A Precipitation-Runoff Model for the 

Blackstone River Basin, 

Massachusetts and Rhode Island

By Jeffrey R. Barbaro and Phillip J. Zarriello

Prepared in cooperation with the 

Rhode Island Water Resources Board

Scientific Investigations Report 2006–5213

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director

U.S. Geological Survey, Reston, Virginia: 2007

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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:

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.
Contents

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

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

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

Previous Investigations........................................................................................................................2

Description of the Basin ...............................................................................................................................4

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

Topography ............................................................................................................................................4

Land Use and Land Cover....................................................................................................................4

Surficial Geology...................................................................................................................................6

Streamflow-Gaging Stations and Hydrology....................................................................................6

Wetlands ................................................................................................................................................9

Water Use ............................................................................................................................................11

Precipitation-Runoff Model for the Blackstone River Basin ................................................................11

Functional Description of HSPF........................................................................................................11

Input Data Used for the Model .........................................................................................................15

Climate.........................................................................................................................................17

Water Withdrawals ..................................................................................................................20

Golf-Course Withdrawals................................................................................................20

Streamflow Depletion by Ground-Water Withdrawals ..............................................25

Wastewater-Return Flows........................................................................................................27

Streamflow..................................................................................................................................27

Representation of the Basin .............................................................................................................30

Data Layer Processing and Basin Simplification .................................................................31

Surficial Geology...............................................................................................................31

Land Use and Land Cover................................................................................................31

Wetlands ............................................................................................................................32

Public Water and Public Sewer Systems .....................................................................32

Hydrologic Response Units......................................................................................................32

Impervious Areas (IMPLNDs).........................................................................................35

Pervious Areas (PERLNDs) .............................................................................................35

Stream Reaches (RCHRES) ......................................................................................................36

Hydraulic Characteristics (FTABLEs).............................................................................36

Wetlands ............................................................................................................................37

Water Use ..........................................................................................................................40

Model Calibration................................................................................................................................45

Annual and Monthly Mean Discharge ...................................................................................47

Daily Mean Discharge .............................................................................................................52

Simulated Hydrologic Response Unit Water Budgets.........................................................52

Summary of Anthropogenic Water Use in Basin..................................................................61

Sensitivity of Model Results to Changes in Values of Parameters ...................................66

Model Limitations................................................................................................................................66

Summary........................................................................................................................................................67

Acknowledgments.......................................................................................................................................68

References Cited..........................................................................................................................................69

Appendix 1. Hydrological Simulation Program–FORTRAN User Control File Input for 

Pervious and Impervious Area Parameters...............................................................................73

iii
iv

Figures

1–6. Maps Showing—

1. The Blackstone River Basin, towns, and climatological stations used to simulate 

streamflow, Massachusetts and Rhode Island ..............................................................3

2. Land use in the Blackstone River Basin ..........................................................................5

3. Surficial geology in the Blackstone River Basin ............................................................7

4. Streamflow-gaging stations in the Blackstone River Basin and 

surrounding areas ...............................................................................................................8

5. Wetlands in the Blackstone River Basin .......................................................................10

6. Distribution of public water and public sewer systems in the Blackstone 

River Basin..........................................................................................................................14

7. Schematic diagram of inflows and outflows to a Hydrological Simulation Program–

FORTRAN stream reach.............................................................................................................16

8–9. Maps Showing—

8. Model reaches, subbasin boundaries, and the boundary between climatological 

zones for the Hydrological Simulation Program–FORTRAN (HSPF) model for the 

Blackstone River Basin.....................................................................................................19

9. Locations of water withdrawals, transfers, and wastewater returns in the 

Blackstone River Basin.....................................................................................................21

10. Graph showing daily withdrawal rate at King’s Grant Water Company Well 1, North 

Attleboro, Massachusetts, 1996–2001, and calculated streamflow depletion.................26

11. Diagram showing areas of hydrologic response units, wetlands, and open water 

as percentages of drainage area.............................................................................................33

12. Map showing water-supply reservoirs in the Blackstone River Basin .............................42

13–24. Graphs Showing—

13. Relation between simulated and observed or computed annual mean discharge 

at streamflow-gaging stations A, Quinsigamond River at North Grafton, Mass. 

(QU1A, 01110000); B, Blackstone River at Millbury, Mass. (BL2B, 01109730); 

C, Nipmuc River near Harrisville, R.I. (NI1A, 01111300); D, Branch River at 

Forestdale, R.I. (BR2A, 01111500); E, Blackstone River at Woonsocket, R.I. 

(BL9A, 01112500); and F, Blackstone River at Pawtucket, R.I. (BL13, 01113895) .....50

14. Relation between simulated and observed or computed monthly mean discharge 

at streamflow-gaging stations A, Quinsigamond River at North Grafton, Mass. 

(QU1A, 01110000); B, Blackstone River at Millbury, Mass. (BL2B, 01109730); 

C, Nipmuc River near Harrisville, R.I. (NI1A, 01111300); D, Branch River at 

Forestdale, R.I. (BR2A, 01111500); E, Blackstone River at Woonsocket, R.I. (BL9A, 

01112500); and F, Blackstone River at Pawtucket, R.I. (BL13, 01113895)...................51

15. Daily precipitation at Worcester Regional Airport, Worcester, Mass. (KORH), and 

T.F. Green Regional Airport, Warwick, R.I. (KPVD), and simulated and observed or 

computed daily mean discharge at streamflow-gaging stations A, Quinsigamond 

River at North Grafton, Mass. (QU1A, 01110000); B, Blackstone River at Millbury, 

Mass. (BL2B, 01109730); C, Nipmuc River near Harrisville, R.I. (NI1A, 01111300); 

D, Branch River at Forestdale, R.I. (BR2A, 01111500); E, Blackstone River at

 Woonsocket, RI (BL9A, 01112500); and F, Blackstone River at Pawtucket, R.I. 

(BL13, 01113895).................................................................................................................54

16. Relations between simulated and observed or computed daily mean discharge 

at streamflow-gaging stations A, Quinsigamond River at North Grafton, Mass. 

(QU1A, 01110000); B, Blackstone River at Millbury, Mass. (BL2B, 01109730); 

C. Nipmuc River near Harrisville, R.I. (NI1A, 01111300); D, Branch River at 

Forestdale, R.I. (BR2A, 01111500); E, Blackstone River at Woonsocket, R.I. 

(BL9A, 01112500); and F, Blackstone River at Pawtucket, R.I. (BL13, 01113895) .....56
13–24. Graphs Showing—Continued

17. Flow-duration curves for simulated and observed or computed daily mean 

discharges at streamflow-gaging stations A, Quinsigamond River at North 

Grafton, Mass. (QU1A, 01110000); B, Blackstone River at Millbury, Mass. 

(BL2B, 01109730); C, Nipmuc River near Harrisville, R.I. (NI1A, 01111300); 

D, Branch River at Forestdale, R.I. (BR2A, 01111500); E, Blackstone River at 

Woonsocket, R.I. (BL9A, 01112500); and F, Blackstone River at Pawtucket, 

R.I. (BL13, 01113895) ..........................................................................................................57

18. Mean annual water budget by component for 1997–2001 for each 

hydrologic response unit simulated by the Hydrological Simulation Program–

FORTRAN model of the Blackstone River Basin, in inches A, per acre; and 

B, over the entire basin.....................................................................................................58

19. A wet month (March 2001) water budget for each hydrologic response unit 

simulated by the Hydrological Simulation Program–FORTRAN model of the 

Blackstone River Basin, in inches A, per acre for moisture supply, total 

runoff to streams, and total losses to evapotranspiration; B, per acre for 

individual components of runoff to streams and losses to evapotranspiration 

and sewers; and C, over the entire basin for individual components of runoff 

to streams and losses to evapotranspiration and sewers..........................................59

20. A dry month (September 1998) water budget for each hydrologic response unit 

simulated by the Hydrological Simulation Program–FORTRAN model of the 

Blackstone River Basin, in inches A, per acre for moisture supply, total runoff to 

streams and total losses to evapotranspiration; B, per acre for individual 

components of runoff to streams and losses to evapotranspiration and sewers; 

and C, over the entire basin for individual components of runoff to streams and 

osses to evapotranspiration and sewers ......................................................................60

21. The mean monthly water budget for 1997–2001 for PERLND 3 (forest overlying till) 

simulated by the Hydrological Simulation Program–FORTRAN model of the 

Blackstone River Basin model, in inches A, per acre for moisture supply, total 

runoff to streams and total losses to evapotranspiration; and B, per acre for 

individual components of runoff to streams and losses to evapotranspiration......62

22. The mean monthly water budget for 1997–2001 for PERLND 11 (forest over­lying 

sand and gravel) simulated by the Hydrological Simulation Program–FORTRAN 

model of the Blackstone River Basin, in inches A, per acre for moisture supply, 

total runoff to streams and total losses to evapotranspiration; and B, per acre for 

individual components of runoff to streams and losses to evapotranspiration......63

 23. The mean monthly water budget for 1997–2001 for PERLND 4 (medium- to lowdensity residential areas with no import or export of water overlying till) simulated 

by the Hydrological Simulation Program–FORTRAN model of the Blackstone 

River Basin, in inches A, per acre for moisture supply, total runoff to streams and 

total losses to evapotranspiration; and B, per acre for individual components of 

runoff to streams and losses to evapotranspiration and sewers..............................64

 24. The mean monthly water budget for 1997–2001 for PERLND 1 (commercialindustrial-transportation areas) simulated by the Hydrological Simulation 

Program–FORTRAN model of the Blackstone River Basin, in inches A, per acre 

for moisture supply, total runoff to streams, and total losses to evapotranspiration; 

and B, per acre for individual components of runoff to streams and losses to 

evapotranspiration and sewers ......................................................................................65
Tables

1. Streamflow-gaging stations in the Blackstone River Basin, Massachusetts and 

Rhode Island..................................................................................................................................9

2. Summary of water use by town in the Blackstone River Basin, Massachusetts 

and Rhode Island ........................................................................................................................12

3. Organization and description of Dataset Numbers in the Watershed Data 

Management file for the Hydrological Simulation Program–FORTRAN model 

of the Blackstone River Basin, Massachusetts and Rhode Island ....................................17

4. Constituent attributes (IDCONs) for the Watershed Data Management file of the 

Hydrological Simulation Program–FORTRAN model of the Blackstone River 

Basin, Massachusetts and Rhode Island. ..............................................................................18

5. Municipal, commercial/industrial, and golf-course withdrawals in the Blackstone 

River Basin, Massachusetts and Rhode Island.....................................................................22

6. Wastewater-return flows in the Blackstone River Basin, Massachusetts and 

Rhode Island................................................................................................................................28

7. Summary of relations between daily mean streamflow at the partial-record 

streamflow-gaging stations and at the continuous-record stations used to 

compute continuous streamflow records at the partial-record stations for 

1997–2001, Blackstone River Basin, Massachusetts and Rhode Island ...........................29

8. Residential densities used in the Hydrological Simulation Program–FORTRAN 

model of the Blackstone River Basin, Massachusetts and Rhode Island ........................31

9. Definitions and areas of hydrologic response units (HRUs), wetlands, and open 

water used to represent the Blackstone River Basin, Massachusetts and 

Rhode Island................................................................................................................................34

10. Effective impervious area by developed land-use type for the Hydrological 

Simulation Program–FORTRAN model of the Blackstone River Basin, 

Massachusetts and Rhode Island ...........................................................................................35

11. Descriptions of stream reaches in the Hydrological Simulation Program–

FORTRAN model of the Blackstone River Basin, Massachusetts and 

Rhode Island................................................................................................................................38

12. Summary of monthly model-fit statistics for flows simulated by the Hydrological 

Simulation Program–FORTRAN model and observed or computed flows at 

15 streamflow-gaging stations in the Blackstone River Basin, Massachusetts and 

Rhode Island, January 1997 through December 2001 ..........................................................48

13. Summary of daily model-fit statistics for flows simulated by the Hydrological 

Simulation Program–Fortran model and observed or computed flows at 

15 streamflow-gaging stations in the Blackstone River Basin, Massachusetts and 

Rhode Island, January 1997 through December 2001 ..........................................................48

14. Summary of model-fit statistics computed by the HSPEXP program for flows 

simulated by the Hydrological Simulation Program–FORTRAN model and 

observed or computed flows at 15 streamflow-gaging stations in the Blackstone 

River Basin, Massachusetts and Rhode Island, January 1997 through December 2001......49

vi
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 0.004047 square kilometer (km2)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

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

Flow rate

foot per day (ft/d) 0.3048 meter per day (m/d)

foot squared per day (ft2/yr) 0.09290 meter squared per day (m2/d)

foot squared per second (ft2/s) 0.09290 meter squared per day (m2/d)

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)

gallon per day per acre

[(gal/d)/acre]

 935.4 liter per day per square

kilometer [(L/d)/km2]

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

inch per hour (in/hr) 0 .0254 meter per hour (m/hr)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

mile per hour (mi/hr) 1.609 kilometer per hour (km/hr) 

Pressure

inch of mercury at 60oF (in Hg) 3.377 kilopascal (kPa) 

Hydraulic conductivity

foot per day (ft/d) 0.3048 meter per day (m/d)

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), 

unless otherwise noted.

*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.

vii
Acronyms and Abbreviations

BL2B Streamflow-gaging station on the Blackstone River at Millbury, Mass. 

(01109730)

BR2A Streamflow-gaging station on the Branch River at Forestdale, R.I. (01111500)

BL9A Streamflow-gaging station on the Blackstone River at Woonsocket, R.I. 

(01112500)

BL13 Streamflow-gaging station on the Blackstone River at Pawtucket, R.I. 

(01113895)

CGAP Channel Geometry Analysis software Program

DSN Data Set Number associated with the Watershed Data Management database

FEMA Federal Emergency Management Agency

FTABLE Function table that defines the relation between depth, storage and discharge 

of water in a reach

GENFTBL GENerate FTaBLe software program

GENSCN GENerate SCeNarios software program

HRU Hydrologic response unit

HSPF Hydrologic Simulation Program–FORTRAN

HSPEXP Expert system for the HSPF model

IDCONS Constituent identification attribute associated with the Watershed Data 

Management database

IDLOCN Location identification attribute associated with the Watershed Data 

Management database

IDSCEN Scenario identification attribute associated with the Watershed Data 

Management database

IMPLND HSPF impervious-area land element

KORH Climatological station at Worcester Regional Airport, Worcester, Mass.

KPVD Climatological station at T.F. Green Regional Airport, Warwick, R.I.

LULC Land Use Land Cover

MFACT Multiplier used to adjust time-series data read from the Watershed Data 

Management database 

MASSGIS Massachusetts Geographic Information System

MADEP Massachusetts Department of Environmental Protection

MOVE.1 Maintenance of Variance Extension, Type 1 

NI1A Streamflow-gaging station on the Nipmuc River near Harrisville, R.I. 

(01111300)

PERLND HSPF pervious-area land element 

PET Potential Evapotranspiration

PEST Parameter estimation software program

QU1A Streamflow-gaging station on the Quinsigamond River at North Grafton, 

Mass. (01110000)

RCHRES HSPF stream or reservoir reach

RIDEM Rhode Island Department of Environmental Management

RIWRB Rhode Island Water Resources Board

RIGIS Rhode Island Geographic Information System

STRMDEPL Analytical program to compute streamflow depletion from a pumped well

UCI HSPF user control input file

USGS U.S. Geological Survey

WDM Watershed Data Management database

WDMUtil Watershed Data Management Utility software 

WMA Water Management Act

viii
Acronyms for HSPF Model Parameters

AGWO Active ground-water outflow from pervious areas

AGWRC Active ground-water recession constant

AGWETP Active ground-water evapotranspiration rate

CEPE Evapotranspiration losses from interception storage

DEEPFR Fraction of ground water that enters a deep flow system

IFWO Interflow outflow from pervious areas

IGWI Deep ground-water discharge

INFILT Infiltration rate

INTFW Interflow inflow parameter

IRC Interflow recession constant

IVOL Inflow volume to a reach

KVARY Parameter that modifies the linearity of the active groundwater recession constant

LZET Evapotranspiration losses from lower-zone storage

LZETP Lower-zone evapotranspiration parameter

LZLI Lower-zone lateral input 

LZSN Lower-zone nominal storage

MON-IRC Monthly interflow recession constant

MON-INTERCEP Monthly interception storage

MON-INTERFLW Monthly interflow controls rate of flow from surface storage 

MON-LZET Monthly lower zone evapotranspiration rate

MON-UZSN Monthly upper zone nominal storage

OUTDGT Volume time series specified for a reach

OVOL Outflow volume from a reach

PERO Total runoff from pervious areas

SURI Surface-water runoff from impervious areas

SURO Surface-water runoff from pervious areas

SUPY Moisture supply to pervious and impervious areas

UZET Evapotranspiration losses from upper-zone storage

UZSN Upper zone nominal storage

ix

A Precipitation-Runoff Model for the 

Blackstone River Basin, 

Massachusetts and Rhode Island

By Jeffrey R. Barbaro and Phillip J. Zarriello

Abstract

A Hydrological Simulation Program–FORTRAN (HSPF) 

precipitation-runoff model of the Blackstone River Basin 

was developed and calibrated to study the effects of changing 

land- and water-use patterns on water resources. The 474.5 mi2

Blackstone River Basin in southeastern Massachusetts and 

northern Rhode Island is experiencing rapid population 

and commercial growth throughout much of its area. This 

growth and the corresponding changes in land-use patterns 

are increasing stress on water resources and raising concerns 

about the future availability of water to meet residential and 

commercial needs. Increased withdrawals and wastewaterreturn flows also could adversely affect aquatic habitat, water 

quality, and the recreational value of the streams in the basin. 

The Blackstone River Basin was represented by 19 hydrologic response units (HRUs): 17 types of pervious areas 

(PERLNDs) established from combinations of surficial geology, land-use categories, and the distribution of public water 

and public sewer systems, and two types of impervious areas 

(IMPLNDs). Wetlands were combined with open water and 

simulated as stream reaches that receive runoff from surrounding pervious and impervious areas. This approach was taken 

to achieve greater flexibility in calibrating evapotranspiration 

losses from wetlands during the growing season. The basin was 

segmented into 50 reaches (RCHRES) to represent junctions 

at tributaries, major lakes and reservoirs, and drainage areas to 

streamflow-gaging stations. Climatological, streamflow, waterwithdrawal, and wastewater-return data were collected during 

the study to develop the HSPF model. Climatological data collected at Worcester Regional Airport in Worcester, Massachusetts and T.F. Green Airport in Warwick, Rhode Island, were 

used for model calibration. A total of 15 streamflow-gaging 

stations were used in the calibration. Streamflow was measured 

at eight continuous-record streamflow-gaging stations that are 

part of the U.S. Geological Survey cooperative streamflowgaging network, and at seven partial-record stations installed in 

2004 for this study. Because the model-calibration period preceded data collection at the partial-record stations, a continuous 

streamflow record was estimated at these stations by correlation with flows at nearby continuous-record stations to provide 

additional streamflow data for model calibration. Water-use 

information was compiled for 1996–2001 and included municipal and commercial/industrial withdrawals, private residential 

withdrawals, golf-course withdrawals, municipal wastewaterreturn flows, and on-site septic effluent return flows. Streamflow depletion was computed for all time-varying ground-water 

withdrawals prior to simulation. Water-use data were included 

in the model to represent the net effect of water use on simulated hydrographs. Consequently, the calibrated values of the 

hydrologic parameters better represent the hydrologic response 

of the basin to precipitation. 

The model was calibrated for 1997–2001 to coincide 

with the land-use and water-use data compiled for the study. 

Four long-term stations (Nipmuc River near Harrisville, 

Rhode Island; Quinsigamond River at North Grafton, Massachusetts; Branch River at Forestdale, Rhode Island; and Blackstone River at Woonsocket, Rhode Island) that monitor flow 

at 3.3, 5.4, 19, and 88 percent of the total basin area, respectively, provided the primary model-calibration points. Hydrographs, scatter plots, and flow-duration curves of observed and 

simulated discharges, along with various model-fit statistics, 

indicated that the model performed well over a range of hydrologic conditions. For example, the total runoff volume for the 

calibration period simulated at the Nipmuc River near Harrisville, Rhode Island; Quinsigamond River at North Grafton, 

Massachusetts; Branch River at Forestdale, Rhode Island; and 

Blackstone River at Woonsocket, Rhode Island streamflowgaging stations differed from the observed runoff volume 

by –8.6, 3.9, –4.7, and –5.3 percent, respectively. The errors 

between the observed and simulated mean daily streamflows 

for the calibration period were less than 10 percent at 12 of 

the 15 stations in the basin. The Nash-Sutcliffe coefficient for 

daily mean flows, a goodness-of-fit measure that represents 

the proportion of the variance in the observed flow explained 

by the model, ranged from 0.61 to 0.78 at the primary calibration stations. The simulated mean annual runoff from the basin 

was 23.1 inches for 1997–2001, of which about 44 percent was 

from forested areas overlying till, and about 11 percent was 

from forested areas overlying sand and gravel. The simulated 

mean annual evapotranspiration loss was 19.5 inches from the 

basin, of which about 63 percent was from forested areas. 
Introduction

The Blackstone River flows through a densely populated 

area of south-central Massachusetts and northern Rhode Island 

(fig. 1). The Blackstone River Basin is experiencing rapid 

population and commercial growth and changing land-use patterns throughout much of its area. The population in 36 of the 

39 towns in the basin increased between 1990 and 2000 (U.S. 

Census Bureau, 2005). Five towns in the Massachusetts part 

of the basin had growth rates of more than 30 percent (U.S. 

Census Bureau, 2005). The majority of the growth was lowdensity residential development outside the established city 

centers. Residential, commercial, and industrial growth and 

transfers of water across basin boundaries are increasing the 

demand on water resources in the basin and raising concerns 

about the future availability of water to meet the needs of 

residents. As communities increase withdrawals to meet growing water-supply demands, streamflows decrease, potentially 

adversely affecting aquatic habitat, water quality, and the 

recreational value of streams in the basin. 

Residents of the Blackstone River Basin use ground water 

and surface water for their drinking-water supplies. Watersupply wells generally tap thin (less than 100-ft thick) aquifers 

that are in direct hydraulic connection with the Blackstone 

River or its tributaries, ponds, and wetlands. As is the case 

with many river basins in New England, aquifers in the 

Blackstone River Basin are discontinuous, with the most 

productive parts of the aquifers following river channels 

(Johnston and Dickerman, 1974a and 1974b; Izbicki, 2000). 

In most instances, ground-water discharging to streams is the 

source of summer streamflow. Ground-water withdrawals 

decrease discharge to streams and can exacerbate low flows 

during dry periods in the summer. Surface-water withdrawals 

from streams have a direct and immediate effect on streamflow. Return flows from wastewater-treatment plants also 

affect streamflow in parts of the basin. Treated wastewater 

is a significant source of streamflow in the Blackstone River 

during the summer; these return flows reduce the effect of 

streamflow depletion on the main stem caused by withdrawals elsewhere in the basin. Land-use change that accompanies 

population growth also has the potential to affect the 

hydrology of the watershed, particularly by reducing recharge 

to the aquifer in developed, impermeable areas. 

Local communities and state agencies have increasing 

concerns that water supplies in the basin may be unable to 

provide enough water to meet future demands. A corresponding environmental concern is that ground-water and surfacewater withdrawals associated with growth are exacerbating 

low-flow and water-quality problems in some parts of the 

Blackstone River Basin. Current (2006) demands on water 

resources and projected growth in the basin have created a 

need for increased understanding of the hydrology of the 

basin. In many areas, stresses to the hydrologically linked 

ground-water and surface-water systems extend across aquifer, 

town, and state boundaries, simultaneously affecting waterresource management and development plans for multiple 

communities. To address these concerns, the U.S. Geological 

Survey (USGS), in cooperation with the Rhode Island Water 

Resources Board (RIWRB), developed a surface-water model 

for the Blackstone River Basin. A Hydrological Simulation 

Program–FORTRAN (HSPF) precipitation-runoff model was 

developed and calibrated to study the effects of water use and 

land use on streamflow and the effects of water-management 

practices on regional water availability. Although the study 

emphasizes the Rhode Island part of the Blackstone River 

Basin, the entire basin was modeled. 

Purpose and Scope

This report describes the development and calibration of 

the HSPF model for the Blackstone River Basin. It includes 

information on the climate, topography, surficial geology, and 

hydrology of the basin, as well as the land use and water use 

for 1997–2001 (the model-calibration period). The report also 

describes the external data used in the model, the methods 

used to process the data for inclusion in HSPF and estimate 

missing periods of record, and the methods used to estimate 

residential water use and wastewater disposal in the basin. 

Previous Investigations

Water resources in the Blackstone River Basin have 

been studied extensively over the years by State and Federal 

agencies and other organizations, but many of these reports 

are not widely available. The most recent comprehensive 

study of water quality in the Blackstone River and its major 

tributaries, the Blackstone River Initiative, was conducted 

by the U.S. Environmental Protection Agency (USEPA), 

the Massachusetts Department of Environmental Protection 

(MADEP), and Rhode Island Department of Environmental 

Management (RIDEM) during the early 1990s (Wright and 

others, 2001). This study included water-quality sampling 

during wet and dry weather and sampling of sediments and 

wastewater effluent. Recent water-quality information for 

many streams and lakes in the basin was summarized by 

Weinstein and others (2001). 

Several comprehensive water-use and management studies have been conducted in the last 20 years by the USGS 

and state agencies. Studies have documented water use in 

the major basins in Rhode Island (Craft and others, 1990); 

the town of Cumberland, Rhode Island (Horn and others, 

1994); and the lower Blackstone River Basin including all of 

the basin area in Rhode Island (Barlow, 2003). Other wateruse information has been compiled in reports by the Rhode 

Island Department of Administration—Division of Planning 

(Rhode Island Department of Administration—Division of 

Planning, 1988 and 1991) and the Massachusetts Department 

of Environmental Management (Massachusetts Department of 

Environmental Management, 1985 and 1991). 

 A Precipitation-Runoff Model for the Blackstone River Basin
Figure 1. The Blackstone River Basin, towns, and climatological stations used to simulate streamflow, 

Massachusetts and Rhode Island.

Introduction 

Mumford 

T.F. Green Regional Airport 

(KPVD)

Worcester Regional Airport

(KORH)

HOLDEN

CHARLTON SUTTON

DOUGLAS

SPENCER

RUTLAND

OXFORD

UPTON

WORCESTER

UXBRIDGE

FRANKLIN

DUDLEY

GRAFTON

HOPKINTON

NATICK

LEICESTER

MENDON

AUBURN

MILLIS

PAXTON

BERLIN

BOYLSTON

WRENTHAM

OAKHAM

HOLLISTON

MILFORD

MILLBURY

SHREWSBURY

WEBSTER

NORFOLK

SHERBORN

ASHLAND

WESTBOROUGH

MEDWAY

NORTHBRIDGE

NORTHBOROUGH

STOW

ATTLEBORO

PLAINVILLE

STERLING

DOVER

CLINTON

BOLTON LINCOLN

SEEKONK

BELLINGHAM

SOUTHBRIDGE

BLACKSTONE

MEDFIELD

WEST 

BOYLSTON

NORTH 

ATTLEBOROUGH

MILLVILLE

HOPEDALE

FOSTER SCITUATE

GLOCESTER

BURRILLVILLE

CRANSTON

SMITHFIELD

JOHNSTON

LINCOLN

CUMBERLAND

PROVIDENCE

WARWICK

NORTH 

SMITHFIELD

EAST 

PROVIDENCE

PAWTUCKET

WOONSOCKET

NORTH 

PROVIDENCE

CENTRAL

 FALLS

MASSACHUSETTS

CONNECTICUT

CONNECTICUT

RHODE ISLAND

MASSACHUSETTS

RHODE ISLAND

Peters River

Branch River

Quinsigamond

River

Mumford

River

West River

Mill River

Mill Brook

Middle

River

Kettle

Brook

Nipmuc River

Chepachet River

Abbott

Run

BLACKSTONE

RIVER

BLACKSTONE RIVER

NARRAGANSETT 

BAY

SEEKONK

RIVER

Base from U.S. Geological Survey, 1:24,000, 1995

Massachusetts state plane projection, NAD83

0 50 KILOMETERS

0 50 MILES

BLACKSTONE

42o00'

41o30'

73o00' 72o

00' 72o 71 00' o

00'

42o30'

MASSACHUSETTS

RHODE

ISLAND

(KPVD)

EXPLANATION

OPEN WATER

BASIN BOUNDARY

CLIMATOLOGICAL

STATION AND 

IDENTIFIER

0 5 10 MILES

0 5 10 KILOMETERS

72° 71°45' 71°30'

41°45'

42°

42°15'
Studies of the ground-water and surface-water hydrology of the basin also have been conducted by the USGS and 

state agencies. These studies provide information on precipitation, recharge, streamflow, drainage-basin boundaries, 

aquifer properties, aquifer yields, and water quality. Study 

areas varied in size and most did not encompass the entire 

basin. Water resources in Massachusetts were investigated by 

Krejmas and Wandle (1982), Walker and Krejmas (1986), and 

Izbicki (2000), and in Rhode Island by Lang (1961), Johnson 

(1962), Johnston and Dickerman (1974a, 1974b, and 1974c), 

and Friesz (2004). Frimpter (1974) investigated ground-water 

management in the entire Blackstone River Basin. Flow 

characteristics of streams in the Massachusetts part of the 

basin were investigated by Wandle and Phipps (1984). The 

study described in this report is the first application of a 

precipitation-runoff model to investigate streamflow and 

water-management alternatives in the Blackstone River Basin.

Description of the Basin

The Blackstone River flows for 46 miles (mi) from its 

headwaters in Worcester, Massachusetts, the third largest city 

in New England, to the head of Narragansett Bay at Providence, 

Rhode Island, the second largest city (fig. 1). The Blackstone 

River Basin encompasses an area of 474.5 square miles (mi2). 

Approximately 71 percent of the basin is in south-central Massachusetts and 29 percent is in northern Rhode Island (fig. 1). 

The Blackstone River begins below the confluence of the Middle River and Mill Brook in Worcester, Massachusetts and ends 

in Pawtucket, Rhode Island, at which point it becomes the tidal 

Seekonk River at the head of Narragansett Bay. The Blackstone 

River is the second largest source of freshwater to Narragansett 

Bay. The major tributaries, the Quinsigamond River, West River, 

Mumford River, Branch River, Mill River, Peters River, and 

Abbott Run, contribute roughly one-half of the total flow in the 

Blackstone River during low-flow conditions. 

Climate

The climate in the basin is humid. Precipitation for 1960–

2004 averaged 46.4 inches per year (in/yr) in the northern part 

of the basin (Worcester Regional Airport, Worcester, Mass., 

station 1999923) and 44.7 in/yr in the southern part of the basin 

(T.F. Green Airport, Warwick, R.I., station 376698). Worcester Regional Airport (also referred to as KORH) is located 

just west of the city of Worcester and T.F. Green Airport (also 

referred to as KPVD) is approximately 10 mi south of the 

basin outlet (fig. 1). Average monthly precipitation is fairly 

uniform throughout the year. At T.F. Green Airport, average 

long-term monthly precipitation ranged from 2.94 inches (in.) 

in July to 4.24 inches in December. At the Worcester Regional 

airport, average long-term monthly precipitation ranged from 

3.13 inches in February to 4.28 inches in September. 

The average annual air temperature for 1960–2004 

ranged from 47.0 °F in the northern part of the basin to 50.8 °F 

in the southern part of the basin. Average monthly temperatures for this period ranged from 23.4 °F to 28.5 °F in January 

and 69.5 °F to 72.7 °F in July in the northern and southern 

parts of the basin, respectively. 

Topography

The regional slope of the basin is to the southeast, with 

altitudes ranging from about 1,390 ft above sea level in the 

hilly region north and west of Worcester to 4 ft above sea level 

where the Blackstone River enters Narragansett Bay at Pawtucket. The mean altitude in the basin is about 460 ft above sea 

level. The western part of the basin is in the Central Highlands 

region and eastern part is in the Eastern Lowlands region 

(Denny, 1982). The topography of the northern and western 

parts of the basin is rolling with numerous steep, rocky hills. 

The southern part of the basin has less relief with relatively 

large areas of flatter ground. Slopes calculated from the USGS 

National Elevation Dataset (U.S. Geological Survey, 2005) 

ranged from 0 to approximately 50 percent, with an average 

slope of about 6 percent. The average slope of the Blackstone 

River Basin is among the steepest of comparably sized coastal 

basins in New England. The steep topography contributed 

to the early, widespread development of water power in the 

basin, which is commonly considered to be the birthplace of 

the industrial revolution in the United States (National Park 

Service, 2005). 

Land Use and Land Cover

The Blackstone River Basin is predominantly forested 

(50.7 percent). The next largest land-use and land-cover 

(LULC) category is residential (21.3 percent), of which 

14.7 percent is medium- to low-density residential and 

6.6 percent is high-density residential, followed by open, 

non-residential (10.7 percent), forested and non-forested wetlands (7.7 percent), and commercial-industrial-transportation 

(5.8 percent). The remaining 3.8 percent of the basin is classified as open water. The methods used to develop these general 

categories from the more-detailed Massachusetts and Rhode 

Island LULC data layers are described in the “Representation 

of the Basin” section of the report. 

Land use in the basin varies geographically (fig. 2). 

The northern and southeastern parts of the basin have substantial urban development, and the eastern side of the basin, 

near the Route 495 corridor, is generally more developed 

and populated than the western side. The western part of the 

basin below Worcester is relatively undeveloped with about 

70 percent of the land classified as forest. Medium- to lowdensity development is distributed fairly uniformly across 

the basin. 

 A Precipitation-Runoff Model for the Blackstone River Basin
0 2.5

2.5

5 MILES

0 5 KILOMETERS

Base from U.S. Geological Survey, 1:24,000, 1995

Massachusetts state plane projection, NAD83

Land-use data from Massachusetts GIS, 1999; RIGIS, 1995

Peters River

Branch River

Mumford

West River

Mill River

Mill Brook

Middle

River

Kettle

Brook

Nipmuc River

Chepachet River

Abbot

Run

B

Abbott

ranch River Peters River

B

L

A

C

KSTONE

RIVER

Mumford River

West River

Mill River

Nipmuc River

Quinsigamond

River

Middle

River

Kettle

Brook BLACKSTONE

RIVER

Mill Brook

Peters River

Branch River

Quinsigamond

River

Mumford River

West River

Mill River

Mill Brook

Middle

River

Kettle

Brook

Nipmuc River

Chepachet River

Abbott

Run

BLACKSTONE

RIVER

B

L

A

C

KSTONE

RIVER

B

L

A

C

KSTONE

RIVER

BLACKSTONE

RIVER

B

L

A

C

KSTONE

RIVER

71°45' 71°30'

42°

42°15'

EXPLANATION

Open water

Forest

Wetland

Open non-residential

High-density residential

Medium- to low-density residential

Commercial-Industrial-Transportation

LAND-USE / LAND-COVER 

CATEGORIES

MASSACHUSETTS

RHODE ISLAND

BLACKSTONE BASIN BOUNDARY

Figure 2. Land use in the Blackstone River Basin.

Description of the Basin 
Surficial Geology

Till and stratified glacial deposits that consist mainly of 

sand and gravel cover most of the basin (fig. 3). Till, which 

covers about 71 percent of the basin, is present mainly in 

upland areas (fig. 3). In southern New England, tills consist 

of unsorted material ranging in size from clay to boulders. 

Because the composition and degree of compaction vary 

widely, the permeability also varies widely. The horizontal 

hydraulic conductivity of tills derived from crystalline rocks 

has been found to range over approximately 4 orders of 

magnitude, from 0.004 feet per day (ft/d) for compact tills 

to 96 ft/d for loose, sandy tills (Melvin and others, 1992a). 

However, tills are compact and silty in most areas, so the 

lower end of this range is more representative of the hydraulic properties of tills in the basin (Randall and others, 1988). 

Tills are typically less than 15 ft thick. Bedrock outcrops are 

prevalent in some upland areas but are not areally extensive in 

the basin. 

Stream valleys are typically underlain by stratified glacial 

deposits. These stratified glacial deposits, which cover the 

remaining 29 percent of the basin, form the major aquifers 

in the basin. The sand and gravel aquifers in the lower part 

of the basin range from 10 to more than 120 ft thick and 

have horizontal hydraulic conductivities from 10 to 480 ft/d 

and transmissivities up to 40,000 feet squared per day (ft2/d) 

(Johnston and Dickerman, 1974a,b). Many of these aquifers 

have been developed for water supply. Recently deposited 

fine-grained alluvial sediments also are present locally in the 

stream valleys. 

Streamflow-Gaging Stations and Hydrology

The USGS currently (2006) operates eight continuousrecord streamflow-gaging stations in the basin as part of the 

ongoing cooperative stream-gaging network (fig. 4; table 1). 

