrawals distributed among

existing supply sources relative to no withdrawals in the upper Sudbury River Basin,

Massachusetts............................................................................................................................63

29. Map showing percent change in the simulated long-term median of the August

mean flows with estimated 2030 land use and water withdrawals dispersed among

self-supply sources with a 20-percent consumptive loss relative to no withdrawals

in the upper Sudbury River Basin, Massachusetts...............................................................64

30. Graphs showing mean August water-budget outflow components by Hydrologic

Response Unit simulated by the Hydrological Simulation Program–FORTRAN in

upper Indian Brook under (A) 1997 land use and (B) projected 2030 land use, upper

Sudbury River Basin, Massachusetts .....................................................................................66

31. Graphs showing mean August water-budget outflow components by Hydrologic

Response Unit simulated by the Hydrological Simulation Program–FORTRAN in

Course Brook under (A) 1997 land use and (B) projected 2030 land-use conditions,

upper Sudbury River Basin, Massachusetts..........................................................................67

32. Graphs showing daily mean flow-duration curves developed from 1960–2004

simulated flows under no withdrawals, average 1993–2003 withdrawals, and

reactivating production wells north of Lake Cochituate assuming water is induced

infiltration from or captured baseflow to Lake Cochituate only, Sudbury River only,

one third of the water is from Lake Cochituate and two thirds is from Sudbury River,

and two thirds of the water is from Lake Cochituate and one third is from Sudbury

River (BIR-LC66) at (A) Lake Cochituate outlet, and (B) Sudbury River at Saxonville,

upper Sudbury River Basin, Massachusetts..........................................................................69

33. Graphs showing daily mean stage of Lake Cochituate in 1999 simulated under no

withdrawals, average 1993–2003 withdrawals, and reactivating production wells

north of Lake Cochituate assuming water is induced infiltration from or captured

baseflow to Lake Cochituate only, Sudbury River only, one third of the water is from

Lake Cochituate and two thirds is from Sudbury River, and two thirds of the water is

from Lake Cochituate and one third is from Sudbury River, upper Sudbury River

Basin, Massachusetts ...............................................................................................................71

34. Photo showng Massachusetts Department of Fish and Game, Division of Fisheries

and Wildlife barge electrofishing to assess river-fish community composition..............77

35. Map showing main-stem fish-sampling sites, cold-water fishery reaches,

stream-temperature gages, and riffle study locations in the Sudbury and Assabet

River Basins, Massachusetts ...................................................................................................78

36. Pie charts showing proportion of the fish community comprised of fluvial

specialists, fluvial dependents, and macrohabitat generalists collected in the main

stem of the (A) upper Sudbury and (B) Assabet Rivers, Massachusetts..........................80

37. Graphs showing stream-water temperature recorded between August 2004 and

June 2006 in reaches unaffected by dams or withdrawals at (A) Jackstraw Brook

near Westborough, (B) Indian Brook near Hopkinton, and (C) Baiting Brook near

Framingham, Sudbury River Basin, Massachusetts.............................................................82
viii

38. Graphs showing stream-water temperature recorded between August 2004 and

June 2006 in reaches below dams or withdrawals, or both, at (A) Whitehall Brook

near Hopkinton, (B) Sudbury River near Hopkinton, (C) Sudbury River near Ashland,

and (D) Cold Spring Brook near Ashland, Sudbury River Basin, Massachusetts............83

39. Cross sections showing riffle-reach study section showing (A) position of

cross-section surveys, (B) cross-section profiles, (C) elevation and wetted

perimeter relation, and (D) streamflow and wetted perimeter, Fort Meadow Brook

near Hudson, Massachusetts...................................................................................................86

40. Photo showing downstream view of riffle on Whitehall Brook at Fruit Street near

Hopkinton, Massachusetts .......................................................................................................87

41. Photo showing upstream view of riffle on Sudbury River at Fruit Street near 

Hopkinton, Massachusetts .......................................................................................................90

42. Photo showing downstream view of riffle on Sudbury River near Ashland,

Massachusetts............................................................................................................................90

43. Photo showing upstream view of riffle from bridge on Indian Brook near Hopkinton,

Massachusetts............................................................................................................................91

44. Photo showing downstream view of riffle on Indian Brook near Ashland,

Massachusetts............................................................................................................................92

45. Photo showing upstream view of riffle on Baiting Brook near Framingham,

Massachusetts............................................................................................................................92

46. Photo showing downstream view of riffle on Assabet River near Westborough,

Massachusetts............................................................................................................................93

47. Photo showing upstream view of riffle on Danforth Brook at Hudson, 

Massachusetts............................................................................................................................94

48. Photo showing upstream view of riffle on Fort Meadow Brook near Hudson,

Massachusetts............................................................................................................................94

49. Photo showing downstream view of riffle on Elizabeth Brook near Stow,

Massachusetts............................................................................................................................95

50. Boxplots showing variation in target flows determined by standard-setting methods 

at 10 riffle sites in the Sudbury and Assabet River Basins, Massachusetts ..................100

51. Graph showing median and quartiles of the monthly median flow in comparison to

standard-setting method target flows determined at 10 riffle sites in the Sudbury

and Assabet River Basins, Massachusetts..........................................................................102

52. Boxplots showing frequency and duration that long-term streamflows simulated

with the Hydrologic Simulation Program–FORTRAN with and without withdrawals

were below target flows determined by six standard-setting methods at 10 riffle

sites in the Sudbury and Assabet River Basins, Massachusetts .....................................103

Tables

1. Population and percent change in population in towns in or partially within the

Sudbury and Assabet River Basins, Massachusetts..............................................................5

2. Registered and permitted water withdrawals from 1993 to 2003 in the Sudbury and

Assabet River Basins, Massachusetts. .................................................................................12

3. Wastewater returns from 1993 to 2003 from public-sewer systems in the Sudbury

and Assabet River Basins, Massachusetts............................................................................14
ix

4. General contents and organization of the Watershed Data Management (WDM)

database.......................................................................................................................................18

5. Streamgages in the Sudbury and Assabet River Basins, Massachusetts .......................19

6. Correlation of partial-record stations in the Sudbury and Assabet River Basins to

index streamgages .....................................................................................................................21

7. Hydrologic Response Units (HRUs) used to develop the Hydrologic Simulation

Program–FORTRAN (HSPF) model for the Sudbury and Assabet River Basins,

Massachusetts............................................................................................................................25

8. Estimated average 1993–2003 annual and spring inflow and infiltration (I&I) into

public sewers by town in the Sudbury and Assabet River Basins, Massachusetts .......28

9. Subbasins and reaches (RCHRES) used in the Hydrologic Simulation

Program–FORTRAN (HSPF) model of the Sudbury and Assabet River Basins,

Massachusetts............................................................................................................................31

10. Model-fit statistics calculated from observed flows and Hydrologic Simulation

Program–FORTRAN (HSPF) simulated flows at four streamgages in the Sudbury

and Assabet River Basins, Massachusetts, 1993 to 2003 ....................................................35

11. Summary of model-run files (uci) and target data-set numbers (DSNs) for output of

Hydrologic Simulation Program–FORTRAN (HSPF) results of the Assabet and

Sudbury River Basin, Massachusetts .....................................................................................48

12. Water-use change by reach from average 1993–2003 withdrawals to projected

2030 demands simulated in the Hydrologic Simulation Program–FORTRAN (HSPF)

model of the Sudbury and Assabet River Basins, Massachusetts ....................................49

13. Summary of Hydrologic Response Unit (HRU) changes simulated in the Hydrologic

Simulation Program–FORTRAN (HSPF) model of the upper Sudbury River Basin,

Massachusetts............................................................................................................................60

14. Summary of the frequency and duration the Lake Cochituate water levels fell

below the outflow spillway from 1961 through 2004 simulated with the Hydrologic

Simulation Program–FORTRAN (HSPF) under average 1993–2003 withdrawals

(AVGWU), without withdrawals (NOWU), and reactivating production wells north of

Lake Cochituate assuming water is induced infiltration or captured baseflow from

lake Cochituate only (BIR_LC), Sudbury River (BIR-SU) only, one third of the water

is from Lake Cochituate and two thirds is from Sudbury River (BIR-LC33), and two

thirds of the water is from Lake Cochituate and one third is from Sudbury River

(BIR-LC66), upper Sudbury River Basin, Massachusetts.....................................................70

15. Fish species and numbers captured at selected free-flowing reaches in the

mainstem of the Sudbury and Assabet Rivers, Massachusetts .........................................79

16. R2Cross method hydraulic criteria in relation to channel bankfull top width ..................84

17. Streamflow targets determined by the R2Cross and Wetted-Perimeter methods at

10 selected riffle sites in the Sudbury and Assabet River Basins, Massachusetts. .......88

18. Condition of aquatic habitat in relation to streamflow as a percentage of the mean

annual flow (QMA) described by Tennant (1976) for small streams in the Rocky

Mountain Region of the United States ....................................................................................96

19. Streamflow targets determined by the Tennant method as percentages of the

means of the mean-annual flows (QMA) computed from long-term (1960–2004)

simulated streamflow with the Hydrologic Simulation Program–FORTRAN with

no water use (NOWU) at 10 riffle sites in the Sudbury and Assabet River Basins,

Massachusetts............................................................................................................................97
x

20. Streamflow standards determined by the New England Aquatic Baseflow (ABF)

method from the median of the monthly mean flow (1960–2004) simulated with the

Hydrologic Simulation Program–FORTRAN (HSPF) with no water use (NOWU) at 10

riffle sites in the Sudbury and Assabet River Basins, Massachusetts..............................98

22. Summary of target flows determined by standard-setting methods at 10 riffle sites

in the Sudbury and Assabet River Basins, Massachusetts.................................................99

21. Quartiles of medians of the monthly mean streamflows determined from Hydrologic

Simulation Program–FORTRAN (HSPF) simulated flow (1960–2004) with no water

use (NOWU) at 10 riffle sites in the Sudbury and Assabet River Basins,

Massachusetts............................................................................................................................99

23. Median frequency and duration long-term (1960–2004) streamflows simulated with

the Hydrologic Simulation Program–FORTRAN (HSPF) with (AVGWU) and without

(NOWU) withdrawals were below target flows determined by four standard-setting

methods at seven riffle sites in the Sudbury and Assabet River Basins, 

Massachusetts..........................................................................................................................105
xi

Conversion Factors

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 0.4047 hectare (ha)

square foot (ft2

) 0.09290 square meter (m2)

square mile (mi2

) 259.0 hectare (ha)

Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3

) 

million gallons (Mgal) 3,785 cubic meter (m3

)

cubic foot (ft3

) 0.02832 cubic meter (m3) 

Flow rate

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

cubic foot per second per square 

mile [(ft3

/s)/mi2]

0.01093 cubic meter per second per square 

kilometer [(m3/s)/km2]

gallon per day (gal/d) 0.003785 cubic meter per day (m3

/d)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3

/s)

inch per acre per year (in/acre/yr) 0.006276 millimeter per square meter per 

year (mm/m2

/yr)

Transmissivity*

foot squared per day (ft2

/d) 0.09290 meter squared per day (m2/d) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F-32)/1.8

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

*Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times 

foot of aquifer thickness [(ft3

/d)/ft2]ft. In this report, the mathematically reduced form, foot 

squared per day (ft2/d), is used for convenience.
This page intentionally left blank.

xii
Introduction

1

Effects of Water Use and Land Use on Streamflow and 

Aquatic Habitat in the Sudbury and Assabet River Basins, 

Massachusetts

By Phillip J. Zarriello, Gene W. Parker, David S. Armstrong, and Carl S. Carlson

Abstract

Water withdrawals from surface-water reservoirs and 

groundwater have affected streamflow in the Sudbury and 

Assabet River Basins. These effects are particularly evident 

in the upper Sudbury River Basin, which prompted the need 

to improve the understanding of water resources and aquatic 

habitat in these basins. In 2004, the U.S. Geological Survey, in 

cooperation with the Massachusetts Department of Conservation and Recreation, developed a precipitation-runoff model 

that uses Hydrologic Simulation Program–FORTRAN (HSPF) 

to evaluate the effects of water use and projected future wateruse and land-use change on streamflow. As part of this study, 

the aquatic habitat in the basins and the effects of streamflow 

alteration also were evaluated. 

Chapter 1 of the report covers the development of the 

HSPF model that focuses on the upper Sudbury River Basin 

(106 square miles) but covers the entire Sudbury and Assabet 

River Basins (339 square miles). The model was calibrated to 

an 11-year period (1993–2003) using observed or estimated 

streamflow at four streamgages. The model was then used to 

simulate long-term (1960–2004) streamflows to evaluate the 

effects of average 1993–2003 water use and projected 2030 

water-use and land-use change over long-term climatic conditions. Simulations indicate that the average 1993–2003 withdrawals most altered streamflow relative to no withdrawals in 

small headwater subbasins where the ratios of mean annual 

withdrawals to mean annual streamflow are the highest. The 

effects of withdrawals are also appreciable in other parts of 

the upper Sudbury River Basin as a result of the perpetuation 

of the effects of large withdrawals in upstream reaches or in 

subbasins that also have a high ratio of withdrawal to streamflow. The simulated effects of potential 2030 water-use and 

land-use change indicate small decreases in flows as a result of 

increased water demands, but these flow alterations were offset as a result of decreased evapotranspiration associated with 

the loss of deep-rooted vegetation. Simulations of reactivating 

production wells near the north end of Lake Cochituate indicate pumping could substantially affect lake levels and flows 

at the lake outlet or in nearby reaches in the Sudbury River 

during periods of low flow, but the effects vary depending on 

the source of the water to the wells, which is largely unknown.

Chapter 2 of the report covers the fish-community assessment and comparison of streamflow-setting standards for 

protecting aquatic habitat. The fish-community assessment 

indicates the main stems of the Sudbury and Assabet Rivers 

are dominated by macrohabitat generalists. Water temperatures recorded in seven free-flowing reaches in the upper 

Sudbury River Basin at three sites unaffected by withdrawals 

or impoundments are generally suitable for cold-water fish; 

however, summer temperatures often rose to a level considered critical to long-term survival of brook trout. At four sites 

downstream from withdrawals or reservoirs, or both, summer 

water temperatures were often in the upper critical range for 

brook trout survival.

Physically and statistically based methods for determining streamflows for protecting aquatic habitat were applied 

at 10 selected riffle sites in the Sudbury and Assabet River 

Basins. Physically based methods, R2Cross and WettedPerimeter, use site-specific physical and hydraulic information and a one-dimensional hydraulics model, HEC-RAS, 

to determine flows that meet the criteria set forth by the 

method. The median flow that meets 2-of-3 of the R2Cross 

hydraulic criteria (percentage of bankfull wetted perimeter, 

average velocity, and mean depth) ranged from about 0.07 to 

0.72 cubic feet per second per square mile (ft3/s/mi2) with an 

overall median of about 0.24 ft3/s/mi2; the median WettedPerimeter target flow ranged from about 0.10 to 0.51 ft3

/s/mi2

with an overall median of about 0.25 ft3/s/mi2. Statistically 

based methods—Tennant, New England Aquatic Base Flow 

(ABF), and the Range-of-Variability Approach (RVA)—utilized HSPF simulated long-term streamflow (1960–2004) 

with no withdrawals to determine target flows or the monthly 

streamflow variability. The Tennant 30-percent of the mean 

annual flow (QMA) ranged from about 0.56 to 0.61 ft3/s/mi2

with an overall median of 0.58 ft3/s/mi2; the ABF low-flow 

target ranged from about 0.14 to 0.62 ft3/s/mi2 with an overall 

median of 0.32 ft3/s/mi2. The frequency and duration target 

flows were not met were evaluated using HSPF simulated 
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Introduction

2

flows with and without water withdrawals. The median annual 

duration and total number of days flows were below the target 

were about three times greater for statistically based standards 

(Tennant 30 QMA and ABF) than for physically based targets 

(Wetted-Perimeter and R2Cross 2-of-3 criteria). Overall, 

physically based target flows were slightly more sensitive to 

flow alterations than the statistically based target flows. 

Introduction

Water resources in the Sudbury and Assabet River Basins 

are of concern to Federal, State, and local government agencies, non-government organizations (NGOs), and citizens. 

Both basins are densely populated and have a long history 

of water alterations by industry, water supply, wastewater 

return flows, and other uses. These changes have altered the 

natural flow conditions and have affected aquatic habitats in 

the basins. 

 The effects of water withdrawals are particularly evident 

in the upper Sudbury River Basin during the summer when 

flows are naturally at their lowest. The Sudbury River Watershed Organization reported that a reach in the main stem of the 

upper Sudbury River went dry (Frederica Gillespie, Sudbury 

River Watershed Organization, written commun., June 2004). 

The Massachusetts Water Resource Commission (2001) classifies the upper Sudbury River Basin as moderately “stressed.” 

Additional land development could further degrade aquatic 

habitat in the Sudbury and Assabet River Basins. The Massachusetts Department of Environmental Protection (MADEP) 

regulates over 80 public-supply withdrawals and 5 wastewater 

return flows in these basins; in addition, the Massachusetts 

Water Resource Authority (MWRA) and the Massachusetts 

Department of Conservation and Recreation (MADCR) manage several reservoirs for recreation, flood control, and emergency water supply. The Metropolitan Area Planning Council 

(MAPC) has shown that permitted withdrawals in 2006 in the 

towns of Hopkinton, Ashland, Wayland, and Sudbury may not 

be sufficient to meet projected demands in 2030 (M. Pillsbury, 

Metropolitan Area Planning Council, written commun., 2006). 

In 2004, the U.S. Geological Survey (USGS) entered into 

a cooperative agreement with MADCR to improve the understanding of water resources and aquatic habitat in the Sudbury 

and Assabet River Basins. The study was also conducted in 

collaboration with MAPC, Massachusetts Division of Fisheries and Wildlife (MADFW), and other governmental and 

non-governmental stakeholders who share concern over the 

water resources and aquatic habitat in these basins. The study 

entailed the development of a precipitation-runoff model, 

using Hydrologic Simulation Program–FORTRAN (HSPF), 

to evaluate the effects of recent water use and projected 

water-use and land-use change on streamflow and to evaluate 

aquatic-habitat conditions in the basins. 

Purpose and Scope

This report includes information about the Sudbury and 

Assabet River Basin study area, climate, streamflow, water 

use, and the methods used to obtain the data. These data provide background information on water resources and aquatic 

habitat in the basin used in the development of the precipitation-runoff model and habitat analysis. Chapter 1 describes the 

development and calibration of the HSPF precipitation-runoff 

model for the Sudbury and Assabet River Basins. The model 

was developed to evaluate the effects of water withdrawals 

and wastewater return flows on streamflow and to simulate 

the effects of water-use and land-use change primarily for the 

upper Sudbury River Basin. Chapter 2 describes fish communities, stream-water temperature, and streamflow targets 

by standard-setting methods for aquatic-habitat protection in 

the upper Sudbury and Assabet River Basins. This chapter 

focuses primarily on streamflows for aquatic-habitat protection, part of which included use of flows simulated through 

the HSPF model for the Assabet and Sudbury River Basins. 

A more detailed description of the purpose and scope of the 

individual aspects of the study are provided in the respective 

report chapters.

Description of the Sudbury and Assabet River 

Basins

The Sudbury and Assabet River Basins are in eastern 

Massachusetts about 25 mi west of the Boston metropolitan area (fig. 1). The Sudbury River flows eastward from its 

headwaters and then northward from the USGS streamgage at 

Ashland (01097480) for about 33 mi until it joins the Assabet 

River to form the Concord River (fig. 1). The Assabet River, 

located to the west of the Sudbury River, generally flows in a 

northeasterly direction for about 30 mi to its confluence with 

the Sudbury River. The Sudbury River Basin (162 mi2) and the 

Assabet River Basin (177 mi2) comprise about 44 and 47 percent of the Concord River Basin drainage area, respectively. 

Thirty-one towns lie within or partially within the Sudbury and Assabet River Basins (fig. 1). The towns of Framingham and Southborough are completely within the Sudbury 

River Basin; portions of 16 other towns (Ashland, Concord, 

Holliston, Hopkinton, Hudson, Lincoln, Marlborough, Natick, 

Northborough, Stow, Sudbury, Sherborn, Upton, Wayland, 

Westborough, and Weston) are in the Sudbury River Basin. 

The towns of Acton, Hudson, Maynard, Northborough, and 

Stow are completely or nearly completely within the Assabet River Basin; portions of 14 other towns (Berlin, Bolton, 

Boylston, Boxborough, Carlisle, Clinton, Concord, Grafton, 

Littleton, Marlborough, Shrewsbury, Sudbury, Westford, and 

Westborough) are within the Assabet River Basin. Seven 

towns (Concord, Hudson, Marlborough, Northborough, Stow, 

Sudbury, and Westborough) straddle the drainage divide 

between the Sudbury and Assabet River Basins. 
Introduction

Introduction

3

Figure 1. Towns, streamgages, and climate stations in and near the Sudbury and Assabet River Basins, Massachusetts.

State Route 9

STATE 

INTERSTATE 90

INTERSTATE 495

STATE ROUTE 20

INTERSTATE 290

ROUTE 2

Sudbury

River

Assabet

River

Whitehall

Reservior

Foss

Reservior

Ashland

Reservior

Hopkinton

Reservior

Fort Meadow

Reservoir

Lake

Cochituate

Gates

Pond

Millham

Reservior Williams

Lake

Warners

Pond

Sandra

Pond

Cedar

Swamp

Sudbury

Reservior

Nagog

Pond

Lake

Boon

Chauncy

Lake

Stearnes

Reservior

A1

Reservior

UPTON

STOW

ACTON

HARVARD

CONCORD

BOLTON

SUDBURY

GRAFTON

HOPKINTON

NATICK

BERLIN

FRAMINGHAM

HOLLISTON

LITTLETON

CARLISLE

WAYLAND

SHERBORN

WESTFORD

MARLBOROUGH

WESTBOROUGH

HUDSON

ASHLAND

BOYLSTON

SHREWSBURY

LINCOLN

WESTON

NORTHBOROUGH

SOUTHBOROUGH

CLINTON

BOXBOROUGH

MAYNARD

EXPLANATION

Sudbury River Basin

Assabet River Basin

Continuous record 

01096880

01097000

Streamgage and number

Partial record 

01097300

01097000

01098530

01097480 01097450

01096945

01096853

01096880

01096600

01097540

01097468

01097481

01097466

01097469

01097459

01097460

KILOMETERS

MILES

10

10 2 3 4 5

0 2 4 6 8

71°40' 71°30' 71°20'

42°10'

42°20'

42°30'

Boston

Climate station First order

Daily precipitation only

Study area

MASSACHUSETTS

Worcester

Base from Massachusetts Executive Office of Energy and Environmental Affairs digital data;

EOTROADS_ARC, 1:5,000, 2006; HYDRO25K_ARC , 1:25,000, 2005; MAJPOND_POLY, 1:100,000, 1998; SUBBASINS_POLY, 1:25,000, 2007; TOWNS_POLY, 1:25,000, 2002

Polyconic projection. North American Datum of 1983

Massachusetts coordinate system mainland zone 1998;
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Introduction

4

Population

Collectively, the population of towns in, or partially 

within, the Sudbury and Assabet River Basins totaled nearly 

0.5 million in 2000 (U.S. Bureau of the Census, 2005). The 

2000 census town population (table 1) ranged from 4,200 

in Sherborn to 66,910 in Framingham in the Sudbury River 

Basin, and from 4,008 in Boylston to 36,255 in Marlborough 

in the Assabet River Basin. On average, town populations 

increased by 13 percent from 1990 to 2000 in both basins, but 

several towns were among the fastest growing in the state. 

These towns include Hopkinton, in the Sudbury River Basin, 

and Boxborough, in the Assabet River Basin, which increased 

in population by about 45 percent between 1990 and 2000. 

Towns with larger established urban areas experienced minor 

changes in population between 1990 and 2000; these included 

the towns of Clinton, Concord, Framingham, Hudson, and 

Maynard. The town of Harvard experienced about a 50-percent decrease in population between 1990 and 2000 because of 

a military-base closure.

Populations within basins were estimated from the 

intersection of census tract data, land-use data, and the basin 

boundary. In 2000, an estimated 185,200 people lived in the 

Sudbury River Basin and 129,000 people lived in the Assabet River Basin (table 1). Average 2000 town population in 

the Sudbury River Basin was about 40 percent greater than 

in the Assabet River Basin. Population per unit area in the 

Sudbury River Basins (1,140 people/mi2

) was estimated to 

be about 60 percent greater than in the Assabet River Basin 

(730 people/mi2). 

Climate

Climate information was compiled from the National 

Weather Service (NWS) station in Worcester, the closest 

first-order weather station located about 22 mi southwest 

from the center of the Sudbury and Assabet River Basins 

(fig. 1). Monthly precipitation from 1892 to 2002 at this 

station (National Oceanic and Atmospheric Administration, 

2009b) had a mean and median annual precipitation of 43.1 

and 41.8 in., respectively. During that period, the recorded 

minimum and maximum annual rainfall ranged from 27.9 to 

71.7 in., respectively. Monthly mean precipitation during 1892 

to 2002 was generally evenly distributed throughout the year 

(standard deviation was 0.23 in.), but varied from 3.04 in. in 

February to 3.88 in. in November. During 1993 to 2002, the 

period that is nearly coincident with the model calibration 

period (1993 to 2003), the mean and median annual precipitation was 42.1 and 43.0 in., respectively.

Mean annual air temperature from 1892 to 2002 

(National Oceanic and Atmospheric Administration, 2009a) 

was 48°F; minimum and maximum monthly mean temperature 

ranged from 25°F in January and February to 70°F in July. 

During 1993 to 2002, the mean annual, mean monthly, and 

minimum and maximum mean monthly temperatures were 

nearly identical to the long-term values.

Annual snowfall reported at the Worcester NWS station 

over the 1892 to 1996 period (National Oceanic and Atmospheric Administration, 2009c) averaged 58 in. and ranged 

from 17 to 120 in. Snowfalls reported in 1997 through 2002 

are suspect, or were not reported, and were not included in the 

summary. During the 1993–96 period, average snowfall was 

above normal (78 in/yr), but the range (25 to 100 in/yr) was 

nearly identical to the long-term range. 

Surface-Water Resources and Streamflow

Utilization of surface-water resources for mill power and 

water supply in the Sudbury and Assabet River Basins has a 

long history dating back to the 1700s. Impoundments constructed to utilize water resources vary in size and influence on 

streamflow in the basin. The upper Sudbury River Basin was 

once a major source of drinking water for the Boston metropolitan area. During the mid to late 1800s, eight reservoirs 

were built in the basin to meet the rapidly growing demand 

for water. These reservoirs include Lake Cochituate, Ashland, 

Hopkinton, Whitehall, Sudbury, Foss, Brackett, and Stearns 

Reservoirs. Soon after these water resources were completed, 

it was realized that additional sources of water were needed 

to meet Boston’s growing demand, which lead to the development of two major reservoirs outside of the basin—Wachusett 

Reservoir to the northwest that began filling in 1905 followed 

by the Quabbin Reservoir to the west that began filling in 1939 

(Massachusetts Water Resources Authority, 2008). After the 

Quabbin Reservoir was constructed, water from the Sudbury 

system (Cochituate, Sudbury, Foss, Brackett, and Stearns Reservoirs) was no longer needed and was of less desirable quality. Whitehall, Hopkinton, Ashland, and Cochituate Reservoirs 

were turned into State Parks in 1947, and in 1976, the entire 

Sudbury system was officially reclassified as an emergency 

water supply. Today, only the Sudbury and Foss Reservoirs are 

classified as a reserve water supply by the MWRA (Massachusetts Department of Conservation and Recreation, 2008). 

Although withdrawals are no longer made from these reservoirs, their operation for recreation and maintenance can still 

affect streamflow in this part of the basin. Sandra Pond has 

been a public water supply for the town of Westborough since 

the late 1800s.

The Assabet River Basin contains several water-supply 

reservoirs—Lake Williams and Millham Reservoir that, 

along with MWRA, supply water to the city of Marlborough, 

and Gates Pond that supplies water to the town of Hudson. 

A number of other reservoirs were built in the 18th and 19th 

centuries for mill power including Warner Pond in Concord, 

Lake Boon in Stow, and Fort Meadow Reservoir in Marlborough that are still regulated for recreational purposes. More 

recently built reservoirs, such as A1 in Westborough, provide 

flood control. 

Streamflow below impoundments can be directly altered 

by flow regulation and indirectly through evaporation losses. 

Natural features such as wetlands, which are extensive in parts 

of the basin, can similarly affect streamflow through storage 
Introduction

Introduction

5

Table 1. Population and percent change in population in towns in or partially within the Sudbury and Assabet River Basins, 

Massachusetts.

[Basin, A, Assabet, S, Sudbury; --, not determined separately by basin, the first set of numbers are the total for the town]

Town Basin U.S. Census town population Estimated 2000 

population in basin

Percent change 

1960 1970 1980 1990 2000 1960 to 2000 1990 to 2000

Acton A 7,238 14,770 17,544 17,872 20,331 20,300 181 14

Ashland S 7,779 8,882 9,165 12,066 14,674 13,400 89 22

Berlin A 1,742 2,099 2,215 2,293 2,380 2,380 37 3.8

Bolton A 1,264 1,905 2,530 3,134 4,148 2,630 228 32

Boxborough A 744 1,451 3,126 3,343 4,868 3,560 554 46

Boylston A 2,367 2,774 3,470 3,517 4,008 560 69 14

Carlisle A 1,488 2,871 3,306 4,333 4,717 1,600 217 8.9

Clinton A 12,848 13,383 12,771 13,222 13,435 1,320 4.6 1.6

Concord S 12,517 16,148 16,293 17,076 16,993 4,750 36 -0.5

Concord A -- -- -- -- -- 8,430 -- --

Framingham S 44,526 64,048 65,113 64,989 66,910 66,900 50 3.0

Grafton A 10,627 11,659 11,238 13,035 14,894 150 40 14

Harvard A 2,563 13,426 12,170 12,329 5,981 1,580 133 -52

Holliston S 6,222 12,069 12,622 12,926 13,801 0 122 6.8

Hopkinton S 4,932 5,981 7,114 9,191 13,346 10,200 171 45

Hudson S 9,666 16,084 16,408 17,233 18,113 220 87 5.1

Hudson A -- -- -- -- -- 17,900 -- --

Lincoln S 5,613 7,567 7,098 7,666 8,056 1,430 44 5.1

Littleton A 5,109 6,380 6,970 7,051 8,184 3,280 60 16

Marlborough S 18,819 27,936 30,617 31,813 36,255 24,200 93 14

Marlborough A -- -- -- -- -- 12,000 -- --

Maynard A 7,695 9,710 9,590 10,325 10,433 10,400 36 1.0

Natick S 28,831 31,057 29,461 30,510 32,170 15,600 12 5.4

Northborough S 6,687 9,218 10,568 11,929 14,013 0 110 18

Northborough A -- -- -- -- -- 14,000 -- --

Sherborn S 1,806 3,309 4,049 3,989 4,200 650 133 5.3

Shrewsbury A 16,622 19,196 22,674 24,146 31,640 11,500 90 31

Southborough S 3,996 5,798 6,193 6,628 8,781 8,780 120 32

Stow S 2,573 3,984 5,144 5,328 5,902 0 129 11

Stow A -- -- -- -- -- 5,900 -- --

Sudbury S 7,447 13,506 14,027 14,358 16,841 14,500 126 17

Sudbury A -- -- -- -- -- 2,320 -- --

Upton S 3,127 3,488 3,886 4,677 5,642 20 80 21

Wayland S 10,444 13,461 12,170 11,874 13,100 12,000 25 10

Westborough S 9,599 12,594 13,619 14,133 17,997 12,100 88 27

Westborough A -- -- -- -- -- 5,660 -- --

Westford A 6,261 10,368 13,434 16,392 20,754 3,510 232 27

Weston S 8,261 10,870 11,169 10,200 11,469 440 39 12
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Introduction

6

and evapotranspiration (ET) losses. In addition, withdrawals, 

diversions, and wastewater-treatment facility discharges can 

also affect streamflow. All these factors affect the observed 

streamflow to varying degrees at streamgages in the basin.

Streamflow has been continuously measured by the 

USGS at Assabet River at Maynard (01097000) since 1941, 

at Nashoba Brook near Acton (01097300) since 1963, and at 

Sudbury River at Saxonville (01098530) since 1979 (fig. 1). 

Streamflow has also been sporadically measured by the USGS 

at Sudbury River at Ashland (01097480) with a continuous 

streamgage operating from April 1994 through October 1995, 

May 2004, October 2004 through May 2005, and October 2006 

through July 2009. 

Assabet River at Maynard (01097000), hereafter referred 

to as the Maynard streamgage, is the only long-term monitoring 

streamgage on the main stem of the Assabet River. Drainage 

area to the Maynard streamgage is 114 mi2 and covers about 

64 percent of the Assabet River Basin area. Annual streamflow 

at the Maynard streamgage over the period of record (water 

years 1942–2006; a water year spans from October 1 through 

September 30) averaged 192 ft3/s (1.66 ft3/s/mi2) and ranged 

from 73 to 320 ft3/s; during water years 1993 to 2003, annual 

flow averaged 200 ft3/s (1.75 ft3/s/mi2) and ranged from 88 to 

286 ft3/s. Mean annual flow at the Maynard streamgage (fig. 2) 

tended to increase over the period of record as indicated by the 

Loess line (Cleveland and Devlin, 1988); part of this increase 

is attributed to increased discharge of treated wastewater above 

the streamgage over the period of record. 

Nashoba Brook near Acton (01097300), hereafter 

referred to as the Nashoba streamgage, has provided longterm streamflow information on one of the main tributaries in the northern part of the Assabet River Basin since 

1963. Drainage area to the Nashoba streamgage is 12.8 mi2

and covers about 7 percent of the Assabet River Basin 

area. Mean annual flow at Nashoba streamgage over the 

period of record (water years 1964–2006) averaged 20 ft3/s 

(1.60 ft3/s/mi2) and ranged from 7.1 to 36 ft3/s. During 

water years 1993–2003, annual flow averaged about 19 ft3/s 

(1.46 ft3/s/mi2) and ranged from 10 to 25 ft3/s. The reason the 

Nashoba streamgage has a lower mean annual flow per unit 

area relative to the Assabet and Saxonville streamgages is 

believed to be related to a higher percentage of wetlands and 

a lower percentage of sand and gravel deposits relative to the 

other basins.

Sudbury River at Saxonville (01098530), hereafter 

referred to as the Saxonville streamgage, is the only longterm continuously operated streamgage in the Sudbury 

River Basin. The 106-mi2 drainage area to the Saxonville 

streamgage, which includes the Sudbury reservoir system, 

covers about 65 percent of the Sudbury River Basin area. 

Mean annual flow at Saxonville streamgage over water years 

1981–2006 averaged 200 ft3/s (1.89 ft3/s/mi2) and ranged 

from 90 to 281 ft3/s. During water years 1993–2003, annual 

flow averaged 194 ft3/s (1.83 ft3/s/mi2) and ranged from 90 to 

241 ft3/s. The record low mean annual flow (90 ft3/s) occurred 

during the 2002 water year.

1940 1950 1960 1970 1980 1990 2000 2010

WATER YEAR

0

100

200

300

400

STREAMFLOW, IN CUBIC FEET PER SECOND

Mean for period of record

Loess smoothed line

Figure 2. Mean annual streamflow, water years 1942–2006, Assabet River at Maynard, Massachusetts.
Introduction

Introduction

7

Topography

The Sudbury and Assabet River Basins are in the coastal 

lowlands near the border with the central highlands along the 

southwestern portion of the basin (Denny, 1982). The central 

lowlands are characterized by low relief with gently rolling 

hills that is more prevalent on the eastern side of the basins, 

particularly the Sudbury River Basin (fig. 3, inset). The hillier 

terrain more common in the central highlands is more prevalent in the southwestern part of the basin, particularly in the 

Assabet River Basin, which lies further to the west. Drumlins, 

low hills of glacial origin, are found throughout the region. 

The Sudbury River drops from a maximum elevation of 

about 700 ft to about 100 ft at its confluence with the Assabet 

River. Along its 33 mi length, the river gradient averages about 

5.2 ft/mi, but low-gradient reaches are common in wetlands 

and reservoirs found in many reaches. Upstream from the Saxonville streamgage, the river gradient averages about 9.0 ft/mi; 

downstream from the Saxonville streamgage, the river gradient flattens and averages about 1.4 ft/mi. 

The Assabet River Basin is topographically similar to the 

Sudbury River Basin. The Assabet River drops from a maximum elevation of about 750 ft to about 100 ft at its confluence with the Sudbury River. Over its 32 mi length, the river 

gradient averages about 6.8 ft/mi, but low-gradient reaches 

behind impoundments are common. The river gradient flattens 

considerably below the Maynard streamgage. 

Surficial Geology

Most of the uplands in the Sudbury and Assabet River 

Basins are glacial till with areas of fine- and coarse-grained 

glacial deposits in the valleys (Flanagan and others, 1999). 

The valley fill was deposited mostly by meltwater from the 

last glacial retreat that are stratified by the sorting processes 

that occurred during transport. Often, the coarse-grained sand 

and gravel deposits are interspersed with fine sands, silts, and 

clays that were deposited in temporary pools and lakes during the glacial retreat (Brackley and Hansen, 1985). Hence, 

valley-fill deposits are often discontinuous and heterogeneous, 

but typically provide the most productive aquifers in the basin 

(DeSimone, 2004). 

Valley-fill glacial sands and gravels are more extensive 

toward the mouths of the basins (fig. 3). These deposits are 

upwards of 160 ft thick, but typically are less than 75 ft thick 

with an average thickness of about 35 ft in the Assabet River 

Basin (Brackley and Hansen, 1985; DeSimone, 2004). Glacial 

valley-fill deposits are overlain by recent fine-grained alluvial 

deposits along stream and river channels. For the purposes 

of this study, the alluvial deposits were grouped with the 

sand and gravel deposits because they are generally thin and 

comprise only a small percentage of the basin area. Sand and 

gravel compose about 52 and 40 percent of the Sudbury and 

Assabet River Basin areas, respectively. 

Till is also a glacial deposit that consists of a heterogeneous mix of clays, sands, pebbles, cobbles, and boulders. 

Tills commonly blanket upland areas (fig. 3) and are typically 

thin with low transmissive properties limiting their use as a 

water supply even for single-family homes. In steep upland 

areas, bedrock outcrops are also present. Areas classified as till 

and bedrock comprise about 48 and 60 percent of the Sudbury 

and Assabet River Basin areas, respectively. 

Wetlands

Wetlands are a prominent hydrological feature in the Sudbury and Assabet River Basins (fig. 4). Wetland information 

obtained from Massachusetts Geographic Information System 

(2007) was simplified into two groups, forested and nonforested, for this study. Forested wetlands are wooded swamps 

with deciduous trees, coniferous trees, or both. Nonforested 

wetlands include bogs, shallow marsh, meadow or fen, and 

shrub swamp. 

Collectively, wetlands cover about 13 percent of the basin 

area and are about equally distributed between the Sudbury 

and Assabet River Basins. Forested wetlands are the most 

prevalent, covering about 10.5 and 9.8 percent of Sudbury and 

Assabet River Basin area, respectively; nonforested wetlands 

cover about 2.5 and 2.8 percent of the Sudbury and Assabet 

River Basin area, respectively. Upstream from the Saxonville 

streamgage, about 10.6 percent of the basin area is wetland, of 

which 8.9 percent is forested and 1.7 percent is nonforested. 

Upstream from the Ashland streamgage, about 13.8 percent of 

the basin area is wetland, of which 11.9 percent is forested and 

1.9 percent is nonforested. Cedar Swamp, an extensive mostly 

nonforested wetland, comprises about half of the wetland 

area above Ashland streamgage. Wetlands upstream from 

the Maynard streamgage comprise about 11.6 percent of the 

basin area. 

Land use

Land-use information classified from 1997, 1:25,000 

scale aerial photographs was obtained from Massachusetts 

Geographic Information System (2009). In general, the 

Sudbury and Assabet River Basins are considered urbanized 

with about 29 percent of the basin area classified as residential 

(fig. 5). About 38 percent of the basin area was classified as 

forested with most of the undeveloped area in the western part 

of the Assabet River Basin. 

In the Sudbury River Basin, land use was classified as 

about 33 percent forested, 32 percent residential, 10 percent 

forested wetlands, 9 percent open, 8 percent commercial, 

industrial, and transportation, 5 percent open water, and 2 percent nonforested wetland. Above the Saxonville streamgage, 

a greater percentage of the basin area (about 11 percent) is 

classified as commercial, industrial, and transportation because 

of the highly developed area along the Route 9 corridor and 

Interstates 90 and 495. 
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Introduction

8

Figure 3. Elevation, simplified surficial geology, and major water withdrawals and return flows in the Sudbury and Assabet 

River Basins, Massachusetts.

KILOMETERS

MILES

10

0 5

0

800

100

Elevation, in feet above

North American Vertical

Datum of 1988

STATE ROUTE 9

STATE 

INTERSTATE 90

INTERSTATE 495

STATE ROUTE 20

INTERSTATE 290

ROUTE 2

Sudbury

River

Assabet

River

Whitehall

Reservior

Foss

Reservior

Ashland

Reservior

Hopkinton

Reservior

Fort Meadow

Reservoir

Lake

Cochituate

Gates

Pond

Millham

Reservior

Williams

Lake

Warners

Pond

Sandra

Pond

Sudbury

Reservior

Nagog

Pond

Lake

Boon

Chauncy

Lake

Stearnes

Reservior

EXPLANATION

Streamgage 

Sand and gravel

Till and bedrock

Groundwater withdrawal

Surface-water withdrawal

Wastewater return

KILOMETERS

MILES

10

10 2 3 4 5

0 2 4 6 8

71°40' 71°30' 71°20'

42°10'

42°20'

42°30'

Base from Massachusetts Executive Office of Energy and Environmental Affairs, IMG_ELEV5K_I, 1:5,000, 2005; SURFGEO250K_POLY, 1:250,000, 1999, PWSDEP_PT, 2002

Polyconic projection. North American Datum of 1983

Massachusetts coordinate system mainland zone
Introduction

Introduction

9

Figure 4. Forested and nonforested wetlands in the Sudbury and Assabet River Basins, Massachusetts.

Nonforested wetland

Forested wetland

STATE ROUTE 9

STATE 

INTERSTATE 90

INTERSTATE 495

STATE ROUTE 20

INTERSTATE 290

ROUTE 2

Sudbury

Assabet

River

River

Cedar

Swamp

EXPLANATION

Streamgage 

Open water

KILOMETERS

MILES

10

10 2 3 4 5

0 2 4 6 8

71°40' 71°30' 71°20'

42°10'

42°20'

42°30'

Base from Massachusetts Executive Office of Energy and Environmental Affairs, WETLANDSDEP_POLY, 1:12,000, 2007

Polyconic projection. North American Datum of 1983

Massachusetts coordinate system mainland zone
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Introduction

10

Figure 5. Land use classified from 1997 aerial photography in the Sudbury and Assabet River Basins, Massachusetts.

Agriculture

Mining

Open land

Forest

Recreation

Commercial, industrial, and transportation

Low-density residential

Moderate-density residential

High-density residential

Wetlands

Open water

Sudbury

Assabet

River

River

EXPLANATION

Streamgage INTERSTATE 495

STATE 

STATE ROUTE 2

INTERSTATE 90

STATE ROUTE 9

ROUTE 20

INTERSTATE 290

Kilometers

Miles

10

10 2 3 4 5

0 2 4 6 8

71°40' 71°30' 71°20'

42°10'

42°20'

42°30'

Base from Massachusetts Executive Office of Energy and Environmental Affairs, LANDUSE_POLY, 1:25,000, 1999

Polyconic projection. North American Datum of 1983

Massachusetts coordinate system mainland zone
Introduction

Introduction

11

In the Assabet River Basin, land use was classified as 

about 42 percent forested, 26 percent residential, 10 percent 

forested wetlands, 10 percent open, 6 percent commercial, 

industrial, and transportation, 3 percent water, and 3 percent 

nonforested wetland. The largest differences in land use 

between the Sudbury River and Assabet River Basins are in 

the size of the forested and residential areas. 

Water Withdrawals and Wastewater Returns

Data on registered and permitted municipal withdrawals and non-municipal withdrawals (non-public supplies that 

withdraw more than 100,000 gal/d) were obtained directly 

from the supplier or from MADEP for the 1993–2003 period. 

Withdrawals are mostly for municipal water supply (table 2); 

withdrawals include 33 from groundwater and 4 from surface 

water in the Sudbury River Basin and 32 from groundwater 

and 9 from surface water in the Assabet River Basin. These 

withdrawals provide all or part of the municipal water supply 

to 17 of the 31 towns in, or partly in, the Assabet and Sudbury 

River Basins. Most of the major supply wells are finished in 

sand and gravel. 

Registered and permitted non-municipal withdrawals are 

mostly for agriculture or golf course irrigation and are mostly 

in the town of Hopkinton. During the peak growing season 

(June through August), irrigation withdrawals composed up to 

a third of the total withdrawals in the Sudbury River Basin and 

up to 15 percent of the total withdrawals in the Assabet River 

Basin, but on average, municipal withdrawals account for 

most withdrawals. The total annual water withdrawals during 

1993–2003 averaged about 12 Mgal/d from the Sudbury River 

Basin and about 9 Mgal/d from the Assabet River Basin.

Treated wastewater is returned to the basin at five locations from different sewer districts operating within the Sudbury and Assabet River Basins—one outfall is in the Sudbury 

River Basin and four are in the Assabet River Basin (fig. 3). 

Two of the wastewater treatment plants (WWTPs), Marlborough West and Westborough, in the Assabet River Basin, 

are connected to regional wastewater systems. WWTPs in 

Hudson and Maynard in the Assabet River Basin, and Marlborough East in the Sudbury River Basin, service only their 

respective communities. 

Daily discharge records were obtained from the five 

WWTPs in the basin (table 3) and cross checked with the 

monthly wastewater discharges reported to the U.S. Environmental Protection Agency (USEPA) for the period January 

1, 1993, through December 31, 2003. Average annual return 

flows ranged from 0.8 to 5.0 Mgal/d at Maynard and Westborough, respectively. Monthly average return flows peaked 

in March and were generally lowest in August; the higher 

return flows in the spring reflect additional water that enters 

the sewer infrastructure through direct inflow and groundwater 

infiltration, which is referred to as I&I. Average March return 

flows accounted for 11 to 16 percent of the average annual 

return flows; average August return flows accounted for 2.7 to 

7.0 percent of the average annual return flows. Overall, annual 

wastewater discharge averaged 7.8 Mgal/d in the Sudbury 

River Basin and 12.4 Mgal/d in the Assabet River Basin. Thus, 

the average WWTP return flows to the Assabet River Basin are 

almost double the return flows to the Sudbury River Basin.

In addition to the direct effect of water withdrawals or 

return flows on streamflows, water and sewer systems can 

affect hydrology by importing or exporting water from a basin. 

Areas that import water are served by public water systems, 

but have on-site septic systems. Areas that export water 

are served by sewers that provide a conduit for I&I losses. 

Monthly records from wastewater treatment systems indicate 

that average March wastewater discharge increased by 30 to 

91 percent relative to the mean annual discharge. Early spring 

is typically the period of highest groundwater infiltration to the 

sewer system because this is typically when the groundwater 

table is at its seasonal high. 

 Stream Habitat

The stream habitats along much of the Sudbury and 

the Assabet Rivers are characterized by low-gradient, slowmoving channels with pools, glides, and runs. Riffles, characterized by fast, turbulent water, are few, in part because dams 

were built at riffles and other riffles were submerged by the 

impoundment. More riffles are located on the tributaries than 

on the main-stem reaches of the river because steeper stream 

gradients are more common. 

Previous Studies

Groundwater resources in the Assabet River Basin were 

investigated by DeSimone (2004). Information from Campbell (1925), Jahns (1953), Hansen (1956), Perlmutter (1962), 

Koteff (1966), Shaw (1969), Pollock and others (1969), Brackley and Hansen (1985), and Bratton and Parker (1995) was 

compiled to characterize the hydrogeology of the area. A number of small-scale hydrogeologic investigations by consultants 

were also compiled; these studies were typically undertaken 

for the purpose of locating water-supply sources, determining 

well-protection areas, locating groundwater contamination, or 

for specific development projects for towns. In addition to the 

hydrogeologic information, partial-record stations were established for low-flow studies by Ries (1993, 1994, 1999) and 

Ries and Friesz (2000). DeSimone (2004) reactivated many 

of these partial-record stations to provide estimates of baseflow from tributary streams to develop a groundwater-flow 

model of the Assabet River Basin used to evaluate the effects 

of water-management alternatives on baseflow. Many of these 

streamgages were reactivated again for this study.

Streamflow targets for protection of aquatic habitat were 

investigated by Parker and others (2004) at six sites in the 

Assabet River Basin. Water use in the Assabet, Concord, and 

Sudbury River Basins was compiled for 1996 through 2000 

by Barlow and others (2009). Colman and others (1999) and 

Waldron and others (2000) investigated total mercury and 
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Introduction

12

Table 2. Registered and permitted water withdrawals from 1993 to 2003 in the Sudbury and Assabet River Basins, 

Massachusetts.—Continued

[DSN, data-set number in Watershed Data Management (WDM) database; SWWD, DEPL, PUMP, WDM identification attribute (IDCONS) for surface-water 

withdrawal, streamflow depletion, and pumped groundwater well, respectively; Distance, length from the pumped well to nearest surface-water body in feet (ft); 

Mgal/d, million gallons per day; MDEP, Massachusetts Department of Environmental Protection; GW, groundwater; SW, surface water; --, not applicable]

Reach 

number Town Source Name

DSN

Distance 

(ft)

Annual 

average 

withdrawal 

1993–2003 

(Mgal/d)

MDEP identification 

or registration number SWWD 

or DEPL PUMP

Sudbury River Basin

1 Westborough GW Morse St. well 1011 2011 33 0.214 2328000-02G

1 Westborough GW Hopkinton Rd. well 1012 2012 7 0.263 2328000-01G

2 Westborough SW Sandra Pond 1021 -- -- 0.774 2328000-01S

3 Hopkinton GW McIntyre GP wells 4 and 5 1031 2031 768 0.234 2139000-04G, -05G

5 Hopkinton GW Fruit St. GP wells 1, 2, 3 1051 2051 62 0.482 2139000-01G, -02G, -03G

5 Westborough GW Industry well 1052 2052 1,250 0.008 21432803

8 Hopkinton GW Nursery (isolated irrigation 

ponds) 15, 16, 17, 18

1081 2081 2,500 0.001 21413902

8 Ashland GW Howe St. well 4, 5, 6, 8, 9 1082 2082 809 1.435 3014000-04G, -5G, -06G, 

-08G, -09G

9 Hopkinton GW Nursery (isolated irrigation 

pond) 14

1091 2091 3,000 0.001 21413902

10 Hopkinton SW Nursery (in-stream ponds 

and canals) 2, 3, 4, 6, 9, 13

1101 -- -- 0.003 21413902

10 Hopkinton GW Nursery (isolated irrigation 

ponds) 1, 5, 7, 8,10, 11

1102 2102 250 0.013 21413902

17 Natick GW Springvale well 1 1171 2171 565 0.354 3198000-01G

17 Natick GW Springvale wells 3, 4, 5 1173 2173 405 1.254 3198000-02G, -07G, -08G

17 Natick GW Evergreen wells 1 and 2 1172 2172 450 1.317 3198000-09G, -10G

31 Hudson GW Cranberry bog well 1311 2311 509 0.558 2141000-02G

31 Sudbury GW Hop Brook well and well 3 1312 2312 79 0.253 3288000-01G, 03G

31 Sudbury GW Well 8 1313 2313 302 0.152 3288000-08G

31 Sudbury GW Well 10 1314 2314 203 0.099 3288000-10G

32 Sudbury GW Well 2A 1321 2321 885 0.210 3288000-02G

32 Sudbury GW Well 4 1322 2322 400 0.149 3288000-04G

32 Sudbury GW Well 6 1323 2323 538 0.494 3288000-06G

32 Sudbury GW Well 7 1324 2324 217 0.301 3288000-07G

32 Sudbury GW Well 9 1325 2325 217 0.269 3288000-09G

33 Concord GW Jennie Dugan well 1331 2331 394 0.267 3067000-01G

33 Concord GW Deaconess well 1332 2332 328 0.671 3067000-03G

33 Concord GW White Pond well 1333 2333 951 0.194 3067000-04G

33 Concord GW Robinson well 1334 2334 315 0.164 3067000-06G

33 Sudbury GW Well 5 1335 2335 164 0.119 3288000-05G

33 Wayland GW Campbell well 1 1336 2336 144 0.152 3315000-02G

33 Wayland GW Happy Hollow well 1 1337 2337 623 0.320 3315000-03G

33 Wayland GW Happy Hollow well 2 1338 2338 866 0.457 3315000-04G

33 Wayland GW Meadowview well 1 1339 2339 886 0.155 3315000-05G

33 Wayland GW Baldwin Pond well 1 and 3 1340 2340 325 0.226 3315000-01G, -07G

33 Wayland GW Baldwin Pond well 2 1341 2341 280 0.243 3315000-06G

33 Concord GW Golf course (isolated 

irrigation pond)

1342 2342 800 0.003 31406708

33 Concord SW Golf course 1343 -- -- 0.003 31406702

33 Concord SW Farm withdrawal 1344 -- -- 0.001 31406707
Introduction

Introduction

13

Table 2. Registered and permitted water withdrawals from 1993 to 2003 in the Sudbury and Assabet River Basins, 

Massachusetts.—Continued

[DSN, data-set number in Watershed Data Management (WDM) database; SWWD, DEPL, PUMP, WDM identification attribute (IDCONS) for surface-water 

withdrawal, streamflow depletion, and pumped groundwater well, respectively; Distance, length from the pumped well to nearest surface-water body in feet (ft); 

Mgal/d, million gallons per day; MDEP, Massachusetts Department of Environmental Protection; GW, groundwater; SW, surface water; --, not applicable]

Reach 

number Town Source Name

DSN

Distance 

(ft)

Annual 

average 

withdrawal 

1993–2003 

(Mgal/d)

MDEP identification 

or registration number SWWD 

or DEPL PUMP

Assabet River Basin

51 Westborough GW Andrews I well 1511 2511 1,080 0.363 2328000-03G

51 Westborough GW Andrews II well 1512 2512 460 0.251 2328000-04G

51 Westborough GW Wilkinson well 1513 2513 1,290 0.113 2328000-06G

52 Shrewsbury GW South St. well 1521 2521 187 0.001 2271000-01G

52 Northborough GW Farm well 1522 2522 1,170 0.001 21428601

52 Northborough GW Nursery well 1523 2523 1,200 0.004 21421502

53 Northborough GW Crawford St. well 1531 2531 200 0.275 2215000-03G

53 Northborough GW Howard St. well 1, 2, and 3 1532 2532 500 0.091 2215000-04G, -05G, -06G

54 Northborough GW Brigham St. well 1541 2541 1,200 0.295 2215000-01G

54 Westborough GW Otis St. well 1542 2542 535 0.314 2328000-05G

54 Westborough GW Indian Meadow well 1543 2543 282 0.004 2328000-10G

54 Northborough SW Golf course 1544 -- -- 0.003 21400205

55 Westborough GW Chauncy Lake wells 1 and 2 1551 2551 1,150 0.198 2328000-07G, -08G

56 Marlborough SW Millham Reservoir 1561 -- -- 1.386 2170000-01S

58 Berlin SW Gates Pond 1581 -- -- 0.135 2141000-01S

60 Stow SW Golf course 1601 -- -- 0.002 21428602

61 Hudson GW Chestnut St. well 2 1611 2611 580 0.640 2141000-05G

61 Hudson GW Chestnut St. well 3 1612 2612 245 0.429 2141000-06G

61 Hudson GW Chestnut St. well 1 and Kane 

well

1613 2613 610 0.531 2141000-03G, 04G

62 Maynard SW White Pond 1621 -- -- 0.244 2174000-01S

63 Hudson GW Industry well 1631 2631 1,550 0.000 21414101

63 Stow SW Golf course 1632 -- -- 0.002 21428602

64 Maynard GW Well 1 Old Marlboro Rd. 1641 2641 361 0.306 2174000-01G

64 Maynard GW Well 1A Old Marlboro Rd. 1642 2642 197 0.033 2174000-02G

64 Maynard GW Well 3 Old Marlboro Rd 1643 2643 98 0.107 2174000-03G

64 Maynard GW Well 4 Great Rd 1644 2644 541 0.079 2174000-04G

66 Acton GW Assabet well 1 1661 2661 770 0.280 2002000-05G

66 Acton GW Assabet well 2 1662 2662 1,030 0.345 2002000-06G

66 Concord GW Second Division well 1663 2663 480 0.511 3067000-05G

66 Acton SW Sand and gravel withdrawal 1664 -- -- 0.005 21400205

67 Acton GW Whitcomb well 1671 2671 290 0.143 2002000-01G

67 Acton GW Lawsbrook well 1672 2672 1,070 0.077 2002000-03G

67 Acton GW Christofferson well 1673 2673 256 0.320 2002000-04G

67 Acton GW Clapp well 1674 2674 575 0.037 2002000-07G

67 Acton GW Scribner well 1675 2675 320 0.028 2002000-08G

67 Maynard GW Bedrock well 5 1676 2676 725 0.064 2174000-07G

67 Acton SW Farm withdrawal 1677 -- -- 0.002 21400202

68 Acton GW Marshall well 1681 2681 249 0.008 2002000-09G

68 Acton GW Kennedy wells 1, 2, 3, 4 1682 2682 615 0.356 2002000-10G,-11G, 12G,13G

69 Acton GW Conant well 1691 2691 125 0.115 2002000-02G

69 Acton GW Conant II wells 1, 2, 3, 4, 5 1692 2692 430 0.059 2002000-14G, 15G,16G, 

17G, 18G

69 Acton SW Nagog Pond 1693 -- -- 0.446 3067000-01S
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Introduction

14

methylmercury in 4 reservoir cores and 12 wetland cores from 

Sudbury River Basin. During that study, a short-term continuous-record streamgage was established on the Sudbury River 

at Ashland, which was reestablished for use in this study. The 

effects on the groundwater resources of channelization of the 

Sudbury River through Cedar Swamp were investigated by 

Walker (1973). 

Acknowledgments

Many individuals provided assistance, guidance, and 

information that were of great value to the study. In particular, 

the authors would like to thank the volunteers from the Sudbury River Watershed Organization (SRWO) coordinated by 

Frederica Gillespie and Linda Hubley, and the Cedar Swamp 

Conservation Trust, who collected data and took photographs 

of flow conditions. We also gratefully acknowledge the many 

town public-works officials who readily provided water-use 

information necessary for this investigation. Martin Pillsbury 

and staff from MAPC provided the projected 2030 population, land-use, and water demands for model scenarios. 

Personnel from MWRA and MADCR provided reservoir 

stage and gate setting data used in the study. Todd Richards 

from the MADFW willingly shared fisheries information used 

in this study that was collected by that agency. Lastly, we 

would like to acknowledge the contributions of the project’s 

Technical Advisory Committee—Linda Hutchins and Bruce 

Hansen (MADCR), Martin Pillsbury (MAPC), Daniel Nvule 

(MWRA), Thomas Lamonte (MADEP), Margaret Kearns 

(Massachusetts Riverways), Todd Richards (MADFW), Frederica Gillespie (SRWO), Nancy Bryant and Barbara Offenhartz (SUASCO Watershed Community Council), and John 

Craycroft (Cedar Swamp Conservation Trust).

References Cited

Barlow, L.K., Hutchins, L.M., and DeSimone, L.A., 2009, 

Water withdrawals, use, and wastewater return flows in the 

Concord River Basin, eastern Massachusetts, 1996–2000: 

U.S. Geological Survey Scientific Investigations Report 

2008–5158, 123 p.

Brackley, R.A., and Hansen, B.P., 1985, Hydrology and water 

resources of the tributary basins to the Merrimack River 

from Salmon Brook to the Concord River, Massachusetts: U.S. Geological Survey Hydrologic Atlas HA–662, 

2 sheets.

Bratton, Lisa, and Parker, G.W., 1995, Estimated availability 

of water resources from stratified-drift aquifers in the Concord River Basin, Massachusetts: U.S. Geological Survey 

Water-Resources Investigations Report 94–4256, 35 p.

Campbell, M.R., 1925, The physical features of central Massachusetts: U.S. Geological Survey Bulletin 760, p. 13–105.

Table 3. Wastewater returns from 1993 to 2003 from public-sewer systems in the Sudbury and Assabet River Basins, Massachusetts.

[Mgal/d, million gallons per day; DSN, data-set number in Watershed Data Management (WDM) database; locations shown on fig. 1]

Reach 

number

Wastewater 

treatment facility

Communities 

served

Receiving 

water 

Average return flow (Mgal/d) DSN

Annual March August

Sudbury River Basin

31 Marlborough East Marlborough Hop Brook 3.3 4.6 2.4 81

Assabet River Basin

54 Westborough Westborough

Shrewsbury 

Hopkinton

Assabet River 5.0 6.6 4.1 82

58 Marlborough West Marlborough

Northborough

Assabet River 2.0 2.5 1.6 83

60 Hudson Hudson Assabet River 1.5 2.9 0.5 84

66 Maynard Maynard Assabet River 0.8 1.4 0.3 85
References Cited

Introduction

15

Cleveland, W.S., and Devlin, S.J., 1988, Locally weighted 

regression—An approach to regression analysis by local fitting: Journal of the American Statistical Association, v. 83, 

no. 403, p. 596–610. 

Colman, J.A., Waldron, M.C., Breault, R.F., and Lent, R.M., 

1999, Distribution and transport of total mercury and 

methylmercury in mercury-contaminated sediments in 

reservoirs and wetlands of the Sudbury River, east-central 

Massachusetts: U.S. Geological Survey Water-Resources 

Investigations Report 99–4060, 15 p.

Denny, C.S., 1982, Geomorphology of New England: U.S. 

Geological Survey Professional Paper 1208, 18 p., 1 pl.

DeSimone, L.A., 2004, Simulation of ground-water flow and 

evaluation of water-management alternatives in the 

Assabet River Basin, eastern Massachusetts: U.S. Geological Survey Scientific Investigations Report 2004–5114, 

133 p.

Flanagan, S.M., Nielsen, K.W., Robinson, K.W., and Coles, 

J.F., 1999, Water-quality assessment of the New England 

coastal basins in Maine, Massachusetts, New Hampshire, 

and Rhode Island: Environmental settings and implications 

for water quality and aquatic biota: U.S. Geological Survey 

Water-Resources Investigations Report 98–4249, 78 p.

Hansen, W.R., 1956, Geology and mineral resources of the 

Hudson and Maynard Quadrangles, Massachusetts: U.S. 

Geological Survey Bulletin 1038, 104 p.

Jahns, R.H., 1953, Surficial geologic map of the Ayer Quadrangle, Massachusetts: U.S. Geological Quadrangle Map 

GQ–21.

Koteff, Carl, 1966, Surficial geologic map of the Clinton 

Quadrangle, Worcester County, Massachusetts: U.S. Geological Quadrangle Map GQ–567.

Massachusetts Department of Conservation and Recreation, 

2008, Sudbury Reservoir: Boston, Mass., accessed February 21, 2008, at http://www.mass.gov/dcr/parks/northeast/

sudbury.htm.

Massachusetts Geographic Information System, 2007, DEP 

wetlands: Boston, Mass., Datalayers/GIS Database, 

accessed December 21, 2009, at http://www.mass.gov/mgis/

wetdep.htm.

Massachusetts Geographic Information System, 2009, Land 

use (1951–1999): GIS Database, accessed December 21, 

2009, as http://www.mass.gov/mgis/ftplus.htm.

