Scientific Investigations Report 2010–5007

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the 

Massachusetts Department of Conservation and Recreation, 

and the U.S. Environmental Protection Agency 

Effects of Selected Low-Impact-Development 

(LID) Techniques on Water Quality and Quantity 

in the Ipswich River Basin, Massachusetts: 

Field and Modeling Studies

Bath House

BURNAP STREET

GROVE AVENUE

98

98

94

94

98

98

98

100

98

96

96

D

Y H

96.5

97.1

98.5

98.1

GRAVEL

PAVERS

POROUS

ASPHALT

IMPERVIOUS

ASPHALT

PAVED PARKING

PAVED WALKWAY TO FISHING PIER

EXISTING

SWALE

SWALE

RAIN GARDEN

RAIN GARDEN

RAIN GARDENS AND

BIORETENTION CELLS

OW#3

MLS#2

OW#1

MLS#1

MLS#3

OW#4

OW#2

USGS OBSERVATION WELLS Silver Lake

USGS SAMPLING WELLS

altitude approximately 93.5 feet 

N

Basemap courtesy of Steven Roy, Geosyntec Consultants
Cover Graphics: Map modifed from Geosyntec Consultants. DCR logo from Massachusetts Department of Recreation. 

Banner photo, Ipswich River from Green Street Bridge, Ipswich, MA. Whipple Annex photo showing green roof, Ipswich, 

MA. Parking lot photo showing porous pavers and asphalt, and bioretention cells at Silver Lake parking lot, Wilmington, MA.

 
Effects of Selected Low-ImpactDevelopment (LID) Techniques on 

Water Quality and Quantity in the 

Ipswich River Basin, Massachusetts: 

Field and Modeling Studies

By Marc J. Zimmerman, Jeffrey R. Barbaro, Jason R. Sorenson, and 

Marcus C. Waldron

Prepared in cooperation with the 

Massachusetts Department of Conservation and Recreation and the 

U.S. Environmental Protection Agency

Scientific Investigations Report 2010–5007

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

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

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Zimmerman, M.J., Barbaro, J.R., Sorenson, J.R., and Waldron, M.C., 2010, Effects of selected low-impact-development (LID) techniques on water quality and quantity in the Ipswich River Basin, Massachusetts—Field and modeling 

studies: U.S. Geological Survey Scientific Investigations Report 2010–5007, 113 p.
iii

Acknowledgments

The authors thank Sara Cohen (Massachusetts Department of Conservation and Recreation) and Ralph Abele and Sandra Fancieullo (U.S. Environmental Protection Agency) who 

provided valuable comments and suggestions throughout the study. Steven Roy, Marcus Quigley, and Andrea Braga (Geosyntec Consultants) freely provided their own insights as well as 

detailed information about the design of the LID enhancements in Wilmington, MA. Members 

of the Technical Advisory Committees, Gregory Krom (Topsfield Water Department), Michael 

O’Halloran (Reading Water Department), Kerry Mackin and Jessica Darling (Ipswich River 

Watershed Association), Kari Winfield, George Zoto, and Thomas Lamont (Massachusetts 

Department of Environmental Protection), Marilyn McCrory and Anne Carroll (Massachusetts 

Department of Conservation and Recreation), Joanne Bissetta (Concord Water Department), 

Paul Lauenstein (Neponset River Watershed Association), James Rolfe (AquaSave), and Yushiou Tsai (Tufts University), formed for this project assisted with the development of the modeling scenarios, provided updated water-withdrawal and water-conservation information used 

in the simulations, and conducted technical reviews. Jamie Magaldi (Wilmington Department 

of Public Works) simplified the logistics of our fieldwork. David Pancoast (Ipswich Conservation Commission) provided specific advice on the siting of our equipment. Rick Doerr (Town of 

Ipswich) provided support with all aspects of our work at the roof-runoff sites.