Seven additional streamflow-gaging stations (also referred to 

as project stations) were installed between October 2003 and 

January 2004 for this study (fig. 4). Flows in the urbanized 

and densely populated headwaters of the basin are measured 

at stations on Kettle Brook at Auburn, Mass. (station no. 

01109439), the Quinsigamond River at North Grafton, Mass. 

(station no. 01110000), and the Blackstone River at Millbury, 

Mass. (station no. 01109730). Flows in these drainage areas 

are influenced by the relatively large amount of impervious 

area (10 percent), the presence of an extensive storm- and 

sanitary-sewer system that includes an area of combined 

sewers in downtown Worcester, and reservoir management 

associated with the Worcester water-supply system. Blackstone River flows at the Millbury station also are strongly 

influenced by return flows from the Upper Blackstone Water 

Pollution Abatement District (UBWPAD) treatment plant, 

2.5 mi upstream. Mean annual discharge at the Millbury station for the period of record (2002–2004 water years1

) was 

175 cubic feet per second (ft3/s). The highest peak discharge 

at this station was 3,450 ft3/s in April 2004 and the lowest 

daily mean discharge was 28 ft3/s in August 2002 and 

October 2003 (Socolow and others, 2005). 

Flows in the major tributaries in the central part of the 

basin are measured at streamflow-gaging stations on the 

Mumford River at Uxbridge, Mass. (station no. 01111050); 

the Branch River at Forestdale, R.I. (station no. 01111500); 

the West River at Uxbridge, Mass. (station no. 01111200); 

the Peters River at Woonsocket, R.I. (station no. 01112382); 

and the Mill River at Woonsocket, R.I. (station no. 01112268) 

(fig. 4). Flows in all four drainage areas are affected to varying 

degrees by water-supply withdrawals, wastewater-return flows 

and reservoir management. In particular, peak flows in the 

West River are affected by regulation at the West Hill Dam for 

flood control, and low flows in the Mill River may be affected 

by periodic withdrawals from Harris Pond to supplement the 

City of Woonsocket water supply during peak demand. The 

drainage area to the station on the Blackstone River at Woonsocket, R.I. (station no. 01112500), below these major tributaries, is 416 mi2

 or approximately 88 percent of the basin area. 

This station has been in operation since 1929, providing a 

long-term record of streamflow in the basin. The mean annual 

discharge at the Woonsocket station for the period of record 

was 775 ft3/s, with a maximum peak discharge of 32,900 ft3/s 

in August 1955, and a minimum daily mean discharge of 

21 ft3/s in August 1934 (Socolow and others, 2005). 

Flows in the drainage area between the Woonsocket station and the mouth of the basin are measured at the stations 

on Abbott Run at Valley Falls, R.I. (station no. 01113760) 

and the Blackstone River at Pawtucket, R.I. (station no. 

01113895). Similar to the Worcester area, this part of the 

basin is relatively urban, with a higher population density, 

more impervious area, and a greater proportion of the drainage area served by public water and sewers than other parts of 

the basin. Water supplies for the cities of Woonsocket (withdrawn from Crookfall Brook and Mill River) and Pawtucket 

(withdrawn from Abbott Run) are obtained from this part of 

the basin. Streamflow in the Abbott Run subbasin is affected 

by surface-water and ground-water withdrawals and reservoir management for the city of Pawtucket water supply. The 

drainage area to the station on the Blackstone River at Pawtucket is 474 mi2

, representing nearly 100 percent of the basin 

area. The mean annual discharge at the Pawtucket streamflow-gaging station for the period of record (2004 water year) 

was 852 ft3/s. Flow at this station is highly correlated to flow 

at the Woonsocket station. 

1

 The water year begins on October 1 and ends on September 30 of the following year. For example, water year 2005 began October 1, 2004 and ended 

September 30, 2005.

 A Precipitation-Runoff Model for the Blackstone River Basin
0 2.5

2.5

5 MILES

0 5 KILOMETERS

Peters River

Quinsigamond

River

Mumford

River

West River

Mill River

Branch River

Chepachet River

Nipmuc River

Kettle 

Brook

Middle

River

Mill Brook

Abbott

Run

BLACKSTONE

RIVER

BLACKSTONE RIVER

Base from U.S. Geological Survey, 1:24,000, 1995

Massachusetts state plane projection, NAD83

Digital surficial geology data from MassGIS, 1999; RIGIS, 1989

71°45' 71°30'

42°

42°15'

EXPLANATION

SAND AND GRAVEL

TILL

OPEN WATER

BASIN BOUNDARY

Figure 3. Surficial geology in the Blackstone River Basin.

Description of the Basin 
#

#

#

#

#

#

#

#

#

#

#

#

#

#

#

#

#

#

#

#

#

#

#

01175670

01115187

01115098

01113695

01112500

01111500 01111300

01110500

01110000

01109403

01103280

01095375

01095220

01111200

01109730

01113760

01113895

01112382 01112268

01111410

01111050

01109439

MASSACHUSETTS

MASSACHUSETTS

CONNECTICUT

RHODE ISLAND

RHODE ISLAND

SEEKONK

RIVER

NARRAGANSETT

BAY

Base from U.S. Geological Survey, 1:24,000, 1995

Massachusetts state plane projection, NAD83

Peters River

Quinsigamond

River

Mumford River

West River

Mill River

Chepachet River

Nipmuc River

Kettle

 Brook

Middle

River

Mill Brook

Abbott

Run

Branch River

BLACKSTONE

RIVER

BLACKSTONE RIVER

01111300

#

EXPLANATION

OPEN WATER

BASIN BOUNDARY

STREAMFLOW-GAGING

STATION AND IDENTIFIER—

Red indicates stations installed

for this study. 

0 5 10 MILES

0 5 10 KILOMETERS

72° 71°45' 71°30'

41°45'

42°

42°15'

Figure 4. Streamflow-gaging stations in the Blackstone River Basin and surrounding areas.

 A Precipitation-Runoff Model for the Blackstone River Basin
The average slope of the Blackstone River between Worcester and the mouth of the basin is about 7 feet per mile (ft/mi). 

Approximately 125 dams with heights greater than 6 ft (Federal 

Emergency Management Agency, 1994) and wetlands in the 

stream valleys create flat-water conditions throughout the basin. 

A majority of the dams are relatively low-profile “run-ofriver” structures that do not produce large ponded areas. 

Larger dams with flow-control structures are present on the 

recreational, flood-control, and water-supply reservoirs. 

There also are five facilities that generate hydroelectric power 

(Riverdale Mills, Thundermist, Synergics, Elizabeth Webbing, 

and Central Falls) and one thermoelectric power-generation 

facility (Ocean State Power) on the Blackstone River. The 

hydroelectric facilities attempt to keep inflow and outflow 

rates equal to maintain aquatic habitat and water quality, and 

are thus considered run-of-river facilities (Barlow, 2003). As 

such, these facilities are not considered explicitly in the HSPF 

model. Withdrawals from the Ocean State Power facility are 

100 percent consumed by evaporation, and hourly withdrawals 

from this facility are included in the model.

Wetlands

Combined forested and non-forested wetlands compose 

about 7.7 percent of the basin area (23,395 acres). Approximately 71 percent of the wetlands are forested (fig. 5). 

Wetlands are fairly evenly distributed throughout the basin, 

mainly as discontinuous areas bordering stream channels. 

More extensive wetlands are present along the Blackstone 

River above the confluence with the West River in Uxbridge, 

and in the southeastern part of the basin. Fewer wetlands are 

in the headwaters of the basin in Worcester and adjacent 

developed areas. Wetlands in proximity to stream channels are 

an important aspect of the hydrology of the basin because they 

reduce peak flows and increase evapotranspiration losses 

(Zarriello and Bent, 2004).

Table 1. Streamflow-gaging stations in the Blackstone River Basin, Massachusetts and Rhode Island.

[USGS, U.S. Geological Survey; period of record represents the streamflow data available at the time of model development; ft3/s, cubic feet per second; 

mi2, square miles; Mass., Massachusetts; R.I., Rhode Island]

Station location

USGS 

station 

number

Period of 

record

Average 

discharge for 

period of record 

(ft3/s)

Drainage 

area 

(mi2)

Number of 

dams in 

drainage area

Station 

installed for 

this study

Kettle Brook, Auburn, Mass. 01109439 10/1/2003–9/30/2004 28.2 18.4 10 X

Quinsigamond River, North Grafton, Mass. 01110000 10/1/1939–9/30/2004 40.8 25.6 5

Blackstone River, Millbury, Mass. 01109730 7/24/2002–9/30/2004 175 72.2 27

Blackstone River, Northbridge, Mass. 01110500 12/7/1939–9/30/2003 269 140 48

Mumford River, Uxbridge, Mass. 01111050 10/1/2003–9/30/2004 92.3 56.2 22 X

West River, Uxbridge, Mass. 01111200 3/23/1962–9/30/1990 48.9 27.9 4

Nipmuc River, Harrisville, R.I. 01111300 3/1/1964–9/30/2004 30.3 15.6 1

Chepachet River, Gazzaville, R.I. 01111410 1/13/2004–9/30/2004 32.0 19.2 5 X

Branch River, Forestdale, R.I. 01111500 1/24/1940–9/30/2004 174 91.3 19

Mill River, Woonsocket, R.I. 01112268 1/13/2004–9/30/2004 49.8 33.1 6 X

Peters River, Woonsocket, R.I. 01112382 1/13/2004–9/30/2004 21.2 12.3 0 X

Blackstone River, Woonsocket, R.I. 01112500 2/22/1929–9/30/2004 775 416 109

Catamint Brook, Cumberland, R.I. 01113695 7/30/1999–9/30/2004 6.20 3.5 1

Abbott Run, Valley Falls, R.I. 01113760 12/9/2003–9/30/2004 51.9 27.7 5 X

Blackstone River, Pawtucket, R.I. 01113895 10/1/2003–9/30/2004 852 474 124 X

Description of the Basin 
0 2.5

2.5

5 MILES

0 5 KILOMETERS

Base from U.S. Geological Survey, 1:24,000, 1995

Massachusetts state plane projection, NAD83

Digital wetland data from MassGIS, 2004; RIGIS, 1993

Peters River

Quinsigamond

River

Mumford

River

West River

Mill River

Branch

River

BLACKSTONE

RIVER

71°45' 71°30'

42°

42°15'

EXPLANATION

FORESTED WETLAND

NON-FORESTED WETLAND 

OPEN WATER

BASIN BOUNDARY

Chepachet River

Kettle 

Brook

Middle

River

Mill Brook

Abbott

Run

Nipmuc River

Figure 5. Wetlands in the Blackstone River Basin.

10 A Precipitation-Runoff Model for the Blackstone River Basin
Water Use

In 2000, approximately 467,000 residents lived in the 

Blackstone River Basin (U.S. Census Bureau, 2004a,b). A 

summary of municipal water use for the towns in the basin is 

provided in table 2. There are 27 major public-water suppliers in the basin, of which 18 are in Massachusetts and 9 are 

in Rhode Island. Water suppliers may rely upon their own 

sources, purchase water from other suppliers, or use a combination of sources. For towns near the basin boundary, water 

from outside the basin may be conveyed across the basin 

boundary to a given distribution area. Similarly, wastewater 

in public sewer systems may be conveyed outside the basin 

for disposal. The distribution of public water and public sewer 

systems is shown in figure 6.

Both surface water and ground water are used for water 

supply. Woonsocket, R.I., and Worcester, Mass., use surface 

water as the sole source, whereas Cumberland, R.I., and Pawtucket, R.I., use a combination of surface water and ground 

water. Worcester also imports water from the Nashua River 

Basin to supplement its water supply. Other communities rely 

primarily on ground water obtained from municipal wells 

completed in sand and gravel aquifers. Residents in areas not 

served by public water systems obtain water from private wells 

completed in either the bedrock or sand and gravel aquifers. 

Water is used to meet domestic, commercial, industrial, 

and agricultural needs. For 1995–1999, the largest aggregate 

withdrawal in the lower Blackstone River Basin (198 mi2) was 

for domestic supply (50 percent), followed by industrial (20 percent), commercial (20 percent), and irrigation (1 percent), which 

includes agricultural and golf-course irrigation (Barlow, 2003). 

The remaining 9 percent of water use was not accounted for in 

supplier’s billing records (non-account water use). Data show 

that domestic water use is highest during the summer months 

due to lawn and garden watering and other seasonal uses. 

Similar water-use statistics for the entire basin are not available, 

but patterns are likely similar. Water-withdrawal information 

compiled for the entire basin for this study indicates that total 

municipal and commercial/industrial water withdrawals averaged about 66 million gallons per day (Mgal/d) for 1997–2001.

Wastewater disposal takes place at National Pollution 

Discharge Elimination System (NPDES) permitted outfalls 

and private septic systems. The Blackstone River Basin 

receives wastewater-return flows from 10 municipal 

wastewater-treatment facilities. In the lower Blackstone River 

Basin, 68 percent of the total wastewater disposal for 1995–

1999 was municipal wastewater disposed at treatment-facility 

outfalls (Barlow, 2003). The remaining 32 percent was selfdisposed, of which 25 percent was disposed at commercial 

and industrial NPDES outfalls and 75 percent was disposed at 

private septic systems. Similar wastewater-disposal statistics 

for the entire basin are not available, but disposal patterns 

are likely similar. Water-return information compiled for the 

entire basin for this study indicates that total return flows from 

wastewater-treatment facilities and commercial and industrial 

NPDES outfalls averaged about 54 Mgal/d for 1997–2001.

Precipitation-Runoff Model for the 

Blackstone River Basin

Streamflow in the Blackstone River Basin was simulated with HSPF, version 12 (Bicknell and others, 2000). 

HSPF was chosen because it produces detailed simulations 

of streamflow, which is a primary subject of the study, and 

because HSPF has been successfully used to study watermanagement alternatives in other basins in New England 

(Zarriello and Bent, 2004; Zarriello and Ries, 2000). The software code for HSPF is publicly available, free, and has been 

rigorously tested by developers and users. The HSPF model of 

the Blackstone River Basin was developed by (1) developing 

a conceptual model to represent the hydrology of the basin, 

(2) compiling and processing the necessary input data and 

constructing the model, (3) calibrating the model to improve 

the simulation accuracy, and (4) evaluating the performance of 

the calibrated model. 

Functional Description of HSPF

HSPF is a mathematical model designed to simulate the 

hydrology and water quality of a river basin; however, only 

the hydrologic-simulation capability of HSPF was used in 

this study. Runoff from a basin is quantified by the continuous simulation of hydrologic response to climatic and human 

stresses on the basis of the principle of conservation of water 

mass—that is, inflow equals outflow plus or minus changes 

in storage. In HSPF, a basin is represented by a group of 

hydrologically similar areas that are referred to as hydrologic 

response units (HRUs) that drain into a network of reaches 

(RCHRESs) consisting of streams, lakes, or reservoirs. The 

drainage area around each RCHRES is referred to as a subbasin. For each HRU and RCHRES, the model computes 

a water budget (inflows, outflows, and changes in storage) 

for each time step. A complete description of the processes 

involved in computing water budgets and required input model 

parameters is given in the “HSPF User’s Manual” (Bicknell 

and others, 2000). In the following discussion, model features 

such as parameters, computed time series, control files, and 

model block names are denoted by capital letters.

HRUs reflect areas of similar land use, surficial geology, and other factors deemed important to produce a similar 

hydrologic response to precipitation and potential evapotranspiration. HRUs are divided into pervious-area land segments 

(PERLNDs) and impervious-area land segments (IMPLNDs). 

These land segments are represented by zones, which define 

storages, and processes, which move water between the zones. 

PERLNDs and IMPLNDs have zones that retain precipitation 

at the surface as interception storage or snowpack storage. 

All water that is not evaporated produces surface runoff from 

IMPLNDs. By contrast, PERLNDs allow excess precipitation 

to infiltrate into the subsurface, where storages and processes 

are represented by upper, lower, and ground-water zones. 

Precipitation-Runoff Model for the Blackstone River Basin 11
Table 2. Summary of water use by town in the Blackstone River Basin, Massachusetts and Rhode Island.—Continued

[Public water and public sewer systems in the basin are shown in fig. 6. Town: For towns that straddle the basin boundary, information refers only to the area of the town in the Blackstone River Basin. UBWPAD, Upper Blackstone Water Pollution Abatement District; WWTP, wastewater-treatment plant; —, not applicable]

Town

Area in 

basin, in 

percent

Water supply Wastewater Time interval 

of reported 

data

Remarks Public 

system

Sources 

in basin

Public 

system

Return 

flows in 

basin

Massachusetts

Attleboro 4.0 Yes No Yes No — No municipal withdrawals from or wastewater returns to the basin.Auburn 93.3 Yes Yes Yes Yes Monthly/

Daily

Municipal supplies also purchased from Worcester Water Department. Parts of town served by private 

wells and septic systems.

Bellingham 48 Yes Yes Yes Yes Monthly Additional municipal withdrawals outside the basin. Parts of town served by private wells and septic 

systems.

Blackstone 100 Yes Yes Yes Yes Daily Additional municipal supplies purchased from Woonsocket Water Division. Parts of town served by 

private wells and septic systems.

Boylston 20.5 Yes Yes No — Monthly Additional municipal withdrawals outside basin. All wastewater goes to septic systems. Parts of town 

served by private wells.

Douglas 86.3 Yes Yes Yes Yes Monthly Most of town served by private wells and septic systems.Franklin 9.2 Yes No Yes No — Most of town served by private wells and septic systems.Grafton 93.3 Yes Yes Yes Yes Monthly Parts of town served by private wells and septic systems.Holden 18.4 Yes Yes Yes Yes Monthly Interbasin transfer from Kendall Reservoir to Holden Reservoir No. 1 to supplement Worcester water 

supply. Municipal supplies purchased from Worcester Water Department. Parts of town served by private wells and septic systems.

Hopedale 80.2 Yes Yes Yes Yes Monthly Municipal supplies also purchased from Milford Water Department. Parts of town served by private 

wells and septic systems.

Hopkinton 12.6 Yes No Yes No — No municipal withdrawals from or wastewater returns to the basin. Parts of town served by private wells 

and septic systems. 

Leicester 32.8 Yes Yes Yes Yes Monthly Additional municipal wells outside basin. Parts of town served by private wells and septic systems. Mendon 98.3 Yes No No — — Municipal supplies purchased from Milford Water Department. Most of town served by private wells 

and septic systems. 

Milford 14.2 Yes No Yes No — No municipal withdrawals from or wastewater returns to the basin. Parts of town served by private wells 

and septic systems.

Millbury 99.6 Yes Yes Yes Yes Monthly Additional municipal supplies purchased from Worcester Water Department. Parts of town served by 

private wells and septic systems. 

Millville 100 No — No — — Town served entirely by private wells and septic systems. North Attleboro 2.0 Yes Yes No — Monthly Parts of town served by private wells. All of town served by septic systems.Northbridge 100 Yes Yes Yes Yes Monthly Parts of town served by private wells and septic systems. Oxford 4.8 No — No — — All of town served by private wells and septic systems. Paxton 24.2 Yes Yes No — Monthly Municipal wells operated by Leicester Water Department. Municipal supplies purchased from Worcester 

Water Department. All of town on septic systems.

12  A Precipitation-Runoff Model for the Blackstone River Basin
Table 2. Summary of water use by town in the Blackstone River Basin, Massachusetts and Rhode Island.—Continued

[Public water and public sewer systems in the basin are shown in fig. 6. Town: For towns that straddle the basin boundary, information refers only to the area of the town in the Blackstone River Basin. UBWPAD, Upper Blackstone Water Pollution Abatement District; WWTP, wastewater-treatment plant; —, not applicable]

Town

Area in 

basin, in 

percent

Water supply Wastewater Time interval 

of reported 

data

Remarks Public 

system

Sources 

in basin

Public 

system

Return 

flows in 

basin

Plainville 13.8 No — No — — All of town served by private wells and septic systems.Shrewsbury 63.2 Yes Yes Yes Yes Monthly Municipal supplies purchased from Worcester Water Department. Most municipal wastewater 

transferred across basin boundary to Westborough for treatment. Small parts of town on private water and septic systems. 

Sutton 98.1 Yes Yes Yes Yes Monthly Most of town served by private wells and septic systems.Upton 96.8 Yes Yes Yes Yes Monthly Most of town served by private wells and septic systemsUxbridge 100 Yes Yes Yes Yes Monthly Parts of town served by private wells and septic systems.Webster 0.9 No — No — — All of town served by private wells and septic systems.West Bolyston 7.9 Yes Yes Yes Yes — Municipal water purchased from Worcester Water Department and municipal wastewater 

returned to UBWPAD.

Westborough 2.1 Yes No Yes No — No municipal withdrawals from or wastewater returns to the basin. Parts of town served by private water 

and septic systems. 

Worcester 99.3 Yes Yes Yes Yes Monthly/ 

Daily

Municipal water supplied by Worcester Water Department. Municipal wastewater returned to UBWPAD 

and Millbury WWTPs. 

Wrentham 27.2 Yes No No — — No municipal withdrawals from or wastewater returns to the basin. All of town served by septic systems. 

Rhode Island

Burrillville 85.2 Yes Yes Yes Yes Monthly Most of town served by private wells and septic systems. Central Falls 60.5 Yes Yes Yes No Monthly Municipal supplies purchased from the Pawtucket Water Supply Board, and wastewater treated by the 

Narragansett Bay Commission Facility at Bucklin Point. 

Cumberland 100 Yes Yes Yes No Monthly Municipal supplies purchased from the Pawtucket Water Supply Board and the Cumberland Water 

Department, and wastewater treated by the Narragansett Bay Commission Facility at Bucklin Point. Northern part of town served by private wells and septic systems. 

Glocester 43.6 No — No — — All of town served by private wells (or minor public suppliers) and septic systems. Lincoln 37.0 Yes Yes Yes No Monthly Municipal water supplied by the Lincoln Water Commission and wastewater treated by the Narragansett 

Bay Commission Facility at Bucklin Point. Parts of town on private wells and septic system. 

North Smithfield 82.4 Yes Yes Yes Yes Monthly Municipal water supplied by Slatersville Public Supply and wastewater treated by the Woonsocket 

Wastewater Treatment Facility. Most of town served by private wells and septic systems. 

Pawtucket 6.3 Yes Yes Yes No Monthly Municipal water supplied by the Pawtucket Water Supply Board and wastewater treated by the Narragansett Bay Commission Facility at Bucklin PointSmithfield 5.9 Yes No Yes No — No municipal withdrawals from or wastewater returns to the basin. Parts of town served by private wells 

and septic systems.

Woonsocket 100 Yes Yes Yes Yes Monthly Small parts of town served by private water and septic systems. 

Precipitation-Runoff Model for the Blackstone River Basin 13
Figure 6. Distribution of public water and public sewer systems in the Blackstone River Basin.

14  A Precipitation-Runoff Model for the Blackstone River Basin

MASSACHUSETTS

CONNECTICUT

RHODE ISLAND

HOLDEN

SUTTON

CHARLTON

DOUGLAS

OXFORD

UPTON

WORCESTER

UXBRIDGE

FRANKLIN

DUDLEY

GRAFTON

HOPKINTON

NATICK

LEICESTER

MENDON

AUBURN

FRAMINGHAM

MILLIS

PAXTON

BOYLSTON

WRENTHAM

HOLLISTON

MILFORD

MILLBURY

WAYLAND

SHREWSBURY

WEBSTER

SHERBORN

MARLBOROUGH

ASHLAND

WESTBOROUGH

MEDWAY

NORTHBRIDGE

NORTHBOROUGH

ATTLEBORO

PLAINVILLE

SOUTHBOROUGH

BELLINGHAM

BLACKSTONE

WEST 

BOYLSTON

NORTH 

ATTLEBOROUGH

MILLVILLE

HOPEDALE

FOSTER

SCITUATE

GLOCESTER

BURRILLVILLE

SMITHFIELD

JOHNSTON

LINCOLN

CUMBERLAND

PROVIDENCE

NORTH 

SMITHFIELD

PAWTUCKET

WOONSOCKET

NORTH 

PROVIDENCE

CENTRAL

 FALLS

0 2.5

2.5

5 MILES

0 5 KILOMETERS

Base from U.S. Geological Survey, 1:24,000, 1995

Massachusetts state plane projection, NAD83

Sewer line and water line data from RIGIS (1995), Central Massachusetts,

Regional Planning Commission, and individual municipalities

Peters River

Quinsigamond

River

Mumford

River

West River

Mill River

Branch

River

Chepachet River

Kettle 

Brook

Middle

River

Mill Brook

Abbott

Run

Nipmuc River

BLACKSTONE

RIVER

BLACKSTONE

RIVER

71°45' 71°30'

42°

42°15'

EXPLANATION

PUBLIC SEWER

PUBLIC SEWER

AND PUBLIC WATER

PUBLIC WATER 

OPEN WATER

BASIN BOUNDARY
Processes that control the rate of infiltration and change 

in subsurface storage make simulation of PERLNDs considerably more complex than simulation of IMPLNDs. In 

the model simulation, surface runoff from PERLNDs and 

IMPLNDs, and subsurface discharge from PERLNDs are 

typically directed into reaches; however, water can be directed 

elsewhere if desired.

RCHRESs are model elements that represent a length 

of stream channel or reservoir. The downstream end of 

each RCHRES is referred to as a node. Nodes are typically 

placed to define channel segments with similar physical 

properties, such as reach segments with similar slope and 

width, junctions of tributary streams, lakes and reservoirs, 

and locations of data-collection sites. Nodes can be placed 

at other locations where estimates of streamflow are desired, 

such as upstream and downstream from municipal well 

fields, water diversions, or discharges of contaminants. The 

hydraulic characteristics used for kinematic wave routing of 

water in a RCHRES are defined by its storage-discharge properties specified in a function table (FTABLE) of the model 

input. The FTABLE characterizes the hydraulic properties 

of the reach by defining the relation between depth, storage, 

and discharge.

HSPF requires two primary input files for its operation, 

the User Control Input (UCI) file and the Watershed Data 

Management (WDM) file. The UCI file directs the modelprocess algorithms and sets user-specified input parameters. 

The three primary model elements, PERLNDs, IMPLNDs, 

and RCHRESs, are organized by blocks in the UCI file. 

Within each block are modules and submodules that define 

the movement of water and changes in storage between zones. 

Some modules are mandatory for simulations and others 

are optional. For example, the PERLND block requires the 

PWATER module to simulate the movement of water, but the 

SNOW module is optional for simulating snowpack buildup 

and melt. The SCHEMATIC or NETWORK blocks are used 

to represent the physical layout of the basin. The area of 

each IMPLND and PERLND that drains to a RCHRES (also 

referred to as a reach) is defined in this section of the model 

to formulate subbasins. The SCHEMATIC or NETWORK 

blocks also are used to define the linkage of one RCHRES to 

another. The MASSLINK section associated with a SCHEMATIC block or NETWORK block controls the linkage of 

flow components between model elements. Typically, this 

linkage involves routing (1) surface runoff from PERLNDs 

and IMPLNDs to reaches, (2) interflow and base flow from 

PERLNDs to reaches, and (3) streamflow from reach to reach. 

A number of other blocks are required for administrative functions, such as controlling the operational sequence of the program, directing the model to external sources of data, writing 

outputted time-series data, and defining the linkage between 

model elements. Blocks also are available for data manipulation, displaying and reporting model results, and other optional 

model features.

The inflows to and outflows from a stream reach, as 

defined for the Blackstone River Basin model, are illustrated in figure 7. Surface runoff can discharge to a reach 

from impervious surfaces (SURI) and pervious surfaces 

(SURO). Infiltrated water can discharge to the reach through 

the subsurface as interflow (IFWO), which is analogous to 

a fast-responding shallow subsurface flow, or from active 

ground water (AGWO), which is analogous to a slow-responding base-flow component, or, optionally, exit from an HRU 

as a deep ground-water flow that discharges outside of the 

basin (IGWI). Inflow to a reach also can come from upstream 

reaches (IVOL), direct precipitation, and other user-specified 

point sources such as treated wastewater. 

Volumetric outflow from a reach can be directed through 

five outflow exits (or gates). As illustrated in figure 7, up to three 

outflow exits were designated for each reach in the Blackstone 

River Basin model. Water from the time series of total municipal 

and commercial/industrial withdrawals was directed through 

the first outflow exit (OVOL 1) in reaches with this type of 

withdrawal. Water from the time series of cumulative residential 

withdrawals from private wells in areas with public sewers in the 

reach was directed through the second outflow exit (OVOL 2) 

in reaches with this type of withdrawal. Time series directed 

through exits 1 and 2 are read from the EXTERNAL SOURCES 

block of the UCI file from arrays OUTDGT 1 and OUTDGT 2, 

respectively. Water was routed downstream through the third outflow exit (OVOL 3) in reaches with both types of withdrawals; in 

reaches with no withdrawals, a single outflow exit representing 

outflow to the downstream reach was specified. 

Input Data Used for the Model

The WDM file is a binary file that efficiently stores large 

amounts of data. The WDM file stores input time-series data 

required for simulations and output time-series data generated 

by the model. The EXTERNAL SOURCES block of the UCI 

file reads data from the WDM file, and model generated timeseries are passed to the WDM file through the EXTERNAL 

TARGETS block of the UCI file. Output time series can be 

generated for any component in the simulation process defined 

in the “Time Series Catalog” section of the user’s manual, but 

streamflow time series are the primary output. Time-series 

data in the WDM file can be accessed, displayed, transformed, 

and plotted by use of software programs such as ANNIE, 

(Flynn and others, 1995), GenScn (Kittle and others, 1998), or 

WDMUtil (U.S. Environmental Protection Agency, 2004).

Dataset numbers (DSNs) and attribute information 

must exist in the WDM file to pass time-series data between 

the WDM file and the model. The WDM file is organized by 

DSNs and relational attribute information. The organization of 

the WDM file developed for the Blackstone River Basin model 

is summarized in table 3. The first 100 DSNs are used to store 

measured climatological and streamflow time series.

Precipitation-Runoff Model for the Blackstone River Basin 15
RCHRES

SURI

Evaporation

Precipitation

Inflow from

upstream

reach

(IVOL) Point-source

wastewater 

inflow

Outflow to 

downstream 

reach (OVOL3)

Outflow to pumped well 

or stream withdrawal 

(OVOL1 and 2)

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 ground-water flow (base flow)

RCHRES–Stream reach or reservoir segment

IVOL–Inflow volume

OVOLx–Outflow volume through individual exits

(x = 1–5) SURI–Surface runoff from impervious 

areas

SURO–Surface runoff from pervious areas

Impervious

surface

Figure 7. Inflows and outflows to a Hydrological Simulation Program–FORTRAN (HSPF) stream reach. 

(Modified from Zarriello and Bent, 2004.)

Datasets with numbers larger than 100 are used to store 

input withdrawal and return flow time series and model-generated streamflow time series, and are generally organized by 

reach. Attributes describe the data type, time step, location, 

and other important features of the data. The data type used 

in GenScn is defined by the constituent attributes IDCONS, 

which are defined for the Blackstone River Basin in table 4. 

The methods used to develop the climatological, withdrawal, 

return flow, and streamflow data time series for the HSPF 

model are described in the following sections. 

16  A Precipitation-Runoff Model for the Blackstone River Basin
Climate

Climatological data were obtained from the Northeast 

Regional Climate Center (NRCC). Data from T.F. Green 

Airport in Warwick, R.I. (KPVD, station no. 376698) and 

Worcester Regional Airport in Worcester, Mass. (KORH, 

station no. 99923), shown in figure 1, were used as input to 

the HSPF model. These two stations are the only first-order 

(stations that collect data in addition to precipitation and daily 

air temperatures) National Weather Service stations near the 

basin. The northwestern part of the basin was assigned the climatological data from the Worcester station and the southeastern part of the basin was assigned the climatological data from 

the Warwick station. The boundary between the two zones was 

set to coincide with the subbasin boundaries (fig. 8). The position of the climatological boundary was determined by calculating long-term precipitation and temperature statistics for 

seven nearby climatological stations, and comparing them to 

statistics from the Worcester and Warwick stations. Although 

there was considerable spatial scatter, a NW-SE trend was 

evident in the data, and the climate boundary was set at the 

approximate geographic midpoint between the two stations. 

Climatological data stored in the WDM file include precipitation, potential evapotranspiration, air temperature, dewpoint temperature, solar radiation, and wind speed. Precipitation and potential evapotranspiration are required by HSPF to 

simulate the movement of water, and the remaining parameters 

are required to simulate the accumulation and melting of 

snow and ice. All these climatological data, with the exception of solar radiation, were obtained in hourly time steps for 

January 1, 1960 to December 31, 2004. NRCC provides daily 

solar radiation (Langleys) computed from other climatological variables. WDMUtil was used to disaggregate the daily 

solar-radiation values to the hourly values needed for the snow 

calculations. The Jensen-Haise method (Jensen and Haise, 

1963; Rosenberry and others, 2004) was used to calculate 

daily potential evapotranspiration. To remove seasonal bias in 

potential evapotranspiration losses, the monthly variable coefficients used in the Jensen-Haise computation were adjusted 

from default values during model calibration. WDMUtil was 

used to disaggregate the daily potential evapotranspiration 

values to the hourly values needed for the simulations. 

Data gaps in the precipitation, air temperature, dew-point 

temperature, and wind speed records were estimated by calculating the mean of the measured values bracketing the missing 

interval. About 25 percent and 14 percent of the data from 

1960–2004 were missing at Worcester and Warwick, respectively. Most of the missing data (about 75 percent at Warwick 

and 98 percent at Worcester) were prior to 1980. The longest 

continuous interval of missing data for each station was 48 hours. 

Table 3. Organization and description of Dataset Numbers (DSNs) in the Watershed Data Management (WDM) file for the 

Hydrological Simulation Program–FORTRAN (HSPF) model of the Blackstone River Basin, Massachusetts and Rhode Island.

DSN Purpose

 1–100 Measured and computed climatic and streamflow data (DSN 6 is a constant used with a multiplier to compute residential 

withdrawals)

101–150 Total withdrawals from a stream reach 

200–250 Simulated hourly streamflow output by reach

301–350 Total withdrawals satisfied by streamflow for a reach

401– 450 Total wastewater returns to a reach 

501–549 Simulated daily streamflow output by reach

1000–1009 Miscellaneous withdrawals and return flows computed from other time series

2010–2509 Individual surface-water withdrawals, constant-rate ground-water withdrawals, and stream depletion from time-varying 

ground-water withdrawals, where

x01x–x50x second and third digits identify reach number, and 

xxx0–xxx9 last digit identifies individual withdrawal points (QU1A has additional withdrawals designated 9110, 9111, and 9112)

3010–3509 Individual wastewater return flows, where 

x01x–x50x second and third digits identify reach number, and 

xxx0–xxx9 last digit identifies individual return points

4001– 4016 Simulated deep ground-water discharge

5000–5149 Output of simulated flow components by drainage area for the Expert System for the Calibration of the Hydrological 

Simulation Program–FORTRAN (HSPEXP) program

Precipitation-Runoff Model for the Blackstone River Basin 17
Table 4. Constituent attributes (IDCONs) for the Watershed Data Management (WDM) file of the Hydrological 

Simulation Program–FORTRAN (HSPF) model of the Blackstone River Basin, Massachusetts and Rhode Island.

[ft3/s, cubic feet per second; mi/hr, miles per hour; °F, degrees Fahrenheit; PERLND, pervious land segment; IMPLND, impervious land 

segment; HSPEXP, expert system for the calibration of the Hydrological Simulation Program–FORTRAN model]

IDCONS Explanation (units)

FLOW Measured streamflow (ft3/s)

SIMQ Simulated streamflow, hourly and daily (ft3/s)

Climatological data

TEMP Measured air temperature, hourly (°F)

MINTEMP Minimum air temperature, daily (°F)

MAXTEMP Maximum air temperature, daily (°F)

DEWP Measured dew-point temperature, hourly (°F)

WIND Measured wind speed, hourly (mi/hr)

PREC Measured precipitation, hourly (inches)

DEVT Computed potential evapotranspiration, daily (inches)

PET Computed potential evapotranspiration, hourly (inches)

SOLR_DA Computed solar radiation, daily (Langleys)

SOLR Computed solar radiation, hourly (Langleys)

Water-use data

IMP/EXP Constant used to calculate residential imports to and exports from reach 

TWITH Total withdrawal from reach, hourly (ft3/s) 

WSPW Total withdrawal satisfied by streamflow from reach, hourly (ft3/s)

TRET Total return to reach, hourly (ft3/s)

SW-WTHDW Individual surface-water withdrawal, daily (ft3/s)

GW-WTHDW Individual ground-water withdrawal (constant rate), daily (ft3/s)

STRMDEPL Individual stream depletion for time-varying ground-water withdrawal, daily (ft3/s)

GC-WTHDR Individual golf-course withdrawal, daily (ft3/s)

RETURN Individual wastewater return flow, daily (ft3/s)

Flow or storage components from PERLNDs and IMPLNDs by drainage area to 

streamflow-gaging stations for HSPEXP computations

PERO Total runoff (inches)

SURO Surface runoff (inches)

IFWO Interflow (inches)

AGWO Active ground-water flow (inches)

UZSX Upper-zone storage (inches) 

LZSX Lower-zone storage (inches)

PETX Potential evapotranspiration (inches)

SAET Actual evapotranspiration (inches)

SNOP Total content of snowpack, water equivalent (inches)

SNOM Water yielded by snowpack to land surface (inches)

18  A Precipitation-Runoff Model for the Blackstone River Basin
Figure 8. Model reaches, subbasin boundaries, and the boundary between climatological zones for the Hydrological 

Simulation Program–FORTRAN (HSPF) model for the Blackstone River Basin.