Massachusetts Water Resources Authority, 2008, Metropolitan Boston’s Water System History: Boston, Mass., 

accessed February 21, 2008, at http://www.mwra.state.

ma.us/04water/html/hist1.htm. 

Massachusetts Water Resources Commission, 2001, Stressed 

basins in Massachusetts: 57 p., accessed March 2, 2008, at 

http://www.mass.gov/Eoeea/docs/eea/wrc/stressed_basins.

pdf.

National Oceanic and Atmospheric Administration, 2009a, 

Monthly average temperature for Worcester, MA: Tauton, 

Mass., National Weather Service Forecast Office, accessed 

December 21, 2009, at http://www.erh.noaa.gov/box/

climate/orhave.shtml.

National Oceanic and Atmospheric Administration, 2009b, 

Monthly precipitation totals for Worcester, MA: Tauton, 

Mass., National Weather Service Forecast Office, accessed 

December 21, 2009, at http://www.erh.noaa.gov/box/

climate/orhpcp.shtml.

National Oceanic and Atmospheric Administration, 2009c, 

Seasonal snowfall totals for Worcester, MA: Tauton, Mass., 

National Weather Service Forecast Office, accessed December 21, 2009, at http://www.erh.noaa.gov/box/climate/

orhsnw.shtml.

Parker, G.W., Armstrong, D.S., and Richards T.A., 2004, 

Comparison of methods for determining streamflow 

requirements for aquatic habitat protection at selected sites 

on the Assabet and Charles Rivers, eastern Massachusetts, 

2000–02: U.S. Geological Survey Scientific Investigations 

Report 2004–5092, 72 p.

Perlmutter, N.M., 1962, Ground-water geology and hydrology of the Maynard area, Massachusetts: U.S. Geological 

Survey Water-Supply Paper 1539-E, 69 p.

Pollock, S.J., Farrell, D.F., and Caswell, W.W., 1969, 

Water resources of the Assabet River Basin, central Massachusetts: U.S. Geological Survey Hydrologic Atlas 

HA–312, 1 sheet.

Ries, K.G., III, 1993, Estimation of low-flow duration discharges in Massachusetts: U.S. Geological Survey OpenFile Report 93–38, 59 p.

Ries, K.G., III, 1994, Development and application of generalized-least-squares regression models to estimate low-flow 

duration discharges in Massachusetts: U.S. Geological Survey Water-Resources Investigations Report 94–4155, 33 p.

Ries, K.G., III, 1999, Streamflow measurements, basin 

characteristics, and streamflow statistics for low-flow 

partial record stations operated in Massachusetts from 1989 

through 1996: U.S. Geological Survey Water-Resources 

Investigations Report 99–4006, 162 p.

Ries, K.G., III, and Friesz, P.J., 2000, Methods for estimating low-flow statistics for Massachusetts streams: U.S. 

Geological Survey Water-Resources Investigations Report 

00–4136, 81 p.
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Introduction

16

Shaw, C.E., 1969, Surficial geologic map of the Shrewsbury 

Quadrangle, Worcester County, Massachusetts: U.S. Geological Survey Quadrangle Map GQ–794.

U.S. Bureau of the Census, 2005, People-Basic counts: 

accessed December 21, 2006, at http://factfinder.census.gov/

home/saff/main.html?_lang=en

Waldron, M.C., Colman, J.A., and Breault, R.F., 2000, Distribution, hydrologic transport, and cycling of total mercury 

and methylmecury in a contaminated river-reservoirwetland system, Sudbury River, Eastern Massachusetts: 

Canadian Journal of Fisheries and Aquatic Sciences, v. 57, 

p. 1080–1091.

Walker, E.H., 1973, The effects on the ground-water resources 

of channelization of the Sudbury River through Cedar 

Swamp, Westborough, Massachusetts: U.S. Geological 

Survey Open-File Report 73–0357, 12 p.
Chapter 1

Chapter 1—Simulated Effects of Water Use, and Projected Water-Use and 

Land-Use Change on Streamflow with a Precipitation-Runoff Model 

Withdrawals from reservoirs and the aquifer have 

affected streamflows in the Sudbury River and its tributaries, especially in the 106-mi2

 upper basin upstream from the 

USGS streamgage at Saxonville (01098530, fig. 1). These 

effects are particularly evident in the summer when flows are 

naturally at their lowest. A precipitation-runoff model, HSPF, 

was developed as part of this study to examine effects of current (1993–2003) water use and the effects of potential future 

(2030) water-use and land-use changes on streamflow. The 

model also provided simulated streamflows for the protection 

of aquatic habitat at critical riffle sites in the basin as described 

in Chapter 2 of this report. 

The HSPF model (Bicknell and others, 2000) was chosen 

as the appropriate modeling tool to simulate runoff in response 

to precipitation and the complex water-withdrawal patterns in 

the basin. The HSPF modeling software is publicly available 

and has been successfully used in similar New England basins 

to assist water-resources managers in basins with similar 

streamflow issues (Zarriello and Ries, 2000; Zarriello and 

Bent, 2004; Barbaro and Zarriello, 2007; Barbaro, 2007).

Purpose and Scope

This chapter describes the development and calibration of the HSPF precipitation-runoff model for the Sudbury 

and Assabet River Basins. The model was calibrated to the 

1993–2003 period primarily for the upper Sudbury River 

Basin using streamflow data from Sudbury River at Ashland 

(01097480) and at Saxonville (01098530). The upper Sudbury 

River Basin is the contributing area above the streamgage at 

Saxonville. Streamflow data at Assabet River Basin near Maynard (01097000) and Nashoba Brook near Acton (01097300) 

were also used in the model calibration. This chapter also 

describes long-term simulations (1960–2004) made with, 

or modifications to, the calibrated model and the results of 

simulations that examine the effects of average recent withdrawals (1993–2003) relative to no withdrawals on streamflows, the effects of groundwater only and surface-water only 

withdrawals on streamflow, and the effects of projected 2030 

land-use and water-use changes on streamflow. This chapter 

also discusses simulations that examine the potential effects 

on streamflow and lake levels of reactivating supply wells near 

Lake Cochituate. 

Time-Series Data 

Climate, water-use (water withdrawals and returns), and 

streamflow time-series data are necessary for developing a 

precipitation-runoff model of a basin. Climate and water-use 

data are required inputs to the model. Hourly precipitation, air 

temperature, dew-point temperature, solar radiation, and windspeed data were used to simulate flows. Daily water-use data 

were used to account for water withdrawals and return flows 

and to simulate alternative water-management conditions. 

Observed streamflow data were used for model calibration, but 

are not needed to run the model. 

These time-series data along with model-generated 

time-series data are stored in a Watershed Data Management 

(WDM) file. The WDM database is a binary file accessed by 

ANNIE (Flynn and others, 1995), GenScn (Kittle and others, 

1998), or WDMUtil (Hummel and others, 2001). These programs are used to manage, display, transform, plot, and analyze time-series data stored in the WDM file. Within the WDM 

database, time-series data are organized by data-set number 

(DSN). Each DSN has attribute information that describes the 

data type, time step, location, and other important characteristics of the data. In the Sudbury and Assabet River Basin HSPF 

model, the associated WDM file was organized into groups 

by data type (table 4). The first 68 DSNs were for observed 

climate and streamflow time-series data. 

The combined withdrawals for a reach from direct 

surface-water withdrawals and streamflow depletion from 

groundwater withdrawals (described later) are stored in DSNs 

101 to 168; the last two digits of the DSN correspond to the 

model reach numbers 1 through 68. The combined withdrawals are identified by the WDM attribute IDCON as WSPD. 

Individual time series of streamflow depletion from pumped 

wells and direct surface-water withdrawals are stored separately in DSNs 1011 to 1693; the second and third digits correspond to the reach number and the last digit corresponds to an 

individual withdrawal from the reach. The streamflow depletions by pumped wells or direct surface-water withdrawals 

are individually identified by the attribute DEPL or SWWD, 

respectively. This scheme allows identification of up to 10 

wells along a reach. In the Sudbury and Assabet River Basin 

HSPF model, only reach 33 had more than 10 simulated withdrawals points; therefore, the 11th withdrawal was numbered 
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

18

with the successive reach number (DSN 1340) because there 

were no withdrawals from this reach. Actual withdrawal rates 

from individual pumped wells are stored in DSNs 2011 to 

2692 using the same numbering scheme described above and 

identified by the attribute PUMP. Daily discharge records from 

five WWTP are stored in DSNs 81–85 and identified by the 

WDM attribute IDCON as WWRE.

Climate

Climate data were obtained from the National Oceanographic and Atmospheric Administration (NOAA) National 

Weather Service (NWS) first-order weather station at Worcester, MA, about 8 mi from the southwest edge of the study area 

(fig. 1). The data include hourly precipitation, air temperature, 

dew-point temperature, solar radiation, and wind speed for the 

period January 1, 1960, through December 31, 2004. Potential 

evapotranspiration (PET) was calculated from daily minimum and maximum temperature and daily solar radiation by 

the Jensen-Haise method (Jensen and Haise, 1963) using the 

WDMUtil utility “compute meteorological time-series” program. Worcester climate data stored in the WDM database are 

identified by the location attribute, IDLOCN, as WORCLIM.

Daily precipitation data were also obtained from four 

NWS second-order climate stations in or within 20 mi to the 

south and east of the study area (fig. 1). These data were used 

for comparison with the Worcester data. Although the secondorder climate data often differed from the Worcester data, the 

differences were not consistent; therefore, no adjustments 

were made to the precipitation input to the model. 

Water Withdrawals and Wastewater Returns

Water withdrawals and WWTP discharges were explicitly 

accounted for in the model by time-series data collected from 

various sources. The water withdrawals and treated wastewater return flows are described in the introduction and summarized in tables 2 and 3, respectively. 

Daily withdrawals were obtained from water suppliers, when possible, for the period January 1, 1993, through 

December 31, 2003. If daily withdrawal data could not be 

obtained, daily withdrawals were calculated from monthly 

water-use records reported to the MADEP. The daily withdrawal information provided by the water suppliers was used 

as a pattern to disaggregate monthly withdrawal records when 

only monthly data were available. Estimated daily values 

may differ from the actual withdrawals, but the total monthly 

withdrawals agree with the withdrawals reported to MADEP. 

Withdrawals specified in the long-term (1960–2004) simulations outside of the 1993–2003 model calibration period were 

determined on the basis of the mean monthly observed withdrawals during 1993–2003. Long-term (1960–2004) WWTP 

returns specified in the simulations outside of the 1993–2003 

period were determined from the mean monthly observed 

return during 1993–2003. Mean monthly withdrawals and 

returns were disaggregated into a daily time step.

The amount of withdrawal eventually equals the amount 

of streamflow depletion, but the rate of streamflow depletion 

can differ from a varying rate of withdrawal because of the 

lag effects of moving water through an aquifer. The effect of 

groundwater withdrawals on streamflow was calculated with 

Table 4. General contents and organization of the Watershed Data Management (WDM) database.

[DSN, data-set number in WDM]

DSN Purpose

1–68 Observed climate and streamflow data

81–85 Discharge to a reach (input) from wastewater treatment plants

101–172 Combined water withdrawals from a reach

1xx–1xx xx corresponds to model reach number, ranges from 1 to 72

2xx–2xx Simulated streamflow output, observed water use

1011–1723 Individual streamflow depletion by well or surface withdrawal

1xx1–1xx9 xx corresponds to model reach number, ranges from 1 to 72

101x–172x x corresponds to individual withdrawal point

2011–2722 Pumpage from individual wells

2xx1– 2xx9 xx corresponds to model reach number, ranges from 1 to 72

201x–272x x corresponds to individual withdrawal point

6101–6972 Simulated streamflow from different scenarios

61xx–69xx xx corresponds to model reach number, ranges from 1 to 72

6x01–6x72 x corresponds to scenario identification number incremented by 100
Time-Series Data 

Chapter 1

19

the analytical program STRMDEPL (Barlow, 2000; Zarriello 

and Ries, 2000), which accounts for the time varying pumping 

rates on streamflow depletion from individual withdrawals on 

the basis of aquifer properties, distance of the well from the 

stream, and a resistance factor representing the stream-aquifer 

boundary. Most supply wells are finished in sand and gravel 

and were assigned a diffusivity (transmissivity divided by 

storativity) of 14,700 ft2

/d on the basis of values reported by 

Brackley and Hansen (1985). One supply well is finished in 

bedrock and was assigned a diffusivity of 41,500 ft2/d on the 

basis of hydraulic properties of bedrock in the area reported by 

Lyford and others (2003). The resistance term representing the 

stream-aquifer boundary was assigned a value of zero for all 

wells, meaning the stream channel is in good hydraulic connection with the aquifer. 

While STRMDEPL provides a reasonable approximation 

of the effect of a pumped well on streamflow, the interaction 

between a well and a stream can be very complex. Some of 

the factors affecting the action between a pumped well and 

a stream include (1) heterogeneous transmissivity and storage properties of the aquifer, (2) types and relative position 

of aquifer boundaries, (3) penetration of the pumped well and 

stream in the aquifer, and (4) transient conditions such as a 

change in recharge. Many authors have described factors that 

affect flow to a well that are summarized by Theis (1940), 

Reilly and Pollock (1993), and Franke and others (1998).

Streamflow 

Streamgages operated continuously by the USGS in 

the Sudbury and Assabet River Basins served as the primary 

calibration points (fig. 1; table 5); these include Sudbury River 

at Ashland (01097480) and at Saxonville (01098530), Assabet 

River at Maynard (01097000), and Nashoba Brook near Acton 

(01097300). Daily mean flow records are available from 

Saxonville, Maynard, and Nashoba streamgages for the entire 

October 1993 through September 2003 calibration period. 

Flows at Sudbury River at Ashland were measured from May 

12, 1994, through October 1, 1995; thus, daily mean flows had 

to be estimated for the other parts of the 1993–2003 calibration period.

Estimated flows at the Ashland streamgage were determined by the Maintenance Of Variance Extension type 3 

(MOVE-3) method (Vogel and Stedinger, 1985). MOVE-3 

uses statistical moments determined from 641 days of concurrent record with an index station (Maynard streamgage). 

Flows above 100 ft3

/s at the Ashland streamgage were adjusted 

because the MOVE-3 analysis indicated a nonlinear relation 

between concurrent high flows measured at the Ashland and 

Maynard streamgages that indicate flows at Ashland were 

increasingly overestimated as flow increases. This nonlinear relation is believed to be caused by dampening of high 

flows by storage in extensive wetlands above the Ashland 

Table 5. Streamgages in the Sudbury and Assabet River Basins, Massachusetts.

[USGS, U.S. Geological Survey; mi2, square mile; location shown in fig. 1; no., number; IDLOCN, location attribute in Watershed Data Management (WDM) 

database; DSN, data-set number in WDM; --, not used]

USGS 

streamgage no. Streamgage name Drainage area(mi2

) Type

Model reach

WDM DSN

No. IDLOCN

Sudbury River Basin

01097459 Whitehall Brook near Hopkinton 6.64 Partial 4 WBHK 24

01097460 Sudbury River at Fruit St. near Hopkinton 19.3 Partial 5 SRHK 25

01097466 Sudbury River at Howe St. near Ashland 23.9 Partial 6 SRAS1 26

01097468 Indian Brook near Hopkinton 4.73 Partial 7 IBHK 27

01097469 Indian Brook near Ashland 6.75 Partial 8 IBAS --

01097480 Sudbury River at Front St. at Ashland 35.4 Continuous1 9 SRAS2 30, 31

01097540 Baiting Brook near Framingham 3.41 Partial 15 BBFR 35

01098530 Sudbury River at Saxonville 106 Continuous 19 SRSX 39

Assabet River Basin

01096600 Assabet River near Westborough 6.88 Partial 51 ARWB 51

01096853 Danforth Brook near Hudson 7.04 Partial 59 DBHU 59

01096880 Fort Meadow Brook near Hudson 6.39 Partial 61 FMBH 61

01096945 Elizabeth Brook near Stow 20 Partial 63 EBST 63

01097000 Assabet River at Maynard 116 Continuous 65 ARMY 65

01097300 Nashoba Brook near Acton 12.3 Continuous 68 NBAC 68

1

Continuous data from June 1994 to October 1995 and from May 2004 to July 2009; two methods used to estimate record, stored in separate data sets.
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

20

streamgage. To compensate, a simple linear regression was 

developed from measured flows above 80 ft3

/s at the Ashland 

streamgage to concurrent flows at the Maynard streamgage to 

adjust MOVE-3 estimated flows above 100 ft3/s; the regression relation had a coefficient of determination (r2

) of 0.88. 

Although the estimated record at Ashland streamgage had a 

root mean square error (RMSE) of 11 ft3/s, the estimated flows 

are still considered to be poor because the observed flow data 

are generally rated poor (the estimated flow differs from the 

true flow by more than 15 percent), which perpetuates through 

the record-extension method. 

Use of streamflow data for model calibration is subject 

to the uncertainties associated with the flow records. Flows 

affected by rating shifts and other factors or extrapolated from 

other records to fill periods of missing record are generally 

considered of poor quality and are subject to greater uncertainty. Flows at Ashland streamgage have a relatively high 

degree of uncertainty because the majority of the calibration 

period was estimated. Flows at Nashoba streamgage also are 

subject to a high degree of uncertainty, particularly at low 

flows, because beaver activity disrupts the stage-discharge rating stability. In addition, simulated flows at all the calibration 

sites can appear to have large error because of flow regulation 

that is unaccounted for in the model. This is a particular issue 

at the Saxonville streamgage because flows can be affected by 

regulation from numerous upstream reservoirs; most of these 

regulated flows are unaccounted for in the model because 

there was no set pattern of regulation or continuous record of 

how flows were regulated. The one exception to this is the outof-basin transfer of water from the Wachusett Reservoir into 

the Sudbury Reservoir; these transfers are accounted for during the model calibration period from records obtained from 

MWRA. To minimize the uncertainty of calibrating the model 

to flow records that were estimated or affected by an unknown 

amount of regulation, or both, the Assabet River Basin was 

included in the model to provide two additional continuousrecord calibration sites. These sites helped constrain the range 

of acceptable values for the model variables, and the extension of the model area also proved useful in the second part 

of the study. 

Streamflow information at 10 partial-record stations 

(6 in the Sudbury River Basin and 4 in the Assabet River 

Basin) that ranged in size from 3.41 to 23.9 mi2

 was used in 

this study (fig. 1, table 5). Daily flows at these streamgages 

were determined from comparison of point streamflow measurements at the partial-record stations during this study or in 

previous studies, or both, to concurrent daily flows at two to 

nine index streamgages using MOVE-3 (table 6). The number of streamflow measurements at the partial-record stations 

ranged from 7 to 78 with a median of 16. Index stations were 

chosen on the basis of their proximity to the partial-record 

station and degree of flow regulation; the final selection was 

made on the basis of their correlation to flow measurements 

made at the partial-record station. If more than one index 

station was used in the MOVE-3 analysis, the selected index 

stations were weighted by the root mean square difference 

between measured and estimated flows. Flow measurements 

at the partial-record stations were typically made at low to 

moderate flows; thus, there is greater uncertainty in estimated 

moderate to high flows. 

All other partial-record stations generally correlated 

best to the Maynard streamgage, which was used in all the 

record-extension analyses, except Indian Brook at Ashland 

(01097469), which did not correlate well with any of the 

selected index stations. The correlation generally improved 

when the flows at the Maynard streamgage were adjusted 

for WWTP return flows (effluent was subtracted from the 

recorded flow at the streamgage prior to the MOVE-3 analysis). Although estimated flows at the partial-record stations 

are subject to a large degree of uncertainty, the additional data 

from these sites provided useful information for evaluating 

and adjusting the model calibration. 

Precipitation-Runoff Model

The HSPF model (Bicknell and other, 2001) was used 

to simulate runoff in response to climate and water use in 

the Sudbury and Assabet River Basins. HSPF is a well-documented non-proprietary model that can represent the hydrology and complex water-withdrawal patterns in the basin. 

The computer code for HSPF and its companion programs 

(U.S. Environmental Protection Agency, 2009) can be modified as necessary; however, no modification of the code was 

needed for this study. The general steps followed to complete 

the modeling effort were to (1) compile, collect, and process 

needed data; (2) build the model to represent the Sudbury and 

Assabet River Basins; (3) calibrate the model to streamflow 

data; (4) create and examine selected water-withdrawal scenarios; and (5) document the model and results. 

Functional Description of the HSPF Model

HSPF is a continuous simulation model based on the 

principle of conservation of water mass; that is, inflow equals 

outflow plus or minus any change in storage. In HSPF, the 

land-surface areas are segmented into hydrologic response 

units (HRUs) that flow into streams, lakes, and reservoirs 

defined by model reaches (RCHRESs). Water budgets 

(inflows, outflows, and changes in storage) are calculated for 

each time step specified in the model for each HRU and for 

each RCHRES. HRUs reflect areas of relatively homogeneous hydrologic response to climate on the basis of similar 

land use, soil, surficial geology, wetlands, and other factors 

considered important to the hydrology of the watershed. HRUs 

are divided into pervious-area land segments (PERLNDs) and 

impervious-area land segments (IMPLNDs). RCHRESs represent stream channels, lakes, and reservoirs. The downstream 

end of each RCHRES is referred to as a node. Nodes are 

typically placed in the model to define channel segments with 
Functional Description of the HSPF Model

Chapter 1

21

Table 6. Correlation of partial-record stations in the Sudbury and Assabet River Basins to index streamgages.[USGS, U.S. Geological Survey; No., number; IDLOCN, location attribute in Watershed Data Management (WDM) database; Bold numbers indicate index stations used to estimate daily flows at the partial-record station; DSN, WDM data-set number where estimated flows are stored; index stations are ranked by the number of partial-record stations they were used in, then by the average mean square difference between measured and estimated flow]

USGS 

station no.

Model reach No. of 

measurements

Correlation coefficient to index streamgages (identified by USGS streamgage no.) 

No. IDLOCN 01097000 01111300 01097300 01105730 01096000 01103500 01105600 01175670 01098530

Sudbury River Basin

01097459 4 WBHK 27 0.866 0.873 0.848 0.744 0.816 0.817 0.742 0.803 0.736

01097460 5 SRHK 10 0.938 0.909 0.655 0.927 0.714 0.837 0.937 0.755 0.803

01097466 6 SRAS1 21 0.964 0.718 0.903 0.859 0.770 0.717 0.876 0.794 0.828

01097468 7 IBHK 16 0.924 0.977 0.903 0.917 0.827 0.868 0.951 0.857 0.801

01097469 8 IBAS 17 0.516 0.412 0.463 0.480 0.573 0.580 0.296 0.507 0.433

01097480 9 SRAS2 1641 0.955 0.883 0.891 0.903 0.917 0.914 0.848 0.858 0.868

01097540 15 BBFR 15 0.929 0.936 0.957 0.901 0.929 0.873 0.926 0.953 0.920

Assabet River Basin

01096600 51 ARWB 14 0.961 0.907 0.901 0.900 0.883 0.920 0.888 0.784 0.670

01096853 59 DBHU 78 0.825 0.756 0.857 0.649 0.868 0.794 0.572 0.853 0.652

01096880 61 FMBH 7 0.974 0.956 0.871 0.975 0.966 0.929 0.950 0.747 0.913

01096945 63 EBST 62 0.909 0.695 0.849 0.553 0.741 0.728 0.480 0.799 0.712

1Number of days of concurrent record used in analysis.
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

22

similar physical properties, at junctures with tributary streams, 

at the downstream end of lakes and reservoirs, at data-collection sites, and at other locations where estimates of streamflow 

are desired, such as the aquatic-habitat study sites. 

HSPF requires two primary input files for its operation, 

the User Control Input (uci) file and the WDM file. The uci

file directs process actions used by the model and sets values 

for input variables. Process actions or algorithms in the model 

calculate the movement of water and changes in storage. The 

uci file is structured in blocks that simulate different processes. 

The three main blocks of the uci file simulate (1) PERLNDs, 

(2) IMPLNDs, and (3) RCHRESs. Within each block are 

modules and sub-modules, some of which are mandatory 

for simulations and others are optional. For example, the 

PWATER module is required to simulate the hydrology of pervious areas, but the SNOW module is optional for simulating 

snowpack buildup and melt on pervious areas. A number of 

modules are used for administrative functions, such as controlling the operational sequence of the program and directing the 

model to external sources and output of time-series data. 

The WDM file contains the input time series needed by 

the model and time series generated by the model. Simulations 

of streamflow require precipitation and PET as time series. 

Simulation of snowpack buildup and melt, which was done in 

this model, requires time series of air temperature, dew-point 

temperature, and solar radiation. Output time series can be 

generated for any component in the simulation process that 

is defined in the Time Series Catalog section of the user’s 

manual, but time series were output mostly for streamflow.

PERLND and IMPLND water-budget calculations 

include surface runoff, but only PERLND water-budget 

calculations include interflow (shallow groundwater flow that 

responds rapidly to precipitation), baseflow (deep groundwater flow that remains relatively constant), and optionally, 

a deep groundwater-flow component that discharges outside 

of the basin. Process actions that control the rate of infiltration and change in subsurface storage make the simulation of 

PERLNDs considerably more complex than the water-budget 

calculations for IMPLNDs. A complete description of the process actions and input model variables is given in the HSPF 

Users Manual by Bicknell and others (2000).

Precipitation is the principal inflow to a basin; however, 

inflows can also include wastewater return flows and other 

sources. Precipitation and other sources of moisture supply to 

impervious and pervious areas can be retained at or above the 

surface as interception storage and as snowpack storage, but 

only pervious areas retain water in the subsurface. PERLNDs 

store soil water in two zones: (1) the upper-zone storage, 

generally considered the upper-soil horizon, and (2) the lowerzone storage, representing a deep-soil zone that only allows 

outward movement of water through ET by deep-rooted vegetation. In addition, water is held in groundwater storage that 

is eventually released to streams and is controlled by recession 

variables. Stream channels, lakes, and reservoirs also have a 

storage component defined by their geometry. 

Precipitation that is not held in storage or is lost to 

ET (or optionally exits through deep groundwater) is discharged to RCHRESs as surface runoff from IMPLNDs and 

PERLNDs and as subsurface outflows from PERLNDs. The 

area of IMPLND and PERLND that drain to a RCHRES and 

the linkage of one RCHRES to another are specified in the 

SCHEMATIC block and associated MASSLINK block or 

the NETWORK block, or both. The SCHEMATIC or NETWORK blocks are used to represent the physical layout of the 

watershed. Relations among stage, storage, surface area, and 

discharge are specified for each RCHRES in user-supplied 

function tables (FTABLEs). Primary inflows to a RCHRES are 

(1) surface runoff from PERLNDs and IMPLNDs, (2) interflow and baseflow from PERLNDs, and (3) inflow from other 

RCHRESs. Inflow as direct precipitation and outflow as ET 

can be simulated for RCHRESs when specified by the user 

and were done only in RCHRES that represent large wetlands, 

lakes, or reservoirs. Inflows and outflows from other sources, 

such as wastewater effluent or water withdrawals were specified for RCHRES where applicable. 

The inflows to and outflows from a RCHRES are 

illustrated in figure 6. Surface runoff enters RCHRES from 

impervious surfaces (SURI) and pervious surfaces (SURO). 

Infiltrated precipitation can flow to the RCHRES as shallow 

quick-responding interflow (IFWO) or as a slow-responding 

active groundwater (baseflow) component (AGWO). Inflow 

can also be from upstream reaches (IVOLs). Two outflow exits 

(or gates) are illustrated (a RCHRES can have up to five exits). 

The first exit gate in figure 6 (OVOL 1) is the volume time 

series of water withdrawals (OUTDGT 1) for each RCHRES, 

read in by the EXTERNAL-SOURCE block. Specifying the 

first outflow gate for water withdrawals requires that these 

withdrawals be satisfied before water is routed through successive outflow gates. In the Sudbury and Assabet River Basin 

model, water usually is routed downstream through the second 

outflow gate (OVOL 2), as illustrated, but in one instance 

(Hopkinton Reservoir outflow), a third outflow gate was specified where the second outflow gate routes a controlled release 

from a reservoir and the third routes an uncontrolled flow 

(spillway) from the reservoir. 

Water is routed through RCHRES using the kinematicwave method that assumes a uniform steady flow through the 

RCHRES. In kinematic-wave routing, lateral and upstream 

inflows are continuously added to solve equations for continuity and uniform flow. The model solves equations for continuity from computed inflows to the RCHRES and from the 

RCHRES storage-discharge properties (FTABLE) at each time 

step specified in the model. 

Representation of the Basin

The physical and spatial representation of the basin 

is represented in the model by HRUs (PERLNDs and 

IMPLNDs), their contributing area to a reach, and the linkage 
Representation of the Basin

Chapter 1

23

RCHRES

SURI

Evaporation

Precipitation

Inflow from

upstream 

reach 

(IVOL) Other 

inflow

Outflow to 

downstrem 

reach (OVOL 2)

Outflow to pumped well 

or stream withdrawal 

(OVOL 1)

Pumped

well

SURO

IFWO

AGWO

Evapotranspiration

EXPLANATION

Precipitation

SURI–Surface runoff from impervious areas

SURO–Surface runoff from pervious areas

IFWO–Interflow (subsurface flow that responds 

rapidly to precipitation)

AGWO–Active groundwater flow (baseflow)

RCHRES–Stream reach or reservoir segment

IVOL–Inflow volume

OVOL x–Outflow volume through individual exits

(x = 1 to 5)

Figure 6. Simplified schematic representation of the Hydrologic Simulation Program–FORTRAN (HSPF) inflows and 

outflows to a stream.
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

24

of one reach to another. The process of defining HRUs, their 

linkage to reaches, and the linkage of reaches to each other is 

commonly referred to as the model schematization or discretization. A Geographic Information System (GIS) was used to 

aid in this process. Basin boundaries for many of the reaches 

in the model were available from a statewide digital data layer 

constructed by the USGS and the Massachusetts Geographic 

Information System (MassGIS). Basin boundaries for reaches 

that were not available from this data layer were delineated 

from 1:25,000-scale Digital Elevation Model (DEM) data 

or were digitized by hand from 1:25,000-scale USGS topographic maps. Other data layers used in the discretization process were obtained from MassGIS and include 1:250,000-scale 

surficial geology, 1:25,000-scale 1999 land use, 1:25,000-scale 

hydrography, and 1:12,000-scale wetlands. These data layers, 

including detailed descriptions, can be obtained at MassGIS 

(Massachusetts Geographic Information System, 2009). Two 

additional GIS data layers used in the model development—

public-water lines and public-sewer lines—were compiled 

from individual towns in the basin (L. Barlow, U.S. Geological Survey, written commun., 2004). 

Development of Hydrologic Response Units 

The spatial data were simplified and grouped to obtain 

categories that were considered important to the hydrology 

of the basin. The surficial-geology data layer was simplified 

from seven categories into two types of material on the basis 

of permeability and storage characteristics—sand and gravel 

or till and bedrock (fig. 3). Till and bedrock is herein referred 

to simply as till because bedrock is seldom exposed. The 1999 

land-use cover (fig. 5), developed from aerial photography 

flown in 1997, was combined with the wetland data layer and 

then simplified from 37 categories to 9 categories: (1) forest, 

(2) open area, (3) open water, (4) forested wetland, (5) nonforested wetland, (6) low-density residential, (7) medium-density 

residential, (8) high-density residential, and (9) commercial, 

industrial, and transportation. Commercial, industrial, and 

transportation areas are generally referred to herein as commercial because this is the dominant land-use type. The 

simplified combinations of surficial geology and developed 

land uses (7, 8, and 9) were intersected with basinwide data 

layers of water and sewer infrastructure obtained from the 

towns to determine areas with net imports or exports of water 

as explained later. 

Out of a potential combination of 54 unique pervious area 

HRUs, half were dropped because individually they account 

for less than about 1 percent of the basin area. A total of 27 

pervious area HRUs and 2 unique impervious area HRUs 

were identified to represent the basin (table 7). The dropped 

HRUs were grouped into the retained HRUs with the most 

similar characteristics. 

Impervious Areas (IMPLNDs)

Impervious areas, such as building roofs, paved roads, 

and parking lots, block infiltration of water into the ground. 

Runoff from some impervious surfaces can eventually 

infiltrate into the ground because these surfaces drain onto surrounding pervious surfaces that allow infiltration. In the HSPF 

model, IMPLNDs are used to simulate effective impervious 

areas, which are impervious surfaces that drain directly to 

streams and thus produce only surface runoff. Not all impervious surfaces drain directly to streams, however. Impervious 

surfaces that drain to pervious surfaces are considered noneffective impervious areas and are incorporated into one of 

several “disturbed” PERLND types as described later. In large 

basins such as the Sudbury and Assabet River Basins, values 

for effective imperviousness are difficult to obtain and were 

estimated from broad land-use categories that were adjusted 

during the model calibration. 

Two IMPLND types were used in the model—commercial and residential. The residential IMPLNDs represent the 

combined impervious area from low-, medium-, and high-density residential areas. Initial estimates of effective impervious 

area were obtained from Zarriello and Ries (2000) for similar 

land-use types. Final IMPLND areas ranged from 70 percent 

for commercial, transportation, and industry to 15 percent 

for high-density residential, 8 percent for medium-density 

residential, 2.5 percent for low-density residential, and 0.1 percent for open space. Other factors were also considered in the 

calibration of effective impervious area, including the overall 

responsiveness of the hydrograph to precipitation, particularly 

for summer storms. 

Overall, about 36 percent of the basin is classified as 

developed, but only about 6.7 percent of the basin area is 

simulated as effective impervious area. The average subbasin effective impervious area ranged from less than 1 to 

37 percent with a median of 5.3 percent. In the Sudbury River 

Basin, about 40 percent is classified as developed and about 

7.8 percent of the basin area is simulated as effective impervious area. In the Assabet River Basin, about 32 percent is 

classified as developed and about 5.4 percent of the basin area 

is simulated as effective impervious area. Above Saxonville 

streamgage, the area that is the focus of the model simulations, 

about 42 percent of the basin is developed and about 10 percent of the basin is simulated as effective impervious area. 

Pervious Areas (PERLNDs)

Of the 27 unique PERLND HRUs defined for the basin 

(table 7), 4 represent open space or forested areas over sand 

and gravel or till. Three HRUs represent nonforested wetlands, 

forested wetlands, and open water; unlike other HRUs, these 

three HRUs are not further distinguished by the underlying 

surficial geology. Open-water HRUs represent small areas of 
Representation of the Basin

Chapter 1

25

Table 7. Hydrologic Response Units (HRUs) used to develop the Hydrologic Simulation Program–FORTRAN (HSPF) model for the 

Sudbury and Assabet River Basins, Massachusetts.

[HRU ID, identifier number; PERLND, pervious area; IMPLND, impervious area; Comm., Commercial; transp., transportation; S&G, sand and gravel; Self, 

private well; Septic, on-site septic system; Public, public water or sewer system; NA, not applicable]

HRU 

ID Land use Surficial geology

Water 

supply 

source

Wastewater 

disposal

HRU 

ID Land use Surficial geology

Water 

supply 

source

Wastewater 

disposal

PERLND

1 Comm./industrial/transp. S&G Self Septic 31 Comm./industrial/transp. Till Self Septic

4 High-density residential S&G Self Septic 34 High-density residential Till Self Septic

7 Medium-density residential S&G Self Septic 37 Medium-density residential Till Self Septic

10 Low-density residential S&G Self Septic 40 Low-density residential Till Self Septic

8 Medium-density residential S&G Public Septic 38 Medium-density residential Till Public Septic

11 Low-density residential S&G Public Septic 41 Low-density residential Till Public Septic

3 Comm./industrial/transp. S&G Public Sewer 33 Comm./industrial/transp. Till Public Sewer

6 High-density residential S&G Public Sewer 36 High-density residential Till Public Sewer

9 Medium-density residential S&G Public Sewer 39 Medium-density residential Till Public Sewer

12 Low-density residential S&G Public Sewer 42 Low-density residential Till Public Sewer

13 Open S&G NA NA 43 Open Till NA NA

14 Forest S&G NA NA 44 Forest Till NA NA

51 Shrub-scrub wetlands NA NA NA

52 Forested wetlands NA NA NA

53 Water NA NA NA

IMPLND

60 Residential NA NA NA

61 Comm./industrial/transp. NA NA NA

water not explicitly accounted for in model reaches described 

later. Sixteen HRUs represent various combinations of 

residential-area densities, surficial geology, and water supply 

and wastewater disposal. Four HRUs represent commercial 

areas over two combinations of surficial geology intersected 

with two types of water supply and wastewater disposal. Commercial HRUs include industrial and transportation areas, but 

most area in these HRUs was originally classified as commercial. The 16 residential and 4 commercial HRUs represent 

disturbed pervious areas and the non-effective impervious 

areas associated with these types of land use.

HRUs for residential areas represent low-, medium-, and 

high-density development. High-density residential HRUs represent multi-family residential and single-family residential on 

lots smaller than or equal to 0.25 acre. Medium-density residential HRUs represent single-family homes on lots between 

0.25 and 0.5 acre. Low-density residential HRUs represent 

single-family homes on lots larger than 0.5 acre. 

Excluding the various combinations of water imports or 

exports in commercial and residential areas, the distribution of 

HRU types is shown in figure 7. Forest HRUs are the dominate HRU type in the basin (38 percent), but collectively, the 

developed HRUs are nearly equal to the area of forest HRUs 

(36 percent). Most developed areas are classified as low- to 

medium-density residential (27 percent).

In general, hydrologic characteristics are similar for 

PERLNDs with similar surficial geology; however, upperand lower-zone storage and infiltration are less for developed 

PERLNDs than for forested PERLNDs. The decreased storage 

allows developed PERLNDs to respond more rapidly to precipitation than the same surficial geology type undisturbed by 

development. The rapid response to precipitation mimics the 
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

26

effect of the more rapid depletion of available storage when 

the area receives lateral inflow from non-effective impervious 

areas or compaction of the native soil associated with development, or both. 

Residential and commercial HRUs were further divided 

by water source (self supplied or public supply) and wastewater disposal (on-site septic or public sewer). These HRUs 

represent net water imports (public water and on-site septic), 

exports (private wells and public sewer), or no net gain or 

loss of water to the basin (private wells with on-site septic 

and public water with sewer). Developed areas with no net 

water gains or losses compose about 9.1 and 13 percent of the 

Sudbury and Assabet River Basin areas, respectively. Areas 

on public sewer can lose water from the basin through I&I. 

Areas served by public water and sewer compose (fig. 8) about 

16 and 7.1 percent of the Sudbury and Assabet River Basin 

areas, respectively. Maps of water and sewer infrastructure 

indicate few areas where withdrawals from private wells are 

disposed of through public sewer (net imports). Therefore, 

separate HRUs were not developed for these areas and were 

combined with similar HRUs that export water from the basin. 

Water imports from areas served by public water and on-site 

septic were limited to medium- and low-density residential 

areas and compose about 6.3 and 6.2 percent of the Sudbury 

and Assabet River Basin areas, respectively. Commercial and 

high-density residential areas on public water with on-site 

septic combined comprised less than 1 percent of the basin 

area and were combined with similar HRUs with public water 

and sewer. 

Imports and exports of water from the basin through the 

water and sewer infrastructure were estimated by first defining 

areas on public water and sewer from town water and sewer 

maps. A 250-ft buffer was added to each side of the water and 

sewer line features to indicate areas of net import, export, or 

no net change in the water budget. The rate of water input to 

areas on public water and on-site septic was determined from 

2000 Topologically Integrated Geographic Encoding and 

Referencing system (TIGER) census-tract data (U.S. Census 

Bureau, 2009) to obtain an average number of households per 

acre and the average occupancy per household. The average 

occupancy per household ranged from 2.38 to 3.03 for the 

towns in the basin with an average occupancy of 2.73 persons 

per household over the basin. The average occupancy was 

multiplied by an average water use of 70 gal/d per person 

0

5

10

15

20

25

30

35

HYDROLOGIC RESPONSE UNIT (HRU) TYPE

Model Area

Sudbury River Basin

Assabet River Basin

PERLNDs IMPLNDs

Sand and Gravel Till Wetland

PERCENT OF BASIN AREA

Commercial

High density

Medium density

Low density

Open

Forest

Commercial

High density

Medium density

Low density

Open

Forest

Commercial

Residential

Nonforested wetlands

Forested wetlands

Water

Residential Residential

Figure 7. Distribution of general Hydrologic Response Unit (HRU) types for pervious area (PERLNDS) and impervious area (IMPLNDS) 

used to develop the Hydrologic Simulation Program–FORTRAN (HSPF) for the Sudbury and Assabet River Basins, Massachusetts.
Representation of the Basin

Chapter 1

27

Figure 8. Public water and sewer infrastructure in the Sudbury and Assabet River Basins, Massachusetts.

STATE ROUTE 9

STATE 

INTERSTATE 90

INTERSTATE 495

STATE

INTERSTATE 290

ROUTE 2

 ROUTE 20

Sudbury

River

Assabet

River

Whitehall

Reservior

Ashland

Reservior

Hopkinton

Reservior

Gates

Pond

Millham

Reservior

Sudbury

Reservior

Nagog

Pond

Lake

Boon

Chauncy

Lake

UPTON

STOW

ACTON

HARVARD

CONCORD

BOLTON

SUDBURY

GRAFTON

HOPKINTON

NATICK

BERLIN

FRAMINGHAM

HOLLISTON

LITTLETON

CARLISLE

WAYLAND

SHERBORN

WESTFORD

MARLBOROUGH

WESTBOROUGH

HUDSON

ASHLAND

BOYLSTON

SHREWSBURY

LINCOLN

WESTON

NORTHBOROUGH

SOUTHBOROUGH

CLINTON

BOXBOROUGH

MAYNARD

EXPLANATION

Sudbury River Basin

Assabet River Basin

Public water line

Public sewer line

Treated wastewater return

Production well

KILOMETERS

MILES

10

10 2 3 4 5

0 2 4 6 8

71°40' 71°30' 71°20'

42°10'

42°20'

42°30'

Base from Massachusetts Executive Office of Energy and Environmental Affairs digital data;

EOTROADS_ARC, 1:5,000, 2006; HYDRO25K_ARC, 1:25,000, 2005; MAJPOND_POLY, 1:100,000, 1998; SUBBASINS_POLY, 1:25,000, 2007; TOWNS_POLY, 1:25,000, 2002

Polyconic projection. North American Datum of 1983 

Massachusetts coordinate system mainland zone
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

28

times 5, 2.5, or 1.25 units per acre for high-, medium-, and 

low-density residential areas minus a 20-percent consumptive loss. This amounts to a net import of about 13, 6.4, and 

3.2 in/acre/yr for high-, medium-, and low-density residential 

areas, respectively, on public water and on-site septic.

The town of Southborough has the highest percentage 

of medium-density residential land area on public water and 

on-site septic in the study area. Initial model calibration runs 

indicated peak flows and runoff volume in the reach associated with this area were oversimulated. Import of water in 

Southborough was modified because further investigation 

determined the average lot size is reported to be about two to 

four times that allowed by zoning and most households in the 

town are single occupancy (43 percent) or double occupancy 

(26 percent) (Chorey and others, 2004). The number of units 

per acre in Southborough was adjusted down to 1.0 and 0.5 

from 2.5 and 1.25 units per acre used in other parts of the 

basin for medium- and low-density areas, respectively. An 

average occupancy of 2.73 people per unit and 70 gal/d per 

person minus a 20-percent consumptive loss was still used, 

which resulted in a net import of 1.3 and 2.6 in/acre/yr on lowand moderate-density residential areas on public water and 

on-site septic in Southborough.

Water imports from HRUs representing areas on public 

water and on-site septic are not linked to any particular source 

and account for withdrawals made from within the basins 

that are returned or imported from outside of the basin. Water 

imports on areas served by public supply and on-site septic 

are simulated as a lateral inflow to the lower-soil zone (LZLI), 

because septic leach fields are typically installed in this part 

of the soil horizon. Inflow to the lower-soil zone in the model 

is not available for discharge to streams, rather, septic effluent 

decreases the opportunity for infiltrated moisture from precipitation to be held in the lower-zone storage because the lateral 

inflow keeps this storage component closer to its capacity than 

would otherwise occur. As a result, more infiltrated water goes 

into active groundwater storage that eventually discharges to 

streams as baseflow than similar areas without septic effluent.

Sewer I&I by town reported by Barlow and others (2008) 

for the 1996–2000 period were extrapolated to the 1993–2003 

period (table 8) to estimate the exports of water from the 

basin; annual I&I losses ranged from 0.26 Mgal/d in Ashland 

to 3.86 Mgal/d in Framingham and averaged 9.53 Mgal/d. 

I&I losses were highest during the spring when the groundwater table at its normal high with estimated average losses 

during March, April, and May of 20.9 Mgal/d. Exported 

water was simulated by the PWATER variable DEEPFR that 

is used to represent the fraction of groundwater lost from an 

HRU. DEEPFR was estimated at 0.22 (22-percent loss) for 

eight HRUs representing sewered areas in commercial, high-, 

medium-, and low-density residential areas over sand and 

gravel or till. The actual rate of export varies by HRU because 

the groundwater contribution to streamflow varies by HRU 

and season. Overall, about 11 percent of the basin is sewered—14 percent in the Sudbury River Basin and 8.1 percent 

in the Assabet River Basin. 

Table 8. Estimated average 1993–2003 annual and spring inflow and infiltration (I&I) into public sewers by town in 

the Sudbury and Assabet River Basins, Massachusetts.

[Mgal/d, million gallons per day; Spring I&I, average for months of March, April, and May; MWRA, Massachusetts Water Resources 

Authority; WWTP, wastewater treatment plant; --, no data available]

Town Facility or 

agency

Annual I&I Spring I&I

Mgal/d Percent of total 

effluent Mgal/d Percent of total effluent

Ashland MWRA 0.26 36 0.61 83

Clinton WWTP 0.71 -- 1.5 --

Framingham MWRA 3.86 45 7.1 83

Hopkinton WWTP -- -- -- --

Hudson WWTP 0.62 27 1.01 44

Marlborough West WWTP 0.57 36 3.89 55

Marlborough East WWTP 1.13 45 1.87 65

Maynard WWTP 0.27 26 0.46 35

Natick MWRA 0.86 55 1.76 114

Northborough WWTP 0.28 37 0.36 60

Shrewsbury WWTP 0.69 -- 1.45 --

Westborough WWTP 0.28 17 0.88 35

Total 9.53 20.9
Representation of the Basin

Chapter 1

29

Stream Reaches (RCHRES)

The Sudbury and Assabet River Basins were discretized 

(divided) into 44 stream reaches (fig. 9) on the basis of hydrologic features, availability of streamflow data, or where simulated flow information is desired. The Sudbury River Basin 

was divided into 23 reaches, 19 of which are upstream from 

the Saxonville streamgage (table 9). Four of the 19 upstream 

Sudbury River reaches are on the main stem. Four tributaries 

upstream from the Saxonville streamgage (Whitehall Brook, 

Indian Brook, Cold Spring Brook, and Lake Cochituate Outlet 

Brook) were subdivided to create reaches at reservoirs, major 

tributary confluences, or habitat sites. The Assabet River 

Basin was divided into 21 reaches, 7 of which are on the main 

stem of the river. RCHRESs are identified by a four-character 

attribute name (IDLOCN) and number (fig. 9 and table 9). 

RCHRESs are numbered in downstream order; the upper 

Sudbury River Basin RCHRESs are numbered 1 through 19, 

RCHRESs below the Saxonville streamgage are numbered 30 

through 33; RCHRESs in the Assabet River Basin are numbered 51 through 72. 

 Linkage of reaches to one another is made in the model 

SCHEMATIC block to target outflow from the upstream 

reaches as inflow to the downstream reaches. In most cases, 

the linkage of one reach to another is easily identified in 

figure 9 and by the reach identification number, which ascends 

from upstream to downstream. In a few instances, the linkage between tributaries and the main stem are less obvious 

because of the juxtaposition of the confluence and reach node. 

For example, in the upper Sudbury River Basin, reach 18 

(Lake Cochituate Outlet Brook) joins the Sudbury River just 

upstream (about 0.15 mi) of the Saxonville streamgage. Specifying outflow from reach 18 as an inflow to reach 19 would 

artificially elevate flows along most of the 5.8-mi length of 

reach 19 except near its outlet. To better represent flows in 

most of reach 19, while appropriately representing flows at 

the streamgage, flows from reaches 18 and 19 were combined 

using the model COPY operation to output simulated flows at 

the streamgage. Similar types of COPY operations were used 

in reaches 63, 64, and 65 (combines flows from Elizabeth 

Brook, Taylor Brook, and Assabet River to represent flows at 

the Maynard streamgage), reaches 67 and 69 (combines flows 

from Fort Pond Brook and Nashoba Brook), and reaches 33 

and 72 (combined flows from the Sudbury and Assabet River 

Basins). A COPY operation was also used in reach 8 (Hopkinton Reservoir outlet) to combine the 2nd exit gate flow, 

which represents controlled releases from the reservoir, with 

the 3rd exit gate flow, which represents uncontrolled flow over 

the spillway; collectively, these flows represent flow in Indian 

Brook below the reservoir. 

RCHRES in the Sudbury and Assabet River Basin HSPF 

model mostly had one or two exit gates to route water from 

the reach (table 9). For about half the reaches, one exit gate 

was specified. In most other reaches, two exit gates were 

specified; the 1st exit gate is used to satisfy the water demand 

when withdrawals are made from the reach and the 2nd is used 

to route water downstream. As previously noted, reach 8 has 

three exit gates. 

Hydraulic Characteristics (FTABLEs)

Stage-storage-discharge relations (FTABLEs) were 

developed for each RCHRES with the channel-geometry 

analysis program (CGAP) by Regan and Schaffranek (1985) 

and a supplemental program, GENFTBL. GENFTBL calculates discharge by Manning’s equation from the hydraulic 

properties of the channel computed by CGAP from specified 

cross-section channel geometry and elevations. The crosssection geometry was obtained from surveys conducted at 

river reaches for flood-insurance studies, and from streamflow 

measurements made at continuous- and partial-record stations 

in the basin. When this detailed information was not available, 

channel widths and cross-section elevations were obtained 

from USGS 1:24,000-scale digital topographic maps and 

field observations. At a minimum, three cross sections were 

used to define the storage-discharge relations for each reach. 

GENFTBL requires Manning’s roughness coefficients for each 

cross section; these coefficients were estimated from published 

guidelines by Chow (1959), Arcement and Schneider (1989), 

and Coon (1998).

Lakes and Impoundments 

Lakes and impoundments are widely scattered throughout 

the Sudbury and Assabet River Basins (fig. 9). The presence 

of a major lake or impoundment can appreciably effect water 

movement through a reach. In these cases, the FTABLE was 

developed from depth, storage, surface area, and outlet discharge of the principal water body in the reach. In the Sudbury River Basin, FTABLES specifically represent Whitehall 

Reservoir (RCHRES 3), Hopkinton Reservoir (RCHRES 8), 

Ashland Reservoir (RCHRES 10), Sudbury Reservoir 

(RCHRES 12), Strearnes Reservoir (RCHRES 13), Foss 

Reservoir (RCHRES 14), and Lake Cochituate (RCHRES 17). 

In the Assabet River Basin, FTABLES represent A-1 Reservoir (RCHRES 51), Millham Reservoir (RCHRES 56), Fort 

Meadow Reservoir (RCHRES 61), Lake Boon (RCHRES 62), 

and Warner Pond (RCHRES 67). Information on depth, surface area, and volume of these water bodies and the shape and 

dimensions of their outlet structures were obtained from the 

MWRA, MADCR, or MADFW or from onsite measurements.

Wetlands

Wetland hydrology is complex and can be an important 

influence on stream hydrology (Lent and others, 1997; Hunt 

and others, 1996; Krabbenhoft and Webster, 1995; Anderson 

and Cheng, 1993; Mills and Zwarich, 1986; Zarriello and Reis, 

2000). Wetlands account for about 13 percent of the total basin 

area, which is about equally distributed between the Sudbury 

River and Assabet River Basins. To account for storage and 

ET losses, wetlands were represented as “virtual” RCHRESs 

or incorporated into the reach FTABLE. Virtual RCHRESs, 
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

30

Figure 9. Discretization of the stream reaches used in the Hydrologic Simulation Program–FORTRAN (HSPF) model of the 

Sudbury and Assabet River Basins, Massachusetts.

STATE ROUTE 9

STATE 

INTERSTATE 90

INTERSTATE 495

STATE 

INTERSTATE 290

ROUTE 2

ROUTE 20

Sudbury

Assabet

River

River

Whitehall

Reservior

Foss

Reservior

Ashland

Reservior

Hopkinton

Reservior

Fort Meadow

Reservoir

Lake

Cochituate

Gates

Pond

Millham

Reservior

Warners

Pond

Sandra

Pond

Cedar

Swamp

Sudbury

Reservior

Nagog

Pond

Lake

Boon

Chauncy

Lake

Stearnes

Reservior

A1

Reservior

WRES IBHK

ARWB

CHHB

HBWB

NBBE

ARES

CBNA

CBAS

SRES

SRHK

STRE

BBFR

SRAS2

FRES

IBAS WBHK

JBWB

PBWB

HPSU

SRSX

LBNA

PBWY

SRCO

ABSU

NBAC

SBCO

DBHU

EBST

FPWB

NBAC2

ARNB

SBNO

MBNR

FMBH

BOON

ARHU

ARST TBMY

ARCO

ARMY

ARCO2

SRAS1

LCNA

33

67

12

63

5

57 31

68

16

53

9

7

6

3

69

58

52

60

19

70

59

51

54

10

61

17

30

66

13

32

55

64

4

8

56

14

65

15

1

18

2

72

62

11

EXPLANATION

Sudbury River Basin

Assabet River Basin

Continuous record 

01096880

01097000

Streamgage and number

Partial record 

Subbasin boundary

HPSU

31

Reach identification name 

and number

(Reach numbers 1 to 33)

(Reach numbers 51 to 72)

01097480

01098530

01097000

01097300

01097450

01096945

01096853

01096880

01096600

01097540

01097468

01097481

01097466

01097469

01097459

01097460

Kilometers

Miles

10

10 2 3 4 5

0 2 4 6 8

71°40' 71°30' 71°20'

42°10'

42°20'

42°30'

Base from Massachusetts Executive Office of Energy and Environmental Affairs digital data;

EOTROADS_ARC, 1:5,000, 2006; HYDRO25K_ARC, 1:25,000, 2005; MAJPOND_POLY, 1:100,000, 1998; SUBBASINS_POLY, 1:25,000, 2007; TOWNS_POLY, 1:25,000, 2002

Polyconic projection. North American Datum of 1983

Massachusetts coordinate system mainland zone
Representation of the Basin

Chapter 1

31

Table 9. Subbasins and reaches (RCHRES) used in the Hydrologic Simulation Program–FORTRAN (HSPF) model of the Sudbury and 

Assabet River Basins, Massachusetts.

[Locations shown in fig. 9; IDLOCN, attribute in the Watershed Data Management (WDM) database that identifies the reach; --, not applicable or no 

streamgage; USGS, U.S. Geological Survey; mi2, square mile; p, indicates partial-record station]

Reach 

number IDLOCN Stream or streamgage name

Number 

of exit 

gates 

Upstream 

reach 

numbers

USGS 

streamgage 

number

Reach 

drainage 

area

(mi2

)

Cumulative 

drainage 

area

(mi2

)

Sudbury River Basin

1 JBWB Jackstraw Brook near Westborough 1 -- 01097450p 1.46 1.46

2 PBWB Piccadilly Brook 1 -- -- 1.21 1.21

3 WRES Whitehall Reservoir 2 -- -- 4.54 4.54

4 WBHK Whitehall Brook at Fruit St. near Hopkinton 2 3 01097459p 2.1 6.64

5 SRHK Sudbury River at Fruit St. near Hopkinton 2 1, 2, 4 01097460p 9.99 19.31

6 SRAS1 Sudbury River at Howe St. near Ashland 2 5 01097466p 4.56 23.86

7 IBHK Indian Brook near Hopkinton 1 -- 01097468p 4.73 4.73

8 IBAS Indian Brook near Ashland (Hopkinton Res. outlet) 3 7 01097469p 2.02 6.75

9 SRAS2 Sudbury River at Front St. at Ashland 1 6, 8 01097480 4.73 35.35

10 ARES Ashland Reservoir 2 -- -- 6.43 6.43

11 CBAS Cold Spring Brook near Ashland 1 10 01097481p 1.45 7.88

12 SRES Sudbury Reservoir 2 -- 01097466p 22.54 22.54

13 FRES Foss Reservoir (no 3) 2 12 -- 5.32 27.86

14 STRE Stearnes Reservoir (no 1) 2 9, 10, 13 01097500p 3.84 74.94

15 BBFR Baiting Brook near Framingham 1 -- 01097540p 3.41 3.41

16 CBNA Course Brook 1 -- -- 11.4 11.4

17 LCNA Lake Cochituate 2 16 -- 6.17 17.57

18 LBNA Lake Cochituate Outlet Brook 1 17 -- 2.54 20.11

19 SRSX Sudbury River at Saxonville 1 14, 15, 18 01098530 7.5 105.96

30 PBWY Pine Brook 1 -- -- 5.69 5.69

31 HBSU Hop Brook near Sudbury 2 -- -- 15.6 15.6

32 ABSU Allowance Brook 2 -- -- 4.6 4.6

33 SRCO Sudbury River at Concord 2 19, 30, 31, 32 -- 30.63 162.49

Assabet River Basin

51 ARWB Assabet River near Westborough 2 -- 01096600p 6.88 6.88

52 HBWB Hop Brook at Westborough 2 -- -- 7.89 7.89

53 CHHB Cold Harbor/Howard Brook 2 -- -- 9.55 9.55

54 ARNB Assabet River at Northborough 2 51, 52, 53 -- 4.36 4.36

55 SBNO Stirrup Brook near Northborough 2 -- -- 3.86 3.86

56 MBMR Millham Brook near Marlborough 1 -- -- 6.74 39.28

57 NBBE North Brook near Berlin 1 -- -- 16.89 16.89

58 ARHU Assabet River at Hudson 2 54, 55, 56, 57 -- 8.01 64.18

59 DBHU Danforth Brook near Hudson 1 -- 01096853p 7.04 7.04

60 ARST Assabet River near Stow 1 58, 59 -- 7.8 79.02

61 FMBH Fort Meadow Brook near Hudson 2 -- 01096880p 6.39 6.39

62 BOON Boon Lake complex 2 -- -- 2.07 2.07

63 EBST Elizabeth Brook near Stow 1 -- 01096945p 20.04 20.04

64 TBMY Taylor Brook near Maynard 2 -- -- 4.21 4.21

65 ARMY Assabet River at Maynard 1 60, 61, 62, 63, 64 01097000 3.78 115.51

66 ARCO Assabet River near Concord 2 65 -- 5.58 121.09

67 FPBW Fort Pond Brook 2 -- -- 25.52 25.52

68 NBAC Nashoba Brook near Acton 2 -- 01097300 12.28 12.28

69 NBAC2 Nashoba Brook at Acton 1 67, 68 -- 8.75 46.54

70 SBCO Spencer Brook near Concord 1 -- -- 7.51 7.51

72 ARCO2 Assabet River at Concord 1 66, 69, 70 -- 2.27 177.41
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

32

described by Zarriello and Ries (2000), simulate wetland storage and ET loss without affecting the upstream channel flow 

through a reach. A virtual RCHRES allows for greater ET loss 

than a wetland treated as an HRU because the available moisture is not limited to precipitation falling on the HRU; rather, 

the available moisture supply is controlled by the amount of 

contributing area from surrounding HRUs that are directed 

into it. In the final model, only the reach representing Cedar 

Swamp (RCHRES 105) was used as a virtual reach because 

this was a focus area of the model and because large wetlands 

in most other areas are in headwater reaches (RCHRESs 3, 7, 

51, 55, 56, 59, 61, 62, 63, 67, and 68) or reaches with large 

open-water features (RCHRESs 8, 13, 14, and 17). In headwater reaches and in reaches with large open-water features, 

the wetland areas were incorporated into the reach FTABLE. 

A separate virtual RCHRES in headwater reaches and in 

reaches with large open-water features would result in no 

or little difference in the simulation. It should be noted that 

RCHRES 7 (fig. 9), a headwater reach, was initially simulated 

with a virtual RCHRES (RCHRES 107) because it was in the 

focus area of the model but was converted to a single reach in 

the final model (RCHRES 107) that retained its virtual-reach 

numbering scheme. 

The surface area of wetlands represented in RCHRES 

was set equal to the corresponding area of wetlands previously 

simulated as HRUs to maintain the same basin area. Precipitation on and ET from these reaches is directly proportional to 

the surface area specified in the FTABLE. At very low flows, 

the surface area was decreased in some FTABLES to limit 

the potential ET loss from the reach to achieve a satisfactory 

model calibration. Although this introduces some structural 

error into the model (because the simulated area of these 

subbasins decreases at very low flows), this modification 

was considered a necessary compromise to better simulate 

low flows. Storage-discharge characteristics of the wetland 

RCHRESs were adjusted empirically to minimize differences 

between simulated and observed streamflows. The wetland 

storage-discharge characteristics, flow-path characteristics, 

and the interaction between groundwater and surface water are 

largely unknown; however, they could be refined when wetland processes and their effects on the hydrology of the basin 

are better understood. 

Water Withdrawals and Wastewater Returns

All water withdrawals from, and wastewater returns to, 

a reach are specified in the EXT SOURCE block of the uci

file. For all major withdrawals within a reach (table 2), the 

combined streamflow depletion from groundwater withdrawals and direct surface-water withdrawals were specified in a 

single DSN (101 to 172) corresponding to RCHRESs 1 to 72, 

respectively. Twenty-four RCHRESs are affected by withdrawals as indicated by more than one exit gate for the reach 

(table 6). The combined water withdrawals are taken through 

the first outflow gate in a RCHRES (OUTDGT 1) and must 

be satisfied before water exits from the next outflow gate that 

typically routes water to the next downstream reach. Return 

flows from WWTP discharge to RCHRES 31, 54, 58, 60, and 

66 are specified as an inflow to the reach (IVOL) from DSN 

81, 82, 83, 84, and 85, respectively. 

Model Calibration

The model was calibrated to an 11-year period, January 1, 

1993, to December 31, 2003, by minimizing the differences 

between simulated and observed streamflow at the four 

streamgages in the model area. Values of variables that control 

runoff, infiltration, storage, and ET from HRUs were determined from spatial data to the extent possible. Many variables 

were initially assigned values similar to those used for comparable HRUs in the Ipswich River Basin HSPF model (Zarriello 

and Ries, 2000). An iterative process was then used to adjust 

variable values for grouped HRUs representing sand and 

gravel, till, and wetlands; the variable values were then refined 

for different land-use types within each group. Storm runoff 

and snowmelt were not given detailed consideration because 

the primary purpose of the model is to simulate the effects of 

withdrawals during low-flow periods. The calibrated-model 

variable values are given in the partial listing of the uci file 

in appendix 1.

Discharge measured at Sudbury River at Ashland 

(01097480) and at Saxonville (01098530), Assabet River 

at Maynard (01097000), and Nashoba Brook near Acton 

(01097300) provided the main data sets for model calibration. Estimates of daily flows at nine partial-record stations 

(five in the Sudbury River Basin and four in the Assabet River 

Basin) were also used to evaluate the model calibration. The 

estimated flows at partial-record stations were used mostly as 

a check of the calibration and to refine the FTABLE values in 

their corresponding upstream reaches (fig. 9). 

The model fit was evaluated by graphical and statistical 

comparisons of the simulated and observed annual, monthly, 

and daily mean flows at the four principal streamgages. 