Precipitation-Runoff Model for the Blackstone River Basin 19

MASSACHUSETTS

RHODE ISLAND

#

#

#

#

#

#

#

#

#

#

#

#

#

#

#

01113695

01112500 01111500

01111300

01110500

01110000

01111200

01109730

01113760

01113895

01112382

01112268

01111410

01111050

01109439

0 2.5

2.5

5 MILES

0 5 KILOMETERS

Base from U.S. Geological Survey, 1:24,000, 1995

Massachusetts state plane projection, NAD83

Peters River

Quinsigamond

River

Mumford River

West River

Mill River

Branch

River

Chepachet River

Kettle

Brook Middle

River

Mill Brook

Abbott

Run

Nipmuc River

BLACKSTONE

RIVER

BLACKSTONE

RIVER

WE1A BL2A

MU3A

QU1A

ML1A

NI1A AB1A

CL2A

BL8A

KE3A

MB1B

ML2A

PE1A

MU2A

QU2A

BR1A

BL7A

CH2A

TA2A

BL11

KE1A

TK1A

WE2A

AB2A

BL4A

PA1A

WH1A

CH1A

EM1A

BL2B

MU1A

BL12

KE2A

TA1A

BL10

BR2A

BL3A

CL3A

CR2A

CA1A

CR1A

DA1A

CL1A

BL9A

BL1A

BL6A

AB3A

BL13

BL5A

BL14

1

3

8

17

21

13

7

4

6

12

2

32 29

10

14

30

23

26

36

31

5

11

43

24

40

50

41

22

34

27

18

49

16

45

37

42

20

9

39

38

33

44

19

35

15

28

46

47

25

48

71°45' 71°30'

42°

42°15' 42°15'

CL2A

10

01111410

#

EXPLANATION

OPEN WATER

BASIN BOUNDARY

SUBBASIN BOUNDARY AND

MODEL LOCATION IDENTIFICATION 

ATTRIBUTE (IDLOCN) 

MODEL REACH NUMBER

CLIMATOLOGICAL ZONE BOUNDARY

STREAMFLOW-GAGING STATION

AND IDENTIFIER
Water Withdrawals 

The water withdrawals simulated in the model include 

(1) the ground-water and surface-water withdrawals for 

municipal water supply and commercial/industrial uses, 

(2) ground-water and surface-water withdrawals for golfcourse irrigation, and (3) ground-water withdrawals from private wells in residential areas with public sewers. The municipal and commercial/industrial withdrawals are described in 

greater detail below. Golf-course withdrawals are discussed 

in the following section. A discussion of how the residential 

withdrawals are treated in the model in areas both with and 

without public sewers is provided in the “Representation of the 

Basin” section of the report.

Detailed ground-water and surface-water withdrawal data 

for municipal and commercial/industrial withdrawals were 

collected for 1996–2001 from a variety of sources. These 

sources include a water-use database (NEWUDS) populated by 

Barlow (2003) for the Blackstone River Basin, Annual Statistical Reports filed by public-water suppliers and provided by 

the MADEP, the Water Management Act database provided 

by the MADEP, and Water Supply System Management Plans 

filed by water suppliers in Rhode Island and provided by the 

RIWRB, or, in some cases, the water suppliers themselves. The 

129 municipal and commercial/industrial withdrawals included 

in the model (including 18 withdrawals for golf-course irrigation that are described in detail in the following section) are 

shown in figure 9 and summarized in table 5. Of these withdrawals, 17 were from surface water and the remaining 112 

were from ground water. Of the ground-water withdrawals, 96 

were from the sand and gravel aquifer and 16 were from bedrock. 

The information available from each source differed considerably and therefore required various degrees of processing 

to format the data for input into the model. Withdrawals from 

municipal wells in Massachusetts typically were reported 

as monthly totals; however, in some cases daily withdrawals were reported. Periods of missing record due to unavailability of withdrawal records or equipment problems were 

most frequent for municipal withdrawals in Rhode Island and 

commercial/industrial withdrawals. At five locations in Rhode 

Island (table 5, shaded rows), measured withdrawals were not 

available, and the population served by the supplier (Barlow, 

2003) was used to estimate constant withdrawal rates for the 

calibration period. Values bracketing the period of missing 

record or average withdrawals for the period of missing record 

calculated from other years were used to estimate gaps in 

withdrawal records. Sixteen municipal and commercial/

industrial withdrawals in the model had periods of missing 

record requiring estimation. 

Withdrawals reported as monthly totals were disaggregated to daily withdrawals before values were stored as a time 

series in the WDM file. Daily withdrawals from surface-water 

sources and ground-water sources in towns with a blend of 

surface-water and ground-water supplies were obtained by 

dividing by the number of days in the month. By contrast, 

daily withdrawals from wells in towns with only ground-water 

supplies were disaggregated by use of smoothed daily withdrawal records from wells in the town of Blackstone, Mass. 

The town of Blackstone, which obtains water from four wells 

adjacent to the Mill River, measured withdrawals on a daily 

basis for the entire calibration period. The total daily withdrawals from these wells averaged 0.74 Mgal/d for 1996–2001. 

Daily fluctuations in these withdrawals were considered 

to reflect day-to-day water-supply demands in other towns 

in response to variable climatological conditions. Town of 

Blackstone records were not used to estimate daily withdrawals from towns that use both ground-water and surface-water 

supplies, however, because in systems such as these, short-term 

increases in demand can be met from reservoir storage rather 

than increased well withdrawals. 

The approach developed by Zarriello and Ries (2000) 

was used to smooth the town of Blackstone daily withdrawal 

record 1996–2001. To smooth the daily record, operationally 

related fluctuations in withdrawal rates were first removed by 

applying a 15-day moving average centered on the 8th day of 

the interval to the raw data. The smoothing period was determined empirically to retain reasonably large variability in the 

daily values while reducing the large operational fluctuations. 

Daily withdrawals were then computed for 71 wells where 

only monthly withdrawals were available by (1) computing 

monthly mean withdrawals from the smoothed town of Blackstone daily withdrawals, (2) computing the ratio between the 

smoothed daily withdrawals and monthly mean withdrawals 

for each day for the town of Blackstone wells, (3) computing 

the average daily withdrawals by month for towns where only 

monthly withdrawals are available, and (4) multiplying the 

average daily withdrawals by the daily ratios computed from 

the town of Blackstone data (Zarriello and Ries, 2000). 

Golf-Course Withdrawals

Irrigation withdrawals were calculated for the 18 golf 

courses in the basin (table 5). For most courses, information 

such as the number of irrigated acres, the source of irrigation 

water (for example, ground-water or surface-water withdrawals), and the volumes of water used for irrigation was 

not available. However, withdrawal data and the number of 

irrigated acres were available for six courses from the Massachusetts Water Management Act database. These measured 

withdrawals, which were reported as total annual volumes 

of water, were used to calibrate a procedure that was used to 

compute daily irrigation withdrawals at the golf courses in the 

basin. In the HSPF model, withdrawals for golf-course irrigation were assumed to be 100 percent consumed. 

To compute daily irrigation withdrawals at the golf 

courses in the basin, a daily irrigation demand was determined from antecedent climatic conditions. The use of 

climatological data (precipitation and potential evapotranspiration) to determine an irrigation demand is consistent 

with the approach used by Zarriello and Bent (2004) in the 

Usquepaug-Queen Basin. In that study, a logistic-regression 

equation was developed from measured irrigation data. 

20 A Precipitation-Runoff Model for the Blackstone River Basin
Figure 9. Locations of water withdrawals, transfers, and wastewater returns in the Blackstone River Basin.

Precipitation-Runoff Model for the Blackstone River Basin  21

MASSACHUSETTS

CONNECTICUT

RHODE ISLAND

MASSACHUSETTS

RHODE ISLAND

;Î"!

;Î"!

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FROM KENDALL RESERVOIR

0 2.5

2.5

5 MILES

0 5 KILOMETERS

Peters River

Quinsigamond

River

Mumford River

West River

Mill River

Chepachet River

Kettle 

Brook

Middle

River

Mill Brook

Abbott

Run

Nipmuc River

BLACKSTONE

RIVER

BLACKSTONE RIVER

71°45' 71°30'

42°

42°15'

Base from U.S. Geological Survey, 1:24,000, 1995

Massachusetts state plane projection, NAD83

;Î"!

EXPLANATION

OPEN WATER

SUBBASINS THAT CONTAIN

RESIDENTIAL AREAS WITH

PUBLIC SEWER AND

PRIVATE WATER

BASIN BOUNDARY

SUBBASIN BOUNDARY

SURFACE-WATER TRANSFER

GROUND-WATER WITHDRAWAL

SURFACE-WATER WITHDRAWAL

WASTEWATER-RETURN FLOW
Table 5. Municipal, commercial/industrial, and golf-course withdrawals in the Blackstone River Basin, 

Massachusetts and Rhode Island.—Continued

[Aquifer refers to the geologic unit from which ground water was withdrawn. Distance to stream refers to the distance used to compute streamflow depletion for 

time-varying ground-water withdrawals. Shading indicates that streamflow depletion was not computed because only a constant ground-water withdrawal rate 

was available. WDM, watershed data management; DSN, dataset number; ft, feet; Mgal/d, million gallons per day; s&g, sand and gravel aquifer; b, bedrock 

aquifer; —, not applicable because the withdrawal was from surface water; NA, not available]

Model 

reach 

number

WDM file 

DSN 

Identification or 

permit number

Source 

name Town Aquifer

Distance 

to stream 

(ft)

Average withdrawal 

rate 1997–2001 

(Mgal/d)

1 2010 2039000-01G Well 1 Boylston s&g 950 0.145

1 2011 2039000-02G Well 2 Boylston s&g 1,470 0.0132

1 2012 2039001-01G Well 1 Boylston s&g 380 0.126

1 2013 21211001 Four wells and Hovey Pond combined North Grafton — — 0.0180

1 2014 2271000-02G Sewell Street Well 4 Shrewsbury s&g 480 0.834

1 2015 2271000-04G Lambert’s Sand Pit Well 3.1 Shrewsbury s&g 1,330 0.365

1 2016 2271000-05G Lambert’s Sand Pit Well 3.2 Shrewsbury s&g 1,330 0.0411

1 2017 2271000-06G Sewell Street Well 5 Shrewsbury s&g 670 0.00251

1 2018 2271000-07G Home Farm Well 6.1 Shrewsbury s&g 80 0.801

1 2019 2271000-08G Home Farm Well 6.2 Shrewsbury s&g 30 1.71

1 9110 9P21227102 Well 1 Shrewsbury s&g 330 0.216

1 9111 NA Worcester Green Hill Municipal Golf 

Club

Worcester s&g 1,000 10.0368

1 9112 NA Worcester Country Club Worcester — — 0.0394

3 2030 21234801 Norton Company five wells combined Worcester s&g 980 0.202

5 2050 2348000-06S Holden Reservoir No. 1 surface-water 

intake

Holden — — 23.3

6 2060 NA Tatnuck Country Club Worcester s&g 1,000 0.0227

7 2070 2110000-02G Worcester Street Gravel Packed Well 1 Grafton s&g 70 0.608

7 2071 2110000-03G East Street Gravel Packed Well 2 Grafton s&g 50 0.138

7 2072 2110000-04G East Street Gravel Packed Well 3 Grafton s&g 70 0.196

7 2073 2110004-01G Countryside Condos Well 1 Grafton s&g 520 0.000498

8 2080 2032000-01G Well 1 Blackstone s&g 200 0.184

8 2081 2032000-02G Well 2 Blackstone s&g 20 0.0517

8 2082 2032000-04G Well 4 Blackstone s&g 130 0.231

8 2083 2032000-05G Well 5 Blackstone s&g 110 0.286

8 2084 NA Harris Pond surface-water intake Woonsocket — — 0.178

9 2090 RI0100129 Wallum Lake surface-water intake Burrillville — — 0.0840

10 2100 1592020-02 Well 2 Burrillville s&g 740 0.0976

10 2101 1592020-03&3A Wells 3 and 3A combined Burrillville s&g 760 0.224

11 2110 2151000-01G Well 1 Paxton b 280 0.0486

11 2111 2151000-02G Well 2 Paxton b 100 0.0377

11 2112 2151000-03G Well 3 Paxton b 260 0.0510

11 2113 2348000-01S Lynde Brook Reservoir 

surface-water intake

Leicester — — 4.23

12 2120 2138000-01G TWF Mill Street Well Hopedale s&g 250 0.285

12 2121 2138000-02G Green Street Well Hopedale s&g 70 0.0763

12 2122 NA Hopedale Country Club Hopedale — — 0.0316

12 2123 NA Milford Country Club Milford s&g 1,000 10.0114

13 2130 2110000-05G Follette Street Gravel Packed Well 4 Grafton s&g 440 0.0394

13 2131 NA Pleasant Valley Country Club Sutton — — 0.0591

13 2132 2186000-01G Millbury Avenue Well Millbury s&g 70 0.502

13 2133 2186000-02G Oak Pond Well Millbury s&g 220 0.0414

13 2134 2290014-01G Hatchery Road Well Sutton s&g 1,350 0.125

13 2135 2290015-01G Pleasant Valley Country Club Sutton b 480 0.0112

13 2136 2290015-02G Pleasant Valley Country Club Sutton b 410 0.00447

22  A Precipitation-Runoff Model for the Blackstone River Basin
Table 5. Municipal, commercial/industrial, and golf-course withdrawals in the Blackstone River Basin, 

Massachusetts and Rhode Island.—Continued

[Aquifer refers to the geologic unit from which ground water was withdrawn. Distance to stream refers to the distance used to compute streamflow depletion for 

time-varying ground-water withdrawals. Shading indicates that streamflow depletion was not computed because only a constant ground-water withdrawal rate 

was available. WDM, watershed data management; DSN, dataset number; ft, feet; Mgal/d, million gallons per day; s&g, sand and gravel aquifer; b, bedrock 

aquifer; —, not applicable because the withdrawal was from surface water; NA, not available]

Model 

reach 

number

WDM file 

DSN 

Identification or 

permit number

Source 

name Town Aquifer

Distance 

to stream 

(ft)

Average withdrawal 

rate 1997–2001 

(Mgal/d)

14 2140 2017000-01G Well 1 Auburn s&g 170 0.367

14 2141 2017000-03G Well 3 Auburn s&g 400 0.149

14 2142 2017000-04G Well 4 Auburn s&g 300 0.193

14 2143 2017000-05G Well 5 Auburn s&g 160 0.249

14 2144 2017000-06G Well 6 Auburn s&g 270 0.131

14 2145 2017000-07G Well 7 Auburn s&g 590 0.145

14 2146 2017000-08G Well 8 Auburn s&g 490 0.0555

14 2147 2017000-09G Satellite Well # 6 West (Well 9) Auburn s&g 220 0.0492

14 2148 2017000-10G Satellite Well # 6 North (Well 10) Auburn s&g 240 0.00814

15 2150 NA Clearview Country Club Millbury s&g 1,000 10.0154

16 2160 2151009-01G Rock Well 1 Leicester b 670 0.00271

16 2161 2151009-02G Rock Well 2 Leicester b 690 0.00271

16 2162 2151009-03G Rock Well 3 Leicester b 600 0.00271

17 2170 21217902 Well 1 Mendon b 520 0.0401

17 2171 2303000-01G TWF Glen Avenue Well Upton s&g 260 0.0834

17 2172 2303000-02G West River Well Upton s&g 260 0.324

20 2200 2110001-01G Providence Road Gravel Packed Well 1 Grafton s&g 70 0.0640

20 2201 2110001-02G Ferry Street Well 1 Grafton s&g 240 0.0575

20 2202 2110001-03G Ferry Street Well 2 Grafton s&g 120 0.104

21 2210 9P321207702 Gilboa Pond surface-water intake Douglas — — 0.248

21 2211 2216000-01G Meadow Pond Tubular Well Field Northbridge s&g 10 0.700

21 2212 2216000-02G Cook Allen Brook Tubular Well Field Northbridge s&g 40 0.826

21 2213 NA Whitinsville Golf Club Whitinsville — — 0.0355

21 2214 NA Edgewood Golf Club Uxbridge s&g 500 10.00639

22 2220 21221602 Well 2 Northbridge s&g 290 0.185

23 2230 2077000-01G West Street Tubular Well Field Douglas s&g 50 0.0850

23 2231 2077000-02G West Street Gravel Packed Well Douglas s&g 640 0.0665

23 2232 2077000-03G Glenn Street Well 1 Douglas s&g 540 0.0534

23 2233 2077000-04G Glenn Street Well 2 Douglas s&g 480 0.0604

23 2234 NA Blackstone National Golf Club Sutton s&g 1,000 10.0387

23 2235 2290001-01G Well 1 Sutton b 140 0.0388

24 2240 2304000-01G Well 1 Uxbridge s&g 80 0.0697

24 2241 2304000-02G Well 2 Uxbridge s&g 70 0.0606

24 2242 2304000-03G Well 3 Uxbridge s&g 110 0.0816

25 2250 2304000-04G Well 4 (Bernat well field) Uxbridge s&g 690 0.384

25 2251 2304000-05G Well 5 (Bernat well field) Uxbridge s&g 420 0.114

25 2252 2304000-06G Well 6 (Bernat well field) Uxbridge s&g 550 0.139

26 2260 2025000-01G Well 1 Bellingham s&g 210 0.199

26 2261 2025000-02G Well 2 Bellingham s&g 100 0.0897

26 2262 2025000-03G Well 3 Bellingham s&g 20 0.0386

26 2263 2025000-04G Well 4 Bellingham s&g 210 0.304

26 2264 2025000-11G Well 11 Bellingham s&g 410 0.157

26 2265 2025000-12G Well 12 Bellingham s&g 360 0.201

26 2266 NA Bungay Brook Golf Club Bellingham s&g 500 10.0230

26 2267 NA The New England Country Club Bellingham — — 0.0369

29 2290 1647530 Sneech Pond surface-water intake Cumberland — — 0.897

Precipitation-Runoff Model for the Blackstone River Basin  23
Table 5. Municipal, commercial/industrial, and golf-course withdrawals in the Blackstone River Basin, 

Massachusetts and Rhode Island.—Continued

[Aquifer refers to the geologic unit from which ground water was withdrawn. Distance to stream refers to the distance used to compute streamflow depletion for 

time-varying ground-water withdrawals. Shading indicates that streamflow depletion was not computed because only a constant ground-water withdrawal rate 

was available. WDM, watershed data management; DSN, dataset number; ft, feet; Mgal/d, million gallons per day; s&g, sand and gravel aquifer; b, bedrock 

aquifer; —, not applicable because the withdrawal was from surface water; NA, not available]

Model 

reach 

number

WDM file 

DSN 

Identification or 

permit number

Source 

name Town Aquifer

Distance 

to stream 

(ft)

Average withdrawal 

rate 1997–2001 

(Mgal/d)

29 2291 NA Wentworth Hills Golf and 

Country Club

Plainville s&g 500 10.0456

29 2292 41235001 Four ponds and two wells combined Wrentham b 430 0.0267

30 2300 NA Seville Dyeing/Dorado Processing

Company surface-water intake

Woonsocket — — 2.04

30 2301 NA Ocean State Power surfacewater intakeWoonsocket — — 2.19

32 2320 NA Blissful Meadows Golf Club Uxbridge s&g 500 10.0493

36 2360 1559519 Wells 1 and 4 combined Burrillville s&g 10 0.00601

36 2361 1583825 Glendale Water Association Wells Burrillville b 1,030 0.00789

36 2362 1592019 Oakland Water Association Well Burrillville s&g 210 0.0170

37 2370 1615614 Driven Well Field North Smithfield s&g 160 0.0600

39 2390 1858411-02 Well 2 Burrillville s&g 150 0.113

39 2391 1858411-03 Well 3 Burrillville s&g 70 0.123

40 2400 1647530 Manville Well 1 Cumberland s&g 210 0.204

40 2401 1647530 Manville Well 2 Cumberland s&g 250 0.181

40 2402 RI12980071 Autocrat Well Lincoln b 1,400 0.0460

40 2403 NA Kirkbrae Country Club Lincoln s&g 1,000 10.0498

41 2410 1647530 Abbott Run Well 2 Cumberland s&g 70 0.00452

41 2411 1647530 Abbott Run Well 3 Cumberland s&g 40 0.00456

41 2412 4211001-01G Well 1 North Attleboro s&g 400 0.0298

41 2413 4211000-08G Adamsdale Well North Attleboro s&g 420 0.232

41 2414 4211000-09G Hillman Well North Attleboro s&g 280 0.821

41 2415 NA Chemawa Golf Course North Attleboro s&g 500 10.0423

41 2416 1592021 Well 6 Pawtucket s&g 10 0.188

41 2417 1592021 Well 7 Pawtucket s&g 150 0.259

41 2418 1592021 Well 8 Pawtucket s&g 80 0.265

41 2419 1592021 Well 9 Pawtucket s&g 10 0.260

42 2420 NA Reservoir No. 1 surface-water intake Woonsocket — — 1.51

43 2430 1900034 Nasonville Well Field B Burrillville s&g 120 0.00944

44 2440 NA Reservoir No. 3 surface-water intake Woonsocket — — 3.52

45 2450 1858423 Lonsdale Well 4 Lincoln s&g 200 0.143

45 2451 NA Lincoln Country Club Lincoln s&g 1,000 10.0440

46 2460 1592021 Happy Hollow surface-water intake Pawtucket — — 11.7

46 2461 1592021 Well 2 Pawtucket s&g 10 0.144

46 2462 1592021 Well 3 Pawtucket s&g 110 0.321

46 2463 1592021 Well 4 Pawtucket s&g 450 0.00465

49 2490 2017003-01G Rock Well 1 Auburn b 280 0.0108

49 2491 2017003-02G Rock Well 2 Auburn b 280 0.00404

49 2492 2017003-04G Rock Well 4 Auburn b 300 0.00462

49 2493 NA Pakachoag Golf Course Auburn s&g 1,000 10.00462

49 2494 2186000-03G No. 1 North Main Street Well Millbury s&g 180 0.485

49 2495 2186000-04G No. 2 North Main Street Well Millbury s&g 280 0.266

1

Measured withdrawals not available. Withdrawals estimated as described in text.

24  A Precipitation-Runoff Model for the Blackstone River Basin
water or from ground water. Ground-water withdrawals were 

processed with the STRMDEPL program (described in the 

following section), and surface-water withdrawals were not 

modified. Water was obtained from unknown sources at five 

courses, from ground-water sources (typically from a mix of 

holding ponds and wells) at eight courses, and from surfacewater sources (typically from instream ponds or directly from 

larger rivers) at the remaining five courses. Because most of 

the courses are in upland areas where surface-water sources 

capable of providing adequate water are scarce, the source of 

water was assumed to be ground water at the 5 courses that 

had no information, resulting in calculation of stream depletion at 13 of 18 golf courses. Because the distances between 

the ground-water wells and the nearest streams typically were 

not known, an assumed distance of 500 ft for courses in areas 

underlain by sand and gravel deposits and 1,000 ft for courses 

in areas underlain by till were used in the STRMDEPL program. A greater distance was used in till areas because these 

courses often are in upland areas where distances to the nearest stream are greater. All other STRMDEPL parameters were 

identical to those used for water-supply withdrawals.

Streamflow Depletion by Ground-Water Withdrawals

Streamflow depletion was determined for all time-varying 

ground-water withdrawals by use of the program STRMDEPL 

(Barlow, 2000). STRMDEPL produces a daily time series of 

the total streamflow depletion computed from the reported 

withdrawal record. Time series of streamflow depletion were 

computed from external to the HSPF program before the 

simulations were conducted. Streamflow-depletion time series 

for individual wells are included in the WDM file as DSN file 

numbers 2010 through 2495, 9110, 9111, and 9112 (table 5). 

Total streamflow depletion has two components: captured (or intercepted) discharge, which is ground water that 

would have discharged to the stream had the well not been 

pumped, and induced infiltration, which is streamflow drawn 

out of the channel to the aquifer. Thus, the total volume of 

streamflow depletion under long-term, steady-state conditions 

is very close to the total volume pumped from the well; the 

main effect of STRMDEPL is to dampen the magnitude and 

timing of the time-varying pumping rate, which results from 

the diffusivity of the aquifer (T/S, where T is the transmissivity and S the storativity or specific yield) and the distance of 

the well from the stream. An example of streamflow depletion computed from daily withdrawals at King’s Grant Water 

Company Well 1, 400 ft from Abbott Run in North Attleboro, Mass., is shown in figure 10. STRMDEPL is based on 

several simplifying assumptions, including that the aquifer is 

homogeneous, isotropic and semi-infinite in areal extent, that 

both the stream and the well fully penetrate the aquifer, and 

that the stage of the stream remains constant with time. To 

simulate long-term operation and produce initial streamflow 

depletion similar to the pumping rate at the start of the calibration period, wells were allowed to pump for 5,000 days 

prior to the analysis. 

It was found that the total potential evapotranspiration in the 

previous 2 days, total potential evapotranspiration in the previous 20 days, and the total precipitation in the previous 10 days 

were the most significant explanatory variables for determining 

the probability of golf-course irrigation taking place on a specific 

day. To determine irrigation demand in the Blackstone River 

Basin, the Worcester climatic data were used for golf courses 

in the northern part of the basin, and the Warwick climatic data 

were used for the courses in the southern part of the basin. 

To determine the irrigation demand, the climatologic 

variables were first adjusted to match the total annual volumes of water used for irrigation during 1996–2001 at the six 

courses with reported data. It was assumed that irrigation only 

took place from April and November (210 days). A reasonable combination was found to be 50 percent (an empirical 

adjustment factor) of the daily irrigation demand, where the 

irrigation demand was computed as the difference between the 

total precipitation in the previous 5 days and the total potential 

evapotranspiration in the previous 2 days. If the total precipitation in the previous 5 days exceeded the total potential evapotranspiration in the previous 2 days, irrigation was not applied. 

If, on the other hand, potential evapotranspiration exceeded 

precipitation, 50 percent of the difference was applied as 

irrigation for that day. The agreement between computed and 

observed annual irrigation volumes was improved further by 

adjusting the amount of irrigated acreage at each course. This 

was done because the year-to-year variability was reasonably 

represented, but the annual irrigation volumes were systematically too high or two low. The best-fit irrigated acreages were 

then used to calculate a ratio of irrigated acreage to golf-course 

size, represented by total yardage, for the six courses used in 

the calibration. This ratio was then applied to the other courses 

to determine the amount of irrigated acreage based on the size 

of the course. To develop time series for inclusion in the HSPF 

model, it was assumed that irrigation was applied at a constant 

rate for 24 hours on each day when irrigation took place.

This approach yielded temporally variable irrigation 

controlled by climate. For example, there were typically some 

long (2–3 week) stretches during the summer when there was 

no irrigation because of wet conditions. Although approximate, 

using climatic data to estimate periods of irrigation is more 

realistic than applying irrigation uniformly on a daily basis 

throughout the irrigation season. Because data were available 

to calibrate annual water use, this approach provided a reasonable estimate of total annual water use at each golf course. The 

median percent differences between observed and calculated 

annual volumes for the 6-year period for the six courses used 

in the calibration ranged from –2.0 percent to 24.2 percent. The 

total annual water use determined with the approach also is in 

reasonably good agreement with total use determined with irrigation water-use coefficients (0.015 Mgal/d/irrigated acre and 

0.012 Mgal/d/1,000 yards) developed by Barlow (2003) from 

an analysis of 70 golf courses in Massachusetts. 

To prepare the golf-course withdrawal time-series 

records for inclusion in the HSPF model, it was necessary to 

determine whether withdrawals were directly from surface 

Precipitation-Runoff Model for the Blackstone River Basin  25
STRMDEPL provides a direct measure of streamflow 

depletion caused by ground-water withdrawals. Therefore, 

although the actual locations of individual wells were used 

to calculate streamflow depletion, the withdrawals that 

result from the calculation are taken directly from the stream 

reach in the HSPF model. Streamflow depletion was computed for withdrawals from wells completed in bedrock and 

sand and gravel aquifers. Lithologic information was not 

readily available for most wells, so the surficial-geology data 

layer was used to determine whether the well was in an area 

underlain by till-mantled bedrock or unconsolidated sand 

and gravel deposits. 

Most of the high-capacity wells are in sand and gravel 

aquifers near streams and induce infiltration from streams to 

improve yields. The median distance of the sand and gravel 

wells to the nearest stream was 255 ft (table 5). Because sitespecific aquifer-thickness and lithologic data were not available for most of the wells in the model, a diffusivity value of 

12,700 ft2/d was used for all withdrawals in the sand and gravel 

aquifer, regardless of location. This value is based on a median 

transmissivity of 3,175 ft2/d for the sand and gravel aquifer 

(from an analysis of 378 wells in the lower Blackstone River 

Basin (P.E. Church, U.S. Geological Survey, written commun., 

2005), and a specific yield of 0.25. Streams underlain by sandand-gravel aquifers tend to have coarse streambed materials that 

do not limit the flux of water across the bed. The streambank 

leakance term was assigned a value of 0, indicating that the bed 

of the stream has the same hydraulic properties as the aquifer, 

which is equivalent to assuming that low-permeability streambed deposits that may impede flow are not present. 

Ground-water/surface-water interactions and aquifer 

properties are less well understood in upland areas underlain 

by till and bedrock than in the areas underlain by sand and 

gravel aquifers. Fourteen bedrock water-supply wells in the 

basin have time-variable withdrawals. Most are in upland 

areas where the rock is covered by till. Reported well depths 

range from 40 to 700 ft, but the depths are not known for most 

wells. The median distance of the bedrock wells included 

to the nearest stream was 420 ft (table 5). Because fractured 

bedrock aquifers in Rhode Island and Massachusetts have very 

low storage, it may be reasonable to assume that streamflow 

responds instantaneously to time-variable pumping. However, 

upland streams typically are underlain by lower-permeability 

till deposits that will dampen time-variable pumping rates. 

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

YEAR

1996 1997 1998 1999 2000 2001

PUMPING RATE AND STREAMFLOW DEPLETION,

 IN CUBIC FEET PER SECOND 

CALCULATED STREAMFLOW DEPLETION

PUMPING RATE AT WELL

Figure 10. Daily withdrawal rate at King’s Grant Water Company Well 1, North Attleboro, Massachusetts, 1996–2001, and 

calculated streamflow depletion.

26  A Precipitation-Runoff Model for the Blackstone River Basin
Thus, STRMDEPL was run with a streambank leakance 

term that represents the thickness and hydraulic properties 

of this lower-permeability till. In applying STRMDEPL, it 

was assumed that shallow bedrock is sufficiently fractured to 

behave as a porous medium, and that the contributing area is 

sufficiently small to fall within the subbasin (that is, recharge 

from the unconsolidated overburden storage supplements small 

bedrock storage). Because the size and density of bedrock fractures decrease within the top 200 ft (Randall and others, 1988), 

a thickness of 200 ft was used to calculate the aquifer transmissivity. A diffusivity value of 1x106

 ft2/d was used for all wells 

in till-mantled bedrock areas. This value is based on a hydraulic 

conductivity (K) of 0.5 ft/d, a thickness (b) of 200 ft, and a 

specific yield of 1x10–4. A streambank leakance (Kb'/K') value 

of 500 ft was used for all withdrawals, where b' is the thickness 

of the till streambank, and K' is the hydraulic conductivity of 

the till. This value is based on a till thickness of 10 ft and a till 

hydraulic conductivity of 0.01 ft/d. Till thicknesses range from 

10 to 30 ft in southeastern New England, with locally thicker 

regions near drumlins and thinner regions near bedrock outcrops 

(Randall and others, 1988; Melvin and others, 1992a,b). The 

hydraulic conductivity of till can range over 4 orders of magnitude in New England; a value of 0.01 ft/d is representative of 

lower, compacted lodgement till (Randall and others, 1988). 

Wastewater-Return Flows

Detailed wastewater return-flow information was collected for 1996–2001 from a variety of sources including 

NPDES databases maintained by the USEPA and RIDEM, 

the water-use database compiled by Barlow (2003), and 

directly from the treatment facilities. The return flows contained in the model include (1) municipal wastewater-return 

flows from the 10 municipal wastewater-treatment plants in 

the basin, (2) commercial and industrial return flows from 

permitted facilities, (3) filter-backwash return flows from 

municipal water-treatment plants, and (4) return flows of septic effluent from residential areas with public-water supplies 

and private sewers (septic systems). Municipal and commercial/industrial return flows are described in greater detail 

below. A discussion of how the septic-effluent discharges are 

treated in the model is provided in the “Representation of the 

Basin” section of the report.

The 29 municipal and commercial/industrial waste­waterreturn flows included in the model are shown in figure 9 and 

table 6. Approximately 15 additional commercial sites with 

discharge permits were excluded from the model because the 

sites were inactive during the calibration period, return-flow 

information could not be located, or the permits were for 

stormwater discharge only. The time intervals and amount 

of missing data varied considerably, and thus required 

various degrees of processing. Return flows from municipal 

wastewater-treatment plants were generally reported as daily 

or monthly totals. Return flows from commercial sites were 

reported as monthly, quarterly, or annual totals, and were missing more data than were municipal sites. Values bracketing 

the period of missing record, or average return flows for the 

period of missing record calculated from adjacent years were 

used to populate the data gaps. Wastewater return-flow records 

at 16 sites contained periods of missing record requiring estimation. To format the return flow data for input to the WDM 

file, annual, quarterly, and monthly returns were disaggregated 

to daily values by assuming a constant daily return flow and 

dividing by the number of days in the reported period. All 

daily values were disaggregated further to hourly values by 

assuming a constant hourly rate within a given day.

Streamflow

The stations in the Blackstone River Basin that have 

measured streamflow for the calibration period include Quinsigamond River at North Grafton, Mass. (station no. 01110000); 

Blackstone River at Northbridge, Mass. (station no. 01110500); 

West River at Uxbridge, Mass. (station no. 01111200); Nipmuc 

River near Harrisville, R.I. (station no. 01111300); Branch 

River at Forestdale, R.I. (station no. 01111500); and Blackstone 

River at Woonsocket, R.I. (station no. 01112500) (fig. 4). At the 

West River at Uxbridge, Mass. station, stage data were collected 

but mean daily discharges were not published by the USGS for 

1997–2001, so discharge for this period was computed in 2004 

to obtain additional data for model calibration. Records at the 

Quinsigamond River, Nipmuc River, Branch River, and Blackstone River at Woonsocket stations are rated as good (95 percent 

of daily discharges are within 10 percent of the true value). 

Records at the Blackstone River at Northbridge also are rated as 

good; however, the rating curve below about 300 ft3/s is considered poor because of variable back­water conditions created by 

downstream flow regulation. Flows are typically below 300 ft3/s 

in the summer and fall. Observed flow data are in DSN numbers 30 through 92 in the WDM file.

At the remaining stations in the Blackstone River Basin 

(the 7 project stations and the Blackstone River at Millbury, 

Mass. station, also referred to as partial-record stations), 

record-extension techniques were used to compute streamflow for 1997–2001. These techniques involve correlating the 

measured streamflow at the project stations (continuous record 

collected mainly during the 2004 water year) with streamflow 

from nearby stations (also referred to as continuous-record stations) that have a measured streamflow record for 1997–2001, 

which include stations in the Blackstone River Basin and 

seven other stations in surrounding drainage basins. The stations used in the analysis are shown in figure 4. Streamflow 

at the Kettle Brook at Auburn, Mass. (station no. 01109439); 

Mumford River at Uxbridge, Mass. (station no. 01111050); 

Chepachet River at Gazzaville, R.I. (station no. 01111410); 

Mill River at Woonsocket, R.I. (station no. 01112268); Peters 

River at Woonsocket, R.I. (station no. 01112382); Abbott Run 

at Valley Falls, R.I. (station no. 01113760); and Blackstone 

River at Pawtucket, R.I. (station no. 01113895) stations was 

estimated for 1997–2001 by using a mathematical procedure known as Maintenance of Variance Extension, type 1 

(MOVE.1) (Hirsch, 1982).

Precipitation-Runoff Model for the Blackstone River Basin  27
Table 6. Wastewater-return flows in the Blackstone River Basin, Massachusetts and Rhode Island.

[WDM, watershed data management; DSN, dataset number; Mgal/d, million gallons per day]

Model 

reach 

number

WDM file 

DSN

Identification or 

permit number Source name Town 

Average return rate 

1997–2001 

(Mgal/d)

3 3030 MA0000817 Norton Company Worcester 0.148

3 3031 MA0102997 Worcester Combined Sewer Overflow Plant Worcester 1.06 

3 3032 MA0001112 Wyman Gordon Worcester 0.350

10 3100 RI0100129 Eleanor Slater Hospital, Zambarano Unit Burrillville 0.0688

12 3120 MA0102202 Hopedale Wastewater-Treatment Plant Hopedale 0.389

13 3130 MAG250969 Lewcott Corporation MIllbury 0.0098

13 3131 MA0100650 Millbury Wastewater-Treatment Plant Millbury 1.06

15 3150 MA0102369 Upper Blackstone Water Pollution 

Abatement District

Millbury 35.4

17 3170 MA0100196 Upton Wastewater-Treatment Plant Upton 0.180

20 3200 MA0101311 Grafton Wastewater-Treatment Plant Grafton 1.52

21 3210 MA0101095 Douglas Wastewater-Treatment Plant Douglas 0.180

22 3220 MA0100722 Northbridge Wastewater-Treatment Plant Northbridge 1.30

30 3300 RI0000566 Atlantic Thermoplastics Company, Incorporated North Smithfield 0.00115

30 3301 RI0000485 Blackstone Smithfield Corporation North Smithfield 0.00313

31 3310 MA0102440 Uxbridge Wastewater-Treatment Facility Uxbridge 0.712

35 3350 RI0021466 CNC International Woonsocket 0.0499

36 3360 RI0000116 Turex Incorporated Burrillville 0.00595

37 3370 RI0000019 Philips Components North Smithfield 0.00297

38 3380 RI0021393 ACS Industries Incorporated Woonsocket 0.204

38 3381 RI0100111 Woonsocket Wastewater-Treatment Facility Woonsocket 9.06

38 3382 RI0001627 Woonsocket Water Division (filter backwash) Woonsocket 0.963

39 3390 RI0100455 Burrillville Wastewater-Treatment Facility Burrillville 0.804

42 3420 RI0000124 A.T. Cross, Outfall 001 Lincoln 0.0906

45 3450 RI0020451 Air Products and Chemicals Incorporated Cumberland 0.130

45 3451 RI0020141 Okonite Company Cumberland 0.114

45 3452 RI0021865 Fleet National Bank Lincoln 0.000123

45 3453 RI0023132 Blackstone Valley Electric Company Lincoln 0.00360

46 3460 RI0001589 Pawtucket Water Supply Board (filter backwash) Cumberland 0.277

47 3470 RI0001180 Osram Sylvania Central Falls 0.325

The MOVE.1 procedure transfers the statistical characteristics 

of the continuous-record station, such as distribution shape, 

seasonality, and amount of serial correlation, to the project 

station. To apply this method, the logarithms of daily mean 

streamflow at the project stations were compared with the 

same-day daily mean streamflow at the selected continuousrecord stations for the common period of record, generally 

the 2004 water year. Continuous-record stations were selected 

based on (1) the correlation and linearity of the log-transformed data and (2) visual inspection of the agreement 

between the measured and computed 2004 water-year hydrographs. The continuous-record stations and methods used to 

estimate streamflow are summarized in table 7.

Scatter plots show that the relations between logarithms 

of streamflow at the project and continuous-record stations 

are linear for all project stations except Abbott Run at Valley Falls, R.I., and Mill River at Woonsocket, R.I. At these 

stations, two distinct linear segments were present on one or 

more of the scatter plots of the log-transformed daily mean 

streamflow, so a model in which a unique MOVE.1 

equation was applied to each straight-line segment (referred to 

in this study as a two-slope model) was used (table 7). After 

the MOVE.1 procedure was applied to the common 2004 data, 

daily mean streamflows for 1997–2001 were computed for 

each project station from the streamflow data collected at each 

of the selected continuous-record stations. If flow at a project 

station correlated equally well with more than one continuousrecord station (for example, Kettle Brook at Auburn, Mass., in 

table 7), all of the highly correlated continuous-record stations 

were used to estimate flow, rather than arbitrarily select one 

station from the group. In these cases, the daily mean streamflow at each project station was computed by a weighed 

average of the daily mean streamflows calculated for each 

continuous-record station, where each continuous-record station streamflow was weighted on the basis of the mean square 

error between the computed streamflow and the measured 

streamflow at the project streamflow-gaging station. 

28  A Precipitation-Runoff Model for the Blackstone River Basin
Table 7. Summary of relations between daily mean streamflow at the partial-record streamflow-gaging stations and at the continuous-record stations used to compute 

continuous streamflow records at the partial-record stations for 1997–2001, Blackstone River Basin, Massachusetts and Rhode Island.[The Blackstone River at Millbury, Mass. station was installed in 2002 as part of the ongoing cooperative stream-gaging network in Massachusetts. The remaining partial-record stations were installed in 2003 for this study. MOVE.1, maintenance of variance extension, type 1; MISTE, missing streamflow estimation; Mass., Massachusetts; R.I., Rhode Island ]

Partialrecord 

station 

number 

Partial-record 

station name 

 Continuousrecord station 

number 

Continuous-record 

station name 

Number of 

streamflow 

measurements 

at partial-record 

station 

Method Correlation coefficient Comments 

01109439 Kettle Brook at Auburn, Mass. 01109403 Ten Mile River, East Providence, R.I. 366 MOVE.1 0.83

01095220 Stillwater River, near Sterling, Mass. 366 MOVE.1 0.8501095375 Quinapoxet River, near Holden, Mass. 366 MOVE.1 0.87

01109730 Blackstone River at Millbury, Mass. 01110000 Quinsigamond River, North Grafton, Mass. 800 MISTE 0.74 Composite approach used to develop 

regression equation. 01110500 Blackstone River, Northbridge, Mass. 435 MISTE 0.93

01112500 Blackstone River, Woonsocket, R.I. 800 MISTE 0.89

01111050 Mumford River at Uxbridge, Mass. 01111300 Nipmuc River, near Harrisville, R.I. 366 MOVE.1 0.91

01111500 Branch River, Forestdale, R.I. 366 MOVE.1 0.9201109403 Ten Mile River, East Providence, R.I. 366 MOVE.1 0.9101103280 Charles River, Medway, Mass. 366 MOVE.1 0.91

01111410 Chepachet River at Gazzaville, R.I. 01111500 Branch River, Forestdale, R.I. 264 MOVE.1 0.94

01109403 Ten Mile River, East Providence, R.I. 264 MOVE.1 0.90

01112268 Mill River at Woonsocket, R.I. 01111300 Nipmuc River, near Harrisville, R.I. 264 MOVE.1 0.91 Non-linear relation with station 

01109403; two-slope model used. 01109403 Ten Mile River, East Providence, R.I. 264 MOVE.1 0.78/0.80

01115098 Peeptoad River, near North Scituate, R.I. 264 MOVE.1 0.90

01112382 Peters River at Woonsocket, R.I. 01109403 Ten Mile River, East Providence, R.I. 264 MOVE.1 0.83

01103280 Charles River, Medway, Mass. 264 MOVE.1 0.86

01113760 Abbott Run at Valley Falls, R.I. 01109403 Ten Mile River, East Providence, R.I. 296 MOVE.1 0.46/0.81 Non-linear relation with station 

01109403; two-slope model used. 

01113895 Blackstone River at Pawtucket, R.I. 01112500 Blackstone River, Woonsocket, R.I. 366 MOVE.1 0.99

Precipitation-Runoff Model for the Blackstone River Basin  29
Streamflow was computed for the Blackstone River at 

Millbury, Mass. (station no. 01109730) station by use of the 

MIssing STreamflow Estimation (MISTE) program contained 

in the USGS Automated Data Processing System (ADAPS) 

database. MISTE is a multi-variant regression procedure 

developed to compute periods of missing data from the relation of flows to user-selected index stations for common 

periods of streamflow-data collection. MISTE allows lag 

periods and multiple index stations to be incorporated into the 

regression to improve the agreement between computed and 

observed flows. 

Streamflow at the Millbury, Mass. station is strongly 

affected by wastewater-return flows and the amount of 

upstream urban land use, so a composite approach involving 

empirical adjustments to the computed record was needed 

to develop a reasonable estimate of streamflow. MISTE was 

used initially to compute flows from log-transformed data 

from the Blackstone River at Woonsocket, R.I. station with a 

1-day lag (hereafter referred to as the Woonsocket equation). 

A 1-day lag in the Woonsocket streamflow data was tested in 

the regression analysis because the site is 28 mi downstream 

from the Millbury station. Estimates of streamflow at the 

Blackstone River at Millbury, Mass. station also were obtained 

from the Blackstone River at Northbridge, Mass. station only 

with no lag (hereafter referred to as the Northbridge equation), 

and the Northbridge and Quinsigamond River at North Grafton, 

Mass. stations combined with no lag (hereafter referred to as 

the Northbridge-Quinsigamond equation). Visual inspection 

of the computed streamflow at Millbury during the period 

when the Northbridge streamflow-gaging station was concurrently operated (July 25, 2002 through September 30, 2003) 

indicated that both equations (Northbridge and NorthbridgeQuinsigamond) appreciably overestimated low flows. This is 

believed to be caused by the poor rating at the Northbridge 

station during low flows because of variable backwater conditions. The Northbridge-Quinsigamond equation provided a 

better estimate of peak flows than the Woonsocket equation 

because the Northbridge and Quinsigamond stations are closer 

to the Millbury station and are less dampened than the flows 

at the Woonsocket station. Neither equation (Woonsocket or 

Northbridge-Quinsigamond) captured the flashiness of the 

streamflow at the Millbury station, which is believed to result 

from the presence of the city of Worcester above the station.

Combining the Woonsocket and the NorthbridgeQuinsigamond equations provided a better estimate of streamflow at the Millbury station than either of these equations 

alone. The combined estimation entailed using an empirically adjusted peak flow from the Northbridge-Quinsigamond 

equation and non-peak flows from the Woonsocket equation. 

The peak flows from the Northbridge-Quinsigamond equation were adjusted by a factor determined from the median 

difference between the estimated and observed flow from the 

common period of record. The differences between the estimated and observed flows generally were greatest during the 

observed peak; the estimated peak flows were underpredicted 

by a median difference of 61 percent. If flows on a given day 

exceeded the flow 2 days previously by 50 percent, and if that 

day’s flow was at the end of a rising hydrograph, the peak flow 

for that day was estimated by the Northbridge-Quinsigamond 

equation multiplied by an adjustment factor 1.61. Flow on 

the following day was estimated by the Northbridge-Quinsigamond equation. For all other days, the flow at the Millbury 

station was estimated by the Woonsocket equation. The root 

mean square error calculated from estimated and observed 

flows from the Woonsocket equation, the Northbridge-Quinsigamond equation, and the combined equation, was 76, 60, 

and 50 ft3/s, respectively.

The accuracy of these record-extension techniques is 

determined by the degree of correlation between the daily 

mean streamflows at the partial-record (project stations and 

Blackstone River at Millbury, Mass. station) and continuousrecord streamflow-gaging stations, the accuracy of the continuous-discharge records, and the range of measured flows 

at the project streamflow-gaging stations (Zarriello and Bent, 

2004). Because of the short period of record at the partialrecord stations, a wide range of flow conditions was not measured and estimates of daily mean streamflows at both high 

and low flows are less accurate. In addition, flow regulation 

may affect specific ranges of flows in the partial- and continuous-record stations, leading to additional error in the computed 

record. Because each of these factors introduces uncertainty, 

computed streamflow records at the partial-record stations are 

considered estimates. Based on visual inspection of computed 

and measured hydrographs for the 2004 water year and the 

correlation coefficients shown in table 7, the computed streamflow record for 1997–2001 is qualitatively considered very 

good at the Blackstone River at Pawtucket, R.I. station, good 

at the Blackstone River at Millbury, Mass., Mumford River 

at Uxbridge, Mass., and Chepachet River at Gazzaville, R.I. 

stations, and fair at the Kettle Brook at Auburn, Mass., Peters 

River at Woonsocket, R.I., Mill River at Woonsocket, R.I., and 

Abbott Run at Valley Falls, R.I. stations. 

Representation of the Basin

The physical and spatial representation of the basin is defined 

by the combination of HRUs (PERLNDs and IMPLNDs), their 

contributing area to a reach, and the linkage of one stream 

reach to another. The process of defining HRUs, their linkage 

to reaches, and the linkage of reaches to each other often is 

referred to as the discretization of a basin. A geographicinformation system (GIS) was used to discretize the Blackstone River Basin. Basin and subbasin boundaries in the model 

study area were obtained from available USGS, Massachusetts 

Geographic Information System (MassGIS), and Rhode Island 

Geographic Information System (RIGIS) sources (Massachusetts Geographic Information System, 2003 and Rhode 

Island Geographic Information System, 2003) or digitized 

from 1:24,000-scale USGS topographic maps when necessary. 

The data layers used in the discretization process include surfi-

30 A Precipitation-Runoff Model for the Blackstone River Basin
cial geology, land use, wetlands, and the distribution of public 

water supply and public sewer systems. 

Data Layer Processing and Basin Simplification

Processing of digital data layers used for HRU development 

and the simplifications to the representation of the basin in 

the model are described in this section. Spatial data from 

Massachusetts and Rhode Island were generally reclassified 

to produce consistent basinwide data layers, and then simplified to obtain categories that were considered important to the 

basin hydrology and HRU development. 

Surficial Geology

The surficial-geology data layers from MassGIS and RIGIS 

were simplified from four types of material (sand and gravel, 

alluvium, till, and bedrock) into two types (sand and gravel 

and till) on the basis of permeability and storage characteristics. Bedrock outcrops and alluvial deposits are not areally 

extensive in the basin, and therefore, were not considered 

explicitly for HRU development. Consequently, areas underlain by bedrock were combined with till, and areas underlain 

by alluvium were combined with sand and gravel. 

Land Use and Land Cover

LULC information was obtained from the MassGIS and 

RIGIS Web sites. The MassGIS data layer represents land 

use in 1999 and has 37 land-use classifications interpreted 

from 1:25,000 aerial photography (Massachusetts Geographic 

Information System, 2003). The minimum mapping unit 

(resolution) used was 1 acre. The Rhode Island data layer 

represents land use in 1995 and has 34 land-use classifications, with a minimum resolution of 0.5 acre (Rhode Island 

Geographic Information System, 2003). To produce consistent LULC categories for the entire basin, the Massachusetts 

and Rhode Island data layers were reclassified to a common 

classification system and then combined to produce a data 

layer for the basin. This data layer was then intersected with a 

basinwide wetlands data layer developed from Massachusetts 

and Rhode Island wetland data layers to produce a composite 

cover consisting of 20 LULC categories. To represent land use 

in the model, the 20 LULC categories were simplified further 

into 7 LULC categories: (1) commercial-industrial-transportation, (2) high-density residential, (3) medium- to low-density 

residential, (4) open non-residential, (5) forest, (6) forested 

and non-forested wetlands, and (7) open water (fig. 2). 

The simplified LULC data indicates that 50.7 percent of 

the basin is forested, excluding forested wetlands which are 

accounted for in the wetlands category. If forested wetlands 

are included in the forest category, 56 percent of the basin is 

forested. An additional 10.7 percent of the basin is classified 

as open, non-residential land. This mixed category includes 

developed recreational spaces, urban open spaces, cemeteries, 

orchards and nurseries, and other agricultural lands such as 

hay fields and cropland. Wetlands, including both forested and 

non-forested, compose 7.7 percent of the basin area. Approximately 5.8 percent of the basin is classified as commercialindustrial-transportation. This mixed category includes all 

roads and transportation facilities, manufacturing and warehouse facilities, landfills, wastewater-treatment plants, junkyards, and quarries. About 3.8 percent of the basin is classified 

as open water, which includes ponds, reservoirs, and the larger 

river channels. 

The remaining 21.3 percent of the basin is classified as 

residential, of which 14.7 percent is medium- to low-density 

residential and 6.6 percent is high-density residential. To obtain 

these percentages, the Massachusetts and Rhode Island residential 

land-use categories were reclassified to a common system consisting of four categories: (1) high-density residential (<1/8-acre 

lots, multifamily), (2) medium-high density residential (1/8- 

to 1/4-acre lots), (3) medium-density residential (1/4- to 1-acre 

lots), and (4) low-density residential (>1-acre lots) (table 8). 

Each of these categories was assigned an average household 

density per acre based on lot size, and an average population 

Table 8. Residential densities used in the Hydrological Simulation Program–FORTRAN (HSPF) model of the Blackstone River Basin, 

Massachusetts and Rhode Island.

[HRU, Hydrologic Response Unit; <, less than; >, greater than]

Reclassified residential categories from state 

land-use data layers

Number of 

households 

per acre

Population 

per acre

Consolidated 

residential categories 

for HRU development

Percentage of 

consolidated 

residential area

Weighted 

number of 

households 

per acre

Weighted 

population 

per acre

High-density residential 

(<1/8-acre lots)

8 20 High-density residential 24.1 5.7 14.3

Medium-high density residential 

(1/4- to 1/8-acre lots)

5 12.5 75.9

Medium-density residential 

(1/4- to 1-acre lots)

2.5 6.3 Medium- to lowdensity residential49.8 1.5 3.7

Low-density residential 

(>1-acre lots)

0.5 1.3 50.2

Precipitation-Runoff Model for the Blackstone River Basin  31
density per acre using an average of 2.5 people per household 

obtained from 2000 census data (U.S. Census Bureau, 2005). 

These categories were then consolidated again by adding high 

density and medium-high density together and medium-density and low-density together, forming the two residential landuse categories, high-density residential and medium- to low-density residential, used in HRU development (table 8). Grouped in 

this manner, medium- to low-density residential areas represent 

single-family households on lots with areas equal to or larger 

than 1/4 acre. 

An average household density per acre for each of 

these final residential land-use categories was then calculated 

as a weighted average of the household densities in the reclassified state residential categories that were grouped together to 

form these categories. For instance, the final high-density 

residential area consists of 24.1 percent high-density residential 

and 75.9 percent medium-high density residential land use, so 

the household density of the medium-high density residential 

land use was given greater weight. Based on this analysis, 

the high-density residential areas and medium- to low-density residential areas contain an average of 5.7 households 

per acre and 1.5 households per acre, respectively. Based on 

2.5 people per household on average, these housing densities 

equate to 14.3 people per acre in high-density residential areas 

and 3.7 people per acre in medium- to low-density residential 

areas. The total estimated population in the basin resulting from 

these residential population densities and corresponding land 

areas was 453,300. The total population in the basin in 2000 

determined from U.S. census block data was 467,200 (U.S. 

Census Bureau, 2004a,b). The difference between these population estimates is 3 percent, and the close agreement indicates 

that residential land use and population are reasonably well 

represented in the model.

Wetlands

Wetland areas were obtained from MassGIS and RIGIS 

for the Massachusetts and Rhode Island parts of the basin, 

respectively. Wetlands in Rhode Island were interpreted 

from 1988 aerial photography to 1/4-acre polygon resolution (Rhode Island Geographic Information System, 2003). 

Wetlands in Massachusetts were interpreted from 1992 aerial 

photography using a classification scheme consisting of 

28 wetland categories (Massachusetts Geographic Information System, 2003). The two data layers were simplified into 

forested and non-forested wetlands and then combined to produce a consistent wetlands data layer for the basin. Wetlands 

were simplified further for model development by combining 

forested and non-forested wetlands into a single land-use type. 

Public Water and Public Sewer Systems

To represent water use in the model, a data layer showing the distribution of public water and public sewer systems 

was compiled (fig. 6). In this report, public systems refer to 

municipal distribution and collection systems associated with 

major water suppliers and regional wastewater-treatment 

plants, respectively. In Rhode Island, sewer-line and water-line 

data were obtained from RIGIS (Rhode Island Geographic 

Information System, 2003) and from individual towns (Burrillville, North Smithfield, and Woonsocket). In Massachusetts, 

data were obtained from the Central Massachusetts Regional 

Planning Commission and individual towns. A basinwide map 

of sewer lines was then generated by digitizing the individual 

sewer maps provided by the towns as necessary, and then 

combining all digital data from Rhode Island and Massachusetts on a single data layer. The same procedure was used to 

develop a basin-scale map of water lines. These maps generally represent the extent of public sewer and public water 

systems in the basin for 1995–2003. Polygon data layers of 

sewer and water areas were then generated from the sewer-line 

and water-line data layers by creating a 1,000-ft buffer zone 

(500 ft per side) around each line. Finally, a combined data 

layer was developed for the entire basin by combining the 

sewer-area and water-area data layers with the basin polygon. 

The resulting data layer was coded so that the entire basin area 

was represented by one of four possible water-sewer infrastructure combinations. These combinations are: (1) areas with 

private water (private wells) and private sewers (on-site septic 

systems) (code 1), (2) areas with private water and public 

sewers (code 2), (3) areas with public water and private sewers 

(code 3), and (4) areas with public water and public sewers 

(municipal water-supply distribution and wastewater-collection systems) (code 4).

When the combined public-water and public-sewer data 

layer was intersected with the reclassified land-use data layer, 

the areal extent of the four possible water-sewer infrastructure 

combinations listed above for each residential land-use category was determined. The areas of these infrastructure combinations were computed for both the medium- to low-density 

residential areas and the high-density residential areas and 

used to develop PERLNDs. In the model, water is exported 

from residential areas with private-water supplies and public 

sewers (code 2), and imported to residential areas with publicwater supplies and private sewers (code 3). There is assumed 

to be no net transfer of water in residential areas with the other 

two infrastructure combinations (codes 1 and 4). 

Hydrologic Response Units

Fifty-six unique HRUs were created by combining the 

simplified surficial-geology, land-use, and public water and 

public sewer system data layers. These combinations were 

grouped further on the basis of size (areas less than about 

0.3 percent of the total basin area were grouped into HRUs 

with the most similar characteristics) and hydrologic importance. For example, in areas classified as commercial-industrial-transportation that likely have disturbed near-surface 

soils and may contain fill, surficial geology was deemed to 

be relatively unimportant; thus, all areas classified as commercial-industrial-transportation land use were combined to 

form a single HRU. Similar reasoning was used to group the 

water-sewer categories for various HRUs. Combining HRUs 

32  A Precipitation-Runoff Model for the Blackstone River Basin
in this manner yielded a more-manageable 17 PERLNDs 

and 2 IMPLNDs (fig. 11). Following the approach used by 

Zarriello and Ries (2000) to simulate flows in the Ipswich 

River Basin in northeastern Massachusetts, wetlands and 

open water were treated as storage components rather than 

PERLNDs. Consequently, they were simulated as “virtual” 

RCHRESs, as described below. A general description of the 

17 PERLND and 2 IMPLND types used in the Blackstone 

River Basin HSPF model and their total areas in the basin are 

given in table 9. The areas of wetlands and open water also 

are given in table 9. The area of each HRU in each subbasin 

was determined by intersecting the HRU data layer with the 

subbasin (reach) delineations.

Two identical sets of HRUs were defined in the UCI 

file: one set (PERLNDs 1 through 17 and IMPLNDs 30 

and 31) was defined for the HRUs in the northern part of the 

basin that use data from the Worcester, Mass. climatological 

station, and a second set with numbers increased by a factor 

of 100 (PERLNDs 101 through 117 and IMPLNDs 130 and 

131) was defined for HRUs in the southern part of the basin 

that use data from the Warwick, R.I. climatological station. 

A single parameter value was used for like HRUs (for example, PERLNDs 1 and 101) in each set. PERLND numbers 1 

Figure 11. Areas of hydrologic response units (HRUs), wetlands, and open water as percentages of drainage area.

Precipitation-Runoff Model for the Blackstone River Basin  33

Blackstone River at Millbury, Massachusetts (station no. 01109730)

EXPLANATION

Branch River at Forestdale, Rhode Island (station no. 01111500)

Blackstone River at Pawtucket, Rhode Island (station no. 0113895) 

Blackstone River at Woonsocket, Rhode Island (station no. 01112500)

Pervious areas (PERLNDs)

HYDROLOGIC RESPONSE UNIT NUMBER

Residential Residential

HYDROLOGIC RESPONSE UNIT AREA

 AS A PERCENTAGE OF DRAINAGE AREA

Impervious areas (IMPLNDs)

Overlying till Overlying sand and gravel

Commercial, industrial

 and transportation

Open nonresidential

Forest

Medium-to-low density

Medium-to-low density

Medium-to-low

 density, with export

Medium-to-low

 density, with export

Medium-to-low

density, with import

Medium-to-low

density, with import

High density

High density,

High density

 with export

High density,

with export

High density,

 with import

High density,

with import

Open nonresidential

Forest

Wetland

Open water

Mixed commercial

development

Residential development/urban open space

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 30 31

0

10

20

30

40

50
Table 9. Definitions and areas of hydrologic response units (HRUs), wetlands, and open water used to represent the Blackstone River Basin, 

Massachusetts and Rhode Island.[Private water refers to private wells and private sewer refers to on-site septic systems. Public water refers to municipal water supply systems and public sewer refers to municipal wastewater-disposal systems. HRU, hydrologic response unit; PERLND, pervious land segment; IMPLND, impervious land segment; —, not applicable]

HRU Surficial geology Water imported or exported from stream reach Acres in basin before computation of impervious area Acres in basin after computation of impervious area Percentage of total basin area Description

PERLND 11 — — 17,572 8,216 2.7 Commercial/industrial/transportationPERLND 2 Till — 21,789 21,229 7.0 Open, non-residentialPERLND 3 Till — 123,084 123,084 41 ForestPERLND 42 Till — 23,932 23,312 7.7 Medium- to low-density residential on private water-private sewer and public 

water-public sewer 

PERLND 5 Till Export 1,095 1,065 0.35 Medium- to low-density residential on private water-public sewerPERLND 6 Till Import 5,266 5,126 1.7 Medium- to low-density residential on public water-private sewer PERLND 72 Till — 11,981 10,191 3.4 High-density residential on private water-private sewer and public 

water-public sewer 

PERLND 8 Till Export 298 254 0.08 High-density residential on private water-public sewerPERLND 9 Till Import 742 633 0.21 High-density residential on public water-private sewerPERLND 10 Sand and gravel — 10,706 10,422 3.4 Open, non-residentialPERLND 11 Sand and gravel — 30,652 30,652 10 ForestPERLND 122 Sand and gravel — 10,164 9,896 3.3 Medium- to low-density residential on private water-private sewer and 

public water-public sewer 

PERLND 13 Sand and gravel Export 449 436 0.14 Medium- to low-density residential on private water-public sewerPERLND 14 Sand and gravel Import 3,724 3,627 1.2 Medium- to low-density residential on public water-private sewer PERLND 152 Sand and gravel — 6,337 5,381 1.8 High-density residential on private water-private sewer and public 

water-public sewer 

PERLND 16 Sand and gravel Export 247 210 0.07 High-density residential on private water-public sewerPERLND 17 Sand and gravel Import 417 357 0.12 High-density residential on public water-private sewerIMPLND 30 — — 0 9,356 3.1 Mixed commercial developmentIMPLND 31 — — 0 5,006 1.7 Residential development and urban open space

— — — 23,395 23,395 7.7 Wetland— — — 11,392 11,392 3.8 Open water

Total acreage: 303,242 303,240

1PERLND 1 includes areas underlain by both till and sand and gravel because surface soils are likely to be disturbed and backfilled.2PERLNDs 4, 7, 12, and 15 include residential areas served by both private water/private sewer and public water/public sewer. 

34  A Precipitation-Runoff Model for the Blackstone River Basin
through 17 and IMPLND numbers 30 and 31 are used hereafter to represent both sets of HRUs. 

Impervious Areas (IMPLNDs)

Impervious areas that drain directly to streams (hydrologically effective impervious areas) are simulated in HSPF 

as IMPLNDs. Impervious areas that drain to pervious areas 

(hydrologically ineffective impervious areas) are incorporated 

into the PERLNDs. Initial estimates of effective impervious area were determined as a percentage of the areas of the 

developed land-use classes in the composite land-use data 

layer consisting of 20 LULC categories created from the 

original state data layers to preserve the information content of 

these categories. The groupings used to compute the effective 

impervious areas differed slightly from the groupings used to 

define the land-use categories in the model.

The initial percentages of impervious area for various 

developed land-use types were obtained from similar land-use 

types reported by Alley and Veenhuis (1983) (data not shown). 

The final percentages used to compute effective impervious area were obtained primarily by visual inspection of the 

overall responsiveness of the hydrograph to precipitation in 

the developed parts of the basin, and also by calibration of 

small summer storms that are considered to generate runoff 

mostly from effective impervious surfaces (table 10) (Zarriello and Ries, 2000). Two IMPLND types were used in the 

model: mixed commercial development (IMPLND 30) and 

residential development and urban open space (IMPLND 31). 

Hydrologically, these two IMPLNDs are similar, but they were 

given unique HRUs for possible future water-quality applications. About 31 percent of the basin is classified as developed, 

but the effective impervious area was estimated to be about 

5 percent of the basin area (table 9). The estimated total effective impervious area as a percentage of basin area ranged from 

about 10 percent in the relatively developed drainage areas 

to about 2 percent in the undeveloped areas. For example, 

the total effective impervious area as a percentage of the 

total drainage area is 10.1 percent in the drainage area to the 

Blackstone River at Millbury, Mass. streamflow-gaging station 

(station no. 01109730), 9.3 percent in drainage area to the 

Quinsigamond River at North Grafton, Mass. station (station 

no. 01110000), 1.7 percent in the drainage area to the Branch 

River at Forestdale, R.I. station (station no. 01111500), and 

4.3 percent in drainage area to the Blackstone River at Woonsocket, R.I. station (station no. 01112500).

Pervious Areas (PERLNDs)

Pervious surfaces that allow infiltration and impervious 

areas that drain to pervious areas are represented in HSPF as 

PERLNDs. Forests are the dominant PERLND type throughout the watershed (table 9); commercial and residential land 

Table 10. Effective impervious area by developed land-use type for the Hydrological Simulation Program–FORTRAN 

(HSPF) model of the Blackstone River Basin, Massachusetts and Rhode Island.

[<, less than; >, greater than]

Land-use classification

Area in 

basin 

(acres)

Percentage of area 

that is effective 

impervious

Effective

 impervious area 

(acres)

Commercial development: 14,619 64 9,356

Sales and service facilities

Industrial manufacturing, design, and assembly facilities

Transportation

High-density residential development (<1/8-acre lots) 4,819 18 867

Medium-high density residential development (1/4- to 1/8-acre lots) 15,203 14 2,128

Medium-density development: 26,874 5 1,344

Medium-density residential (1- to 1/4-acre lots)

Water and wastewater-treatment facilities, active landfills, and junkyards

Developed recreational

Low-density development: 33,360 2 667

Low-density residential (> 1-acre lots)

Urban open space

Total: 94,876 14,363

Precipitation-Runoff Model for the Blackstone River Basin  35
uses are more extensive in the developed north and southeastern parts of the basin (fig. 2).

Pervious areas in the basin are represented by eight 

PERLNDs overlying till, eight PERLNDs overlying sand and 

gravel, and one PERLND overlying both surficial-geology types 

combined (table 9). Two HRUs represent open, non-residential 

space (PERLND 2 overlying till and PERLND 10 overlying sand 

and gravel), two HRUs represent forested areas (PERLND 3 

overlying till; PERLND 11 overlying sand and gravel), six 

HRUs represent medium- to low-density development with 

different water-supply and wastewater-disposal combinations 

(PERLNDs 4, 5, and 6 overlying till and PERLNDs 12,13, and 

14 overlying sand and gravel), and the remaining six HRUs represent high-density development with the same water-supply and 

wastewater-disposal combinations as for medium- to low-density 

development (PERLNDs 7, 8, and 9 overlying till; PERLNDs 

15,16, and 17 overlying sand and gravel). The residential HRUs 

are discussed in greater detail below. Areas classified as commercial-industrial-transportation overlying both till and sand and 

gravel were combined to form a single HRU (PERLND 1). 

Open, non-residential land composes about 10.4 percent of the watershed, with 7.0 percent in areas underlain by 

till (PERLND 2) and 3.4 percent in areas underlain by sand 

and gravel (PERLND 10). Because this category combines a 

mixture of different land-uses (developed recreational spaces, 

urban open spaces, cemeteries, orchards and nurseries, and 

other agricultural lands such as hay fields and cropland), both 

developed and undeveloped areas are represented by these 

HRUs. The developed areas contain both effective and ineffective impervious surfaces, while the undeveloped areas do not. 

Consequently, about 40 percent of the total initial area of these 

HRUs (developed recreational space and urban open space) 

was treated as developed land and used in the calculation 

of effective impervious area. Calibrated evapotranspiration, 

infiltration, soil-water storage parameter values were similar 

to values for medium- to low-density residential HRUs for 

similar types of surficial geology (appendix 1). 

Forest overlying till (PERLND 3), which represents about 

41 percent of the total area in the basin, is the dominant HRU 

in the watershed followed by forest overlying sand and gravel 

(PERLND 11), which represents about 10 percent of the 

total area (table 9). Forests compose up to 75 percent of the 

area in subbasins in the relatively undeveloped western part 

of the basin and as little as 13 percent in subbasins in urban 

areas. Forests compose 39 percent of the drainage area to the 

Blackstone River at Millbury, Mass. streamflow-gaging station 

(station no. 01109730), 66 percent of the drainage area to the 

Branch River at Forestdale, R.I. station (station no. 01111500), 

and 52 percent of the drainage area to the Blackstone River at 

Woonsocket, R.I. station (station no. 01112500). 

Residential areas of similar density were divided into 

three HRUs for each type of surficial geology to account for 

differences in the water and sewer infrastructure serving these 

areas. Residential areas on public water and on-site septic 

systems were considered to produce a net inflow (or import) 

of water to the area—PERLNDs 6 (till) and 14 (sand and 

gravel) represent medium- to low-density residential areas, 

and PERLNDs 9 (till) and 17 (sand and gravel) represent 

high-density residential areas. Residential areas on private 

wells and public sewer systems were considered to produce a 

net outflow (or export) of water from the area—PERLNDs 5 

(till) and 13 (sand and gravel) represent medium- to low-density residential areas, and PERLNDs 8 (till) and 16 (sand and 

gravel) represent high-density residential areas. The water 

imported to or exported from these residential areas is not 

linked to any specific source or treatment facility. Thus, the 

location of the public water-supply sources or treatment facilities is inconsequential to these transfers.

Residential areas with the other two water supply and 

disposal combinations, private wells and septic systems and 

public water and public sewer systems, were considered to 

produce no net transfer of water from the area. PERLNDs 4 

(till) and 12 (sand and gravel) represent medium- to low-density residential areas, and PERLNDs 7 (till) and 15 (sand and 

gravel) represent high-density residential areas. In areas where 

water is self-supplied and wastewater is self-disposed, water 

is cycled (withdrawn and returned) locally. In areas where 

residences and businesses are connected to both public water 

and public sewer systems, there is no net import or export of 

water from the area. Because of the lack of import and export, 

the model was simplified by combining the residential areas 

with these water-sewer infrastructure combinations to form 

PERLNDs 4, 7, 12, and 15 (table 9).

Stream Reaches (RCHRES)

The Blackstone River and its main tributaries were segmented into 50 reaches (fig. 8; table 11). Segmentation was 

based on hydrologic characteristics, the availability of streamflow data, and to a lesser extent, the size of the drainage area 

and water- and land-use characteristics. Fourteen reaches were 

established along the main stem of the Blackstone River, and 

36 reaches were established on the tributaries. Most tributaries 

were subdivided into multiple reaches. For example, Abbott 

Run was represented by 3 reaches, the Branch River and its 

main tributaries by 10 reaches, Kettle Brook and the Mumford 

River by 4 reaches each, and the Quinsigamond River, Mill 

River, and West River by 2 reaches each. 

The linkage of reaches to one another is specified in the 

SCHEMATIC block. In most cases, the linkages are obvious 

(as shown in fig. 8), with a single reach flowing into the adjacent downstream reach. Where the confluence does not coincide with a reach junction (node), the linkages between some 

tributaries and the main stem are less obvious. An example 

is reach 37 on the lower Branch River, which together with 

reach 31, flows into reach 30. Other locations where multiple 

reaches are linked are shown in table 11.

Hydraulic Characteristics (FTABLEs)

Stage-storage-discharge characteristics (FTABLEs) were 

developed for the outflow gate used to route water from each of 

36  A Precipitation-Runoff Model for the Blackstone River Basin
the 50 reaches. These characteristics are usually defined by the 

hydraulic properties at the downstream end of the reach, but the 

discharge-volume relation is a function of the properties of the 

entire reach. FTABLEs were developed to represent lake or 

reservoir (hereafter referred to as reservoir FTABLEs) depthstorage-discharge relations in the 14 reaches dominated by 

large surface-water bodies (table 11). FTABLEs representing 

stream reaches were developed for the remaining 36 reaches. 