Hydrographs and flow-duration curves of the daily mean flow 

reflect climate, topography, and hydrogeologic conditions of 

the basin. Summary statistics including the differences and 

percent difference between simulated and observed streamflow 

means and medians, the RMSE, the r2

, and the Nash-Sutcliffe 

model-fit efficiency coefficient (E) were used to measure the 

quality of the model fit. The r2 and E provide measures of the 

variation in the simulated value explained by the observed 

value (Neilson and others, 2003). The Nash-Sutcliffe E provides a more rigorous evaluation of the fit quality than r2

 does 

because E is sensitive to differences between the observed 

and simulated means and variances, whereas r2 measures only 

the differences between mean values (Legates and McCabe, 

1999). In cases where the observed values and model residuals 

are normally distributed, the value of r2 and E should be equal 

(Duncker and Melching, 1998). Mean spring and summer 

simulated and observed flows over the calibration period were 

also compared to evaluate the model fit during seasonal highflow and low-flow months. 
Model Calibration

Chapter 1

33

The model was developed primarily for use in the 

upper Sudbury River Basin above the Saxonville streamgage 

(01098530; fig. 9); therefore, calibration focused on minimizing differences between simulated and observed flows at the 

streamgages at Saxonville and upstream at Ashland. Calibration also focused on summer low flows when streamflow 

stresses are most prevalent and flow alterations are of most 

concern. Unknown flow regulation in the observed streamflow 

at the Saxonville streamgage can cause unexplained differences between observed and simulated flows. Flows at the 

Ashland streamgage have a high degree of uncertainty because 

most of the record was estimated and the short period of actual 

record (641 days) was of questionable quality. Hence, fitting 

the model to the Saxonville and Ashland streamgages was 

weighed against the benefits of fitting the model to the Maynard streamgage, which was less affected by reservoir operations, and the Nashoba streamgage, which was least affected 

by regulation. However, flows at the Nashoba streamgage, 

particularly low flows, were often rated of fair to poor quality 

because of unstable control conditions, a factor that was also 

considered in the overall model calibration. Eventually, a point 

of diminishing returns is reached in the calibration process 

where any improvement in the model fit for one period or one 

location, or both, results in a deterioration of the model fit at 

another period or location, or both. 

Some of the model error can be explained by the precipitation variability over the basin. Mean annual flow was 

oversimulated when annual precipitation measured at the 

Worcester climate station (model input climate data) was 

greater than the collective average precipitation measured at 

nearby climate stations (includes the Worcester station and 

four 2nd order stations in or near the basin) and undersimulated 

when Worcester precipitation was less than the collective 

average precipitation (fig. 10A). The r2 between precipitation 

variability and model error ranged between 0.36 and 0.51. 

The regression line for Sudbury River at Saxonville had the 

lowest r2 and also deviated most from the other stations, which 

may reflect the unaccounted for releases or diversions from 

the Sudbury Reservoir system, or both. In general, flows were 

oversimulated the most in 1993 and 1994 and undersimulated 

the most in 1998 and 2001, when precipitation recorded at 

Worcester was the greatest and least, respectively, relative to 

surrounding climate stations. 

A similar pattern was observed between monthly 

model errors in relation to monthly precipitation variability 

(fig. 10B); however, the pattern is not as distinct as the relation 

between the annual model error and precipitation variability. 

The wide scatter in the relation between monthly model error 

and precipitation variability indicates other potential reasons 

for model error. These reasons include uncertainty of the 

estimated or observed flow data, flow regulation (including 

withdrawals and return flows) not accounted for in the model, 

particularly at the Saxonville streamgage, and representativeness of the input climate data. Model error can also result 

from variable values used in the model; the goodness of these 

values is dependent on the data used to calibrate the model. 

These factors are discussed in the model calibration at the four 

principal streamgages below. 

Sudbury River at Ashland 

Simulated streamflows at the Sudbury River at Ashland 

streamgage (SRAS2, RCHRES 9; fig. 9) were compared to 

observed data (when available) and estimated flows (January 

1993 through April 1994 and July 1995 through December 

2003) made using MOVE-3 as previously described in the 

Time-Series Data Streamflow section. Estimated flows were 

unadjusted (DSN 31) and adjusted (DSN 30) to correct for 

potential overestimation of flows above 100 ft3/s. In general, 

the simulated flows are in good agreement with observed and 

estimated flows for the 11-year calibration period (table 10), 

but the simulated flows are in slightly better agreement with 

observed and adjusted estimated flows than to the observed 

and unadjusted flows. 

The simulated mean daily flow during the calibration 

period (57 ft3/s) was about midway between observed and 

estimated unadjusted and adjusted mean daily flow (54 and 

59 ft3/s, respectively); the difference between simulated and 

adjusted and unadjusted estimated daily mean flow was about 

2.6 and -2.3 percent, respectively (table 10). Scatter plots of 

simulated daily mean flow in relation to observed and adjusted 

estimated flows (fig. 11A) generally indicate an equal distribution around the line of equality. Monthly and annual mean 

flow scatter plots (fig. 11B and C, respectively) indicate the 

simulated flows are slightly oversimulated relative to observed 

and adjusted estimated flows and slightly undersimulated 

relative to observed and unadjusted estimated flows. The split 

between the simulated and the adjusted and unadjusted flows 

is particularly evident in the daily mean flow-duration curves 

(fig. 11D) above 100 ft3/s, or flows that are exceeded less than 

about 10 percent of the time; the simulated flow-duration 

curve is about mid-way between the unadjusted and adjusted 

“observed” flow-duration curves in this range. This suggests 

that the linear regression used to adjust high flows for the estimated record may overcompensate for the effects of wetland 

storage because the equation was developed from a limited 

period of actual record that generally had lower seasonal high 

flows than the remainder of the calibration period. 

The model fit improved substantially when simulated 

flows were compared to the period of actual streamflow 

record (May 1994 through June 1995). The model fit for 

the period of actual record relative to the 11-year calibration period (using the adjusted estimated flows) increased 

the r2

 from 0.60 to 0.78, increased E from 0.50 to 0.75, and 

decreased RMSE from 38 to 27 ft3/s (table 10). The model 

fit especially improved during the normal high-flow period 

(March and April); the difference between simulated flows 

and observed flows was about half for the period of actual 

record (-7.3 percent) relative to the 11-year calibration period 

record (-13 percent). The model fit during the summer months 

(June through September), however, was better for the 11-year 

calibration period than the period of actual record (summers 
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

34

EXPLANATION

-100

-50

50

100

150

200

-100 -50 0 50 100

PERCENT DEVIATION OF TOTAL PRECIPITATION AT WORCESTER CLIMATE STATION FROM MEAN 

PRECIPITATION AT WORCESTER AND FOUR NEARBY SECOND-ORDER CLIMATE STATIONS

B Monthly Error

SRAS2

(01097480)

ARMY

(01097000)

NBAC

(01097300)

SRSX

(01098530)

SRAS2

(01097480)

ARMY

(01097000)

NBAC

(01097300)

SRSX

(01098530)

0

MODEL ERROR (SIMULATED-OBSERVED/OBSERVED), IN PERCENT

Line is linear 

regression fit

-40

-30

-20

-10

10

20

30

40

A Annual Error

-10 -5 0 5 10 15 20

0

Figure 10. Annual (A) and monthly (B) precipitation variability in relation to model error at streamgages on the Sudbury 

River at Ashland (01097480; SRAS2) and Saxonville (01098530; SRSX), Assabet River at Maynard (01097000; ARMY), and 

Nashoba Brook near Acton (01097300; NBAC), Massachusetts, 1993 to 2003. Locations shown in figure 9.
Model Calibration

Chapter 1

35

Table 10. Model-fit statistics calculated from observed flows and Hydrologic Simulation Program–FORTRAN (HSPF) simulated flows 

at four streamgages in the Sudbury and Assabet River Basins, Massachusetts, 1993 to 2003.

[Streamgage location shown on fig. 9; ft3/s, cubic feet per second; r2, coefficient of determination; E, Nash-Sutcliffe model-fit efficiency coefficient; RMSE, 

Root Mean Square Error]

Calibration period January 1993 to December 2003 Summer

(June–Sept.)

Spring

(March–April)

Mean daily 

flow

(ft3

/s)

Difference

(percent)

Daily mean Monthly mean Mean daily 

flow

(ft3/s)

Difference

(percent)

Mean daily 

flow

(ft3/s)

Difference

(percent) r

2 E RMSE

(ft3

/s) r

2 E RMSE

(ft3

/s)

Sudbury River at Ashland (01097480)

Observed 1

54/59 124/25 1114/134

Simulated 57 2.6 0.60 0.50 38 0.72 0.70 24 26 8.3 99 -13

-2.3 0.56 0.55 44 0.69 0.68 30 4.0 -26

May 1994 through September 1995 (period of measured streamflow)

Observed 40 16 41

Simulated 46 5.1 0.78 0.70 27 0.90 0.88 12 21 31 38 -7.3

Sudbury River at Saxonville (01098530)

Observed 193 85 387

Simulated 187 -5.9 0.53 0.49 143 0.68 0.68 90 92 7.5 275 -22

Assabet River at Maynard (01097000)

Observed 201 92 433

Simulated 208 3.4 0.52 0.48 39 0.72 0.72 90 107 16 354 -18

Nashoba Brook near Acton (01097300)

Observed 19 7.1 42

Simulated 19 0 0.31 0.23 24 0.68 0.67 10 9.3 31 33 -21

1

A portion of the record was estimated, one was adjusted (DSN 30) and the other unadjusted (DSN 31) for high flows; the model-fit statistics that follow 

correspond to these data sets in sequential order.
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

36

Figure 11. Simulated flow in relation to observed and estimated (adjusted and unadjusted for high flow) flow 

for (A) daily mean, (B) mean monthly, (C) mean annual, (D) daily mean flow-duration curves, and (E) daily mean 

hydrographs, at Sudbury River at Ashland, Massachusetts, 1993 to 2003 (01097480, RCHRES 9; fig. 9). (DSN, Data-set 

number in Watershed Data Management (WDM) database).

OBSERVED STREAMFLOW, IN CUBIC FEET PER SECOND

SIMULATED STREAMFLOW, IN CUBIC FEET PER SECOND

20

30

40

50

60

70

80

90

100

20 30 40 50 60 70 80 90 100

C MEAN ANNUAL 

Adjusted (DSN 30) 

Unadjusted (DSN 31)

0

20

40

60

80

100

120

140

160

180

200

0 20 40 60 80 100 120 140 160 180 200

OBSERVED STREAMFLOW, IN CUBIC FEET PER SECOND

SIMULATED STREAMFLOW, IN CUBIC FEET PER SECOND

B MEAN MONTHLY

Adjusted (DSN 30) 

Unadjusted (DSN 31)

Observed and estimated 

streamflow

1

10

100

1,000

1 10 100 1,000

OBSERVED STREAMFLOW, IN CUBIC FEET PER SECOND

SIMULATED STREAMFLOW, IN CUBIC FEET PER SECOND

A DAILY MEAN 

Observed and adjusted 

estimated streamflow 

(DSN 30)

Adjusted (DSN 30) 

Unadjusted (DSN 31)

Simulated

1

10

100

1,000

STREAMFLOW, IN CUBIC FEET PER SECOND

PERCENT OF TIME STREAMFLOW WAS EQUAL OR EXCEEDED

D DAILY MEAN FLOW DURATION 

0.5 1 2 5 10 20 30 50 70 80 90 95 98 99 99.8

Observed and estimated streamflow

Simulated 1

10

100

1,000

STREAMFLOW, IN CUBIC FEET PER SECOND

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Estimated Measured Estimated

E DAILY MEAN HYDROGRAPH

Observed and adjusted estimated streamflow (DSN 30)

Observed and estimated 

streamflow
Model Calibration

Chapter 1

37

of 1994 and 1995). Again, it should be noted that the measurements of flows below 20 ft3

/s reported during this period 

were rated poor, which means the recorded values may differ 

from the actual values by more than 15 percent. In addition, 

precipitation during August 1994 at the Worcester station 

(data used for the simulation) was 1.16 to 2.54 in. greater than 

precipitation recorded at the surrounding stations, indicating 

precipitation from localized convective storms was unevenly 

distributed and could potentially result in an oversimulation 

of streamflow.

Sudbury River at Saxonville 

Simulated streamflow in the Sudbury River at the 

Saxonville streamgage is generally in good agreement with 

observed flow over a wide range of flow conditions and 

seasons (fig. 12). Scatter plots of simulated flows in relation to observed flows (fig. 12 A–C) indicate a slight undersimulation of high flows and a slight oversimulation of low 

flows. Years with undersimulated or oversimulated flows 

are consistent with the difference in annual precipitation 

recorded at the Worcester station relative to precipitation 

recorded at nearby surrounding climate stations. Differences 

between simulated and observed flows may also be caused by 

uncounted transfers of water into the Sudbury Reservoir from 

outside the basin or by uncounted regulation of the Sudbury 

Reservoir system.

Daily mean flow hydrographs (fig. 12E) indicate the simulated flows vary more than the observed flows, suggesting 

a possible underestimation of storage in upstream reservoirs; 

however, when storage was added to the reaches representing 

the reservoirs, the daily mean flow-duration curve indicated 

an undersimulation of high flows and an oversimulation of 

moderate flows. Because of unknown reservoir operations, 

the storage-discharge representing the Sudbury reservoirs was 

adjusted to best fit the scatter of daily flows along the line of 

equality with observed flows (fig. 12A). 

On average, the mean daily flow over the calibration 

period was undersimulated by about 5.9 percent (table 10), 

which is largely attributed to the representativeness of precipitation over the basin or inaccurate accounting of transfers of 

water into the basin, or both. Flows, on average, during spring 

months were undersimulated by about 22 percent and oversimulated by about 7.5 percent during the summer months. 

This difference also may be caused by unaccounted reservoir 

operations. The model fit for the daily mean and monthly 

mean flow had an r2 of 0.53 and 0.68, respectively, and an 

E of 0.49 and 0.68, respectively; the RMSE was 143 and 

90 ft3/s, respectively (table 10).

Assabet River at Maynard

Simulated streamflow in the Assabet River at the Maynard streamgage is generally in good agreement with the 

observed flow over a wide range of flow conditions and seasons (fig. 13). The difference between simulated and observed 

flows over the calibration period for daily, monthly, and 

annual mean flows (fig. 13 A–C) was the most tightly grouped 

around the line of equality of the four main model calibration 

sites; this is believed to reflect the quality of the flow record 

and the lack of unaccounted flow regulation in the measured 

flows relative to the other calibration sites. Simulated and 

observed flow-duration curves are closely matched over the 

entire exceedence probability (fig. 13D). 

On average, the mean daily flow over the calibration 

period was oversimulated by about 3.4 percent (table 10). In 

addition, the close agreement in simulated and observed mean 

daily flows is also attributed to a better representation of precipitation at the Worcester climate station for this part of the 

basin, which is geographically closer in position and elevation 

than the contributing areas to the other calibration sites. Flows, 

on average, were undersimulated by 18 percent during spring 

months and oversimulated by about 16 percent during the 

summer months. The model fit for the daily mean and monthly 

mean flow had an r2 of 0.52 and 0.72, respectively, and an E 

of 0.48 and 0.72, respectively; the RMSE was 39 and 90 ft3/s, 

respectively (table 10).

Nashoba Brook near Acton

Streamflows at Nashoba streamgage are affected by 

occasional regulation of an upstream pond that is unaccounted 

for in the model and by alteration of the stage-discharge relation by beavers, resulting in streamflow records that are often 

rated as poor during the calibration period, particularly at low 

flows. These factors are believed to be the primary reason for 

the large scatter between simulated and observed daily and 

monthly mean flows below 10 ft3/s (fig. 14 A–B). Simulated 

and observed flow-duration curves (fig. 14D) are generally in 

close agreement, however. 

On average, the simulated mean daily flow over the 

calibration period was the same as the observed (table 10). 

The model fit for the daily mean and monthly mean flow 

had an r2 of 0.31 and 0.68, respectively, and an E of 0.23 and 

0.67, respectively; the RMSE was 24 and 10 ft3/s, respectively (table 10). Flows, on average, during spring months 

were undersimulated by 21 percent and oversimulated by 

about 31 percent during the summer months. Although the 

seasonal differences between simulated and observed flows at 

Nashoba Brook and Assabet River at Maynard streamgages 

are relatively consistent (table 10), the differences between 

streamgages were not always consistent from year to year or in 

relation to precipitation variability. For example, 1996 summer 

flows were consistently undersimulated by an average of about 

11 percent at the Maynard streamgage and oversimulated by 

an average of 74 percent at the Nashoba streamgage. Spring 

flows in 2002, on average, were oversimulated by about 

56 percent at the Maynard streamgage and undersimulated 

by about 1.1 percent at the Nashoba streamgage. Although 

the seasonal model errors are considered large at times, the 

inconsistent differences did not warrant further changes to the 

model because these changes could adversely affect the model 

calibration in the Sudbury River Basin.
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

38

1

10

100

1,000

10,000

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Observed 

Simulated

STREAMFLOW, IN CUBIC FEET PER SECOND

E DAILY MEAN HYDROGRAPH

1

10

100

1,000

10,000

1 10 100 1,000 10,000

OBSERVED STREAMFLOW, IN CUBIC FEET PER SECOND

SIMULATED STREAMFLOW, IN CUBIC FEET PER SECOND

A DAILY MEAN

10

100

1,000

10 100 1,000

OBSERVED STREAMFLOW, IN CUBIC FEET PER SECOND

SIMULATED STREAMFLOW, IN CUBIC FEET PER SECOND

B MEAN MONTHLY

100

150

200

250

300

100 150 200 250 300

OBSERVED STREAMFLOW, IN CUBIC FEET PER SECOND

SIMULATED STREAMFLOW, IN CUBIC FEET PER SECOND

C MEAN ANNUAL 

1

10

100

1,000

10,000

STREAMFLOW, IN CUBIC FEET PER SECOND

PERCENT OF TIME STREAMFLOW WAS EQUAL OR EXCEEDED

D DAILY MEAN FLOW DURATION 

0.5 1 2 5 10 20 30 50 70 80 90 95 98 99 99.8

Observed 

Simulated

Figure 12. Simulated flow in relation to observed flow for (A) daily mean, (B) mean monthly, (C) mean annual, (D) daily 

mean flow-duration curves, and (E) daily mean hydrographs, at Sudbury River at Saxonville, Massachusetts, 1993 to 2003

(01098530, RCHRES 19; fig. 9).
Model Calibration

Chapter 1

39

1

10

100

1,000

10,000

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Observed 

Simulated

STREAMFLOW, IN CUBIC FEET PER SECOND

E DAILY MEAN HYDROGRAPH

1

10

100

1,000

10,000

1 10 100 1,000 10,000

OBSERVED STREAMFLOW, IN CUBIC FEET PER SECOND

SIMULATED STREAMFLOW, IN CUBIC FEET PER SECOND

A DAILY MEAN 

10

100

1,000

10 100 1,000

OBSERVED STREAMFLOW, IN CUBIC FEET PER SECOND

SIMULATED STREAMFLOW, IN CUBIC FEET PER SECOND

B MEAN MONTHLY

OBSERVED STREAMFLOW, IN CUBIC FEET PER SECOND

SIMULATED STREAMFLOW, IN CUBIC FEET PER SECOND

C MEAN ANNUAL 

100

150

200

250

300

350

400

100 150 200 250 300 350 400

1

10

100

1,000

10,000

STREAMFLOW, IN CUBIC FEET PER SECOND

PERCENT OF TIME STREAMFLOW WAS EQUAL OR EXCEEDED

D DAILY MEAN FLOW DURATION 

0.5 1 2 5 10 20 30 50 70 80 90 95 98 99 99.8

Observed 

Simulated

Figure 13. Simulated flow in relation to observed flow for (A) daily mean, (B) mean monthly, (C) mean annual, (D) daily mean 

flow-duration curves, and (E) daily mean hydrographs, at Assabet River at Maynard, Massachusetts, 1993 to 2003 (01097000, 

RCHRES 65; fig. 9).
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

40

1

10

100

1,000

0.1

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Observed 

Simulated

Observed 

Simulated

STREAMFLOW, IN CUBIC FEET PER SECOND

E DAILY MEAN HYDROGRAPH

1

10

100

1,000

0.1

0.1 1 10 100 1,000

OBSERVED STREAMFLOW, IN CUBIC FEET PER SECOND

SIMULATED STREAMFLOW, IN CUBIC FEET PER SECOND

A DAILY MEAN

1

10

100

1 10 100

OBSERVED STREAMFLOW, IN CUBIC FEET PER SECOND

SIMULATED STREAMFLOW, IN CUBIC FEET PER SECOND

B MEAN MONTHLY 

OBSERVED STREAMFLOW, IN CUBIC FEET PER SECOND

SIMULATED STREAMFLOW, IN CUBIC FEET PER SECOND

C MEAN ANNUAL

10

15

20

25

30

35

40

10 15 20 25 30 35 40

1

10

100

1,000

0.1

STREAMFLOW, IN CUBIC FEET PER SECOND

PERCENT OF TIME STREAMFLOW WAS EQUAL OR EXCEEDED

D DAILY MEAN FLOW DURATION 

0.5 1 2 5 10 20 30 50 70 80 90 95 98 99 99.8

Figure 14. Simulated flow in relation to observed flow for (A) daily mean, (B) mean monthly, (C) mean annual, (D) daily 

mean flow-duration curves, and (E) daily mean hydrographs, at Nashoba Brook near Acton, Massachusetts, 1993 to 2003

(01097300, RCHRES 68; fig. 9).
Hydrologic Flow Components and Water Budgets

Chapter 1

41

Hydrologic Flow Components and Water 

Budgets

Discharge to streams and the loss of water through ET 

for each HRU compose the majority of the outflows in the 

water budget. Outflows are characterized by various hydrologic flow components that include discharge to streams 

through surface runoff, interflow, and active groundwater, 

and ET losses through interception, upper-zone, lower-zone, 

and active groundwater storages. These flow components are 

controlled by the variable values assigned to the HRUs. In 

addition to these components, the model also includes lateral 

inflows to lower-zone storage from areas served by public 

water with on-site septic and areas that lose water through 

sewer I&I. Outflow to streams and water losses by component 

are illustrated (figs. 15–17) for the various HRUs developed 

to simulate the Sudbury and Assabet River Basins. It should 

be noted that the HRU water budgets do not include the gains 

or losses in reaches, such as in large wetlands or water bodies 

that are specified as direct precipitation gains and evaporation 

losses, or from withdrawals from reaches. 

Flow components for each of the HRUs were computed 

from the annual means for the calibration period (January 

1993 through December 2003) and from the monthly means 

for March, the normal high-flow month, and August, the normal low-flow month, for the 1993–2003 period. Annual water 

budgets per unit area are generally similar for HRUs with 

similar surficial geology types, but still differ among landuse types (fig. 15A). Annually, discharge to streams per unit 

area from HRUs overlying sand and gravel averaged about 

87 percent from active groundwater flow, about 13 percent 

from interflow, and a negligible amount from surface runoff. 

Discharge to streams from HRUs overlying till averaged about 

50 percent from active groundwater, 38 percent from interflow, 

and 12 percent from surface runoff. Discharge components to 

streams from wetland HRUs are relatively evenly distributed 

between active groundwater flow, interflow, and surface runoff 

(about 30, 40, and 30 percent, respectively). All discharge 

to streams from impervious area HRUs (IMPLND) is from 

surface runoff. 

On average, about 45 in. of precipitation fell on the basin 

during 1993–2003, of which about 49, 54, and 61 percent per 

unit area discharged to streams from HRUs overlying sand 

and gravel, till, and wetlands, respectively. The remainder 

was mostly lost to ET, per unit area, from lower-zone storage (LZET) that ranged from 24 to 19 percent for sand and 

gravel and till HRUs, respectively. ET loss per unit area from 

interception and upper-zone storages (CEPE and UZET, 

respectively) accounts for about 16 to 18 percent of the annual 

moisture supply to the basin. ET loss per unit area from active 

groundwater (AGWET) accounts for about 3 to 6 percent of 

the annual moisture supply to the basin. 

Additional moisture supply on HRUs representing areas 

on public water and on-site septic systems is not directly 

represented in the water budgets shown on figure 15; rather, 

these gains are reflected in additional outflows to streams or 

ET losses relative to similar HRUs without these gains or 

losses. The additional moisture supply to areas on public water 

and on-site septic systems amounts to about 11 and 5.7 percent 

of the total mean annual precipitation during the 1993–2003 

period in medium- and low-density residential HRUs, respectively. Water gains on these HRUs are represented as lateral 

inflows to lower-zone storage that do not discharge directly 

to streams; rather, it allows more precipitation on these HRUs 

to infiltrate and discharge to streams mostly as active groundwater. Discharge to streams from areas on public water and 

on-site septic compared to similar HRU types without lateral 

inflows increased the mean annual groundwater discharge, 

per unit area, by about 21 and 26 percent for medium-density 

residential areas overlying sand and gravel, and tills, respectively, and by about 10 and 12 percent for low-density residential area overlying sand and gravel, and tills, respectively. 

Interflow also increased slightly as a result of lateral inflows 

compared to similar HRU types by about 11 and 7 percent for 

medium-density residential areas overlying sand and gravel, 

and tills, respectively, and by about 6 and 3 percent for lowdensity residential areas overlying sand and gravel, and tills, 

respectively. The basin is comprised of about 4.0 and 3.6 percent medium- and low-density residential area on public 

water and on-site septic, respectively; the discharge to streams 

from lateral inflows from these areas was minor over the 

basin, accounting for less than 1 percent of the total discharge 

to streams. 

On average, annual ET losses account for 40 to 50 percent of the moisture supply, per unit area. In areas served by 

public sewer, additional losses were simulated to account for 

sewer I&I; these losses were offset by decreases in active 

groundwater discharge to streams. Mean annual I&I loss is 

about 25 percent greater in sewered areas overlying sand 

and gravel than in sewered areas overlying till, per unit area. 

Excluding withdrawals, mean annual I&I loss accounted for 

about 2 percent of the total water loss from the basin; about 

11 percent of the basin area is sewered. 

Forested HRUs compose the major portion of the basin 

water budget (fig. 15B), expressed in inches over the basin, 

because forested HRUs represent about 48 percent of the total 

basin area. Forested HRUs contributed about 11 in. (44 percent), mostly from active groundwater, of the 24.7 in. of total 

mean annual discharge to streams. Discharge to streams from 

forested areas came predominantly from HRUs overlying 

till (5.7 in.) and about equal amounts from forested HRUs 

overlying sand and gravel, and forested wetlands (about 2.5 

and 2.7 in., respectively). The amount of forested area over 

till is about the same as the combined forested area over sand 

and gravel and forested wetland. Combined, forested HRUs 

accounted for about 50 percent (10.6 in.) of the total ET losses 

(20.7 in.) from the basin. Mean annual loss from lower-zone 

storage was about equal to the combined losses from interception, upper-zone, and active groundwater storages.

During the normal seasonal high flow, the mean March 

discharge to streams is proportionally similar to the mean 

annual discharge to streams (fig. 16A). In HRUs overlying 
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

42

Figure 15. Mean annual 1993–2003 water-budget outflow components (A) in inches per acre and (B) in inches over the basin from 

each Hydrologic Response Unit (HRU) simulated by the Hydrological Simulation Program–FORTRAN (HSPF) model of the Sudbury and 

Assabet River Basins, Massachusetts.

Sand and Gravel Till Wetland

PERLNDs IMPLND

Sand and Gravel Till Wetland

PERLNDs IMPLND

HYDROLOGIC RESPONSE UNITS (HRUs)

PERLNDs- Pervious area HRUs; IMPLNDs- Impervious area HRUs

B Basin Water Budget 

-4

-2

0

2

4

6

INCHES PER ACRE INCHES OVER BASIN

-40

-30

-20

-10

0

10

20

30

40

50

Open

Forest

Open

Forest

Commercial

Residential

Nonforested wetlands

Forested wetlands

Open water

1 3 5 6 7 8 9 10 11 12 13 14 31 33 34 36 37 38 39 40 41 42 43 44 51 52 53 61 62 HRU Number

A Water Budget per Unit Area

Evapotranspiration

loss

Discharge to 

streams

Self-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied septic

Public-supplied sewer

Commercial

High density

Medium density

Low density

Residential

-6

Evapotranspiration

loss

Surface

Interflow

Active

groundwater

Interception

Upper zone

Lower zone

Active

groundwater

Discharge to 

streams

Loss to sewer 

inflow and 

infiltration

Self-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied septic

Public-supplied sewer

Commercial

High density

Medium density

Low density

Residential

EXPLANATION
Hydrologic Flow Components and Water Budgets

Chapter 1

43

Figure 16. Mean 1993–2003 March water-budget outflow components (A) in inches per acre and (B) in inches over the basin from 

each Hydrologic Response Unit (HRU) simulated by the Hydrological Simulation Program–FORTRAN (HSPF) model of the Sudbury and 

Assabet River Basins, Massachusetts.

Sand and Gravel Till Wetland

PERLNDs IMPLND

B Basin Water Budget 

INCHES OVER BASIN

-0.1

0

0.2

0.3

0.4

0.5

0.6

0.7

0.1

Sand and Gravel Till Wetland

PERLNDs IMPLND

INCHES PER ACRE

A Water Budget per Unit Area

-1.0

0

1.0

1.5

2.0

2.5

3.0

3.5

0.5

-0.5

Evapotranspiration

loss

Discharge to 

streams

Evapotranspiration

loss

Surface

Interflow

Active

groundwater

Interception

Upper zone

Lower zone

Active

groundwater

Discharge to 

streams

Loss to sewer 

inflow and 

infiltration

1 3 5 6 7 8 9 10 11 12 13 14 31 33 34 36 37 38 39 40 41 42 43 44 51 52 53 61 62 HRU Number

HYDROLOGIC RESPONSE UNITS (HRUs)

PERLNDs- Pervious area HRUs; IMPLNDs- Impervious area HRUs

Open

Forest

Open

Forest

Commercial

Residential

Nonforested wetlands

Forested wetlands

Open water

Self-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied septic

Public-supplied sewer

Commercial

High density

Medium density

Low density

Residential

Self-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied septic

Public-supplied sewer

Commercial

High density

Medium density

Low density

Residential

EXPLANATION
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

44

sand and gravel, discharge to streams per unit area averages 

about 80 percent from active groundwater flow, 20 percent 

from interflow, and a negligible amount from surface runoff. 

In HRUs overlying till, discharge to streams is about equally 

split between active groundwater flow and interflow (about 

44 percent each), and 11 percent from surface runoff. Discharge to streams from wetland PERLND HRUs is relatively 

evenly distributed between active groundwater flow, interflow, 

and surface runoff (25, 45, and 29 percent, respectively). The 

water loss to ET during March differs appreciably from the 

mean annual ET losses, accounting for about 2 to 3 percent 

of the water budget per unit area. In HRUs where I&I loss 

is specified, the water loss per unit area accounts for 12 to 

20 percent of the water budget in low- and medium-density 

residential areas, respectively. 

The mean moisture supply to the basin during March 

1993–2003 was about 4.3 in., and on average, about 57 percent was from precipitation and 43 percent was from snowmelt. Overall, on average, about 47 percent of the available 

moisture is discharged to streams (2.4 in.), about 1.6 percent is 

lost to ET (0.2 in.), and the remainder goes into storage (about 

1.7 in.). Expressed in inches over the basin, about 48 percent 

of the average streamflow contribution comes from forested 

HRUs (fig. 16B), about half of which was from forested areas 

overlying till. Overall, discharge to streams in March was 

mostly from active groundwater (about 58 percent), followed 

by interflow (30 percent) and surface runoff (12 percent). 

ET losses were minor during March and were mostly from 

interception storage. In HRUs where I&I loss is specified, the 

water loss per unit area accounts for 14 to 27 percent of the 

water budget losses in low- and medium-density residential 

areas, respectively.

The mean August water budget per unit area during 

1993–2003 (fig. 17A) is markedly different from the mean 

annual (fig. 15A) and March (fig. 16A) water budgets. Discharge to streams per unit area in August is mostly from active 

groundwater (about 80 percent), followed by interflow (about 

14 percent) and surface runoff (about 6 percent). In HRUs representing areas overlying sand and gravel, active groundwater 

accounts for 99 percent of the discharge to streams. 

During August 1993–2003, in inches over the basin 

(fig. 17B), the average combined discharge to streams (0.9 in.) 

and ET loss (4.6 in.) amount to nearly twice the average 

moisture supply to the basin (3.3 in.); the excess discharge 

and ET loss relative to the moisture supply reflect losses from 

storage mostly from the lower-soil zone. About 70 percent of 

total discharge to streams was from active groundwater mostly 

from forested HRUs. Water loss from I&I represents a small 

fraction (0.3 percent) of the total water loss during August. 

The magnitude of simulated flow components, in inches 

over the basin, for the annual mean and the monthly means 

for March and August during 1993–2003 are readily apparent 

when compared side by side (fig. 18). Annually, the average 

total discharge to streams (24.7 in.) is about 20 percent more 

than the average total ET loss (20.7 in.); combined, they are 

about equal to the total average moisture supply to the basin 

(45.2 in). The slight discrepancy between moisture supply 

and the combined streamflow and ET loss is caused by lateral 

inflows to lower-zone storage that are not accounted for in the 

available moisture supply in these numbers (but are accounted 

for in the model) and minor change in storage components 

over the 1993–2003 period. The average March and average 

August water budgets stand out in sharp contrast to the annual 

average discharge to streams and ET losses and especially 

in contrast to each other. In March, the average discharge to 

streams is about 2.4 in. and losses to ET are about 0.1 in.; 

whereas, in August, the average discharge to streams is about 

0.9 in. and losses to ET are about 4.6 in.

Sensitivity Analysis

Sensitivity analysis typically measures the response of 

the model-simulated discharges to changes in the value of 

variables representing the hydrologic processes in the basin. 

Thus, for the model structure under consideration, the most 

influential variables can be revealed by iteratively changing 

the value of a particular model variable. 

The Sudbury and Assabet River Basins HSPF model 

structure and HRUs are similar to the HSPF models developed for the Ipswich River Basin (Zarriello and Ries, 2000) 

and the Usquepaug-Queen River Basin (Zarriello and Bent, 

2004). Hydrologic budgets by flow component from these 

models indicate that the dominant discharge to streams is from 

active groundwater (AGWO) and interflow (IFWO) and the 

dominant loss of water is through ET from lower-zone storage. 

Therefore, the sensitivity analyses conducted for the Ipswich 

River Basin and Usquepaug-Queen models, which produced 

similar results, are considered applicable to the Sudbury and 

Assabet River Basin model. Details of iteratively changing 

HSPF variable values on various metrics of the model fit are 

given in tables for the Ipswich River Basin model (Zarriello 

and Ries, 2000) and graphically for the Usquepaug-Queen 

River Basin model (Zarriello and Bent, 2004).

In general, the Ipswich River and Usquepaug-Queen 

River Basin model sensitivity analyses indicated that the 

changes in the variables that affect groundwater and interflow recession cause the largest changes in various measures 

of model fit. The groundwater discharge to streams is most 

affected by the groundwater recession constant (AGWRC), 

the groundwater recession variable that determines the degree 

of nonlinearity of the recession rate (KVARY). The interflow 

discharge to streams is most affected by the coefficient that 

determines the amount of water that enters the ground from 

surface storage and becomes interflow (INTFLW) and the 

interflow recession constant (IRC). Uncertainties in these 

groundwater and interflow variables, thus, have a large effect 

on the performance of the HSPF model relative to most other 

model variables. Model results were also sensitive to changes 

in variables that determined the amount of precipitation that 

would eventually discharge as groundwater or interflow. These 

variables include the infiltration (INFILT), the lower-zone 
Hydrologic Flow Components and Water Budgets

Chapter 1

45

Figure 17. Mean 1993–2003 August water-budget outflow components (A) in inches per acre and (B) in inches over the basin from 

each Hydrologic Response Unit (HRU) simulated by the Hydrological Simulation Program–FORTRAN (HSPF) model of the Sudbury and 

Assabet River Basins, Massachusetts.

Sand and Gravel Till Wetland

PERLNDs IMPLND

B Basin Water Budget 

INCHES OVER BASIN

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

Sand and Gravel Till Wetland

PERLNDs IMPLND

INCHES PER ACRE

A Water Budget per Unit Area

-8

-5

-4

-3

-2

-1

0

1

2

3

4

-7

-6

Evapotranspiration

loss

Discharge to 

streams

Evapotranspiration

loss

Surface

Interflow

Active

groundwater

Interception

Upper zone

Lower zone

Active

groundwater

Loss to sewer 

inflow and 

infiltration

Discharge to streams

1 3 5 6 7 8 9 10 11 12 13 14 31 33 34 36 37 38 39 40 41 42 43 44 51 52 53 61 62 HRU Number

HYDROLOGIC RESPONSE UNITS (HRUs)

PERLNDs- Pervious area HRUs; IMPLNDs- Impervious area HRUs

Open

Forest

Open

Forest

Commercial

Residential

Nonforested wetlands

Forested wetlands

Open water

Self-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied septic

Public-supplied sewer

Commercial

High density

Medium density

Low density

Residential

Self-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied septic

Public-supplied sewer

Commercial

High density

Medium density

Low density

Residential

EXPLANATION
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

46

storage (LZSN), and the lower-zone ET (LZETP). LZETP is 

the dominant flow component during dry periods and exerts a 

large influence on other hydrologic components. More detailed 

explanation of all these variables can be found in Bicknell and 

others (2000). The Ipswich River Basin model analysis also 

indicated that model results were sensitive to how the wetlands were represented, especially during low-flow periods, 

because of differences in the amount of moisture supply 

available or ET. 

Model Uncertainty and Limitations

The Sudbury and Assabet River Basins HSPF model 

should be used with an understanding of the model limitations, the uncertainty of the data used, and the possibility of 

alternate model structures. Numerical-simulation models use 

simplifications of complex hydrologic processes and physical 

basin characteristics to approximate streamflow in response 

to climatic conditions. Despite these limitations, models 

can be useful tools to evaluate the hydrologic responses of a 

basin, provided that the model structure and variable values 

adequately reflect the hydrologic responses of the system to 

the stresses evaluated. The uncertainty associated with data 

and the possibility that alternative model structures and variable values may produce similar results have been described 

by Beven (1993) and Beven and Binley (1992).The use of the 

climate data from the Worcester NWS station, located about 

20 mi west of the study basin, has been shown to affect the 

model calibration. Extrapolation of a point measurement to 

define spatially varied precipitation and potential ET over the 

basin adds uncertainty to the identification of the best-fit variable values. For example, the lowest flows during the calibration period were in 1999. Total precipitation between May 29 

and June 28, 1999, of 0.13 in. recorded at the Worcester NWS 

station (data used for model calibration) is less than the 0.23, 

0.17, and 0.21 in. recorded at daily precipitation stations closer 

to the basin (Bedford, Natick, and West Medway, respectively). The spatial precipitation differences could explain 

some of the difference between simulated and observed flows 

during this time. Additionally, model variables that control 

the rate of ET loss could have been skewed to compensate 

for spatial differences in precipitation. This is one example of 

how the representativeness of a point value can influence the 

performance of a model that spans a large area. 

Water-use information is another area of data uncertainty. Known water withdrawals are subtracted directly from 

simulated streamflow. Once withdrawals are accounted for, the 

model variable values are adjusted to calibrate the response 

of the basin to precipitation and ET. Unaccounted withdrawals, or inaccurate withdrawal information, can skew model 

variable values to compensate for these data deficiencies 

Figure 18. Summary of 1993–2003 mean (A) annual, (B) March, and (C) August water-budget outflow components 

simulated by the Hydrological Simulation Program–FORTRAN (HSPF) model of the Sudbury and Assabet River 

Basins, Massachusetts. 

-25

-20

-10

0

10

20

30

A Annual

INCHES PER YEAR OVER THE BASIN

-15

-5

5

15

25

C August

-5

-4

-3

-2

-1

0

1

2

-0.5

0

1.0

2.0

2.5

3.0

B March

0.5

1.5

EXPLANATION

Evapotranspiration

loss

Surface

Interflow

Active

groundwater

Interception

Upper zone

Lower zone

Active

groundwater

Discharge to 

streams

Loss to sewer 

inflow and 

infiltration
Simulated Effects of Water Use and Land Use on Streamflow

Chapter 1

47

during the calibration process. In addition, the model does 

not account for withdrawals in excess of streamflow, which 

means the simulated amount of water withdrawn does not 

exceed streamflow to maintain the mass balance of water. 

Withdrawals in excess of streamflow can be represented in 

the HSPF model through the use of Special Actions (Zarriello 

and Ries, 2000) that accounts for withdrawals in excess of 

streamflow and satisfies the excess withdrawals by decreasing 

streamflow later when it rises above the withdrawal rate as a 

surrogate measure of lost groundwater-storage and replenishment. This feature was not utilized in the Sudbury and Assabet 

River Basin HSPF model because it adds complexity to the 

model and was not considered a factor in most reaches. Where 

withdrawals deplete groundwater storage, streamflow may be 

oversimulated at times because the process of replenishing lost 

storage is not simulated; this condition is mostly a factor in 

headwater basins where the ratio of withdrawals to streamflow 

is largest.

The HRUs are simplifications of hydrologically complex and spatially variable land use, soils, surficial-geology 

types, and anthropogenic infrastructure. The model calibration 

reflects the combined interaction of various HRUs (PERLNDs 

and IMPLNDs) and reaches. Best hydrologic judgment was 

used to represent the responses of different PERLND and 

IMPLND HRUs. Although a reasonable fit was generally 

obtained between simulated and observed flows over a wide 

range of conditions, information was not available to calibrate 

individual HRUs explicitly. Thus, simulation results from 

ungaged areas or those that reflect changes of one type of 

HRU to another (such as projected 2030 land-use changes) 

have a high degree of uncertainty, and therefore, simulated 

flows for different scenarios are best viewed as a relative 

change instead of an absolute value. 

Uncertainty in the stage, storage, and discharge characteristics of reaches (including wetlands) affects simulated 

streamflow and stage. These characterizations are determined 

from measured channel geometry to the extent possible, but 

many factors, such as channel roughness and the large number 

of changes in channel geometry along a river reach, could 

not be measured. Uncertainties in the reach stage-storagedischarge relation could be a factor in simulated flows in the 

late summer of 1999 at Sudbury River near Hopkinton at Fruit 

Street (RCHRES 5, WBHK; fig. 9), which reached a minimum 

of 0.2 ft3

/s (the lowest flow simulated during the calibration 

period) that is nearly consistent with an observation of no 

flow reported by the Sudbury River Watershed Organization 

(Frederica Gillespie, Sudbury River Watershed Organization, 

written commun., June 2004). The small difference between 

simulated and observed flows could also be attributed to 

underflow, or subsurface flow, at an observation point. In 

HSPF, water that flows to a reach as baseflow or interflow is 

routed downstream through the reach channel; however, under 

certain geohydrologic settings, a portion of groundwater may 

continue to pass an observation point through the subsurface. 

As a result, during very low flows, the model may appear 

to oversimulate flow in the reach that could be unaccounted 

underflow at the streamgage. 

The HSPF model was conceptualized and calibrated 

to evaluate the effects of withdrawals on streamflow. Many 

water-resource-management questions can be addressed by 

model simulations, but the model may not be appropriate for 

some analyses. For example, groundwater withdrawals were 

represented in the model by an analytical solution that may 

not represent the actual flow path or source of water to a well. 

A pumped well that captures groundwater from an adjacent 

basin or subbasin could result in oversimulated flows in one 

basin and undersimulated flow in the other basin. As with all 

models, care should be taken to consider the model uncertainties and limitations to ensure that the simulation results do not 

lead to inaccurate conclusions. 

Simulated Effects of Water Use and Land Use on 

Streamflow

Model results provide a quantitative assessment of flow 

and flow alterations under various conditions. Although measured data are preferable, obtaining data takes considerable 

time and expense, and often the data are not available in the 

time needed to make appropriate planning decisions. Further, 

the data represent the climate and withdrawal conditions under 

which the data were collected, often making the evaluation of 

water-management alternatives difficult because conditions 

can change over time. Use of simulated flows is often the only 

practical means to evaluate the effects of water-management 

practices over a wide range of climatic conditions.

Although many types of hydrologic issues or questions 

can be posed within the bounds of the model’s limitations and 

uncertainties, the initial application of the model was limited 

to six scenarios agreed to by the Technical Advisory Committee (TAC). In addition to these scenarios, six additional 

simulations were made to examine projected 2030 water- and 

land-use change on streamflow and the effects of reactivating 

production wells near the northern end of Lake Cochituate. 

These scenarios entailed various combinations of land-use 

and water-use change simulated with an hourly time step over 

a wide range of climate conditions spanning the 1960–2004 

period. Simulation focused on the upper Sudbury River Basin 

(area above the Saxonville streamgage—01097300; fig. 9), 

where flows were of greatest concern; however, the model 

was constructed to output results for any of the subbasins 

represented in the Sudbury and Assabet River Basins, with the 

exception of the land-use change simulations that were limited 

to the upper Sudbury River Basin and the simulations of reactivating production wells near Lake Cochituate.

Each scenario required modification of the calibrated 

model to change water-use rates or HRUs representing landuse change, or both. Each scenario is uniquely identified by 

the uci file name, the IDSCEN attribute, and the data-set 

number (table 11). The two baseline simulations characterize 
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

48

long-term streamflow under current (1993–2003) average 

water-use conditions (AVGWU) and under no water use 

(NOWU). The NOWU simulation approximates a natural flow 

condition in which withdrawals and wastewater return flows 

are removed from the simulation; however, the 1997 landuse conditions represented in the calibrated model were not 

changed. The AVGWU simulation reflects the average calibration period (1993–2003) withdrawals and return flows. These 

flows were averaged by month and repeated over the simulation period, except for the calibration period, in which the 

actual water-use information was used. The NOWU simulation 

affects point withdrawals, point return flows, and distributed 

water gains or losses incorporated into HRUs associated with 

water supply or wastewater infrastructure, including water 

imports in areas on public-water supply and on-site septic, 

and water exports from sewer I&I losses; flow alterations that 

result from these features were essentially turned off. 

Effects of Current Water Use on Streamflow 

Streamflow simulated with no withdrawals, I&I loss, 

or return flows (NOWU) relative to average 1993–2003 

conditions (AVGWU) provides a relative basis for comparison of other simulation results. Average annual withdrawal 

in 1993–2003 in the upper Sudbury River Basin varied; 

withdrawals occurred in 8 of the 19 subbasins and ranged from 

about 0.001 to 2.92 Mgal/d with a median annual withdrawal 

of 0.48 Mgal/d (table 12). The degree to which streamflow is 

affected by withdrawals is determined by the magnitude of the 

withdrawals relative to the flow in the reach. Hence, reaches 

most susceptible to flow alteration are in headwater basins, but 

the effects of withdrawals can be transmitted downstream for 

some distance depending on the magnitude of the losses relative to the gains in streamflow.

The change in AVGWU simulated streamflows relative 

to NOWU simulated streamflows was most pronounced in 

Piccadilly Brook (PBWB, RCHRES 2) and Jackstraw Brook 

(JBWB, RCHRES 1). These are relatively small headwater 

subbasins where the ratios of mean annual withdrawals to 

mean annual streamflow are the highest in the basin (0.25 and 

0.48, respectively). Daily mean flow-duration curves (fig. 19A 

and B) developed from the 1960–2004 simulated flows indicate that AVGWU simulated flows begin to noticeably depart 

from NOWU simulated flows at about the 20- to 30-percent 

exceedence interval and are appreciably altered by about the 

50-percent exceedence interval. AVGWU simulated flows are 

less than 0.01 ft3

/s about 20 percent of the time in Jackstraw 

Brook and about 30 percent of the time in Piccadilly Brook, 

whereas NOWU simulated flows maintain a minimum flow of 

about 0.05 ft3

/s in both brooks. 

Table 11. Summary of model-run files (uci) and target data-set numbers (DSNs) for output of Hydrologic Simulation Program–

FORTRAN (HSPF) results of the Assabet and Sudbury River Basin, Massachusetts.

[IDSCEN, scenario-identification attribute in the Watershed-Data-Management (WDM) database; water use refers to withdrawals and return flows]

uci and IDSCEN 

name Output DSN Description

Baseline simulations–1999 land use

AVGWU 6101–6173 Average 1993–2003 water use

NOWU 6201–6273 No water use (no withdrawals, return flows, or imports and exports)

1999 land use and specified water-use change

GWoWU 6301–6373 Groundwater withdrawals only (surface-water withdrawals stopped)

SWoWU 6401–6473 Surface-water withdrawals only (groundwater withdrawals stopped)

Projected 2030 water-use or land-use conditions, or both

30WU99LU 6501–6573 2030 water use and 1999 land use 

30WULU 6601–6673 2030 water use and land use (limited to upper Sudbury River Basin)

30WULUalt 6701–6773 2030 water-use alternative (distributed water use–20 percent consumptive loss) and 2030 land use

30WUa99LU 6801–6873 2030 water-use alternative (distributed water use–20 percent consumptive loss) and 1999 land use

Reactivation of Framingham Birch Road supply wells

BIR_LC 6901–6904 Assumes all water is from Lake Cochituate 

BIR_LC66 6906–6909 Assumes two thirds of the water is from Lake Cochituate and the remainder is from Sudbury River

BIR_LC33 6911–6914 Assumes one third of the water is from Lake Cochituate and the remainder is from Sudbury River

BIR_SU 6916–6919 Assumes all water is from Sudbury River 
Simulated Effects of Water Use and Land Use on Streamflow

Chapter 1

49

Table 12. Water-use change by reach from average 1993–2003 withdrawals to projected 2030 demands simulated in the Hydrologic 

Simulation Program–FORTRAN (HSPF) model of the Sudbury and Assabet River Basins, Massachusetts.

[External target is the file read from the Watershed Data Management (WDM) database that reflects withdrawals from a reach; withdrawals in million gallons 

per day]

Reach 

number

Average annual withdrawals Distributed demand with 80-percent return 

1993–2003 2030 Percent 

change

External target 

multiplier

2030 annual 

withdrawal

External target 

multiplier

Sudbury River Basin

1 0.476 0.549 15 1.152 0.491 1.030

2 0.774 0.899 16 1.161 0.799 1.032

3 0.234 0.258 10 1.101 0.239 1.020

5 0.490 0.567 16 1.157 0.505 1.031

8 1.436 1.760 23 1.227 1.441 1.003

9 0.001 0.000 -100 0.0 0.030 1

0.0209

10 0.016 0.000 -100 0.0 0.030 1

0.0209

17 2.925 3.132 7.1 1.071 2.966 1.014

31 1.061 1.182 11 1.114 1.085 1.023

32 1.423 1.594 12 1.120 1.458 1.024

33 2.974 3.305 11 1.111 3.040 1.022

Assabet River Basin

51 0.727 0.838 15 1.153 0.749 1.031

52 0.006 0.006 0 1.000 0.006 1.000

53 0.366 0.399 9.1 1.091 0.373 1.018

54 0.616 0.692 12 1.122 0.631 1.024

55 0.198 0.227 15 1.146 0.204 1.029

56 1.386 1.386 0 1.000 1.386 1.000

58 0.135 0.151 12 1.119 0.138 1.024

60 0.002 0.002 0 1.000 0.002 1.000

61 1.599 1.769 11 1.106 1.633 1.021

62 0.244 0.244 0 1.000 0.244 1.000

63 0.002 0.002 0 1.000 0.002 1.000

64 0.525 0.570 8.6 1.086 0.534 1.017

66 1.141 1.309 15 1.147 1.175 1.029

67 0.672 0.783 16 1.165 0.694 1.033

68 0.364 0.426 17 1.170 0.377 1.034

69 0.620 0.667 7.6 1.076 0.629 1.015

1

Multiplier applies to projected municipal demand from reach 8.
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

50

The change in AVGWU simulated streamflows relative to NOWU simulated streamflows was also appreciable 

at the Ashland Reservoir outlet (ARES, RCHRES 10) and 

Lake Cochituate outlet (LCNA, RCHRES 16). Although 

these reaches drain larger areas than Jackstraw and Piccadilly 

Brooks, the ratios of mean annual withdrawals to mean annual 

streamflow are also high for Lake Cochituate outlet (0.13) and 

seasonally high for Ashland Reservoir outlet. Withdrawals 

from the Ashland Reservoir subbasin are mostly for irrigation; 

thus, on an annual basis, the ratio of mean annual withdrawals 

to mean annual streamflow is low (0.002), but during the peak 

irrigation period (June through August), the ratio of withdrawals to streamflow is large (0.13). Daily mean flow-duration 

curves (fig. 19C and D) developed from the 1960–2004 

simulated flows indicate that flows under AVGWU conditions 

begin to noticeably depart from NOWU flows at about the 

70-percent exceedence interval. AVGWU simulated flows are 

less than 0.1 ft3

/s about 10 percent of the time in Ashland Reservoir outlet (fig. 19C) and about 2 percent of the time in Lake 

Cochituate outlet (fig. 19D). Under NOWU simulated flows, 

Lake Cochituate outlet maintains a minimum flow of about 

0.2 ft3/s, whereas Ashland Reservoir outlet flows fall below 

0.1 ft3/s about 2 percent of the time. 

Flows are better sustained under NOWU in Jackstraw 

and Piccadilly Brooks than in Ashland Reservoir and Lake 

Cochituate outlets because of subtle differences in basin 

PERCENT OF TIME STREAMFLOW WAS EQUAL OR EXCEEDED

D Lake Cochituate outlet (LCNA, RCHRES 17) 

0.5 1 2 5 10 20 30 50 70 80 90 95 98 99 99.8

1

10

100

1,000

STREAMFLOW, IN CUBIC FEET PER SECOND

PERCENT OF TIME STREAMFLOW WAS EQUAL OR EXCEEDED

C Ashland Reservoir outlet (ARES, RCHRES 10) 

0.5 1 2 5 10 20 30 50 70 80 90 95 98 99 99.8

0.1

B Piccadilly Brook (PBWB, RCHRES 2) 

0.1

1

10

100

STREAMFLOW, IN CUBIC FEET PER SECOND

A Jackstraw Brook (JBWB, RCHRES 1) 

AVGWU

NOWU

GWoWU

SWoWU

0.01

Figure 19. Daily mean flow-duration curves from long-term (1960–2004) simulations with no withdrawals (NOWU), 

average 1993–2003 withdrawals (AVGWU), groundwater-only withdrawals (GWoWU), and surface-water-only withdrawals

(SWoWU) at (A) Jackstraw Brook (JBWB, RCHRES 1), (B) Piccadilly Brook (PBWB, RCHRES 2), (C) Ashland Reservoir 

Outlet (ARES, RCHRES 10), and (D) Lake Cochituate outlet (LCNA, RCHRES 17), upper Sudbury River Basin, Massachusetts. 

Locations are shown in figure 9.
Simulated Effects of Water Use and Land Use on Streamflow

Chapter 1

51

characteristics. Jackstraw and Piccadilly Brooks maintain 

about the same minimum flow when normalized for drainage 

area (about 0.46 and 0.41 ft3/s/mi2, respectively); each of these 

subbasins has a comparable percentage of contributing area of 

sand and gravel (18 percent each), forest (51 and 60 percent, 

respectively), and wetlands (8.2 and 5.1 percent, respectively). 

Although the percentages of the drainage area underlain by 

sand and gravel, which generally helps sustain low flows 

relative to other areas, are larger in the Ashland Reservoir and 

Lake Cochituate outlet subbasins (29 and 40 percent, respectively) than in Jackstraw and Piccadilly Brooks, the area of 

lakes and wetlands, which generally loses a greater amount of 

water to ET relative to other areas, is greater in Ashland Reservoir and Lake Cochituate outlet subbasins (16 and 18 percent, 

respectively) compared to Jackstraw and Piccadilly Brooks. 

Moreover, flow in the Ashland Reservoir and Lake Cochituate 

outlets is affected by large surface-water bodies and wetland 

areas (4.7 and 16 percent of the subbasin area, respectively) 

that are represented in the model as RCHRESs (10 and 17, 

respectively), which receive direct precipitation and lose 

water at the potential evaporation rate. This allows for greater 

evaporation loss per unit area in the Ashland Reservoir and 

Lake Cochituate outlet subbasins resulting in lower flows per 

unit area relative to the Jackstraw and Piccadilly Brooks, in 

which ET losses were limited by water availability in HRUs 

representing open water and wetlands. 

The effects of withdrawals on streamflow in other subbasins in the upper Sudbury River Basin are less pronounced 

than those shown for Jackstraw and Piccadilly Brooks, and 

Ashland Reservoir and Lake Cochituate outlets (fig. 19). In 

other subbasins, the largest differences in streamflow with 

and without withdrawals are in reaches immediately downstream from the four reaches noted above. To illustrate the 

effects of withdrawals over the entire upper Sudbury River 

Basin, the change in streamflow under average 1993–2003 

withdrawals (AVGWU) relative to no withdrawals (NOWU) 

is shown for the mean annual flow (fig. 20) and for the 

median of the August mean flow (fig. 21) simulated over the 

1960–2004 period. 

Withdrawals decreased the mean annual streamflow 

in the upper Sudbury River subbasins from 0.6 to 31 percent—the largest changes are in Piccadilly Brook (31 percent; 

PBWB, RCHRES 2), Jackstraw Brook (24 percent; JBWB, 

RCHRES 1), Indian Brook (17 percent; IBAS, RCHRES 8), 

and Lake Cochituate outlet (15 percent; LCNA, RCHRES 17), 

followed by reaches immediately downstream from these 

reaches (fig. 20). Minor changes between simulations with 

and without withdrawals are indicated in subbasins with no 

withdrawals because these reaches are affected by upstream 

reaches or by small I&I losses to sewer lines, or both. 

The effects of withdrawals on streamflow are generally 

more pronounced in the summer low flows as indicated by the 

median of the August mean flows, which decreased from 

83 to 0 percent (fig. 21). The largest changes in streamflow 

are generally in the same reaches as previously noted, except 

for Ashland Reservoir outlet (ARES, RCHRES 10), which 

now ranks among the reaches most affected by withdrawals because of the seasonal irrigation use. The median of the 

August mean flows with and without withdrawals decreased 

by 83 percent in Piccadilly Brook (PBWB, RCHRES 2), 

67 percent in Jackstraw Brook (JBWB, RCHRES 1), and 

31 percent in Lake Cochituate outlet (LCNA, RCHRES 17). 

Similar to the changes in the mean annual flow, changes in the 

median of the August mean flows with and without withdrawals in most other reaches reflect the cumulative effects of 

withdrawals on streamflow or small I&I losses to sewer lines, 

or both.

At Ashland Reservoir outlet (ARES, RCHRES 10), simulations with and without withdrawals indicate the median of 

the August mean flows decreased by 34 percent, whereas the 

mean annual flows decreased by only 4.4 percent. Withdrawals 

within the Ashland Reservoir subbasin are mostly for irrigation and, thus, are typically at a maximum during August when 

streamflow is typically at a minimum. As a result, differences 

between median of the August mean flows with and without 

withdrawals are large relative to differences in the annual 

mean flows with and without withdrawals. 

At Indian Brook (IBAS, RCHRES 8), simulations with 

and without withdrawals indicate a large change (-17 percent) in mean annual flows (fig. 20) relative to the change 

(-5.0 percent) in the median of the August mean flows 

(fig. 21). Streamflow in the lower part of Indian Brook (IBAS, 

RCHRES 8) is affected by Hopkinton Reservoir, which is 

a State recreational resource. The reservoir outflow can be 

regulated but was assumed to be released through a lower 

outflow gate at a relatively constant rate of 2 ft3/s when the 

water level in the reservoir falls below its spillway (outflows 

from the reservoir still decrease somewhat as the head in the 

reservoir drops). The flow-duration plot (fig. 22) indicates 

that streamflow below the reservoir is maintained at 2 ft3/s or 

more about 80 percent of the time under NOWU and about 

65 percent of the time under AVGWU. The relatively small 

change in the median of the August mean flow under NOWU 

(2.0 ft3

/s) and under AVGWU (1.9 ft3/s) likely reflects a 

change in reservoir storage because withdrawals from supply 

wells adjacent to the reservoir typically peak during August. 

Streamflow in RCHRES 8 over 1960–2004 averaged about 11 

and 13 ft3/s with and without withdrawals, respectively; flows 

of this magnitude affect the flow-duration curve, but the difference between duration curves continues to widen (fig. 22) as 

streamflow decreases until the lines converge corresponding to 

the release from the lower outflow gate of the reservoir (about 

2 ft3/s). It should be noted that releases from the reservoir 

can be regulated for recreation or other purposes and that 

downstream flows can be appreciably altered in response to 

this regulation.
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

52

Figure 20. Percent change in the simulated long-term (1960–2004) mean annual streamflows with average 1993–2003 withdrawals (AVGWU) relative to no withdrawals

(NOWU) in the upper Sudbury River Basin, Massachusetts.

71°20' 71°25' 71°30' 71°35'

42°20'42°15'

-0.6

-0.8

-2.6

-4.6

-7.0

-1.6

-6.2

-4.4

-1.3

-15

-17

-4.0

-6.6 -5.0

-3.5

-14

-24

-3.7

-31

HOPKINTON

NATICK

FRAMINGHAM

SHERBORN

MARLBOROUGH

ASHLAND

WESTBOROUGH

HOLLISTON

WAYLAND

UPTON

SUDBURY

SOUTHBOROUGH

NORTHBOROUGH

BERLIN

WESTON

HUDSON

From U.S. Geological Survey and MassGIS data sources, Massachusetts State Plane Coordinate System, Mainland ZonePolyconic projection

SRES

SRHK

IBHK

WRES

WBHK

ARES

CBNA

LBNA SRSX

FRES

BBFR

STRE

SRAS2

SRAS1

IBAS CBAS JBWB

PBWB

LCNA

0 1 2 3 4 MILES0 4 6 2 KILOMETERS

Subbasin boundary and model name (ARES)Town boundary

EXPLANATION

Minimum changeMaximum change 

Percent change

Calculated percent changeshown in subbasin

to
Simulated Effects of Water Use and Land Use on Streamflow

Chapter 1

53

Figure 21. Percent change in the simulated long-term (1960–2004) median of the August mean streamflows with average 1993–2003 withdrawals (AVGWU) relative 

to no withdrawals (NOWU) in the upper Sudbury River Basin, Massachusetts.

71°20' 71°25' 71°30' 71°35'

42°20'42°15'

HOPKINTON

NATICK

FRAMINGHAM

SHERBORN

MARLBOROUGH

ASHLAND

WESTBOROUGH

HOLLISTON

WAYLAND

UPTON

SUDBURY

SOUTHBOROUGH

NORTHBOROUGH

BERLIN

WESTON

HUDSON

From U.S. Geological Survey and MassGIS data sources, Massachusetts State Plane Coordinate System, Mainland ZonePolyconic projection

SRES

SRHK

IBHK

WRES

WBHK

ARES

CBNA

LBNA SRSX

FRES

BBFR

STRE

SRAS2

SRAS1

IBAS CBAS JBWB

PBWB

LCNA

0 1 2 3 4 MILES0 4 6 2 KILOMETERS

Subbasin boundary and model name (ARES)Town boundary

EXPLANATION

Minimum changeMaximum change 

Percent change

Calculated percent changeshown in subbasin

to

-2.0

0

0

-5.6

-19

0

-15

-34

-7.1

-31

-5.0

-9.6

-11 -15

-9.5

-23

-67

-30

-83
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

54

Figure 22. Daily mean flow-duration curves from longterm (1960–2004) simulations with no withdrawals (NOWU) 

and average 1993–2003 withdrawals (AVGWU), at Indian 

Brook (IBAS, RCHRES 8), upper Sudbury River Basin, 

Massachusetts. Location is shown in figure 9.

1

10

100

1,000

STREAMFLOW, IN CUBIC FEET PER SECOND

PERCENT OF TIME STREAMFLOW WAS EQUAL OR EXCEEDED

0.5 1 2 5 10 20 30 50 70 80 90 95 98 99 99.8

AVGWU

NOWU

Effects of Groundwater and Surface-Water 

Withdrawals on Streamflow

Groundwater-only (GWoWU) and surface-water only 

(SWoWU) withdrawals were simulated to isolate their effects 

on streamflow. These simulations held return flows, net water 

gains through public water supply and on-site septic, and net 

I&I losses the same as the AVGWU scenario. Most of the 

upper Sudbury River Basin is unaffected by these factors, but 

additional changes to the model uci file may be warranted 

when simulating other parts of the Sudbury and Assabet River 

Basins.

In general, the percent change in the median of the 

August mean flows with GWoWU relative to NOWU (fig. 23) 

are similar to that for AVGWU relative to NOWU (fig. 21) 

because most withdrawals in the upper Sudbury River Basin 

are from groundwater sources. Conversely, the percent change 

in the median of the August mean flows with SWoWU relative to NOWU are mostly small, except in Piccadilly Brook 

(fig. 24). Most changes in the median of the August mean 

flows with SWoWU and in many of the subbasins with 

GWoWU, relative to NOWU (fig. 23), result from sewer 

I&I losses.

Flow-duration curves developed from simulated streamflow in Jackstraw Brook and Lake Cochituate outlet indicate 

that GWoWU are the same as AVGWU and that SWoWU are 

the same as NOWU (fig. 19); flow-duration curves are slightly 

offset for clarity. This indicates groundwater is the sole source 

of water withdrawn from these basins. In Piccadilly Brook, the 

opposite is true; flow-duration curves (fig. 19B) indicate that 

surface water is the sole source of water withdrawn from the 

subbasin. At Ashland Reservoir outlet (fig. 19C), flow-duration curves developed from GWoWU and SWoWU simulated 

streamflows are between that developed from NOWU and 

AVGWU—the GWoWU curve is closer to the AVGWU curve 

and the SWoWU curve is closer to the NOWU curve. As previously noted, however, most withdrawals from this subbasin 

are from surface-water sources, but a number of these sources 

are isolated ponds (disconnected from the streams) and were 

treated as a groundwater withdrawal because they indirectly 

affect streamflows much like a pumped large-diameter shallow 

well would. Turning off all direct and indirect surface-water 

withdrawals in this subbasin would result in streamflows being 

similar to the no-withdrawal simulation.

Effects of Potential Water- and Land-Use Change 

on Streamflow

Four simulations examined the effects on streamflow of 

potential 2030 water- and land-use change (table 11) projected 

by the MAPC (M. Pillsbury, Metropolitan Area Planning 

Council, written comm., 2006). Two simulations (30WU99LU 

and 30WUa99LU) reflect changes in withdrawals and wastewater return-flow rates to projected 2030-use rates, but land 

use remained unchanged from the calibrated model (1997 

land-use conditions). In the 30WU99LU simulation, changes 

in water use were distributed among existing supply sources, 

and in the 30WUa99LU simulation, changes in water use 

were distributed among dispersed domestic supply sources. In 

the other two simulations (30LUWU and 30WULUalt), both 

water and land use were changed to reflect projected 2030 

conditions. In these simulations, land-use change was the 

same, but water-use change was simulated as described above; 

the 30LUWU simulation distributed the water-use change 

among existing sources and the 30WULUalt simulation distributed water change among dispersed domestic sources. 

In the 30WU99LU and 30WULU simulations, the 

MAPC-projected 2030 water demands by town were distributed among existing sources in proportion to the average 

amount each source supplied in 1993–2003. The projected 

2030 demand, in excess of the average 1993–2003 demand, 

was used as a multiplier in the uci file External Source Block

to reflect the total projected withdrawals from a reach; this 

approach maintains the same pattern of withdrawals over the 

1960–2004 climatic conditions as was used in the simulation 

of long-term average 1993–2003 withdrawals (AVGWU). The 

projected 2030 withdrawals in the upper Sudbury River Basin 

relative to the average 1993–2003 withdrawals changed by 

-100 to 23 percent with a median increase of about 13 percent 

(table 12). In RCHRES 9 and 10, current withdrawals are for 

irrigation purposes that were projected to be converted to residential land use resulting in no withdrawals from these reaches 

(-100 percent change) when distributed among existing supply 
Simulated Effects of Water Use and Land Use on Streamflow

Chapter 1

55

Figure 23. Percent change in the simulated long-term (1960–2004) median of the August mean flows with average 1993–2003 groundwater withdrawals (GWoWU) 

relative to no withdrawals (NOWU) in the upper Sudbury River Basin, Massachusetts.

71°20' 71°25' 71°30' 71°35'

42°20'42°15'

HOPKINTON

NATICK

FRAMINGHAM

SHERBORN

MARLBOROUGH

ASHLAND

WESTBOROUGH

HOLLISTON

WAYLAND

UPTON

SUDBURY

SOUTHBOROUGH

NORTHBOROUGH

BERLIN

WESTON

HUDSON

From U.S. Geological Survey and MassGIS data sources, Massachusetts State Plane Coordinate System, Mainland ZonePolyconic projection

SRES

SRHK

IBHK

WRES

WBHK

ARES

CBNA

LBNA SRSX

FRES

BBFR

STRE

SRAS2

SRAS1

IBAS CBAS JBWB

PBWB

LCNA

0 1 2 3 4 MILES0 4 6 2 KILOMETERS

Subbasin boundary and model name (ARES)Town boundary

EXPLANATION

Minimum changeMaximum change 

Percent change

Calculated percent changeshown in subbasin

to

-2.0

0

0

-5.6

-15

0

-14

-24

-7.1

-31

-5.0

-7.5

-7.7 -10

-9.5

-23

-67

-22

0
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

56

Figure 24. Percent change in the simulated long-term (1960–2004) median of the August mean flows with average 1993–2003 surface-water withdrawals (SWoWU) 

relative to no withdrawals (NOWU) in the upper Sudbury River Basin, Massachusetts.

71°20' 71°25' 71°30' 71°35'

42°20'42°15'

HOPKINTON

NATICK

FRAMINGHAM

SHERBORN

MARLBOROUGH

ASHLAND

WESTBOROUGH

HOLLISTON

WAYLAND

UPTON

SUDBURY

SOUTHBOROUGH

NORTHBOROUGH

BERLIN

WESTON

HUDSON

From U.S. Geological Survey and MassGIS data sources, Massachusetts State Plane Coordinate System, Mainland ZonePolyconic projection

SRES

SRHK

IBHK

WRES

WBHK

ARES

CBNA

LBNA SRSX

FRES

BBFR

STRE

SRAS2

SRAS1

IBAS CBAS JBWB

PBWB

LCNA

0 1 2 3 4 MILES0 4 6 2 KILOMETERS

Subbasin boundary and model name (ARES)Town boundary

EXPLANATION

Minimum changeMaximum change 

Percent change

Calculated percent changeshown in subbasin

to

-2.0

0

0

-5.6

-7.3

0

-4.0

-6.9

-7.1

-2.9

0

-3.1

-1.9 -3.4

-9.5

-2.2

0

-8.1

-83
Simulated Effects of Water Use and Land Use on Streamflow

Chapter 1

57

sources. Discharge from WWTPs in the 30WU99LU and 

30WULU simulations was increased in proportion to the additional projected withdrawals in the areas served by the facility.

In the 30WULUalt and 30WUa99LU simulations, the 

MAPC-projected 2030 water demands were distributed as dispersed domestic wells that return most water through on-site 

septic disposal. It was assumed that 80 percent of the projected 

increase in withdrawals would be returned through on-site septic systems; that is, 20 percent is lost from the basin, which is 

often referred to as consumptive use. These values were considered to reflect an end-member condition that is considered 

appropriate for peak summer consumptive use, but this value 

likely overestimates consumptive use during other periods of 

the year. The majority of land-use change (described later) 

is from forest to low-density residential development, and 

dispersed withdrawals will likely reflect much of the water-use 

change associated with the land-use change.

To simulate the dispersed withdrawals in the 30WULUalt 

and 30WUa99LU simulations, the projected change in withdrawals from a reach were increased by 20 percent of the projected 2030 withdrawal rate (table 12), except for RCHRESs 

8, 9, and 10. In these three reaches, the projected publicsupply withdrawal was assumed to come from RCHRES 8, 

the reach with the closest public supply source; therefore, the 

projected increase in demand from RCHRES 8 was distributed 

in proportion to the land-use change among RCHRESs 8, 9, 

and 10. Return flows, net water gains through public-water 

supply and on-site septic, and net I&I losses in the 30WULUalt and 30WUa99LU simulations were held the same as the 

AVGWU simulation.

Land-use change from 1997 to the MAPC-projected 2030 

conditions are illustrated in figures 25A and 25B for the simplified land-use categories used to develop the model HRUs. 

In general, the majority of land-use change was from forest 

to low-density residential development. In the upper Sudbury 

River Basin, forest area decreased by about 52 percent and 

low-density residential area increased by about 145 percent 

(table 13). As a percentage of the upper Sudbury River Basin 

area, forested area decreased by about half (from about 33 to 

16 percent); whereas low-density residential area more than 

doubled (from about 10 to 25 percent). 

Overall, the area of the upper Sudbury River Basin 

classified as some type of developed land-use category was 

projected to increase from about 42 percent in 1997 to about 

64 percent in 2030. Only modest changes were made to the 

amount of effective impervious area because most of the 

anticipated development is low-density residential and most 

new development is designed to minimize the effects of imperviousness on streamflow. Collectively, the effective impervious area in the upper Sudbury River Basin increased from 10 

to 13 percent from 1997 to 2030, respectively. The projected 

land-use change was generally similar in the Assabet River 

Basin—overall areas classified as some type of developed land 

increased from about 32 percent in 1997 to about 60 percent 

in 2030. It should be noted, however, that the uci file was 

modified to only reflect projected land-use change in the upper 

Sudbury River Basin (RCHRES 1 through 19). It should also 

be noted that the exact nature of land-use change is unknown 

and that the model variables associated with different types of 

land use are largely unknown because the model is calibrated 

to points that represent a mix of many land-use types. As a 

result, the simulations of land-use change have a large degree 

of uncertainty. Changes in streamflow as a result of changes in 

water use also have a large degree of uncertainty—in particular, how water is withdrawn from the basin (existing supply 

wells or dispersed domestic wells) and disposed (public sewer 

or on-site septic). Although the simulations presented cover a 

range of possible land- and water-use conditions, the results 

of the simulations should be used with these uncertainties 

in mind. 

In general, simulations of projected water-use change 

only (30WU99LU, fig. 26 and 30WUa99LU, fig. 27) produced results similar to those shown for the effects of average 1993–2003 withdrawals (AVGWU, fig. 21). Streamflow 

simulated under estimated 2030 demands distributed among 

existing supply sources (30WU99LU) indicates only minor 

decreases (1 to 5 percent) in the median of the August mean 

flows relative to AVGWU (figs. 26 and 21, respectively). The 

largest decrease (5 percent) relative to AVGWU was in lower 

Indian Brook (IBAS, RCHRES 8) because the supply well in 

this subbasin was assumed to cover RCHRES 9 and 10. The 

median August mean streamflow did not change appreciably 

in other reaches even though projected 2030 withdrawals 

increased. In these reaches, such as Jackstraw Brook (JBWB, 

RCHRES 1) and Piccadilly Brook (PBWB, RCHRES 2), 

expected 2030 withdrawals increased by 15 to 16 percent, 

respectively, relative to AVGWU, but no change in the median 

August mean streamflow was indicated. The mean annual 

streamflow in these reaches decreased by about 3 percent, 

however. This indicates that the streamflow in August was 

already less than the average 1993–2003 withdrawals most of 

the time and any increases in withdrawals, therefore, would 

have little or no effect on streamflow. Withdrawals from these 

reaches are met through changes in groundwater storage, 

which generally decrease streamflow later in the fall when 

streamflow exceeds the withdrawal rate and water would be 

available to replenish that lost from storage. This condition is 

accounted for in lost storage from the surface-water reservoir 

in Jackstraw Brook, but not in lost groundwater storage from 

pumped wells as previously described. 

The median of the August mean flows simulated under 

projected 2030 water demands distributed among existing 

supply sources (30WU99LU) indicate Ashland Reservoir 

outlet (ARES, RCHRES 10) and the next downstream reach, 

Cold Spring Brook (CBAS, RCHRES 11), increased substantially relative to AVGWU (figs. 26 and 21, respectively). The 

median of the August mean flow under AVGWU decreased 

by 34 and 30 percent relative to NOWU in RCHRES 10 and 

11, respectively. Simulated flows under 30WU99LU indicate no change from the NOWU in RCHRES 10 and 11. 

As previously described, withdrawals in ARES are largely 

for irrigation; if irrigated lands are converted to low-density 
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

58

Figure 25. Generalized land use as (A) classified from 1997 interpreted 1:25,000 aerial photographs, and (B) projected 

2030 buildout analysis by the Metropolitan Area Planning Council (M. Pillsbury, Metropolitan Area Planning Council, written 

commun., 2006), upper Sudbury River Basin, Massachusetts.

STATE ROUTE 9

STATE 

INTERSTATE 90

INTERSTATE 495

STATE ROUTE 20

INTERSTATE 290

ROUTE 2

A 1997 Land Use

UPTON

STOW

ACTON

HARVARD

CONCORD

BOLTON

SUDBURY

GRAFTON

HOPKINTON

NATICK

BERLIN

FRAMINGHAM

HOLLISTON

LITTLETON

CARLISLE

WAYLAND

SHERBORN

WESTFORD

MARLBOROUGH

WESTBOROUGH

HUDSON

ASHLAND

BOYLSTON

SHREWSBURY

LINCOLN

WESTON

NORTHBOROUGH

SOUTHBOROUGH

CLINTON

BOXBOROUGH

MAYNARD

EXPLANATION

Commercial, industrial, and transporation

High-density residential

Moderate-density residential

Low-density residential

Open land

Forest

Nonforested wetland

Forested wetland

Open water

KILOMETERS

MILES

10

10 2 3 4 5

0 2 4 6 8

71°40' 71°30' 71°20'

42°10'

42°20'

42°30'

Base from Massachusetts Executive Office of Energy and Environmental Affairs digital data;

EOTROADS_ARC, 1:5,000, 2006; HYDRO25K_ARC , 1:25,000, 2005; MAJPOND_POLY, 1:100,000, 1998; SUBBASINS_POLY, 1:25,000, 2007; TOWNS_POLY, 1:25,000, 2002

Polyconic projection. North American Datum of 1983 

Massachusetts coordinate system mainland zone
Simulated Effects of Water Use and Land Use on Streamflow

Chapter 1

59

Figure 25. Generalized land use as (A) classified from 1997 interpreted 1:25,000 aerial photographs, and (B) projected 

2030 buildout analysis by the Metropolitan Area Planning Council (M. Pillsbury, Metropolitan Area Planning Council, written 

commun., 2006), upper Sudbury River Basin, Massachusetts.—Continued

STATE ROUTE 9

STATE 

INTERSTATE 90

INTERSTATE 495

STATE ROUTE 20

INTERSTATE 290

ROUTE 2

UPTON

STOW

ACTON

HARVARD

CONCORD

BOLTON

SUDBURY

GRAFTON

HOPKINTON

NATICK

BERLIN

FRAMINGHAM

HOLLISTON

LITTLETON

CARLISLE

WAYLAND

SHERBORN

WESTFORD

MARLBOROUGH

WESTBOROUGH

HUDSON

ASHLAND

BOYLSTON

SHREWSBURY

LINCOLN

WESTON

NORTHBOROUGH

SOUTHBOROUGH

CLINTON

BOXBOROUGH

MAYNARD

EXPLANATION

Commercial, industrial, and transporation

High-density residential

Moderate-density residential

Low-density residential

Open land

Forest

Nonforested wetland

Forested wetland

Open water

B Projected 2030 Land Use

KILOMETERS

MILES

10

10 2 3 4 5

0 2 4 6 8

71°40' 71°30' 71°20'

42°10'

42°20'

42°30'

Base from Massachusetts Executive Office of Energy and Environmental Affairs digital data;

EOTROADS_ARC, 1:5,000, 2006; HYDRO25K_ARC , 1:25,000, 2005; MAJPOND_POLY, 1:100,000, 1998; SUBBASINS_POLY, 1:25,000, 2007; TOWNS_POLY, 1:25,000, 2002

Polyconic projection. North American Datum of 1983

Massachusetts coordinate system mainland zone
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

60

residential development that imports water from a neighboring subbasin, streamflow in the basin would be about the same 

as the no-withdrawal condition. Water demands in ARES in 

the 30WU99LU simulation were assumed to be met through 

increased withdrawals in the Indian Brook subbasins (IBAS, 

RCHRES 8; fig. 26), but without any net import of water 

through on-site septic disposal. 

When 2030 demands are met through dispersed 

domestic-well withdrawals (30WUa99LU) that are mostly 

returned through on-site septic disposal (assuming a 20-percent consumptive loss), streamflow in Ashland Reservoir 

outlet (ARES, RCHRES 10) and in downstream Cold Spring 

Brook (CBAS, RCHRES 11) increased substantially relative 

to AVGWU simulated streamflows (figs. 27 and 21, respectively), but not to the extent of NOWU simulated streamflow 

(fig. 19). The 30WUa99LU simulated median of the August 

mean flows still indicates a modest reduction in flow in these 

reaches relative to NOWU of 3.4 and 2.7 percent, respectively. Most other changes in streamflow simulated under 

30WUa99LU conditions indicate little change relative to 

AVGWU simulated flows (figs. 27 and 21, respectively). 

The effects of land-use and water-use change (30WULU 

and 30WULUalt) on streamflow are markedly different from 

AVGWU and from projected water-use change only simulations (30WU99LU and 30WUa99LU). However, changes 

are not in the direction normally expected as a result of 

development because many reaches indicate an increase in 

the median of the August mean flows relative to the NOWU 

(figs. 28 and 29). In subbasins with large municipal withdrawals, the median of the August mean flows under 30WULU 

and 30WULUalt decreased by a comparable amount to that 

simulated for AVGWU conditions (fig. 21) because municipal 

withdrawals remained unchanged. In most other subbasins, 

the median of the August mean flows for 30WULU and 

30WULUalt simulated flows increased substantially relative to 

AVGWU simulated flows and in 13 of 19 subbasins increased 

above the NOWU simulated flows. 

Typically, low flows are expected to decrease with 

development as a result of increased impervious area that 

decreases the opportunity for precipitation to infiltrate into the 

groundwater, thereby, decreasing the baseflow contribution to 

streams. The amount of precipitation diverted from infiltration 

is largely a function of the impervious area directly connected 

to the streams, or effective impervious area. However, development can also cause a loss in deep-rooted vegetation that 

decreases ET losses and increases baseflow to streams. The 

balance between decreased baseflow and ET determines the 

streamflow response associated with development. 

As previously noted, MAPC-projected land-use change 

in upper Sudbury River Basin was predominantly from forest 

to low-density residential development. As a result, all reaches 

in the upper Sudbury River Basin indicate an increase in the 

long-term (1960–2004) median of the August mean flows 

under projected 2030 land use (30WULU and 30WULUalt) 

relative to 1997 land use (figs. 28 and 29, respectively, 

compared to fig. 21), despite increased water withdrawals. 

The changes in the median of the August mean flows were 

modest in reaches where withdrawals have the greatest effect 

on streamflows, but in reaches where withdrawals do not 

greatly affect streamflows, the effect of land-use change is 

pronounced, often resulting in streamflows above the NOWU 

simulated flows. For example, in upper Indian Brook (IBHK, 

Table 13. Summary of Hydrologic Response Unit (HRU) changes simulated in the Hydrologic Simulation Program–FORTRAN (HSPF) 

model of the upper Sudbury River Basin, Massachusetts.

[Percent area may not add to 100 because of rounding]

HRU type

Area (acres) Percent 

change

Percent of basin area

1997 2030 1997 2030

Commercial-industrial-transportation 2,263 2,975 31 3.3 4.4

High-density residential 2,797 3,429 23 4.1 5.1

Moderate-density residential 9,642 10,914 13 14 16

Low-density residential 6,973 17,086 145 10 25

Open 5,911 2,621 -56 8.7 3.9

Forest 22,165 10,593 -52 33 16

Nonforested wetland 1,166 1,166 0 1.7 1.7

Forested wetland 6,045 6,045 0 8.9 8.9

Water 4,007 4,007 0 5.9 5.9

Effective impervious area 

Residential 1,512 1,992 32 2.2 2.9

Commercial-industrial-transportation 5,289 6,942 31 7.8 10
Simulated Effects of Water Use and Land Use on Streamflow

Chapter 1

61

Figure 26. Percent change in the simulated long-term (1960–2004) median of the August mean flows with estimated 2030 water withdrawals distributed among 

existing supply sources (30WU99LU) relative to no withdrawals (NOWU) in the upper Sudbury River Basin, Massachusetts. 

71°20' 71°25' 71°30' 71°35'

42°20'42°15'

HOPKINTON

NATICK

FRAMINGHAM

SHERBORN

MARLBOROUGH

ASHLAND

WESTBOROUGH

HOLLISTON

WAYLAND

UPTON

SUDBURY

SOUTHBOROUGH

NORTHBOROUGH

BERLIN

WESTON

HUDSON

From U.S. Geological Survey and MassGIS data sources, Massachusetts State Plane Coordinate System, Mainland ZonePolyconic projection

SRES

SRHK

IBHK

WRES

WBHK

ARES

CBNA

LBNA SRSX

FRES

BBFR

STRE

SRAS2

SRAS1

IBAS CBAS JBWB

PBWB

LCNA

0 1 2 3 4 MILES0 4 6 2 KILOMETERS

Subbasin boundary and model name (ARES)Town boundary

EXPLANATION

Minimum changeMaximum change 

Percent change

Calculated percent changeshown in subbasin

to

-2.0

0

0

-5.6

-21

0

-14

0

-7.1

-34

-10

-7.2

-12 -16

-9.5

-24

-67

0

-85
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

62

Figure 27. Percent change in the simulated long-term (1960–2004) median of the August mean flows with estimated 2030 water withdrawals dispersed among selfsupply sources and a 20-percent consumptive use (30WUa99LU) relative to no withdrawals (NOWU) in the upper Sudbury River Basin, Massachusetts.

71°20' 71°25' 71°30' 71°35'

42°20'42°15'

HOPKINTON

NATICK

FRAMINGHAM

SHERBORN

MARLBOROUGH

ASHLAND

WESTBOROUGH

HOLLISTON

WAYLAND

UPTON

SUDBURY

SOUTHBOROUGH

NORTHBOROUGH

BERLIN

WESTON

HUDSON

From U.S. Geological Survey and MassGIS data sources, Massachusetts State Plane Coordinate System, Mainland ZonePolyconic projection

SRES

SRHK

IBHK

WRES

WBHK

ARES

CBNA

LBNA SRSX

FRES

BBFR

STRE

SRAS2

SRAS1

IBAS CBAS JBWB

PBWB

LCNA

0 1 2 3 4 MILES0 4 6 2 KILOMETERS

Subbasin boundary and model name (ARES)Town boundary

EXPLANATION

Minimum changeMaximum change 

Percent change

Calculated percent changeshown in subbasin

to

-2.0

0

0

-5.6

-20

0

-14

-3.4

-7.1

-31

-5.0

-7.2

-11 -15

-9.5

-23

-67

-2.7

-83
Simulated Effects of Water Use and Land Use on Streamflow

Chapter 1

63

Figure 28. Percent change in the simulated long-term (1960–2004) median of the August mean flows with estimated 2030 land use and water withdrawals distributed 

among existing supply sources (30WULU) relative to no withdrawals (NOWU) in the upper Sudbury River Basin, Massachusetts.

71°20' 71°25' 71°30' 71°35'

42°20'42°15'

HOPKINTON

NATICK

FRAMINGHAM

SHERBORN

MARLBOROUGH

ASHLAND

WESTBOROUGH

HOLLISTON

WAYLAND

UPTON

SUDBURY

SOUTHBOROUGH

NORTHBOROUGH

BERLIN

WESTON

HUDSON

From U.S. Geological Survey and MassGIS data sources, Massachusetts State Plane Coordinate System, Mainland ZonePolyconic projection

SRES

SRHK

IBHK

WRES

WBHK

ARES

CBNA

LBNA SRSX

FRES

BBFR

STRE

SRAS2

SRAS1

IBAS CBAS JBWB

PBWB

LCNA

0 1 2 3 4 MILES0 4 6 2 KILOMETERS

to

Subbasin boundary and model name (ARES)Town boundary

EXPLANATION

Maximum positive change No change Maximum negative change 

Percent change

Calculated percent changeshown in subbasin

63

39

20

3.7

-1.0

8.7

5.2

17

50

-24

-5.0

20

9.0 4.2

4.8

-16

-67

19

-81
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

64

Figure 29. Percent change in the simulated long-term (1960–2004) median of the August mean flows with estimated 2030 land use and water withdrawals dispersed 

among self-supply sources with a 20-percent consumptive loss (30WULUalt) relative to no withdrawals (NOWU) in the upper Sudbury River Basin, Massachusetts.

71°20' 71°25' 71°30' 71°35'

42°20'42°15'

HOPKINTON

NATICK

FRAMINGHAM

SHERBORN

MARLBOROUGH

ASHLAND

WESTBOROUGH

HOLLISTON

WAYLAND

UPTON

SUDBURY

SOUTHBOROUGH

NORTHBOROUGH

BERLIN

WESTON

HUDSON

From U.S. Geological Survey and MassGIS data sources, Massachusetts State Plane Coordinate System, Mainland ZonePolyconic projection

SRES

SRHK

IBHK

WRES

WBHK

ARES

CBNA

LBNA SRSX

FRES

BBFR

STRE

SRAS2

SRAS1

IBAS CBAS JBWB

PBWB

LCNA

0 1 2 3 4 MILES0 4 6 2 KILOMETERS

Subbasin boundary and model name (ARES)Town boundary

EXPLANATION

Maximum positive change No change Maximum negative change 

Percent change

Calculated percent changeshown in subbasin

to

63

39

20

3.7

0

8.7

5.9

17

50

-23

-5.0

20

9.6 5.0

4.8

-15

-67

19

-79
Simulated Effects of Water Use and Land Use on Streamflow

Chapter 1

65

RCHRES 7), the long-term median of the August mean flows 

was 50 percent greater under projected 2030 land use simulated flows (30WULU and 30WULUalt; figs. 28 and 29, 

respectively) than NOWU flows (fig. 21). The median of the 

August mean AVGWU simulated flows in upper Indian Brook 

(fig. 23) are about 7.1 percent less than NOWU simulated 

flows (fig. 21). No withdrawals were specified from this 

subbasin; therefore, the net loss shown in figure 21 is from 

groundwater routed out of the basin to represent sewer I&I 

losses. The same losses to sewer I&I are specified in the projected 2030 simulations (30WULU and 30WULUalt), but the 

decrease in ET losses more than offsets these losses, resulting 

in an increase in the median of the August mean flows relative 

to 1997 land-use conditions.

Examination of the water-budget outflows for August 

reveals why the simulated land-use change resulted in an 

increase in the median of the August mean flows. In upper 

Indian Brook (IBHK, RCHRES 7), projected 2030 land use 

decreased forested HRUs by about 72 percent, and mediumand low-density residential HRUs increased by about 300 

and 430 percent, respectively. The August mean water-budget 

outflows (fig. 17) indicate that ET losses from medium- and 

low-density residential HRUs are about 15 percent less than 

ET losses from forested HRUs per unit area. When these 

values are applied to the distribution of HRU types in upper 

Indian Brook (IBHK) under 1997 land use (fig. 30A) and 

under the projected 2030 land use (fig. 30B), it becomes more 

apparent why the simulated median of the August mean flows 

increased. The resulting subbasin water-budget outflows 

indicate that the average 1993–2003 August inflow to streams 

increased by about 20 percent, and ET losses decreased by 

about 11 percent under project 2030 land use relative to 1997 

land use. 

In Course Brook (CBNA, RCHRES 16), the long-term 

median of the August mean flows increased by 3.7 percent 

under projected 2030 land use (figs. 28 and 29) relative to 

1997 land use (fig. 23). Similar to simulations in upper Indian 

Brook, withdrawals in Course Brook are not a factor and the 

small decrease in AVGWU simulated streamflow (7.1 percent) relative to NOWU simulated streamflow (fig. 21) is 

attributed to sewer I&I losses. Projected 2030 land use in the 

Course Brook subbasin decreased forested HRUs by about 

64 percent, and medium- and low-density residential HRUs 

increased by about 412 and 166 percent, respectively. Waterbudget outflows computed from the distribution of HRU types 

under 1997 land use (fig. 31A) and projected 2030 land use 

(fig. 31B) indicate that the average 1993–2003 median of the 

August mean flows increased by about 7.5 percent, and ET 

losses decreased an equal amount. 

Although changes in the median of the August mean 

flows associated with development can be pronounced, the 

changes in the long-term mean annual flows associated with 

development are relatively modest. Simulations of projected 

2030 water-use change only (30WU99LU and 30WUa99LU) 

indicate flow in most reaches remained about the same as 

AVGWU simulated flows; at most, long-term mean annual 

flows associated with water-use change only were about 3 percent more than the change in AVGWU simulated flows relative 

to NOWU simulated flows. The long-term mean annual flows 

simulated with projected 2030 water-use and land-use change 

(30WULU and 30WULUalt) generally increased relative to 

the AVGWU simulated flows (fig. 21); the change in mean 

annual flows decreased as the effect of withdrawals increased, 

but these changes were small relative to changes in the median 

of the August mean flows. 

The simulations of projected 2030 water-use and landuse change on streamflow reflect several possibilities, none of 

which can be viewed with certainty, however. The exact nature 

of future development is unknown, thus, the representation of 

these changes in the model are unknown. Given the projected 

land-use change in the upper Sudbury River Basin is predominantly from forest to medium- and low-density residential 

development, the increased water demands associated with 

development will likely be partially offset by decreased ET 

losses from the loss of deep-rooted vegetation also associated 

with development. The degree increased demands are offset by 

decreased ET losses will vary locally and may be reflected in 

one simulation more than another. However, the potential for 

increased low flows associated with low- to medium-density 

development is not a rationale for development because the 

effect of development on water quality, stream-water temperature, and other factors should also be considered.

Potential Effects of Reactivating Production 

Wells near Lake Cochituate

During the course of the study, reactivating production 

wells by the town of Framingham became of interest as did 

concern over their potential effects on streamflow and Lake 

Cochituate water levels. The production wells consist of a 

cluster of three wells in the Sudbury River Basin near the 

Saxonville streamgage about 1,400 ft from the northern edge 

of Lake Cochituate and about 600 ft from the upstream boundary of the SRCO (RCHRES 33) subbasin (fig. 3). Collectively, 

these wells are referred to as the Birch Road wells and were 

discontinued in 1979 when the town converted entirely to 

MWRA water supply. The town maintained the wells for 

emergency use and in June 2009 submitted a Draft Environmental Impact Report (DEIR) with the Commonwealth to 

reactivate the Birch Road wells for regular supply use. 

The source of water to these wells is not readily defined 

because the wells are near the border of several subbasin 

boundaries and pumping these wells will likely affect local 

groundwater flow paths so that the subsurface-water divides 

are no longer coincident with the surface-water divides. The 

potential sources of water to these wells is further complicated by the hydrogeology of the area. Gay (1985) shows a 

confining layer below the northern end of Lake Cochituate 

that pinches out as it slopes northward toward the production wells. Gay (1985) also shows that the hydraulic head in 

the confined aquifer on June 5, 1979 (it is not known if the 
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

66

Figure 30. Mean August (1993–2003) water-budget outflow components by Hydrologic Response Unit (HRU) simulated by the 

Hydrological Simulation Program–FORTRAN (HSPF) in upper Indian Brook (IBHK, RCHRES 7) under (A) 1997 land use and (B) projected 

2030 land use, upper Sudbury River Basin, Massachusetts. Location shown in figure 9.

Sand and Gravel Till Wetland

PERLNDs IMPLND

B Projected 2030 Land Use

INCHES OVER BASIN

-2.5

-2.0

-1.5

-1.0

-0.5

0

0.5

Sand and Gravel Till Wetland

PERLNDs IMPLND

A 1997 Land Use

INCHES OVER BASIN

-2.5

-2.0

-1.5

-1.0

-0.5

0

0.5

Evapotranspiration

loss

Evapotranspiration

loss

Surface

Interflow

Active

groundwater

Interception

Upper zone

Lower zone

Active

groundwater

Loss to sewer 

inflow and 

infiltration

Discharge to streams HRU Number

1 3 5 6 7 8 9 10 11 12 13 14 31 33 34 36 37 38 39 40 41 42 43 44 51 52 53 61 62

HYDROLOGIC RESPONSE UNITS (HRUs)

PERLNDs- Pervious area HRUs; IMPLNDs- Impervious area HRUs

Open

Forest

Open

Forest

Commercial

Residential

Nonforested wetlands

Forested wetlands

Open water

Self-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied septic

Public-supplied sewer

Commercial

High density

Medium density

Low density

Residential

Self-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied septic

Public-supplied sewer

Commercial

High density

Medium density

Low density

Residential

EXPLANATION

Discharge to streams
Simulated Effects of Water Use and Land Use on Streamflow

Chapter 1

67

Figure 31. Mean August (1993–2003) water-budget outflow components by Hydrologic Response Unit (HRU) simulated by the 

Hydrological Simulation Program–FORTRAN (HSPF) in Course Brook (CBNA, RCHRES 16) under (A) 1997 land use and (B) projected 2030 

land-use conditions, upper Sudbury River Basin, Massachusetts. Location is shown in figure 9.

Sand and Gravel Till Wetland

PERLNDs IMPLND

B Projected 2030 Land Use

INCHES OVER BASIN

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

Sand and Gravel Till Wetland

PERLNDs IMPLND

A 1997 Land Use

INCHES OVER BASIN

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

Evapotranspiration

loss

Discharge to streams

Discharge to streams

1 3 5 6 7 8 9 10 11 12 13 14 31 33 34 36 37 38 39 40 41 42 43 44 51 52 53 61 62 HRU Number

HYDROLOGIC RESPONSE UNITS (HRUs)

PERLNDs- Pervious area HRUs; IMPLNDs- Impervious area HRUs

Open

Forest

Open

Forest

Commercial

Residential

Nonforested wetlands

Forested wetlands

Open water

Self-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied septic

Public-supplied sewer

Commercial

High density

Medium density

Low density

Residential

Self-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied septic

Public-supplied sewer

Self-supplied septic

Public-supplied septic

Public-supplied sewer

Commercial

High density

Medium density

Low density

Residential

EXPLANATION

Evapotranspiration

loss

Surface

Interflow

Active

groundwater

Interception

Upper zone

Lower zone

Active

groundwater

Loss to sewer 

inflow and 

infiltration
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

68

Birch Road wells were active at this time), was below the 

lake level, indicating a downward gradient from the lake to 

the lower aquifer, which may have been caused by pumping 

of the Birch Road wells. Additional information is needed 

to understand and quantify the subsurface-water movement 

in this area, possibly requiring a multi-layer groundwater 

model to simulate the hydrologic response of a pumping 

stress in this complex hydrogeologic setting. Lacking this 

information, the HSPF model was used to simulate a steadystate pumping of 4.3 Mgal/d (6.65 ft3

/s), which was proposed in the DEIR, assuming four possible sources of water 

to the wells from induced infiltration or captured baseflow, or 

both, from (1) Lake Cochituate (BIR_LC) only, (2) Sudbury 

River (BIR-SU) only, (3) one third of the water is from Lake 

Cochituate and two thirds is from Sudbury River (BIR-LC33), 

and (4) two thirds of the water is from Lake Cochituate and 

one third is from Sudbury River (BIR-LC66). Whether water 

is from induced infiltration or captured baseflow that would 

normally discharge to the water feature is not distinguished 

in these simulations. These simulations were compared to 

long-term simulations reflecting average 1993–2003 water use 

(AVGWU), during which time the Birch Road wells were not 

active, and no water use (NOWU); the AVGWU and NOWU 

simulated conditions apply throughout the Sudbury and Assabet River Basins.

Although the entire Sudbury and Assabet River Basin 

hydrology was simulated in each of these scenarios, the 

output of the model was restricted to Lake Cochituate water 

level, and flows at the lake outlet (LCNA, RCHRES 17), the 

lake outlet brook near the confluence with the Sudbury River 

(LBNA, RCHRES 18), and Sudbury River at Saxonville 

(SRSX, RCHRES 19). Flow at the Saxonville streamgage 

was considered the most representative flow in the river near 

the withdrawals, although the effects of these withdrawals 

may occur mostly below the streamgage. In addition, simulated lake levels may not reflect actual levels because the 

lake outflow can be manually regulated. Simulations of lake 

levels, therefore, should be viewed as a relative change for 

comparison to other simulations. In addition, the FTABLE 

representing Lake Cochituate was modified to better represent 

changes in the stage-storage relation below the spillway. The 

FTABLE modification to RCHES 17 was limited to the uci

files associated with the reactivation of production wells near 

Lake Cochituate. 

Effects of reactivating the Birch Road wells on the water 

level of Lake Cochituate, its outflow, and in downstream 

reaches depend on the hydraulic connection of the well with 

the aquifer, the aquifer properties, and the distance of the 

pumped wells from these water features. Again, it should be 

noted that the simulation results presented assume a steady 

withdrawal rate of 4.3 Mgal/d (6.65 ft3

/s) and the lake levels are not managed. Unsteady withdrawal rates and active 

management of the lake levels can yield different results from 

those shown.

Assuming all water to the wells is from induced infiltration from or captured baseflow to Lake Cochituate (BIR_LC), 

long-term (1961–2004) outflow from the lake (LNCA, 

RCHRES 17) equals or exceeds 0.1 ft3/s about 80 percent 

of the time; in other words, streamflow ceases, or nearly 

ceases, about 20 percent of the time (fig. 32A). Under average 1993–2003 withdrawals (AVGWU), in which Birch 

Road wells are inactive, outflow from the lake equals or 

exceeds 0.1 ft3/s about 95 percent of the time. Under NOWU, 

simulated outflows equals or exceeds about 1 ft3/s all the 

time. Assuming all water to the Birch Road wells is induced 

infiltration from or captured baseflow to the Sudbury River 

(BIR_SU), outflows from the lake are identical to the AVGWU 

simulated flows, as would be expected (fig. 32A). Simulations 

that assume one third of the water to the wells is from Lake 

Cochituate and two thirds is from Sudbury River (BIR-LC33) 

and, alternatively, two thirds of the water is from Lake Cochituate and one third is from Sudbury River (BIR-LC66) result in 

flow-duration curves at the lake outlet that are proportionally 

spaced between simulations that assume all water to the wells 

is from the lake (BIR_LC) and none of the water to the wells 

is from the lake (BIR_SU). Flow-duration curves affected by 

withdrawals begin to noticeably depart from one another at 

about the 30-percent exceedence interval. These simulations 

illustrate the potential range of effects from reactivating the 

Birch Road wells on the lake outflows and flow in the Sudbury 

River near the pumped wells. 

The simulated long-term (1961–2004) streamflow at the 

Saxonville streamgage (SRSX, RCHRES 19) under average 

1993–2003 withdrawals (AVGWU) is about 6 ft3

/s or greater 

and under no withdrawals (NOWU) streamflow is about 8 ft3/s 

or greater. If all water to the Birch Road wells is induced infiltration from or captured baseflow to the Sudbury River, the 

simulated long-term streamflow at the Saxonville streamgage 

is about 1 ft3/s or less about 1 percent of the time (fig. 32B). 

It should be noted that flow at the Saxonville streamgage is a 

proxy for changes in flow that would likely be realized near, 

but downstream from the streamgage if the source water to 

the wells is induced infiltration from or captured baseflow that 

normally flows to the Sudbury River.

Changes in flow in the Sudbury River that result from 

pumping the Birch Street wells, unlike the changes in flow at 

Lake Cochituate outlet, do not change proportionally on the 

basis of the assumed source of water (fig. 32). This is because 

flows in the Sudbury River at the Saxonville streamgage are 

affected by flows from Lake Cochituate outlet. When the 

source of water to the Birch Street wells is assumed to come 

solely from Lake Cochituate, the changes in the lake outflow 

equally affect flows in the Sudbury River except when the rate 

of depletion (the pump rate that is assumed to come from Lake 

Cochituate) exceeds the rate of streamflow at which point 

water comes from lake storage. Changes in storage that result 

from depletion rates that exceed streamflow were simulated 

as a change in lake storage but may also result in a change in 

groundwater storage. 

Regardless of the assumed source of water in these 

simulations, flow-duration curves (fig. 32) indicate that the 

effects of pumping the Birch Street wells on streamflows at 
Simulated Effects of Water Use and Land Use on Streamflow

Chapter 1

69

Saxonville are nearly identical up to the 90-percent duration 

interval. At this point, the flow-duration curve developed from 

the BIR_LC simulated flows begins to move toward the flowduration curve for AVGWU simulated flows and are nearly the 

same at about the 98-percent duration interval. This indicates 

that, for the BIR_LC simulation, the streamflow contribution from the Lake Cochituate outflow to the Sudbury River 

diminishes when the flow in the river is below about 20 ft3

/s 

and there is no appreciable contribution when the flow in the 

river is below about 9 ft3/s. 

The Sudbury River flow in response to pumping the 

Birch Street wells incrementally changes in proportion to 

the source of water to the wells from the lake and the river 

(BIR_LC33 and BIR_LC66) at the lowest flows (fig. 32). Otherwise, the effects of pumping the wells on the Sudbury River 

are the same regardless of the sources of water simulated. The 

differences in the flow-duration curves at the lowest flows are 

proportional to the rate of depletion assumed to come from 

the Sudbury River, with the remainder of the total withdrawal 

coming from lake storage. 

Simulated stage in Lake Cochituate, when not managed, 

indicates water levels periodically fall below the spillway 

under average 1993–2003 withdrawals. For example, during 

1999, which had below-normal precipitation during the late 

spring and early summer, lake levels fell below the spillway 

for about 13 days in late June, recovered in early July, then fell 

below the spillway for about 56 days as dry-weather conditions continued until early September (fig. 33). As the pumped 

wells induce more infiltration from the lake, the number of 

episodes (a continuous period when water levels are below the 

spillway) and the length of the time the lake stage fell below 

the spillway increased. Over the 1961–2004 period, simulated water levels in Lake Cochituate under no withdrawals 

(NOWU) fell below the spillway five times lasting a total of 

29 days (the longest episode lasting 12 days in 1999 (table 14). 

For the same period, under average 1993–2003 withdrawals, 

the lake level fell below the spillway 53 times lasting a total 

of 731 days. The number of times (episodes) the lake fell 

below the spillway relative to average 1993–2003 withdrawals 

increased by 38, 60, and 77 percent for simulations that obtain 

one third (BIR_LC33), two thirds (BIR_LC66), and all water 

(BIR_LC) from induced infiltration from the lake, respectively 

(table 14). The total number of days lake levels fell below the 

spillway also increased substantially as more water is induced 

from lake infiltration as indicated in table 14 and as illustrated 

in figure 33. 

Simulations of withdrawals from reactivation of the Birch 

Road wells indicate that the lake stage and streamflow at the 

lake outlet and in the Sudbury River just below the Saxonville 

streamgage could be substantially affected during periods of 

low flow. These effects vary depending on the source of the 

water to the wells and are largely unknown. It should also be 

noted that the simulation results represent a constant pumping rate. If pumping rates varied, the effects on lake stage and 

flow could be mitigated if withdrawals were decreased at the 

appropriate times and by the appropriate amounts because 

the effects on lake level and flow were relatively small during 

periods of average or above-average discharge. 

PERCENT OF TIME STREAMFLOW WAS EQUAL OR EXCEEDED

B Sudbury River at Saxonville (SRSX, RCHRES 19)

0.5 1 2 5 10 20 30 50 70 80 90 95 98 99 99.8

AVGWU

NOWU

BIR_LC

BIR_LC33

BIR_LC66

BIR_SU

1

10

100

1,000

10,000

1

10

100

1,000

STREAMFLOW, IN CUBIC FEET PER SECOND

A Lake Cochituate outlet (LCNA, RCHRES 17)

0.1

AVGWU and BIR_SU

NOWU

BIR_LC

BIR_LC33

BIR_LC66

PERCENT OF TIME STREAMFLOW WAS EQUAL OR EXCEEDED

0.5 1 2 5 10 20 30 50 70 80 90 95 98 99 99.8

Figure 32. Daily mean flow-duration curves developed from 1960–2004 simulated flows under no withdrawals (NOWU), 

average 1993–2003 withdrawals (AVGWU), and reactivating production wells north of Lake Cochituate assuming water is 

induced infiltration from or captured baseflow to Lake Cochituate only (BIR_LC), Sudbury River only (BIR-SU), one third of 

the water is from Lake Cochituate and two thirds is from Sudbury River (BIR-LC33), and two thirds of the water is from Lake 

Cochituate and one third is from Sudbury River at (A) Lake Cochituate outlet, and (B) Sudbury River at Saxonville, upper 

Sudbury River Basin, Massachusetts. Locations shown in figure 9. 
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

70

Figure 33. Daily mean stage of Lake Cochituate in 1999 simulated under no withdrawals (NOWU), average 1993–2003 withdrawals

(AVGWU), and reactivating production wells north of Lake Cochituate assuming water is induced infiltration from or captured baseflow 

to Lake Cochituate only (BIR_LC), Sudbury River only (BIR_SU), one third of the water is from Lake Cochituate and two thirds is from 

Sudbury River (BIR_LC33), and two thirds of the water is from Lake Cochituate and one third is from Sudbury River (BIR_LC66), upper 

Sudbury River Basin, Massachusetts. Location shown in figure 9.

Table 14. Summary of the frequency and duration the Lake Cochituate water levels fell below the outflow spillway from 1961 through 

2004 simulated with the Hydrologic Simulation Program–FORTRAN (HSPF) under average 1993–2003 withdrawals (AVGWU), without 

withdrawals (NOWU), and reactivating production wells north of Lake Cochituate assuming water is induced infiltration or captured 

baseflow from Lake Cochituate only (BIR_LC), Sudbury River (BIR_SU) only, one third of the water is from Lake Cochituate and two 

thirds is from Sudbury River (BIR_LC33), and two thirds of the water is from Lake Cochituate and one third is from Sudbury River 

(BIR_LC66), upper Sudbury River Basin, Massachusetts.

[Episode, a period of continuous days water levels were below the spillway] 

NOWU

AVGWU 

and 

BIR_SU 

Percent 

change 

relative to 

NOWU

BIR_LC33

Percent 

change 

relative to 

AVGWU

BIR_LC66

Percent 

change 

relative to 

AvgWU

BIR_LC

Percent 

change 

relative to 

AvgWU

Number of episodes 5 53 960 73 38 85 60 94 77

Longest episode (days) 12 58 383 128 121 162 179 220 279

Total number of days water level 

below spillway

29 731 2,421 1,390 90 2,103 188 2,968 306

Mean duration of annual episodes 

(days)

0.49 8.4 1,616 15 85 28 232 32 277

Mean duration of annual episodes 

with non-zero values (days)

5.8 14 138 19 38 25 79 14 0

0

1

2

3

4

5

STAGE, IN FEET (DATUM IS ARBITRARY)

MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

1999

AVGWU and BIR_SU

NOWU

BIR_LC

BIR_LC33

BIR_LC66

JAN FEB

121

122

123

124

125

126

127

128

Spillway 

PRECIPITATION, IN INCHES
Summary

Chapter 1

71

Summary

Water withdrawals from reservoirs and the aquifer 

have affected streamflows in the Sudbury and Assabet River 

Basins, especially the upper Sudbury River Basin upstream 

from the USGS Saxonville streamgage. These effects are 

particularly evident in the summer when flows are at their 

lowest. A precipitation-runoff model, Hydrologic Simulation 

Program–FORTRAN (HSPF), was developed as part of this 

study to examine effects of current (1993–2003) water use and 

the effects of potential future (2030) water use and land use on 

streamflow. 

 The HSPF model was developed for the entire Sudbury 

and Assabet River Basins (339 mi2), but focused on the 106-

mi2 upper Sudbury River Basin, which was the primary interest of the study. The model was calibrated to daily streamflow 

records at four continuous-record streamgages operated by the 

USGS—Sudbury River at Ashland (01097480) and at Saxonville (01098530), Assabet River at Maynard (01097000), 

and Nashoba Brook near Acton (01097300)—for an 11-year 

period from January 1, 1993, through December 31, 2003. 

Flows at Sudbury River at Ashland were measured from May 

12, 1994, through October 1, 1995, but were estimated for 

the other parts of the 1993–2003 calibration period primarily 

by the Maintenance Of Variance Extension type 3 (MOVE-3) 

method. Nine partial-record stations (five in the Sudbury River 

Basin and four in the Assabet River Basin) were also used to 

evaluate and modify the model calibration.

The HSPF model is developed from hydrologic response 

units (HRUs) that are divided into pervious (PERLNDs) and 

impervious (IMPLNDs) areas to reflect relatively homogeneous hydrologic responses to climate on the basis of similar 

land use, surficial geology, and other factors. From each HRU, 

water is lost to evapotranspiration or routed into streams, 

lakes, and reservoirs defined by model reaches (RCHRESs). 

The HSPF model of the Sudbury and Assabet River Basins 

was represented by 27 PERLNDs and 2 IMPLNDs that connect to a network of 44 RCHRESs—23 represent the Sudbury 

River Basin, of which 21 represent the upper basin above 

the Saxonville streamgage. An hourly time step was used for 

all simulations. 

The HRUs were developed from 1997 land-use information that was simplified into nine classes and intersected with 

two types of surficial geology. Developed lands were further 

divided into areas of net water imports and exports determined 

from public water and sewer infrastructure. Collectively, 

land use in the Sudbury and Assabet River Basins is primarily forested (38 percent) or developed (36 percent), mostly as 

low- to medium-density residential (26 percent); forested and 

nonforested wetlands, and open water, compose about 13 and 

3.6 percent of the basin area, respectively. Open areas compose about 9.8 percent of the basin area. About 52 percent of 

the basin is underlain by sand and gravel, and the remainder 

is underlain by till and bedrock. Generally, the distribution of 

HRUs in the upper Sudbury River Basin is similar to other 

parts of the basin with the exception of open water (5.9 percent), which is a more dominant feature because of the large 

reservoirs. Effective impervious area (impervious area directly 

connected to streams) exerts a large influence on the hydrologic response of a basin; overall, 6.7 percent of the basin 

area was simulated as effective impervious area; in the upper 

Sudbury River Basin, about 10 percent of the basin area was 

simulated as effective impervious. 

Water-withdrawal information from January 1, 1993, 

through December 31, 2003, obtained from water suppliers for 

17 towns and from the Massachusetts Water Resource Authority (MWRA), was entered into the associated model database, 

the Watershed Data Management (WDM) system. Discharge 

data from five wastewater treatment plants were obtained 

for the same period from sewer districts for six towns in the 

Sudbury and Assabet River Basins and entered into the WDM 

database. Water withdrawals and wastewater return flows were 

applied to the appropriate reaches in the model; the lag effect 

of groundwater withdrawals on streamflow depletion was 

estimated through the analytical program STRMDEPL. Net 

imports of water through areas served by public supply and 

on-site septic disposal, and net exports of water through sewer 

inflow and infiltration (I&I) were simulated by additional 

HRU types modified from appropriate HRUs representing 

developed areas. 

Simulated streamflows for the 11-year calibration period 

generally agree well with observed streamflows at the four 

continuous-record streamgages given the potential error in 

observed data and by regulation of streamflow not accounted 

for in the model. The Nash-Sutcliffe model-fit efficiency 

coefficient (E) ranged from 0.23 to 0.55 for daily mean flows 

and from 0.67 to 0.72 for monthly mean flows; E appreciably 

improved at Sudbury River at Ashland to 0.70 for daily mean 

flows and 0.88 for monthly mean flows for the 1.5-year period 

of observed record. The difference between simulated and 

observed mean daily flow over the calibration period ranged 

from -5.9 to 5.1 percent. Much of the model error could be 

explained by spatial variability of precipitation over the basin.

The calibrated model was modified to simulate the effects 

on streamflow for various water uses, and for projected 2030 

water-use and land-use change, over long-term (1960–2004) 

climatic conditions. Additional simulations were made to 

simulate the effects of reactivating a cluster of production 

wells north of Lake Cochituate. The model results focused on 

the effects on streamflow in the upper Sudbury River basin 

(RCHRESs 1 through 19).

Water uses simulated include no withdrawals (NOWU), 

average 1993–2003 withdrawals (AVGWU), groundwateronly withdrawals (GWoWU), and surface-water-only withdrawals (SWoWU). The NOWU scenario shut off all withdrawals, return flows (discharges from wastewater treatment 

plants), water imports from areas on public water supply 

and on-site septic disposal, and water exports through sewer 
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

72

I&I losses. Average water use (AVGWU) applied the mean 

monthly withdrawals from 1993 through 2003 and computed 

streamflow depletion to the long-term (1960–2004) period 

except when actual withdrawals and associated streamflow 

depletion data were available. GWoWU and SWoWU simulations are similar to the AVGWU simulation except for turning 

off surface-water withdrawals and groundwater withdrawals, 

respectively.

 The change in AVGWU simulated streamflows relative 

to NOWU simulated streamflows was most pronounced in 

Piccadilly Brook (PBWB, RCHRES 2) and Jackstraw Brook 

(JBWB, RCHRES 1). These are relatively small headwater 

subbasins where the ratios of mean annual withdrawals to 

mean annual streamflow are the highest. Daily mean flowduration curves developed from 1960–2004 simulated flows 

indicate that the AVGWU curve noticeably departs from 

the NOWU curve at about the 20- to 30-percent exceedence 

interval and is appreciably altered by about the 50-percent 

exceedence interval in these reaches. Current withdrawals 

result in flows of 0.01 ft3

/s or less about 20 percent of the time 

in Jackstraw Brook and about 30 percent of the time in Piccadilly Brook, whereas under no withdrawals, both brooks maintain a minimum flow of about 0.4 ft3

/s/mi2. AVGWU simulated 

flows were also appreciably smaller than NOWU simulated 

flows in Ashland Reservoir outlet (ARES, RCHRES 10) 

and Lake Cochituate outlet (LCNA, RCHRES 16). Flowduration curves developed from 1960–2004 simulated flows 

indicate that the AVGWU curve begins to noticeably depart 

from the NOWU curve at about the 70-percent exceedence 

interval in these reaches. AVGWU simulated flows indicate 

that flows are less than 0.1 ft3/s about 10 percent of the time 

in Ashland Reservoir outlet and about 2 percent of the time 

in Lake Cochituate outlet. NOWU simulations indicate Lake 

Cochituate outlet maintains a minimum flow of about 0.2 ft3/s, 

whereas in the Ashland Reservoir, outlet flows fall below 

0.1 ft3/s about 2 percent of the time. The effects of withdrawals 

on streamflow in other subbasins in the upper Sudbury River 

Basin are less pronounced and mainly reflect the perpetuation 

of the effects of withdrawals from the reaches noted above. In 

general, the change in streamflow associated with groundwater-only withdrawals (GWoWU) relative to no withdrawals is 

similar to that for average 1993–2003 withdrawals relative to 

NOWU because most withdrawals in the upper Sudbury River 

Basin are from groundwater sources. The change in streamflow with surface-water-only withdrawals (SWoWU) relative 

to NOWU was only notable in Piccadilly Brook.

Four simulations examined the effects of potential 2030 

water- and land-use change projected by the Metropolitan 

Area Planning Council (MAPC). Two simulations evaluated 

the effects of water-use change only—30WU99LU, changes in 

water demand were distributed among existing supply sources, 

and 30WUa99LU, changes in water demand were simulated as 

dispersed domestic wells with a 20-percent consumptive-loss 

rate. In 30WUa99LU simulations, the remaining 80 percent 

was assumed to be returned through on-site septic disposal. 

Two other simulations evaluated the effects of both land-use 

and water-use change—30LUWU, which distributed projected 

withdrawals among existing sources, and 30WULUalt, which 

dispersed withdrawals among domestic wells and returns as 

described above. Simulations of land-use change redistributed 

the HRU areas to reflect the projected 2030 land-use conditions. In general, the majority of land-use change was from 

forest to low-density residential development. In the upper 

Sudbury River Basin, open forest area decreased by about 

52 percent and low-density residential area increased by 

about 145 percent. Overall, the area classified in some type 

of developed land-use category in the upper Sudbury River 

Basin changed from about 42 percent in the calibrated model 

(1997 land use) to about 64 percent in 2030. Because most of 

the anticipated development is low-density residential and new 

development employs techniques that minimize the effects of 

imperviousness, the simulated change in effective impervious 

area increased only by 3 percent in the upper Sudbury River 

Basin (from 10 to 13 percent). 

Streamflow simulated under estimated 2030 withdrawal demands distributed among existing supply sources 

(30WU99LU) indicates only minor decreases in the median of 

the August mean flows relative to AVGWU (1 to 5 percent). In 

the two headwater basins with large withdrawals (Jackstraw 

and Piccadilly Brooks), the small decreases reflect that the 

model does not account for withdrawals in excess of streamflow, which is a limitation of the model. The median August 

mean streamflow simulated under estimated 2030 withdrawal 

demands (30WU99LU and 30WUa99LU) indicates Ashland 

Reservoir outlet (ARES, RCHRES 10) and the next downstream reach, Cold Spring Brook (CBAS, RCHRES 11), 

increased substantially relative to AVGWU. Withdrawals from 

the ARES subbasin are largely for irrigation purposes; those 

agricultural lands were converted to low-density residential 

development. Under average 1993–2003 withdrawals, the 

median August mean streamflow decreased by 34 and 30 percent relative to NOWU in RCHRES 10 and 11, respectively. 

Projected 2030 demands distributed among existing supply 

sources (30WU99LU) indicate no change from the NOWU 

simulation in these reaches and modest reduction in flow of 

3.4 and 2.7 percent in reaches 10 and 11, respectively, relative 

to the NOWU when 2030 demands are from dispersed domestic well withdrawals (30WUa99LU). 

The effects of land-use and water-use change (30WULU 

and 30WULUalt) are markedly different from AVGWU and 

from simulations of projected water-use change only. In subbasins with large municipal withdrawals, the median of the 

August mean streamflow decreased by an amount comparable 

to AVGWU simulated flows. In most other subbasins, the 

median of the August mean streamflow increased substantially relative to the AVGWU simulated flows; streamflows 
Summary

Chapter 1

73

increased above the NOWU simulated flow in 13 of 19 subbasins. The increase in low flow is attributed to a decrease in 

evapotranspiration loss associated with a loss of deep-rooted 

vegetation. Changes in the long-term mean annual flows 

associated with development (30WU99LU and 30WUa99LU) 

indicate flow in most reaches remained about the same as 

AVGWU simulated flows. At most, long-term mean annual 

flow associated with water-use change only was about 3 percent more than the change in AVGWU simulated flow relative 

to NOWU simulated flows.

Simulations of withdrawals from reactivation of the Birch 

Road production wells near the north end of Lake Cochituate indicate lake stage and discharge at the lake outlet and 

in the Sudbury River at the Saxonville streamgage (a proxy 

for changes in flow below the streamgage) could be substantially affected during periods of low flow. These effects vary 

depending on the sources of the water to the wells, which 

are unknown. It should also be noted that the simulation 

results are based on a constant pumping rate, but if pumping 

rates were varied, the effects on lake stage and flow could be 

mitigated if withdrawals were decreased at the appropriate 

times and by the appropriate amounts. 

The HSPF model was conceptualized and calibrated 

to evaluate the effects of withdrawals on streamflow. Many 

water-resource-management questions can be addressed by 

model simulations, but the model may not be appropriate for 

some analyses. Care should be taken to consider the model 

uncertainties and limitations to ensure that the simulation 

results do not lead to inaccurate conclusions. Simulations of 

projected 2030 water-use and land-use changes on streamflows have inherent limitations and uncertainty because the 

exact nature of future development is unknown. The extent 

to which increased water demands are offset by decreased 

evapotranspiration losses will vary locally and may be 

reflected by one simulation more than another. Although tools 

such as HSPF are designed to simulate the effects of alternative water-management strategies and basin changes on water 

resources, it is necessary to determine whether model results 

can be appropriately used in making a specific water-resources 

management decision.
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 1

74

References Cited

Anderson, M.P., and Cheng, Xiangxue, 1993, Long- and shortterm transience in a ground-water/lake system in Wisconsin, 

U.S.A.: Journal of Hydrology, v. 145, p. 1–18.

Arcement, G.J., Jr., and Schneider, V.R., 1989, Guide for 

selecting Manning’s roughness coefficients for natural 

channels and flood plains: U.S. Geological Survey WaterSupply Paper 2339, 38 p.

Barbaro, J.R., 2007, Simulation of the effects of water withdrawals, wastewater-return flows, and land-use change on 

streamflow in the Blackstone River Basin, Massachusetts 

and Rhode Island: U.S. Geological Survey Scientific Investigations Report 2007–5183, 98 p.

Barbaro, J.R., and Zarriello, P.J., 2007, A precipitation-runoff 

model for the Blackstone River Basin, Massachusetts and 

Rhode Island: U.S. Geological Survey Scientific Investigations Report 2006–5213, 95 p.

Barlow, P.M., 2000, Documentation of computer program 

STRMDEPL—A program to calculate streamflow depletion 

by wells using analytical solutions, in Zarriello, P.J., and 

Ries, K.G., III, A precipitation-runoff model for the analysis 

of the effects of water withdrawals on streamflow, Ipswich 

River Basin, Massachusetts: U.S. Geological Survey WaterResources Investigations Report 00–4029, 99 p.

Barlow, L.K., Hutchins, L.M., and DeSimone, L.A., 2008, 

Water withdrawals, use, and wastewater return flows in the 

Concord River Basin, Eastern Massachusetts, 1996–2000: 

U.S. Geological Survey Scientific Investigations Report 

2008–5158, 125 p.

Beven, K.J., 1993, Prophecy, reality, and uncertainty in distributed hydrologic modeling: Advances in Water Resources, 

v. 6, p. 253–254.

Beven, K.J., and Binley, A.M., 1992, The future of distributed 

models—Model calibration and predictive uncertainty: 

Hydrological Processes, v. 6, p. 279–298.

Bicknell, B.R., Imhoff, J.C., Kittle, J.L., Jr., Jobes, T.H., and 

Donigian, A.S., Jr., 2000, Hydrological simulation programFortran, HSPF version 12 user’s manual: Mountain View, 

Calif., AQUA TERRA Consultants, EPA Contract No. 68-C98-010, 845 p.

Brackley, R.A., and Hansen, B.P., 1985, Hydrology and water 

resources of tributary basins to the Merrimack River from 

Salmon Brook to the Concord River, Massachusetts: 

U.S. Geological Survey Hydrologic Investigation Atlas 

HA–662, 2 pls.

Chorey, S., D’Andrea, L., Estella, E., Gaffney, C., Gerson, 

C., Meyer, E., Phaneuf, B., Titus, R., and Kolias, V., 2004, 

Town of Southborough, Massachusetts Affordable Housing 

Strategic Plan: accessed at http://www.southboroughtown.

com/Planning/Planning/strategic%20plan%20121704%20

-%20Final.pdf.

Chow, V.T., 1959, Open channel hydraulics: New York, 

McGraw-Hill, 680 p.

Coon, W.F., 1998, Estimation of roughness coefficients for 

natural stream channels with vegetated banks: U.S. Geological Survey Water-Supply Paper 2441, 133 p.

Duncker, J.J., and Melching, C.S., 1998, Regional rainfallrunoff relations for simulation of streamflow for watersheds 

in DuPage County, Illinois: U.S. Geological Survey WaterResources Investigations Report 98–4035, 80 p.

Flynn, K.M., Hummel, P.R., Lumb, A.M., and Kittle, J.L., 

Jr., 1995, User’s manual for ANNIE, version 2, a computer 

program for interactive hydrologic data management: 

U.S. Geological Survey Water-Resources Investigations 

Report 95–4085, 211 p.