For most of the stream reaches in the model, the channelgeometry analysis program (CGAP) by Regan and Schaffranek (1985) was used to define the relations among 

depth, surface area, and volume. A supplemental program, 

GENFTBL, reads the channel-geometry output from CGAP 

to calculate the stage-storage-discharge relation by solving 

Manning’s equation for open-channel flow. CGAP requires 

cross-sectional channel geometry, which was obtained from 

discharge-measurement notes at each of the streamflow-gaging 

stations in the basin and from field data collected for Federal 

Emergency Management Agency (FEMA) flood-insurance 

reports. For reaches in which channel-geometry measurements 

were not available, measurements from nearby streams with 

similar hydraulic characteristics were used in the CGAP and 

GENFTBL programs or channel-geometry and flood plain 

information from topographic maps of the area was used in 

the program XSECT (AquaTerra Consultants, 1998, written 

commun.) to develop FTABLEs. XSECT differs from CGAP 

in that the channel cross section is assumed to be trapezoidal. 

Both GENFTBL and XSECT require Manning’s roughness 

coefficients to calculate flow velocity; these coefficients were 

estimated from guidelines by Coon (1998) and Arcement and 

Schneider (1989). In reaches with streamflow-gaging stations, calculated stage-discharge relations were compared with 

measured discharges, and the stage-storage-discharge relations 

in the FTABLE were adjusted, if necessary, to improve the 

representation of the hydraulic characteristics of the reach. 

Stream lengths and slopes were determined from geospatial data describing stream centerlines and altitudes. The 

numerous dams in the basin have a substantial effect on the 

hydraulic characteristics of the stream reaches; where dams are 

prevalent, the elevation difference in a reach is represented by a 

series of flat-water impoundments separated by abrupt hydraulic drops. Because altitude drops at dams do not contribute to 

the energy slope of a reach, the total hydraulic height of the 

dams in a reach was subtracted when calculating the slope. 

As an example of the effect of dams on slope, the altitude of 

the main stem of the Blackstone River (represented by reaches 

BL1A–BL13), drops from 402 ft to 20 ft, for a total 382 ft, 

and there are 16 dams in these reaches with a total hydraulic 

drop of 207 ft, or 54 percent of the total elevation drop.

For reservoirs, various methods were used to define the 

stage-storage-discharge relations. Reservoir capacity data were 

available for 7 of 14 reservoirs simulated in the model. For the 

remaining reservoirs, stage-storage relations were estimated by 

use of bathymetry data (Massachusetts Department of Fisheries 

and Wildlife, 2004) or the topography of the stream valley near 

the reservoir along with the dam height. Similar bathymetry 

data were not available for Rhode Island water bodies. Most of 

the storage volume of a reservoir does not play a role in precipitation-runoff relations under normal climatic conditions; however, 

to allow for possible future use of the model for water-quality 

simulations, when reservoir volumes may be more relevant, the 

full storage volumes of the reservoirs were included in most of 

the FTABLEs. 

On the basis of visual inspection and other documentation, reservoir outlet structures included spillways of various 

designs equipped with flashboards, weirs, or low-level gates. 

The stage-storage-discharge relations were developed to represent the observed outlet structure as realistically as possible. 

Data on the size, shape, and altitude of the outlet structures 

were used where available; otherwise, approximations based 

on visual inspection were made to develop the FTABLEs. 

Weir rating curves were available for Lynde Brook and Kettle 

Brook No. 1 reservoirs (reach 11) and Holden Reservoir No. 2 

(reach 5). For all other reservoirs, flow was calculated with a 

broad-crested weir-flow equation (Crowe and others, 2001) or 

an orifice-flow equation (Fread, 1993). Reservoir management 

activities, such as adding or removing flashboards or changing 

gate settings, were not considered for the base calibration. 

Wetlands

Wetlands and open water, which account for 11.5 percent 

of the basin area, represent an important storage component 

of the watershed. To account for this storage, wetlands and 

open water were combined and simulated as “virtual” reaches. 

Representing wetlands as reaches that exchange water with the 

atmosphere through precipitation and evapotranspiration and 

receive inflows from adjacent PERLNDs and IMPLNDs, rather 

than as PERLNDs where evapotranspiration losses are limited 

to precipitation falling directly on the wetlands, was found to be 

an effective means of simulating wetlands in the Ipswich River 

Basin in Massachusetts (Zarriello and Ries, 2000). The amount of 

evapotranspiration loss in wetlands is typically much larger than 

the direct precipitation on the wetlands because additional water 

is available from surface and subsurface flows from surrounding 

uplands. When wetlands are simulated as PERLNDs, evapotranspiration loss is limited to the difference between precipitation 

falling directly on the wetland and runoff from the wetland, which 

can result in oversimulation of observed flows. All PERLNDS 

and IMPLNDS were assumed to drain into the virtual reaches 

before draining into the stream and reservoir reaches. 

Virtual reaches were developed for all subbasins. They 

represent the combined storage of all wetlands and open water 

in the reach. To account for the area of wetlands and open water 

in a reach, the surface area in the virtual reaches was set equal to 

the combined area of wetlands and open water. This resulted 

in an accurate total surface area for each subbasin. However, 

surface areas were decreased at the lowest flows (below approximately 1.0 ft3

/s) to account for decreases in free-water surface 

in wetlands and open water during dry periods and prevent 

excessive evapotranspiration loss during these periods. To compensate for the presence of the virtual reaches, precipitation and 

evapotranspiration were not simulated on the regular channel 

Precipitation-Runoff Model for the Blackstone River Basin  37
Table 11. Descriptions of stream reaches (RCHRES) in the Hydrological Simulation Program–FORTRAN (HSPF) model of the Blackstone River Basin, 

Massachusetts and Rhode Island.—Continued[Data from climatological stations used to simulate streamflow. Reaches and corresponding subbasins shown in fig. 8. IDLOCN, attribute in the Watershed Data Management file that identifies the reach and corresponding subbasin; W, reach was simulated as a reservoir and a weir-flow equation was used to compute flow from the reach; S, reach was simulated as a stream and an open-channel flow equation was used to compute flow from the reach; O, reach was simulated as a reservoir and an orifice-flow equation was used to compute flow from the reach, UBWPAD, Upper Blackstone Water Pollution Abatement District; KORH, Worcester Regional Airport climatological station; KPVD, T.F. Green Airport climatological station; —, not applicable]

Model 

reach 

number

IDLOCN and 

streamflow-gaging 

station identification 

number

Reach description

Direct 

drainage 

area 

(acres)

Total 

drainage 

area 

(acres)

Upstream 

reach 

number(s)

Stream geometry 

information 

available for 

reach

Method used 

to develop 

FTABLE

Climatological 

station

11 KE1A Kettle and Lynde Brook above Smiths Pond 6,287 6,287 — W KORH19 DA1A Dark Brook at Dark Brook Reservoir outlet 1,701 1,701 — W KORH16 KE2A (01109439) Kettle Brook above Rockland Road bridge 3,813 11,801 11,19 X S KORH14 KE3A Kettle Brook above confluence with Middle River 9,085 20,886 16 X S KORH

5 TA1A Tatnuck Brook above Holden Reservoir No. 2 outlet 3,363 3,363 — W KORH6 TA2A Tatnuck Brook above confluence with Middle River 6,384 9,747 5 X S KORH3 MB1B Mill Brook and Middle River 9,562 40,196 14,6 S KORH

15 BL1A Blackstone River above UBWPAD wastewater return 1,535 41,731 3 X S KORH49 BL2B (01109730) Blackstone River above station at Millbury 4,497 46,228 15 X S KORH13 BL2A Blackstone River above confluence with Quinsigamond River 16,075 62,302 49 X S KORH

1 QU1A (01110000) Quinsigamond River above station at North Grafton 16,402 16,402 — X W KORH7 QU2A Quinsigamond River above confluence with Blackstone River 7,853 24,255 1 X S KORH

20 BL3A (01110500) Blackstone River above station at Northbridge 3,138 89,695 13,7 X S KORH22 BL4A Blackstone River above confluence with Mumford River 5,392 95,087 20 X S KORH50 WH1A Unnamed tributary to Mumford River at Whitin Reservoir 5,748 5,748 — O KORH18 MU1A Mumford River above Stevens Pond 4,796 4,796 — O KORH23 MU2A Mumford River above East Douglas 8,075 18,619 50,18 X S KORH21 MU3A (01111050) Mumford River above confluence with Blackstone River 17,321 35,940 23 X S KORH25 BL5A Blackstone River above confluence with West River 569 131,596 22,21 X S KPVD17 WE1A (01111200) West River above West Hill Dam 17,883 17,883 — X S KORH24 WE2A West River above confluence with Blackstone River 6,045 23,928 17 S KPVD28 BL6A Blackstone River above confluence with Emerson Brook 1,075 156,600 25,24 X S KPVD27 EM1A Emerson Brook above confluence with Blackstone River 4,811 4,811 — S KPVD31 BL7A Blackstone River above confluence with Branch River 7,201 168,612 28,27 X S KPVD

9 CL1A Clear River at Wallum Lake 1,551 1,551 — O KPVD2 PA1A Pascoag River at Pascoag Reservoir 5,221 5,221 — W KPVD

10 CL2A Clear River above confluence with Nipmuc River 9,251 16,023 9,2 S KPVD

38  A Precipitation-Runoff Model for the Blackstone River Basin
Table 11. Descriptions of stream reaches (RCHRES) in the Hydrological Simulation Program–FORTRAN (HSPF) model of the Blackstone River Basin, 

Massachusetts and Rhode Island.—Continued[Data from climatological stations used to simulate streamflow. Reaches and corresponding subbasins shown in fig. 8. IDLOCN, attribute in the Watershed Data Management file that identifies the reach and corresponding subbasin; W, reach was simulated as a reservoir and a weir-flow equation was used to compute flow from the reach; S, reach was simulated as a stream and an open-channel flow equation was used to compute flow from the reach; O, reach was simulated as a reservoir and an orifice-flow equation was used to compute flow from the reach, UBWPAD, Upper Blackstone Water Pollution Abatement District; KORH, Worcester Regional Airport climatological station; KPVD, T.F. Green Airport climatological station; —, not applicable]

Model 

reach 

number

IDLOCN and 

streamflow-gaging 

station identification 

number

Reach description

Direct 

drainage 

area 

(acres)

Total 

drainage 

area 

(acres)

Upstream 

reach 

number(s)

Stream geometry 

information 

available for 

reach

Method used 

to develop 

FTABLE

Climatological 

station

32 NI1A (01111300) Nipmuc River above station at Harrisville 10,003 10,003 — X S KPVD39 CL3A Clear River above confluence with Branch River 3,080 29,106 10,32 S KPVD34 CH1A Chepachet River at Smith and Sayles Reservoir 5,227 5,227 — W KPVD

4 CH2A (01111410) Chepachet River above station at Gazzaville 7,085 12,312 34 X S KPVD

43 TK1A Tarkiln Brook above Slatersville Reservoir 6,072 6,072 — S KPVD36 BR1A Branch River above Slatersville Reservoir outlet 7,540 55,030 39,4,43 S KPVD37 BR2A (01111500) Branch River above station at Forestdale 3,371 58,401 36 X S KPVD30 BL8A Blackstone River Above Woonsocket Falls 8,948 235,962 31,37 S KPVD12 ML1A Mill River above Bellingham Street, South Milford 12,204 12,204 — X S KORH

8 ML2A (01112268) Mill River above station at Harris Pond Outlet 8,951 21,155 12 X W KPVD

26 PE1A (01112382) Peters River above station at Route 114 bridge 7,870 7,870 — X S KPVD35 BL9A (01112500) Blackstone River above station at Woonsocket 1,544 266,530 30,8,26 X S KPVD38 BL10 Blackstone River above confluence with Crookfall Brook 3,065 269,596 35 X S KPVD44 CR1A Crookfall Brook above Woonsocket Reservoir No. 3 outlet 1,999 1,999 — O KPVD42 CR2A Crookfall Brook above Woonsocket Reservoir No. 1 outlet 3,197 5,196 44 X W KPVD40 BL11 Blackstone River above Route 116 at Cumberland 5,929 280,721 42,38 X S KPVD45 BL12 Blackstone River above confluence with Abbott Run 3,537 284,258 40 X S KPVD33 CA1A (01113695) Catamint Brook above station at Cumberland 2,216 2,216 — X S KPVD29 AB1A Abbott Run above Arnold Mills Pond outlet 9,832 12,048 33 X W KPVD41 AB2A (01113760) Abbott Run above station at Robin Hollow Pond outlet 5,669 17,717 29 X S KPVD46 AB3A Abbott Run above Happy Hollow Pond outlet 730 18,447 41 W KPVD47 BL13 (01113895) Blackstone River above Elizabeth Webbing dam 626 303,331 45,46 X S KPVD48 BL14 Blackstone River above Old Slater Mill 310 303,642 47 X S KPVD

Precipitation-Runoff Model for the Blackstone River Basin  39
and reservoir reaches because this would have added surface 

area, and corresponding atmospheric exchanges, to the model. 

Storage-discharge characteristics for the virtual reaches 

were similar to those developed by Zarriello and Ries (2000) 

for the Ipswich River Basin. Further empirical adjustments 

were made to about 20 virtual-reach FTABLEs by matching the 

simulated and observed hydrographs. Simulating wetlands as 

reaches yielded good agreement between simulated and observed 

hydrographs; however, the storage-discharge characteristics and 

interactions between ground water and surface water are not well 

defined for virtual reaches. Also, simulating wetlands as reaches 

with a variable area introduces a structural error in the model, 

because the drainage area that exchanges water with the atmosphere decreases during dry periods (Zarriello and Ries, 2000). 

Future investigations that involve HSPF simulation would benefit 

from measuring ground-water levels in wetlands so that the wetlands module in HSPF (version 12) could be used to simulate the 

hydrology of wetlands in a less empirical manner. 

Approximately one-third of the virtual-reach FTABLEs 

were adjusted empirically during calibration. These changes 

typically involved changing the functional relation between 

storage and discharge (that is, the rate of change of discharge 

for a given change in storage) for specific flow ranges to 

improve the model fit. 

Water Use

Certain aspects of the complex water use in the basin were 

simplified for inclusion in the HSPF model. For example, in 

most cases, transfers of water across the basin boundary and 

between towns and water suppliers in the basin are not explicitly represented in the model. Rather, all major water-supply 

withdrawals from ground-water and surface-water sources that 

are distributed through public water systems and the wastewater-return flows through municipal wastewater-treatment 

plants are represented in the model as individual withdrawal 

and return time series in the individual reaches (or subbasins) 

where they are located; the difference between total withdrawals 

and total return flows represents the net overall import or export 

of water for the basin. The model does not explicitly simulate 

leakage (unaccounted for water) from municipal water-supply 

systems, which is estimated to be 10 to 15 percent of the water 

withdrawn for municipal water supply (Barlow, 2003); however, 

most of this water is likely accounted for in the HSPF model 

by the difference between reported water-supply withdrawals 

and wastewater-return flows. Withdrawals from minor suppliers (such as housing developments, apartment complexes, and 

nursing homes), private wells that are returned locally to on-site 

septic systems (that is, supplies not connected to a distribution 

system), and permitted wells with reported withdrawals below 

about 1 Mgal/yr (0.0027 Mgal/d) also were not included in the 

model. Further simplifications include omitting agricultural 

withdrawals, with the exception of golf-course withdrawals, 

and consumptive losses associated with residential withdrawals 

and minor public suppliers. Agricultural water use was omitted because total agricultural water use is less than 1 percent 

of the total water use in the basin, and withdrawals are widely 

dispersed as numerous small withdrawals throughout the basin. 

An analysis of 1997 county-level farm statistics indicates that 

total agricultural water use from irrigation of crops and nursery 

plants and livestock consumption averages about 0.44 Mgal/d 

for the entire basin, or about 0.0013 Mgal/d per square mile in 

Rhode Island and 0.00078 Mgal/d per square mile in Massachusetts (U.S. Department of Agriculture, 1999a,b). 

Thirty-six of the reaches in the model contain municipal 

and commercial/industrial withdrawals, and 20 reaches contain 

municipal and commercial/industrial wastewater-return flows 

(fig. 9). Thirty-five reaches contain withdrawals from residential 

areas with private wells and public sewers (fig. 9). Septic-effluent 

returns are associated with specific HRUs and thus are distributed throughout the basin. Withdrawals, returns, and transfers are 

specified in the EXTERNAL SOURCES block of the UCI file. 

In HSPF, outflows from different exits must be satisfied 

in successive order. For example, the time-dependent volumeoutflow demands for municipal and commercial/industrial 

withdrawals (exit 1) must be satisfied before water is routed 

downstream (exit 2). In reaches where there are only municipal 

and commercial/industrial withdrawals (9 of 50 reaches) or 

residential withdrawals (8 of 50 reaches), the withdrawals are 

taken from the first exit and the remaining flow is routed downstream through the second exit. In reaches where there are both 

municipal and commercial/industrial withdrawals and residential withdrawals (27 of 50 reaches), the withdrawals are taken 

from the first and second exits, respectively, and the remaining 

flow is routed downstream through the third exit. The first outflow exit is used to route water downstream in reaches where 

no withdrawals occur (6 of 50 reaches). In reach 14 (lower 

Kettle Brook), a fourth exit is specified to direct flow through 

a flood-control structure (Kettle Brook diversion tunnel) that 

links Kettle Brook to the Blackstone River in reach 49.

Municipal and Commercial/Industrial Withdrawals.

Time series for each of the 129 municipal and commercial/

industrial withdrawals in the basin were grouped by reach. 

When a reach contained multiple withdrawals (table 5), 

they were summed to obtain a total streamflow-depletion 

rate (demand) for that reach and stored in DSNs 101 to 150 

(table 3), corresponding to reaches 1 through 50 respectively. 

These demands were routed through the first outflow exit 

(OVOL 1) from the reach (fig. 7). 

The water-supply systems for Worcester, Mass., 

Woonsocket, R.I., and Pawtucket, R.I. are large and generally consist of multiple surface-water sources with intrabasin 

transfers of surface water. The Worcester and Woonsocket 

systems consist of multiple surface-water sources, and the 

Pawtucket system consists of both surface-water and groundwater sources. The representations of these relatively complex 

systems in the HSPF model are described below. 

The water-supply system for the city of Worcester and 

surrounding communities is composed of seven surfacewater reservoirs in the Blackstone River basin (fig. 12), and 

an additional three reservoirs in the Nashua River Basin. The 

reservoirs are in the towns of Holden, Leicester, and Paxton, 

40 A Precipitation-Runoff Model for the Blackstone River Basin
Mass. Worcester also has access to, but rarely uses, the Wachusett Reservoir, Quabbin Aqueduct Shaft 3, and ground-water 

sources for emergency supply. All the active reservoirs in the 

system feed Holden Reservoir No. 1, where water is withdrawn 

to the adjacent filtration plant for distribution. Water flows by 

gravity through the Kettle Brook reservoir system to Lynde 

Brook Reservoir, and then is piped to Holden Reservoir No. 1. 

Flows through the Kettle Brook system are controlled by gates, 

but the gate settings and associated flow rates are not available. The flow from Lynde Brook to Holden Reservoir No. 1 

is metered (table 5; DSN 2113). Holden Reservoir No. 1 also 

receives metered flow from Kendall Reservoir in the Nashua 

River Basin and Holden Reservoir No. 2, which is on Tatnuck 

Brook immediately downstream from Holden Reservoir No. 1. 

Spills from Kettle Brook No. 1, Lynde Brook, and Holden No. 2 

reservoirs are lost from the water-supply system. 

To represent this system in the HSPF model, the four 

Kettle Brook reservoirs and the Lynde Brook Reservoir were 

enclosed within a single subbasin (KE1A, reach 11) so that 

the individual flows between the reservoirs did not need to be 

explicitly defined, and the storage volumes could be combined in 

the reach FTABLE (fig. 8). Similarly, Holden Reservoirs No. 1 

and 2 were enclosed within reach 5 so that the transfer of water 

from Reservoir No. 2 to Reservoir No. 1 could be omitted and 

their storages combined. The water diverted from Lynde Brook 

Reservoir to Holden Reservoir No. 1 was represented as a 

withdrawal from reach 11 (table 5; DSN 2113) and a return flow 

to reach 5 (table 5; DSN 2113) in the EXTERNAL SOURCES 

block of the UCI file. The transfer of water from Kendall Reservoir also was represented as a return flow to reach 5 (DSN 405). 

The removal of water from Holden Reservoir No. 1 to the 

filtration plant was represented as a withdrawal from reach 5 

(DSN 2050). Thus, reach 5 receives water from two external 

sources and loses water to one external output demand. 

During calibration, it was determined that the output 

demand from reach 5 was not being satisfied by the two 

external sources of water plus runoff from precipitation on the 

subbasin. The deficit was mainly during the winter months. 

To provide sufficient water to meet the demand, a time series 

of supplemental water (DSN 1009) was developed by calculating the deficit between the sum of the inputs from the Lynde 

Brook and Kendall Reservoirs and the withdrawal to the 

filtration plant for each day of the calibration period, and then 

reducing the deficit by a smoothed time series of simulated 

runoff from the reach under unstressed conditions. The daily 

time series of simulated runoff under unstressed conditions 

was smoothed by use of a 90-day moving average to reduce 

the effect of short-term variability in runoff on the time series 

of supplemental water. The resulting time series of supplemental water (DSN 1009) was added to reach 5 as an additional 

return flow. For 1997–2001, the average supplemental flow 

needed to satisfy the demand was 4.4 Mgal/d, which is 19 percent of the average flow rate of 23.3 Mgal/d to the filtration 

plant. Considering the reported flows from Kendall Reservoir 

(9.3 Mgal/d) and the supplemental flow (4.4 Mgal/d), an average of 13.7 Mgal/d was imported from the Nashua River Basin 

for these simulations. Walker and Krejmas (1986) stated that 

45 percent of the Worcester water supply was obtained from 

the Nashua River Basin, but cited no source for this information. They reported 11 Mgal/d diverted from the Nashua 

River Basin in 1978 when total water-supply withdrawals 

were 25.0 Mgal/d. The ratio for the current study is 59 percent (13.7 Mgal/d of 23.3 Mgal/d), which may indicate that 

reported diversions from Lynde Brook Reservoir also were 

low during the winter months and contributed to the imbalance. The reported summer diversions from Lynde Brook Reservoir are near the maximum rate of 6 Mgal/d (Phillip Guerin, 

Worcester Sewer Department, oral commun., 2005).

The water-supply system for the city of Woonsocket is 

composed of three surface-water reservoirs (fig. 12). Two reservoirs, No. 1 and No. 3, are on Crookfall Brook in Smithfield 

and North Smithfield, R.I. The third reservoir, Harris Pond, is 

on the Mill River in Blackstone, Mass. Water is withdrawn from 

Reservoir No. 1 to the adjacent filtration plant for distribution. 

Harris Pond is used as a supplementary supply, mainly during 

the dry summer months. Outflow from Harris Pond is transferred 

to a pump station and then to Reservoir No. 1. A record of these 

transfers is available (table 5; DSN 2084). Spills from Harris 

Pond enter the Blackstone River and are lost from the water-supply system. Reservoir No. 3 is in the headwaters of the Crookfall 

Brook watershed. Outflow from this reservoir is controlled by 

two low-level gated outlet pipes. Water is released to Crookfall 

Brook on an as-needed basis to meet water-supply demands in 

Reservoir No. 1. Gate settings and associated flow rates from 

Reservoir No. 3 for 1997–2001 were not available. Thus, Reservoir No. 1 receives water from precipitation on its watershed, 

Harris Pond, and Reservoir No. 3. Spills from Reservoir No. 1 

enter the Blackstone River and are lost from the water-supply 

system. The reported withdrawals from Reservoir No. 1 to the 

public-water distribution system (DSN 1009) were assumed to 

represent the combined withdrawals from the entire reservoir 

system, including unmeasured flows from Reservoir No. 3.

To represent this system in the HSPF model, each of 

the three reservoirs is contained within a different subbasin 

(Harris Pond, reach 8; Reservoir No. 1, reach 42; and 

Reservoir No. 3, reach 44) (fig. 8). Although only a 

combined withdrawal record was available for Reservoirs 

No. 1 and No. 3, they were kept separate for possible future 

simulations of this water-supply system. The transfer of 

water from Harris Pond to Reservoir No. 1 was represented 

in the model as a withdrawal from reach 8 (table 5; 

DSN 2084) and a return flow to reach 42 (table 5; DSN 2084). 

The removal of water from Reservoir No. 1 was represented 

as a withdrawal from reach 42 and a withdrawal from reach 

44. The total withdrawal was split between the two reaches 

because it was determined during calibration that the output 

demand from reach 42 could not be met during the summer 

when the entire withdrawal was taken from this reach (that is, 

insufficient water was flowing from Reservoir No. 3 in reach 

44 despite repeated adjustments to the FTABLE). Therefore, 

the percentages of the total withdrawal (DSN 1009) needed 

to meet the output demand were determined empirically to be 

Precipitation-Runoff Model for the Blackstone River Basin  41
Peters River

Quinsigamond

River

Mumford River

West River

Mill River

Branch River

Chepachet River

Nipmuc River

Kettle 

Brook

Middle

River

Mill Brook

Abbott

Run

BLACKSTONE

RIVER

BLACKSTONE

RIVER

Base from U.S. Geological Survey, 1:24,000, 1995

Massachusetts state plane projection, NAD83

71°45' 71°30'

42°

42°15'

MASSACHUSETTS

CONNECTICUT

RHODE ISLAND

HOLDEN RESERVOIRS

KENDALL RESERVOIR

KETTLE BROOK

RESERVOIRS

#4

#3

#2

#1

#1

LYNDE BROOK

RESERVOIR

HARRIS POND

DIAMOND

HILL

RESERVOIR

ARNOLD

MILLS

RESERVOIR

CROOKFALL

RESERVOIRS

#3

#1

SNEECH

POND

HAPPY

HOLLOW

POND

#2

#2

0 2.5

2.5

5 MILES

0 5 KILOMETERS

EXPLANATION

OPEN WATER

BASIN BOUNDARY

SUBBASIN BOUNDARY

WATER-SUPPLY

RESERVOIR NAME

AND NUMBER

Figure 12. Water-supply reservoirs in the Blackstone River Basin. 

42  A Precipitation-Runoff Model for the Blackstone River Basin
30 percent from reach 42 (table 5; DSN 2420) and 70 percent 

from reach 44 (table 5; DSN 2440). 

The water-supply system for the cities of Pawtucket and 

Central Falls and part of the Town of Cumberland consists of 

two surface-water reservoirs (Diamond Hill and Arnold Mills) 

in the headwaters of Abbott Run, and eight wells along Abbott 

Run downstream from the reservoirs that are used to supplement the surface-water supply (fig. 12). The intake for the 

Pawtucket Water Treatment Plant is located at the south end of 

Happy Hollow Pond, near the confluence of Abbott Run and 

the Blackstone River (fig. 12). Outflow from the reservoirs is 

controlled by gates. Flow rates to Abbott Run are regulated on 

an as-needed basis to meet water-supply demands at Happy 

Hollow Pond, but gate settings and associated flow rates are 

not available. To represent this system in the HSPF model, the 

two reservoirs were enclosed within a single subbasin (AB1A, 

reach 29) so that the individual flows between the reservoirs 

did not need to be explicitly defined, and the storage volumes 

could be combined in the reach FTABLE (fig. 8). The reach of 

Abbott Run downstream from the reservoirs, which includes 

ground-water withdrawals, was represented by reach 41, and 

Happy Hollow Pond, which includes the intake for the watertreatment plant and additional ground-water withdrawals, was 

represented by reach 46 (fig. 8). The removal of surface water 

from Happy Hollow Pond was represented by a withdrawal 

from reach 46 (table 5; DSN 2460), and the removal of ground 

water was represented by individual withdrawals from reaches 

41 and 46 (table 5). Downstream releases of water from the 

reservoirs were treated as unregulated flows from reach 29; 

the flow rate was controlled by the volume-discharge relation 

specified in the reach FTABLE. It was not necessary to specify 

any intrabasin transfers to represent this water-supply system 

in the model. 

Withdrawals in Residential Areas with Public Sewers.

Time series for residential withdrawals were estimated from 

population-density and water-use data. The quantity of water 

exported from residential areas with private wells and public 

sewers per reach was calculated by multiplying the population 

density by an average rate of water use of 71 gallons per day 

(gal/d) per person (Korzendorfer and Horn, 1995), resulting in 

export rates of 1,016 gal/d per acre for high-density residential areas, and 265 gal/d per acre for medium- to low-density 

residential areas. These export rates were then multiplied by 

the total area of the appropriate residential density in each subbasin and added together to obtain a total rate of export from 

the reach. Values were converted to cubic feet per second and 

read into the model as external withdrawal time series in the 

EXTERNAL SOURCES block of the UCI file. Total residential withdrawals were routed through the second outflow 

exit (fig. 7; OVOL 2). Because only 1,965 acres of pervious 

residential land have private wells and public sewers in the 

basin (table 9), the quantity of this type of exported water is 

small; nonetheless, water exported from residential areas was 

included in the model to represent residential water use in the 

basin as realistically as possible.

Municipal and Commercial/Industrial Waste­waterReturn Flows and Interbasin Transfers. Wastewater is 

returned to the reach in which the outfall is located as an 

inflow time series (fig. 7; IVOL) specified in the EXTERNAL 

SOURCES block. When a reach contained multiple return 

flows (table 6), they were summed to obtain a total return-flow 

rate for that reach and stored in DSNs 401 to 450 (table 3), 

corresponding to reaches 1 through 50 respectively. Interbasin 

transfers and transfers between subbasins also are represented 

as inflows to a reach, where necessary. 

Wastewater returned to the stream network through 

treatment-plant outfalls originates from a variety of sources: 

domestic wastewater from residential and institutional sources, 

non-domestic wastewater from commercial and industrial 

sources, storm water from combined sewers, and ground 

water and storm water from infiltration and inflow (I/I). In 

the context of a sanitary-sewer system, infiltration refers to 

ground water that enters the system through leaks in pipes, 

connections, and manhole walls, and inflow refers to storm 

water that inadvertently enters the system through interconnections with roof and foundation drains, sump pumps, and 

manhole covers. Combined sewers (CSs) refer to systems in 

which storm and sanitary sewers are combined and a portion 

of the storm runoff is intentionally diverted to the treatment 

plant. In these systems, combined sewer overflows (CSOs) 

also may occur during heavy rainfall and snowmelt events. 

Precipitation on the sewered areas in the basin is the source of 

I/I and CS return flow. Thus, because wastewater returns are 

added to reaches as external sources of water in HSPF, I/I and 

CS contributions to wastewater-return flows represent excess 

water (that is, water added to the model as both precipitation 

and wastewater-return flow). 

HSPF is not designed to simulate the movement of water 

in sewer systems in urban areas; however the model has the 

flexibility to account for the effects of I/I and CS return flow 

in a simplified manner. To account for infiltration, the parameter DEEPFR was used to represent empirically the flow of 

ground water into public sewer systems in the basin. DEEPFR 

is the fraction of infiltrating water lost to deep aquifers, with 

the remaining fraction assigned to active ground-water storage 

that contributes base flow to stream reaches. DEEPFR can be 

used to represent any loss from the ground-water flow system 

(typically lateral flow from deeper aquifers to adjacent basins 

or flow under a streamflow-gaging station) that occurs and 

reduces outflow from ground-water storage (U.S. Environmental Protection Agency, 2000). DEEPFR is one of three mechanisms, along with evapotranspiration and discharge to streams, 

for removing water from a pervious land segment. In this study, 

all residential and commercial-industrial-transportation areas 

that intersect with a public sewer system (table 9; PERLNDs 

1, 4, 5, 7, 8, 12, 13, 15, and 16) were assigned non-zero values 

for DEEPFR to represent infiltration. 

Final DEEPFR values of 0.35 for commercial-industrial-transportation areas (PERLND 1), 0.45 for high-density 

residential areas (PERLNDs 7, 8, 15, and 16), and 0.28 for 

medium- to low-density residential areas (PERLNDs 4, 5, 

Precipitation-Runoff Model for the Blackstone River Basin  43
12, and 13) were used to empirically represent the differing 

sewer-line densities in these land-use categories. Values were 

adjusted during calibration to obtain a total sewer infiltration 

loss of about 17 Mgal/d for the entire basin, which is equal to 

34 percent of the total wastewater-return flow of 50.6 Mgal/d 

in the basin for 1997–2001. However, roughly 15 percent of 

the sewered areas in the basin (predominantly the sewered 

areas in Cumberland and Lincoln, R.I.) discharge to facilities 

outside the basin, so total wastewater-return flow is closer to 

60 Mgal/d for the basin, and infiltration losses computed with 

the DEEPFR parameter are closer to 28 percent of the total 

return flow. DEEPFR losses are stored in the inactive groundwater inflow (IGWI) time series. Although DEEPFR provides 

only a rough approximation of the spatial and temporal distribution of infiltration losses in the basin, accounting for these 

losses is more realistic than leaving excess water in the basin, 

which could skew parameter values. 

The sewer system in the Worcester area is the largest 

(fig. 6) and most complex in the basin and thus required special attention in the model to enable simulation of streamflow 

from the headwaters of the basin. The total sewered population 

in the UBWPAD service area was estimated to be 160,900 in 

2000 (Camp, Dresser, and McKee, 2001). Return flow from 

the UBWPAD treatment plant averaged about 35.4 Mgal/d 

(55 ft3/s) during the calibration period (table 6), which constituted approximately 20 percent of the summer low flow at 

the mouth of the basin. A small amount of this flow (about 

1.3 Mgal/d) originated from outside the basin in Rutland, 

Mass.; however, for simplicity this flow was not removed from 

the total UBWPAD return flow in the analysis that follows. 

The Regional Wastewater Treatment Facilities Plan, conducted for UBWPAD by Camp, Dresser, and McKee, indicates that the average annual wastewater flow for 1993–1998 

was 37.4 Mgal/d, of which 19.6 Mgal/d was sanitary sewage, 14.0 Mgal/d was infiltration, and 3.8 Mgal/d was inflow 

(Camp, Dresser, and McKee, 2001). The average dry-day 

wastewater-return flow from UBWPAD for the period was 

33.6 Mgal/d. The average inflow rate was calculated as the 

difference between the total flow and the dry-day flow, and 

the average infiltration rate was calculated as the difference 

between the sanitary flow and the dry-day flow. It should 

be noted that, for this study, measured inflow to UBWPAD 

was assumed to represent stormwater composed of both the 

intentional CS return flows and the unintentional stormwater 

inflows, and is referred to as “inflow plus CS return flow.” 

These calculations indicate that for 1993–98, the total amount 

of water derived from precipitation on the sewered area (infiltration and inflow plus CS return flow) was about 48 percent 

of the average wastewater flow to UBWPAD. For 1997–2001, 

conditions were drier than for 1993–98. Assuming that the 

lower flows to UBWPAD for 1997–2001 (35.4 Mgal/d) were 

caused by less infiltration and inflow plus CS return flow (that 

is, the sanitary-sewage flow rate was unchanged), the total 

contribution from infiltration and inflow plus CS return flow 

would be about 15.8 Mgal/d (35.4 Mgal/d minus 19.6 Mgal/d), 

of which about 12.4 Mgal/d was infiltration and the remaining 

3.4 Mgal/d was inflow plus CS return flow. 

Stormwater from combined sewers that is included in 

the wastewater flow to UBWPAD was addressed by removing impervious area from the model. The sewer system in 

the city of Worcester contains approximately 2,500 acres of 

combined sewers (P. Moosey, Worcester Sewer Department, 

oral commun., 2005). Wastewater and stormwater flows from 

the combined-sewer area are directed to the Quinsigamond 

Avenue CSO treatment facility. Under normal conditions, this 

facility operates as a pumping station, transferring water to 

the UBWPAD facility; however, during extremely wet periods 

when the capacity of the UBWPAD facility has been reached, 

flow from the combined-sewer area is bypassed to the CSO 

facility, where it is treated and released to the Blackstone 

River. A time series of the intermittent releases from the CSO 

facility during the calibration period is included as an inflow 

to reach 3 (table 6; DSN 3031). The average flow rate from 

the CSO facility was 1.1 Mgal/d for 1997–2001. Because the 

precipitation that falls on the CS area is accounted for in the 

CSO and UBWPAD return flows to the model, 1,800 acres of 

impervious area were removed: 1,200 acres were removed 

from reach 3, which encompasses most of downtown Worcester, and 600 acres were removed from reach 6 (fig. 8). The CS 

area removed from the model was reduced from the reported 

area of 2,500 acres to achieve streamflow reductions consistent with inflows reported in the Regional Wastewater Treatment Facilities Plan (Camp, Dresser, and McKee, 2001) and 

releases from the CSO plant.

The effect of removing impervious area was determined 

by computing the average simulated surface-runoff rate from 

the impervious area for 1997–2001. Removing 1,800 acres of 

impervious area reduced runoff by 4.9 Mgal/d (7.6 ft3/s) for 

1997–2001. The effect of using the DEEPFR parameter to represent ground-water infiltration to sewers was determined by 

observing simulated changes in the mean annual flows at the 

Blackstone River at Millbury, Mass. station. Infiltration losses 

computed with the DEEPFR parameter reduced the simulated 

mean annual streamflow by 3.5 Mgal/d (5.2 ft3/s). Together, 

these simulated losses of 8.4 Mgal/d are about 50 percent of 

the estimated 16.9 Mgal/d contribution from infiltration and 

inflow plus CS return flows to UBWPAD (15.8 Mgal/d) and 

releases from the CSO facility (1.1 Mgal/d) for 1997–2001. 

The average infiltration loss of 3.5 Mgal/d computed with the 

DEEPFR parameter was less than the actual average infiltration loss of 12.4 Mgal/d for 1997–2001. On the other hand, the 

average stormwater loss of 4.9 Mgal/d computed by removing impervious area was in good agreement with the actual 

average stormwater loss of 4.5 Mgal/d (3.4 Mgal/d from 

inflow plus CS return flow to UBWPAD plus 1.1 Mgal/d from 

releases from the CSO facility) for 1997–2001. The disparity in infiltration rates is assumed to reflect uncertainty in the 

reported relative contributions of ground-water infiltration and 

stormwater runoff to UBWPAD, as well as the use of DEEPFR 

to represent ground-water infiltration to sewers. 

44  A Precipitation-Runoff Model for the Blackstone River Basin
Septic-Effluent Returns in Residential Areas with 

Public Water. The quantity of septic effluent imported to 

residential areas served by public water systems was calculated by multiplying the population density by the average 

rate of water use of 67 gal/d per person (Korzendorfer and 

Horn, 1995), resulting in import rates of 959 gal/d per acre 

for high-density residential areas and 251 gal/d per acre and 

medium- to low-density residential areas. These import rates 

were converted to inches per hour per acre (0.00147 in/hr/acre 

for high-density residential area and 0.000384 in/hr/acre for 

medium- to low-density residential areas), and added to the 

applicable HRUs (PERLNDs 6, 9, 14, and 17) as inflow to 

lower-zone storage (LZLI) using an external time series in 

the EXTERNAL SOURCES block of the UCI file. Applying 

water to lower-zone storage is appropriate because septic leach 

fields typically are installed in this part of the soil horizon. In 

HSPF, water in the lower soil zone is not available to runoff or 

discharge as interflow or base flow. Rather, this storage zone 

holds water that is removed to the atmosphere through evapotranspiration. Adding septic effluent to lower-zone storage 

decreases the storage available in this zone for infiltrating precipitation. Consequently, more infiltrated precipitation reaches 

active ground-water storage, which is available to discharge as 

base flow, in areas receiving septic effluent relative to similar 

areas not receiving effluent.

The estimated import rate from septic systems is 

12.9 in/yr in high-density residential areas and 3.4 in/yr in 

medium- to low-density residential areas. These rates represent about 31 and 8 percent of the average annual precipitation 

of 42 in/yr on these areas, respectively. Pervious residential 

areas on public water and private sewers compose about 

3 percent (9,743 acres) of the basin, of which the majority 

(8,753 acres) is medium- to low-density development. Thus, 

the widely distributed septic effluent constitutes a relatively 

small percentage (about 6 percent) of the total wastewaterreturn flow in the basin. Total return flow of septic effluent 

averaged 3.1 Mgal/d for the entire basin.

Model Calibration

The Blackstone River Basin model was calibrated for January 1, 1997 to December 31, 2001 using an hourly time step 

and climatological data from the KORH (Worcester, Mass.) and 

KPVD (Warwick, R.I.) climatological stations. The precipitation during the calibration period of 1997–2001 was slightly 

lower than the long-term average precipitation (1960–2004). 

Precipitation for the calibration period averaged 39.4 in/yr in 

the northern part of the basin and 43.1 in/yr in the southern part 

of the basin. Of these years, 1998 was the wettest and 2001 

was the driest. The 1997–2001 period was used for calibration 

because land-use data from 1995 (R.I.) and 1999 (Mass.) were 

used to define the PERLNDs, and considerable water-use data 

were available from Barlow (2003). Water-use data were available for years more recent than 2001, but because land use is 

changing rapidly in the basin, a calibration period centered on 

1999 (the Mass. data layer represents land use in 71 percent 

of the basin) was believed to best represent the basin. Initially, 1996 was to be included in the calibration, but it was 

determined that the reliability of the precipitation records at 

KORH and KPVD was poor for that year because of changes in 

data-collection methods. Consequently, the model was run from 

1996 onward to allow the initial values for the less-dynamic soil 

and ground-water storages (upper-zone storage (UZS), lowerzone storage (LZS), active ground-water storage (AGWS), and 

the initial index to ground-water slope (GWVS) to approach 

dynamic equilibrium, but 1996 was not used to determine the 

goodness-of-fit between simulated and observed flows. Wateruse data are needed to calibrate the model parameters. The 

inclusion of the major stresses in the basin ensures that the net 

effect of the stresses on simulated hydrographs is represented. 

Consequently, the calibrated values of the hydrologic parameters better represent the hydrologic response of the basin to 

precipitation (Zarriello and Ries, 2000). 

Simulations for model validation were not conducted 

because of limited data availability and the intended uses of 

the model. Water-use information was obtained for 1997–2001 

to coincide with the available digital land-use information, 

and all 5 years of data were used for parameter calibration to 

represent variability in climatic conditions to the fullest extent 

possible. Validation would require breaking up the data into 

shorter periods for calibration and validation, thus reducing the 

reliability of parameter calibration. The model fit to observed 

flows during this period provides the best validation of the 

calibrated model parameters over the widest range of climatic 

conditions. This approach was deemed appropriate because the 

model was primarily developed to evaluate relative changes in 

streamflow that take place in response to predetermined landand water-use conditions in the basin, and to compute flow 

frequency probabilities for these conditions from long-term 

climatological data. 

The model was calibrated in accordance with guidelines 

by Donigian and others (1984) and Lumb and others (1994). 

Calibration entailed first adjusting the parameter values to 

fit the model output to total and seasonal water budgets, 

and then adjusting values to improve the model fit for daily 

flows while maintaining the total and seasonal water budgets. 

Generally, annual and seasonal flows are affected most by the 

parameters LZSN (lower-zone nominal storage parameter), 

LZETP (lower-zone evapotranspiration parameter), DEEPFR 

(fraction of ground water that enters a deep flow system), 

UZSN (upper-zone nominal storage parameter), KVARY 

(ground-water recession parameter that determines the degree 

of nonlinearity of the recession rate), and AGWRC (active 

ground-water recession constant). Storm flows are affected 

most by INFILT (infiltration parameter), INTFW (coefficient 

that determines the amount of water that enters the ground 

from surface storage and becomes interflow) and IRC (interflow recession constant). The model was calibrated by first 

adjusting parameter values as a group for PERLNDs overlying 

sand and gravel and PERLNDs overlying till. Once reasonable 

simulation results were obtained, judgments based on hydroPrecipitation-Runoff Model for the Blackstone River Basin  45
logic experience were used to make further adjustments to 

parameter values for individual PERLNDs representing different land-use types in each of these geologic groups. Parameters representing snow accumulation and melt processes were 

given less consideration because the primary purpose of the 

model is to simulate the effects of changes in water demand 

and land-use on low flows. The snow accumulation and melt 

routines were included primarily to adjust precipitation data 

to compensate for inefficiencies in precipitation measurements during cold periods when precipitation was in the form 

of snow. SNOW section parameters were obtained mostly 

from other HSPF studies (U. S. Environmental Protection 

Agency, 2000). 

Values for some parameters, such as the slopes and mean 

altitudes of HRUs, were determined from spatial data. However, most parameters could not be measured directly and were 

initially assigned values similar to those used for comparable 

HRUs in the Ipswich River Basin model (Zarriello and Ries, 

2000) or values developed from other applications of HSPF 

across North America (U.S. Environmental Protection Agency, 

2000). The iterative process described above then was used 

to adjust these values to minimize the difference between 

simulated and observed flows displayed as hydrographs, scatter plots, and flow-duration curves, and reduce the errors in 

the model-fit statistics. The PERLND parameters that affect 

the rate of ground-water and interflow recession (AGWRC, 

KVARY, IRC, and INTFW) and the amount of discharge as 

base flow and interflow (INFILT, LZSN, UZSN, and LZETP) 

were adjusted most extensively to calibrate the model. These 

parameters are discussed in greater detail in the “Sensitivity 

to Model Parameters” section of the report. Simulation results 

were insensitive to most of the remaining parameters; consequently, values for these parameters were not adjusted from 

initial values during the calibration. Parameter values for the 

calibrated model are given in the partial listing of the UCI file 

in appendix 1. 

Streamflow data from the 15 streamflow-gaging stations 

in the basin (fig. 4) provided the model-calibration points; 

however, long-term stations with measured streamflow for 

the calibration period (Quinsigamond River at North Grafton, 

Mass. [station no. 01110000]; Branch River at Forestdale, R.I. 

[station no. 01111500]; Nipmuc River near Harrisville, R.I. 

[station no. 01111300]; and Blackstone River at Woonsocket, 

R.I. [station no. 01112500]) provided the primary data for 

determining calibrated parameter values. In addition to the 

availability of streamflow measurements during the calibration period, these stations were chosen because the flows are 

relatively unaffected by regulation, and the drainage areas differ with respect to the amount of development. For example, 

the drainage area to the Quinsigamond River at North Grafton, 

Mass. station is relatively developed, whereas the drainage 

area to the Branch River at Forestdale, R.I. station is dominated by undeveloped, forested land use. Parameter values 

obtained by fitting the model to data from these four stations 

best represent the hydrologic response of the basin. Agreement between simulated and observed flows was taken into 

consideration at the other stations in the basin, but, in general, standards for model performance were relaxed slightly 

at these stations because observed flows were computed 

and(or) strongly affected by regulation. Model calibration 

at these locations was achieved mainly by FTABLE adjustment. It should be noted that all streamflow measurements, 

whether measured directly during the calibration period or 

computed by use of record-extension techniques, are referred 

to as “observed” streamflow in the following discussion of 

model performance. 

The quality of the model fit was examined by mathematical summary statistics provided by utilities in the programs 

GenScn, HSPEXP, and PEST (Doherty, 2003). The timeseries-compare utility in GenScn provides fit statistics computed from daily and monthly discharge values. The statistics 

reported here include the simulated and observed mean-flow 

rates, the mean error, the percent mean error, the root mean 

square error (RMSE), and the coefficient of determination 

(r2) for monthly and daily flows during the calibration period 

(tables 12 and 13). The mean error is defined as the absolute 

difference between the mean observed and mean simulated 

flow rates. The percent mean error is defined as the ratio of 

the mean error to the mean observed flow rate expressed as 

a percentage. The RMSE and mean error express the difference between the observed and simulated streamflow 

in original (ft3/s) units. Tables 12 and 13 show that percent 

mean errors ranged from –1.6 percent at the Blackstone River 

at Pawtucket, R.I. station to 16 percent at the Mill River at 

Woonsocket, R.I. station. Love and Donigian (2002) indicate 

that HSPF model fits for streamflow are considered very good 

when errors are less than 10 percent, good when errors are 

between 10 and 15 percent, and fair when errors are between 

15 and 25 percent. The errors in mean monthly and daily flows 

for the calibration period were within 10 percent at 12 stations, 

within 10 to 15 percent at 2 stations, and within 15 to 25 percent at 1 station (tables 12 and 13).

The series-compare utility in PEST provided other fit 

statistics computed from daily mean discharge and total 

monthly runoff values. These statistics include the NashSutcliffe coefficient (R2

), and the index of agreement 

(tables 12 and 13). The coefficient of determination, NashSutcliffe coefficient, and index of agreement are common 

goodness-of-fit measures of the performance of watershed 

models. All three statistics provide a measure of the amount of 

the variance in the observed values explained by the simulated 

values. The Nash-Sutcliffe coefficient and index of agreement, 

however, provide a more rigorous evaluation of the fit quality 

than does r2 because they are sensitive to differences between 

the observed and simulated means and variances, whereas r2

measures differences between means only and is insensitive 

to the magnitude of the differences between observed and 

simulated values (Legates and McCabe, 1999). For example, 

the widely used Nash-Sutcliffe coefficient, which ranges from 

minus infinity to 1.0, is defined as

46  A Precipitation-Runoff Model for the Blackstone River Basin
( )

2

2

1

2

1

R 1 0

O S

O O

i i

i

N

i i

= - N

-

-

=

=

å

å

.

( )

 (1)

Where Si and Oi are 

the model-simulated and observed values, respectively, at time 

i, N is the number of values for the time period of the evaluation, and O is the observed mean for the entire time period of 

the evaluation. When R2 equals zero, the observed mean is as 

good a predictor of observed values as the model (that is, the 

simulated values) (Legates and McCabe, 1999). The Nash-Sutcliffe coefficient for daily mean flows ranged from 0.22 at the 

West River at Uxbridge, Mass. station to 0.78 at the Blackstone River at Woonsocket, R.I. station (table 13). Results for 

the index of agreement, which ranges from 0.0 to 1.0 with 

higher values indicating a better fit, were consistent with 

results for the Nash-Sutcliffe coefficient, with values ranging 

from 0.76 at the West River at Uxbridge, Mass. station to 0.94 

at the Blackstone River at Woonsocket, R.I. and Pawtucket, 

R.I. stations (table 13). Overall, the statistics shown in tables 

12 and 13 indicate that the agreement between simulated and 

observed values was poorest at the West River at Uxbridge, 

Mass. station, possibly due to the regulation of peak flows 

at the West Hill Dam that is not accounted for in the model. 

Agreement was best at the Blackstone River at Woonsocket, 

R.I. and Blackstone River at Pawtucket, R.I. stations.

The HSPEXP program provides model-fit information 

in terms of the error between various measures of simulated 

and observed values (table 14). These measures include error 

during the calibration period in the total and seasonal runoff 

volumes, flows above the 10th percentile (high flows) and 

below the 50th percentile (low flows), and the base-flow recession constant, which is the difference in the ratio of the current 

day’s discharge to the previous day’s discharge for simulated 

and observed flows. Errors also are computed for storm-runoff volumes and peak discharges for selected summer storms. 

These statistics were designed to work with the “expert” 

advice feature of HSPEXP. In general, errors in the total runoff 

volumes, low-flow recession constant, high and low flows, and 

summer storm volumes are within the criteria for acceptable 

model performance defined by Donigian and others (1984), 

whereas errors in the storm peaks and seasonal volumes are 

outside these criteria at most stations (table 14). 

Overall, the statistics indicate that the model performs 

relatively well at the four stations on the Blackstone River and 

tributaries such as the Mumford River, the Chepachet River, the 

Peters River, and Abbott Run (tables 12 through 14); however, 

as discussed in the “Streamflow” section of the report, errors in 

observed streamflow may be substantial at the stations where 

streamflow was computed by correlation with surrounding stations. Also, measurement error and flow regulation may result 

in differences between the measured streamflow record and the 

natural watershed response at the stations where streamflow 

measurements were made during the calibration period. Thus, 

model-fit statistics may reflect the quality of the observed data 

as well as model performance, particularly at the stations with 

estimated data. It also should be noted that model-fit statistics 

reported as a percentage can be a poor indicator of the quality of the fit for low flows because a small absolute difference 

between the observed and simulated value can appear as a 

large percentage difference. Visual inspection of the hydrographs, flow-duration curves, and scatter plots of simulated and 

observed streamflows at varying time scales provide additional 

information to evaluate model performance. 

Annual and Monthly Mean Discharge

Scatter plots of observed and simulated annual mean discharges for 1997–2001 at selected streamflow-gaging stations 

are shown in figure 13. Observed annual mean discharges at 

the stations shown in figure 13 ranged from 30 ft3/s (Quinsigamond River at North Grafton, Mass., 2001) to 1,020 ft3

/s 

(Blackstone River at Pawtucket, R.I., 1998). These plots show 

that the simulated and observed annual mean discharges are 

generally close to the lines of equality at the three Blackstone River stations (fig. 13B, E, and F), the Branch River 

at Forestdale, R.I. station (fig. 13D), and the Nipmuc River 

near Harrisville, R.I. station (fig. 13C). The agreement is not 

as good at the Quinsigamond River at North Grafton, Mass. 

station (fig. 13A). Annual mean discharge at the Quinsigamond River at North Grafton, Mass. and Blackstone River 

at Pawtucket, R.I. stations is oversimulated on average by 

6.0 percent and 1.5 percent, respectively, during the calibration period. Annual mean discharge at the Blackstone River at 

Millbury, Mass., Nipmuc River near Harrisville, R.I., Branch 

River at Forestdale, R.I., and Blackstone River at Woonsocket, 

R.I. is undersimulated on average by 2.0 percent, 9.1 percent, 

4.7 percent, and 5.0 percent, respectively, during the calibration period. These errors are calculated as the mean of the 

percent differences for each year in the calibration period. The 

maximum single-year difference was an oversimulation of 36 

percent in 1999 at the Quinsigamond River at North Grafton, 

Mass. station. The minimum single-year difference was an 

undersimulation of 0.4 percent in 2000 at the Blackstone River 

at Woonsocket, R.I. station. Annual mean discharges were 

most consistently undersimulated during 2001, when undersimulation at all six stations ranged from 19 percent at the 

Nipmuc River near Harrisville, R.I. station to 4.4 percent at 

the Blackstone River at Millbury, Mass. station. 

Scatter plots of observed and simulated monthly mean 

discharges for 1997–2001 at selected streamflow-gaging 

stations are shown in figure 14. Observed monthly mean 

discharges at the stations shown in figure 14 ranged from 

0.1 ft3/s (Quinsigamond River at North Grafton, Mass., 

August 1999) to 2,320 ft3/s (Blackstone River at Woonsocket, 

R.I., March 2001). These plots show that the simulated and 

observed mean monthly discharges are generally close to the 

lines of equality over much of the observed range of flows, 

including months with the lowest flows. Correlation coefficients ranged from 0.91 (Nipmuc River near Harrisville, R.I. 

Precipitation-Runoff Model for the Blackstone River Basin  47
Table 12. Summary of monthly model-fit statistics for flows simulated by the Hydrological Simulation Program–FORTRAN (HSPF) model and observed or computed flows at 

15 streamflow-gaging stations in the Blackstone River Basin, Massachusetts and Rhode Island, January 1997 through December 2001.[Streamflow-gaging stations shown in fig. 4. Parameter Estimation Program used to compute the Nash-Sutcliffe coefficient and index of agreement. GenScn program used to compute other statistics. Statistics for Catamint Brook are for August 1999 through December 2001. Shading denotes the primary stations for model calibration. Computed, streamflow records used to evaluate model performance computed by correlation with records from other continuous-record streamflow-gaging stations. ft3/s, cubic feet per second]

Statistic

Kettle 

Brook

KE2A

01109439

Computed

Blackstone

 River at 

Millbury 

BL2B

01110000

Computed

Quinsigamond 

River 

QU1A

01109730

Blackstone 

River at 

Northbridge

BL3A

01110500

Mumford 

River 

MU3A 

01111050 

Computed

West 

River 

WE1A 

01111200

Nipmuc 

River

NI1A 

01111300

Chepachet 

River 

CH2A 

01111410 

Computed

Branch 

River 

BR2A 

01111500

Mill 

River 

ML2A 

01112268

Computed

Peters 

River PE1A 

01112382

Computed

Blackstone 

River at 

Woonsocket 

BL9A 

01112500

Catamint 

Brook 

CA1A 

01113695

Abbott 

Run 

AB2A 

01113760 

Computed

Blackstone 

River at Pawtucket 

BL13

01113895

Computed

Number of months 60 60 60 60 60 60 60 60 60 60 60 60 29 60 60Mean observed flow rate (ft3/s) 27.4 157 35.0 275 85.7 42.7 28.6 33.3 161 64.2 22.3 748 5.47 49.6 787Mean simulated flow rate (ft3/s) 23.8 154 36.6 260 87.9 44.3 26.1 32.4 154 53.8 20.1 710 5.55 45.9 800Mean error (ft3/s) 3.56 3.10 –1.61 14.4 –2.17 –1.57 2.44 0.89 7.47 10.3 2.23 38.0 –0.09 3.70 –12.7Percent mean error 13.0 1.98 –4.60 5.25 –2.53 –3.67 8.55 2.66 4.64 16.1 10.0 5.07 –1.61 7.46 –1.62Root mean square error (ft3/s) 11.4 31.1 13.5 92.6 21.5 20.0 12.7 8.83 45.0 28.9 6.10 201 2.35 11.6 178Coefficient of determination (r2) 0.83 0.90 0.83 0.82 0.90 0.77 0.83 0.90 0.89 0.88 0.89 0.91 0.86 0.84 0.92Nash-Sutcliffe coefficient (R2) 0.81 0.88 0.82 0.82 0.89 0.77 0.79 0.89 0.88 0.80 0.87 0.89 0.81 0.82 0.91Index of agreement 0.95 0.97 0.95 0.94 0.97 0.93 0.93 0.97 0.97 0.93 0.96 0.97 0.93 0.95 0.98

Table 13. Summary of daily model-fit statistics for flows simulated by the Hydrological Simulation Program–Fortran (HSPF) model and observed or computed flows at 15 streamflow-gaging stations in the Blackstone River Basin, Massachusetts and Rhode Island, January 1997 through December 2001.[Streamflow-gaging stations shown in fig. 4. Parameter Estimation Program used to compute the Nash-Sutcliffe coefficient and index of agreement. GenScn program used to compute other statistics. Statistics for Catamint Brook are for August 1999 through December 2001. Shading denotes the primary stations for model calibration. Computed, streamflow records used to evaluate model performance computed by correlation with records from other continuous streamflow-gaging stations. ft3/s, cubic feet per second]

Statistic

Kettle 

Brook

KE2A

01109439

Computed

Blackstone 

River at 

Millbury

BL2B

01110000

Computed

Quinsigamond 

River

QU1A

01109730

Blackstone 

River at 

Northbridge

BL3A

01110500

Mumford 

River

MU3A

01111050

Computed

West 

River 

WE1A

01111200

Nipmuc 

River

NI1A

01111300

Chepachet 

River 

CH2A

01111410

Computed

Branch 

River

BR2A

01111500

Mill 

River 

ML2A

01112268

Computed

Peters 

RiverPE1A

01112382

Computed

Blackstone 

River at 

Woonsocket

BL9A

01112500

Catamint 

Brook

CA1A

01113695

Abbott Run

AB2A

01113760

Computed

Blackstone 

River at 

Pawtucket

BL13

01113895

Computed

Number of days 1,826 1,826 1,826 1,826 1,826 1,826 1,826 1,826 1,826 1,826 1826 1,826 884 1,826 1,826Mean observed flow rate (ft3/s) 27.3 156 34.9 274 85.4 42.5 28.4 33.2 160 63.9 22.2 745 5.45 49.4 784Mean simulated flow rate (ft3/s) 23.7 153 36.5 259 87.5 44.1 26.0 32.3 153 53.6 20.0 707 5.54 45.7 796Mean error (ft3/s) 3.59 3.10 –1.57 14.4 –2.12 –1.58 2.43 0.90 7.50 10.3 2.22 37.8 –0.08 3.68 –12.5Percent mean error 13.2 1.99 –4.50 5.26 –2.48 –3.70 8.56 2.70 4.68 16.1 10.0 5.08 –1.53 7.45 –1.60Root mean square error (ft3/s) 20.6 89.8 22.8 160 50.5 50.9 27.7 21.3 117 58.0 12.2 390 4.09 24.2 395Coefficient of determination (r2) 0.72 0.70 0.74 0.73 0.73 0.36 0.61 0.74 0.70 0.71 0.76 0.79 0.73 0.67 0.80Nash-Sutcliffe coefficient (R2) 0.66 0.51 0.70 0.71 0.69 0.22 0.61 0.74 0.70 0.67 0.74 0.78 0.75 0.66 0.77Index of agreement 0.91 0.90 0.92 0.92 0.92 0.76 0.86 0.92 0.91 0.87 0.93 0.94 0.91 0.89 0.94

48  A Precipitation-Runoff Model for the Blackstone River Basin
Table 14. Summary of model-fit statistics computed by the HSPEXP program for flows simulated by the Hydrological Simulation Program–FORTRAN (HSPF) model and 

observed or computed flows at 15 streamflow-gaging stations in the Blackstone River Basin, Massachusetts and Rhode Island, January 1997 through December 2001.[Streamflow-gaging stations shown in fig. 4. Numbers in table represent percent error between simulated and observed flow at streamflow-gaging stations. Negative numbers indicate that simulated values are less than observed or computed values. Statistics for Catamint Brook are for August 1999 through December 2001. Shading denotes primary stations used for model calibration. Computed, streamflow records used to evaluate model performance computed by correlation with records from other streamflow-gaging stations. %, percent]

Statistic

Acceptance 

criteria

(% error)

Kettle 

Brook

KE2A

01109439

Computed

Blackstone 

River at 

Millbury

BL2B

01110000

Computed

Quinsigamond 

River

QU1A

01109730

Blackstone 

River at 

Northbridge

BL3A

01110500

Mumford 

River

MU3A

01111050

Computed

West 

River 

WE1A

01111200

Nipmuc

 River

NI1A

01111300

Chepachet 

River 

CH2A

01111410

Computed

Branch 

River

BR2A

01111500

Mill River 

ML2A

01112268

Computed

Peters 

RiverPE1A

01112382

Computed

Blackstone 

River at 

Woonsocket

BL9A

01112500

Catamint 

Brook

CA1A

01113695

Abbott Run

AB2A

01113760

Computed

Blackstone 

River at 

Pawtucket

BL13

01113895

Computed

Total runoff volume 10 –13.2 –3.3 3.9 –6.0 2.5 3.7 –8.5 –2.7 –4.6 –16.0 –10.0 –5.2 1.5 –7.4 1.3Low-flow recession 0.01 –0.02 0.00 –0.03 –0.01 –0.01 0.01 -0.01 –0.01 –0.02 –0.01 –0.03 –0.01 –0.03 –0.02 0.00Lowest 50% of flows 10 –30.4 –9.8 5.7 –2.7 –2.9 40.4 34.9 –2.7 –0.10 15.6 –12.2 4.7 71.5 0.50 6.0Highest 10% of flows 15 –2.4 17.2 4.0 –5.3 3.6 –3.7 –13.5 –7.5 –6.2 –27.0 –0.5 –5.4 –16.1 –14.3 4.0Storm peaks 15 6.8 73.4 12.4 12.4 23.4 61.2 54.9 34.8 24.4 –16.6 17.7 10.5 41.9 48.9 21.6Seasonal volume 10 18.9 7.4 31.6 23.9 12.5 19.4 10.8 26.6 20.8 10.7 23.3 15.7 7.1 4.2 16.1Summer storm volume 15 –9.2 –15.4 –6.5 –12.1 –15.8 –21.4 5.9 –7.3 –16.9 0.40 4.5 –14.3 22.4 8.6 –16.1

Precipitation-Runoff Model for the Blackstone River Basin  49
600

700

800

900

1,000

1,100

600 700 800 900 1,000 1,100

Correlation

coefficient = 0.94

500

600

700

800

900

1,000

500 600 700 800 900 1,000

Correlation

coefficient = 0.91

120

144

168

192

216

240

120 144 168 192 216 240

Correlation

coefficient = 0.97

20

24

28

32

36

40

20 24 28 32 36 40

Correlation

coefficient = 0.94

100

120

140

160

180

200

100 120 140 160 180 200

Correlation

coefficient = 0.95

25

30

35

40

45

50

25 30 35 40 45 50

Correlation

coefficient = 0.75

A. QU1A B. BL2B

C. NI1A D. BR2A

E. BL9A F. BL13

OBSERVED OR COMPUTED DISCHARGE, IN CUBIC FEET PER SECOND

SIMULATED DISCHARGE, IN CUBIC FEET PER SECOND

Figure 13. Relation between simulated and observed or computed annual mean discharge at streamflowgaging stations A, Quinsigamond River at North Grafton, Mass. (QU1A, 01110000); B, Blackstone River at 

Millbury, Mass. (BL2B, 01109730); C, Nipmuc River near Harrisville, R.I. (NI1A, 01111300); D, Branch River at 

Forestdale, R.I. (BR2A, 01111500); E, Blackstone River at Woonsocket, R.I. (BL9A, 01112500); and F, Blackstone 

River at Pawtucket, R.I. (BL13, 01113895). Dashed line shows the 1-to-1 relation between simulated 

and observed or computed discharge.

50 A Precipitation-Runoff Model for the Blackstone River Basin
10

100

1,000

10,000

10 100 1,000 10,000

Correlation

coefficient = 0.96

10

100

1,000

10,000

10 100 1,000 10,000

Correlation

coefficient = 0.95

1

10

100

1,000

1 10 100 1,000

Correlation

coefficient = 0.95

0.1

 1

10

100

1,000

0.1 1 10 100 1,000

Correlation

coefficient = 0.91

10

100

1,000

10 100 1,000

Correlation

coefficient = 0.95

0.01

0.1

 1

10

100

1,000

0.01 0.1 1 10 100 1,000

Correlation

coefficient = 0.91

A. QU1A B. BL2B

C. NI1A D. BR2A

E. BL9A F. BL13

OBSERVED OR COMPUTED DISCHARGE, IN CUBIC FEET PER SECOND

SIMULATED DISCHARGE, IN CUBIC FEET PER SECOND

Figure 14. Relation between simulated and observed or computed monthly mean discharge at streamflowgaging stations A, Quinsigamond River at North Grafton, Mass. (QU1A, 01110000); B, Blackstone River at 

Millbury, Mass. (BL2B, 01109730); C, Nipmuc River near Harrisville, R.I. (NI1A, 01111300); D, Branch River at 

Forestdale, R.I. (BR2A, 01111500); E, Blackstone River at Woonsocket, R.I. (BL9A, 01112500); and F, Blackstone 

River at Pawtucket, R.I. (BL13, 01113895). Dashed line shows the 1-to-1 relation between simulated 

and observed or computed discharge.

Precipitation-Runoff Model for the Blackstone River Basin  51
station) to 0.96 (Blackstone River at Pawtucket, R.I. station). 

Flows are slightly undersimulated for the months with the 

highest flows at most of these stations. Because the study 

focus is on the effects of development and land-use change 

on low flows, the agreement between observed and simulated 

discharge during the wet months was considered adequate. 

Monthly mean discharge was oversimulated on average by 

8.8 percent at the Quinsigamond River at North Grafton, Mass. 

station, 57 percent at the Nipmuc River near Harrisville, R.I. 

station, 3.3 percent at the Branch River at Forestdale, R.I. station, 3.7 percent at the Blackstone River at Woonsocket, R.I. 

station, and 7.6 percent at the Blackstone River at Pawtucket, 

R.I. station for the calibration period. Monthly mean discharge 

at the Blackstone River at Millbury, Mass. station was undersimulated on average by 1.8 percent for the calibration period. 

These errors are calculated as the mean of the percent differences for each month in the calibration period. The NashSutcliffe coefficients indicate that the model accounted for 

79 percent (Nipmuc River near Harrisville, R.I.) or better of the 

variation in the observed monthly mean discharge at these six 

stations (table 12). 

Daily Mean Discharge 

Hydrographs of observed and simulated daily mean 

discharges indicate that the model performed well over a 

range of flows of about three orders of magnitude (fig. 15). 

Observed daily mean discharges at the stations shown in figure 

15 ranged from 0.03 ft3/s (September 12, 2001) at the Quinsigamond River at North Grafton, Mass. station to 8,320 ft3

/s 

(March 23, 2001) at the Blackstone River at Pawtucket, R.I. 

station. The Nash-Sutcliffe coefficient indicated that the model 

explained 51 percent (Blackstone River at Millbury, Mass.) 

to 78 percent (Blackstone River at Woonsocket, R.I.) of the 

variation in the observed daily mean discharge at these stations 

(table 13). 

The range in the magnitude of model errors for the 15 stations in the basin is the result of attempting to achieve a reasonable calibration across the basin (table 13); improvements 

in model error at a given location often worsened the model 

performance at other locations. In general, there were more 

discrepancies between observed and simulated daily mean discharge at stations that were simulated with climatological data 

from KPVD. For example, the difference between simulated 

and observed flows during the latter part of 2001 is relatively 

large at all stations with drainage areas in the southern part of 

the basin. This appears to indicate that the KPVD precipitation record, which is measured 10 mi south of the basin, is 

not always representative of day-to-day precipitation in the 

southern part of the basin. In other instances, further adjustments to the model were not made because of uncertainty in the 

measured data. For example, the spring recession in 1999 was 

oversimulated at the Branch River at Forestdale, R.I. station, 

but this discrepancy could be the result of flow regulation in 

the basin. Overall, however, there is good agreement between 

simulated and observed spring hydrograph recessions at all 

stations for 1997–2001, indicating that the storage processes in 

the basin are reasonably well represented in the model. 

Scatter plots generally show good agreement between 

observed and simulated daily mean discharges over the 

observed range of flow (fig. 16). Correlation coefficients 

ranged from 0.78 (Nipmuc River near Harrisville, R.I. station) 

to 0.89 (Blackstone River at Pawtucket, R.I. station). At the 

Nipmuc River near Harrisville, R.I. station, the model consistently oversimulated low flows (fig. 16C). Possible explanations include (1) underflow (ground-water flow through 

the aquifer) that bypasses the streamflow-gaging station, 

thus causing the model to oversimulate low flows, (2) more 

seasonal evapotranspiration losses from storage in wetlands 

than is represented by the model, or (3) some combination of 

these factors.

Flow-duration curves show the percentage of time a specified discharge is equaled or exceeded (fig. 17). These plots 

represent the combined effects of climate, surficial geology, 

topography, and hydrologic conditions such as anthropogenic 

stresses on the distribution of the magnitude of flow through 

time (Searcy, 1959). Overall, the flow-duration curves of 

simulated daily mean discharge closely match the observed 

discharge (fig. 17). The largest discrepancies are at the 

extreme high and low flows. At extreme low flows (discharges 

that are exceeded about 98 percent of the time), the flow-duration curve for simulated discharges lies above the curve for 

observed discharges at all stations, but the oversimulation of 

low flows was very small at the Quinsigamond River at North 

Grafton, Mass., Branch River at Forestdale, R.I., Blackstone 

River at Woonsocket, R.I., and Blackstone River at Pawtucket, 

R.I. stations. Low-flow discrepancies were larger at the Nipmuc River near Harrisville, R.I. station (for flows exceeded 

50 percent of the time) and the Blackstone River at Millbury, 

Mass. station (for flows exceeded 90 percent of the time) 

(fig. 17). As discussed above, these discrepancies may partially result from errors associated with the measured streamflow record at the Nipmuc River near Harrisville, R.I. station, 

and the computed streamflow record at the Blackstone River at 

Millbury, Mass. station. At extreme high flows (discharges that 

are exceeded only about 0.2 percent of the time), the model 

undersimulated flow at the Nipmuc River near Harrisville, 

R.I. station and Branch River at Forestdale, R.I. station, and 

oversimulated flow at the Blackstone River at Millbury, Mass. 

and Pawtucket, R.I. stations (fig. 17).

Simulated Hydrologic Response Unit 

Water Budgets

Parameter values assigned primarily to the pervious land 

segments determine the predominant pathways and rates of flow 

to streams, and the magnitudes of losses of water by evapotranspiration. For example, discharge to streams from HRUs in areas 

52  A Precipitation-Runoff Model for the Blackstone River Basin
underlain by sand and gravel is dominated by active groundwater flow mainly because the parameter that controls the infiltration rate (INFILT) is set to a high value (appendix 1), which 

allows more available moisture to reach subsurface flow and 

storage components. Hydrologic budgets computed from the 

major discharge and evapotranspiration components illustrate 

the hydrologic response characteristics of each HRU and the 

relative influence of the various HRUs in the Blackstone River 

Basin model. The major discharge components from PERLNDs 

to streams are active ground-water flow (AGWO), interflow 

(IFWO), and surface runoff (SURO), and the major evapotranspiration components are losses from lower-zone storage 

(LZET), upper-zone storage (UZET), and interception storage 

(CEPE). Total discharge is represented by the sum of the discharge components. Total evapotranspiration is represented by 

the sum of the evapotranspiration components. All discharge to 

streams from IMPLNDs is from surface runoff. The moisturesupply (SUPY) parameter represents total moisture supply to 

an HRU. Deep ground-water discharge (IGWI) was specified 

by use of the DEEPFR parameter from PERLNDs 1, 4, 5, 7, 8, 

12, 13, 15, and 16 to account for the presence of sewers receiving ground-water infiltration. Water was added to lower-zone 

storage in PERLNDs 6, 9, 14, and 17 by use of the lower-zone 

lateral input (LZLI) parameter to account for septic effluent 

from residential areas on public water systems. 