Franke, O.L., Reilly, T.E., Pollock, D.W., and Labaugh, J.W., 

1998, Estimating areas contributing recharge to wells—

Lessons from previous studies: U.S. Geological Survey 

Circular 1174, 14 p.

Gay, F.B., 1985, Estimated water and nutrient inflows and 

outflows, Lake Cochituate, eastern Massachusetts, 1977–79: 

U.S. Geological Survey Water-Resources Investigations 

Report 84–4315, 59 p.

Hunt, R.J., Krabbenhoft, D.P., and Anderson, M.P., 1996, 

Ground-water inflow measurements in wetland systems: 

Water Resource Research, v. 32, no. 3, p. 495–507.

Hummel, P.R., Kittle, J.L., Jr., and Gray, M.H., 2001, 

WDMUtil—A Tool for managing watershed modeling 

time-series data user’s manual, Version 2.0: Decatur, Ga., 

AQUA TERRA Consultants, 165 p., accessed February 10, 

2008, at http://hspf.com/pub/basins3/doc/WDMUtil.pdf. 

Jensen, M.E., and Haise, H.R., 1963, Estimating evapotranspiration from solar radiation: Proceeding of the American 

Society of Civil Engineers, Journal of Irrigation and Drainage, v. 89, no. IR4, p. 15–41.

Kittle, J.L., Jr., Lumb, A.M., Hummel, P.R., Duda, P.B., and 

Gray, M.H., 1998, A tool for the generation and analysis of 

model simulation scenarios for watersheds (GenScn): 

U.S. Geological Survey Water-Resources Investigation 

Report 98–4134, 152 p.
References Cited

Chapter 1

75

Krabbenhoft, D.P., and Webster, K.E., 1995, Transient hydrogeological controls on the chemistry of a seepage lake: 

Water Resources Research, v. 31, no. 9, p. 2295–2305.

Legates, D.R., and McCabe, G.J., 1999, Evaluating the use 

the “goodness-of-fit” measure in hydrologic and hydroclimatic model validation: Water Resources Research, v. 35, 

p. 233–241.

Lent, R.M., Weiskel, P.K., Lyford, F.P., and Armstrong, D.S., 

1997, Hydrologic indices for nontidal wetlands: Wetlands, 

v. 17, no. 1, p. 19–30.

Lyford, F.P., Carlson, C.S., and Hansen, B.P., 2003, Delineation of water sources for public-supply wells in three 

fractured-bedrock aquifer systems in Massachusetts: 

U.S. Geological Survey Water-Resources Investigations 

Report 02–4290, 114 p.

Massachusetts Geographic Information System, 2009, 

MassGIS data: Boston, Mass., Data layers/GIS Database, 

accessed December 22, 2009, at http://www.mass.gov/mgis/.

Mills, J.G., and Zwarich, M.A., 1986, Transient ground-water 

flow surrounding a recharge slough in a till plain: Canadian 

Journal of Soil Science, v. 66, no. 1, p. 21–134.

Neilson, B.T., Horsburgh, J.S., Stevens, D.K., Matassa, M.R., 

and Brogdon, J.N., 2003, EPRI’s Watershed Analysis Risk 

Management Framework (WARMF) vs. USEPA’s Better 

Assessment Science Integrating Point and Nonpoint Sources 

(BASINS), in Total Maximum Daily Load (TMDL) Environmental Regulations–II Proceedings of the 8–12 November 2003 Conference, Albuquerque, New Mexico: 

St. Joseph, Mich., American Society of Agricultural and 

Biological Engineers, p. 460–470.

Regan, R.S., and Schaffranek, R.W., 1985, A computer program for analyzing channel geometry: U.S. Geological Survey Water-Resources Investigations Report 85–4335, 40 p.

Reilly, T.E., and Pollock, D.W., 1993, Factors affecting areas 

contributing recharge to wells in shallow aquifers: 

U.S. Geological Survey Water-Supply Paper 2412, 21 p.

Theis, C.V., 1940, The source of water derived from wells: 

Civil Engineering, v. 10, p. 277–280.

U.S. Census Bureau, 2009, Geography—TIGER: Washington, 

D.C., accessed December 22, 2009, at http://www.census.

gov/.

U.S. Environmental Protection Agency, 2009, BASINS (Better 

Assessment Science Integrating point & Non-point Sources: 

Washington, D.C., Water Quality Models and Tools, 

accessed December 22, 2009, at http://www.epa.gov/waterscience/basins/basinsv3.htm.

Vogel, R.M., and Stedinger, J.R., 1985, Minimum variance streamflow record augmentation procedures: Water 

Resources Research, v. 21, no. 5, p. 715–723.

Zarriello, P.J., and Bent, G.C., 2004, A precipitation-runoff 

model for the analysis of the effects of water withdrawals 

and land-use change on streamflow in the UsquepaugQueen River Basin, Rhode Island: U.S. Geological Survey 

Scientific Investigations Report 2004–5139, 75 p.

Zarriello, P.J., and Ries, K.G., III, 2000, A precipitation-runoff 

model for the analysis of the effects of water withdrawals 

on streamflow, Ipswich River Basin, Massachusetts: 

U.S. Geological Survey Water-Resources Investigations 

Report 00–4029, 99 p.
Chapter 2

Chapter 2—Fish Communities, Stream Temperature, and Assessment of 

Minimum Streamflow Targets for Aquatic Habitat at Selected Sites in the 

Sudbury and Assabet River Basins, Massachusetts

When streamflows are naturally low, typically during 

the summer between July and September, a conflict for water 

often arises between the needs of humans and those of aquatic 

life. This conflict is often veiled but is increasingly moving to 

the forefront as government agencies, nongovernment agencies, and water suppliers try to find the appropriate balance to 

meet conflicting water needs. The quality and quantity of the 

habitat that supports the biological integrity of the Sudbury 

and Assabet River Basins in eastern Massachusetts are of 

growing concern because of streamflow alterations by water 

withdrawals and wastewater returns. 

To help address these concerns, streamflows, fish communities, and stream temperatures were characterized at selected 

sites in the Sudbury and Assabet River Basins to evaluate the 

current condition of the aquatic habitat. These types of studies provide critical information for policy makers and other 

interested stakeholders that can assist in the determination of 

an appropriate balance between the needs for human water 

supply and aquatic habitat. These studies also help provide 

quantitative measures of some of the common aquatic stresses 

and their potential causes that could inform the managementdecision process. 

Purpose and Scope

This chapter describes fish communities, variation in 

stream-water temperature, and the streamflow needed to support aquatic habitat in the upper Sudbury and Assabet River 

Basins. The fish-community data, collected by the MADFW, 

are summarized for flowing reaches (not impounded) at 

five sites in the Sudbury River main stem and eight sites in 

the Assabet River main stem. Additional cold-water fishcommunity data are summarized for tributary reaches to these 

rivers. Water-temperature data were collected at seven sites 

in the upper Sudbury River Basin between August 2004 and 

June 2006. These data are summarized and characterized with 

respect to water-temperature tolerances of brook trout, a coldwater fish.

Streamflow targets intended to preserve aquatic habitat 

were determined by standard-setting methods at riffle reaches 

at six sites in the Sudbury River Basin and four sites in the 

Assabet River Basin. Standard-setting methods included the 

Wetted-Perimeter, R2Cross, Tennant, Aquatic Base Flow 

(ABF), and the Range-of-Variation (RVA) for a select set 

of hydrologic statistics; the last three methods relied on 

simulated unaltered streamflows determined by the HSPF 

precipitation-runoff model developed for the Sudbury and 

Assabet River Basins described in the first chapter of this 

report. Streamflows simulated by the HSPF model at the riffle 

sites were also used to determine and contrast the frequency 

and the duration that streamflows were below the flow thresholds determined by the various standard-setting methods. 

Fish Communities

Fish-community composition is generally considered a 

good measure of the ecological condition of a river because 

fish are sensitive to a wide range of stresses that reflect conditions over time. Although fish can live in different aquatic 

habitats, many species of fish are adapted to life in flowing 

waters and are considered riverine or fluvial fish. Ecologically 

healthy rivers have fish communities that are predominantly 

fluvial (Bain and Meixler, 2000, 2008). Many fluvial fish species require riffle habitat for part or all of their life cycle. Most 

streams in coastal Massachusetts naturally lack riffle habitat 

because of low gradients. Although streams in central Massachusetts have abundant riffles, many of these riffles have 

been hydrologically altered for many years by past mill dams, 

road crossings, and other uses. Fish-community composition 

can also be influenced by water temperature and quality. Data 

on fish-community composition in free-flowing reaches of the 

Sudbury and Assabet River Basins collected by the MADFW 

as part of their Statewide Fisheries Assessment Program were 

compiled to better understand the condition of river habitat. 

Fish were sampled during the summer during low to 

moderate flows because fish-community assemblages at this 

time are relatively stable and reflect the range of resident species (Gibson and others, 1996). The fish-community assessment was designed to characterize the diversity and relative 

abundance of fish species. The MADFW fish data also include 

the length-frequency distribution; however, these characteristics were not examined as part of this study. Sampling was 

conducted in selected free-flowing reaches on the river main 

stem and on tributaries. Where possible, a minimum reach 

length of 300 ft was sampled by electrofishing with pulsed 

direct current (DC) backpack units and barges. Backpack electrofishing units are best used in small or shallow streams and 

were used for sampling most tributary and headwater reaches 

in the Assabet and Sudbury River Basins. Barge electrofishing 

units (fig. 34) were used in many of the main-stem reaches of 

the Assabet and Sudbury Rivers where a strong power supply 

was needed. 
Fish Communities

Chapter 2

77

Fish were classified into three habitat-use categories—

macrohabitat generalists, fluvial dependents, and fluvial 

specialists (Bain and Knight, 1996; Bain and Meixler, 2000, 

2008). Macrohabitat-generalist fish species use a broad range 

of habitat to complete their life cycle and are commonly found 

in lakes, reservoirs, and streams. Fluvial-dependent fish species require access to flowing-water habitats for a specific life 

stage, but can complete part of their life cycle in non-flowing 

waters such as lakes and reservoirs. Fluvial-specialist fish species require flowing-water habitats throughout their life cycle 

and, therefore, are limited to free-flowing reaches (Bain and 

Travnichek, 1996).

Fish can live in different habitat conditions in different 

geographic areas. For the purposes of this study, habitat-use 

classifications were modified from Bain and Meixler (2000) to 

accommodate regional differences in habitat requirements. For 

example, the creek chub was reclassified from macrohabitat 

generalist to fluvial specialist on the basis of its habitat use in 

Massachusetts streams (M. Kearns, Massachusetts Department 

of Fish and Game, written commun., 2006). 

Main-Stem River Fish Communities 

Fish-community samples were collected at five locations 

on the main stem of the Sudbury River in July and August 

2001 (fig. 35). The sampled reaches are downstream from 

Whitehall Brook and upstream from Cold Spring Brook in the 

upper part of the basin. A total of 390 fish of 14 species were 

collected (table 15); of these, nearly 71 percent were macrohabitat generalists (fig. 36A).

Fish-community samples were collected at eight locations 

on the main stem of the Assabet River (fig. 35); most sampling was done in June through August 2001 and one sample 

(91) was collected in August 1999. A total of 1,065 fish of 22 

species were collected (table 15), including a tiger trout that is 

a cross species of brown and brook trout. Stocked salmonids, 

Figure 34. Massachusetts Department of Fish and Game, Division of Fisheries and Wildlife (MADFW) barge electrofishing to 

assess river-fish community composition. Photo courtesy of MADFW.
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 2

78

Figure 35. Main-stem fish-sampling sites, cold-water fishery reaches, stream-temperature gages, and riffle study locations 

in the Sudbury and Assabet River Basins, Massachusetts. MADFW, Massachusetts Division of Fisheries and Wildlife.

1

4

5

6

7

11

15

51

61

63

59

8

STATE ROUTE 9

STATE 

INTERSTATE 90

INTERSTATE 495

STATE ROUTE 20

INTERSTATE 290

ROUTE 2

308

306

309 310

311

373

399

433

496

497

502 579

91

Allowance Bk

Pine Bk

Jackstraw Bk

Piccadilly Bk

Hop Brook

unnamed

unnamed

unnamed

unnamed

A1 Reservoir

Howard Bk

North Bk

Hop Bk

Flagg Bk

Hog Bk

unnamed

Danforth Bk

Great Bk

Nagog Bk

Baiting Bk

Indian Bk

Whitehall Bk

Cold Spring Bk

Sudbury

River

Assabet

River

Sudbury

River

Hayward Bk

unnamed

unnamed Elizabeth Bk

Fort Meadow Bk

EXPLANATION

Sudbury River Basin

Assabet River Basin

308

Stream-temperature gage and number

MADFW main-stem fish sample site

and identification number

Riffle reach and number 8

1

Riffle reach with temperature

gage and number

6

MADFW designated Cold-water 

Fishery Reach (CFR)

KILOMETERS

MILES

10

10 2 3 4 5

0 2 4 6 8

71°40' 71°30' 71°20'

42°10'

42°20'

42°30'

Base from Massachusetts Executive Office of Environmental Affairs digital data, 1:24,000, 1995

Polyconic projection. North American Datum of 1983 

Massachusetts coordinate system mainland zone
Fish Communities

Chapter 2

79

Table 15. Fish species and numbers captured at selected free-flowing reaches in the main stem of the Sudbury and Assabet Rivers, 

Massachusetts.

[Data courtesy of Massachusetts Division of Fisheries and Wildlife; Habitat class; FD, fluvial dependent; FS, fluvial specialist; MG, macrohabit generalist]

Common name Species name Count Habitat class

Percent

Total Total in habitat 

class

Sudbury River

White sucker Catostomus commersoni 20 FD 5.1 100

Fallfish Semotilus corporalis 93 FS 34 99

Rainbow trout1 Oncorhynchus mykiss 1 FS 0.3 1.1

Redfin pickerel Esox americanus americanus 154 MG 39 56

Largemouth bass Micropterus salmoides 30 MG 11 11

Rock bass Ambloplites rupestris 23 MG 7.7 8.3

Yellow bullhead Ameiurus natalis 19 MG 5.9 6.9

Redbreast sunfish Lepomis auritus 16 MG 4.9 5.8

Bluegill Lepomis macrochirus 9 MG 3.3 3.3

Yellow perch Perca flavescens 9 MG 3.3 3.3

Pumpkinseed Lepomis gibbosus 7 MG 2.5 2.5

Chain pickerel Esox niger 5 MG 1.3 1.8

Brown bullhead Ameiurus nebulosus 3 MG 0.8 1.1

Golden shiner Notemigonus crysoleucas 1 MG 0.3 0.4

Assabet River

White sucker Catostomus commersoni 305 FD 29 100

Fallfish Semotilus corporalis 78 FS 7.3 38

Blacknosed dace Rhinichthys atratulus 74 FS 6.9 36

Brown trout1 Salmo trutta 20 FS 1.9 9.7

Rainbow trout1 Oncorhynchus mykiss 16 FS 1.5 7.8

Creek chubsucker Erimyzon oblongus 15 FS 1.4 7.3

Brook trout1 Salvelinus fontinalis 2 FS 0.2 1.0

Tiger trout1 Salvelinus fontinalis X Salmo trutta 1 FS 0.1 0.5

Largemouth bass Micropterus salmoides 82 MG 7.7 15

Bluegill Lepomis macrochirus 77 MG 7.2 14

American eel Anguilla rostrata 75 MG 7.0 14

Golden shiner Notemigonus crysoleucas 71 MG 6.7 13

Redbreast sunfish Lepomis auritus 56 MG 5.3 10

Yellow bullhead Ameiurus natalis 56 MG 5.3 10

Redfin pickerel Esox americanus americanus 55 MG 5.2 9.9

Pumpkinseed Lepomis gibbosus 33 MG 3.1 6.0

Chain pickerel Esox niger 16 MG 1.5 2.9

Spottail shiner Notropis hudsonius 11 MG 1.0 2.0

Yellow perch Perca flavescens 8 MG 0.8 1.4

Black crappie Pomoxis nigromaculatus 6 MG 0.6 1.1

Brown bullhead Ameiurus nebulosus 6 MG 0.6 1.1

Banded sunfish Enneacanthus obesus 2 MG 0.2 0.4

1

Stocked salmonid.
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 2

80

which included 20 brown trout, 16 rainbow trout, 2 brook 

trout, and 1 tiger trout, were removed from the description 

of the fish-community assessment below because they were 

stocked in the stream or adjacent waters by the MADFG and 

are not considered part of the self-sustaining native fish population. White suckers, a pollution-tolerant species, dominated 

the fish community in the main stem of the Assabet River (29 

and 100 percent of the total and fluvial communities, respectively), indicating that water quality may be a factor affecting 

the fish-community composition. Although the Assabet River 

contains a diversity of species similar to that expected in a 

natural river in southern New England (Kashiwagi and Richards, 2009), macrohabitat generalists still dominated the river 

(52 percent; fig. 36B), indicating other hydrologic alterations 

may be affecting the fish community. 

Cold-Water Fishery Resources 

The fish communities sampled in the main stem of the 

Sudbury and Assabet Rivers were primarily composed of fish 

that could tolerate warmer summer water temperatures. The 

tributaries to the Sudbury and Assabet Rivers vary greatly with 

respect to the degree of habitat, flow, and water-quality alteration. Some of these streams maintain a population of native 

cold-water fish, in this case brook trout, which is identified in 

the Massachusetts Wildlife Action Plan (Massachusetts Division of Fisheries and Wildlife, 2006) as a species in greatest 

need of conservation. 

The status of brook trout in the Sudbury and Assabet 

River tributaries was characterized by the Conservation Strategy Work Group Eastern Brook Trout Joint Venture (2005) as 

greatly reduced or even extirpated in some areas. The Eastern 

Brook Trout Joint Venture identified that stresses to populations of brook trout in Massachusetts were primarily caused 

by hydrologic alterations from dams, roads, and urbanization. 

These alterations result in increases in temperature and sedimentation, and changes to the natural flow regime.

Although the presence of brook trout in a water body 

does not mean the stream is pristine, it does indicate that the 

water quantity, water quality, and physical habitat are sufficient to maintain this sensitive species. The MADFG has 

identified 21 tributary reaches (fig. 35) as Cold-water Fishery 

Resources (CFRs) in the Sudbury (6 reaches) and Assabet 

(15 reaches) River Basins. Other CFRs may exist in the basin 

but have not yet been sampled. Many CFRs in the Sudbury 

and Assabet River Basins have drainage areas in or near 

Interstate 495 that are increasingly affected by urbanization. 

Even though some of these reaches have fish communities 

dominated by cold-water species, other reaches have been 

impacted by flow and water-quality alteration to the point that 

the cold-water community is reduced or absent in recently collected samples by the MADFG.

Stream Temperature

Water-temperature data were collected at seven sites in 

the upper Sudbury River Basin between August 2004 and 

June 2006 (fig. 35). Data were collected at 30-minute intervals with instream data loggers installed inside perforated 

PVC pipes mounted about 0.5 ft above the streambed on staff 

gages, trees, or a steel bar set in the streambed. Because water 

withdrawals and impoundment releases have been shown to 

Figure 36. Proportion of the 

fish community comprised 

of fluvial specialists, 

fluvial dependents, and 

macrohabitat generalists 

collected in the main stem 

of the (A) upper Sudbury 

and (B) Assabet Rivers, 

Massachusetts.

71

24

5

A Sudbury River

52

19

29

B Assabet River

Fluvial dependent

Fluvial specialist

Macrohabitat generalist

EXPLANATION

Numbers are percentage of total
Stream Temperature

Chapter 2

81

effect the downstream water temperature (Poole and Berman, 

2001), the seven water-temperature sites were divided into two 

groups related to their position relative to impoundments and 

water withdrawals. Three sites were on free-flowing tributaries upstream from water withdrawals and impoundments: 

(1) Jackstraw Brook near Westborough, (7) Indian Brook near 

Hopkinton, and (15) Baiting Brook near Framingham. Jackstraw Brook is identified by the MADFW as a CFR. Four sites 

were downstream from impoundments or water withdrawals, 

or both: (4) Whitehall Brook near Hopkinton, (5) Sudbury 

River near Hopkinton, (6) Sudbury River near Ashland, and 

(11) Cold Spring Brook near Ashland. Note the number in 

parentheses above refers to the gage identification number 

shown in figure 35, which is referenced to the reach number 

(RCHRES) in the HSPF model. 

Stream temperatures were evaluated relative to the 

tolerances of brook trout because of State and local concerns 

regarding maintenance of these native fish and their sensitivity 

to water temperature. In general, summer stream temperatures 

below 66°F are considered favorable for brook trout, and temperatures in the range of 68–84°F are considered precarious 

for brook-trout survival (Elliot, 1994). Although brook trout 

can tolerate temperatures in the 68–84°F range, their normal 

behavior is affected and can vary from cessation of feeding 

to death. These physiological effects increase in intensity as 

stream temperatures rise and are sustained for longer periods. 

During prolonged warm periods, populations of brook trout 

can exist in thermally marginal streams if sufficient cold-water 

refuges exist, such as shaded margins, springs, or pools that 

receive cool groundwater discharge. However, the distribution and abundance of brook trout in relation to temperatures 

of local cold-water refuges were not determined in this study. 

Stream temperatures recorded at the study sites provide a 

general indication of the suitability of summer stream temperatures for cold-water fish species (figs. 37 and 38). A 

7-day moving mean of daily maximum stream temperature 

was computed to illustrate differences in stream temperatures 

between the study sites and to more easily evaluate the duration and magnitude of stream temperatures in the critical range 

for brook trout.

The 7-day mean maximum daily temperature in Jackstraw Brook was generally below the critical range for brook 

trout (68–84°F) for all but a few days during the summer. 

When the temperatures were above the critical threshold, it 

was usually near the lower limit. In addition, the 7-day mean 

maximum daily temperatures in Jackstraw Brook were near 

or below the upper optimum summer temperature (66°F) for 

brook trout. The minimum daily temperatures were generally in the optimum range (55–66°F) for most of the summer 

period, but the daily maximums still rose into the critical 

range during part of the day. The cool stream temperatures in 

this segment of Jackstraw Brook are believed to be caused by 

the combined effects of groundwater discharge and shading of the stream channel. Jackstraw Brook provided the 

best water-temperature habitat for brook trout of the seven 

sites examined. 

Stream temperatures recorded at Indian and Baiting 

Brooks, the other two sites unaffected by dams or withdrawals, were in the critical temperature range for longer periods 

and at higher temperatures than at Jackstraw Brook (fig. 37), 

but temperatures were less than those recorded at the four sites 

affected by dams or withdrawals, or both (fig. 38). The higher 

7-day mean maximum daily temperature and intradaily temperatures in Indian and Baiting Brooks relative to Jackstraw 

Brook are believed to be caused by the large wetlands in the 

headwaters of Indian Brook subbasin, the removal of riparian 

vegetation, and the greater amount of impervious area in the 

Baiting Brook subbasin. 

The cooler summer water temperatures measured in the 

three unregulated tributary streams could potentially support a 

cold-water fishery, and brook trout have been found in samples 

collected at Jackstraw Brook by MADFW in the area of the 

temperature recorder. Although stream temperatures measured 

in Indian Brook and Baiting Brook were also near or within 

the summer optimum water-temperature range for brook trout, 

other conditions such as altered habitat, water quality, low 

flows, and impairments to stream passage may limit the ability 

of brook trout to find survivable habitat or move between suitable habitats.

The 7-day mean maximum daily temperatures observed 

at four study sites downstream from reservoirs and withdrawals (Whitehall Brook near Hopkinton, Sudbury River near 

Hopkinton, Sudbury River near Ashland, and Cold Spring 

Brook near Ashland) are generally similar and tend to be in 

the upper end of the critical range for brook trout survivability 

for a substantial time during the summer (fig. 38). Further, the 

temperature fluctuations during the day tend to be less at these 

sites compared to sites unaffected by reservoirs or withdrawals. This is likely caused by warm water released from the epilimnion (upper stratified water layer in the reservoir), whereas 

streams unaffected by dams have relatively large diurnal 

temperature fluctuations that are caused by discharge of cool 

groundwater to the stream, which warms during the day 

from solar radiation and increased daytime air temperatures. 

Hence, stream-water temperature can increase if the amount 

of groundwater discharging to a stream is reduced (Baevsky, 

1991; Stark and others, 1994; Picard, 1995). This may be 

a factor at the temperature monitoring sites in the Sudbury 

River. The small daily temperature fluctuations likely result in 

fewer temporary refuges from warmer waters creating a morestressed environment for temperature-sensitive fish. Overall, 

the 7-day mean maximum daily temperatures at the four sites 

affected by dams or withdrawals, or both, indicate that habitat 

for brook trout was marginal or poor in these reaches. 
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 2

82

Figure 37. Stream-water temperature recorded between August 2004 and June 2006 in reaches unaffected by dams or withdrawals 

at (A) Jackstraw Brook near Westborough, (B) Indian Brook near Hopkinton, and (C) Baiting Brook near Framingham, Sudbury River 

Basin, Massachusetts. 

A Jackstraw Brook near Westborough (1) 

20

30

40

50

60

70

80

90

STREAM-WATER TEMPERATURE, IN DEGREES FAHRENHEIT

B Indian Brook near Hopkinton (7)

20

30

40

50

60

70

80

90

20

30

40

50

60

70

80

90

C Baiting Brook near Framingham (15)

2005

A S O N D J F M A M J J A S O N D J F M A M J

2004 2006

Optimum summer 

temperature range for 

brook trout

Critical temperature 

threshold for brook 

trout survival

7-day moving mean of 

daily maximum 

temperature

Recorded temperature 

at 30-minute intervals

EXPLANATION

Number in parentheses 

following the site name 

refers to the gage 

identification number shown 

in figure 35.
Stream Temperature

Chapter 2

83

Figure 38. Stream-water temperature recorded between August 2004 and June 2006 in reaches below dams or withdrawals, or both, 

at (A) Whitehall Brook near Hopkinton, (B) Sudbury River near Hopkinton, (C) Sudbury River near Ashland, and (D) Cold Spring Brook 

near Ashland, Sudbury River Basin, Massachusetts. 

2005

A S O N D J F M A M J J A S O N D J F M A M J

2004 2006

STREAM-WATER TEMPERATURE, IN DEGREES FAHRENHEIT

Optimum summer 

temperature range for 

brook trout

Critical temperature 

threshold for brook 

trout survival

7-day moving mean of 

daily maximum 

temperature

Recorded temperature 

at 30-minute intervals

EXPLANATION

Number in parentheses 

following the site name 

refers to the gage 

identification number shown 

in figure 35.

A Whitehall Brook near Hopkinton (4)

20

30

40

50

60

70

80

90

20

30

40

50

60

70

80

90

C Sudbury River near Ashland (6)

B Sudbury River near Hopkinton (5)

20

30

40

50

60

70

80

90

D Cold Spring Brook near Ashland (11)

20

30

40

50

60

70

80

90
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 2

84

Determination and Assessment of Target 

Streamflows for Aquatic Habitat at 10 Riffle 

Sites

 Streamflow needs to maintain a healthy aquatic habitat 

were determined at 10 selected riffle sites in the Sudbury and 

Assabet River Basins (fig. 35) using 5 standard-setting methods. Five of these sites (4, 5, 6, 7, and 15) are coincident with 

the stream-temperature monitoring sites. The riffle identification number is the HSPF-model reach number associated 

with the riffle site. Streamflows computed by standard-setting 

methods are considered the minimal flow necessary to protect 

aquatic habitat and are referred to in this report as target 

streamflows. Most methods identify target streamflows appropriate for normal seasonal low- and high-flow periods. 

The standard-setting methods were divided into two 

categories—physically based and statistically based methods. Physically based methods included Wetted-Perimeter 

(Nelson, 1984; Leath and Nelson, 1986; Lohr, 1993) and the 

R2Cross (Nehring, 1979; Espegren, 1996, 1998); statistically 

based methods included Tennant (Tennant, 1976) and New 

England ABF (U.S. Fish and Wildlife Service, 1981; Lang, 

1999). A limited set of statistics from the RVA method (Richter 

and others, 1996) was also used. The RVA method is considered a diagnostic flow-assessment technique by the Instream 

Flow Council (2004) but was grouped with the statistical 

methods because only a limited set of flow statistics from 

the method were used in the analysis. The physical characteristics of the riffle reaches are described with the results of 

the physically based target flow determinations because they 

are inherently linked. 

Physically Based Streamflow Targets

The physically based target standard-setting methods, 

R2Cross and Wetted-Perimeter, were applied at six riffle 

reaches in the Sudbury River Basin and at four riffle reaches in 

the Assabet River Basin. These methods require site-specific 

physical and hydraulic data and can be applied at ungaged or 

flow-altered sites. However, values obtained by these methods 

are still subject to limitations as described later. Cross-section 

data and measurements of water-surface elevations in a riffle 

over a range of flows were used to develop and calibrate a 

one-dimensional hydraulic flow model, HEC-RAS (Brunner, 2006), for each site. The HEC-RAS model was used to 

compute streamflows that satisfy criteria for the R2Cross and 

Wetted-Perimeter methods. In general, the HEC-RAS models, documented in appendix 2 for the Sudbury River Basin 

sites and in Parker and others (2004) for the Assabet River 

Basin sites, were well calibrated to the observed water-surface 

gradients. 

Streamflow needed to satisfy the criteria for the 

physically based methods was determined from HEC-RAS 

simulations at one to five cross sections within each riffle 

that varied on the basis of their suitability for inclusion in the 

analysis. The streamflows reported for each method are the 

minimum flows needed to satisfy the method. The number 

of cross sections used for determining streamflow targets 

was typically less than the number of cross sections used for 

developing the HEC-RAS models. This was mostly because 

downstream cross sections were dropped from the determination of streamflow targets because of backwater conditions. 

The channel in each study reach was generally trapezoidal and 

its geometry was generally not a limiting factor in determining 

streamflow targets with physically based methods. 

Physically based methods assume that a streamflow 

chosen to maintain a riffle habitat is sufficient to maintain the 

habitat in nearby pools and runs for most life stages of fish 

and aquatic invertebrates (Nehring, 1979; Annear and Conder, 

1984; Lohr, 1993; Nelson, 1984). The R2Cross method 

considers three channel hydraulic properties in the determination of a streamflow target—average velocity, mean depth, 

and a percentage of the bankfull wetted perimeter; the latter 

two variables vary according to the bankfull top width of the 

stream (table 16). The wetted perimeter of a stream is defined 

as the cross-sectional length of channel (streambed and banks) 

in contact with water, but in R2Cross, this variable is defined 

as the flow necessary to maintain between 50 and 70 percent 

of the bankfull wetted perimeter in contact with water, depending on the bankfull top width. Bankfull refers to the normal 

channel incision into the landscape for conveying all but the 

highest streamflows. 

To account for seasonal streamflow variability, the 

R2Cross method establishes different streamflow targets for 

the summer and winter seasons on the basis of the number 

of criteria met. The R2Cross streamflow targets in Colorado 

(Espegren, 1996), where the method was developed, are based 

Table 16. R2Cross method hydraulic criteria in relation to 

channel bankfull top width.

[ft, feet; ft/s, foot per second]

Bankfull 

top width

(ft)

Average 

depth1

(ft)

Bankfull wetted 

perimeter2

(percent)

Average 

velocity

(ft/s)

1–20 0.2 50 1

21–50 0.2–0.5 50 1

51–60 0.5–0.6 50–60 1

61–100 0.6–1.0 70 1

1

 Values are scaled between 21 and 100 feet for the ranges shown.

2

 Values are scaled between 51 and 61 feet for the range shown.
Determination and Assessment of Target Streamflows for Aquatic Habitat at 10 Riffle Sites

Chapter 2

85

on flows that meet or exceed any two of the three criteria 

(2-of-3) during the normal low-flow period and all three criteria (3-of-3) during the normal high-flow period. The R2Cross 

2-of-3 and 3-of-3 criteria flows are reported, but as explained 

later, flows required to meet the 3-of-3 criteria do not appear 

to be applicable to seasonal high flows in this region. 

In the Wetted-Perimeter method, the flow necessary to 

keep the channel cross section in contact with water at the 

lower edges of the streambanks is the streamflow target. 

In trapezoidal-shaped channels with steep banks, the flow 

needed to maintain a wetted perimeter to the bottom edges 

of the streambanks is usually easily identifiable by a sharp 

break in the wetted perimeter-discharge relation. In triangular, 

bowl-shaped, or gently sloping trapezoidal-shaped channels, 

a clear breakpoint in the wetted perimeter-discharge relation 

may not be easily identifiable. An example of a breakpoint 

in the wetted perimeter-streamflow relation that cannot be 

easily identified is shown in figure 39D for cross section XS4 

in Fort Meadow Brook. In these types of situations, breakpoints in the water-surface elevation in relation to the wetted 

perimeter were used as a surrogate measure to define the flow 

corresponding to the wetted perimeter extending to the edges 

of the streambanks (fig. 39C). A cross check was made of the 

field-surveyed elevations of the bottom edges of the streambank with the elevation-wetted perimeter breakpoint. If these 

were reasonably consistent, the flow corresponding to that 

wetted perimeter determined at the breakpoints was used as 

the streamflow requirement for that cross section. If no distinct 

breakpoints were observed in the elevation-wetted perimeter 

relation, or if the points didn’t reasonably correspond to the 

field observations, a streamflow requirement was not determined for that cross section.

It should be noted that application of the R2Cross and 

Wetted-Perimeter methods requires careful selection of riffle 

sites. A riffle is a section of channel, usually between pools, 

that has gravel-to-cobble-sized bed material and a relatively 

steep channel slope. Differences in channel geometry throughout the riffle create variability in the determination of the 

flow needed to satisfy the method. To minimize some of the 

variability, cross sections in riffles that have large boulders or 

woody debris in the channel or altered streambeds or streambanks were avoided. For each method, flow targets were 

determined at each cross section used in the analysis, but to 

minimize the variability of these values, a median value was 

computed from the individual target values within a reach. 

Artificial widening or narrowing of the stream channel, 

such as bank reinforcement with riprap, affects the wetted 

perimeter, average velocity, and average depth; hence, altered 

channels were avoided in the selection of riffle cross sections. Flow targets computed by physically based methods in 

artificially restricted channels may be excessive compared to 

nearby natural riffle sites; conversely, flow targets determined 

for natural riffle sites may not be sufficient to protect habitat in 

artificially widened channels. 
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 2

86

6

10

STREAMFLOW, IN CUBIC 

FEET PER SECOND

0 10 15 20 25

498.0

498.2

498.4

498.6

498.8

499.0

ELEVATION, IN FEET

WETTED PERIMETER, IN FEET

18.4

Bottom, right bank

Bottom, left bank

2.2

8

4

2

0

5

C ELEVATION-WETTED PERIMETER RELATION

D STREAMFLOW-WETTED PERIMETER RELATION

Wetted-Perimeter Flow Requirement

497

498

499

500

501

502

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75

497

498

499

500

501

502

0 5 10 15 20 25 30 35 40 45 50 55 60 65

XS4

LB RB

XS5

LB RB

497

498

499

500

501

502

0 5 10 15 20 25 30 35 40 45 50

ELEVATION, IN FEET

XS3

LB RB

497

498

499

500

501

502

0 5 10 15 20 25 30 35 40 45 50 55 60 65

XS2

LB RB

497

498

499

500

501

502

0 5 10 15 20 25 30 35 40 45 50 55 60

CROSS-SECTION DISTANCE, IN FEET

B CROSS-SECTION PROFILES

XS1

LB RB

EXPLANATION

Survey points

Reference nail

Field determination of the bottom left (LB) and 

right (RB) streambanks

Surface-water level at time of survey

Field determination of normal channel flow (area 

of channel not vegetated)

X STATION, IN FEET

Y STATION, IN FEET

XS1

XS2

XS3

XS4

XS5

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70 80 90

Flow

direction

A CROSS-SECTION PLAN VIEW

Left

bank

Right

bank

Field determination 

of normal full 

channel flow

Figure 39. Riffle-reach study section showing (A) position of cross-section surveys, (B) cross-section profiles, (C) elevation and wetted 

perimeter relation, and (D) streamflow and wetted perimeter, Fort Meadow Brook near Hudson, Massachusetts. Elevation is an arbitrary 

reference datum.
Determination and Assessment of Target Streamflows for Aquatic Habitat at 10 Riffle Sites

Chapter 2

87

Whitehall Brook near Hopkinton

The riffle reach on Whitehall Brook (fig. 40; reach 4, 

fig. 35) is about 60 ft downstream from the Fruit Street Bridge 

near Hopkinton. Four cross sections were surveyed in September 2003 along a 90-ft reach. The streambed is primarily sand 

and gravel with a few cobbles; about 90 percent or more of the 

bed is covered by eel grass with an open section through the 

middle of the reach. Channel banks are primarily silt and sand 

with a mix of organic material. The left bank is covered by 

grass and sedge with a narrow border of hardwood trees; the 

right bank is covered by scattered trees, wetland shrubs, and 

lawn grass. The water-surface gradient in the reach is moderately sloped with a measured drop of about 0.5 ft for streamflows ranging from 1.1 to 196 ft3

/s. 

The HEC-RAS simulations indicate that cross sections 

at stations 118, 128, and 136 were unaffected by backwater 

during low to moderate flows and were used in the R2Cross 

analysis. The top width at normal channel flow (the stream 

channel that is mostly void of vegetation) in these sections 

ranged from about 16 to 23 ft with a median width of about 

21 ft. The limiting hydraulic metric (depth, velocity, or wetted 

perimeter) varied with the R2Cross 3-of-3 and 2-of-3 criteria at the three cross sections (table 17). Overall, depth was 

the most limiting factor, followed by wetted perimeter and 

velocity. Streamflows meeting the R2Cross 3-of-3 criteria 

ranged from 3.3 to 4.2 ft3

/s with a median of 3.6 ft3/s; streamflows meeting the R2Cross 2-of-3 criteria ranged from 1.1 to 

1.4 ft3/s with a median of 1.2 ft3/s. 

The same three cross sections were used in HEC-RAS 

simulations for the Wetted-Perimeter method analysis; target 

streamflows ranged from 1.5 to 2.1 ft3

/s with a median of 

1.8 ft3/s (table 17). The median Wetted-Perimeter streamflow 

target was about 50 percent greater than the median determined from the R2Cross 2-of-3 criteria method. 

Sudbury River near Hopkinton

The riffle reach on the Sudbury River near Hopkinton 

(fig. 41; reach 5, fig. 35) is about 100 ft downstream from the 

Fruit Street Bridge. Three cross sections were surveyed in 

September 2003 along a 15-ft reach. The streambed is primarily sand and gravel with cobbles and a few small boulders. 

Channel banks are composed of silt and sand mixed with 

organic material. The left bank is covered by a narrow border 

of hardwood trees and shrubs; the right bank is covered by 

scattered trees, wetland shrubs, and grasses. A railroad-bed 

embankment constricts the left-bank flood plain but does not 

directly affect the riffle habitat. The surface-water gradient in 

the reach is moderately sloped with a measured drop of 0.4 to 

0.2 ft for streamflows of 5.2 to 32 ft3/s, respectively. The riffle 

is short and becomes a run (a flooded riffle) at moderate to 

high flows. Longer riffles that are located downstream may 

provide suitable habitat, but because of channel alterations, 

these cross sections were not surveyed for use in the determination of flow standards.

The HEC-RAS simulations indicate that only one of 

the three sections surveyed (station 128) was unaffected by 

Figure 40. Downstream view 

of riffle on Whitehall Brook at 

Fruit Street near Hopkinton, 

Massachusetts. Location (site 4) 

shown in figure 35.
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 2

88

Table 17. Streamflow targets determined by the R2Cross and Wetted-Perimeter methods at 10 selected riffle sites in the Sudbury and Assabet River Basins, 

Massachusetts.—Continued

[Reach location shown on fig. 35; mi2, square miles; ft3/s, cubic foot per second; ft3/s/mi2, cubic foot per second per square mile; R2Cross limiting criterion- D, depth, V, velocity, WP, wetter perimeter; 

~, means cross section not used]

Reach 

number Reach name

Drainage 

area

(mi2

)

Crosssection 

station1

R2Cross 3-of-3 criterion R2Cross 2-of-3 criterion Wetted Perimeter

Discharge Limiting 

variable

Discharge Limiting 

variable

Discharge

(ft3/s) (ft3/s/mi2

) (ft3/s) (ft3/s/mi2

) (ft3/s) (ft3/s/mi2

)

Sudbury River Basin

4 Whitehall Brook near Hopkinton 6.64 118 4.2 0.633

D 1.4 0.211 WP 1.5 0.226

128 3.3 0.497

D 1.1 0.166 WP 2.1 0.109

136 3.6 0.542

V 1.2 0.181

D 1.8 0.093

5 Sudbury River near Hopkinton 19.3 128 18 0.933 WP 14 0.725

D 7.0 0.363

6 Sudbury River near Ashland 23.9 157 20 0.837

V 7.0 0.293

D 6.8 0.282

171

~

~

~

~

~

~ 10 0.418

192 30 1.255

V 8.0 0.335

D 3.0 0.126

209 25 1.046

D 6.1 0.255 WP 23 0.962

223 15 0.628

V 13 0.561

D 4.5 0.188

7 Indian Brook near Hopkinton 4.73 222 26 5.497

V 0.4 0.093

D 0.2 0.049

225 14 2.960

V 1.0 0.211

D 2.0 0.423

230 14 2.960

V 0.3 0.055

D 1.4 0.296

8 Indian Brook near Ashland 6.75 157 9.5 1.407

V 0.4 0.059

D 0.6 0.089

181 8.0 1.185

V 0.6 0.089

D 0.8 0.119

196 5.6 0.830

V 0.2 0.030

D 0.6 0.089

214 4.0 0.593

V 0.6 0.089 WP 1.1 0.163

15 Baiting Brook near Framingham 3.41 198 5.7 1.663

V 1.9 0.548

D 0.6 0.164

218 6.0 1.748

V 0.9 0.252

D 1.1 0.323

245

~

~

~

~

~

~ 0.8 0.220

265 8.2 2.390

V 1.2 0.340

D 0.2 0.067

285 5.7 1.663

V 3.0 0.868

D 0.9 0.267

Median (Sudbury River Basin) 1.185 0.211 0.188
Determination and Assessment of Target Streamflows for Aquatic Habitat at 10 Riffle Sites

Chapter 2

89

Table 17. Streamflow targets determined by the R2Cross and Wetted-Perimeter methods at 10 selected riffle sites in the Sudbury and Assabet River Basins, 

Massachusetts.—Continued

[Reach location shown on fig. 35; mi2, square miles; ft3/s, cubic foot per second; ft3/s/mi2, cubic foot per second per square mile; R2Cross limiting criterion- D, depth, V, velocity, WP, wetter perimeter; 

~, means cross section not used]

Reach 

number Reach name

Drainage 

area

(mi2

)

Crosssection 

station1

R2Cross 3-of-3 criterion R2Cross 2-of-3 criterion Wetted Perimeter

Discharge Limiting 

variable

Discharge Limiting 

variable

Discharge

(ft3/s) (ft3/s/mi2

) (ft3/s) (ft3/s/mi2

) (ft3/s) (ft3/s/mi2

)

Assabet River Basin

51 Assabet River near Westborough 6.79 117 5.8 0.854

V 0.6 0.088

D 0.6 0.088

128 6.8 1.001

V 0.4 0.059

D 0.2 0.029

136 8.0 1.178

V 0.5 0.066

D 0.2 0.029

59 Danforth Brook at Hudson 5.12 26 14 2.813

V 0.2 0.035

D 0.5 0.195

52 10 1.973

V 0.4 0.078

D

~

~

61 8.1 1.582

V 1.2 0.234

D

~

~

69 10 2.031

V 0.9 0.176

D

~

~

82 12 2.246

V 2.0 0.391

D 2.0 0.820

61 Fort Meadow Brook near Hudson 4.85 134 7.3 1.505

V 2.2 0.454

D 1.7 0.351

63 Elizabeth Brook near Stow 18.7 202 10 0.535

D 5.0 0.267

V 3.5 0.187

214 9.0 0.481

V 6.5 0.348

D 1.8 0.096

229 11 0.561

D 3.6 0.193

V 5.5 0.294

241 12 0.642

D 10 0.548

V 3.0 0.160

Median (Assabet River Basin) 1.178 0.193 0.174

Overall median 1.182 0.211 0.187

1Station position rounded to nearest foot.
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 2

90

Figure 41. Upstream view 

of riffle on Sudbury River at 

Fruit Street near Hopkinton, 

Massachusetts. Location (site 5) 

shown in figure 35.

Figure 42. Downstream view 

of riffle on Sudbury River near 

Ashland, Massachusetts. 

Location (site 6) shown in 

figure 35.

backwater and was used in the R2Cross and Wetted-Perimeter 

analyses. The top width in this section at bankfull flow is 

about 15 ft. The limiting R2Cross hydraulic factor at this 

section was wetted perimeter (streamflow of 18 ft3/s) for the 

3-of-3 criteria and depth (streamflow of 14 ft3/s) for the 2-of-3 

criteria (table 17). A streamflow of 7 ft3/s was needed to meet 

the criteria for the Wetted-Perimeter method for the same 

reach (table 17), which is half that determined by the R2Cross 

2-of-3 criteria method.

Sudbury River near Ashland

The riffle reach at the Sudbury River near Ashland 

(fig. 42; reach 6, fig. 35) is about 400 ft downstream from 

the Howe Street Bridge. Six cross sections were surveyed 

in September 2003 along a 100-ft reach. The streambed is 

primarily sand, gravel, and cobbles with emergent vegetation 

in the pool areas. Channel banks are composed of silt and 

sand mixed with organic material and an occasional boulder. 

The left bank is lined with shrubs that overhang the stream 

and thick forested vegetation further inland. The right bank at 

the downstream-most section is composed of natural riparian 

vegetation, but most of the natural vegetation on the right 

bank is replaced by a mowed lawn. The water-surface 

gradient in the reach is moderately sloped with a measured drop of 0.8 to 0.4 ft for streamflows ranging from 

4.7 to 70 ft3/s. 

The HEC-RAS simulations at stations 157, 192, 209, 

and 223 were used in the R2Cross analysis. The top width 

at normal full channel flow in these sections ranged from 

about 36 to 47 ft with a median width of about 42 ft. Velocity was the limiting hydraulic factor for the R2Cross 3-of-3 

criteria in three of the four sections and depth was the limiting 
Determination and Assessment of Target Streamflows for Aquatic Habitat at 10 Riffle Sites

Chapter 2

91

factor in the other section (table 17). Streamflows meeting 

the R2Cross 3-of-3 criteria varied from 15 to 30 ft3

/s with a 

median of 22 ft3/s. Depth was the limiting hydraulic factor for 

the R2Cross 2-of-3 criteria in three of the four sections and 

wetted perimeter was the limiting factor in the other section 

(table 17). Streamflow meeting the 2-of-3 criteria varied from 

6.1 to 13 ft3/s with a median of 7.5 ft3/s and was about a third 

of the flow meeting the 3-of-3 criteria. 

The same four cross sections, plus one additional section 

(station 171), were used in HEC-RAS simulations to determine streamflow targets by the Wetted-Perimeter method. 

Streamflows meeting the Wetted-Perimeter criteria ranged 

from 3.0 to 23 ft3/s with a median of 6.8 ft3/s (table 17). The 

median Wetted-Perimeter streamflow target was similar to 

the median flow target determined from the R2Cross 2-of-3 

criteria method. 

Indian Brook near Hopkinton

The riffle reach at the Indian Brook near Hopkinton 

(fig. 43; reach 7, fig. 35) is about 1,600 ft upstream from 

Hopkinton Reservoir and 1,300 ft west of Cedar Street along 

a walking trail near the Hopkinton State Park Headquarters. 

Seven cross sections were surveyed in October 2004 along 

a 100-ft reach. At about the middle of the reach, the walking 

trail crosses the brook over a bridge with a center pier that 

was also surveyed and included in the HEC-RAS model. The 

streambed is primarily cobbles with a few boulders, gravel, 

and silt. Channel banks are composed of silt over sand mixed 

with cobbles, boulders, and organic material. Shrubs and hardwood trees border both banks. The water-surface gradient is 

gently sloped with a measured drop of about 0.2 ft through the 

reach at streamflows ranging from 0.34 to 41 ft3/s. 

The HEC-RAS simulations indicate that cross sections at 

stations 222, 225, and 230 were unaffected by backwater and 

Figure 43. Upstream view of 

riffle from bridge on Indian Brook 

near Hopkinton, Massachusetts. 

Location (site 7) shown in figure 35.

were used in the R2Cross analysis. The top width at normal 

channel flow in these sections ranged from about 15 to 18 ft 

with a median width of about 17 ft. Velocity was the limiting 

hydraulic factor for all sections meeting the R2Cross 3-of-3 

criteria and depth was the limiting factor in all sections meeting the 2-of-3 criteria. Streamflow meeting the R2Cross 3-of-3 

criteria ranged from 14 to 26 ft3/s with a median of 14 ft3/s; 

streamflows meeting the R2Cross 2-of-3 criteria ranged from 

0.3 to 1.0 ft3/s with a median of 0.4 ft3/s (table 17). The large 

difference in the streamflow requirement between the 3-of-3 

and the 2-of-3 criteria is attributed to the low gradient in the 

reach, which required a high flow to meet the velocity criteria. 

The same three cross sections were used to determine 

streamflow targets by the Wetted-Perimeter method. Streamflows meeting the Wetted-Perimeter criteria ranged from 0.2 to 

2.0 ft3/s with a median of 1.4 ft3/s (table 17). The median Wetted-Perimeter streamflow target was about three times larger 

than that determined from the R2Cross 2-of-3 criteria method. 

Indian Brook near Ashland

The riffle reach at Indian Brook near Ashland (fig. 44; 

reach 8, fig. 35) is about 2,600 ft downstream from Hopkinton 

Reservoir and about 600 ft upstream from Cross Street. Five 

cross sections were surveyed in November 2004 along a 100-ft 

reach. The streambed is primarily gravel with a few cobbles. 

Channel banks are primarily silt over sand mixed with cobbles, gravel, and organic material. Shrubs and hardwood trees 

cover both banks, although some shrubs have been removed 

from the left bank. The water-surface gradient is moderately 

sloped with a measured drop of about 0.4 ft through the reach 

at streamflows ranging from 1.1 to 6.6 ft3/s. 

The HEC-RAS simulations indicate that cross sections at 

stations 157, 181, 196, and 214 were unaffected by backwater and were used in the R2Cross analysis. The top width at 
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 2

92

normal channel flow in these sections ranged from about 14 to 

16 ft with a median width of about 14 ft. Velocity was the 

limiting hydraulic factor for all sections meeting the R2Cross 

3-of-3 criteria; depth was the limiting factor in three of four 

sections meeting the 2-of-3 criteria and wetted perimeter was 

the limiting factor in the other section. Streamflows meeting the R2Cross 3-of-3 criteria ranged from 4.0 to 9.5 ft3

/s 

with a median of 6.8 ft3/s; streamflows meeting the R2Cross 

2-of-3 criteria ranged to 0.2 to 0.6 ft3/s with a median of 

0.5 ft3/s (table 17). 

The same four cross sections were used to determine 

streamflow targets by the Wetted-Perimeter method. Streamflows meeting the Wetted-Perimeter criteria ranged from 0.6 to 

1.1 ft3/s with a median of 0.7 ft3/s (table 17). The median 

wetted-perimeter streamflow target was similar to that determined by the R2Cross 2-of-3 criteria method. 

Baiting Brook near Framingham

The riffle reach at Baiting Brook near Framingham 

(fig. 45; reach 15, fig. 35) is about 400 ft downstream from 

Maple Street and about 250 ft upstream from its mouth on the 

Sudbury River. Nine cross sections were surveyed in October 2004 along a 170-ft reach. The streambed is primarily 

gravel with a few cobbles. Channel banks are composed of silt 

over sand mixed with cobbles, gravel, and organic material. 

Figure 44. Downstream view 

of riffle on Indian Brook near 

Ashland, Massachusetts. 

Location (site 8) shown in 

figure 35.

Figure 45. Upstream view 

of riffle on Baiting Brook near 

Framingham, Massachusetts. 

Location (site 15) shown in 

figure 35.
Determination and Assessment of Target Streamflows for Aquatic Habitat at 10 Riffle Sites

Chapter 2

93

Channel banks are bounded by shrubs and hardwood trees. 

The water-surface gradient is moderately sloped with a measured drop of about 1.5 ft through the reach for streamflows 

ranging from 0.4 to 9.6 ft3

/s. 

The HEC-RAS simulations indicate that cross sections at 

stations 198, 218, 245, 265, and 285 were unaffected by backwater and were used in the R2Cross analysis. The top width 

at normal full channel flow in these sections ranged from 

about 22 to 36 ft with a median width of about 24 ft. Velocity 

was the limiting hydraulic factor for all sections meeting the 

R2Cross 3-of-3 criteria, and depth was the limiting factor in 

all sections meeting the 2-of-3 criteria. Streamflows meeting 

the R2Cross 3-of-3 criteria ranged from 5.7 to 8.2 ft3/s with a 

median of 5.8 ft3/s; streamflows meeting the R2Cross 2-of-3 

criteria ranged from 0.9 to 3.0 ft3/s with a median of 1.5 ft3/s 

(table 17). 

The same four cross sections were used to determine 

streamflow targets by the Wetted-Perimeter method. Streamflows meeting the Wetted-Perimeter criteria ranged from 0.2 to 

1.1 ft3/s (table 17) with a median of 0.8 ft3/s. The median 

wetted-perimeter streamflow target was about half that determined by the R2Cross 2-of-3 criteria method. 

Assabet River near Westborough

The riffle reach at the Assabet River near Westborough 

(fig. 46; reach 51, fig. 35) is about 100 ft downstream from 

Fisher Street Bridge. Five cross sections were surveyed on 

July 2002 along a 100-ft reach. The streambed is primarily silt 

and sand with a few cobbles. Channel banks are composed 

of silt and sand mixed with organic material. The banks are 

bounded by a narrow border of shrubs then hardwood forest. 

The water-surface gradient is moderately sloped with a measured drop of 0.5 to 0.1 ft through the reach for flows ranging 

from 0.05 to 27 ft3/s.

The HEC-RAS simulations indicate that cross sections at 

stations 117, 128, and 136 were unaffected by backwater and 

were used in the R2Cross analysis. The top width at normal 

channel flow in these sections ranged from about 14 to 21 ft 

with a median width of about 15 ft. Velocity was the limiting hydraulic factor for all sections meeting the R2Cross 

3-of-3 criteria and depth was the limiting factor in all sections 

meeting the 2-of-3 criteria. Streamflows meeting the R2Cross 

3-of-3 criteria ranged from 5.8 to 8.0 ft3/s with a median of 

6.8 ft3/s; streamflows meeting the R2Cross 2-of-3 criteria 

ranged to 0.4 to 0.6 ft3/s with a median of 0.5 ft3/s (table 17). 

The same three cross sections were used to determine 

streamflow targets by the Wetted-Perimeter method. Streamflows meeting the Wetted-Perimeter criteria ranged from 0.2 

to 0.6 ft3/s with a median of 0.2 ft3/s (table 17). The median 

wetted-perimeter streamflow target was about half that determined by the R2Cross 2-of-3 criteria method. 

Danforth Brook at Hudson

The riffle reach on Danforth Brook (fig. 47; reach 59, 

fig. 35) is about 300 ft upstream from the Route 85 culvert in a 

conservation area owned by the town of Hudson. Seven cross 

sections were surveyed in September 2001 along an 80-ft 

reach of pool and riffle habitats. The streambed is primarily 

cobbles with a few scattered large boulders. Channel banks 

are composed of rich organic soil, silt, sand, and cobbles. The 

banks are bounded by scattered trees and shrubs. The channel 

takes a shallow bend to the left looking downstream along the 

study reach. The water-surface gradient is moderately steep 

with a measured drop of 1.8 to 1.6 ft through the reach for 

flows ranging from 0.01 to 28 ft3/s. 

The HEC-RAS simulations indicate that cross sections 

at stations 26, 52, 61, 69, and 82 were unaffected by backwater and were used in the R2Cross analysis. The top width 

Figure 46. Downstream view 

of riffle on Assabet River near 

Westborough, Massachusetts. 

Location (site 51) shown in 

figure 35.
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 2

94

at normal channel flow in these sections ranged from about 

20 to 25 ft with a median width of about 23 ft. Velocity was 

the limiting hydraulic factor for all sections meeting the 

R2Cross 3-of-3 criteria and depth was the limiting factor in 

all sections meeting the 2-of-3 criteria. Streamflows meeting 

the R2Cross 3-of-3 criteria ranged from 8.1 to 14 ft3

/s with a 

median of 10 ft3/s; streamflows meeting the R2Cross 2-of-3 

criteria ranged from 0.2 to 2.0 ft3/s with a median of 0.9 ft3/s 

(table 17). 

The target flows were determined at only two cross sections (26 and 82) by the Wetted-Perimeter method. Streamflows meeting the Wetted-Perimeter criteria were 0.5 and 

2.0 ft3/s at cross sections 26 and 82, respectively (table 17). 

The median Wetted-Perimeter streamflow target (1.2 ft3/s) 

was about equal to that determined from the R2Cross 2-of-3 

criteria method. 

Fort Meadow Brook near Hudson

The riffle reach on Fort Meadow Brook (fig. 48; reach 

61, fig. 35) is 1,350 ft upstream from the Shay Street culvert in 

Hudson. Five cross sections were surveyed in July 2002 along 

a 90-ft reach. The streambed is primarily cobble and gravel. 

Channel banks are composed of rich organic material bordered 

by large pine trees. The water-surface gradient is moderately 

sloped with a measured drop of about 0.6 ft through the reach 

for flows ranging from 0.84 to 6.8 ft3/s. 

The HEC-RAS simulations indicate that only one cross 

section (station 134) was unaffected by backwater and was 

used in the R2Cross and Wetted-Perimeter analyses. The 

bankfull top width was about 19 ft at this section. Velocity 

was the limiting hydraulic factor meeting the R2Cross 3-of-3 

criteria and depth was the limiting factor meeting the 2-of-3 

Figure 47. Upstream view of riffle on 

Danforth Brook at Hudson, Massachusetts. 

Location (site 59) shown in figure 35.

Figure 48. Upstream view of riffle on Fort 

Meadow Brook near Hudson, Massachusetts. 

Location (site 61) shown in figure 35. 
Determination and Assessment of Target Streamflows for Aquatic Habitat at 10 Riffle Sites

Chapter 2

95

Figure 49. Downstream view of 

riffle on Elizabeth Brook near Stow, 

Massachusetts. Location (site 63) 

shown in figure 35.

criteria. Streamflows meeting the R2Cross 3-of-3 and 2-of-3 

criteria were 7.3 and 2.2 ft3/s, respectively (table 17). Streamflow meeting the Wetted-Perimeter target (1.7 ft3

/s; table 17) 

is about 23 percent less than that determined by the R2Cross 

2-of-3 criteria method. 

Elizabeth Brook near Stow

The riffle reach on Elizabeth Brook (fig. 49; reach 63, 

fig. 35) is about 0.2 mi south of White Pond Road in Stow and 

just downstream from an unnamed washed-out road that still 

has three culverts in the channel. Six cross sections were surveyed in September 2001 along a 70-ft reach. The streambed 

is primarily gravel and cobbles. Channel banks are composed 

of a mixture of rich organic soil, sand, and cobbles and are 

bordered by shrubs and larger deciduous trees further from 

the channel. The channel bends slightly to the right looking 

downstream in the study reach. The water-surface gradient 

is moderately sloped with a measured drop of 0.7 to 1.1 ft 

through the reach at streamflows ranging from 1.8 to 50 ft3/s. 

The HEC-RAS simulations indicate that cross sections at 

stations 202, 214, 229, and 241 were unaffected by backwater 

and were used in the R2Cross analysis. The top width at 

normal channel flow in these sections ranged from about 

23 to 32 ft with a median width of about 27 ft. Depth was the 

limiting hydraulic factor for all but one section 

meeting the R2Cross 3-of-3 criteria, and velocity was the 

limiting factor in all but one section meeting the 2-of-3 

criteria. In the one section, the limiting hydraulic factor was 

reversed from that of the other sections. Streamflows meeting 

the R2Cross 3-of-3 criteria ranged from 9.0 to 12 ft3/s with a 

median of 10 ft3/s; streamflows meeting the R2Cross 2-of-3 

criteria ranged to 3.6 to 10 ft3/s with a median of 5.8 ft3/s 

(table 17). 

The same four cross sections were used to determine 

target flows by the Wetted-Perimeter analysis. Streamflows 

meeting the Wetted-Perimeter criteria ranged from 1.8 to 

5.5 ft3/s with a median of 3.2 ft3/s (table 17). The median 

Wetted-Perimeter flow target was half that determined from 

the R2Cross 2-of-3 criteria method. 
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 2

96

Statistically Based Streamflow Targets

Tennant and New England ABF methods calculate 

streamflow targets from statistical measures of long-term 

daily flow values at a site. The RVA also calculates statistical 

properties of long-term streamflows that reflect natural streamflow variability, which is considered important to preserve the 

ecological integrity of the stream. RVA is mainly used in the 

following analysis for comparative purposes with the other 

statistically based streamflow methods. 

In general, these methods are applicable only at unregulated sites where long-term daily streamflow data are available. Typically, the availability of this type of data, particularly in streams affected by withdrawals, limits their use, but 

because unregulated long-term daily flows were simulated 

with the HSPF model, the methods could be applied to all 

10 selected riffle reaches in this study. The HSPF simulated long-term daily flows (1960–2004) under no water use 

(NOWU) were used to determine flow targets. The NOWU 

simulation zeros out surface-water withdrawals and streamflow depletion from groundwater withdrawals in each model 

reach; the NOWU simulation also excludes other water 

imports and exports, such as areas on public water and onsite septic systems (net import), sewer inflow and infiltration 

losses (net export), and treatment-facility wastewater returns. 

Streamflows for the analyses were simulated at model 

nodes (end of a reach) at or near the riffle sites. In the Sudbury 

River Basin, riffles were close enough to model nodes that 

no adjustment to the simulated flows was necessary. In the 

Assabet River Basin, riffles 51, 59, 61, and 63 (fig. 35) were 

sufficiently upstream from model nodes to warrant adjustment of the simulated flows by the drainage-area ratio at the 

node and riffle. It should be noted that flow targets determined 

from simulated flows are subject to the model uncertainties 

and limitations described previously. Statistically based target 

flows were normalized by drainage area to facilitate comparisons between sites.

Tennant Method

The Tennant method (Tennant, 1976) calculates streamflow targets as percentages of the mean annual flow (QMA). 

Seasonally variable streamflow targets are identified by the 

Tennant method by assigning different percentages of the QMA

for the summer and winter periods (table 18). The method was 

developed in the Rocky Mountain region of the United States, 

which has distinctly different high- and low-flow seasons from 

southern New England. Thus, the October through March flow 

condition described by Tennant (1976) is more applicable to 

the summer through early fall flows in southern New England. 

The percentages of QMA that reflect the quality of stream habitat (table 18) were determined at each of the riffle sites from 

HSPF simulated flows without withdrawals (table 19). This 

study focused primarily on the 30- and 50-percent QMA flows, 

which Tennant considered an excellent flow for aquatic habitat 

for seasonal low and high flows, respectively. However, the 

magnitude of the high-flow standard in relation to the percentage of QMA does not appear to reflect the high-flow regime in 

this region as discussed later.

At 30 percent of the QMA, flows ranged from about 

0.56 to 0.61 ft3/s/mi2 in the Sudbury and Assabet River Basins 

with an overall median of about 0.58 ft3/s/mi2. Flows at 10 and 

20 percent of the QMA, considered poor to fair for seasonal 

low-flow habitat (Tennant, 1976), had overall medians of 

about 0.19 and 0.39 ft3/s/mi2, respectively. These values are 

closest to the overall medians of the flow standards determined 

by the physically based R2Cross 2-of-3 criteria (0.24 ft3/s/mi2) 

and Wetted-Perimeter (0.25 ft3/s/mi2) methods. At 50 percent 

of the QMA, the overall median was about 0.97 ft3/s/mi2, which 

is close to the overall median flow (1.18 ft3/s/mi2) computed 

by the R2Cross 3-of-3 criteria method. 