Discharge and evapotranspiration components computed for the HRUs in the model were compiled for the mean 

annual water budget for 1997–2001 (fig. 18), March 2001, a 

wet month (fig. 19), September 1998, a dry month (fig. 20), 

and mean monthly budgets for 1997–2001 for four of the 

largest PERLNDs in the basin (figs. 21 through 24). The 

four PERLNDs in figures 21 through 24 represent forest overlying till (PERLND 3), forest overlying sand and 

gravel (PERLND 11), commercial-industrial-transportation 

(PERLND 1), and medium- to low-density residential overlying 

till (PERLND 4), respectively. Discharge (flow) components are 

shown as positive quantities, and evapotranspiration components 

are shown as negative quantities. Values for the HRUs shown in 

figures 18 through 24 are averages of the values from the individual HRUs in the northern (KORH climatological data) and 

southern (KPVD climatological data) parts of the basin. 

The mean annual water budgets show that the underlying geologic material (sand and gravel or till) strongly affects 

the hydrologic response of the PERLND; budgets are similar 

for PERLNDs overlying till and for PERLNDs overlying 

sand and gravel, but the two groups are distinctly different 

from each other (fig. 18). Discharge per unit area to streams 

from PERLNDs overlying sand and gravel averaged about 

93 percent from active ground-water flow, about 7 percent 

from interflow, and less than 0.1 percent from surface runoff 

(fig. 18A). Discharge per unit area to streams from PERLNDs 

overlying till averaged about 34 percent from active groundwater flow, about 56 percent from interflow, and 10 percent 

from surface runoff. Discharge per unit area to streams from 

commercial-industrial-transportation areas (PERLND 1) was 

dominated by interflow (55 percent) with approximately equal 

contributions from surface runoff and active ground-water 

flow (28 and 17 percent, respectively) (fig. 18A). 

Simulated losses by sewer infiltration (water lost from 

the basin by use of the DEEPFR parameter) per unit area in 

PERLNDs overlying sand and gravel (PERLNDs 12, 13, 15, 

and 16) averaged about 51 percent of the total discharge to 

streams. Simulated losses to sewer infiltration per unit area in 

PERLNDs overlying till (PERLNDs 4, 5, 7, and 8) averaged 

about 13 percent of the total discharge to streams. Simulated 

losses to sewer infiltration per unit area in commercialindustrial-transportation areas (PERLND 1) averaged about 

8.8 percent of total discharge to streams. PERLNDs 1, 4, 5, 

7, 8, 12, 13, 15, and 16 cover 16.7 percent of the basin area 

(table 9). The total loss from these PERLNDs over the entire 

basin averaged 17.0 Mgal/d. 

The relative magnitudes of the discharge components 

indicate that PERLNDs underlain by till and the commercialindustrial-transportation PERLND will produce larger storm 

flows (more discharge from interflow [IFWO] and surface 

runoff [SURO]) and smaller low flows (less discharge from 

active ground-water flow [AGWO]) than PERLNDs underlain 

by sand and gravel. There is less variability in losses from the 

major evapotranspiration components than discharge components among the PERLNDs. Evapotranspiration losses per 

unit area were mainly from lower-zone storage in PERLNDs 

overlying by sand and gravel, and were more equally distributed between upper-zone and lower-zone storage in PERLNDs 

overlying till (fig. 18A). Losses from interception storage 

were similar and relatively minor in all PERLNDs. 

The simulated mean annual runoff from the basin (excluding wetland and open-water areas) was 23.1 in. for 1997–2001, 

of which about 44 percent (10.1 in.) was from forested areas 

overlying till, and about 11 percent (2.5 in.) was from forest overlying sand and gravel (fig. 18b). Overall, PERLNDs 

overlying till accounted for 67 percent of discharge to streams, 

PERLNDs overlying sand and gravel accounted for 21 percent, 

IMPLNDs accounted for 9 percent, and commercial-industrialtransportation areas for the remaining 3 percent. Forested areas 

accounted for about 63 percent (12.2 in.) of the mean annual ET 

loss (19.5 in.) from the basin during this period. Thus, because 

of the large amount of forested acreage in the basin and associated large fluxes of water, the hydrologic response of forested 

areas overlying till strongly affects the basin water budget. 

The water budget for the wet month (March 2001) 

(fig. 19) is fairly similar to the mean annual water budget 

(fig. 18). Discharge per unit area from PERLNDs overlying 

sand and gravel was dominated by active ground-water flow, 

whereas discharge per unit area from PERLNDs overlying till 

was more evenly distributed among the flow components, with 

interflow being the dominant component. However, there was 

less total discharge to streams from areas underlain by sand and 

gravel because more water was entering ground-water storage 

(fig. 19A). In contrast to the mean annual water budget, only 

Precipitation-Runoff Model for the Blackstone River Basin  53
F A J A O D

1997

F A J A O D

1998

F A J A O D

1999

F A J A O D

2000

F A J A O D

2001

OBSERVED

SIMULATED

0.001

0.01

0.1

1

10

100

1,000

1997 1998 1999 2000 2001

COMPUTED

SIMULATED

10

100

1,000

10,000

0

0.1

1

10

100

1,000

1997 1998 1999 2000 2001

OBSERVED

SIMULATED

0

1

2

3

4

5

1997 1998 1999 2000 2001

0

1

2

3

4

5

1997 1998 1999 2000 2001

0

1

2

3

4

5

1997 1998 1999 2000 2001

OBSERVED OR COMPUTED AND SIMULATED FLOW, IN CUBIC FEET PER SECOND

KORH

KPVD

A. QU1A

B. BL2B

C. NI1A

PRECIPITATION, IN INCHES

Figure 15. Daily precipitation at Worcester Regional Airport, Worcester, Mass. (KORH), and T.F. Green 

Regional Airport, Warwick, R.I. (KPVD), and simulated and observed or computed daily mean discharge at 

streamflow-gaging stations A, Quinsigamond River at North Grafton, Mass. (QU1A, 01110000); 

B, Blackstone River at Millbury, Mass. (BL2B, 01109730); C, Nipmuc River near Harrisville, R.I. (NI1A, 

01111300); D, Branch River at Forestdale, R.I. (BR2A, 01111500); E, Blackstone River at Woonsocket, RI 

(BL9A, 01112500); and F, Blackstone River at Pawtucket, R.I. (BL13, 01113895).

54  A Precipitation-Runoff Model for the Blackstone River Basin
10

100

1,000

10,000 COMPUTED

SIMULATED

F A J A O D

1997

F A J A O D

1998

F A J A O D

1999

F A J A O D

2000

F A J A O D

2001

1997 1998 1999 2000 2001

10

100

10,000

OBSERVED

SIMULATED

OBSERVED OR COMPUTED AND SIMULATED FLOW, IN CUBIC FEET PER SECOND

1

10

100

1,000

10,000

1997 1998 1999 2000 2001

OBSERVED

SIMULATED

1,000

0

1

2

3

4

5

1997 1998 1999 2000 2001

0

1

2

3

4

5

1997 1998 1999 2000 2001

0

1

2

3

4

5

1997 1998 1999 2000 2001

PRECIPITATION, IN INCHES

KORH

KPVD

D. BR2A

E. BL9A

F. BL13

Figure 15. Daily precipitation at Worcester Regional Airport, Worcester, Mass. (KORH), and T.F. Green 

Regional Airport, Warwick, R.I. (KPVD), and simulated and observed or computed daily mean discharge at 

streamflow-gaging stations A, Quinsigamond River at North Grafton, Mass. (QU1A, 01110000); B, Blackstone 

River at Millbury, Mass. (BL2B, 01109730); C, Nipmuc River near Harrisville, R.I. (NI1A, 01111300); D, Branch 

River at Forestdale, R.I. (BR2A, 01111500); E, Blackstone River at Woonsocket, RI (BL9A, 01112500); and 

F, Blackstone River at Pawtucket, R.I. (BL13, 01113895).—Continued

Precipitation-Runoff Model for the Blackstone River Basin  55
Correlation

coefficient = 0.89

10

100

1,000

10,000

10 100 1,000 10,000

Correlation

coefficient = 0.89

10

100

1,000

10,000

10 100 1,000 10,000

Correlation

coefficient = 0.84

1

10

100

1,000

10,000

1 10 100 1,000 10,000

Correlation

coefficient = 0.78

0.01

0.1

1

10

100

1,000

0.01 0.1 1 10 100 1,000

Correlation

coefficient = 0.84

10

100

1,000

10,000

0.01 0.1 1 10 100 1,000 10 100 1,000 10,000

0.1

0.01

1

10

100

1,000

Correlation

coefficient = 0.86

A. QU1A B. BL2B

C. NI1A D. BR2A

E. BL9A F. BL13

OBSERVED OR COMPUTED DISCHARGE, IN CUBIC FEET PER SECOND

SIMULATED DISCHARGE, IN CUBIC FEET PER SECOND

Figure 16. Relations between simulated and observed or computed daily mean discharge at streamflowgaging stations A, Quinsigamond River at North Grafton, Mass. (QU1A, 01110000); B, Blackstone River at 

Millbury, Mass. (BL2B, 01109730); C, Nipmuc River near Harrisville, R.I. (NI1A, 01111300); D, Branch River at 

Forestdale, R.I. (BR2A, 01111500); E, Blackstone River at Woonsocket, R.I. (BL9A, 01112500); and F, Blackstone River at Pawtucket, R.I. (BL13, 01113895). Dashed line shows the 1-to-1 relation between simulated 

and observed or computed discharge. 

56  A Precipitation-Runoff Model for the Blackstone River Basin
COMPUTED

SIMULATED

0.5 2 5 10 30 50 70 90 95 98 99 99.8

10

100

1,000

10,000

OBSERVED

SIMULATED

0.5 2 5 10 30 50 70 90 95 98 99 99.8

10

100

1,000

10,000

OBSERVED

SIMULATED

0.5 2 5 10 30 50 70 90 95 98 99 99.8

1

10

100

1,000

10,000

OBSERVED

SIMULATED

0.5 2 5 10 30 50 70 90 95 98 99 99.8

0.001

0.01

0.1

1

10

100

1,000

COMPUTED

SIMULATED

10

100

1,000

10,000

0.5 2 5 10 30 50 70 90 95 98 99 99.8

OBSERVED

SIMULATED

0.01

0.1

1

10

100

1,000

0.5 2 5 10 30 50 70 90 95 98 99 99.8

A. QU1A B. BL2B

C. NI1A D. BR2A

E. BL9A F. BL13

PERCENTAGE OF THE TIME DISCHARGE WAS EQUALED OR EXCEEDED

DISCHARGE, IN CUBIC FEET PER SECOND

Figure 17. Flow-duration curves for simulated and observed or computed daily mean discharges at streamflow-gaging stations A, Quinsigamond River at North Grafton, Mass. (QU1A, 01110000); B, Blackstone River at 

Millbury, Mass. (BL2B, 01109730); C, Nipmuc River near Harrisville, R.I. (NI1A, 01111300); D, Branch River at 

Forestdale, R.I. (BR2A, 01111500); E, Blackstone River at Woonsocket, R.I. (BL9A, 01112500); and F, Blackstone 

River at Pawtucket, R.I. (BL13, 01113895).

Precipitation-Runoff Model for the Blackstone River Basin  57
Overlying sand 

and gravel

Overlying till

Effective

impervious

area

Overlying sand 

and gravel

Overlying till

Effective

impervious

area

-10

-8

-6

-4

-2

0

2

4

6

8

10

-20

0

10

20

30

40

-30

INCHES PER ACRE

-10

INCHES OVER ENTIRE BASIN

HYDROLOGIC RESPONSE UNIT

A. Water budget per unit area

B. Basin water budget 

Runoff to

streams

Losses to

evapotranspiration

and sewers

Runoff to

streams

Losses to

evapotranspiration

and sewers

IGWI – Deep ground-water 

discharge (DEEPFR)

LZET – Lower zone

UZET – Upper zone

AGWO – Active ground water CEPE – Interception 

IFWO – Interflow 

SURO – Surface runoff

Losses to evapotranspiration from:

Losses to sewers from:

Runoff to streams from:

EXPLANATION

Commercial, industrial, transportation

Open nonresidential

Forest

Medium-to-low density

Medium-to-low density, with export

Medium-to-low density, with import

High density

High density, with export

High density, with import

Open nonresidential

Forest

Medium-to-low-density

Medium-to-low density, wtih export

Medium-to-low density, with import

High density

High density, with export

High density, with import

Mixed commercial development

Residential development/urban open space

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 30 31

Residential Residential

Figure 18. Mean annual water budget by component for 1997–2001 for each hydrologic 

response unit (HRU) simulated by the Hydrological Simulation Program–FORTRAN (HSPF) 

model of the Blackstone River Basin, in inches A, per acre; and B, over the entire basin.

58  A Precipitation-Runoff Model for the Blackstone River Basin
Figure 19. A wet month (March 2001) water budget for each hydrologic response unit 

(HRU) simulated by the Hydrological Simulation Program–FORTRAN (HSPF) model of the 

Blackstone River Basin, in inches A, per acre for moisture supply, total runoff to streams, 

and total losses to evapotranspiration; B, per acre for individual components of runoff to 

streams and losses to evapotranspiration and sewers; and C, over the entire basin for 

individual components of runoff to streams and losses to evapotranspiration and sewers. Commercial, industrial, transportation Open nonresidential Forest Medium-to-low density Medium-to-low density, with export Medium-to-low density, with import High density High density, with export High density, with import Open nonresidential Forest Medium-to-low density Medium-to-low density, wtih export Medium-to-low density, with import High density High density, with export High density, with import Mixed commercial development Residential development/urban open space

Overlying sand 

and gravel

Overlying till

Effective

impervious

area

Overlying sand 

and gravel

Overlying till

Effective

impervious area

Effective

impervious area

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

-2

-4

0

2

4

6

8

0

2

4

6

8

LZET – Lower zone

UZET – Upper zone

CEPE – Interception 

AGWO – Active ground water 

IFWO – Interflow 

SURO – Surface runoff

Losses to evapotranspiration from:

Runoff to streams from:

EXPLANATION

MOISTURE SUPPLY

TOTAL RUNOFF

TOTAL EVAPOTRANSPIRATION

IGWI–- Deep ground-water 

discharge (DEEPFR)

Losses to sewers from:

INCHES PER ACRE INCHES OVER ENTIRE BASIN

HYDROLOGIC RESPONSE UNIT

A. Total water budget per unit area

B. Water budget per unit area

C. Basin water budget 

Runoff to

streams

Losses to

evapotranspiration

and sewers

Runoff to

streams

Losses to

evapotranspiration

and sewers

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 30 31

Residential Residential

Precipitation-Runoff Model for the Blackstone River Basin  59
LZET – Lower zone

UZET – Upper zone

CEPE – Interception 

AGWO – Active ground water 

IFWO – Interflow 

SURO – Surface runoff

Losses to evapotranspiration from:

Runoff to streams from:

EXPLANATION

MOISTURE SUPPLY

TOTAL RUNOFF

TOTAL EVAPOTRANSPIRATION

IGWI – Deep ground-water 

discharge (DEEPFR)

Losses to sewers from:

Overlying sand 

Overlying till and gravel

Effective

impervious area

Overlying sand 

and gravel

Overlying till Effective

impervious

area

Effective

impervious

area

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0

1

2

-3

-2

-1

0.0

0.5

1.0

1.5

2.0

2.5

INCHES PER ACRE INCHES OVER ENTIRE BASIN

HYDROLOGIC RESPONSE UNIT

A. Total water budget per unit area

B. Water budget per unit area

C. Basin water budget 

Runoff to

streams

Losses to

evapotranspiration

and sewers

Runoff to

streams

Losses to

evapotranspiration

and sewers

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 30 31

Residential Residential

Commercial, industrial, transportation

Open nonresidential

Forest

Medium-to-low density

Medium-to-low density, with export

Medium-to-low density, with import

High density

High density, with export

High density, with import

Open nonresidential

Forest

Medium-to-low density

Medium-to-low density, wtih export

Medium-to-low density, with import

High density

High density, with export

High density, with import

Mixed commercial development

Residential development/urban open space

Figure 20. A dry month (September 1998) water budget for each hydrologic response unit 

(HRU) simulated by the Hydrological Simulation Program–FORTRAN (HSPF) model of the 

Blackstone River Basin, in inches A, per acre for moisture supply, total runoff to streams and 

total losses to evapotranspiration; B, per acre for individual components of runoff to streams 

and losses to evapotranspiration and sewers; and C, over the entire basin for individual 

components of runoff to streams and losses to evapotranspiration and sewers.

60 A Precipitation-Runoff Model for the Blackstone River Basin
a small amount of water (about 0.3 in.) was lost to evapotranspiration during March 2001. The moisture supply of 7.2 in. 

for the month was distributed, on average, between discharge 

to streams (5.0 in.), percolation to deep ground water (0.2 in.), 

evapotranspiration (0.3 in.), and inflow to storage (1.7 in.).

The water budget for the dry month (September 1998) 

(fig. 20) is substantially different than the mean annual and 

wet-month water budgets (figs. 18 and 19). Discharge per 

unit area to streams from all PERLNDs was composed almost 

entirely of active ground-water flow. In contrast to the wet 

month, there was less total discharge to streams from areas 

underlain by till because less water is available from groundwater storage in till relative to sand and gravel (fig. 20A). 

During dry periods, streamflow is generated predominantly 

by ground-water discharge from sand and gravel deposits. 

Evapotranspiration per unit area generally exceeds discharge 

to streams for all PERLNDs, and is dominated by losses 

from lower-zone storage. The moisture supply of 1.7 in. for 

the month was distributed, on average, between discharge to 

streams (0.58 in.), percolation to deep ground water (0.02 in.), 

evapotranspiration (1.74 in.). Because the sum of evapotranspiration and total discharge exceeded the moisture supply, 

water was removed from storage (0.64 in.). Evapotranspiration 

losses from forested areas dominate the basin water budget 

during the dry month (fig. 20C). This is because forests are 

areally extensive and have abundant deep-rooted vegetation.

The mean monthly water budgets for 1997–2001 illustrate the seasonal changes in discharges to streams and evapotranspiration losses and the corresponding gains or losses from 

storage. Forested areas (PERLNDs 3 and 11 in figs. 21 and 22, 

respectively) are characterized by high rates of evapotranspiration from lower-zone storage during the growing season resulting in rapid declines in the total discharge to streams as the 

summer progresses. During the first few months of the year, 

total discharge tracks the moisture supply closely, but begins 

diverging as evapotranspiration increases in the spring. From 

about May through September, the sum of evapotranspiration 

and total discharge exceeds the moisture supply, indicating 

that water is being removed from storage. As the growing 

season ends and evapotranspiration decreases, the sum of 

evapotranspiration and discharge fall well below the moisture 

supply, indicating that soil moisture is being replenished. This 

also is indicated by runoff which lags the total moisture supply 

in the fall and winter after evapotranspiration has decreased to 

its seasonal low. One notable difference between the forested 

PERLNDs is that there is a larger percentage of discharge 

from active ground-water flow in areas underlain by sand 

and gravel than in areas underlain by till, resulting in a flatter 

hydrograph with lower flows through the winter and higher 

flows through the summer and early fall (figs. 21A and 22A). 

The mean monthly budget for PERLND 4 (medium- to 

low-density residential area overlying till; fig. 23) is very 

similar to PERLND 3 (forest overlying till; fig. 21). The similarity in the simulations indicates that medium- to low-density 

development, as represented in the model, does not significantly 

alter the hydrologic response to precipitation relative to undeveloped, forested land; however, other possible changes that might 

accompany development, such as increased impervious area or 

decreased wetland area, are not represented. The net effect of 

low-density development is better understood by simulating the 

response of streamflow to changing land use in the basin.

The mean monthly water budget for commercialindustrial-transportation areas (PERLND 1) is characterized by less vigorous evapotranspiration during the summer months (fig. 24); however, because lower-zone storage 

is smaller, less water reaches ground-water storage. Total 

runoff, which is composed mainly of interflow and surface 

flow, declines sharply as the summer progresses. This condition also allows runoff to recover more rapidly in the fall 

and early winter in contrast to the forested PERLNDs. The 

hydrologic response of PERLND 1 generally is similar to the 

response of the till PERLNDs (figs. 18 through 20). A short 

period (2 months) when water is lost from storage takes place 

during late summer. 

Summary of Anthropogenic Water Use in Basin

The magnitudes of the withdrawals and return flows compiled from external sources and included in the model provide 

an indication of the anthropogenic stress placed on the basin, 

and the overall quality and completeness of the water-use 

information. The total withdrawal rate for all the municipal 

and commercial/industrial withdrawals in the basin (table 5), 

minus the intrabasin transfers, averaged about 64 Mgal/d for 

1997–2001. This value probably slightly underestimates the 

actual loss of water because minor withdrawals (for example, 

from agricultural water use) and consumptive losses associated 

with private wells were not included. The total return-flow 

rate for all the permitted municipal and commercial/industrial 

return flows in the basin (54 Mgal/d) (table 6), the transfers 

from the Nashua River Basin (13.7 Mgal/d; DSNs 405 and 

1009), and the septic effluent in areas with public-water supplies (3.1 Mgal/d) averaged about 71 Mgal/d for 1997–2001. 

If the simulated flow derived from precipitation on the basin 

(ground-water infiltration to municipal sewers in the basin 

(17.0 Mgal/d) and inflows from combined-sewer areas in 

Worcester (4.9 Mgal/d) is subtracted from 71 Mgal/d, the 

total return-flow rate to the basin was about 49 Mgal/d for 

1997–2001. Thus, the total withdrawals exceeded the total 

return flows by roughly 15 Mgal/d, indicating that there was a 

net export of water across basin boundaries. 

In comparison, Barlow (2003) found that total withdrawals exceeded total returns by a factor of nearly 2 in the lower 

part of the basin. The significant export in the lower part of the 

basin is largely the result of water withdrawn by the Pawtucket 

Water Supply Board from the Abbott Run subbasin being used 

in communities that discharge their wastewater to the Narragansett Bay Commission wastewater-treatment facility at 

Bucklin Point, which is outside the basin. The closer balance 

for the basin as a whole indicates that there is a net import of 

water in the northern part of the basin, which is consistent with 

the 13.7 Mgal/d import of water from Kendall Reservoir to 

Precipitation-Runoff Model for the Blackstone River Basin  61
-5

-4

-3

-2

-1

0

1

2

3

4

5

0

1

2

3

4

5

6

INCHES PER ACRE

A. Total water budget per unit area

B. Water budget per unit area January February March April May

June

July

August

September

October

NovemberDecember

Runoff to

streams

Losses to

evapotranspiration

LZET – Lower zone

UZET – Upper zone

CEPE – Interception 

AGWO – Active ground water 

IFWO – Interflow 

SURO – Surface runoff

Losses to evapotranspiration from:

Runoff to streams from:

EXPLANATION

MOISTURE SUPPLY

TOTAL RUNOFF

TOTAL EVAPOTRANSPIRATION

Figure 21. The mean monthly water budget for 1997–2001 for PERLND 3 (forest overlying till) simulated by the Hydrological Simulation Program–FORTRAN (HSPF) model 

of the Blackstone River Basin model, in inches A, per acre for moisture supply, total 

runoff to streams and total losses to evapotranspiration; and B, per acre for 

individual components of runoff to streams and losses to evapotranspiration.

62  A Precipitation-Runoff Model for the Blackstone River Basin
-5

-4

-3

-2

-1

0

1

2

3

4

5

0

1

2

3

4

5

6

INCHES PER ACRE

January

February

March

April

May

June

July

August

September

October

NovemberDecember

A. Total water budget per unit area

B. Water budget per unit area

Runoff to

streams

Losses to

evapotranspiration

LZET – Lower zone

UZET – Upper zone

CEPE – Interception 

AGWO – Active ground water 

IFWO – Interflow 

SURO – Surface runoff

Losses to evapotranspiration from:

Runoff to streams from:

EXPLANATION

MOISTURE SUPPLY

TOTAL RUNOFF

TOTAL EVAPOTRANSPIRATION

Figure 22. The mean monthly water budget for 1997–2001 for PERLND 11 (forest overlying sand and gravel) simulated by the Hydrological Simulation Program–FORTRAN 

(HSPF) model of the Blackstone River Basin, in inches A, per acre for moisture supply, 

total runoff to streams and total losses to evapotranspiration; and B, per acre for 

individual components of runoff to streams and losses to evapotranspiration.

Precipitation-Runoff Model for the Blackstone River Basin  63
-5

-4

-3

-2

-1

0

1

2

3

4

5

0

1

2

3

4

5

6

INCHES PER ACRE

January

February

March

April

May

June

July

August

September

October

NovemberDecember

A. Total water budget per unit area

B. Water budget per unit area

Runoff to

streams

Losses to

evapotranspiration

and sewers

LZET – Lower zone

UZET – Upper zone

CEPE – Interception 

AGWO – Active ground water 

IFWO – Interflow 

SURO – Surface runoff

Losses to evapotranspiration from:

Runoff to streams from:

EXPLANATION

MOISTURE SUPPLY

TOTAL RUNOFF

TOTAL EVAPOTRANSPIRATION

IGWI – Deep ground-water 

discharge (DEEPFR)

Losses to sewers from:

Figure 23. The mean monthly water budget for 1997–2001 for PERLND 4 (mediumto low-density residential areas with no import or export of water overlying till) 

simulated by the Hydrological Simulation Program–FORTRAN (HSPF) model of the 

Blackstone River Basin, in inches A, per acre for moisture supply, total runoff to 

streams and total losses to evapotranspiration; and B, per acre for individual 

components of runoff to streams and losses to evapotranspiration and sewers.

64  A Precipitation-Runoff Model for the Blackstone River Basin
-5

-4

-3

-2

-1

0

1

2

3

4

5

0

1

2

3

4

5

6

INCHES PER ACRE

January

February

March

April

May

June

July

August

September

October

NovemberDecember

A. Total water budget per unit area

B. Water budget per unit area

Runoff to

streams

Losses to

evapotranspiration

and sewers

LZET – Lower zone

UZET – Upper zone

CEPE – Interception 

AGWO – Active ground water 

IFWO – Interflow 

SURO – Surface runoff

Losses to evapotranspiration from:

Runoff to streams from:

EXPLANATION

MOISTURE SUPPLY

TOTAL RUNOFF

TOTAL EVAPOTRANSPIRATION

IGWI – Deep ground-water 

discharge (DEEPFR)

Losses to sewers from:

Figure 24. The mean monthly water budget for 1997–2001 for PERLND 1 (commercialindustrial-transportation areas) simulated by the Hydrological Simulation Program–FORTRAN 

(HSPF) model of the Blackstone River Basin, in inches A, per acre for moisture supply, total 

runoff to streams, and total losses to evapotranspiration; and B, per acre for individual 

components of runoff to streams and losses to evapotranspiration and sewers.

Precipitation-Runoff Model for the Blackstone River Basin  65
the Worcester water-supply system. The imbalance in withdrawals and returns is small in comparison to the average rate 

of precipitation on the basin of 948 Mgal/d (42 in/yr) for the 

calibration period.

Sensitivity of Model Results to Changes in 

Values of Parameters 

Sensitivity analysis determines the response of the modelsimulated discharge to changes in the values of parameters. 

Systematic perturbation of model parameters reveals the most 

influential parameters for a given model structure and set of 

basin characteristics. The Blackstone River Basin HSPF model 

is very similar in structure to the Ipswich River Basin model 

of Zarriello and Ries (2000). Both models represent wetlands 

as virtual RCHRESs and are constructed from a similar group 

of PERLNDs and IMPLNDs. Simulated flow budgets from 

both models indicate that subsurface discharge consisting 

of ground-water discharge (base flow) and interflow are the 

dominant flow components to stream reaches. The results of 

the sensitivity analysis conducted for the Ipswich River Basin 

model are therefore considered to be applicable to the Blackstone model. Overall, the Ipswich-River sensitivity analysis 

indicates that the changes in the parameters that affect groundwater and interflow recession cause the largest changes in various measures of model fit. These parameters include the active 

ground-water recession constant (AGWRC), the ground-water 

recession parameter that determines the degree of nonlinearity of the recession rate (KVARY), 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 parameters 

will have the largest effect on model performance. Model 

results also are sensitive to changes in parameters that determine the amount of precipitation that eventually discharges as 

base flow or interflow; these include the infiltration parameter 

(INFILT), the lower-zone nominal storage parameter (LZSN), 

the upper-zone nominal storage parameter (UZSN), and the 

lower-zone evapotranspiration parameter (LZETP). Further 

explanation of these parameters can be found in Bicknell and 

others (2000). Zarriello and Ries (2000) found also that model 

results, particularly during low flows, were sensitive to the 

manner in which wetlands were represented in the model.

Model Limitations

Numerical watershed models necessarily simplify the 

complex processes and physical characteristics of a basin. 

Consequently, there are limitations to the types of questions 

that can be addressed by the model. Nonetheless, the model 

can be used effectively to address many water-resource 

management questions, provided that the limitations and 

uncertainties are considered. One uncertainty associated with 

complex watershed models such as HSPF is the possibility of 

constructing models with differing structures and parameter 

values that produce equally acceptable results; typically data 

needed to select the most appropriate model are lacking. Thus, 

the calibrated Blackstone River Basin HSPF model, which was 

developed to assess the effects of development and changing 

water and land use on streamflow, should be viewed as one of 

many possible representations of the basin and sets of HSPF 

parameters. Uncertainty also is inherent in the data used to 

develop and calibrate the model. These data include climatological data, water-use data, channel-geometry and other 

hydraulic data used to construct FTABLEs, and the geospatial 

data used to define the HRUs. 

Uncertainty in the climatological data results from (1) the 

use of point measurements to represent variables that have a 

high degree of spatial variability, (2) the presence of regional 

climatic differences across the basin, (3) the presence of systematic measurement bias, or (4) some combination of these 

factors. Extrapolating a point measurement of precipitation 

over a large area of the basin disregards the spatial variability of the intensity and duration of precipitation events. The 

climatological data from KORH (Worcester Regional Airport) 

generally provided better agreement between simulated and 

observed flows in the northern part of the basin than the data 

from KPVD (T.F. Green Airport) in the southern part of the 

basin. Climatological conditions at KPVD, which is outside 

the basin, may differ appreciably from local conditions in the 

lower basin due to a regional gradient in weather patterns. The 

uncertainties in the climatological data may lead to error in 

simulating storms and daily streamflow in the basin; however, 

the model reasonably represents regional climatological conditions and therefore this error is inconsequential for long-term 

simulations of water-management alternatives. 

Uncertainty in water-use data and simplification of the 

complexities of water use in the basin also affect calibrated 

parameter values. Known water withdrawals are removed 

directly from simulated streamflow. Similarly, known wastewater-return flows are added directly to simulated streamflow. 

For time-varying ground-water withdrawals, streamflow 

depletion was first calculated with the STRMDEPL program, 

which is subject to several simplifying assumptions; the 

accuracy of streamflow depletion calculated in this manner 

depends on the degree to which the underlying assumptions 

of STRMDEPL are met. For golf-course irrigation withdrawals, measured data were sparse, and the withdrawals for 

most courses could only be estimated. Septic effluent from 

households on public water supplies was added directly to 

lower-zone soil storage, and ground-water withdrawals from 

households on private wells and public sewer were subtracted 

directly from simulated streamflow. Residential water-use 

rates were based on household population densities, and per 

capita water-use estimates were obtained from other studies. Once these disparate water uses are accounted for in 

the model, the parameter values are adjusted to calibrate the 

model’s response to precipitation and evapotranspiration. 

Therefore, parameter values can be skewed during calibration 

to compensate for inaccuracies in the water-use data (due to 

66  A Precipitation-Runoff Model for the Blackstone River Basin
assumptions, reporting errors, or estimation of missing data) 

or inadvertent omission of major withdrawals or returns. 

Model calibration and performance reflect the combined 

response of the PERLNDs, IMPLNDs, and reaches used 

to represent the basin. Most HSPF parameters, as well as 

IMPLND areas, cannot be measured independently and are 

obtained through the calibration process. In general, judgment 

based on hydrologic experience and results from previous 

HSPF studies are used to determine the parameter values for 

individual HRUs. Although agreement was good between 

observed and simulated flows for a wide range of flow conditions and HRU combinations, information was not available 

to calibrate individual HRUs. Therefore, simulation results 

from analyses in which one type of HRU is changed to another 

(such as a buildout scenario) or flow from an individual type 

of HRU is of interest (such as a water-quality study), have 

a high degree of uncertainty and should be interpreted cautiously to avoid reaching inaccurate conclusions. 

Stage, storage, and discharge characteristics of stream 

reaches are determined from measured channel geometry to 

the extent possible, but the spatial variability of these characteristics cannot be measured or fully represented in the model. 

Similarly, stage, storage, and discharge characteristics of reservoir and wetland reaches were determined from available data 

to the extent possible, but for most reaches these data were not 

available and their values could only be estimated. Reservoirmanagement activities, such as seasonal water-level changes 

for recreational purposes or regulation for flood control or 

water-supply management, and run-of-river diversions for 

power generation or industrial use, also were not represented 

in the model. As part of the calibration process, storage-discharge relations were adjusted empirically in the 15 reaches 

with observed streamflow data; direct calibration of the other 

35 reaches was not conducted. Thus, simulation results from 

ungaged areas of the basin have a high degree of uncertainty. 

Summary

The 474.5 square mile Blackstone River Basin in southeastern Massachusetts and northern Rhode Island is experiencing rapid population and commercial growth throughout much 

of its area. This growth and the corresponding changes in landuse patterns are placing increasing stress on water resources in 

the basin and raising concerns about the future availability of 

water. Increased withdrawals needed to meet growing watersupply demand could adversely affect aquatic habitat, water 

quality, and the recreational value of the streams in the basin. 

To address these concerns, the U.S. Geological Survey, in 

cooperation with the Rhode Island Water Resources Board, 

developed a Hydrological Simulation Program–FORTRAN 

(HSPF) precipitation-runoff model of the Blackstone River 

Basin. The model will be used to study the effects of changing 

land and water use on streamflow and evaluate water-resources 

management alternatives. 

In 2000, approximately 467,000 people lived in the 

Blackstone River Basin. Population is concentrated in 

Worcester, Massachusetts, and surrounding communities in 

the headwaters of the basin and in Woonsocket, Cumberland, 

and Pawtucket, Rhode Island, in the lower part of the basin. 

The eastern side of the basin, near the Route 495 corridor, 

is generally more developed and populated than the western side. State land-use data layers representing 1995–1999 

indicate that land is predominantly forested (50.7 percent). 

The next largest land-use category is residential (21.3 percent), 

of which 14.7 percent is medium- to low-density residential 

and 6.6 percent is high-density residential; followed by open, 

non-residential (10.7 percent); forested and non-forested 

wetlands (7.7 percent); commercial-industrial-transportation 

(5.8 percent); and open water (3.8 percent). The hydrology of 

the watershed has been affected by the long history of industrial activity and development. Currently, hydrologic effects 

are caused by water withdrawals; wastewater-return flows; 

flow regulation for recreation, flood control, and hydropower; 

impoundments created by dams; and land-use change.

Climatological, streamflow, water-withdrawal, and wastewater-return data were collected during the study to develop 

the HSPF model. Climatological data included precipitation, 

air temperature, dew-point temperature, solar radiation, and 

wind speed. These data were collected at stations at Worcester 

Regional Airport (KORH) in Worcester, Massachusetts; and T.F. 

Green Airport (KPVD) in Warwick, Rhode Island. Data from 

both stations were used for model calibration; data from KORH 

were used for the northern part of the basin, and data from 

KPVD were used for the southern part of the basin. Data from 

these stations were used to calculate potential evapotranspiration 

by the Jensen-Haise method. Streamflow was measured at eight 

continuous-record streamflow-gaging stations that are part of 

the U.S. Geological Survey cooperative stream-gaging network, 

and at seven new stations installed in 2004 for this study. A 

continuous streamflow record was computed for the calibration 

period for the new stations to provide additional information for 

model calibration and evaluation of model performance. 

Water-use data were included in the model to represent 

the net effect of water use on simulated hydrographs. Consequently, the calibrated values of the hydrologic parameters 

better represent the hydrologic response of the basin to precipitation. Water-use data compiled for 1996–2001 include municipal and commercial/industrial withdrawals, private residential 

withdrawals, golf-course withdrawals, municipal wastewaterreturn flows, and on-site septic effluent return flows. Irrigation withdrawals for agricultural purposes were not compiled 

because they are a minor component of total withdrawals in 

the basin (about 1 percent) and widely distributed as numerous small withdrawals throughout the basin. Total withdrawals 

from 129 municipal and commercial/industrial withdrawals in 

the basin averaged about 66 million gallons per day (Mgal/d) for 

the model-calibration period of 1997–2001. Stream depletion 

was computed for all time-varying ground-water withdrawals 

prior to simulation. Total municipal wastewater returns from 

the 10 wastewater-treatment plants and permitted commercial 

Summary  67
facilities averaged about 54 Mgal/d for the period. Withdrawals 

from private wells in areas with public sewers and returns from 

on-site septic systems in areas with public-water supplies represent net transfers of water in the basin. These transfers were 

much lower than municipal withdrawals and returns, but they 

were simulated to represent water use comprehensively in the 

model. The model parameter DEEPFR was used to represent 

ground-water infiltration into municipal sewers in the basin. 