New England Aquatic Base Flow Method (ABF)

The U.S. Fish and Wildlife Service developed the ABF 

method to establish standards for seasonal low (summer), 

moderate (fall and winter), and high flow (spring) for different 

life stages of the aquatic biota (U.S. Fish and Wildlife Service, 

1981; Lang, 1999). Default standards for these flow regimes 

(0.5, 1.0, and 4.0 ft3/s/mi2, respectively) were developed from 

streamflow records at 48 unregulated streamgages throughout New England to provide flow standards at ungaged sites 

or at gaged sites that have short-term records or are affected 

by regulation. It should be noted that these defaults were not 

intended for sites with contributing areas less than 50 mi2. 

Where long-term unregulated flow information is available, 

ABF standards can be directly calculated from site-specific 

Table 18. Condition of aquatic habitat in relation to streamflow 

as a percentage of the mean annual flow (QMA) described by 

Tennant (1976) for small streams in the Rocky Mountain Region of 

the United States.

[<, less than]

Rated aquatic-habitat 

condition

Percentage of QMA

April–September1 October–March2

Excellent 50 30

Good 40 20

Fair 30 10

Poor 10 10

Degraded <10 <10

1

 Generally reflects seasonal high flows. 

2

 Generally reflects seasonal low flows. 
Determination and Assessment of Target Streamflows for Aquatic Habitat at 10 Riffle Sites

Chapter 2

97

data, which were made possible by HSPF simulated flows 

under no water use (NOWU) at each of the 10 riffle sites. 

The ABF low-flow target is calculated as the median of 

the August mean flows over the period of record. August was 

chosen as the low-flow target because it’s typically the month 

with the lowest flow. The original ABF fall-winter target was 

calculated from the median of the February mean flows that 

limits favorable aquatic habitat on the basis of low flows, 

cold temperatures, and icing. Examination of the simulated 

hydrographs at the riffle sites indicates that the median of 

the January mean flow best represented these limiting winter conditions in this area and, thus, was used for the ABF 

fall-winter flow target. The spring flow target was intended 

to address flow needs for fish spawning and incubation that, 

for some species, require overbank flooding. The spring flow 

target was originally computed from the mean of the median 

April and May mean monthly flows. Examination of the 

simulated hydrographs at the riffle sites indicates the highest monthly flows, which often result in overbank flooding, 

typically occur during March and April and, thus, the mean 

of the median of these monthly mean flows was used as the 

ABF high-flow target. 

The ABF low-flow target computed from NOWU simulated flows varied from about 0.14 to 0.62 ft3

/s/mi2 among the 

10 riffle sites (table 20); riffles in the Sudbury River Basin 

had a median value that was about 32 percent larger than the 

median of the riffle sites in the Assabet River Basin (0.41 and 

0.28 ft3

/s/mi2, respectively). The computed ABF low-flow 

target was below the default target (0.5 ft3/s/mi2) at 9 of the 

10 riffle sites; the overall median (0.32 ft3/s/mi2) was about 

36 percent less than the default target. Excluding outliers 

on Whitehall Brook and Sudbury River near Hopkinton and 

near Ashland, the computed ABF low-flow target is moderately correlated (r2

 0.68) with the percentage of the basin 

underlain by sand and gravel. The area underlain by sand 

and gravel at the riffle sites, excluding Whitehall Brook and 

the two Sudbury River sites, ranged from about 13 to 34 percent and yielded computed ABF low-flow targets of 0.43 to 

0.59 ft3/s/mi2, respectively. The outliers at Whitehall Brook 

and the Sudbury River sites have relatively low ABF target 

flows compared to the other riffle sites, but comparatively 

similar area, in percent, underlain by sand and gravel. The 

outliers likely reflect a greater percentage of the basin area 

classified as water and wetlands, which is weakly inversely 

correlated (r2

 -0.27) with the ABF low-flow target. The positive correlation with area underlain by sand and gravel reflects 

the larger sustained baseflow from these deposits relative to 

other surficial deposits; the negative correlation with area of 

Table 19. Streamflow targets determined by the Tennant method as percentages of the means of the mean annual flows (QMA) 

computed from long-term (1960–2004) simulated streamflow with the Hydrologic Simulation Program–FORTRAN with no water use 

(NOWU) at 10 riffle sites in the Sudbury and Assabet River Basins, Massachusetts.

[Reach location shown on fig. 35; mi2, square mile; ft3/s/mi2, cubic foot per second per square mile]

Reach 

number Reach

Drainage 

area 

(mi2

)

Flow as a percentage of QMA (ft3

/s/mi2) 

10 20 30 40 50

Sudbury River Basin

4 Whitehall Brook near Hopkinton 6.64 0.191 0.381 0.572 0.762 0.953

5 Sudbury River near Hopkinton 19.3 0.197 0.394 0.591 0.788 0.985

6 Sudbury River near Ashland 23.9 0.198 0.396 0.595 0.793 0.991

7 Indian Brook near Hopkinton 4.73 0.196 0.391 0.587 0.783 0.979

8 Indian Brook near Ashland 6.75 0.193 0.386 0.579 0.772 0.965

15 Baiting Brook near Framingham 3.41 0.204 0.407 0.611 0.814 1.018

Median 0.196 0.393 0.589 0.786 0.982

Assabet River Basin

51 Assabet River near Westborough 6.79 0.191 0.381 0.572 0.762 0.953

59 Danforth Brook at Hudson 5.12 0.189 0.378 0.567 0.756 0.945

61 Fort Meadow Brook near Hudson 4.85 0.194 0.388 0.582 0.777 0.971

63 Elizabeth Brook near Stow 18.7 0.187 0.375 0.562 0.749 0.936

Median 0.190 0.380 0.569 0.759 0.949

Overall median 0.194 0.387 0.581 0.774 0.968
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 2

98

the basin in water and wetlands reflects the greater ET losses 

relative to other land-use types. It should be noted that the correlations were made from simulated flows that have an inherent degree of circularity between flow standards and basin 

characteristics; thus, conclusions drawn this analysis should be 

used with caution. 

The computed ABF winter- and spring-flow targets were 

less variable than the low-flow targets among riffle sites, but 

were considerably different than the ABF default target flows. 

The median of the January mean flows (winter) were about 

2.4 and 2.5 ft3

/s/mi2 at selected riffles in the Sudbury and 

Assabet River Basins, respectively (table 20); this is about two 

and a half times greater than the default ABF fall-winter flow 

target (1.0 ft3/s/mi2). The ABF spring-flow target (high flow) 

was also less variable than the low-flow target among the 

riffle sites. The median spring-flow target was 3.1 ft3/s/mi2 for 

10 riffles in the Sudbury and Assabet River Basins (table 20); 

this is about 22 percent less than the default ABF spring-flow 

target (4.0 ft3/s/mi2). 

Range of Variability Approach (RVA)

RVA was developed by the Nature Conservancy (Richter and others, 1996) to characterize natural flow variability 

considered necessary to preserve the ecological integrity of the 

stream. RVA considers the interquartile ranges of 33 indicators of hydrologic alteration (IHA) that are a suite of statistical 

measures calculated from daily streamflow values (The Nature 

Conservancy, 2009). About half the statistics measure the 

central tendency of various flow conditions and the other half 

focus on the magnitude, duration, timing, and frequency of 

extreme events. 

The RVA analyses for all 33 IHA statistics are presented 

in appendix 3, but only the medians and upper and lower quartiles of the mean monthly flows are presented in the following 

section because they represent the monthly flow variation that 

the other standard-setting methods can be compared to. The 

medians and upper and lower quartiles of the mean monthly 

flows were computed from HSPF simulated unregulated flows 

(NOWU scenario) for a 45-year period (1960–2004). The 

values presented herein were calculated from the medians of 

the monthly mean values calculated at each of the 10 riffle 

sites; 25th, 50th, and 75th percentiles represent the combined 

values among the riffle sites. For clarity, only the percentiles 

are referred to.

The 50th-percentile flow at 10 riffle sites (table 21) was 

lowest in August (0.32 ft3/s/mi2) and slightly larger in July 

and September (0.42 and 0.47 ft3/s/mi2, respectively); the 

50th-percentile flow was highest in March (3.41 ft3/s/mi2) and 

somewhat lower in February and April (2.80 and 2.85 ft3/s/mi2, 

Table 20. Streamflow standards determined by the New England Aquatic Baseflow (ABF) method from the median of the 

monthly mean flow (1960–2004) simulated with the Hydrologic Simulation Program–FORTRAN (HSPF) with no water use 

(NOWU) at 10 riffle sites in the Sudbury and Assabet River Basins, Massachusetts.

[Reach location shown on fig. 35; ft3/s/mi2, cubic foot per second per square mile]

Reach 

number Reach Median of mean monthly flow (ft3

/s/mi2)

August January March–April1

Sudbury River Basin

4 Whitehall Brook near Hopkinton 0.331 2.425 3.110

5 Sudbury River near Hopkinton 0.492 2.430 2.964

6 Sudbury River near Ashland 0.499 2.452 3.041

7 Indian Brook near Hopkinton 0.296 2.474 3.129

8 Indian Brook near Ashland 0.296 2.533 3.222

15 Baiting Brook near Framingham 0.616 2.346 3.211

Median 0.412 2.441 3.119

Assabet River Basin

51 Assabet River near Westborough 0.247 2.355 3.183

59 Danforth Brook at Hudson 0.142 2.500 3.168

61 Fort Meadow Brook near Hudson 0.329 2.535 3.059

63 Elizabeth Brook near Stow 0.314 2.470 3.036

Median 0.281 2.470 3.119

Overall median 0.322 2.461 3.119

1

Mean of the median monthly mean flow.
Determination and Assessment of Target Streamflows for Aquatic Habitat at 10 Riffle Sites

Chapter 2

99

respectively). Differences between the 75th percentile and the 

50th percentile were proportionally greater in the low-flow 

months (about twice the 50th percentile) than in the high-flow 

months (about 25 to 50 percent greater than the 50th percentile). The differences between the 25th and the 50th percentiles 

were also proportionally larger in the low-flow months than in 

the high-flow months, but to a lesser degree. In effect, streamflow standards based on the median monthly or seasonal flows 

would less likely be met during the low-flow season than 

during the high-flow season because the variation around the 

median (as a percentage) is greater in the normal low-flow 

period than in the normal high-flow period. 

Comparison of Computed Target Flows

Computed target flows determined by standard-setting 

methods for aquatic-habitat protection at 10 riffle sites in the 

Sudbury and Assabet River Basins yielded variable results 

when normalized for drainage area (table 22 and fig. 50). In 

general, the variability in the target flows was larger among 

sites for physically based methods than for statistically based 

methods. Physically based methods also yielded lower flow 

targets than statistically based methods, with the exception of 

the R2Cross 3-of-3 criteria. 

Table 21. Quartiles of medians of the monthly mean 

streamflows determined from Hydrologic Simulation Program–

FORTRAN (HSPF) simulated flow (1960–2004) with no water 

use (NOWU) at 10 riffle sites in the Sudbury and Assabet River 

Basins, Massachusetts

[ft3/s/mi2, cubic foot per second per square mile]

Month

Streamflow (ft3

/s/mi2)

25th percentile 50th percentile 75th percentile

October 0.451 1.022 1.652

November 1.322 1.718 2.491

December 1.524 2.437 3.270

January 1.632 2.461 3.759

February 2.108 2.795 3.499

March 2.475 3.413 4.160

April 2.078 2.854 3.822

May 1.381 1.790 2.495

June 0.609 0.976 1.837

July 0.301 0.421 0.827

August 0.215 0.322 0.729

September 0.224 0.468 0.915

Table 22. Summary of target flows determined by standard-setting methods at 10 riffle sites in the Sudbury and Assabet River Basins, 

Massachusetts.

[ABF, aquatic base flow median of August monthly mean flow; QMA, mean annual flow]

Reach

number Reach

Flow standard, in cubic feet per second per mile square (ft3

/s/mi2)

Physically based methods1 Statistically based methods2

Wetted 

Perimeter

R2Cross Tennant

ABF 2-of-3 

criteria

3-of-3 

criteria

30-percent 

QMA

50-percent 

QMA

Sudbury River Basin

4 Whitehall Brook near Hopkinton 0.109 0.181 0.542 0.572 0.953 0.331

5 Sudbury River near Hopkinton 0.363 0.725 0.933 0.591 0.985 0.492

6 Sudbury River near Ashland 0.282 0.314 0.942 0.595 0.991 0.499

7 Indian Brook near Hopkinton 0.296 0.093 2.960 0.587 0.979 0.296

8 Indian Brook near Ashland 0.104 0.074 1.008 0.579 0.965 0.296

15 Baiting Brook near Framingham 0.220 0.444 1.706 0.611 1.018 0.616

Median 0.251 0.247 0.975 0.589 0.982 0.412

Assabet River Basin

51 Assabet River near Westborough 0.029 0.066 1.001 0.572 0.953 0.247

59 Danforth Brook at Hudson 0.508 0.176 2.031 0.567 0.945 0.142

61 Fort Meadow Brook near Hudson 0.351 0.454 1.505 0.582 0.971 0.329

63 Elizabeth Brook near Stow 0.174 0.308 0.548 0.562 0.936 0.314

Median 0.262 0.242 1.253 0.569 0.949 0.281

Overall Median 0.251 0.244 1.005 0.581 0.968 0.322

1

 Median target flows determined at multiple cross sections. 

2

 Determined from Hydrologic Simulation Program–FORTRAN (HSPF) simulated flows without water use (NOWU scenario).
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 2

100

Figure 50. Variation 

in target flows 

determined by 

standard-setting 

methods at 10 

riffle sites in the 

Sudbury and Assabet 

River Basins, 

Massachusetts.

50th percentile

75th percentile

90th percentile

25th percentile

EXPLANATION

10th percentile

Outlier

(10) Number of 

observations

R2Cross

2-of-3

Criteria

R2Cross

3-of-3

Criteria

Tennant

30-Percent

Mean

Annual

Flow

Tennant

50-Percent

Mean

Annual

Flow

Aquatic

Base

Flow

Median

of

August

Means

Wetted

Perimeter

0

1.0

2.0

3.0

6.0

STREAMFLOW, IN CUBIC FEET PER SECOND PER SQUARE MILE

Physical Methods Statistical Methods

Determined from long-term simulated 

daily flows (1960–2004) with the 

Hydrologic Simulation Program– 

FORTRAN (HSPF) with no water use 

(NOWU scenario) 

Paired boxplots–boxes on left (blue) are the 

median target flow determined by a method 

from multiple cross sections; boxes on the 

right (yellow) are the target flows determined 

by a method from individual cross sections 

(10) (31) (10) (32)

(10) (32)

(10) (10) (10)

The R2Cross 3-of-3 criteria yielded the highest (with 

one exception) and most variable flows among the methods 

examined; the median flow determined from the multiple 

cross sections within a riffle reach ranged from about 0.54 to 

3.0 ft3/s/mi2 (table 22) with an overall median of 1.0 ft3/s/mi2

and an interquartile range of about 0.94 to 1.7 ft3/s/mi2. The 

variation in the target flows determined by this method was 

much larger for the individual cross sections (fig. 50), indicating individual cross sections may underrepresent or overrepresent the flow required to protect aquatic habitat in the reach. 

Again, it should be noted that the R2Cross 3-of-3 criteria was 

designed as a seasonal high-flow target for the Rocky Mountain region and may not be applicable to this region.

The R2Cross 2-of-3 criteria target flow was substantially 

lower and less variable than that produced from the 3-of-3 

criteria, but the variability of the target flows computed by this 

method was still the 2nd highest relative to the flows computed 

by the other methods. Although the interquartile range of target flows determined by R2Cross 2-of-3 criteria method from 

32 individual cross sections was about equal to that determined from medians of the multiple cross sections at each of 

the 10 riffle sites, the relatively large variability underscores 

that too few cross sections may not yield a representative 

target flow for aquatic-habitat needs. The median target flows 

computed from individual cross sections determined by the 

R2Cross 2-of-3 criteria and Wetted-Perimeter methods were 

in closest agreement among the methods examined with an 

overall median of about 0.24 and 0.25 ft3/s/mi2, respectively, 

and an interquartile range of about 0.13 to 0.38 and 0.14 to 

0.32 ft3/s/mi2, respectively. These findings are comparable to 

target flows determined by these methods at riffle sites in the 

Charles River Basin (Parker and others, 2004) and in other 

basins throughout the state (Armstrong and others, 2004). 

The R2Cross and Wetted-Perimeter methods are direct 

measures of stream-channel features such as width, depth, 

slope, roughness, and other features. Channel geometry usually obtains a state of quasi-equilibrium over time in response 

to normal conveyance needs for water and sediment, but a new 

state of quasi-equilibrium will develop in response to longterm changes in the conveyance need (Leopold and Maddock, 

1953). For example, changes in land use, such as urbanization, can increase runoff and result in increased channel width, 

whereas impoundments can mitigate high flows that could 

decrease downstream channel cross-section area (Jacobson 

and others, 2001). 

The degree to which a channel adjusts to altered flows 

and the effects these adjustments have on physically based 

methods for determining target flows are not well understood. 
Determination and Assessment of Target Streamflows for Aquatic Habitat at 10 Riffle Sites

Chapter 2

101

The physically based target flows at Indian Brook near Ashland, in contrast to the upstream riffle site near Hopkinton, 

suggest that the Hopkinton Reservoir may have decreased 

the downstream conveyance needs, resulting in a target flow 

that was lower below the reservoir than above the reservoir 

(table 17). The median flows determined by the R2Cross 

2-of-3 criteria and the Wetted-Perimeter methods decreased 

from the upstream to the downstream riffle sites on Indian 

Brook (from about 0.09 to 0.07 ft3

/s/mi2 and from about 

0.30 to 0.10 ft3/s/mi2, respectively). Further evidence of a 

decreased channel conveyance is indicated by the median 

top width of the channel that decreased by about 18 percent 

(from 17 to 14 ft) from the upstream to the downstream 

riffle sites on Indian Brook. Development of regional flow 

targets from physically based methods underscores the need 

to consider channels that may have been directly or indirectly altered in response to upstream changes that affect the 

downstream hydrology.

Of the statistically based methods, the computed ABF 

low-flow target was closest to the target flows determined by 

the R2Cross 2-of-3 criteria and Wetted-Perimeter methods; 

these physically based methods were about 22 to 24 percent 

less than the computed ABF low-flow target. The overall 

median ABF low flow (0.32 ft3/s/mi2) was about 45 percent 

less than the Tennant 30-percent QMA (0.58 ft3/s/mi2). The ABF 

target low-flow interquartile range (0.30 to 0.45 ft3/s/mi2) was 

smaller than that determined by the R2Cross 2-of-3 criteria 

and Wetted-Perimeter methods but larger than that determined 

by the Tennant method. 

Streamflow targets determined by the Tennant method 

varied least among standard-setting methods over the 10 riffle 

sites. The interquartile target flows ranged from about 0.57 

to 0.59 ft3/s/mi2 and from 0.95 to 0.98 ft3/s/mi2 determined 

by the Tennant 30-percent QMA and 50-percent QMA methods, 

respectively. The small variability in target flows determined 

by the Tennant method relative to other methods is expected 

because the value is computed from the mean annual flow that, 

when normalized for drainage area, tends to be comparable in 

similar hydrogeologic settings. It should be noted that medians 

of the R2Cross 2-of-3 criteria and Wetted-Perimeter target 

flows were between 10 and 20 percent of the QMA (table 19), 

which Tennant (1976) ranked as fair to poor for seasonal low 

flows (table 18). 

The R2Cross 3-of-3 criteria and the Tennant 50-percent 

QMA methods, designed for setting high-flow targets, yielded 

comparable median target flows. The overall median determined by the Tennant 50-percent QMA (0.97 ft3

/s/mi2) is about 

3 percent less than the overall median determined by the 

R2Cross 3-of-3 criteria (1.00 ft3/s/mi2). However, the upper 

quartile of median flows determined by the R2Cross 3-of-3 

criteria (1.66 ft3/s/mi2) is about twice that determined by the 

Tennant 50-percent QMA (0.98 ft3/s/mi2)(fig. 50). 

Simulated streamflows at the 25th, 50th, and 75th percentiles of median monthly mean flows represent the normal 

range in flow variability during the year (fig. 51). The ABF 

median of the August mean flow (0.32 ft3/s/mi2) is between the 

25th- and 50th-percentile flows for the July through September 

period (0.22 and 0.42 ft3/s/mi2, respectively) at the 10 riffle 

sites. This indicates that unregulated summer streamflows are 

below the ABF target low flow about 35 percent of the time. 

The Tennant 30-percent QMA criterion flow (0.58 ft3/s/mi2) 

is between the 50th and 75th percentiles for the July through 

September period (0.42 and 0.83 ft3/s/mi2, respectively) at the 

10 riffle sites. The median R2Cross 2-of-3 criteria and WettedPerimeter flow targets (0.24 and 0.25 ft3

/s/mi2, respectively) 

were about equal to the 25th-percentile flows for the July 

through September period at the 10 riffle sites. 

The Tennant 50-percent QMA and the R2Cross 3-of-3 

criteria target flows are well above the 75th-percentile flows 

during the normally low-flow period (July through September) 

and well below the 25th-percentile flows during the normally 

high-flow period (March and April). This underscores that 

target flows determined by the Tennant 50-percent QMA and 

the R2Cross 3-of-3 criteria methods have limited applicability 

to the seasonal flow regimes in this region because they were 

intended to represent the Rocky Mountain region. 

Statistically based target flows cannot be met 100 percent of the time because they reflect statistical properties of 

the observed or simulated streamflows they were derived 

from. Physically based target flows also are not typically met 

100 percent of the time, but are more likely to be met because 

they are derived from physical characteristics of a stream 

reach. Regardless of the method used to set a target flow, two 

important questions are often asked that can be addressed 

by the use of simulated flows—(1) how often do unaltered 

flows meet, or not meet, a target flow, and (2) how would this 

change in response to flow alterations. Regulation at the riffle 

sites examined in this study was limited to the effects of water 

withdrawals, which affected 6 of the 10 sites. Affected riffle 

reaches (fig. 35) included Whitehall Brook near Hopkinton 

(4), Sudbury River near Hopkinton (5), Sudbury River near 

Ashland (6), and Indian Brook near Ashland (8) in the Sudbury River Basin, and Assabet River at Westborough (51) and 

Fort Meadow Brook near Hudson (61) in the Assabet River 

Basin. Elizabeth Brook near Stow (63) is also affected by 

withdrawals, but these withdrawals were minor; therefore, this 

reach was not included in the comparison of reaches with and 

without flow alteration.

Frequency and Duration Streamflows were 

below Target Flows 

Flow-duration curves are a useful method for determining 

the percentage of flows that fall below a given threshold, but 

they reflect the flows over the entire period of record that the 

curves were developed from. Duration curves do not provide 

information on the magnitude, frequency, and duration that 

streamflows were below a specified threshold. Marsh and 

others (2003) developed the River Analysis Package (RAP) 
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 2

102

to compute a suite of quantitative measures of flow, some of 

which were used to determine the number of continuous days 

(duration) and the number of episodes (frequency) streamflows fell below specified thresholds. An episode is a period of 

continuous days a flow target was not met. 

Flow thresholds used in the RAP analysis were determined from standard-setting methods for each of the 10 riffle 

sites examined in the Sudbury and Assabet River Basins previously described. Flow thresholds for physically based methods 

(R2Cross and Wetted-Perimeter) represent the median target 

flows from multiple cross sections at each riffle site. Flow 

thresholds for statistically based methods (Tennant and ABF) 

are a unique value for each riffle site. 

For each site, the duration and frequency that streamflows 

fell below a threshold were determined from the long-term 

(1960–2004) HSPF simulated flows without withdrawals (NOWU) and with average 1993–2003 withdrawals 

(AVGWU). Withdrawals affected flows in 7 of the 10 riffle 

reaches. For each riffle site, the ability to meet the target flow 

over the 45-year simulation period was evaluated by (1) the 

median number of episodes per year the flow threshold was 

not met, (2) the median number of days per year the flow 

threshold was not met, (3) the median duration (days) of 

the longest annual episode the flow threshold was not met, 

(4) the longest continuous duration the flow threshold was not 

met, and (5) the total number of days the flow threshold was 

not met. 

The frequency and duration NOWU simulated streamflows fell below a given threshold varied by method and by 

site (appendix 4, fig. 52). Flow thresholds determined by the 

Tennant 50-percent QMA and the R2Cross 3-of-3 criteria methods are not met at a greater frequency and for a longer duration of time than other flow thresholds determined by the other 

methods (appendix 4, tables 4-1 to 4-6 and fig. 52); thus, their 

applicability requires greater consideration to the flow regimes 

they are intended to be used for. Overall, flow thresholds 

determined by the Tennant 50-percent QMA and the R2Cross 

3-of-3 criteria methods were not met about 40 percent of the 

time over the 45-year period (appendix 4; tables 4-3 and 4-5). 

In general, the frequency and duration the R2Cross 3-of-3 

criteria flow target was not met varied more among sites than 

the other target flows (fig. 52). The frequency and duration 

target flows determined by the Tennant 50-percent QMA and the 

R2Cross 3-of-3 criteria methods are not met are excluded from 

Figure 51. Median and quartiles of the monthly median flow in comparison to standard-setting method target flows determined at 10 

riffle sites in the Sudbury and Assabet River Basins, Massachusetts.

50th percentile

75th percentile

25th percentile

Monthly median

EXPLANATION

R2Cross 3-of-3 criterion

Tennant 50 percent of mean annual flow

Aquatic Base Flow median of monthly means

Wetted Perimeter

Physical Methods Statistical Methods

Determined from long-term simulated daily flows (1960–2004) with the Hydrologic 

Simulation Program–FORTRAN (HSPF) with no water use (NOWU scenario) 

Determined from the median flow requirement 

at multiple cross sections 

Tennant 30 percent of mean annual flow

R2Cross 2-of-3 criterion

0

1.0

2.0

3.0

4.0

STREAMFLOW, IN CUBIC FEET PER 

SECOND PER SQUARE MILE

OCT. NOV. DEC. JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT.

1.5

2.5

3.5

4.5

0.5
Determination and Assessment of Target Streamflows for Aquatic Habitat at 10 Riffle Sites

Chapter 2

103

Figure 52. Frequency and duration that long-term (1960–2004) streamflows simulated with the Hydrologic Simulation 

Program–FORTRAN (HSPF) with (AVGWU) and without (NOWU) withdrawals were below target flows determined by 

six standard-setting methods at 10 riffle sites in the Sudbury and Assabet River Basins, Massachusetts.

0

5

10

15

25

20

COUNT

Median number of episodes per year below threshold

0

40

80

120

160

DAYS

200 Median duration of longest annual episode below threshold

0

20

40

60

80

100 Median number of days per year below threshold

DAYS

0

50

100

150

200

250

300

350 Duration of longest episode below threshold for period of record

DAYS

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000 Total number of days below threshold for period of record

DAYS

Low-flow standards High-flow

standards

Median

Upper quartile

90 percent

Lower quartile

EXPLANATION

10 percent

Outlier

R2Cross

2-of-3

Criteria

R2Cross

3-of-3

Criteria

Tennant

30-Percent

Mean

Annual

Flow

Tennant

50-Percent

Mean

Annual

Flow

Wetted

Perimeter

Aquatic 

Base Flow 

Median of 

August 

Means

NOWU AVGWU
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 2

104

the remainder of the analyses because they are not intended 

to reflect a low-flow target and are not comparable to results 

from the other methods.

The median frequency and duration NOWU simulated 

streamflows fell below a flow threshold for a given method 

(fig. 52) indicate that the statistically based methods (Tennant 

30-percent QMA and ABF) tend to have a greater number of 

episodes that were of longer duration than the physically based 

methods (Wetted-Perimeter and R2Cross 2-of-3 criteria). Flow 

thresholds determined by the Wetted-Perimeter and R2Cross 

2-of-3 criteria methods have a median of about 0.25 ft3/s/mi2, 

which is about 45 percent less than the flow thresholds determined by the Tennant 30-percent QMA and the ABF, which 

have a median of about 0.45 ft3/s/mi2. As a result, the median 

annual duration of an episode and total number of days simulated flows were below the flow threshold were about three 

times greater for statistically based standards than for physically based standards. 

In almost all cases, as would be expected, the frequency 

and duration flows fell below a given threshold were greater 

for AVGWU simulated streamflows than for NOWU simulated 

streamflows (appendix 4, fig. 52). The only exception to this 

was the median annual number of episodes (continuous periods when flows were below a threshold). In a few instances, 

the number of episodes was less for AVGWU simulated flows 

than for NOWU simulated flows because the duration flows 

fell below the threshold was greater, resulting in fewer breaks 

between episodes. Differences in the frequency and duration 

AVGWU simulated streamflows fell below a given threshold 

relative to NOWU simulated streamflows largely depend on 

the degree of flow alteration. The total number of days the 

long-term (1960–2004) AVGWU simulated streamflows fell 

below a threshold relative to NOWU increased from 17 to 

130 percent at the seven riffle sites affected by withdrawals 

(table 23). The median difference in total number of days that 

NOWU and AVGWU simulated flows were below physically 

based target flows (58 percent) was nearly three times that for 

statistically based target flows (20 percent) (table 23). This 

indicates that overall, physically based target flows are more 

sensitive to flow alterations than statistically based target flows 

because the flow targets are generally lower.

Overall, the differences between frequency and duration 

simulated flows with and without withdrawals fell below a 

given flow threshold were significant at the 95-percent confidence interval as determined by the paired two-sample t-test or 

by the Wilcoxon signed-rank test (TIBCO Spotfire S+®, 2008; 

30 matched pairs that represent 5 RAP metrics measured at 6 

sites). In addition to the three sites not affected by withdrawals 

(Indian Brook near Hopkinton, Baiting Brook near Framingham, and Danforth Brook at Hudson), Elizabeth Brook near 

Stow was excluded from the paired-test analysis because 

withdrawals from this subbasin minimally affect streamflow. Paired differences were not always significant at the 

95-percent confidence interval for individual sites (combined 

RAP metrics at a site) or for individual RAP metrics (combined sites for individual RAP metrics). Differences between 

simulated flows with and without withdrawals were not significant, by either test, at the 95-percent confidence interval at 

Whitehall Brook near Hopkinton (reach 4) for all RAP metrics 

or for the median number of annual episodes at all sites except 

Sudbury River near Ashland (reach 6). Additional sites with 

paired information on the ability to meet flow targets with and 

without withdrawals are needed to better determine statistically valid differences in the frequency and duration flow 

targets are not met. 

Summary

The U.S. Geological Survey (USGS), in cooperation with 

the Massachusetts Department of Conservation and Recreation 

(MADCR), began a study in 2004 of the Sudbury and Assabet River Basins to determine the condition of fisheries and 

to assess target streamflows determined by standard-setting 

methods intended to protect aquatic habitat. Fish-community 

data, collected by the Massachusetts Division of Fisheries and 

Wildlife (MADFW), for flowing (not impounded) reaches in 

the main stem of the Sudbury and Assabet Rivers were compiled and assessed. Stream-temperature data were collected at 

seven sites in the upper Sudbury River Basin and evaluated 

with respect to habitat for brook trout. Two of the water-temperature monitoring sites are coincident with the river fishsampling sites on the main stem. The main focus of the habitat 

study was the determination and comparison of target streamflows at 10 riffle reaches in the Sudbury and Assabet River 

Basins determined by standard-setting methods designed to 

protect aquatic habitat. These flow targets were evaluated with 

respect to the frequency and duration streamflows were not 

met using HSPF simulated flows developed for the Sudbury 

and Assabet River Basins. 

 The fish-community assessment characterized the diversity and relative abundance of fish species in the main stems of 

the Sudbury and Assabet Rivers. These rivers have a diversity 

of species expected in rivers in southern New England; however, the community is dominated by macrohabitat generalists, 

indicating the fish community is under some degree of stress. 

A total of 390 fish of 14 species were captured at 5 sites on the 

main stem of the Sudbury River; nearly 71 percent of the fish 

captured are classified as macrohabitat generalists. A total of 

1,065 fish of 21 species were captured at 8 sites on the main 

stem of the Assabet River; 54 percent of the fish captured are 

macrohabitat generalists. White suckers, a fluvial species that 

is pollution tolerant, composed 30 and 60 percent of the total 

and fluvial communities, respectively, indicating that water 

quality may be a factor affecting community composition. The 

main-stem fish communities of the Sudbury and Assabet Rivers were primarily composed of species that could tolerate the 

warmer summer water temperatures.

Twenty-one tributary stream reaches in the Sudbury and 

Assabet River Basins have been identified by the MADFG as a 

cold-water fishery resource (CFR); 7 are in the Sudbury River 

Basin and 15 are in the Assabet River Basin. Cold-water fish 
Summary

Chapter 2

105

species were dominant in some CFR reaches; however, other 

CFR reaches that had contained cold water species in the past 

contained few, if any, cold-water species during recent sampling efforts. Cold-water fish species in many CFR reaches 

are between these extremes because of stress from hydrologic 

alterations, increasing stream temperature, and sedimentation 

from rapid urbanization around the Interstate-495 corridor in 

which these basins are located.

Stream temperature was recorded in seven free-flowing 

reaches in the upper Sudbury River Basin to provide a general indication of the suitability for cold-water fish species, 

particularly brook trout. Three of the sites were unaffected by 

upstream water withdrawals or impoundments—Jackstraw 

Brook near Westborough, Indian Brook near Hopkinton, and 

Baiting Brook near Framingham. The other four sites were 

affected by withdrawals or impoundments, or both—Whitehall Brook near Hopkinton, Sudbury River near Hopkinton, 

Sudbury River near Ashland, and Cold Spring Brook at Ashland. The sites unaffected by withdrawals or impoundments 

generally maintained water temperatures that could potentially 

sustain brook trout; however, daily water temperatures at these 

sites often rose to levels considered precarious to the longterm survival of brook trout. Summer water temperatures in 

Jackstraw Brook were more favorable for brook trout (cooler) 

than Indian and Baiting Brook because the reach generally had 

a denser canopy cover and was affected less by wetlands and 

Table 23. Median frequency and duration long-term (1960–2004) streamflows simulated with the Hydrologic Simulation Program–

FORTRAN (HSPF) with (AVGWU) and without (NOWU) withdrawals were below target flows determined by four standard-setting 

methods at seven riffle sites in the Sudbury and Assabet River Basins, Massachusetts.

[Episode, a period of continuous days a target flow was not met; n, number of observations used to determine the median; ft3/s/mi2, cubic feet per second per 

square mile; QMA, mean annual flow]

n

Median annual Period of Record

Median flow 

threshold

(ft3

/s/mi2)

Number of 

episodes

(count)

Duration of 

episodes

(days)

Duration of 

longest 

episode

(days)

Longest 

episode

(days)

Total days 

below 

threshold

(days)

Wetted Perimeter (WP)

NOWU 7 1.5 7.0 5 67 999 0.251

AVGWU 7 2.0 9.8 22 97 2,302

Percent difference 33 40 340 45 130

R2Cross 2-of-3 criteria

NOWU 7 2.0 10 21 73 2,087 0.244

AVGWU 7 2.0 13 26 134 2,585

Percent difference 0 31 24 84 24

Tennant 30-percent QMA

NOWU 7 8.0 12 50 168 4,611 0.581

AVGWU 7 8.0 17 83 176 5,395

Percent difference 0 33 66 4.8 17

Aquatic Baseflow (ABF)

NOWU 7 4.0 18 39 112 3,434 0.322

AVGWU 7 4.0 23 45 141 4,260

Percent difference 0 25 15 26 24

Median of the medians for physically based methods (WP & R2Cross 2-of-3)

NOWU 7 1.8 8.5 13.0 70 1,543 0.248

AVGWU 7 2.0 11.5 24.0 116 2,444

Percent difference 14 35 85 65 58

Median of the medians for statistically based methods (Tennant 30-QMA & ABF)

NOWU 7 6.0 15.0 44.5 140 4,023 0.452

AVGWU 7 6.0 19.5 64.0 159 4,828

Percent difference 0 30 44 13 20
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 2

106

urbanization. The 7-day mean of the maximum daily stream 

temperatures during the summer at the four sites downstream 

from withdrawals or reservoirs, or both, were warmer (often in 

the upper range for brook-trout survivability) for longer periods of time compared to the unaffected sites. These sites also 

had smaller fluctuations in daily temperature that combined 

with the warmer temperatures provide less opportunity for 

cold-water fish to find temporary refuge during warm periods. 

Stream temperatures in the reaches examined below reservoirs 

or withdrawals, or both, were marginal to poor for supporting 

brook trout. 

 Standard-setting methods for determining flows to 

protect aquatic habitat were applied at 10 riffle sites; 6 in the 

Sudbury River Basin and 4 in the Assabet River Basin. Drainage areas to these sites ranged in size from 3.4 to 24 mi2

. The 

methods were divided into two general categories—physical 

and statistical; flows determined by these methods are referred 

to as target flows and are intended to represent the minimal 

flow needed to protect aquatic habitat. Target flows vary to 

reflect normal seasonal low- and high-flow periods. 

 The physically based methods used included R2Cross 

and Wetted-Perimeter. These methods require site-specific 

physical and hydraulic data and can be applied to reaches 

that are ungaged or altered by withdrawals (subject to some 

constraints). A calibrated one-dimensional hydraulics model, 

HEC-RAS, was developed for each riffle reach to determine 

flows that meet the criteria set forth by the method. Models 

were developed for the six riffle reaches in the Sudbury River 

Basin for this study; HEC-RAS models developed previously 

were used for the Assabet River Basin riffle reaches. The 

HEC-RAS models were developed from multiple cross sections and calibrated to measured water levels over a range of 

flows, but not all cross sections were used in the determination 

of physically based target flows. 

The R2Cross method establishes flow targets on the basis 

of three channel hydraulic characteristics—average velocity, 

wetted perimeter, and mean depth; the latter two variables 

vary according to the top width of the stream. To account for 

seasonal streamflow variability, summer and winter target 

flows vary according to the number of hydrologic criteria met. 

Flows that meet 2-of-3 criteria were considered applicable 

to low-flow conditions in southern New England. Flows that 

meet all three hydraulic criteria, intended to reflect seasonal 

high flows for the Rocky Mountain region, were not considered representative of seasonal high flows in southern New 

England. The Wetted-Perimeter method defines the target 

flow as the flow necessary to keep the riffle cross section 

between the lower streambank edges in contact with water. 

The flow required to satisfy the wetted-perimeter variable in 

the R2Cross method is defined as a percentage of the bankfull 

wetted perimeter. The median flow targets developed with 

the R2Cross 2-of-3 criteria at the 10 riffle sites ranged from 

about 0.07 to 0.72 ft3/s/mi2 with an overall median of about 

0.24 ft3/s/mi2. The Wetted-Perimeter flow targets at the same 

riffle sites ranged from about 0.10 to 0.51 ft3/s/mi2 with an 

overall median of about 0.25 ft3/s/mi2. 

The statistically based methods used included Tennant 

and New England Aquatic Baseflow (ABF), and although not 

considered a standard-setting method, the Range-of-Variability Approach (RVA) was used to characterize the monthly 

streamflow variability. These methods typically are limited 

to unregulated sites with long-term daily streamflow data. It 

was possible to employ these statistically based methods at the 

10 riffle sites by using the HSPF simulated long-term (1960–

2004) daily flows with no water use (NOWU scenario). The 

simulated unregulated flows were also used to characterize 

monthly flow variability at the 25th, 50th, and 75th percentiles of 

median monthly flow. 

The Tennant method flow target is calculated as a percentage of the mean annual flow (QMA). Seasonal flow targets 

are identified by the Tennant method by assigning different 

percentages of the QMA. The Tennant high-flow target (50-percent QMA), like the R2Cross 3-of-3 criteria method, was not 

considered representative of seasonal high flows in southern 

New England. The 30-percent QMA, considered by the Tennant 

method to be an excellent low-flow target, ranged from about 

0.56 to 0.61 ft3/s/mi2 with an overall median of 0.58 ft3/s/mi2 at 

the 10 riffle sites.

The ABF low-flow standard is calculated as the median 

of the August mean flow for each year over the period of 

record. ABF flow targets were calculated for winter and spring 

as the median of the January mean flows and the mean of the 

median monthly mean flows in March and April, respectively. 

The computed ABF low-flow targets ranged from about 0.14 

to 0.62 ft3/s/mi2 among the 10 riffle sites; the overall median 

low-flow target, 0.32 ft3/s/mi2, was about 36 percent less than 

the ABF default standard (0.50 ft3/s/mi2). The computed ABF 

low-flow target was moderately correlated (r2 0.62) with the 

percentage of the contributing area underlain by sand and 

gravel, excluding Whitehall Brook, which is affected by 

Whitehall Reservoir. The computed ABF low-flow targets 

were weakly inversely correlated (r2 -0.27) with the percentage 

of the basin area classified as water and wetlands, reflecting 

greater evapotranspiration losses from these areas. Computed ABF winter and spring flow targets at the riffle sites 

ranged from about 2.4 to 2.5 ft3

/s/mi2 and 3.0 to 3.2 ft3/s/mi2, 

respectively. The overall median ABF winter flow target 

(2.5 ft3/s/mi2) was about two and a half times greater than the 

default ABF fall-winter standard (1.0 ft3/s/mi2), and the overall 

median spring flow target (3.1 ft3/s/mi2) was about 22 percent 

less than the default ABF spring flow standard (4.0 ft3/s/mi2).

RVA is considered a diagnostic tool for evaluating hydrologic variability necessary to preserve the ecological integrity 

of a stream. Of the 33 statistical measures determined by this 

method, the median (50th percentile), upper (75th percentile), 

and lower (25th percentile) quartiles of the median monthly 

flows were used to reflect the normal seasonal flow variability, which the other methods could be compared to. The 

50th-percentile flow at 10 riffle sites was lowest in August 

(0.32 ft3/s/mi2) and highest in March (3.4 ft3/s/mi2).

Flow targets determined by the various methods at the 

10 riffle sites, normalized for drainage area, yielded a broad 
Summary

Chapter 2

107

range of flows. In general, the variability was larger among 

sites for physically based methods than for statistically based 

methods, and the physically based methods generally yielded 

lower flow targets than the statistically based methods. The 

R2Cross 3-of-3 criteria yielded the largest flow target among 

the methods examined. Flows that satisfy all the R2Cross 

3-of-3 criteria do not appear to reflect the normal magnitude of 

seasonal-low or seasonal-high flows in southern New England. The R2Cross 2-of-3 criteria flow target was substantially 

lower and less variable than the 3-of-3 criteria target flow, but 

with the exception of the 3-of-3 criteria target flow, the 2-of-3 

criteria target flows varied the most among the sites and methods examined. This indicates that if an insufficient number 

of cross sections are used, the target flow determined by the 

R2Cross method may not represent the aquatic-habitat needs 

of the reach. 

The target flows determined by the R2Cross 2-of-3 criteria and Wetted-Perimeter methods were in closest agreement 

among the methods examined; the median values determined 

at the 10 riffle sites were about 0.24 and 0.25 ft3/s/mi2, respectively. Of the statistically based methods, the ABF low-flow 

target (median of about 0.32 ft3/s/mi2) was closest to the flow 

targets determined by the R2Cross 2-of-3 criteria and WettedPerimeter methods. The Tennant 30-percent QMA target flow 

(median of about 0.58 ft3/s/mi2) was about 81 percent greater 

than the median ABF low-flow target. The Tennant method 

varied least among standard-setting methods over the 10 riffle 

sites. The flow targets determined by R2Cross 2-of-3 criteria 

and Wetted-Perimeter methods were between 10 and 20 percent of the QMA. 

The ABF low-flow target (0.32 ft3/s/mi2) is between the 

25th and 50th percentiles of the median monthly flow for the 

period July through September (0.22 and 0.42 ft3/s/mi2, respectively). The flow targets determined by the R2Cross 2-of-3 

criteria and Wetted-Perimeter methods (0.24 and 0.25 ft3/s/mi2, 

respectively) were about equal to the 25th percentile of the 

median monthly flow for the period July through September. 

The target flow determined by the Tennant 30-percent QMA

criteria method (0.58 ft3/s/mi2) is between the 50th and 75th

percentiles of the median monthly flow for the period July 

through September (0.42 and 0.83 ft3

/s/mi2, respectively). The 

target flows determined by the Tennant 50-percent QMA and 

the R2Cross 3-of-3 criteria methods are well above the upper 

quartile of median monthly flows during the summer and well 

below the lower quartile of monthly median flows during the 

normal high-flow period. This underscores that the target flows 

determined by these particular methods are not representative 

of the low- and high-flow regimes in southern New England.

Through use of HSPF simulated flows it was possible 

to evaluate the frequency and duration that flow targets were 

not met over a 45-year period (1960–2004) without water 

withdrawals (NOWU scenario) and with average 1998–2003 

water withdrawals (AVGWU scenario). The ability to meet the 

flow targets over the long-term period was evaluated by (1) the 

median number of episodes (an episode is a continuous period 

that streamflow fell below a target flow) per year the flow 

target was not met, (2) the median number of days per year 

the flow target was not met, (3) the median duration (days) of 

the longest annual episode the flow target was not met, (4) the 

longest continuous duration the flow target was not met, and 

(5) the total number of days the flow target was not met. 

At the 10 riffle sites, the NOWU simulated streamflows 

were below the statistically based target flows (Tennant 

30-percent QMA and ABF), as measured by the median duration of annual episodes and total number of days below the 

flow target over the 45-year period, about three times more 

than that determined by physically based target flows (Wetted-Perimeter and R2Cross 2-of-3 criteria). This is because 

the median target flow determined by Wetted-Perimeter 

and R2Cross 2-of-3 criteria methods (about 0.25 ft3/s/mi2) 

is about 45 percent less than the median target flow determined by the Tennant 30-percent QMA and ABF methods 

(about 0.45 ft3/s/mi2). 

The frequency and duration that flows fell below a given 

target flow were almost always greater for AVGWU simulated 

streamflows than for NOWU simulated streamflows. Paired 

two-sample t-test and Wilcoxon signed-rank tests indicate 

these differences were mostly significant at the 95-percent 

confidence interval except at Whitehall Brook near Hopkinton 

and, at most sites, for the median number of annual episodes. 

The reason the difference in the number of annual episodes 

was largely insignificant is because AVGWU simulated 

streamflows generally have more days in an episode, resulting 

in fewer breaks between episodes compared to episodes computed from NOWU simulated streamflows. Overall, physically 

based target flows were slightly lower than statistically based 

target flows, making them slightly more likely to not meet a 

flow target as a result of flow alteration. 

The range of target flows determined by the different 

methods and among sites within the Sudbury and Assabet 

River Basins indicates additional information would be 

needed to determine regional flow standards for protection of 

aquatic habitat. The fish-community data, available at only 

two of the riffle sites examined (both along the upper Sudbury 

River), limits the conclusions that can be drawn among these 

data and the target flows. Further work would be needed to 

determine which methods are most sensitive to hydrologic 

alteration and fish-community composition to provide the 

appropriate balance between human water-supply needs and 

aquatic-habitat needs. 
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 2

108

References Cited

Annear, C.T., and Conder, A.L., 1984, Relative bias of several 

fisheries instream flow methods: North American Journal 

of Fisheries Management, v. 4, p. 531–539.

Armstrong, D.S., Parker, G.W., and Richards, T.A., 2004, 

Evaluation of streamflow requirements for habitat protection by comparison to streamflow characteristics at index 

streamflow-gaging stations in Southern New England: U.S. 

Geological Survey Water-Resources Investigations Report 

03–4332, 108 p.

Bain, M.B., and Knight, J.G., 1996, Classifying stream habitat 

using fish community analyses, in Leclerc, Michel, Capra, 

Herve, Valentin, Sylvie, Boudreault, Andre, and Cote, Yvon, 

eds., Proceedings of the second IAHR Symposium on habitat hydraulics: Quebec, Canada, June Ecohydraulics 2000, 

Institut National de la Recherche Scientifique-Eau, Ste-Foy, 

p. B107–B117.

Bain, M.B., and Meixler, M.S., 2000, Defining a target fish 

community for planning and evaluating enhancement of the 

Quinebaug River in Massachusetts and Connecticut: Ithaca, 

N.Y., New York Cooperative Fish and Wildlife Research 

Unit, Cornell University, 20 p.

Bain, M.B., and Meixler, M.S., 2008, A target fish community 

to guide river restoration: River Research and Applications, 

v. 24, p. 453–458.

Bain, M.B., and Travnichek, V.H., 1996, Assessing impacts 

and predicting restoration benefits of flow alterations in 

rivers developed for hydroelectric power production, in

Leclerc, Michel, Capra, Herve, Valentin, Sylvie, Boudreault, 

Andre, and Cote, Yvon, eds., Proceedings of the second 

IAHR Symposium on habitat hydraulics: Quebec, Canada, 

June Ecohydraulics 2000, Institut National de la Recherche 

Scientifique-Eau, Ste-Foy, p. B543–B552.

Baevsky, Y.H., 1991, Physical and water-quality characteristics affecting trout-spawning habitat in the Quashnet River, 

Cape Cod, Massachusetts: U.S. Geological Survey WaterResources Investigations Report 91–4045, 21 p.

Brunner, G.W., 2006, HEC-RAS, River Analysis System 

user’s manual: U.S. Army Corps of Engineers Hydrologic 

Engineering Center, CPD-68, 420 p.

Conservation Strategy Work Group Eastern Brook Trout Joint 

Venture, 2005, Conserving the Eastern Brook Trout—An 

overview of status, threats, and trends: 14 p., at http://www.

mmbtu.org/Conserving_Eastern_Brook_Trout.pdf.

Elliot, J.M., 1994, Quantitative ecology and the Brown Trout: 

New York, Oxford University Press, 286 p. 

Espegren, G.D., 1996, Development of instream flow recommendations in Colorado using R2CROSS: Denver, Colo., 

Water Conservation Board, 34 p.

Espegren, G.D., 1998, Evaluation of the standards and methods used for quantifying instream flows in Colorado: 

Denver, Colo., Water Conservation Board, 18 p.

Gibson, G.R., Barbour, M.T., Stribling, J.B., Gerritsen, J., and 

Karr, J.R., 1996, Biological criteria—Technical guidance 

for streams and small rivers (revised edition): U.S. Environmental Protection Agency, EPA 822B96001, 176 p.

Instream Flow Council, 2004, Instream flow for riverine 

resource stewardship (revised edition): Instream Flow 

Council, 268 p.

Jacobson, R.B., Femmer, S.R., and McKenney, R.A., 2001, 

Land-use changes and the physical habitat of streams—A 

review with emphasis on studies within the U.S. Geological 

Survey Federal–State Cooperative Program: U.S. Geological Survey Circular 1175, 63 p.

Kashiwagi, Michael, and Richards, T.A., 2009, Development 

of target fish community models for Massachusetts mainstem rivers: Boston, Massachusetts Department of Fish and 

Game, Division of Fisheries and Wildlife, 85 p.

Lang, Vernon, 1999, Questions and answers on the New England flow policy: Concord, N.H., U.S. Fish and Wildlife 

Service, 9 p.

Leathe, S.A., and Nelson, F.A., 1986, A literature evaluation 

of Montana’s wetted perimeter inflection point method for 

deriving instream flow recommendations: Helena, Mont., 

Department of Fish, Wildlife, and Parks, 70 p.

Leopold, L.B., and Maddock, Thomas, Jr., 1953, The hydraulic geometry of stream channels and some physiographic 

implications: U.S. Geological Survey Professional 

Paper 252, 57 p.

Lohr, S.C., 1993, Wetted stream channel, fish-food organisms 

and trout relative to the wetted perimeter inflection method: 

Bozeman, Mont., Montana State University, Ph.D. dissertation, 246 p.

Marsh, N.A., Stewardson, M.J., and Kennard, M.J., 2003, 

River Analysis Package (V2.0.4), Cooperative Research 

Center for Catchment Hydrology: Melbourne, Australia, 

Monash University [variously paged], accessed May 12, 

2009, at http://www.toolkit.net.au/Tools/RAP.
References Cited

Chapter 2

109

Massachusetts Division of Fisheries and Wildlife, 2006, Comprehensive wildlife conservation: Massachusetts Department of Fish and Game, Executive Office of Environmental 

Affairs, 791 p., accessed December 9, 2009, at http://www.

mass.gov/dfwele/dfw/habitat/cwcs/pdf/mass_cwcs_final.pdf.

Nehring, R.B., 1979, Evaluation of instream flow methods and 

determination of water quantity needs for streams in the State 

of Colorado: Fort Collins, Colo., Division of Wildlife, 144 p.

Nelsen, F.A., 1984, Guidelines for using the wetted perimeter 

(WETP) computer program of the Montana Department 

of Fish, Wildlife, and Parks: Bozeman, Mont., Montana 

Department of Fish, Wildlife, and Parks [variously paged].

Parker, G.W., Armstrong, D.S., and Richards T.A., 2004, Comparison of methods for determining streamflow requirements 

for aquatic habitat protection at selected sites on the Assabet 

and Charles Rivers, eastern Massachusetts, 2000–02: U.S. 

Geological Survey Scientific Investigations Report 2004–

5092, 72 p.

Picard, C.R., 1995, Factors that predict brook trout distribution, thermal habitat, and abundance in northwestern Ontario 

streams: Lakehead University, Canada, Master’s thesis, 

282 p.

Poole, G.C., and Berman, C.H., 2001, An ecological perspective on instream temperature—Natural heat dynamics and 

mechanisms of human-caused thermal degradation: Environmental Management, v. 27, no. 6, p. 787–802.

Richter, B.D., Baumgartner, J.V., Powell, Jennifer, and 

Braun, D.P., 1996, A method for assessing hydrologic 

alteration within ecosystems: Conservation Biology, v. 10, 

p. 1163–1174.

TIBCO Software Inc., 2008, Spotfire S+, v.8.1: accessed 

May 29, 2009 at http://spotfire.tibco.com/.

Stark, J.R., Armstrong, D.S., and Zwilling, D.R., 1994, 

Stream-aquifer interactions in the Straight River area, 

Becker and Hubbard Counties, Minnesota: U.S. Geological Survey Water-Resources Investigations Report 

94–4009, 83 p.

Tennant, D.L., 1976, Instream flow regimens for fish, wildlife, recreation, and related environmental resources, in

Instream flow needs, volume II: Boise, Idaho, Proceedings 

of the symposium and specialty conference on instream 

flow needs, May 3–6, American Fisheries Society, 

p. 359–373.

The Nature Conservancy, 2009, Indicators of Hydrologic 

Alteration, Version 7 Users Manual: The Nature Conservancy, Totter Software Design, and Smythe Scientific 

Software, 76 p. (available online at http://www.nature.org/

initiatives/freshwater/files/ihav7.pdf)

U.S. Fish and Wildlife Service, 1981, Interim regional policy 

for New England stream flow recommendations: Newton Corner, Mass., Region 5 of U.S. Fish and Wildlife 

Service, 3 p.
Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Chapter 2

110

This page intentionally left blank.
Appendix 1

Partial Listing of the Hydrologic Simulation Program–FORTRAN (HSPF) Model Run File (uci)
Appendix 1

112 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

*** HSPF model run for Sudbury-Assabet River Basin, MA 

RUN

GLOBAL

 Sudbury-Assabet River Basin, MA, Base calibration

 START 1992/10/01 00:00 END 2003/12/31 24:00 

 RUN INTERP OUTPUT LEVEL 4 6 

 RESUME 0 RUN 1 

END GLOBAL 

 

FILES 

<FILE> <UN#>***<----FILE NAME------------------------------------------------->

WDM 20 Sud1.WDM

MESSU 22 sud1.ech

15 sud1.out

BINO 16 sud1.hbn 

END FILES 

OPN SEQUENCE

 INGRP INDELT 01:00

 IMPLND 60

 IMPLND 61

 PERLND 1

 PERLND 3

 PERLND 4

 PERLND 6

 PERLND 7

 PERLND 8

 PERLND 9

 PERLND 10

 PERLND 11

 PERLND 12 

 PERLND 13

 PERLND 14

 PERLND 31

 PERLND 33

 PERLND 34

 PERLND 36

 PERLND 37

 PERLND 38

 PERLND 39

 PERLND 40

 PERLND 41

 PERLND 42 

 PERLND 43

 PERLND 44

 PERLND 51 

Appendix 1. Partial Listing of the Hydrologic Simulation

Program–FORTRAN (HSPF) Model Run File (uci)
Appendix 1

Appendix 1: HSPF model run for Sudbury-Assabet River Basin, MA 113

 PERLND 52

 PERLND 53

 RCHRES 1

 RCHRES 2

 RCHRES 3

 RCHRES 4

 RCHRES 105

 RCHRES 5

 RCHRES 6

 RCHRES 107

 RCHRES 8

 RCHRES 9

 RCHRES 10

 RCHRES 11

 RCHRES 12

 RCHRES 13

 RCHRES 14

 RCHRES 15

 RCHRES 16

 RCHRES 17

 RCHRES 18

 RCHRES 19

 RCHRES 30

 RCHRES 31

 RCHRES 32

 RCHRES 33

 

 RCHRES 51

 RCHRES 52

 RCHRES 53

 RCHRES 54

 RCHRES 55

 RCHRES 56

 RCHRES 57

 RCHRES 58

 RCHRES 59

 RCHRES 60

 RCHRES 61

 RCHRES 62

 RCHRES 63

 RCHRES 64

 RCHRES 65

 RCHRES 66

 RCHRES 67

 RCHRES 68

 RCHRES 69

 RCHRES 70

 RCHRES 72 

 RCHRES 73 

 COPY 1

 COPY 5

 END INGRP

END OPN SEQUENCE
Appendix 1

114 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

************************************************** 

*** PERLND - Pervious land surface *** 

*** *** 

************************************************** 

PERLND

 ACTIVITY

 <PLS > Active Sections (1=Active; 0=Inactive) ***

 ### -### ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ***

 1 53 0 1 1

 END ACTIVITY

 PRINT-INFO

 <PLS > <-*** Print-flags: 2-PIVL, 3-dy, 4-mn, 5-yr, 6-never ***-> PIVL PYR

 ### -### ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ***

 1 53 5 5 1 12

 END PRINT-INFO

 BINARY-INFO ***

 <PLS > <-*** Print-flags: 2-PIVL, 3-dy, 4-mn, 5-yr, 6-never ***-> PIVL PYR

 ### -### ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ***

 1 53 5 5 1 12

 END BINARY-INFO ***

 GEN-INFO 

 <PLS ><-------Name------->NBLKS Unit-systems Printer Binary *** 

 ###--### User t-series Engl Metr Engl Metr *** 

 1 S&G Comm/Ind 1 1 1 1 15 0 16 0 

 2 S&G Comm/Ind Imp 1 1 1 1 15 0 16 0 

 3 S&G Comm/Ind Exp 1 1 1 1 15 0 16 0 

 4 S&G hi resid 1 1 1 1 15 0 16 0

 5 S&G hi resid Imp 1 1 1 1 15 0 16 0

 6 S&G hi resid Exp 1 1 1 1 15 0 16 0

 7 S&G mod resid 1 1 1 1 15 0 16 0

 8 S&G mod resid Imp 1 1 1 1 15 0 16 0

 9 S&G mod resid Exp 1 1 1 1 15 0 16 0

 10 S&G low resid 1 1 1 1 15 0 16 0

 11 S&G low resid Imp 1 1 1 1 15 0 16 0

 12 S&G low resid Exp 1 1 1 1 15 0 16 0

 13 S&G Open 1 1 1 1 15 0 16 0

 14 S&G Forest 1 1 1 1 15 0 16 0

 31 Till Comm/Ind 1 1 1 1 15 0 16 0 

 32 Till Comm/Ind Imp 1 1 1 1 15 0 16 0 

 33 Till Comm/Ind Exp 1 1 1 1 15 0 16 0 

 34 Till hi resid 1 1 1 1 15 0 16 0

 35 Till hi resid Imp 1 1 1 1 15 0 16 0

 36 Till hi resid Exp 1 1 1 1 15 0 16 0

 37 Till mod resid 1 1 1 1 15 0 16 0

 38 Till mod resid Imp 1 1 1 1 15 0 16 0

 39 Till mod resid Exp 1 1 1 1 15 0 16 0

 40 Till low resid 1 1 1 1 15 0 16 0

 41 Till low resid Imp 1 1 1 1 15 0 16 0

 42 Till low resid Exp 1 1 1 1 15 0 16 0

 43 Till Open 1 1 1 1 15 0 16 0
Appendix 1

Appendix 1: HSPF model run for Sudbury-Assabet River Basin, MA 115

 44 Till Forest 1 1 1 1 15 0 16 0

 51 Non-forest wetland 1 1 1 1 15 0 16 0 

 52 Forested wetland 1 1 1 1 15 0 16 0 

 53 Water 1 1 1 1 15 0 16 0

 END GEN-INFO 

 

*** ------------------------------------------------------------------------ 

*** PERLND - Section SNOW 

 ICE-FLAG 

 <PLS > 0= Ice formation not simulated, 1= Simulated *** 

 ### -###ICEFG *** 

 1 53 1 

 END ICE-FLAG 

 

 SNOW-PARM1 

 <PLS > Snow input info: Part 1 *** 

 ### -### LAT MELEV SHADE SNOWCF COVIND *** 

 1 6 42.4 281. 0.15 1.35 0.75

 7 12 42.4 281. 0.35 1.35 0.75

 13 42.4 281. 0.15 1.35 0.75

 14 42.4 281. 0.50 1.35 0.75

 31 36 42.4 281. 0.15 1.35 0.75

 37 42 42.4 281. 0.35 1.35 0.75

 43 42.4 281. 0.15 1.35 0.75

 44 42.4 281. 0.50 1.35 0.75

 51 42.4 281. 0.10 1.35 0.75

 52 42.4 281. 0.50 1.35 0.75

 53 42.4 281. 0.05 1.35 0.75

 END SNOW-PARM1 

 

 SNOW-PARM2 

 <PLS > Snow input info: Part 2 *** 

 ### -### RDCSN TSNOW SNOEVP CCFACT MWATER MGMELT *** 

 1 53 0.15 32. 0.03 1.25 0.15 0.0200

 END SNOW-PARM2 

 

 

***----------------------------------------------------------------------------*

*** PERLND - Section PWATER 

 

 PWAT-PARM1 

*** CSNO=1 snowmelt on ; 1=varies monthly 0=does not

*** <PLS > <PWATER flags><monthly parameter value flags>< other proc >

***## -### CSNO RTOP UZFG VCS VUZ VNN VIFW VIRC VLET IFFC HWT IRRG

 1 13 1 0 1 1 0 0 1 0 1 0 0 0

 14 1 0 1 1 0 0 1 0 1 0 0 0 

 31 43 1 0 1 1 0 0 1 0 1 0 0 0

 44 1 0 1 1 0 0 1 0 1 0 0 0 

 51 53 1 0 1 1 0 0 1 0 1 0 0 0

 END PWAT-PARM1 

 

 PWAT-PARM2 

 ### -### ***FOREST LZSN INFILT LSUR SLSUR KVARY AGWRC

 *** (none) (in) (in/hr) (ft) (none) (l/in) (l/in)
Appendix 1

116 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

 1 9 0.050 4.60 0.400 150. 0.021 0.05 0.990

 10 12 0.100 4.80 0.480 200. 0.021 0.05 0.992

 13 0.050 4.90 0.500 300. 0.021 0.05 0.993

 14 0.250 5.00 0.520 300. 0.021 0.05 0.993

 31 39 0.050 2.70 0.100 150. 0.021 0.28 0.980

 40 42 0.100 2.50 0.120 200. 0.021 0.28 0.981

 43 0.050 2.70 0.130 300. 0.021 0.28 0.982

 44 0.250 2.70 0.140 300. 0.021 0.28 0.982

 51 0.050 1.70 0.050 100. 0.015 0.55 0.890

 52 0.250 1.20 0.050 100. 0.015 0.55 0.870

 53 0.010 1.20 0.050 100. 0.005 0.55 0.722 

 END PWAT-PARM2

 

 

 PWAT-PARM3 

 <PLS > *** PWATER input info: Part 3 

 ### -### ***PETMAX PETMIN INFEXP INFILD DEEPFR BASETP AGWETP

 1 2 40. 35. 2.0 2.0 0.00 0.000 0.120

 3 40. 35. 2.0 2.0 0.22 0.000 0.120

 4 5 40. 35. 2.0 2.0 0.00 0.000 0.120

 6 40. 35. 2.0 2.0 0.22 0.000 0.120

 7 8 40. 35. 2.0 2.0 0.00 0.000 0.120

 9 40. 35. 2.0 2.0 0.22 0.000 0.120

 10 11 40. 35. 2.0 2.0 0.00 0.000 0.120

 12 40. 35. 2.0 2.0 0.22 0.000 0.120

 13 40. 35. 2.0 2.0 0.00 0.000 0.120

 14 40. 35. 2.0 2.0 0.00 0.000 0.280

 31 32 40. 35. 2.0 2.0 0.00 0.000 0.120

 33 40. 35. 2.0 2.0 0.22 0.000 0.120

 34 35 40. 35. 2.0 2.0 0.00 0.000 0.120

 36 40. 35. 2.0 2.0 0.22 0.000 0.120

 37 38 40. 35. 2.0 2.0 0.00 0.000 0.120

 39 40. 35. 2.0 2.0 0.22 0.000 0.120

 40 41 40. 35. 2.0 2.0 0.00 0.000 0.120

 42 40. 35. 2.0 2.0 0.22 0.000 0.120

 43 40. 35. 2.0 2.0 0.00 0.000 0.120

 44 40. 35. 2.0 2.0 0.00 0.000 0.280

 51 40. 35. 2.0 2.0 0.00 0.000 0.300

 52 40. 35. 2.0 2.0 0.00 0.000 0.380

 53 40. 35. 2.0 2.0 0.00 0.000 0.340

 END PWAT-PARM3 

 

 PWAT-PARM4 

 <PLS > PWATER input info: Part 4 *** 

 varies monthly Y Y-N NO Y Y Y *** 

 Flag PARM1 VCS VUZ VUR VMN VIFW VLE *** 

 ### -### CEPSC UZSN NSUR INTFW IRC LZETP *** 

 (in) (in) (none) (none) (l/da) (none) *** 

 1 9 0.020 0.21 0.190 2.60 0.65 0.18

 10 12 0.020 0.25 0.200 2.70 0.75 0.18

 13 0.040 0.28 0.210 2.80 0.80 0.28

 14 0.040 0.31 0.250 2.80 0.85 0.88

 31 39 0.040 0.12 0.180 2.00 0.55 0.18

 40 42 0.040 0.18 0.210 2.15 0.65 0.18

 43 0.040 0.20 0.210 2.25 0.68 0.28

 44 0.040 0.22 0.220 2.30 0.70 0.88
Appendix 1

Appendix 1: HSPF model run for Sudbury-Assabet River Basin, MA 117

 51 52 0.020 0.12 0.250 1.00 0.75 0.88

 53 0.020 0.12 0.150 1.00 0.75 0.38

 END PWAT-PARM4 

 

 MON-INTERCEP 

 Monthly interception storage ***

 <PLS> Only required if VCSFG=1 in PWAT-PARM1 ***

 ### -### Interception storage capacity at start of each month ***

 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ***

 1 6 0.02 0.02 0.02 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.02 0.02

 7 12 0.02 0.02 0.02 0.03 0.05 0.10 0.12 0.10 0.10 0.08 0.02 0.02

 13 0.02 0.02 0.02 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.02 0.02

 14 0.02 0.02 0.02 0.02 0.05 0.12 0.14 0.12 0.14 0.10 0.04 0.03

 31 36 0.02 0.02 0.02 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.02 0.02

 37 42 0.02 0.02 0.02 0.03 0.05 0.10 0.12 0.10 0.10 0.08 0.02 0.02

 43 0.02 0.02 0.02 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.02 0.02

 44 0.02 0.02 0.02 0.02 0.05 0.12 0.14 0.12 0.14 0.10 0.04 0.03

 51 52 0.02 0.02 0.02 0.02 0.03 0.04 0.04 0.04 0.04 0.04 0.03 0.02

 53 0.02 0.02 0.02 0.02 0.03 0.03 0.03 0.03 0.03 0.02 0.02 0.02

 END MON-INTERCEP 

 

 

 MON-INTERFLW 

 Inc INTERFLW inc interflow & dec surface runoff (1- 3.0 typical) ***

 Interflow (range 0.0 to ~) Only required if VIFWFG=1 in PWAT-PARM1 ***

 inc.INTFW dec peak & extends recession ***

 < PLS > Monthly interflow at start of each month ***

 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ***

 1 9 2.80 2.80 2.80 2.85 2.85 2.85 2.85 2.85 2.85 2.80 2.80 2.80

 10 13 3.00 3.00 3.00 3.05 3.05 3.05 3.05 3.05 3.05 3.00 3.00 3.00

 14 3.20 3.20 3.20 3.25 3.25 3.25 3.25 3.25 3.25 3.20 3.20 3.20

 31 39 1.20 1.20 1.20 1.35 1.35 1.35 1.35 1.35 1.35 1.20 1.20 1.20

 40 43 2.40 2.40 2.40 2.45 2.45 2.45 2.45 2.45 2.45 2.40 2.40 2.40

 44 2.80 2.80 2.80 2.85 2.85 2.85 2.85 2.85 2.85 2.80 2.80 2.80

 51 53 1.40 1.40 1.40 1.45 1.45 1.45 1.45 1.45 1.45 1.40 1.40 1.40

 END MON-INTERFLW 

 MON-LZETPARM 

 Lower zone ET *** 

 <PLS > Only required if VLEFG=1 in PWAT-PARM1 (max < 1.0) *** 

 ### -### Lower zone ET parameter at start of each month *** 

 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ***

 1 6 .03 .03 .03 .06 .15 .35 .42 .42 .36 .26 .12 .08 

 7 13 .04 .04 .04 .07 .19 .68 .68 .68 .64 .56 .32 .18 

 14 .05 .05 .05 .08 .24 .70 .74 .74 .72 .66 .40 .22 

 31 36 .03 .03 .03 .05 .15 .35 .40 .40 .34 .26 .10 .16 

 37 43 .04 .04 .04 .06 .19 .68 .68 .68 .64 .56 .30 .16 

 44 .06 .06 .06 .08 .24 .70 .74 .74 .72 .66 .40 .22 

 51 52 .06 .06 .06 .08 .38 .75 .78 .78 .75 .62 .52 .32 

 53 .04 .04 .04 .07 .26 .42 .45 .45 .40 .42 .32 .16 

 END MON-LZETPARM 

 

 PWAT-STATE1 

 <PLS > *** Initial conditions at start of simulation 

 ### -### *** CEPS SURS UZS IFWS LZS AGWS GWVS

 1 13 0.02 0.00 0.50 0.055 9.63 6.40 3.58
Appendix 1

118 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

 14 0.02 0.00 0.59 0.084 8.31 7.80 3.91 

 31 43 0.02 0.00 0.30 0.108 4.78 2.19 2.34

 44 0.02 0.00 0.50 0.093 4.59 2.72 2.84

 51 53 0.02 0.00 0.40 0.425 4.55 0.83 0.44

 END PWAT-STATE1 

 

END PERLND 

 

************************************************************************** 

*** IMPLND - Impervious land 

************************************************************************** 

IMPLND 

 ACTIVITY 

 <ILS > Active Sections (1-active, 0-inactive) *** 

 ### -### ATMP SNOW IWAT SLD IWG IQAL *** 

 60 0 1 1 

 61 0 1 1 

 END ACTIVITY 

 

 PRINT-INFO 

 2-PIVL, 3-dy, 4-mn, 5-yr, 6-never user end *** 

 <ILS > <------ Print-flags --------> PIVL PYR *** 

 ### -### ATMP SNOW IWAT SLD IWG IQAL #### ## *** 

 60 6 5 1 12 

 61 6 5 1 12 

 END PRINT-INFO 

 BINARY-INFO *** 

 2-PIVL, 3-dy, 4-mn, 5-yr, 6-never user end *** 

 <ILS > <------ Print-flags --------> PIVL PYR *** 

 ### -### ATMP SNOW IWAT SLD IWG IQAL #### ## *** 

 60 61 5 5 1 12 

 END BINARY-INFO *** 

 GEN-INFO 

 <ILS ><-------Name-------> Unit-systems Printer Binary *** 

 ### -### User t-series Engl Metr Engl Metr *** 

 in out i/o# *** 

 60 Residential 1 1 1 15 0 16 0 

 61 Commercial 1 1 1 15 0 16 0 

 END GEN-INFO 

 ICE-FLAG 

 <PLS > 0= Ice formation not simulated, 1= Simulated *** 

 ### -###ICEFG *** 

 60 61 1 

 END ICE-FLAG 

 

 SNOW-PARM1 

 <PLS > Snow input info: Part 1 *** 

 ### -### LAT MELEV SHADE SNOWCF COVIND *** 

 60 61 42. 60. 0.20 1.35 0.75 

 END SNOW-PARM1 

 

 SNOW-PARM2 
Appendix 1

Appendix 1: HSPF model run for Sudbury-Assabet River Basin, MA 119

 <PLS > Snow input info: Part 2 *** 

 ### -### RDCSN TSNOW SNOEVP CCFACT MWATER MGMELT *** 

 60 61 0.15 32. 0.02 1.25 0.30 0.1100 

 END SNOW-PARM2 

 

*** ---------------------------------------------------------------------- 

*** IMPLND - Section IWATER i 

 

 IWAT-PARM1 

 <ILS > Flags *** 

 ### -### CSNO RTOP VRS VNN RTLI *** 

 60 0 1 0 

 61 0 1 0 

 END IWAT-PARM1 

 

 IWAT-PARM2 

 <ILS > *** 

 ### -### LSUR SLSUR NSUR RETSC *** 

 60 200. .014 .010 .04 

 61 100. .010 .010 .08 

 END IWAT-PARM2 

 

 IWAT-PARM3 

 <ILS > *** 

 ### -### PETMAX PETMIN *** 

 60 40. 35. 

 61 40. 35. 

 END IWAT-PARM3 

 

 IWAT-STATE1 

 <ILS > IWATER state variables *** 

 ### -### RETS SURS *** 

 60 .04 .00 

 61 .08 .00 

 END IWAT-STATE1 

END IMPLND 

********************************************************************************

*** RCHRES Block 

********************************************************************************

RCHRES 

 ACTIVITY 

 RCHRES Active Sections (1=Active, 0=Inactive) *** 

 ### -### HYFG ADFG CNFG HTFG SDFG GQFG OXFG NUFG PKFG PHFG *** 

 1 73 1 

 105 112 1 

 END ACTIVITY 

 

 PRINT-INFO 

 RCHRES <-Print-flags: 2-PIVL,3-dy,4-mn,5-yr,6-never ***> PIVL PYR 

 ### -### HYDR ADCA CONS HEAT SED GQL OXRX NUTR PLNK PHCB   ** * 

 1 8 6 6 6 6 6 6 6 6 6 6 1 12 

 9 6 6 6 6 6 6 6 6 6 6 1 12 
Appendix 1

120 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

 10 18 6 6 6 6 6 6 6 6 6 6 1 12 

 19 6 6 6 6 6 6 6 6 6 6 1 12 

 30 64 6 6 6 6 6 6 6 6 6 6 1 12 

 65 6 6 6 6 6 6 6 6 6 6 1 12 

 66 67 6 6 6 6 6 6 6 6 6 6 1 12 

 68 6 6 6 6 6 6 6 6 6 6 1 12 

 69 73 6 6 6 6 6 6 6 6 6 6 1 12 

 105 112 6 1 12

 END PRINT-INFO 

 BINARY-INFO 

 RCHRES <-Print-flags: 2-PIVL,3-dy,4-mn,5-yr,6-never ***> PIVL PYR 

 ### -### HYDR ADCA CONS HEAT SED GQL OXRX NUTR PLNK PHCB   ** * 

 1 73 6 1 12 

 105 112 6 1 12 

 END BINARY-INFO 

 

 GEN-INFO 

 RCHRES<-------Name------->Nexit Unit Systems Printer Binary *** 

 ### -### User t-series Engl Metr LKFG Engl Metr ***

 in out *** 

 1 Jackstraw Bk 2 1 1 15 0 16 0

 2 Piccadilly BK 2 1 1 15 0 16 0

 3 Whitehall Res 2 1 1 15 0 16 0

 4 Whitehall Bk 1 1 1 15 0 16 0

 5 Sudbury R Fruite St 2 1 1 15 0 16 0

 6 Sudbury R Howe St 1 1 1 15 0 16 0

 7 Indian Bk Hopkinton 1 1 1 15 0 16 0

 8 Hopkington Res outfl 3 1 1 15 0 16 0

 9 Sudbury R Front St 2 1 1 15 0 16 0

 10 Ashland Res 2 1 1 15 0 16 0

 11 Cold Spring Bk 1 1 1 15 0 16 0

 12 Sudbury Res 2 1 1 15 0 16 0

 13 Foss Res (no 3) 2 1 1 15 0 16 0

 14 Stearnes Res (no 1) 2 1 1 15 0 16 0

 15 Baiting Bk 1 1 1 15 0 16 0

 16 Course Bk 1 1 1 15 0 16 0

 17 Lake Cochituate 2 1 1 15 0 16 0

 18 Lake Cochituate Out 1 1 1 15 0 16 0

 19 Sudbury R Saxonvil 1 1 1 15 0 16 0

 30 Pine Bk 1 1 1 15 0 16 0

 31 Hop Bk Sudbury 2 1 1 15 0 16 0

 32 Allowance Bk 2 1 1 15 0 16 0

 33 Sudbury R Concord 2 1 1 15 0 16 0

 51 Assabet R Headwat 2 1 1 15 0 16 0

 52 Hop Bk Westboro 2 1 1 15 0 16 0

 53 ColdHarbor/Howard B 2 1 1 15 0 16 0

 54 Assabet R Northb 2 1 1 15 0 16 0

 55 Stirrup Bk Northb 2 1 1 15 0 16 0

 56 Millham Bk Marlb 2 1 1 15 0 16 0

 57 North Bk Berlin 1 1 1 15 0 16 0

 58 Abbabet R Hudson 2 1 1 15 0 16 0

 59 Danforth Bk 1 1 1 15 0 16 0

 60 Assabet R Stow 2 1 1 15 0 16 0

 61 Fort Meadow Bk 2 1 1 15 0 16 0

 62 Boon Lake complex 2 1 1 15 0 16 0
Appendix 1

Appendix 1: HSPF model run for Sudbury-Assabet River Basin, MA 121

 63 Elizabeth Bk 2 1 1 15 0 16 0

 64 Taylor Bk Maynard 2 1 1 15 0 16 0

 65 Assabet R Maynard g 1 1 1 15 0 16 0

 66 Assabet R Concord 2 1 1 15 0 16 0

 67 Fort Pnd Bk 2 1 1 15 0 16 0

 68 Nashoba Bk Gage 2 1 1 15 0 16 0

 69 Nashoba Bk 2 2 1 1 15 0 16 0

 70 Spencer Bk 1 1 1 15 0 16 0

 72 Assabet R Low Main 1 1 1 15 0 16 0

 73 Confluence 1 1 1 15 0 16 0

 105 Sudbury R Fruite St 2 1 1 15 0 16 0

 107 Indian Bk Hopkinton 1 1 1 15 0 16 0

 112 Sudbury Res 2 1 1 15 0 16 0

 END GEN-INFO

*** ----------------------------------------------------------------------- *** 

*** RECHRES - Section HYDR input 

 HYDR-PARM1 

 RCHRES Flags for HYDR section *** 

 ### -### VC A1 A2 A3 ODFVFG for each ODGTFG for each *** FUNCT for each

 FG FG FG FG possible exit possible exit *** possible exit

 1 2 3 4 5 1 2 3 4 5 *** 1 2 3 4 5 

 1 3 0 1 0 0 0 4 1 0 0 1

 4 0 1 0 0 4 0 0 1

 5 0 1 0 0 0 4 1 0 0 1

 6 7 0 1 0 0 4

 8 0 1 0 0 0 4 5 1 0 0 1

 9 10 0 1 0 0 0 4 1 0 1

 11 0 1 0 0 4

 12 14 0 1 0 0 0 4 1 0 0 1

 15 16 0 1 0 0 4

 17 0 1 0 0 0 4 1 0 0 1

 18 19 0 1 0 0 4

 30 0 1 0 0 4

 31 33 0 1 0 0 0 4 1 0 1

 51 56 0 1 0 0 0 4 1 0 0 1

 57 0 1 0 0 4

 58 0 1 0 0 0 4 1 0 0 1

 59 0 1 0 0 4

 60 64 0 1 0 0 0 4 1 0 0 1

 65 0 1 0 0 4

 66 69 0 1 0 0 0 4 1 0 0 1

 70 73 0 1 0 0 4

 105 0 1 0 0 0 4 1 0 0 1

 107 0 1 0 0 4

 112 0 1 0 0 0 4 1 0 0 1

 END HYDR-PARM1 

 HYDR-PARM2 

 RCHRES *** 

 ### -### FTB FTA LEN DELTH STCOR SED *** 

 ### -### DSN BNO (miles) (feet) (feet) KS DB50 *** 

 1 1 1.629 222. 0.0 0.5 

 2 2 1.292 37. 0.0 0.5 
Appendix 1

122 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

 3 3 1.910 11. 0.0 0.5 

 4 4 2.608 50. 0.0 0.5 

 5 5 2.659 168. 0.0 0.5 

 6 6 3.450 67. 0.0 0.5 

 7 7 2.940 113. 0.0 0.5 

 8 8 1.650 20. 0.0 0.5 

 9 9 2.758 33. 0.0 0.5 

 10 10 1.197 15. 0.0 0.5 

 11 11 0.790 14. 0.0 0.5 

 12 12 5.943 49. 0.0 0.5 

 13 13 2.130 22. 0.0 0.5 

 14 14 3.149 26. 0.0 0.5 

 15 15 3.515 99. 0.0 0.5 

 16 16 4.452 34. 0.0 0.5 

 17 17 3.591 13. 0.0 0.5 

 18 18 1.348 32. 0.0 0.5 

 19 19 5.811 42. 0.0 0.5 

 30 30 3.109 52. 0.0 0.5 

 31 31 8.502 110. 0.0 0.5

 32 32 3.398 102. 0.0 0.5

 33 33 16.62 41. 0.0 0.5

 51 51 1 .05 1.3 0.0 0.5

 52 52 4.445 194. 0.0 0.5

 53 53 7.004 305. 0.0 0.5

 54 54 4.754 62. 0.0 0.5

 55 55 4.754 82. 0.0 0.5

 56 56 4.386 109. 0.0 0.5

 57 57 4.386 152. 0.0 0.5

 58 58 4.774 94. 0.0 0.5

 59 59 5.026 70. 0.0 0.5

 60 60 8.387 99. 0.0 0.5

 61 61 4.774 19. 0.0 0.5

 62 62 7.361 62. 0.0 0.5

 63 63 8.387 96. 0.0 0.5

 64 64 1.886 53. 0.0 0.5

 65 65 5.236 74. 0.0 0.5

 66 66 5.236 74. 0.0 0.5

 67 67 5.236 74. 0.0 0.5

 68 68 5.236 74. 0.0 0.5

 69 69 5.236 74. 0.0 0.5

 70 70 5.236 74. 0.0 0.5

 72 72 5.236 74. 0.0 0.5

 73 73 5.236 74. 0.0 0.5

 105 105 2 600 74. 0.0 0.5

 107 107 2.900 74. 0.0 0.5

 112 112 5.900 74. 0.0 0.5

 END HYDR-PARM2 
Appendix 2

Calibration of a One-Dimensional Channel Hydraulic Model (HEC-RAS) used to Determine 

Physically Based Target Flows at Six Riffle Reaches in the Sudbury River Basin

Water-Surface-Profile Model..........................................................................................124

 Whitehall Brook near Hopkinton...........................................................................125

 Sudbury River near Hopkinton...............................................................................127

 Sudbury River near Ashland..................................................................................128

 Indian Brook near Hopkinton.................................................................................132

 Indian Brook near Ashland ....................................................................................135

 Baiting Brook near Framingham............................................................................136
Appendix 2

124 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Appendix 2. Calibration of a One-Dimensional Channel

Hydraulic Model (HEC-RAS) used to Determine Physically Based 

Target Flows at Six Riffle Reaches in the Sudbury River Basin 

Water-Surface-Profile Model 

Channel hydraulic properties were determined using 

HEC-RAS, a one-dimensional channel hydraulics model. The 

model entailed entering detailed cross-sectional information 

along a reach and initial values of channel roughness (Manning’s “n” value), type of flow regime (subcritical or supercritical defined by the Froude number, which characterizes the 

energy gradient of the channel), and downstream hydraulic 

gradient. In all reaches, the computed Froude number indicated subcritical flow (value less than 1); therefore, the standard upstream-step energy method was used to simulate watersurface profiles. The hydraulic gradient at the downstream 

end of each reach was estimated from the measured difference 

in the water-surface elevation at the downstream section and 

surveyed reference points further downstream. 

Final “n” values were empirically determined by altering 

their value until the simulated surface-water profile closely 

matched the observed profile over a range of flows. The variability in the calibrated “n” value over the range of flows at 

a cross section and between cross sections is because of the 

variability of the flow-path length. As the flow path lengthens, 

the energy gradient decreases. To compensate for the change 

in flow-path length that changes with flow, the only variable 

that can be altered in a one-dimensional model is the channel 

roughness. 

The number of cross sections in a reach and the number 

and range of flows over which the water-surface profile was 

obtained varied by site. Occasionally, additional cross sections 

were needed to reduce simulated velocity head drops between 

surveyed cross sections to maintain model stability. When 

needed, these sections were interpolated and added to the 

model. Occasionally, several of the downstream cross sections 

were not used in the R2Cross and Wetted-Perimeter analysis 

because downstream backwater affected the hydraulic characteristics of the section.

 The model was considered calibrated when the root 

mean square error (RMSE) between observed and simulated 

water-surface elevations was minimized. The calibrated 

model was then used to compute the flows that satisfied the 

hydraulic criteria for physically based target flow standardsetting methods. The tables in this appendix show by site the 

observed water-surface elevation over a range of flows and the 

calibrated water-surface elevation for those flows. Also shown 

are the calibrated “n” value and computed Froude number and 

other hydraulic properties over the range of flows.
Appendix 2

Appendix 2: Water-Surface-Profile Model 125

Whitehall Brook near Hopkinton

Four cross sections (109, 118, 128, and 136) and water levels over 15 flows ranging from 1.1 to 198 ft3/s were used to calibrate the HEC-RAS model in this reach (table 2–1). A slope of 0.001 ft/ft was specified as the downstream boundary condition. 

The RMSE was 0.008 ft over the entire reach for all measured flows. 

All four cross sections were used in the R2Cross analysis, but the flow standard was determined from the three upstream 

stations (118, 128, and 136) because the downstream section was affected by backwater. For the same reason, the three upstream 

cross sections were used for the Wetted-Perimeter analysis.

Table 2–1. Simulated water-surface elevations made with the HEC-RAS model calibrated to observed water-surface elevations at 

multiple cross sections over a range of discharges at Whitehall Brook near Hopkinton, Massachusetts.—Continued

[Elevation is an arbitrary datum; ft, foot; ft/ft, foot per foot; ft2, square foot; ft3/s, cubic foot per second; --, not determined]

Station Flow 

(ft3

/s)

Manning’s 

coefficient

Flow area 

(ft2)

Hydraulic 

radius 

(ft)

Slope 

(ft/ft)

Froude 

number

Water-surface elevation

Observed 

(ft)

Simulated 

(ft)

109 1.1 0.040 1.1 0.14 0.012 0.51 497.75 497.75

109 1.7 0.058 1.8 0.19 0.012 0.38 497.84 497.84

109 2.6 0.060 2.5 0.23 0.012 0.37 498.05 497.91

109 3.5 0.063 3.4 0.25 0.012 0.36 498.01 497.97

109 3.9 0.064 3.7 0.27 0.012 0.36 498.00 498.00

109 4.0 0.065 3.8 0.27 0.012 0.36 498.16 498.00

109 4.1 0.068 4.0 0.29 0.012 0.34 498.07 498.02

109 4.3 0.073 4.3 0.30 0.012 0.32 498.27 498.04

109 5.8 0.107 6.6 0.43 0.012 0.23 498.20 498.20

109 6.5 0.113 7.5 0.47 0.012 0.22 498.60 498.26

109 9.1 0.132 10 0.61 0.012 0.20 498.73 498.43

109 10 0.140 12 0.66 0.012 0.19 498.89 498.50

109 74 0.096 33 1.3 0.012 0.32 499.56 499.56

109 77 0.094 34 1.3 0.012 0.33 499.56 499.57

109 198 0.045 40 1.2 0.012 0.71 499.77 499.77

118 1.1 0.053 1.1 0.11 0.024 0.53 497.95 497.97

118 1.7 0.087 1.5 0.13 0.063 0.54 498.00 498.01

118 2.6 0.135 2.1 0.16 0.134 0.52 498.14 498.05

118 3.5 0.175 2.7 0.20 0.206 0.52 498.10 498.10

118 3.9 0.180 2.9 0.21 0.208 0.51 498.12 498.12

118 4.0 0.180 3.0 0.21 0.207 0.51 498.18 498.12

118 4.1 0.188 3.1 0.22 0.219 0.50 498.13 498.12

118 4.3 0.197 3.2 0.23 0.228 0.50 498.29 498.13

118 5.8 0.121 4.8 0.31 0.045 0.38 498.27 498.24

118 6.5 0.100 5.5 0.35 0.026 0.35 498.61 498.29

118 9.1 0.100 8.1 0.48 0.015 0.29 498.75 498.45

118 10 0.100 9.3 0.52 0.013 0.27 498.90 498.52

118 74 0.002 33 1.2 0.000 0.35 499.54 499.56

118 77 0.002 34 1.2 0.000 0.36 499.57 499.57

118 198 0.002 43 1.4 0.000 0.66 499.80 499.89
Appendix 2

126 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Table 2–1. Simulated water-surface elevations made with the HEC-RAS model calibrated to observed water-surface elevations at 

multiple cross sections over a range of discharges at Whitehall Brook near Hopkinton, Massachusetts.—Continued

[Elevation is an arbitrary datum; ft, foot; ft/ft, foot per foot; ft2, square foot; ft3/s, cubic foot per second; --, not determined]

Station Flow 

(ft3

/s)

Manning’s 

coefficient

Flow area 

(ft2)

Hydraulic 

radius 

(ft)

Slope 

(ft/ft)

Froude 

number

Water-surface elevation

Observed 

(ft)

Simulated 

(ft)

128 1.1 0.032 1.1 0.10 0.011 0.59 498.17 498.13

128 1.7 0.032 1.4 0.12 0.012 0.62 498.16 498.16

128 2.6 0.058 2.2 0.18 0.020 0.48 498.23 498.23

128 3.5 0.051 2.7 0.21 0.015 0.49 498.27 498.26

128 3.9 0.081 3.3 0.25 0.027 0.42 498.33 498.31

128 4.0 0.084 3.3 0.25 0.029 0.42 -- 498.31

128 4.1 0.094 3.5 0.26 0.033 0.41 498.32 498.32

128 4.3 0.108 3.7 0.28 0.041 0.39 498.43 498.34

128 5.8 0.197 4.9 0.35 0.101 0.35 498.43 498.43

128 6.5 0.195 5.3 0.37 0.097 0.35 -- 498.46

128 9.1 0.174 7.1 0.47 0.061 0.33 -- 498.58

128 10 0.165 7.9 0.51 0.050 0.32 498.90 498.64

128 74 0.039 27 1.1 0.004 0.47 -- 499.55

128 77 0.038 27 1.1 0.004 0.48 499.56 499.56

128 198 0.025 33 1.2 0.007 0.98 499.77 499.79

136 1.1 0.150 1.9 0.15 0.046 0.27 498.25 498.25

136 1.7 0.121 2.2 0.18 0.038 0.32 498.28 498.28

136 2.6 0.139 2.9 0.22 0.050 0.33 498.36 498.33

136 3.5 0.150 3.5 0.26 0.060 0.34 498.38 498.38

136 3.9 0.095 3.8 0.28 0.024 0.35 498.43 498.40

136 4.0 0.094 3.8 0.28 0.024 0.35 498.40 498.40

136 4.1 0.101 3.9 0.28 0.028 0.35 498.44 498.41

136 4.3 0.130 4.1 0.30 0.041 0.33 498.77 498.42

136 5.8 0.160 5.4 0.37 0.050 0.31 498.54 498.51

136 6.5 0.160 5.8 0.40 0.049 0.31 498.65 498.54

136 9.1 0.160 7.4 0.49 0.044 0.30 498.78 498.65

136 10 0.160 8.1 0.53 0.042 0.30 498.92 498.70

136 74 0.160 23 0.97 0.094 0.52 499.56 499.55

136 77 0.159 23 0.98 0.098 0.53 -- 499.56

136 198 0.013 40 1.1 0.001 0.77 499.79 500.10
Appendix 2

Appendix 2: Water-Surface-Profile Model 127

Sudbury River near Hopkinton

Three cross sections (112, 121, and 128) and water levels over 10 flows ranging from 5.1 to 32 ft3/s were used to calibrate 

the HEC-RAS model in this reach (table 2–2). A slope of 0.006 ft/ft was specified as the downstream boundary condition. The 

RMSE was 0.000 ft over the entire reach for all measured flows. 

All three cross sections were used in the R2Cross analysis, but the flow standard was determined from the upstream station 

(128) because the downstream sections were affected by backwater during low to moderate flows. For the same reason, only the 

most upstream cross section was used for the Wetted-Perimeter analysis.

Table 2–2. Simulated water-surface elevations made with the HEC-RAS model calibrated to observed water-surface elevations at 

multiple cross sections over a range of discharges at Sudbury River near Hopkinton, Massachusetts.

[Elevation is an arbitrary datum; ft, foot; ft/ft, foot per foot; ft2, square foot; ft3/s, cubic foot per second; --, not determined]

Station Flow

(ft3

/s)

Manning’s 

coefficient

Flow area

(ft2)

Hydraulic 

radius

(ft)

Slope

(ft/ft) Froude number

Water-surface elevation

Observed 

(ft)

Simulated 

(ft)

112 5.1 0.022 3.2 0.18 0.006 0.68 497.95 497.95

112 5.5 0.034 4.5 0.23 0.006 0.45 498.02 498.02

112 6.2 0.035 5.0 0.24 0.006 0.45 -- 498.04

112 8.9 0.035 6.3 0.29 0.006 0.46 -- 498.10

112 9.1 0.035 6.4 0.30 0.006 0.46 -- 498.11

112 14 0.067 14 0.44 0.006 0.27 -- 498.38

112 15 0.068 14 0.47 0.006 0.26 -- 498.41

112 20 0.075 19 0.58 0.006 0.25 498.54 498.54

112 25 0.080 22 0.68 0.006 0.24 498.65 498.65

112 32 0.080 28 0.61 0.006 0.24 -- 498.74

121 5.1 0.900 3.7 0.26 4.318 0.48 498.17 498.14

121 5.5 0.589 4.4 0.29 1.267 0.41 -- 498.19

121 6.2 0.439 4.6 0.30 0.816 0.44 498.20 498.20

121 8.9 0.257 5.3 0.33 0.369 0.51 -- 498.25

121 9.1 0.244 5.4 0.33 0.336 0.52 498.25 498.25

121 14 0.021 8.4 0.36 0.002 0.47 498.39 498.39

121 15 0.022 8.9 0.38 0.002 0.47 498.42 498.42

121 20 0.020 12 0.49 0.001 0.42 498.54 498.54

121 25 0.020 14 0.58 0.001 0.39 498.65 498.65

121 32 0.180 23 0.60 0.044 0.30 498.83 498.83

128 5.1 0.044 3.9 0.26 0.008 0.44 498.30 498.30

128 5.5 0.042 4.2 0.25 0.007 0.43 498.32 498.32

128 6.2 0.044 4.5 0.24 0.008 0.44 -- 498.34

128 8.9 0.050 6.0 0.29 0.011 0.46 -- 498.42

128 9.1 0.052 6.1 0.30 0.011 0.45 498.42 498.42

128 14 0.123 8.7 0.41 0.052 0.43 -- 498.55

128 15 0.140 9.4 0.44 0.063 0.42 498.58 498.58

128 20 0.150 11 0.51 0.075 0.44 498.67 498.67

128 25 0.121 16 0.46 0.039 0.40 498.74 498.74

128 32 0.169 22 0.60 0.047 0.33 498.92 498.92
Appendix 2

128 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Sudbury River near Ashland

Six cross sections (120, 157, 171, 192, 209, and 223) and water levels over 22 flows ranging from 4.7 to 70 ft3/s were used 

to calibrate the HEC-RAS model in this reach (table 2–3). A slope of 0.002 ft/ft was specified as the downstream boundary condition. The RMSE was 0.021 ft over the entire reach for all measured flows. 

All cross sections were used in the R2Cross analysis, but the flow standard was determined from the four upstream stations 

(157, 171, 192, and 209) that are unaffected by backwater during low to moderate flows. Stations 157, 171, 192, and 223 were 

used in the Wetted-Perimeter analysis.

Table 2–3. Simulated water-surface elevations made with the HEC-RAS model calibrated to observed water-surface elevations at 

multiple cross sections over a range of discharges at Sudbury River near Ashland, Massachusetts.—Continued

[Elevation is an arbitrary datum; ft, foot; ft/ft, foot per foot; ft2, square foot; ft3/s, cubic foot per second; --, not determined]

Station Flow

(ft3

/s)

Manning’s 

coefficient

Flow area

(ft2)

Hydraulic 

radius

(ft)

Slope

(ft/ft)

Froude 

number

Water-surface elevation

Observed

(ft)

Simulated

(ft)

120 4.7 0.060 6.7 0.38 0.002 0.20 498.19 498.07

120 6.1 0.060 8.1 0.42 0.002 0.20 498.17 498.15

120 6.8 0.062 8.9 0.44 0.002 0.20 498.19 498.19

120 8.9 0.051 10 0.45 0.002 0.24 498.22 498.22

120 12 0.056 12 0.52 0.002 0.23 498.35 498.35

120 13 0.056 14 0.55 0.002 0.23 498.44 498.41

120 14 0.056 14 0.56 0.002 0.23 498.34 498.42

120 17 0.054 16 0.59 0.002 0.24 498.44 498.48

120 17 0.053 16 0.60 0.002 0.24 498.46 498.49

120 20 0.050 17 0.62 0.002 0.26 498.46 498.53

120 20 0.050 17 0.63 0.002 0.26 498.54 498.54

120 22 0.050 18 0.66 0.002 0.26 498.53 498.57

120 23 0.052 20 0.69 0.002 0.25 498.58 498.63

120 27 0.056 25 0.56 0.002 0.25 498.63 498.72

120 27 0.056 26 0.57 0.002 0.25 498.73 498.73

120 32 0.057 30 0.56 0.002 0.25 498.71 498.81

120 33 0.058 31 0.56 0.002 0.25 498.65 498.84

120 34 0.058 32 0.57 0.002 0.25 498.69 498.85

120 37 0.059 34 0.60 0.002 0.24 498.75 498.90

120 64 0.066 56 0.82 0.002 0.21 499.25 499.25

120 69 0.074 65 0.90 0.002 0.19 499.22 499.37

120 70 0.076 67 0.92 0.002 0.18 499.40 499.40

157 4.7 0.067 6.7 0.27 0.005 0.23 498.30 498.19

157 6.1 0.068 8.6 0.33 0.004 0.22 498.26 498.26

157 6.8 0.068 10 0.35 0.004 0.21 498.28 498.30

157 8.9 0.069 11 0.38 0.005 0.23 498.34 498.34

157 12 0.070 14 0.48 0.004 0.21 498.42 498.46

157 13 0.070 16 0.53 0.004 0.20 498.52 498.52

157 14 0.069 16 0.54 0.004 0.20 498.45 498.53

157 17 0.065 18 0.59 0.003 0.21 498.55 498.59

157 17 0.064 18 0.59 0.003 0.21 498.60 498.60

157 20 0.062 19 0.62 0.003 0.22 498.60 498.63

157 20 0.062 20 0.64 0.003 0.23 498.67 498.65

157 22 0.061 21 0.66 0.003 0.23 498.66 498.68

157 23 0.058 22 0.70 0.003 0.22 498.72 498.72
Appendix 2

Appendix 2: Water-Surface-Profile Model 129

Table 2–3. Simulated water-surface elevations made with the HEC-RAS model calibrated to observed water-surface elevations at 

multiple cross sections over a range of discharges at Sudbury River near Ashland, Massachusetts.—Continued

[Elevation is an arbitrary datum; ft, foot; ft/ft, foot per foot; ft2, square foot; ft3/s, cubic foot per second; --, not determined]

Station Flow

(ft3

/s)

Manning’s 

coefficient

Flow area

(ft2)

Hydraulic 

radius

(ft)

Slope

(ft/ft)

Froude 

number

Water-surface elevation

Observed

(ft)

Simulated

(ft)

157 27 0.047 24 0.75 0.002 0.22 498.79 498.79

157 27 0.047 25 0.77 0.002 0.22 498.84 498.81

157 32 0.047 27 0.82 0.002 0.22 498.82 498.88

157 33 0.047 28 0.85 0.002 0.23 498.84 498.91

157 34 0.047 29 0.86 0.002 0.23 498.92 498.92

157 37 0.049 30 0.89 0.002 0.23 498.94 498.97

157 64 0.064 43 1.2 0.003 0.24 499.34 499.34

157 69 0.057 47 1.3 0.002 0.23 499.29 499.45

157 70 0.056 47 1.3 0.002 0.23 499.47 499.47

171 4.7 0.274 12 0.36 0.016 0.11 498.37 498.31

171 6.1 0.266 15 0.40 0.015 0.11 498.38 498.37

171 6.8 0.224 16 0.41 0.012 0.12 498.39 498.39

171 8.9 0.146 17 0.43 0.007 0.14 498.43 498.42

171 12 0.104 21 0.48 0.003 0.14 498.51 498.51

171 13 0.102 23 0.54 0.003 0.14 498.62 498.57

171 14 0.101 23 0.55 0.003 0.14 498.54 498.58

171 17 0.089 26 0.60 0.003 0.15 498.64 498.64

171 17 0.083 26 0.60 0.002 0.15 498.67 498.64

171 20 0.064 27 0.63 0.002 0.16 498.67 498.67

171 20 0.068 28 0.65 0.002 0.16 498.75 498.69

171 22 0.076 29 0.68 0.002 0.16 498.75 498.72

171 23 0.083 31 0.72 0.002 0.15 498.79 498.77

171 27 0.083 34 0.77 0.003 0.16 498.85 498.83

171 27 0.082 35 0.78 0.002 0.16 498.93 498.84

171 32 0.081 38 0.85 0.002 0.16 498.89 498.92

171 33 0.080 39 0.87 0.002 0.16 498.91 498.95

171 34 0.080 40 0.88 0.002 0.16 499.01 498.96

171 37 0.079 42 0.92 0.002 0.16 499.01 499.01

171 64 0.098 61 1.2 0.004 0.16 499.41 499.40

171 69 0.098 66 1.3 0.003 0.16 499.39 499.50

171 70 0.098 67 1.3 0.003 0.16 499.58 499.53

192 4.7 0.108 12 0.35 0.003 0.12 498.51 498.43

192 6.1 0.109 14 0.41 0.003 0.12 498.51 498.50

192 6.8 0.108 14 0.43 0.004 0.13 498.51 498.52

192 8.9 0.107 15 0.45 0.005 0.15 498.55 498.54

192 12 0.105 17 0.50 0.006 0.17 498.63 498.60

192 13 0.104 19 0.54 0.006 0.17 -- 498.65

192 14 0.103 19 0.55 0.006 0.17 498.67 498.66

192 17 0.101 21 0.60 0.006 0.18 498.73 498.71

192 17 0.101 21 0.60 0.006 0.19 498.76 498.71

192 20 0.100 22 0.61 0.007 0.20 498.76 498.73

192 20 0.099 22 0.63 0.007 0.20 498.82 498.75

192 22 0.097 24 0.66 0.006 0.20 498.84 498.79
Appendix 2

130 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Table 2–3. Simulated water-surface elevations made with the HEC-RAS model calibrated to observed water-surface elevations at 

multiple cross sections over a range of discharges at Sudbury River near Ashland, Massachusetts.—Continued

[Elevation is an arbitrary datum; ft, foot; ft/ft, foot per foot; ft2, square foot; ft3/s, cubic foot per second; --, not determined]

Station Flow

(ft3

/s)

Manning’s 

coefficient

Flow area

(ft2)

Hydraulic 

radius

(ft)

Slope

(ft/ft)

Froude 

number

Water-surface elevation

Observed

(ft)

Simulated

(ft)

192 23 0.095 25 0.69 0.005 0.19 498.86 498.83

192 27 0.092 28 0.74 0.005 0.20 498.92 498.90

192 27 0.091 28 0.75 0.005 0.20 498.96 498.91

192 32 0.088 31 0.80 0.005 0.20 498.99 498.98

192 33 0.087 32 0.82 0.005 0.20 499.01 499.01

192 34 0.085 32 0.83 0.005 0.20 499.05 499.02

192 37 0.082 34 0.87 0.004 0.20 499.07 499.07

192 64 0.047 50 1.1 0.001 0.21 499.43 499.44

192 69 0.047 54 1.2 0.001 0.20 499.43 499.53

192 70 0.047 55 1.2 0.001 0.20 -- 499.56

209 4.7 0.020 4.0 0.18 0.002 0.48 498.55 498.47

209 6.1 0.020 5.4 0.23 0.002 0.42 498.54 498.53

209 6.8 0.022 5.9 0.24 0.002 0.41 498.55 498.55

209 8.9 0.035 7.6 0.26 0.004 0.40 498.61 498.61

209 12 0.037 10 0.28 0.004 0.40 498.71 498.68

209 13 0.038 11 0.31 0.004 0.38 498.72 498.72

209 14 0.039 12 0.33 0.004 0.37 498.68 498.74

209 17 0.047 14 0.37 0.005 0.35 498.75 498.79

209 17 0.047 14 0.38 0.005 0.35 498.80 498.80

209 20 0.046 15 0.40 0.005 0.37 498.80 498.83

209 20 0.045 16 0.41 0.005 0.36 498.84 498.84

209 22 0.043 17 0.42 0.004 0.35 498.89 498.87

209 23 0.040 18 0.44 0.003 0.34 498.90 498.90

209 27 0.040 20 0.48 0.003 0.34 498.96 498.96

209 27 0.040 21 0.49 0.003 0.33 499.02 498.97

209 32 0.040 23 0.54 0.003 0.32 499.09 499.03

209 33 0.040 25 0.57 0.003 0.32 499.03 499.06

209 34 0.040 25 0.58 0.003 0.31 499.07 499.07

209 37 0.040 27 0.61 0.002 0.31 -- 499.11

209 64 0.036 42 0.91 0.001 0.28 499.45 499.45

209 69 0.036 47 0.99 0.001 0.26 -- 499.55

209 70 0.036 48 1.0 0.001 0.26 -- 499.57

223 4.7 0.066 6.6 0.21 0.007 0.27 498.84 498.56

223 6.1 0.064 8.0 0.25 0.006 0.27 498.82 498.60

223 6.8 0.064 8.6 0.27 0.006 0.27 498.84 498.62

223 8.9 0.062 11 0.32 0.005 0.26 498.86 498.69

223 12 0.061 12 0.37 0.005 0.27 498.94 498.74

223 13 0.060 14 0.41 0.005 0.27 499.01 498.78

223 14 0.060 14 0.42 0.005 0.26 498.78 498.80

223 17 0.059 16 0.47 0.005 0.26 499.00 498.85

223 17 0.059 16 0.48 0.005 0.27 499.02 498.86

223 20 0.059 17 0.51 0.005 0.28 499.02 498.89

223 20 0.059 18 0.52 0.005 0.28 499.02 498.90
Appendix 2

Appendix 2: Water-Surface-Profile Model 131

Table 2–3. Simulated water-surface elevations made with the HEC-RAS model calibrated to observed water-surface elevations at 

multiple cross sections over a range of discharges at Sudbury River near Ashland, Massachusetts.—Continued

[Elevation is an arbitrary datum; ft, foot; ft/ft, foot per foot; ft2, square foot; ft3/s, cubic foot per second; --, not determined]

Station Flow

(ft3

/s)

Manning’s 

coefficient

Flow area

(ft2)

Hydraulic 

radius

(ft)

Slope

(ft/ft)

Froude 

number

Water-surface elevation

Observed

(ft)

Simulated

(ft)

223 22 0.058 19 0.54 0.005 0.28 499.04 498.93

223 23 0.058 19 0.56 0.005 0.28 499.10 498.95

223 27 0.058 21 0.60 0.005 0.28 499.13 499.01

223 27 0.058 22 0.61 0.005 0.28 499.14 499.02

223 32 0.057 24 0.66 0.004 0.28 499.14 499.08

223 33 0.057 25 0.68 0.004 0.28 499.17 499.11

223 34 0.057 25 0.69 0.004 0.28 499.23 499.12

223 37 0.057 27 0.72 0.004 0.28 499.19 499.15

223 64 0.072 39 0.99 0.006 0.28 499.63 499.49

223 69 0.076 43 1.1 0.006 0.27 499.50 499.58

223 70 0.077 44 1.1 0.006 0.27 499.86 499.60
Appendix 2

132 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Indian Brook near Hopkinton

Seven cross sections (125, 163, 182, 208, 222, 225, and 230) and water levels over 11 flows ranging from 0.3 to 41 ft3/s 

were used to calibrate the HEC-RAS model in this reach (table 2–4). A slope of 0.004 ft/ft was specified as the downstream 

boundary condition. The RMSE was 0.020 ft over the entire reach for all measured flows. About in the middle of the reach, the 

walking trail crosses the brook over a double-arched stone bridge that was also surveyed and included in the HEC-RAS model 

but does not appear to alter low to moderate flows. 

All cross sections were used in the R2Cross analysis, but the flow standard was determined from the three upstream stations 

(222, 225, and 230) that are unaffected by backwater during low to moderate flows. For the same reason, the three upstream 

cross sections were used for the Wetted-Perimeter analysis.

Table 2–4. Simulated water-surface elevations made with the HEC-RAS model calibrated to observed water-surface elevations at 

multiple cross sections over a range of discharges at Indian Brook near Hopkinton, Massachusetts.—Continued

[Elevation is an arbitrary datum; ft, foot; ft/ft, foot per foot; ft2, square foot; ft3/s, cubic foot per second; --, not determined]

Station Flow 

(ft3

/s)

Manning’s 

coefficient

Flow area 

(ft2)

Hydraulic 

radius 

(ft)

Slope 

(ft/ft)

Froude 

number

Water-surface elevation

Observed 

(ft)

Simulated 

(ft)

125 0.3 0.031 0.5 0.10 0.004 0.36 495.04 495.04

125 0.8 0.068 2.0 0.15 0.004 0.18 495.23 495.22

125 0.8 0.070 2.1 0.16 0.004 0.17 495.23 495.23

125 0.9 0.075 2.3 0.17 0.004 0.16 495.36 495.25

125 1.2 0.095 3.3 0.23 0.004 0.13 495.32 495.32

125 1.4 0.124 4.2 0.28 0.004 0.11 495.39 495.39

125 2.7 0.135 7.0 0.40 0.004 0.10 495.57 495.57

125 5.2 0.140 11 0.60 0.004 0.10 495.80 495.80

125 7.7 0.135 14 0.73 0.004 0.11 495.96 495.96

125 29 0.092 24 1.2 0.004 0.18 496.57 496.57

125 41 0.072 26 1.3 0.004 0.23 496.65 496.68

163 0.3 0.497 4.4 0.41 0.002 0.02 495.16 495.16

163 0.8 0.303 5.8 0.52 0.002 0.03 495.32 495.32

163 0.8 0.288 5.8 0.52 0.002 0.03 495.33 495.32

163 0.9 0.213 5.9 0.52 0.001 0.03 495.34 495.33

163 1.2 0.074 6.0 0.53 0.000 0.04 495.34 495.34

163 1.4 0.178 7.1 0.60 0.001 0.04 495.46 495.46

163 2.7 0.062 8.4 0.68 0.000 0.06 495.60 495.60

163 5.2 0.055 11 0.80 0.000 0.08 495.84 495.84

163 7.7 0.020 12 0.86 0.000 0.10 495.97 495.97

163 29 0.034 19 1.1 0.001 0.21 496.63 496.63

163 41 0.036 21 1.2 0.002 0.27 496.70 496.76

182 0.3 0.200 14 0.68 0.000 0.01 495.17 495.16

182 0.8 0.200 17 0.81 0.000 0.01 495.33 495.32

182 0.8 0.200 17 0.82 0.000 0.01 495.34 495.32

182 0.9 0.200 17 0.82 0.000 0.01 495.36 495.33

182 1.2 0.200 17 0.84 0.000 0.01 495.37 495.35

182 1.4 0.037 20 0.93 0.000 0.01 495.46 495.46

182 2.7 0.168 22 1.1 0.000 0.02 495.64 495.60
Appendix 2

Appendix 2: Water-Surface-Profile Model 133

Table 2–4. Simulated water-surface elevations made with the HEC-RAS model calibrated to observed water-surface elevations at 

multiple cross sections over a range of discharges at Indian Brook near Hopkinton, Massachusetts.—Continued

[Elevation is an arbitrary datum; ft, foot; ft/ft, foot per foot; ft2, square foot; ft3/s, cubic foot per second; --, not determined]

Station Flow 

(ft3

/s)

Manning’s 

coefficient

Flow area 

(ft2)

Hydraulic 

radius 

(ft)

Slope 

(ft/ft)

Froude 

number

Water-surface elevation

Observed 

(ft)

Simulated 

(ft)

182 5.2 0.108 27 1.3 0.000 0.03 495.86 495.84

182 7.7 0.100 30 1.4 0.000 0.04 496.01 495.98

182 29 0.044 43 1.9 0.000 0.08 496.64 496.67

182 41 0.182 47 2.0 0.005 0.10 496.86 496.84

208 0.3 0.200 9.3 0.55 0.000 0.01 495.17 495.16

208 0.8 0.200 12 0.67 0.000 0.01 495.33 495.32

208 0.8 0.200 12 0.67 0.000 0.01 495.34 495.32

208 0.9 0.200 12 0.68 0.000 0.02 495.37 495.33

208 1.2 0.200 12 0.69 0.000 0.02 495.37 495.35

208 1.4 0.038 14 0.79 0.000 0.02 495.46 495.46

208 2.7 0.185 17 0.90 0.000 0.03 495.62 495.61

208 5.2 0.200 22 1.1 0.001 0.04 495.86 495.84

208 7.7 0.200 24 1.2 0.002 0.05 496.01 495.98

208 29 0.047 38 1.6 0.000 0.10 496.64 496.67

208 41 0.194 42 1.7 0.007 0.12 496.86 496.85

222 0.3 0.050 2.0 0.15 0.000 0.08 495.09 495.16

222 0.8 0.050 4.1 0.28 0.000 0.06 495.33 495.32

222 0.8 0.050 4.2 0.29 0.000 0.06 495.35 495.32

222 0.9 0.050 4.3 0.29 0.000 0.07 495.36 495.33

222 1.2 0.050 4.5 0.31 0.000 0.08 495.37 495.35

222 1.4 0.035 6.2 0.39 0.000 0.06 495.46 495.46

222 2.7 0.048 8.6 0.52 0.000 0.08 495.63 495.61

222 5.2 0.050 13 0.72 0.000 0.08 495.88 495.85

222 7.7 0.050 15 0.82 0.000 0.10 496.03 495.99

222 29 0.022 27 1.3 0.000 0.15 496.64 496.67

222 41 0.035 31 1.4 0.001 0.18 496.86 496.86

225 0.3 0.350 0.9 0.15 0.104 0.17 495.36 495.36

225 0.8 0.350 1.4 0.15 0.200 0.24 495.44 495.42

225 0.8 0.350 1.5 0.16 0.201 0.25 495.44 495.43

225 0.9 0.350 1.6 0.16 0.203 0.25 495.48 495.44

225 1.2 0.350 1.9 0.18 0.208 0.26 495.50 495.47

225 1.4 0.350 2.3 0.20 0.173 0.24 495.54 495.50

225 2.7 0.350 4.1 0.29 0.119 0.21 495.69 495.64

225 5.2 0.350 7.6 0.49 0.068 0.17 495.94 495.88

225 7.7 0.350 9.7 0.61 0.068 0.18 496.04 496.02

225 29 0.026 21 1.1 0.001 0.22 496.66 496.68

225 41 0.100 24 1.3 0.009 0.25 496.88 496.88
Appendix 2

134 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Table 2–4. Simulated water-surface elevations made with the HEC-RAS model calibrated to observed water-surface elevations at 

multiple cross sections over a range of discharges at Indian Brook near Hopkinton, Massachusetts.—Continued

[Elevation is an arbitrary datum; ft, foot; ft/ft, foot per foot; ft2, square foot; ft3/s, cubic foot per second; --, not determined]

Station Flow 

(ft3

/s)

Manning’s 

coefficient

Flow area 

(ft2)

Hydraulic 

radius 

(ft)

Slope 

(ft/ft)

Froude 

number

Water-surface elevation

Observed 

(ft)

Simulated 

(ft)

230 0.3 0.110 1.6 0.18 0.003 0.09 -- 495.39

230 0.8 0.110 2.4 0.24 0.004 0.12 -- 495.48

230 0.8 0.108 2.5 0.24 0.004 0.12 495.48 495.48

230 0.9 0.099 2.5 0.25 0.004 0.13 495.52 495.49

230 1.2 0.071 2.7 0.26 0.003 0.15 495.51 495.51

230 1.4 0.109 3.4 0.26 0.005 0.14 495.57 495.57

230 2.7 0.111 5.2 0.37 0.005 0.15 495.70 495.70

230 5.2 0.160 8.7 0.59 0.008 0.14 495.95 495.95

230 7.7 0.090 10 0.68 0.004 0.16 496.05 496.05

230 29 0.053 19 1.1 0.002 0.23 -- 496.68

230 41 0.040 23 1.2 0.002 0.26 496.89 496.89
Appendix 2

Appendix 2: Water-Surface-Profile Model 135

Indian Brook near Ashland

Five cross sections (123, 157, 181, 196, and 214) and water levels over six flows ranging from 1.1 to 6.6 ft3/s were used to 

calibrate the HEC-RAS model in this reach (table 2–5). A slope of 0.003 ft/ft was specified as the downstream boundary condition. The RMSE was 0.029 ft over the entire reach for all measured flows. 

All cross sections were used in the R2Cross analysis, but the flow standard was determined from the four upstream sections 

(157, 181, 196, and 214) that are unaffected by backwater during low to moderate flows. For the same reason, the four upstream 

cross sections were used for the Wetted-Perimeter analysis.

Table 2–5. Simulated water-surface elevations made with the HEC-RAS model calibrated to observed water-surface elevations at 

multiple cross sections over a range of discharges at Indian Brook near Ashland, Massachusetts.

[Elevation is an arbitrary datum; ft, foot; ft/ft, foot per foot; ft2, square foot; ft3/s, cubic foot per second; --, not determined]

Station Flow

(ft3

/s)

Manning’s 

coefficient

Flow area

(ft2)

Hydraulic 

radius

(ft)

Slope

(ft/ft)

Froude 

number

Water-surface elevation

Observed 

(ft)

Simulated 

(ft)

123 1.1 0.169 5.1 0.35 0.003 0.07 498.03 498.03

123 1.2 0.161 5.3 0.36 0.003 0.07 498.22 498.04

123 2.0 0.125 6.1 0.41 0.003 0.09 498.23 498.10

123 2.4 0.112 6.4 0.43 0.003 0.10 498.12 498.12

123 2.9 0.105 6.9 0.46 0.003 0.11 498.15 498.15

123 6.6 0.073 9.3 0.58 0.003 0.16 498.32 498.32

157 1.1 0.100 3.4 0.28 0.003 0.11 498.12 498.12

157 1.2 0.095 3.5 0.28 0.003 0.12 498.25 498.13

157 2.0 0.070 4.2 0.33 0.002 0.15 498.23 498.18

157 2.4 0.060 4.4 0.34 0.002 0.16 498.20 498.20

157 2.9 0.041 4.6 0.35 0.001 0.19 498.21 498.22

157 6.6 0.058 7.3 0.50 0.003 0.22 498.41 498.41

181 1.1 0.020 2.8 0.23 0.000 0.15 498.14 498.14

181 1.2 0.029 3.0 0.24 0.000 0.15 498.25 498.15

181 2.0 0.088 4.2 0.32 0.004 0.15 498.25 498.25

181 2.4 0.111 4.6 0.35 0.006 0.16 498.23 498.28

181 2.9 0.128 5.0 0.37 0.010 0.17 498.30 498.30

181 6.6 0.030 7.1 0.51 0.001 0.23 498.46 498.46

196 1.1 0.150 2.8 0.25 0.011 0.14 498.26 498.26

196 1.2 0.149 2.9 0.26 0.011 0.15 498.36 498.27

196 2.0 0.140 3.7 0.29 0.013 0.18 498.34 498.34

196 2.4 0.076 3.9 0.30 0.005 0.20 498.35 498.35

196 2.9 0.045 4.2 0.33 0.002 0.21 498.36 498.38

196 6.6 0.045 6.0 0.45 0.003 0.29 498.52 498.52

214 1.1 0.040 2.3 0.18 0.002 0.21 498.49 498.40

214 1.2 0.040 2.4 0.19 0.002 0.21 498.52 498.41

214 2.0 0.040 3.2 0.25 0.002 0.22 498.48 498.47

214 2.4 0.040 3.4 0.26 0.002 0.24 498.51 498.49

214 2.9 0.040 3.6 0.27 0.003 0.27 498.57 498.50

214 6.6 0.040 4.7 0.35 0.006 0.42 498.58 498.59
Appendix 2

136 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Baiting Brook near Framingham

Nine cross sections (stations 116, 135, 156, 180, 198, 218, 245, 265, and 285) and water levels over 11 flows ranging from 

0.4 to 9.6 ft3/s were used to calibrate the HEC-RAS model in this reach (table 2–6). A slope of 0.017 ft/ft was specified as the 

downstream boundary condition. The RMSE was 0.020 ft over the entire reach for all measured flows. 

All cross sections were used in the R2Cross analysis, but the flow standard was determined from the five upstream stations 

(198, 218, 245, 265, and 285) that are unaffected by backwater during low to moderate flows. For the same reason, the five 

upstream cross sections were used for the Wetted-Perimeter analysis.