The HSPF model simulates runoff from precipitation and 

potential-evapotranspiration time-series data. Processes simulate the transport and fate of water for hydrologic response 

units (HRUs) and stream reaches (RCHRES) that define the 

hydrologic characteristics of the basin. The Blackstone River 

Basin was represented by HRUs composed of 17 pervious 

areas (PERLNDs), established from combinations of surficial geology, land-use classes, and the distribution of public 

water and public sewer systems, and 2 impervious areas 

(IMPLNDs). Wetlands were combined with open water and 

simulated as stream reaches that receive runoff from surrounding pervious and impervious areas. This approach was taken 

to achieve greater flexibility in calibrating evapotranspiration 

losses from wetlands during the growing season. The basin was 

segmented into 50 reaches to represent junctions at tributaries, 

major lakes and reservoirs, and drainage areas to streamflowgaging stations. Thirty-six reaches were simulated as stream 

reaches, and the remaining 14 as lake or reservoir reaches. 

The model was calibrated for 1997–2001 to coincide 

with the land-use and water-use data compiled for the study. 

Streamflow data from a total of 15 streamflow-gaging stations 

were used to evaluate model performance across the watershed. 

Four long-term streamflow-gaging stations (Nipmuc River 

near Harrisville, Rhode Island [station no. 0111300]; Quinsigamond River at North Grafton, Massachusetts [station no. 

0110000]; Branch River at Forestdale, Rhode Island [station 

no. 01111500]; and Blackstone River at Woonsocket, Rhode 

Island [station no. 01112500]) that monitor flow at 3.3, 5.4, 19, 

and 88 percent of the total basin area, respectively, provided the 

primary model-calibration points. Hydrographs, scatter plots, 

and flow-duration curves of observed and simulated discharges, 

along with various model-fit statistics, indicated that the model 

performed well over a range of hydrologic conditions and time 

scales. For example, the total runoff volume for the calibration 

period simulated at the Nipmuc River near Harrisville, Rhode 

Island; Quinsigamond River at North Grafton, Massachusetts; 

Branch River at Forestdale, Rhode Island; and Blackstone River 

at Woonsocket, Rhode Island streamflow-gaging stations differed from the observed runoff volume by –8.6, 3.9, –4.7, and 

–5.3 percent, respectively. The Nash-Sutcliffe coefficient for 

daily mean flows, a goodness-of-fit measure that represents the 

amount of the variance in the observed flow explained by the 

model, ranged from 0.61 to 0.78 at these stations. The errors 

between the observed and simulated mean daily streamflows 

for the calibration period were within 10 percent at 12 stations, 

15 percent at 2 stations, and 25 percent at 1 station. 

Simulated flow components for mean annual water budgets 

indicate that active ground-water flow was about 93 percent 

of the discharge from PERLNDs overlying sand and gravel 

and 34 percent of the discharge from PERLNDs overlying till. 

Interflow was about 7 percent of the discharge from PERLNDs 

overlying sand and gravel and 56 percent of the discharge from 

PERLNDs overlying till. Surface runoff was less than 0.1 percent from PERLNDs overlying sand and gravel and 10 percent 

of the discharge from PERLNDs overlying till. All discharge 

to streams from IMPLNDs was from surface runoff. Evapotranspiration losses per unit area were mainly from lower-zone 

storage in PERLNDs overlying sand and gravel and were more 

equally distributed between upper-zone and lower-zone storage 

in PERLNDs overlying till. The simulated mean annual runoff 

from the basin was 23.1 inches (in.) for 1997–2001, of which 

about 44 percent (10.1 in.) was from forested areas overlying 

till, and about 11 percent (2.5 in.) was from forest overlying 

sand and gravel. Forested areas also accounted for about 63 

percent of the mean annual evapotranspiration loss of 19.5 in. 

from the basin. Overall, the hydrologic response of the extensive forested areas overlying till exerts a strong influence on 

the basin water budget. The simulated hydrologic response of 

medium- to low-density residential development, one of the 

largest and fastest growing land uses in the basin, is similar 

to forested areas. Because model calibration and performance 

reflect the combined response of all the HRUs used to represent 

the basin, simulation results from analyses in which one type of 

HRU is changed to another have a high degree of uncertainty. 

Numerical watershed models necessarily simplify the 

complex processes and physical characteristics of a basin. 

Consequently, there are limitations to the types of questions 

that can be addressed by the model. Nonetheless, the model 

can be used effectively to address many water-resource management questions, provided that the limitations and uncertainties are considered. The assumptions, estimation procedures, 

and data used to develop and calibrate the model, and the possible applicability of alternative model structures and parameter values should be considered when evaluating the model 

and using its results for water-management decisions.

Acknowledgments

The authors thank USGS employees John Eggleston for 

project management and the initial stages of the development 

of the HSPF model, Lora Barlow and Emily Wild for assistance with water-use data collection and management, Andrew 

Massey and Tomas Smieszek for assistance with HSPF 

model development and report preparation, Lance Ostiguy 

for guidance on GIS analysis, and Douglas Moyer and Stacey 

Archfield for colleague reviews of the report. Support was 

also provided by the USGS data-collection staff for streamflow-gaging station installation and maintenance, and by the 

USGS publications staff for report preparation. Student interns 

William Hansen, Sarah Lovell, and Rebecca Batchelder are 

thanked for assistance with data acquisition and processing. The authors thank the Central Massachusetts Regional 

68  A Precipitation-Runoff Model for the Blackstone River Basin
Planning Commission for assistance with GIS information on 

public water and public sewer systems, and the Massachusetts 

Department of Environmental Protection and Rhode Island 

Department of Environmental Management for assistance with 

procuring municipal water withdrawal and wastewater return 

data. The authors also thank the managers of municipal water 

supply and sewer systems in numerous towns in the basin for 

data, engineering drawings and reports, and explanations of 

water-supply and wastewater-disposal infrastructures. 

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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 Investigation 

Report 00–4029, 99 p.

References Cited  71
Appendix 1 73

Appendix 1. Hydrological Simulation Program – FORTRAN User Control 

File Input for Pervious and Impervious Area Parameters

****************************************************************************** 

*** PERLND - Pervious land surface Princ 4.2(1).1 pg 37 *** 

*** Coding 4.4(1) pg 300 *** 

******************************************************************************* 

PERLND

 ACTIVITY

 <PLS > Active Sections (1=Active; 0=Inactive) ***

 # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ***

 1 17 0 1 1

 101 117 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 17 6 4 1 12

 101 117 6 4 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 17 6 4 1 12

 101 117 6 4 1 12

 END BINARY-INFO

 GEN-INFO 

 <PLS ><-------Name------->NBLKS Unit-systems Printer Binary *** 

 ###--### User t-series Engl Metr Engl Metr *** 

*** NW climate 

 in out *** 

 1 commer/trans/ind 1 1 1 1 15 0 16 0

 2 open undevel till 1 1 1 1 15 0 16 0

 3 forest on till 1 1 1 1 15 0 16 0

 4 LDres/till/noI/E 1 1 1 1 15 0 16 0

 5 LDRes/till/Export 1 1 1 1 15 0 16 0

 6 LDRes/till/Import 1 1 1 1 15 0 16 0

 7 HDRes/till/no I/E 1 1 1 1 15 0 16 0

 8 HDRes/till/Export 1 1 1 1 15 0 16 0

 9 HDRes/till/Import 1 1 1 1 15 0 16 0

 10 open undevel drift 1 1 1 1 15 0 16 0

 11 forest on drift 1 1 1 1 15 0 16 0

 12 LDres/drift/no I/E 1 1 1 1 15 0 16 0

 13 LDres/drift/Export 1 1 1 1 15 0 16 0

 14 LDres/drift/Import 1 1 1 1 15 0 16 0

 15 HDres/drift/no I/E 1 1 1 1 15 0 16 0
74 A Precipitation-Runoff Model for the Blackstone River Basin

 16 HDres/drift/Export 1 1 1 1 15 0 16 0

 17 HDres/drift/Import 1 1 1 1 15 0 16 0

*** SE climate

 101 commer/trans/ind 1 1 1 1 15 0 16 0

 102 open undevel till 1 1 1 1 15 0 16 0

 103 forest on till 1 1 1 1 15 0 16 0

 104 LDres/till/noI/E 1 1 1 1 15 0 16 0

 105 LDRes/till/Export 1 1 1 1 15 0 16 0

 106 LDRes/till/Import 1 1 1 1 15 0 16 0

 107 HDRes/till/no I/E 1 1 1 1 15 0 16 0

 108 HDRes/till/Export 1 1 1 1 15 0 16 0

 109 HDRes/till/Import 1 1 1 1 15 0 16 0

 110 open undevel drift 1 1 1 1 15 0 16 0

 111 forest on drift 1 1 1 1 15 0 16 0

 112 LDres/drift/no I/E 1 1 1 1 15 0 16 0

 113 LDres/drift/Export 1 1 1 1 15 0 16 0

 114 LDres/drift/Import 1 1 1 1 15 0 16 0

 115 HDres/drift/no I/E 1 1 1 1 15 0 16 0

 116 HDres/drift/Export 1 1 1 1 15 0 16 0

 117 HDres/drift/Import 1 1 1 1 15 0 16 0

 END GEN-INFO 

 

*** ------------------------------------------------------------------------ 

*** PERLND - Section SNOW Princ 4.2(1).2 pg 40 

*** Coding 4.4(1).3 pg 309 

*** ------------------------------------------------------------------------ 

 

 ICE-FLAG 

 <PLS > 0= Ice formation not simulated, 1= Simulated *** 

 ### -###ICEFG *** 

 1 17 1 

 101 117 1 

 END ICE-FLAG 

 

 SNOW-PARM1 

 <PLS > Snow input info: Part 1 *** 

 ### -### LAT MELEV SHADE SNOWCF COVIND *** 

 1 42. 550. 0.15 1.50 0.30 

 2 42. 550. 0.05 1.50 0.30

 3 42. 550. 0.50 1.50 0.30 

 4 9 42. 550. 0.15 1.50 0.30

 10 42. 550. 0.05 1.50 0.30 

 11 42. 550. 0.50 1.50 0.30

 12 17 42. 550. 0.15 1.50 0.30 

 101 42. 371. 0.15 1.60 0.30 

 102 42. 371. 0.05 1.60 0.30

 103 42. 371. 0.50 1.60 0.30 

 104 109 42. 371. 0.15 1.60 0.30

 110 42. 371. 0.05 1.60 0.30 

 111 42. 371. 0.50 1.60 0.30

 112 117 42. 371. 0.15 1.60 0.30 

 END SNOW-PARM1 

 
Appendix 1 75

 SNOW-PARM2 

 <PLS > Snow input info: Part 2 *** 

 ### -### RDCSN TSNOW SNOEVP CCFACT MWATER MGMELT *** 

 1 3 0.15 32. 0.15 1.00 0.03 0.0100

 4 9 0.15 32. 0.15 1.00 0.03 0.0100

 10 0.15 32. 0.15 1.00 0.03 0.0100

 11 0.15 32. 0.15 1.00 0.03 0.0100

 12 17 0.15 32. 0.15 1.00 0.03 0.0100

 101 103 0.15 32. 0.15 1.00 0.03 0.0100

 104 109 0.15 32. 0.15 1.00 0.03 0.0100

 110 0.15 32. 0.15 1.00 0.03 0.0100

 111 0.15 32. 0.15 1.00 0.03 0.0100

 112 117 0.15 32. 0.15 1.00 0.03 0.0100

 

 END SNOW-PARM2 

 

 SNOW-INIT1 *** 

 <PLS > Initial snow conditions: Part 1 *** 

 ### -### PACKSNOW PACKICE PACKWATER RDENPF DULL PAKTMP *** 

 1 17 0.60 0.0 0.30 0.30 200. 31.5 

 101 117 0.60 0.0 0.30 0.30 200. 31.5 

 END SNOW-INIT1 *** 

 

 SNOW-INIT2 *** 

 <PLS > Initial snow conditions: Part 2 *** 

 ### -### COVINX XLNMLT SKYCLR *** 

 1 17 0.20 0.01 1.00 

 101 117 0.20 0.01 1.00 

 END SNOW-INIT2 *** 

***----------------------------------------------------------------------------*

*** PERLND - Section PWATER Princ. 4.2(1).3 pg 54 *

*** Coding 4.4(1).4 pg 317 *

*** Water Budget *

***----------------------------------------------------------------------------*

 

 PWAT-PARM1 

*** 1=varies monthly 0=does not

*** <PLS > <PWATER flags><monthly parameter value flags> 

***## -### CSNO RTOP UZFG VCS VUZ VNN VIFW VIRC VLE 

 1 17 1 0 0 1 0 1 0 0 1 

 101 117 1 0 0 1 0 1 0 0 1 

 END PWAT-PARM1 

 
76 A Precipitation-Runoff Model for the Blackstone River Basin

 PWAT-PARM2 

 <PLS > *** PWATER input info: Part 2 

 ### -### ***FOREST LZSN INFILT LSUR SLSUR KVARY AGWRC

 ***(none) (in) (in/hr) (ft) (none) (l/in) (l/in)

 1 0.010 3.40 0.020 100. 0.044 1.70 0.986

 2 0.020 4.50 0.044 300. 0.065 1.70 0.994

 3 0.500 4.50 0.046 400. 0.077 1.70 0.994

 4 6 0.050 4.50 0.044 300. 0.067 1.70 0.992

 7 9 0.030 3.60 0.024 200. 0.057 1.70 0.986

 10 0.020 7.40 0.541 300. 0.051 0.70 0.998

 11 0.500 7.40 0.571 500. 0.065 0.70 0.998

 12 14 0.050 7.40 0.521 300. 0.067 0.70 0.994

 15 17 0.030 6.60 0.471 200. 0.057 0.70 0.992

 

 101 0.010 3.40 0.020 100. 0.044 1.70 0.986

 102 0.020 4.50 0.044 300. 0.065 1.70 0.994

 103 0.500 4.50 0.046 400. 0.077 1.70 0.994

 104 106 0.050 4.50 0.044 300. 0.067 1.70 0.992

 107 109 0.030 3.60 0.024 200. 0.057 1.70 0.986

 

 110 0.020 7.40 0.541 300. 0.051 0.70 0.998

 111 0.500 7.40 0.571 500. 0.065 0.70 0.998

 112 114 0.050 7.40 0.521 300. 0.067 0.70 0.994

 115 117 0.030 6.60 0.471 200. 0.057 0.70 0.992

 END PWAT-PARM2

 

 

 PWAT-PARM3 

 <PLS > *** PWATER input info: Part 3 

 ### -### ***PETMAX PETMIN INFEXP INFILD DEEPFR BASETP AGWETP

 1 40. 35. 2.0 2.0 0.35 0.00 0.000

 2 3 40. 35. 2.0 2.0 0.00 0.00 0.000

 4 5 40. 35. 2.0 2.0 0.28 0.00 0.000

 6 40. 35. 2.0 2.0 0.00 0.00 0.000

 7 8 40. 35. 2.0 2.0 0.45 0.00 0.000

 9 11 40. 35. 2.0 2.0 0.00 0.00 0.000

 12 13 40. 35. 2.0 2.0 0.28 0.00 0.000

 14 40. 35. 2.0 2.0 0.00 0.00 0.000

 15 16 40. 35. 2.0 2.0 0.45 0.00 0.000 

 17 40. 35. 2.0 2.0 0.00 0.00 0.000

 

 101 40. 35. 2.0 2.0 0.35 0.00 0.000

 102 103 40. 35. 2.0 2.0 0.00 0.00 0.000

 104 105 40. 35. 2.0 2.0 0.28 0.00 0.000

 106 40. 35. 2.0 2.0 0.00 0.00 0.000

 107 108 40. 35. 2.0 2.0 0.45 0.00 0.000

 109 111 40. 35. 2.0 2.0 0.00 0.00 0.000

 112 113 40. 35. 2.0 2.0 0.28 0.00 0.000

 114 40. 35. 2.0 2.0 0.00 0.00 0.000

 115 116 40. 35. 2.0 2.0 0.45 0.00 0.000 

 117 40. 35. 2.0 2.0 0.00 0.00 0.000

 END PWAT-PARM3 

 
Appendix 1 77

 

 *** Inc INTFW increases interflow & dec surface flow affect Interflow vol

 *** Inc IRC more like baseflow -dec IRC inc peaks

 PWAT-PARM4 

*** Varied Season Y N Y N N Y ***

 <PLS > PWATER input info: Part 4 *** 

 Flag PARM4 VCS VUZ VUR VMN VIFW VLE *** 

 ### -### CEPSC UZSN NSUR INTFW IRC LZETP *** 

 (in) (in) (none) (none) (l/da) (none) *** 

 1 0.030 0.56 0.200 4.00 0.36 0.20

 2 0.020 0.62 0.250 8.00 0.50 0.40

 3 0.050 0.65 0.230 9.00 0.56 0.70

 4 6 0.040 0.65 0.210 6.00 0.54 0.40

 7 9 0.040 0.65 0.210 4.00 0.46 0.30

 10 0.020 0.75 0.250 10.00 0.90 0.40

 11 0.080 0.77 0.230 12.00 0.90 0.70

 12 14 0.040 0.77 0.210 10.00 0.86 0.40

 15 17 0.040 0.77 0.210 9.50 0.82 0.30

 101 0.030 0.56 0.200 4.00 0.36 0.20

 102 0.020 0.62 0.250 8.00 0.50 0.40

 103 0.050 0.65 0.230 9.00 0.56 0.70

 104 106 0.040 0.65 0.210 6.00 0.54 0.40

 107 109 0.040 0.65 0.210 4.00 0.46 0.30

 110 0.020 0.75 0.250 10.00 0.90 0.40

 111 0.080 0.77 0.230 12.00 0.90 0.70

 112 114 0.040 0.77 0.210 10.00 0.86 0.40

 115 117 0.040 0.77 0.210 9.50 0.82 0.30

 END PWAT-PARM4 

 

 MON-INTERCEP 

 Monthly interception storage capacity *** 

 <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 0.02 0.02 0.02 0.03 0.03 0.05 0.05 0.05 0.05 0.03 0.02 0.02 

 2 0.02 0.02 0.02 0.03 0.03 0.04 0.04 0.04 0.04 0.03 0.02 0.02

 3 0.04 0.04 0.04 0.04 0.05 0.12 0.14 0.16 0.17 0.16 0.04 0.04 

 4 9 0.02 0.02 0.02 0.03 0.03 0.05 0.05 0.05 0.05 0.03 0.02 0.02 

 10 0.02 0.02 0.02 0.03 0.03 0.04 0.04 0.04 0.04 0.03 0.02 0.02

 11 0.04 0.04 0.04 0.04 0.05 0.12 0.14 0.16 0.17 0.16 0.04 0.04 

 12 17 0.02 0.02 0.02 0.03 0.03 0.05 0.05 0.05 0.05 0.03 0.02 0.02 

 101 0.02 0.02 0.02 0.03 0.03 0.05 0.05 0.05 0.05 0.03 0.02 0.02 

 102 0.02 0.02 0.02 0.03 0.03 0.04 0.04 0.04 0.04 0.03 0.02 0.02

 103 0.04 0.04 0.04 0.04 0.05 0.12 0.14 0.16 0.17 0.16 0.04 0.04 

 104 109 0.02 0.02 0.02 0.03 0.03 0.05 0.05 0.05 0.05 0.03 0.02 0.02 
78 A Precipitation-Runoff Model for the Blackstone River Basin

 110 0.02 0.02 0.02 0.03 0.03 0.04 0.04 0.04 0.04 0.03 0.02 0.02

 111 0.04 0.04 0.04 0.04 0.05 0.12 0.14 0.16 0.17 0.16 0.04 0.04 

 112 117 0.02 0.02 0.02 0.03 0.03 0.05 0.05 0.05 0.05 0.03 0.02 0.02 

 END MON-INTERCEP 

*** <<< NOT VARIED MONTHLY>>> 

 MON-UZSN 

 Upper zone nominal storage ***

 UZSN inversly affects peak flow - as UZSN goes up peaks go down ***

 <PLS> Only required if VUZFG=1 in PWAT-PARM1 *** 

 ### -### Upper zone storage at start of each month *** 

 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC *** 

 1 .56 .56 .56 .56 .56 .56 .56 .56 .56 .56 .56 .56 

 2 .62 .62 .62 .62 .62 .62 .62 .62 .62 .62 .62 .62 

*** 3 .75 .75 .75 .75 .75 .75 .75 .75 .75 .75 .75 .75 

 3 .65 .65 .65 .65 .65 .65 .65 .65 .65 .65 .65 .65 

 4 9 .65 .65 .65 .65 .65 .65 .65 .65 .65 .65 .65 .65

 10 11 .75 .75 .75 .75 .75 .75 .75 .75 .75 .75 .75 .75

***11 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00

 12 17 .77 .77 .77 .77 .77 .77 .77 .77 .77 .77 .77 .77

 101 .56 .56 .56 .56 .56 .56 .56 .56 .56 .56 .56 .56 

 102 .62 .62 .62 .62 .62 .62 .62 .62 .62 .62 .62 .62 

 103 .75 .75 .75 .75 .75 .75 .75 .75 .75 .75 .75 .75 

 104 109 .65 .65 .65 .65 .65 .65 .65 .65 .65 .65 .65 .65

 110 111 .75 .75 .75 .75 .75 .75 .75 .75 .75 .75 .75 .75

***11 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00

 112 117 .77 .77 .77 .77 .77 .77 .77 .77 .77 .77 .77 .77

 END MON-UZSN 

 

 MON-MANNING 

 Manning’s “n” for overland flow plans *** 

 <PLS > Only required if VNNFG=1 in PWAT-PARM1 *** 

 ### -### Manning’s n for overland flow at start of each month *** 

 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC *** 

 1 0.22 0.22 0.22 0.22 0.23 0.26 0.26 0.26 0.26 0.25 0.23 0.22 

 2 0.25 0.25 0.25 0.25 0.27 0.30 0.30 0.30 0.30 0.27 0.25 0.25 

 3 0.28 0.28 0.28 0.28 0.29 0.29 0.29 0.29 0.29 0.29 0.28 0.28 

 4 9 0.22 0.22 0.22 0.22 0.23 0.26 0.26 0.26 0.26 0.25 0.23 0.22 

 10 0.25 0.25 0.25 0.25 0.27 0.30 0.30 0.30 0.30 0.27 0.25 0.25 

 11 0.28 0.28 0.28 0.28 0.29 0.29 0.29 0.29 0.29 0.29 0.28 0.28 

 12 17 0.22 0.22 0.22 0.22 0.23 0.36 0.26 0.26 0.26 0.25 0.23 0.22 

 101 0.22 0.22 0.22 0.22 0.23 0.26 0.26 0.26 0.26 0.25 0.23 0.22 

 102 0.25 0.25 0.25 0.25 0.27 0.30 0.30 0.30 0.30 0.27 0.25 0.25 

 103 0.28 0.28 0.28 0.28 0.29 0.29 0.29 0.29 0.29 0.29 0.28 0.28 

 104 109 0.22 0.22 0.22 0.22 0.23 0.26 0.26 0.26 0.26 0.25 0.23 0.22 

 110 0.25 0.25 0.25 0.25 0.27 0.30 0.30 0.30 0.30 0.27 0.25 0.25 

 111 0.28 0.28 0.28 0.28 0.29 0.29 0.29 0.29 0.29 0.29 0.28 0.28 

 112 117 0.22 0.22 0.22 0.22 0.23 0.36 0.26 0.26 0.26 0.25 0.23 0.22 

 END MON-MANNING 
Appendix 1 79

*** <<< NOT VARIED MONTHLY >>> 

 MON-INTERFLW 

 Monthly interflow parameter *** 

 <PLS > Only required if VIFWFG=1 in PWAT-PARM1 *** 

 ### -### Monthly interflow at start of each month *** 

 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC *** 

 1 8.30 8.30 8.30 8.30 8.35 8.35 8.35 8.35 8.35 8.30 8.30 8.30

 2 5.80 5.80 5.80 5.80 5.85 5.85 5.85 5.85 5.85 5.80 5.80 5.80

 3 5.90 5.90 5.90 5.95 5.95 5.95 5.95 5.95 5.95 5.90 5.90 5.90

 4 9 5.70 5.70 5.70 5.70 5.75 5.75 5.75 5.75 5.75 5.70 5.70 5.70

 10 8.50 8.50 8.50 8.50 8.55 8.55 8.55 8.55 8.55 8.50 8.50 8.50

 11 8.60 8.60 8.60 8.65 8.65 8.65 8.65 8.65 8.65 8.70 8.70 8.70

 12 17 8.30 8.30 8.30 8.30 8.35 8.35 8.35 8.35 8.35 8.30 8.30 8.30

 101 8.30 8.30 8.30 8.30 8.35 8.35 8.35 8.35 8.35 8.30 8.30 8.30

 102 5.80 5.80 5.80 5.80 5.85 5.85 5.85 5.85 5.85 5.80 5.80 5.80

 103 5.90 5.90 5.90 5.95 5.95 5.95 5.95 5.95 5.95 5.90 5.90 5.90

 104 109 5.70 5.70 5.70 5.70 5.75 5.75 5.75 5.75 5.75 5.70 5.70 5.70

 110 8.50 8.50 8.50 8.50 8.55 8.55 8.55 8.55 8.55 8.50 8.50 8.50

 111 8.60 8.60 8.60 8.65 8.65 8.65 8.65 8.65 8.65 8.70 8.70 8.70

 112 117 8.30 8.30 8.30 8.30 8.35 8.35 8.35 8.35 8.35 8.30 8.30 8.30

 END MON-INTERFLW 

*** <<< NOT VARIED MONTHLY >>> 

 MON-IRC 

 Monthly interflow recession (inc IRC dec peak) *** 

 <PLS > Only required if VIRCFG=1 in PWAT-PARM1 (max < 1.0) *** 

 ### -### Monthly interflow at start of each month *** 

 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC *** 

 1 0.82 0.82 0.82 0.82 0.84 0.86 0.86 0.86 0.84 0.82 0.82 0.82 

 2 3 0.90 0.90 0.90 0.90 0.91 0.92 0.92 0.92 0.91 0.90 0.90 0.90 

 4 6 0.88 0.88 0.88 0.88 0.89 0.90 0.90 0.90 0.89 0.88 0.88 0.88 

 7 9 0.86 0.86 0.86 0.86 0.87 0.88 0.88 0.88 0.87 0.86 0.86 0.86

 10 11 0.90 0.90 0.90 0.90 0.91 0.92 0.92 0.92 0.91 0.90 0.90 0.90 

 12 14 0.88 0.88 0.88 0.88 0.89 0.90 0.90 0.90 0.89 0.88 0.88 0.88 

 15 17 0.86 0.86 0.86 0.86 0.87 0.88 0.88 0.88 0.87 0.86 0.86 0.86

 101 0.82 0.82 0.82 0.82 0.84 0.86 0.86 0.86 0.84 0.82 0.82 0.82 

 102 103 0.90 0.90 0.90 0.90 0.91 0.92 0.92 0.92 0.91 0.90 0.90 0.90 

 104 106 0.88 0.88 0.88 0.88 0.89 0.90 0.90 0.90 0.89 0.88 0.88 0.88 

 107 109 0.86 0.86 0.86 0.86 0.87 0.88 0.88 0.88 0.87 0.86 0.86 0.86

 110 111 0.90 0.90 0.90 0.90 0.91 0.92 0.92 0.92 0.91 0.90 0.90 0.90 

 112 114 0.88 0.88 0.88 0.88 0.89 0.90 0.90 0.90 0.89 0.88 0.88 0.88 

 115 117 0.86 0.86 0.86 0.86 0.87 0.88 0.88 0.88 0.87 0.86 0.86 0.86

 END MON-IRC 

 
80 A Precipitation-Runoff Model for the Blackstone River Basin

 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 .08 .08 .08 .14 .15 .29 .31 .31 .30 .16 .14 .08 

 2 .12 .12 .12 .20 .33 .35 .36 .36 .31 .29 .18 .12 

 3 .20 .20 .22 .35 .49 .75 .80 .80 .65 .50 .25 .20 

 4 9 .18 .18 .20 .32 .45 .61 .65 .65 .53 .44 .22 .18 

 

 10 .12 .12 .22 .20 .33 .35 .36 .36 .31 .29 .18 .12 

 11 .20 .20 .22 .35 .49 .75 .80 .80 .65 .50 .25 .20 

 12 17 .18 .18 .20 .32 .45 .61 .65 .65 .53 .44 .22 .18 

 101 .08 .08 .08 .14 .15 .29 .31 .31 .30 .16 .14 .08 

 102 .12 .12 .12 .20 .33 .35 .36 .36 .31 .29 .18 .12 

 103 .20 .20 .22 .35 .49 .65 .80 .80 .65 .50 .25 .20 

 104 109 .18 .18 .20 .32 .45 .61 .65 .65 .63 .44 .22 .18 

 

 110 .12 .12 .12 .20 .33 .35 .36 .36 .31 .29 .28 .26 

 111 .20 .20 .22 .35 .49 .75 .80 .80 .65 .50 .25 .20 

 112 117 .18 .18 .20 .32 .45 .61 .65 .65 .53 .44 .22 .18 

 END MON-LZETPARM 

 

 PWAT-STATE1 

 <PLS > *** Initial conditions at start of simulation (from Jan. 1998 values in 

.out file) 

 ### -### *** CEPS SURS UZS IFWS LZS AGWS GWVS

 1 0.020 0.000 1.056 0.035 4.139 0.453 0.338 

 2 0.020 0.000 1.072 0.037 5.638 1.553 0.691 

 3 0.040 0.000 1.050 0.029 5.203 1.392 0.596 

 4 0.020 0.000 1.074 0.032 5.310 1.101 0.631 

 5 0.020 0.000 1.074 0.032 5.310 1.043 0.568 

 6 0.020 0.000 1.126 0.042 5.686 1.321 0.892 

 7 0.020 0.000 1.159 0.043 4.254 0.524 0.423 

 8 0.020 0.000 1.159 0.043 4.254 0.524 0.423 

 9 0.020 0.000 1.297 0.087 5.344 0.983 1.622 

 

 10 0.020 0.000 0.597 0.001 10.034 11.892 1.157 

 11 0.040 0.000 0.342 0.001 8.565 10.561 0.802 

 12 0.020 0.000 0.395 0.001 8.820 2.833 0.904 

 13 0.020 0.000 0.395 0.001 8.820 2.779 0.858 

 14 0.020 0.000 0.452 0.001 9.352 3.251 1.234 

 15 0.020 0.000 0.437 0.001 8.507 1.823 0.719 

 16 0.020 0.000 0.437 0.001 8.507 1.823 0.719 

 17 0.020 0.000 0.680 0.002 10.230 3.181 2.345 

 

 101 0.020 0.000 1.141 0.035 3.885 0.469 0.351 

 102 0.020 0.000 1.186 0.037 5.543 1.659 0.796 

 103 0.040 0.000 1.131 0.029 4.990 1.384 0.645 
Appendix 1 81

 104 0.020 0.000 1.166 0.032 5.132 1.153 0.694 

 105 0.020 0.000 1.166 0.032 5.132 1.082 0.624 

 106 0.020 0.000 1.234 0.042 5.545 1.416 0.968 

 107 0.020 0.000 1.275 0.043 4.126 0.561 0.453 

 108 0.020 0.000 1.275 0.043 4.126 0.561 0.453 

 109 0.020 0.000 1.390 0.087 5.265 1.088 1.650 

 

 110 0.020 0.000 0.504 0.001 9.671 12.115 1.407 

 111 0.040 0.000 0.261 0.001 8.093 10.464 0.914 

 112 0.020 0.000 0.336 0.001 8.535 2.867 1.078 

 113 0.020 0.000 0.336 0.001 8.535 2.804 1.024 

 114 0.020 0.000 0.386 0.001 9.067 3.342 1.424 

 115 0.020 0.000 0.372 0.001 8.234 1.877 0.861 

 116 0.020 0.000 0.372 0.001 8.234 1.877 0.861 

 117 0.020 0.000 0.588 0.002 9.972 3.496 2.557 

 

 END PWAT-STATE1 

 

END PERLND 

 

************************************************************************** 

*** IMPLND - Impervious land 4.2(2) Prin. 4.2(2) pg 114 *** 

*** Coding 4.4(2) pg 457 *** 

************************************************************************** 

IMPLND 

 ACTIVITY 

 <ILS > Active Sections (1-active, 0-inactive) *** 

 ### -### ATMP SNOW IWAT SLD IWG IQAL *** 

 30 0 1 1

 31 0 1 1 

 130 0 1 1

 131 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 #### ## *** 

 30 6 4 1 12 

 31 6 4 1 12 

 130 6 4 1 12 

 131 6 4 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 #### ## *** 

 30 31 6 4 1 12 

 130 131 6 4 1 12

 END BINARY-INFO 

 
82 A Precipitation-Runoff Model for the Blackstone River Basin

 GEN-INFO 

 <ILS ><-------Name-------> Unit-systems Printer Binary *** 

 ### -### User t-series Engl Metr Engl Metr *** 

 in out i/o# *** 

 30 commercial NW 1 1 1 15 0 16 0 

 31 residental NW 1 1 1 15 0 16 0 

 130 commercial SE 1 1 1 15 0 16 0 

 131 residental SE 1 1 1 15 0 16 0 

 END GEN-INFO 

*** ------------------------------------------------------------------------ 

*** IMPLND- Same as PERLND Section SNOW 

*** see 4.4(1).3 pg 309 

*** ------------------------------------------------------------------------ 

 

 ICE-FLAG 

 <PLS > 0= Ice formation not simulated, 1= Simulated *** 

 ### -###ICEFG *** 

 30 31 1 

 130 131 1 

 END ICE-FLAG 

 

 SNOW-PARM1 

 <PLS > Snow input info: Part 1 *** 

 ### -### LAT MELEV SHADE SNOWCF COVIND *** 

 30 31 42. 550. 0.20 1.50 0.30 

 130 131 42. 371. 0.20 1.60 0.30 

 END SNOW-PARM1 

 

 SNOW-PARM2 

 <PLS > Snow input info: Part 2 *** 

 ### -### RDCSN TSNOW SNOEVP CCFACT MWATER MGMELT *** 

 30 31 0.20 32. 0.02 1.00 0.03 0.0100 

 130 131 0.20 32. 0.02 1.00 0.03 0.0100 

 END SNOW-PARM2 

 

 SNOW-INIT1 *** 

 <PLS > Initial snow conditions: Part 1 *** 

 ### -### PACKSNOW PACKICE PACKWATER RDENPF DULL PAKTMP *** 

 30 31 0.6 0.0 0.30 0.30 200. 31.5 

 130 131 0.6 0.0 0.30 0.30 200. 31.5 

 END SNOW-INIT1 *** 

 

 SNOW-INIT2 *** 

 <PLS > Initial snow conditions: Part 2 *** 

 ### -### COVINX XLNMLT SKYCLR *** 

 30 31 0.20 0.01 1.00 

 130 131 0.20 0.01 1.00 

 END SNOW-INIT2 *** 

 
Appendix 1 83

*** ---------------------------------------------------------------------- 

*** IMPLND - Section IWATER input Prin. 4.2(2).3 pg 114 

*** Coding 4.4(2).4 pg 464 

*** ---------------------------------------------------------------------- 

 

 IWAT-PARM1 

 <ILS > Flags *** 

 ### -### CSNO RTOP VRS VNN RTLI *** 

 30 1 1 0 

 31 1 1 0 

 130 1 1 0 

 131 1 1 0 

 END IWAT-PARM1 

 

 IWAT-PARM2 

 <ILS > *** 

 ### -### LSUR SLSUR NSUR RETSC *** 

 30 100. .010 .050 .10 

 31 200. .014 .050 .05 

 130 100. .010 .050 .10 

 131 200. .014 .050 .05 

 END IWAT-PARM2 

 

 IWAT-PARM3 

 <ILS > *** 

 ### -### PETMAX PETMIN *** 

 30 40. 35. 

 31 40. 35. 

 130 40. 35. 

 131 40. 35. 

 END IWAT-PARM3 

 

 IWAT-STATE1 

 <ILS > IWATER state variables *** 

 ### -### RETS SURS *** 

 30 .10 .00 

 31 .05 .00 

 130 .10 .00 

 131 .05 .00 

 END IWAT-STATE1 

END IMPLND