Table 2–6. Simulated water-surface elevations made with the HEC-RAS model calibrated to observed water-surface elevations at 

multiple cross sections over a range of discharges at Baiting Brook near Framingham, Massachusetts.—Continued

[Elevation is an arbitrary datum; ft, foot; ft/ft, foot per foot; ft2, square foot; ft3/s, cubic foot per second; --, not determined]

Station Discharge

(ft3

/s)

Manning’s 

coefficient

Flow area

(ft2)

Hydraulic 

radius

(ft)

Slope

(ft/ft)

Froude 

number

Water-surface elevation

Observed 

(ft)

Simulated 

(ft)

116 0.4 0.070 0.8 0.07 0.017 0.31 496.91 496.91

116 0.7 0.093 1.5 0.12 0.017 0.25 496.96 496.96

116 1.0 0.093 1.8 0.14 0.017 0.26 496.99 496.99

116 1.2 0.128 2.4 0.18 0.017 0.20 497.03 497.03

116 1.5 0.110 2.5 0.19 0.017 0.23 497.04 497.04

116 3.5 0.083 3.6 0.26 0.017 0.33 497.24 497.12

116 5.0 0.071 4.1 0.30 0.017 0.39 497.16 497.16

116 6.3 0.100 6.0 0.41 0.017 0.29 497.77 497.29

116 7.4 0.100 6.6 0.45 0.017 0.29 497.56 497.33

116 8.6 0.100 7.2 0.49 0.017 0.30 497.88 497.38

116 9.6 0.100 7.8 0.52 0.017 0.30 497.41 497.41

135 0.4 0.100 1.1 0.08 0.015 0.21 497.21 497.21

135 0.7 0.082 1.5 0.10 0.013 0.25 497.24 497.24

135 1.0 0.065 1.8 0.12 0.011 0.30 497.25 497.25

135 1.2 0.072 2.1 0.14 0.011 0.27 497.30 497.27

135 1.5 0.080 2.5 0.16 0.011 0.26 497.29 497.30

135 3.5 0.053 3.3 0.22 0.010 0.39 497.47 497.36

135 5.0 0.042 3.7 0.24 0.009 0.48 497.38 497.38

135 6.3 0.037 4.7 0.30 0.006 0.43 497.70 497.45

135 7.4 0.034 5.1 0.33 0.005 0.44 497.57 497.48

135 8.6 0.032 5.6 0.35 0.004 0.45 497.90 497.50

135 9.6 0.030 6.0 0.38 0.004 0.46 497.53 497.53

156 0.4 0.100 1.4 0.11 0.006 0.14 497.40 497.39

156 0.7 0.100 2.0 0.15 0.007 0.16 497.44 497.44

156 1.0 0.105 2.4 0.17 0.010 0.18 497.53 497.47

156 1.2 0.112 2.6 0.19 0.010 0.18 497.48 497.48

156 1.5 0.130 3.3 0.24 0.011 0.16 497.53 497.53

156 3.5 0.103 4.4 0.31 0.014 0.25 497.68 497.61

156 5.0 0.095 5.0 0.35 0.017 0.30 497.65 497.65
Appendix 2

Appendix 2: Water-Surface-Profile Model 137

Table 2–6. Simulated water-surface elevations made with the HEC-RAS model calibrated to observed water-surface elevations at 

multiple cross sections over a range of discharges at Baiting Brook near Framingham, Massachusetts.—Continued

[Elevation is an arbitrary datum; ft, foot; ft/ft, foot per foot; ft2, square foot; ft3/s, cubic foot per second; --, not determined]

Station Discharge

(ft3

/s)

Manning’s 

coefficient

Flow area

(ft2)

Hydraulic 

radius

(ft)

Slope

(ft/ft)

Froude 

number

Water-surface elevation

Observed 

(ft)

Simulated 

(ft)

156 6.3 0.175 5.8 0.40 0.054 0.30 497.82 497.71

156 7.4 0.227 6.4 0.44 0.094 0.30 497.81 497.75

156 8.6 0.263 6.8 0.46 0.142 0.33 497.93 497.78

156 9.6 0.273 6.9 0.47 0.184 0.36 497.79 497.79

180 0.4 0.035 1.6 0.22 0.000 0.09 497.41 497.41

180 0.7 0.020 1.9 0.24 0.000 0.13 497.45 497.45

180 1.0 0.010 2.0 0.26 0.000 0.17 497.53 497.47

180 1.2 0.008 2.1 0.27 0.000 0.18 497.48 497.49

180 1.5 0.008 2.5 0.30 0.000 0.19 497.53 497.53

180 3.5 0.006 3.1 0.34 0.000 0.32 497.68 497.61

180 5.0 0.005 3.4 0.37 0.000 0.41 497.65 497.65

180 6.3 0.005 3.9 0.40 0.000 0.43 497.82 497.71

180 7.4 0.006 4.3 0.39 0.000 0.46 497.81 497.75

180 8.6 0.006 4.7 0.35 0.000 0.53 497.93 497.78

180 9.6 0.006 4.8 0.35 0.000 0.59 497.79 497.79

198 0.4 0.220 1.5 0.10 0.033 0.15 497.85 497.77

198 0.7 0.220 2.5 0.13 0.026 0.14 497.83 497.83

198 1.0 0.247 3.5 0.18 0.023 0.12 497.88 497.88

198 1.2 0.232 3.7 0.19 0.023 0.13 497.91 497.89

198 1.5 0.206 3.9 0.20 0.025 0.15 497.90 497.90

198 3.5 0.102 4.9 0.25 0.015 0.25 498.02 497.95

198 5.0 0.070 5.3 0.27 0.011 0.32 497.97 497.97

198 6.3 0.068 6.1 0.30 0.011 0.33 498.03 498.01

198 7.4 0.067 6.8 0.34 0.010 0.33 498.05 498.05

198 8.6 0.066 7.4 0.36 0.010 0.34 498.10 498.08

198 9.6 0.065 7.8 0.38 0.011 0.35 498.10 498.10

218 0.4 0.200 2.6 0.20 0.003 0.06 497.91 497.91

218 0.7 0.100 2.9 0.22 0.002 0.09 497.93 497.93

218 1.0 0.109 3.8 0.26 0.002 0.09 497.99 497.99

218 1.2 0.106 3.9 0.26 0.003 0.10 498.03 498.00

218 1.5 0.099 4.2 0.28 0.003 0.12 498.02 498.02

218 3.5 0.070 5.3 0.34 0.004 0.20 498.17 498.09

218 5.0 0.062 5.6 0.36 0.005 0.26 498.12 498.12

218 6.3 0.051 6.0 0.38 0.005 0.30 498.14 498.14

218 7.4 0.042 6.2 0.39 0.004 0.33 498.19 498.16

218 8.6 0.036 6.4 0.40 0.004 0.37 498.20 498.17

218 9.6 0.030 6.6 0.41 0.003 0.39 498.18 498.18
Appendix 2

138 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Table 2–6. Simulated water-surface elevations made with the HEC-RAS model calibrated to observed water-surface elevations at 

multiple cross sections over a range of discharges at Baiting Brook near Framingham, Massachusetts.—Continued

[Elevation is an arbitrary datum; ft, foot; ft/ft, foot per foot; ft2, square foot; ft3/s, cubic foot per second; --, not determined]

Station Discharge

(ft3

/s)

Manning’s 

coefficient

Flow area

(ft2)

Hydraulic 

radius

(ft)

Slope

(ft/ft)

Froude 

number

Water-surface elevation

Observed 

(ft)

Simulated 

(ft)

245 0.4 1.000 0.6 0.12 2.583 0.30 498.16 497.98

245 0.7 1.000 1.2 0.16 1.838 0.26 498.47 498.08

245 1.0 1.000 1.5 0.18 2.169 0.29 498.22 498.11

245 1.2 1.000 1.7 0.19 2.022 0.28 498.29 498.13

245 1.5 1.000 2.0 0.20 2.080 0.29 498.29 498.18

245 3.5 0.367 4.1 0.25 0.279 0.30 498.32 498.32

245 5.0 0.152 4.4 0.27 0.080 0.39 498.34 498.34

245 6.3 0.102 4.8 0.29 0.042 0.43 498.37 498.37

245 7.4 0.110 5.5 0.32 0.046 0.42 498.36 498.41

245 8.6 0.120 6.2 0.35 0.051 0.41 498.45 498.45

245 9.6 0.120 6.7 0.37 0.051 0.41 498.48 498.48

265 0.4 0.200 2.4 0.17 0.005 0.07 498.35 498.35

265 0.7 0.191 3.5 0.22 0.005 0.07 498.44 498.43

265 1.0 0.163 4.5 0.23 0.005 0.08 498.47 498.45

265 1.2 0.146 4.6 0.23 0.004 0.09 498.52 498.46

265 1.5 0.117 4.8 0.24 0.004 0.11 498.47 498.47

265 3.5 0.065 6.1 0.30 0.003 0.18 498.58 498.53

265 5.0 0.054 6.5 0.32 0.004 0.24 498.55 498.55

265 6.3 0.069 7.8 0.38 0.005 0.23 498.62 498.62

265 7.4 0.058 8.1 0.39 0.004 0.25 498.70 498.63

265 8.6 0.048 8.3 0.40 0.004 0.28 498.62 498.64

265 9.6 0.040 8.5 0.41 0.003 0.31 498.65 498.65

285 0.4 0.100 1.2 0.18 0.004 0.13 498.45 498.45

285 0.7 0.050 1.6 0.20 0.002 0.18 498.49 498.49

285 1.0 0.061 1.9 0.20 0.004 0.21 498.57 498.53

285 1.2 0.064 2.0 0.21 0.005 0.22 498.62 498.54

285 1.5 0.069 2.2 0.22 0.007 0.25 498.57 498.56

285 3.5 0.070 3.1 0.26 0.017 0.39 -- 498.64

285 5.0 0.070 3.6 0.29 0.023 0.46 498.77 498.68

285 6.3 0.070 4.7 0.34 0.017 0.40 498.77 498.77

285 7.4 0.070 4.8 0.34 0.022 0.46 498.80 498.78

285 8.6 0.070 4.9 0.34 0.029 0.53 498.82 498.78

285 9.6 0.070 4.7 0.34 0.040 0.62 498.87 498.77
Appendix 3

Indicators of Hydrologic Alterations (IHA) Computed from Long-Term (1960–2004) Daily 

Streamflows Simulated with the Hydrologic Simulation Program–FORTRAN (HSPF) without 

Withdrawals (NOWU) at 10 Riffle Reaches in the Sudbury and Assabet River Basins

Indicators of Hydrologic Alteration (IHA) Statistics .....................................................................140

References Cited...........................................................................................................................140

Table 3–1. Hydrologic statistics computed by Indicators of Hydrologic Alteration (IHA).........141

Table 3–2. Indicators of Hydrologic Alteration (IHA) statistics determined from simulated 

long-term (1960–2004) daily flows with the Hydrologic Simulation Program–FORTRAN 

(HSPF) without withdrawals (NOWU) at Whitehall Brook near Hopkinton, 

Massachusetts.........................................................................................................................142

Table 3–3. Indicators of Hydrologic Alteration (IHA) statistics determined from simulated 

long-term (1960–2004) daily flows with the Hydrologic Simulation Program–FORTRAN 

(HSPF) without withdrawals (NOWU) at Sudbury River near Hopkinton, Massachusetts......143

Table 3–4. Indicators of Hydrologic Alteration (IHA) statistics determined from simulated 

long-term (1960–2004) daily flows with the Hydrologic Simulation Program–FORTRAN 

(HSPF) without withdrawals (NOWU) at Sudbury River near Ashland, Massachusetts.........144

Table 3–5. Indicators of Hydrologic Alteration (IHA) statistics determined from simulated 

long-term (1960–2004) daily flows with the Hydrologic Simulation Program–FORTRAN 

(HSPF) without withdrawals (NOWU) at Indian Brook near Hopkinton, Massachusetts........145

Table 3–6. Indicators of Hydrologic Alteration (IHA) statistics determined from simulated 

long-term (1960–2004) daily flows with the Hydrologic Simulation Program–FORTRAN 

(HSPF) without withdrawals (NOWU) at Indian Brook near Ashland, Massachusetts...........146

Table 3–7. Indicators of Hydrologic Alteration (IHA) statistics determined from simulated 

long-term (1960–2004) daily flows with the Hydrologic Simulation Program–FORTRAN 

(HSPF) without withdrawals (NOWU) at Baiting Brook near Framingham, Massachusetts...147

Table 3–8. Indicators of Hydrologic Alteration (IHA) statistics determined from simulated 

long-term (1960–2004) daily flows with the Hydrologic Simulation Program–FORTRAN 

(HSPF) without withdrawals (NOWU) at Assabet River near Westborough, 

Massachusetts.........................................................................................................................148

Table 3–9. Indicators of Hydrologic Alteration (IHA) statistics determined from simulated 

long-term (1960–2004) daily flows with the Hydrologic Simulation Program–FORTRAN 

(HSPF) without withdrawals (NOWU) at Danforth Brook near Hudson, Massachusetts........149

Table 3–10. Indicators of Hydrologic Alteration (IHA) statistics determined from simulated 

long-term (1960–2004) daily flows with the Hydrologic Simulation Program–FORTRAN 

(HSPF) without withdrawals (NOWU) at Fort Meadow Brook near Hudson, 

Massachusetts.........................................................................................................................150

Table 3–11. Indicators of Hydrologic Alteration (IHA) statistics determined from simulated 

long-term (1960–2004) daily flows with the Hydrologic Simulation Program–FORTRAN 

(HSPF) without withdrawals (NOWU) at Elizabeth Brook near Stow, Massachusetts. ..........151
Appendix 3

140 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Appendix 3. Indicators of Hydrologic Alterations (IHA)

Computed from Long-Term (1960–2004) Daily Streamflows 

Simulated with the Hydrologic Simulation Program–FORTRAN 

(HSPF) without Withdrawals (NOWU) at 10 Riffle Reaches in the 

Sudbury and Assabet River Basins

Indicators of Hydrologic Alteration (IHA) Statistics

The tables in this appendix are output from the Indicators of Hydrologic Alteration (IHA) software, version 7.0.3 (The 

Nature Conservancy, 2009). The IHA program calculates the median of annual or monthly values (considered a nonparametric 

analysis by IHA). A low-flow pulse was defined by a flow less than or equal to the 25th percentile of all flows, and a high-flow 

pulse was defined by a flow greater than or equal to the 75th percentile of all flows. The input to the IHA program is the longterm (1960–2004) daily mean flow simulated with no water use (NOWU) by the Hydrologic Simulation Program—FORTRAN 

(HSPF) model developed for the Sudbury and Assabet River Basins. The model outputs flows at or near the 10 riffle sites. All 

metrics were computed using the water year (October 1 through September 30) except for the Group 2 minimum 1-, 3-, 7- , 30-, 

and 90-day low flows, which used the climate year (April 1 through March 31). The climate year was used for the low-flow 

metric because the extended periods of low flow commonly cross over the water year.

The IHA method was developed by The Nature Conservancy to characterize the variation in flow by a suite of 33 hydrologic statistics (Richter and others, 1996). The 33 IHA statistics are divided into five general groups (table 3–1). Group 1 

represents the monthly flow variation. Group 2 reflects the magnitude of low and high flows for varying time spans. Group 3 

measures when the annual low and high flows typically occur. Group 4 measures the frequency and duration that flows were 

below the 25th and above the 75th flow percentiles. Group 5 measures the rate of change in flow. About half the indices measure 

the central tendency of the magnitude or rate of change of flow and the other half focus on the magnitude, duration, timing, and 

frequency of extreme events.

References Cited

Richter, B.D., Baumgartner, J.V., Powell, Jennifer, and Braun, D.P., 1996, A method for assessing hydrologic alteration within 

ecosystems: Conservation Biology, v. 10, p. 1163–1174.

The Nature Conservancy, 2009, Indicators of Hydrologic Alteration, Version 7.1 Users Manual: The Nature Conservancy with 

rPurview LLC, Totter Software Design, and Smythe Scientific Software, 76 p. (available online at http://www.nature.org/

initiatives/freshwater/conservationtools/art17004.html)
Appendix 3

Appendix 3: Indicators of Hydrologic Alteration (IHA) Statistics 141

Table 3–1. Hydrologic statistics computed by Indicators of Hydrologic Alteration (IHA).

[ft3/s, cubic feet per second; ≤, less than or equal to; ≥, greater than or equal to]

Metric Definition

Group 1–Percentiles of monthly median flow

October (ft3

/s)

November (ft3

/s)

December (ft3

/s)

January (ft3

/s)

February (ft3

/s)

March (ft3

/s) Annual monthly median flow

April (ft3

/s)

May (ft3

/s)

June (ft3

/s)

July (ft3

/s)

August (ft3

/s)

September (ft3

/s)

Group 2–Percentiles of the n-day annual low and high flow

1-day minimum (ft3

/s) Annual 1-day minimum daily flow 

3-day minimum (ft3

/s) Annual mean 3-day minimum continuous daily flow

7-day minimum (ft3

/s) Annual mean 7-day minimum continuous daily flow

30-day minimum (ft3

/s) Annual mean 30-day minimum continuous daily flow

90-day minimum (ft3

/s) Annual mean 90-day minimum continuous daily flow

1-day maximum (ft3

/s) Annual 1-day maximum daily discharge

3-day maximum (ft3

/s) Annual mean 3-day maximum continuous daily flow

7-day maximum (ft3

/s) Annual mean 3-day maximum continuous daily flow

30-day maximum (ft3

/s) Annual mean 3-day maximum continuous daily flow

90-day maximum (ft3

/s) Annual mean 3-day maximum continuous daily flow

Number of zero days Annual number of days with no flow 

Baseflow index (ft3

/s) Annual 7-day minimum flow divided by mean annual flow 

Group 3–Percentiles of the timing of annual minimum and maximum flow

Date of minimum (Julian date) Julian date of annual daily maximum flow

Date of maximum (Julian date) Julian date of annual daily minimum flow

Group 4–Percentiles of the frequency and duration of low and high flows

Low-pulse count Number of low-flow pulses each year (continuous period of flow ≤ 25th percentile)

Low-pulse duration (days) Median annual duration of low-flow pulses

High-pulse count Number of high-flow pulses each year(continuous period of flow ≥ 75th percentile)

High-pulse duration (days) Median annual duration of high-flow pulses

Group 5–Percentiles of the rate of change in flow

Rise rate Annual median of all positive differences between consecutive daily mean flows

Fall rate Annual median of all negative differences between consecutive daily mean flows

Number of reversals Number of times in which flow switched from a rising period to a falling period or from a 

falling period to a rising period
Appendix 3

142 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Table 3–2. Indicators of Hydrologic Alteration (IHA) statistics determined from simulated long-term (1960–2004) daily flows with the 

Hydrologic Simulation Program–FORTRAN (HSPF) without withdrawals (NOWU) at Whitehall Brook near Hopkinton, Massachusetts.

[ft3/s, cubic foot per second; ~, not applicable; metrics calculated for water years (October 1 through September 31), except for Group 2 minimum flows, which 

used climate years (April 1 through March 31)]

Metric

Percentile

10 25 50 75 90 (75-25)/50

Group 1

October (ft3

/s) 0.70 1.5 3.8 7.3 13 1.5

November (ft3

/s) 3.2 6.2 9.1 13 18 0.71

December (ft3

/s) 6.8 8.2 11 16 23 0.68

January (ft3

/s) 5.7 7.8 13 17 25 0.72

February (ft3

/s) 8.1 11 14 17 25 0.49

March (ft3

/s) 11 13 18 23 30 0.53

April (ft3

/s) 7.9 11 16 20 23 0.56

May (ft3

/s) 3.6 6.6 9.6 12 18 0.61

June (ft3

/s) 2.0 2.4 3.8 7.5 15 1.3

July (ft3

/s) 1.2 1.5 1.9 2.7 4.3 0.61

August (ft3

/s) 0.85 1.1 1.6 2.0 2.6 0.56

September (ft3

/s) 0.70 0.96 1.4 2.0 3.7 0.74

Group 2

1-day minimum (ft3

/s) 0.35 0.52 0.85 1.2 1.3 0.79

3-day minimum (ft3

/s) 0.35 0.55 0.88 1.2 1.4 0.74

7-day minimum (ft3

/s) 0.36 0.62 0.91 1.2 1.5 0.68

30-day minimum (ft3

/s) 0.55 0.88 1.3 1.6 2.1 0.55

90-day minimum (ft3

/s) 0.83 1.4 2.1 3.6 5.2 1.0

1-day maximum (ft3

/s) 70 79 110 150 190 0.65

3-day maximum (ft3

/s) 53 62 85 100 150 0.50

7-day maximum (ft3

/s) 36 45 55 72 99 0.50

30-day maximum (ft3

/s) 23 27 32 40 48 0.41

90-day maximum (ft3

/s) 17 20 23 28 32 0.38

Number of zero days 0 0 0 0 0 0

Baseflow index (ft3

/s) 0.04 0.05 0.07 0.09 0.10 0.47

Group 3

Date of minimum (Julian date) 240 260 270 280 300 ~

Date of maximum (Julian date) 340 24 64 110 170 ~

Group 4

Low-pulse count 4.0 6.0 8.0 10 14 0.50

Low-pulse duration (days) 3.2 5 6.2 11 15 0.96

High-pulse count 12 14 18 20 22 0.32

High-pulse duration (days) 2.0 2.0 3.0 4.0 5.0 0.67

Group 5

Rise rate 1.5 2.2 2.5 3.1 4.2 0.35

Fall rate -1.9 -1.7 -1.4 -1.1 -0.90 -0.44

Number of reversals 100 100 110 120 120 0.11
Appendix 3

Appendix 3: Indicators of Hydrologic Alteration (IHA) Statistics 143

Table 3–3. Indicators of Hydrologic Alteration (IHA) statistics determined from simulated long-term (1960–2004) daily flows with the 

Hydrologic Simulation Program–FORTRAN (HSPF) without withdrawals (NOWU) at Sudbury River near Hopkinton, Massachusetts.

[ft3/s, cubic foot per second; ~, not applicable; metrics calculated for water years (October 1 through September 31), except for Group 2 minimum flows, which 

used climate years (April 1 through March 31)]

Metric

Percentile

10 25 50 75 90 (75-25)/50

Group 1

October (ft3

/s) 4.2 7.4 15 27 56 1.3

November (ft3

/s) 8.9 20 29 45 63 0.88

December (ft3

/s) 22 25 40 59 87 0.84

January (ft3

/s) 19 25 42 57 83 0.77

February (ft3

/s) 24 36 46 59 71 0.51

March (ft3

/s) 32 40 60 73 90 0.55

April (ft3

/s) 23 32 52 63 78 0.61

May (ft3

/s) 12 19 30 43 60 0.79

June (ft3

/s) 5.3 6.4 13 25 56 1.4

July (ft3

/s) 2.8 3.8 4.8 8.2 18 0.92

August (ft3

/s) 2.4 2.8 4.8 8.0 12 1.1

September (ft3

/s) 2.6 3.7 5.8 10 19 1.1

Group 2

1-day minimum (ft3

/s) 1.3 1.6 2.4 2.7 3.0 0.45

3-day minimum (ft3

/s) 1.4 1.6 2.4 2.8 3.1 0.46

7-day minimum (ft3

/s) 1.6 1.8 2.6 3.0 3.5 0.45

30-day minimum (ft3

/s) 2.1 2.8 3.7 5.2 7.4 0.64

90-day minimum (ft3

/s) 3.5 4.7 8.2 13 17 1.0

1-day maximum (ft3

/s) 130 150 210 280 350 0.61

3-day maximum (ft3

/s) 120 140 190 240 320 0.57

7-day maximum (ft3

/s) 98 120 150 200 250 0.51

30-day maximum (ft3

/s) 70 80 93 120 140 0.39

90-day maximum (ft3

/s) 50 57 65 80 93 0.35

Number of zero days 0 0 0 0 0 0

Baseflow index (ft3

/s) 0.05 0.05 0.06 0.08 0.09 0.40

Group 3

Date of minimum (Julian date) 200 220 240 250 270 ~

Date of maximum (Julian date) 340 24 74 120 200 ~

Group 4

Low-pulse count 4.0 5.0 7.0 9.0 12 0.57

Low-pulse duration (days) 2.8 5.0 7.0 17 22 1.7

High-pulse count 8.0 10 13 15 18 0.38

High-pulse duration (days) 2.5 3.0 4.8 5.9 7.8 0.61

Group 5

Rise rate 3.5 4.8 6.1 6.9 8.8 0.36

Fall rate -5.4 -4.1 -3.2 -2.2 -1.7 -0.62

Number of reversals 86 90 95 100 110 0.13
Appendix 3

144 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Table 3–4. Indicators of Hydrologic Alteration (IHA) statistics determined from simulated long-term (1960–2004) daily flows with the 

Hydrologic Simulation Program–FORTRAN (HSPF) without withdrawals (NOWU) at Sudbury River near Ashland, Massachusetts.

[ft3/s, cubic foot per second; ~, not applicable; metrics calculated for water years (October 1 through September 31), except for Group 2 minimum flows, 

which used climate years (April 1 through March 31)]

Metric

Percentile

10 25 50 75 90 (75-25)/50

Group 1

October (ft3

/s) 5.1 9.2 18 32 64 1.3

November (ft3

/s) 11 25 35 59 76 0.98

December (ft3

/s) 27 31 50 73 100 0.83

January (ft3

/s) 23 33 51 68 100 0.69

February (ft3

/s) 29 43 56 71 90 0.49

March (ft3

/s) 40 51 74 90 110 0.52

April (ft3

/s) 29 40 64 80 97 0.63

May (ft3

/s) 17 25 37 51 74 0.69

June (ft3

/s) 8.4 10 19 31 67 1.2

July (ft3

/s) 4.4 5.5 7.4 12 23 0.90

August (ft3

/s) 3.4 3.8 6.8 11 16 1.0

September (ft3

/s) 3.1 4.5 7.6 12 23 0.97

Group 2

1-day minimum (ft3

/s) 1.9 2.1 3.2 3.7 4.4 0.5

3-day minimum (ft3

/s) 2.0 2.2 3.4 3.8 4.4 0.49

7-day minimum (ft3

/s) 2.2 2.4 3.6 4.2 5.0 0.49

30-day minimum (ft3

/s) 2.7 3.7 5.2 7.1 8.8 0.65

90-day minimum (ft3

/s) 4.5 6.4 10 16 21 0.92

1-day maximum (ft3

/s) 160 180 260 350 440 0.63

3-day maximum (ft3

/s) 150 170 230 300 390 0.56

7-day maximum (ft3

/s) 120 150 190 240 320 0.46

30-day maximum (ft3

/s) 86 98 120 140 170 0.39

90-day maximum (ft3

/s) 62 71 82 100 120 0.36

Number of zero days 0 0 0 0 0 0

Baseflow index (ft3

/s) 0.05 0.06 0.07 0.09 0.10 0.40

Group 3

Date of minimum (Julian date) 220 230 250 260 280 ~

Date of maximum (Julian date) 340 24 74 120 200 ~

Group 4

Low-pulse count 3.0 4.2 7.0 8.8 11 0.64

Low-pulse duration (days) 3.0 5.0 7.8 17 26 1.5

High-pulse count 7.0 10 12 14 16 0.33

High-pulse duration (days) 3.0 3.6 5.0 6.9 8.5 0.65

Group 5

Rise rate 5.0 5.4 6.7 8.3 9.8 0.43

Fall rate -6.0 -4.6 -3.5 -2.5 -1.9 -0.61

Number of reversals 84 90 96 100 110 0.10
Appendix 3

Appendix 3: Indicators of Hydrologic Alteration (IHA) Statistics 145

Table 3–5. Indicators of Hydrologic Alteration (IHA) statistics determined from simulated long-term (1960–2004) daily flows with the 

Hydrologic Simulation Program–FORTRAN (HSPF) without withdrawals (NOWU) at Indian Brook near Hopkinton, Massachusetts.

[ft3/s, cubic foot per second; ~, not applicable; metrics calculated for water years (October 1 through September 31), except for Group 2 minimum flows, which 

used climate years (April 1 through March 31)]

Metric

Percentile

10 25 50 75 90 (75-25)/50

Group 1

October (ft3

/s) 0.75 1.3 2.0 4.3 8.4 1.5

November (ft3

/s) 1.8 3.7 5.7 7.8 12 0.73

December (ft3

/s) 4.2 5.1 7.8 11 16 0.71

January (ft3

/s) 3.8 5.0 8.6 12 17 0.84

February (ft3

/s) 5.0 6.5 9.0 11 17 0.56

March (ft3

/s) 7.0 8.6 12 16 20 0.62

April (ft3

/s) 4.4 6.8 9.6 13 15 0.60

May (ft3

/s) 1.8 3.4 5.0 7.7 10 0.87

June (ft3

/s) 1.1 1.3 1.9 4.6 9.2 1.7

July (ft3

/s) 0.45 0.6 0.95 1.3 2.1 0.71

August (ft3

/s) 0.2 0.42 0.85 1.2 1.3 0.91

September (ft3

/s) 0.3 0.56 0.92 1.3 1.9 0.80

Group 2

1-day minimum (ft3

/s) 0 0.10 0.25 0.48 0.7 1.5

3-day minimum (ft3

/s) 0.02 0.10 0.28 0.5 0.7 1.4

7-day minimum (ft3

/s) 0.04 0.11 0.32 0.56 0.76 1.4

30-day minimum (ft3

/s) 0.14 0.28 0.52 0.9 1.1 1.2

90-day minimum (ft3

/s) 0.37 0.62 1.2 2.6 3.7 1.6

1-day maximum (ft3

/s) 65 75 100 140 170 0.60

3-day maximum (ft3

/s) 45 52 68 89 110 0.54

7-day maximum (ft3

/s) 29 35 44 57 74 0.49

30-day maximum (ft3

/s) 18 21 24 30 36 0.40

90-day maximum (ft3

/s) 13 15 17 20 24 0.35

Number of zero days 0 0 0 0 4.5 0

Baseflow index (ft3

/s) 0.01 0.01 0.03 0.05 0.08 1.2

Group 3

Date of minimum (Julian date) 200 210 240 260 280 ~

Date of maximum (Julian date) 320 22 66 110 200 ~

Group 4

Low-pulse count 2.0 3.0 4.0 5.0 7.0 0.50

Low-pulse duration (days) 3.0 5.0 9.0 26 54 2.3

High-pulse count 18 20 23 28 30 0.35

High-pulse duration (days) 2.0 2.0 2.0 2.0 3.0 0

Group 5

Rise rate 1.9 2.2 2.8 3.9 5.2 0.60

Fall rate -1.6 -1.2 -1.0 -0.8 -0.6 -0.45

Number of reversals 94 100 110 120 130 0.15
Appendix 3

146 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Table 3–6. Indicators of Hydrologic Alteration (IHA) statistics determined from simulated long-term (1960–2004) daily flows with the 

Hydrologic Simulation Program–FORTRAN (HSPF) without withdrawals (NOWU) at Indian Brook near Ashland, Massachusetts.

[ft3/s, cubic foot per second; ~, not applicable; metrics calculated for water years (October 1 through September 31), except for Group 2 minimum flows, which 

used climate years (April 1 through March 31)]

Metric

Percentile

10 25 50 75 90 (75-25)/50

Group 1

October (ft3

/s) 1.8 1.9 4.0 7.4 13 1.4

November (ft3

/s) 1.9 4.7 8.1 13 18 1.1

December (ft3

/s) 6.7 8.2 13 17 23 0.70

January (ft3

/s) 6.6 8.0 13 18 25 0.72

February (ft3

/s) 7.7 12 14 18 24 0.42

March (ft3

/s) 11 14 18 23 30 0.56

April (ft3

/s) 7.8 11 16 19 23 0.51

May (ft3

/s) 4.6 7.0 9.0 13 18 0.65

June (ft3

/s) 2.8 3.5 5.3 7.6 15 0.77

July (ft3

/s) 2.0 2.0 2.0 3.5 6.0 0.72

August (ft3

/s) 1.9 1.9 2.0 2.6 3.8 0.35

September (ft3

/s) 1.8 1.9 2.0 2.8 4.6 0.48

Group 2

1-day minimum (ft3

/s) 1.8 1.9 1.9 2.0 2.0 0.05

3-day minimum (ft3

/s) 1.8 1.9 1.9 2.0 2.0 0.05

7-day minimum (ft3

/s) 1.8 1.9 1.9 2.0 2.0 0.05

30-day minimum (ft3

/s) 1.8 1.9 1.9 2.0 2.9 0.06

90-day minimum (ft3

/s) 1.8 1.9 2.1 3.6 5.2 0.83

1-day maximum (ft3

/s) 74 91 120 170 210 0.66

3-day maximum (ft3

/s) 57 65 88 120 150 0.64

7-day maximum (ft3

/s) 39 48 58 79 100 0.54

30-day maximum (ft3

/s) 25 29 34 43 51 0.42

90-day maximum (ft3

/s) 18 21 24 29 34 0.35

Number of zero days 0 0 0 0 0 0

Baseflow index (ft3

/s) 0.11 0.13 0.15 0.18 0.21 0.36

Group 3

Date of minimum (Julian date) 200 220 250 280 280 ~

Date of maximum (Julian date) 340 22 56 100 150 ~

Group 4

Low-pulse count 1.0 1.0 2.0 2.0 3.0 0.50

Low-pulse duration (days) 5.5 25 61 99 120 1.2

High-pulse count 8.0 10 15 17 19 0.47

High-pulse duration (days) 3.0 3.5 4.0 5.0 7.0 0.38

Group 5

Rise rate 1.2 1.8 2.7 3.7 4.6 0.72

Fall rate -1.8 -1.4 -0.88 -0.62 -0.48 -0.87

Number of reversals 57 63 72 85 90 0.31
Appendix 3

Appendix 3: Indicators of Hydrologic Alteration (IHA) Statistics 147

Table 3–7. Indicators of Hydrologic Alteration (IHA) statistics determined from simulated long-term (1960–2004) daily flows with the 

Hydrologic Simulation Program–FORTRAN (HSPF) without withdrawals (NOWU) at Baiting Brook near Framingham, Massachusetts.

[ft3/s, cubic foot per second; ~, not applicable; metrics calculated for water years (October 1 through September 31), except for Group 2 minimum flows, which 

used climate years (April 1 through March 31)]

Metric

Percentile

10 25 50 75 90 (75-25)/50

Group 1

October (ft3

/s) 0.80 1.2 2.4 3.9 7.2 1.1

November (ft3

/s) 1.6 3.0 4.2 6.8 9.2 0.89

December (ft3

/s) 3.4 3.9 5.6 8.0 12 0.73

January (ft3

/s) 3.2 4.1 6.2 8.2 12 0.66

February (ft3

/s) 4.2 5.3 7.3 9.3 13 0.55

March (ft3

/s) 6.0 7.0 9.6 12 15 0.55

April (ft3

/s) 4.6 6.2 8.6 11 12 0.52

May (ft3

/s) 3.4 4.8 5.9 7.6 10 0.47

June (ft3

/s) 2.5 3.1 4.1 5.9 9.1 0.69

July (ft3

/s) 1.2 1.6 2.2 3.4 4.6 0.81

August (ft3

/s) 0.75 1.0 1.6 2.2 3.0 0.73

September (ft3

/s) 0.60 0.92 1.5 2.0 2.9 0.69

Group 2

1-day minimum (ft3

/s) 0.30 0.52 0.8 1.1 1.4 0.72

3-day minimum (ft3

/s) 0.30 0.52 0.82 1.1 1.4 0.73

7-day minimum (ft3

/s) 0.35 0.59 0.87 1.2 1.5 0.71

30-day minimum (ft3

/s) 0.61 0.93 1.4 1.7 2.2 0.56

90-day minimum (ft3

/s) 0.97 1.4 2.0 2.7 3.7 0.68

1-day maximum (ft3

/s) 33 39 59 81 110 0.71

3-day maximum (ft3

/s) 26 31 44 53 74 0.50

7-day maximum (ft3

/s) 18 22 30 38 52 0.56

30-day maximum (ft3

/s) 12 14 17 21 24 0.42

90-day maximum (ft3

/s) 9.2 10 12 15 17 0.35

Number of zero days 0 0 0 0 0 0

Baseflow index (ft3

/s) 0.07 0.10 0.12 0.15 0.18 0.48

Group 3

Date of minimum (Julian date) 240 260 270 280 300 ~

Date of maximum (Julian date) 360 22 51 100 160 ~

Group 4

Low-pulse count 5.5 8.0 10 14 18 0.57

Low-pulse duration (days) 3.2 4.0 5.0 6.4 10 0.48

High-pulse count 10 12 15 18 21 0.38

High-pulse duration (days) 2.0 2.6 4.0 4.5 5.8 0.47

Group 5

Rise rate 1.1 1.2 1.4 1.6 2.2 0.28

Fall rate -0.75 -0.60 -0.50 -0.40 -0.30 -0.40

Number of reversals 95 100 110 110 120 0.11
Appendix 3

148 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Table 3–8. Indicators of Hydrologic Alteration (IHA) statistics determined from simulated long-term (1960–2004) daily flows with the 

Hydrologic Simulation Program–FORTRAN (HSPF) without withdrawals (NOWU) at Assabet River near Westborough, Massachusetts.

[ft3/s, cubic foot per second; ~, not applicable; metrics calculated for water years (October 1 through September 31), except for Group 2 minimum flows, which 

used climate years (April 1 through March 31)]

Metric

Percentile

10 25 50 75 90 (75-25)/50

Group 1

October (ft3

/s) 0.95 1.7 3.8 7.2 14 1.5

November (ft3

/s) 2.8 6.1 9.0 13 18 0.82

December (ft3

/s) 7.2 8.4 12 16 23 0.65

January (ft3

/s) 5.8 8.0 13 17 25 0.67

February (ft3

/s) 8.3 11 14 18 26 0.55

March (ft3

/s) 12 14 18 25 31 0.59

April (ft3

/s) 8.2 11 17 20 24 0.55

May (ft3

/s) 4.6 7.5 10 14 19 0.60

June (ft3

/s) 1.8 2.8 5.2 8.8 16 1.2

July (ft3

/s) 0.55 0.72 1.6 3.1 5.7 1.5

August (ft3

/s) 0 0.32 1.2 1.8 2.5 1.3

September (ft3

/s) 0.05 0.60 1.3 2.0 4.0 1.1

Group 2

1-day minimum (ft3

/s) 0 0 0.10 0.48 0.90 4.8

3-day minimum (ft3

/s) 0 0 0.18 0.50 0.93 2.7

7-day minimum (ft3

/s) 0 0 0.26 0.67 1.1 2.5

30-day minimum (ft3

/s) 0.01 0.14 0.70 1.2 2.1 1.6

90-day minimum (ft3

/s) 0.34 0.84 1.7 3.5 5.2 1.5

1-day maximum (ft3

/s) 64 81 100 130 170 0.51

3-day maximum (ft3

/s) 54 63 89 110 150 0.49

7-day maximum (ft3

/s) 38 47 61 78 100 0.52

30-day maximum (ft3

/s) 25 28 35 43 51 0.43

90-day maximum (ft3

/s) 18 21 24 30 34 0.36

Number of zero days 0 0 0 22 34 0

Baseflow index (ft3

/s) 0 0 0.02 0.04 0.07 2.4

Group 3

Date of minimum (Julian date) 200 210 230 250 270 ~

Date of maximum (Julian date) 340 19 54 110 160 ~

Group 4

Low-pulse count 2.5 4.0 6.0 7.8 11 0.62

Low-pulse duration (days) 2.0 3.1 6.5 13 26 1.5

High-pulse count 10 12 16 19 21 0.42

High-pulse duration (days) 2.0 2.6 3.0 4.0 5.8 0.46

Group 5

Rise rate 1.2 1.8 2.1 2.7 3.5 0.45

Fall rate -1.6 -1.3 -1.1 -0.82 -0.7 -0.43

Number of reversals 94 100 100 110 110 0.10
Appendix 3

Appendix 3: Indicators of Hydrologic Alteration (IHA) Statistics 149

Table 3–9. Indicators of Hydrologic Alteration (IHA) statistics determined from simulated long-term (1960–2004) daily flows with the 

Hydrologic Simulation Program–FORTRAN (HSPF) without withdrawals (NOWU) at Danforth Brook near Hudson, Massachusetts.

[ft3/s, cubic foot per second; ~, not applicable; metrics calculated for water years (October 1 through September 31), except for Group 2 minimum flows, which 

used climate years (April 1 through March 31)]

Metric

Percentile

10 25 50 75 90 (75-25)/50

Group 1

October (ft3

/s) 0.50 1.5 3.0 5.9 13 1.5

November (ft3

/s) 2.6 5.7 8.0 13 18 0.90

December (ft3

/s) 6.6 8.1 12 16 25 0.68

January (ft3

/s) 5.8 8.0 13 19 23 0.81

February (ft3

/s) 8.2 11 14 18 25 0.5

March (ft3

/s) 12 14 19 24 33 0.56

April (ft3

/s) 7.8 11 16 20 24 0.57

May (ft3

/s) 3.2 6.0 8.9 13 18 0.81

June (ft3

/s) 1.0 1.8 3.3 7.0 15 1.6

July (ft3

/s) 0.30 0.40 0.85 1.6 3.1 1.4

August (ft3

/s) 0.10 0.30 0.60 1.1 1.8 1.3

September (ft3

/s) 0.12 0.32 0.78 1.5 2.3 1.5

Group 2

1-day minimum (ft3

/s) 0 0.10 0.20 0.40 0.50 1.5

3-day minimum (ft3

/s) 0 0.10 0.22 0.40 0.57 1.4

7-day minimum (ft3

/s) 0.04 0.10 0.26 0.45 0.64 1.4

30-day minimum (ft3

/s) 0.11 0.17 0.4 0.77 1.3 1.5

90-day minimum (ft3

/s) 0.21 0.41 1.2 3.0 4.7 2.2

1-day maximum (ft3

/s) 85 100 130 190 250 0.68

3-day maximum (ft3

/s) 62 70 97 120 160 0.48

7-day maximum (ft3

/s) 41 49 62 81 110 0.52

30-day maximum (ft3

/s) 26 29 36 44 53 0.42

90-day maximum (ft3

/s) 19 21 25 31 36 0.37

Number of zero days 0 0 0 0 5.0 0

Baseflow index (ft3

/s) 0 0.01 0.02 0.03 0.04 1.1

Group 3

Date of minimum (Julian date) 200 210 230 250 280 ~

Date of maximum (Julian date) 340 25 76 130 200 ~

Group 4

Low-pulse count 1.5 2.2 4.0 6.0 8.0 0.94

Low-pulse duration (days) 3.2 4.5 10 26 74 2.1

High-pulse count 18 21 23 27 31 0.26

High-pulse duration (days) 1.0 1.0 2.0 2.0 3.0 0.50

Group 5

Rise rate 2.0 2.6 3.5 4.3 6.0 0.48

Fall rate -2.4 -1.8 -1.4 -1.1 -0.95 -0.48

Number of reversals 100 110 120 130 140 0.12
Appendix 3

150 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Table 3–10. Indicators of Hydrologic Alteration (IHA) statistics determined from simulated long-term (1960–2004) daily flows with the 

Hydrologic Simulation Program–FORTRAN (HSPF) without withdrawals (NOWU) at Fort Meadow Brook near Hudson, Massachusetts.

[ft3/s, cubic foot per second; ~, not applicable; metrics calculated for water years (October 1 through September 31), except for Group 2 minimum flows, which 

used climate years (April 1 through March 31)]

Metric

Percentile

10 25 50 75 90 (75-25)/50

Group 1

October (ft3

/s) 1.2 2.2 5.4 9.3 15 1.3

November (ft3

/s) 2.8 5.3 9.0 14 18 0.98

December (ft3

/s) 7.5 9.2 13 18 26 0.68

January (ft3

/s) 7.2 9.2 14 17 25 0.57

February (ft3

/s) 8.0 13 16 18 23 0.33

March (ft3

/s) 12 14 18 23 29 0.45

April (ft3

/s) 8.6 12 17 20 24 0.5

May (ft3

/s) 5.5 8.3 11 14 17 0.47

June (ft3

/s) 3.4 4.6 6.7 10 16 0.86

July (ft3

/s) 1.4 1.6 2.8 5.2 7.4 1.3

August (ft3

/s) 0.80 1.3 1.8 3.2 5.8 1.1

September (ft3

/s) 0.75 1.2 2.1 3.5 6.2 1.1

Group 2

1-day minimum (ft3

/s) 0.55 0.70 1.1 1.4 2.2 0.64

3-day minimum (ft3

/s) 0.57 0.74 1.1 1.5 2.4 0.69

7-day minimum (ft3

/s) 0.59 0.78 1.2 1.7 2.5 0.77

30-day minimum (ft3

/s) 0.68 0.89 1.4 2.2 3.6 0.95

90-day minimum (ft3

/s) 0.86 1.5 2.1 4.1 5.7 1.2

1-day maximum (ft3

/s) 44 57 74 100 140 0.59

3-day maximum (ft3

/s) 38 49 66 87 120 0.57

7-day maximum (ft3

/s) 33 40 50 67 89 0.54

30-day maximum (ft3

/s) 23 26 31 39 46 0.41

90-day maximum (ft3

/s) 17 19 22 27 32 0.36

Number of zero days 0 0 0 0 0 0

Baseflow index (ft3

/s) 0.05 0.07 0.09 0.12 0.14 0.59

Group 3

Date of minimum (Julian date) 210 230 250 270 280 ~

Date of maximum (Julian date) 350 22 67 95 150 ~

Group 4

Low-pulse count 1.0 2.0 2.0 3.0 5.0 0.50

Low-pulse duration (days) 4.0 7.2 35 81 100 2.1

High-pulse count 4.0 6.0 8.0 11 13 0.62

High-pulse duration (days) 5.0 6.0 8.0 9.9 12 0.48

Group 5

Rise rate 0.55 0.72 1.0 1.3 2.0 0.58

Fall rate -0.90 -0.7 -0.55 -0.40 -0.30 -0.55

Number of reversals 69 73 80 90 97 0.21
Appendix 3

Appendix 3: Indicators of Hydrologic Alteration (IHA) Statistics 151

Table 3–11. Indicators of Hydrologic Alteration (IHA) statistics determined from simulated long-term (1960–2004) daily flows with the 

Hydrologic Simulation Program–FORTRAN (HSPF) without withdrawals (NOWU) at Elizabeth Brook near Stow, Massachusetts.

[ft3/s, cubic foot per second; ~, not applicable; metrics calculated for water years (October 1 through September 31), except for Group 2 minimum flows, which 

used climate years (April 1 through March 31)]

Metric

Percentile

10 25 50 75 90 (75-25)/50

Group 1

October (ft3

/s) 3.4 6.6 14 25 43 1.3

November (ft3

/s) 8.4 15 27 42 56 1.0

December (ft3

/s) 23 28 40 54 87 0.64

January (ft3

/s) 20 27 43 55 85 0.64

February (ft3

/s) 27 37 45 58 73 0.47

March (ft3

/s) 36 44 60 73 92 0.48

April (ft3

/s) 28 39 52 66 78 0.51

May (ft3

/s) 15 27 35 41 57 0.42

June (ft3

/s) 10 13 18 33 48 1.1

July (ft3

/s) 3.8 5.3 8.3 13 21 0.94

August (ft3

/s) 1.5 3.6 5.5 9.8 14 1.1

September (ft3

/s) 1.4 3.2 6.0 9.6 14 1.1

Group 2

1-day minimum (ft3

/s) 0.60 0.90 2.5 4.6 7.0 1.5

3-day minimum (ft3

/s) 0.62 0.98 2.6 5.0 7.0 1.5

7-day minimum (ft3

/s) 0.68 1.0 3.0 5.6 7.4 1.5

30-day minimum (ft3

/s) 1.1 1.9 4.4 7.1 9.7 1.2

90-day minimum (ft3

/s) 1.9 4.0 6.3 12 16 1.2

1-day maximum (ft3

/s) 120 150 240 340 480 0.76

3-day maximum (ft3

/s) 110 140 200 260 390 0.63

7-day maximum (ft3

/s) 98 120 150 190 280 0.5

30-day maximum (ft3

/s) 68 79 94 120 140 0.42

90-day maximum (ft3

/s) 52 59 68 84 97 0.37

Number of zero days 0 0 0 0 0 0

Baseflow index (ft3

/s) 0.02 0.04 0.07 0.11 0.14 0.9

Group 3

Date of minimum (Julian date) 210 230 250 270 280 ~

Date of maximum (Julian date) 360 20 54 88 140 ~

Group 4

Low-pulse count 1.0 1.0 2.0 3.0 4.0 1.0

Low-pulse duration (days) 4.5 11 37 84 100 2.0

High-pulse count 5.0 6.2 9.0 12 14 0.64

High-pulse duration (days) 4.0 5.5 7.0 8.4 10 0.41

Group 5

Rise rate 1.7 1.9 3.0 3.9 5.9 0.65

Fall rate -3.0 -2.2 -1.7 -1.0 -0.80 -0.71

Number of reversals 77 84 90 95 100 0.12
Appendix 3

152 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

This page intentionally left blank.
Appendix 4

Duration and Frequency Long-Term (1960–2004) Daily Streamflow Simulated with the Hydrologic 

Simulation Program–FORTRAN (HSPF) with (AVGWU) and without (NOWU) Withdrawals were 

below Target Flows Determined by Six Standard-Setting Methods at 10 Riffle Sites in the 

Sudbury and Assabet River Basins

Frequency and Duration Simulated Streamflows were below Target Flows.............................. 154

References Cited.......................................................................................................................... 154

Table 4–1. Duration and frequency the Wetted-Perimeter flow standard was not met using 

long-term (1960–2004) Hydrologic Simulation Program–FORTRAN simulated flows with 

(AVGWU) and without withdrawals (NOWU) at 10 riffle sites in the Sudbury and Assabet 

River Basins, Massachusetts.................................................................................................. 155

Table 4–2. Duration and frequency the R2Cross 2-of-3 criterion flow standard was not met 

using long-term (1960–2004) Hydrologic Simulation Program–FORTRAN simulated flows 

with (AVGWU) and without withdrawals (NOWU) at 10 riffle sites in the Sudbury 

and Assabet River Basins, Massachusetts............................................................................. 156

Table 4–3. Duration and frequency the R2Cross 3-of-3 criterion flow standard was not met 

using long-term (1960–2004) Hydrologic Simulation Program–FORTRAN simulated flows 

with (AVGWU) and without withdrawals (NOWU) at 10 riffle sites in the Sudbury 

and Assabet River Basins, Massachusetts............................................................................. 157

Table 4–4. Duration and frequency the Tennant 30 percent of the mean annual flow 

standard was not met using long-term (1960–2004) Hydrologic Simulation Program–

FORTRAN simulated flows with (AVGWU) and without withdrawals (NOWU) at 10 riffle 

sites in the Sudbury and Assabet River Basins, Massachusetts. .......................................... 158

Table 4–5. Duration and frequency the Tennant 50 percent of the mean annual flow 

standard was not met using long-term (1960–2004) Hydrologic Simulation Program–

FORTRAN simulated flows with (AVGWU) and without withdrawals (NOWU) at 10 riffle 

sites in the Sudbury and Assabet River Basins, Massachusetts. .......................................... 159

Table 4–6. Duration and frequency the New England Aquatic Baseflow (ABF) low-flow 

standard was not met using long-term (1960–2004) Hydrologic Simulation Program–

FORTRAN simulated flows with (AVGWU) and without withdrawals (NOWU) at 10 riffle 

sites in the Sudbury and Assabet River Basins, Massachusetts. .......................................... 160
Appendix 4

154 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Appendix 4. Duration and Frequency Long-Term (1960–2004) 

Daily Streamflow Simulated with the Hydrologic Simulation 

Program–FORTRAN (HSPF) with (AVGWU) and without (NOWU) 

Withdrawals were below Target Flows Determined by Six 

Standard-Setting Methods at 10 Riffle Sites in the Sudbury and 

Assabet River Basins

Frequency and Duration Simulated Streamflows were below Target Flows

The tables in this appendix are summarized output from the River Analysis Package (RAP) by Marsh and others (2003) 

that determined the number of continuous days (duration) and the number of episodes (frequency) streamflows fall below a 

threshold. Thresholds were computed by six standard-setting methods—Wetted-Perimeter, R2Cross 2-of-3 criterion and 3-of-3 

criterion, Tennant 30- and 50-percent mean annual flow, and Aquatic Base Flow (ABF). Flow thresholds were computed by each 

method for each of the 10 riffle sites examined. The Wetted-Perimeter and R2Cross flow thresholds were computed from sitespecific hydrologic characteristics, typically determined from multiple cross sections, and a channel surface-water profile model 

(HEC-RAS). The Tennant and ABF flow thresholds were computed from statistical measures of long-term flows (1960–2004) 

simulated with the Hydrologic Simulation Program–FORTRAN (HSPF) with no withdrawals (NOWU).

The RAP program provides a number of measures of when threshold values are not met. Five measures were chosen 

that were considered a good representation of the duration and frequency a flow target could not be met. These include (1) the 

median annual number of episodes, (2) the median annual duration of an episode, (3) the median duration of the longest annual 

episode, (4) the longest duration of an episode for the 45-year simulated record, and (5) the total number of days over the 

45-year period the threshold was not met. These metrics were determined by method, by site, and between simulated flows 

with and without withdrawals. The duration and frequency flows did not meet the flow target were determined from long-term 

simulated daily flows with (AVGWU) and without (NOWU) withdrawals. The median annual duration and frequency simulated 

flows were below the target flow were computed outside of the RAP because the program excludes years from the analysis the 

target flow was always met. 

References Cited

Marsh, N.A., Stewardson, M.J., and Kennard, M.J., 2003, River Analysis Package (V2.0.4), Cooperative Research Center for 

Catchment Hydrology: Melbourne, Australia, Monash University [variously paged], accessed May 12, 2009, at http://www.

toolkit.net.au/Tools/RAP.
Appendix 4

Appendix 4 155

Table 4–1. Duration and frequency the Wetted-Perimeter flow standard was not met using long-term (1960–2004) Hydrologic 

Simulation Program–FORTRAN (HSPF) simulated flows with (AVGWU) and without withdrawals (NOWU) at 10 riffle sites in the Sudbury 

and Assabet River Basins, Massachusetts.

[ft3/s, cubic feet per second]

Site Scenario

Flow 

threshold

(ft3

/s)

Median annual Period of record

Number of 

episodes

(count)

Duration of 

episodes

(days)

Duration 

of longest 

episode

(days)

Longest 

episode

(days)

Total days 

below 

threshold

(days)

Sudbury River Basin

Whitehall Brook near Hopkinton NOWU 0.7 1

0 0 0 40 521

AVGWU 1

0 0 0 40 516

Percent difference 0 0 0 0 -1

Sudbury River near Hopkinton NOWU 7.0 6 12 33 97 3,514

AVGWU 6 14 42 97 4,141

Percent difference 0 16 27 0 18

Sudbury River near Ashland NOWU 6.7 5 9 19 67 2,337

AVGWU 6 10 22 74 2,755

Percent difference 20 5 16 10 18

Indian Brook near Hopkinton2 NOWU 1.4 6 17 55 167 4,592

Indian brook near Ashland NOWU 0.7 0 0 0 0 0

AVGWU 0 0 0 0 0

Percent difference 0 0 0 0 0

Baiting Brook near Framingham2 NOWU 0.8 0 0.0 0 25 570

Assabet River Basin

Assabet River at Westborough NOWU 0.2 1 4 3 59 621

AVGWU 2 22 26 146 2,302

Percent difference 100 450 767 147 271

Danforth Brook at Hudson2 NOWU 2.6 8 14 59 169 5,040

Fort Meadow Brook near Hudson NOWU 1.7 2 20 25 135 2,005

AVGWU 2 50 93 205 4,336

Percent difference 0 148 272 52 116

Elizabeth Brook near Stow NOWU 3.2 1 7 5 100 999

AVGWU 1 8 5 100 1,047

Percent difference 0 14 0 0 5

Median3 NOWU 1.7 1.5 7.0 5 67 999

AVGWU 2.0 9.8 22 97 2,302

Percent difference 33 40 340 45 130

1

Fell below threshold once during period of record.

2

No water withdrawals or returns in this subbasin.

3

Medians determined from sites with both AVGWU and NOWU; excludes sites unaffected by withdrawals or returns.
Appendix 4

156 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Table 4–2. Duration and frequency the R2Cross 2-of-3 criterion flow standard was not met using long-term (1960–2004) Hydrologic 

Simulation Program–FORTRAN (HSPF) simulated flows with (AVGWU) and without withdrawals (NOWU) at 10 riffle sites in the Sudbury 

and Assabet River Basins, Massachusetts.

[ft3/s, cubic feet per second]

Site Scenario

Flow 

threshold

(ft3

/s)

Median annual Period of record

Number of 

episodes

(count)

Duration of 

episodes

(days)

Duration 

of longest 

episode

(days)

Longest 

episode

(days)

Total days 

below 

threshold

(days)

Sudbury River Basin

Whitehall Brook near Hopkinton NOWU 1.2 5 6.4 12 63 1,687

AVGWU 5 6.2 12 79 1,701

Percent difference 0 -3 0 25 1

Sudbury River near Hopkinton NOWU 14 9 12 45 98 5,158

AVGWU 10 13 52 134 5,898

Percent difference 11 5 16 37 14

Sudbury River near Ashland NOWU 7.5 6 9 21 73 2,637

AVGWU 6 11 26 75 3,044

Percent difference 0 23 24 3 15

Indian Brook near Hopkinton1 NOWU 0.4 1 12 9 63 945

Indian brook near Ashland NOWU 0.5 0 0 0 0 0

AVGWU 0 0 0 0 0

Percent difference 0 0 0 0 0

Baiting Brook near Framingham1 NOWU 1.5 8 6.1 15 54 2,359

Assabet River Basin

Assabet River at Westborough NOWU 0.5 1 10 8 67 925

AVGWU 2 25 30 148 2,585

Percent difference 100 145 275 121 179

Danforth Brook at Hudson1 NOWU 1.2 3 20 43 162 2,992

Fort Meadow Brook near Hudson NOWU 2.2 2 28 34 161 2,550

AVGWU 2 53 96 214 4,773

Percent difference 0 89 182 33 87

Elizabeth Brook near Stow NOWU 6.2 2 20 25 134 2,087

AVGWU 6.2 2 21 25 139 2,129

Percent difference 0 5 0 4 2

Median2 NOWU 2.0 10 21 73 2,087

AVGWU 2.0 13 26 134 2,585

Percent difference 0 31 24 84 24

1

 No water withdrawals or returns in this subbasin.

2

 Medians determined from sites with both AVGWU and NOWU; excludes sites unaffected by withdrawals or returns.
Appendix 4

Appendix 4 157

Table 4–3. Duration and frequency the R2Cross 3-of-3 criterion flow standard was not met using long-term (1960–2004) Hydrologic 

Simulation Program–FORTRAN (HSPF) simulated flows with (AVGWU) and without withdrawals (NOWU) at 10 riffle sites in the Sudbury 

and Assabet River Basins, Massachusetts.

[ft3/s, cubic feet per second]

Site Scenario

Flow 

threshold

(ft3

/s)

Median annual Period of record

Number of 

episodes

(count)

Duration of 

episodes

(days)

Duration 

of longest 

episode

(days)

Longest 

episode

(days)

Total days 

below 

threshold

(days)

Sudbury River Basin

Whitehall Brook near Hopkinton NOWU 3.6 10 11 45 134 5,116

AVGWU 9 13 46 134 5,302

Percent difference -10 15 2 0 4

Sudbury River near Hopkinton NOWU 18 11 12 51 123 6,140

AVGWU 12 13 54 138 6,902

Percent difference 9 5 6 12 12

Sudbury River near Ashland NOWU 22 10 13 51 123 6,079

AVGWU 11 13 55 138 6,681

Percent difference 10 0 8 12 10

Indian Brook near Hopkinton1 NOWU 14 24 12 88 217 13,214

Indian brook near Ashland NOWU 6.8 5 31 110 235 7,160

AVGWU 6 34 159 286 9,054

Percent difference 20 8 45 22 26

Baiting Brook near Framingham1 NOWU 5.8 18 12 58 158 9,737

Assabet River Basin

Assabet River at Westborough NOWU 6.8 12 13 58 169 6,922

AVGWU 13 14 97 209 8,028

Percent difference 8 7 67 24 16

Danforth Brook at Hudson1 NOWU 10 23 9 79 171 9,649

Fort Meadow Brook near Hudson NOWU 7.3 5 31 109 220 6,762

AVGWU 5 40 162 281 9,075

Percent difference 0 29 49 28 34

Elizabeth Brook near Stow NOWU 10 2 44 78 174 3,870

AVGWU 2 44 78 174 3,911

Percent difference 0 0 0 0 1

Median2 NOWU 10 13 58 169 6,140

AVGWU 9 14 78 174 6,902

Percent difference -10 3 34 3 12

1

 No water withdrawals or returns in this subbasin.

2

 Medians determined from sites with both AVGWU and NOWU; excludes sites unaffected by withdrawals or returns.
Appendix 4

158 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Table 4–4. Duration and frequency the Tennant 30 percent of the mean annual flow standard was not met using long-term (1960–

2004) Hydrologic Simulation Program–FORTRAN (HSPF) simulated flows with (AVGWU) and without withdrawals (NOWU) at 10 riffle 

sites in the Sudbury and Assabet River Basins, Massachusetts.

[ft3/s, cubic feet per second]

Site Scenario

Flow 

threshold

(ft3

/s)

Median annual Period of record

Number of 

episodes

(count)

Duration of 

episodes

(days)

Duration 

of longest 

episode

(days)

Longest 

episode

(days)

Total days 

below 

threshold

(days)

Sudbury River Basin

Whitehall Brook near Hopkinton NOWU 3.8 10 11 46 134 5,241

AVGWU 9 13 48 134 5,441

Percent difference -10 15 4 0 4

Sudbury River near Hopkinton NOWU 11 8 12 41 98 4,611

AVGWU 9 13 47 122 5,301

Percent difference 13 4 15 24 15

Sudbury River near Ashland NOWU 14 8 12 42 97 4,477

AVGWU 8 14 46 122 4,981

Percent difference 0 13 10 26 11

Indian Brook near Hopkinton1 NOWU 2.8 11 12 58 189 5,847

Indian brook near Ashland NOWU 3.9 3 37 93 211 5,144

AVGWU 3 54 136 265 7,145

Percent difference 0 45 46 26 39

Baiting Brook near Framingham1 NOWU 2.1 10 7 19 74 3,352

Assabet River Basin

Assabet River at Westborough NOWU 3.9 9 12 50 168 4,960

AVGWU 8 17 86 205 5,975

Percent difference -11 38 72 22 20

Danforth Brook at Hudson1 NOWU 2.9 8 14 61 169 5,205

Fort Meadow Brook near Hudson NOWU 2.8 2 36 58 168 3,248

AVGWU 2 61 105 222 5,395

Percent difference 0 69 81 32 66

Elizabeth Brook near Stow NOWU 10 2 44 83 174 3,972

AVGWU 2 44 83 176 4,008

Percent difference 0 0 0 1 1

Median2 NOWU 8.0 12 50 168 4,611

AVGWU 8.0 17 83 176 5,395

Percent difference 0 33 66 5 17

1

 No water withdrawals or returns in this subbasin.

2

 Medians determined from sites with both AVGWU and NOWU; excludes sites unaffected by withdrawals or returns.
Appendix 4

Appendix 4 159

Table 4–5. Duration and frequency the Tennant 50 percent of the mean annual flow standard was not met using long-term (1960–

2004) Hydrologic Simulation Program–FORTRAN (HSPF) simulated flows with (AVGWU) and without withdrawals (NOWU) at 10 riffle 

sites in the Sudbury and Assabet River Basins, Massachusetts.

[ft3/s, cubic feet per second]

Site Scenario

Flow 

threshold

(ft3

/s)

Median annual Period of record

Number of 

episodes

(count)

Duration of 

episodes

(days)

Duration 

of longest 

episode

(days)

Longest 

episode

(days)

Total days 

below 

threshold

(days)

Sudbury River Basin

Whitehall Brook near Hopkinton NOWU 6.3 13 12 58 189 6,938

AVGWU 13 12 59 193 7,142

Percent difference 0 2 2 2 3

Sudbury River near Hopkinton NOWU 19 12 12 51 123 6,400

AVGWU 12 13 55 138 7,156

Percent difference 0 13 8 12 12

Sudbury River near Ashland NOWU 24 11 13 53 138 6,347

AVGWU 11 14 57 193 6,925

Percent difference 0 11 8 40 9

Indian Brook near Hopkinton1 NOWU 4.6 18 10 60 194 7,993

Indian brook near Ashland NOWU 6.5 5 30 106 223 6,902

AVGWU 5 39 158 285 8,815

Percent difference 0 30 49 28 28

Baiting Brook near Framingham1 NOWU 3.5 14 9.1 34 83 5,869

Assabet River Basin

Assabet River at Westborough NOWU 6.5 12 12 58 169 6,713

AVGWU 12 15 94 209 7,833

Percent difference 0 22 62 24 17

Danforth Brook at Hudson1 NOWU 4.8 14 10 62 170 6,250

Fort Meadow Brook near Hudson NOWU 4.7 2 50 90 195 4,670

AVGWU 3 53 143 263 6,992

Percent difference 50 5 59 35 50

Elizabeth Brook near Stow NOWU 18 5 27 97 204 6,053

AVGWU 5 27 97 204 6,065

Percent difference 0 0 0 0 0

Median2 NOWU 12 12.4 58 179 6,557

AVGWU 12 14.4 77 201 7,149

Percent difference 0 17 32 12 9

1

 No water withdrawals or returns in this subbasin.

2

 Medians determined from sites with both AVGWU and NOWU; excludes sites unaffected by withdrawals or returns.
Appendix 4

160 Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts

Table 4–6. Duration and frequency the New England Aquatic Baseflow (ABF) low-flow standard was not met using long-term 

(1960–2004) Hydrologic Simulation Program–FORTRAN (HSPF) simulated flows with (AVGWU) and without withdrawals (NOWU) at 10 

riffle sites in the Sudbury and Assabet River Basins, Massachusetts.

[ft3/s, cubic feet per second]

Site Scenario

Flow 

threshold

(ft3

/s)

Median annual Period of record

Number of 

episodes

(count)

Duration of 

episodes

(days)

Duration 

of longest 

episode

(days)

Longest 

episode

(days)

Total days 

below 

threshold

(days)

Sudbury River Basin

Whitehall Brook near Hopkinton NOWU 2.2 7 11 28 82 3,739

AVGWU 8 10 26 82 3,841

Percent difference 14 -9 -7 0 3

Sudbury River near Hopkinton NOWU 9.5 7 13 40 97 4,259

AVGWU 8 13 45 116 4,871

Percent difference 14 3 13 20 14

Sudbury River near Ashland NOWU 12 7 12 40 97 4,050

AVGWU 7 14 44 115 4,519

Percent difference 0 19 10 19 12

Indian Brook near Hopkinton1 NOWU 1.4 6 17 55 167 4,592

Indian brook near Ashland NOWU 2.0 1 80 63 187 3,434

AVGWU 2 64 113 255 5,581

Percent difference 100 -20 79 36 63

Baiting Brook near Framingham1 NOWU 2.1 10 7.9 19 74 3,524

Assabet River Basin

Assabet River at Westborough NOWU 1.7 4 18 39 112 3,223

AVGWU 4 23 67 183 4,260

Percent difference 0 28 72 63 32

Danforth Brook at Hudson1 NOWU 0.7 3 15 30 140 2,463

Fort Meadow Brook near Hudson NOWU 1.6 2 18 22 133 1,899

AVGWU 2 49 91 205 4,257

Percent difference 0 169 314 54 124

Elizabeth Brook near Stow NOWU 5.9 2 22 26 140 2,171

AVGWU 2 23 26 141 2,220

Percent difference 0 2 0 1 2

Median2 NOWU 4 18 39 112 3,434

AVGWU 4 23 45 141 4,260

Percent difference 0 25 15 26 24

1

 No water withdrawals or returns in this subbasin.

2

 Medians determined from sites with both AVGWU and NOWU; excludes sites unaffected by withdrawals or returns.
For additional information, write to:

Director

U.S. Geological Survey

Massachusetts Water Science Center

10 Bearfoot Road

Northborough, MA 01532

or visit our Web site at:

http://ma.water.usgs.gov/

Document prepared by the West Trenton Publishing Service Center
Zarriello and others—Effects of Water Use and Land Use on Streamflow and Aquatic Habitat in the Sudbury and Assabet River Basins, Massachusetts—SIR 2010–5042

ISBN

Printed on recycled paper