USGS colleagues Phillip Zarriello, Leslie DeSimone, Roy Socolow, Andrew Massey, 

Kimberly Campo, Linda Comeau, Timothy McCobb, John Masterson, Kirk Smith, David 

Lorenz, and Joyce Williamson provided invaluable technical assistance at various stages of this 

project. USGS colleagues Leslie DeSimone, Chad Ostheimer, Peter Hughes, and Marie Peppler, 

and Michael Dietz (Utah State University) served as colleague reviewers, and their thoughtful comments and suggestions substantially improved the clarity and technical accuracy of the 

report.
iv

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v

Contents

Acknowledgments........................................................................................................................................iii

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

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

Applications of Low-Impact-Development (LID) Principles and Techniques.............................4

Previous Studies ...................................................................................................................................4

Purpose and Scope ..............................................................................................................................4

Environmental Setting..........................................................................................................................5

Field Studies of Low-Impact-Development Techniques..........................................................................5

Porous Parking Lot Enhancements at

Silver Lake Beach ...................................................................................................................5

Design of Low-Impact-Development Enhancements to Increase Infiltration...................7

Monitoring Approach..................................................................................................................7

Regional and Local Groundwater Flow...........................................................................7

Water-Table Altitude and Water Quality.......................................................................10

Changes in Groundwater Quality Following the Installation of Low-ImpactDevelopment Enhancements .....................................................................................10

Specific Conductance, Dissolved Oxygen, and pH.....................................................10

Nutrients, Dissolved Metals, and Total Petroleum Hydrocarbons ...........................23

Nutrients....................................................................................................................23

Dissolved Metals .....................................................................................................23

Total Petroleum Hydrocarbons..............................................................................30

Low-Impact-Development Enhancements at the Silver Lake Avenue/Dexter Street 

Neighborhood and Water Quantity and Quality of Stormwater Runoff........................30

Design of Low-Impact-Development Enhancements to Increase Infiltration.................32

Monitoring Approach................................................................................................................32

Changes in Runoff Quantity and Quality Following Installation of Low-ImpactDevelopment Enhancements .....................................................................................37

Runoff Quantity..................................................................................................................37

Runoff Quality ....................................................................................................................41

Green and Conventional Roofs and the Quantity and Quality of Stormwater Runoff..............47

Monitoring Approach................................................................................................................47

Comparison of Conventional and Green Roof Runoff Quantity and Quality.....................51

Roof-Runoff Quantity........................................................................................................52

Roof-Runoff Quality ..........................................................................................................58

Simulation of the Effects of Land-Use Change and Low-Impact Development on Streamflow at 

Multiple Spatial Scales .................................................................................................................68

Description of Original Baseline Model..........................................................................................68

Modifications to the Original Baseline Model ......................................................................70

Model Limitations.......................................................................................................................70

Description of Basin-Scale and Local-Scale Simulations...........................................................71

Basin-Scale Simulations ..........................................................................................................71

Original Baseline Simulation...........................................................................................71

Updated Baseline Simulation .........................................................................................71
vi

Buildout Simulation ..........................................................................................................73

Simulation of Low-Impact-Development Retrofits Upstream from the South 

Middleton Streamgage.......................................................................................77

Water Conservation Simulation......................................................................................77

Local-Scale Simulations...........................................................................................................80

Conventional Development .............................................................................................80

Cluster Development........................................................................................................82

Clustering Practices for High-Density Residential Development....................82

Clustering Practices for Low-Density Residential Development.....................84

Effects of Water-Withdrawal Changes and Low-Impact-Development Practices on 

Streamflow .............................................................................................................................84

Basin-Scale Simulations ..........................................................................................................84

Updated Baseline Simulation .........................................................................................84

Buildout Simulation ..........................................................................................................87

Simulation of Low-Impact-Development Retrofits Upstream from the South 

Middleton Streamgage.......................................................................................90

Water Conservation Simulation......................................................................................93

Local-Scale Simulations...........................................................................................................93

Conventional Development .............................................................................................93

Flood-Peak Ratios...........................................................................................................102

Cluster Development......................................................................................................103

Summary and Conclusions.......................................................................................................................105

Field-Study Findings .........................................................................................................................105

Simulation Findings...........................................................................................................................105

References Cited........................................................................................................................................107

Appendix 1. Data, calculations, and assumptions used to scale up data to the town

level from the water-conservation pilot study conducted in the Ipswich

River Basin, MA............................................................................................................................111
vii

Figures

1. Map showing location of streamgages, wells, and weather station in the Ipswich

River Basin, MA ............................................................................................................................3

2. Photographs showing views of Silver Lake Beach parking lot in Wilmington, MA,

prior to renovation, (A) looking west and (B) looking north...................................................6

3. Photograph showing water fowl feeding on Silver Lake Beach in Wilmington, MA,

prior to installation of low-impact-development features .....................................................7

4. Photographs showing views of (A) partially completed porous parking lot at Silver

Lake Beach, Wilmington, MA, showing bioretention cells, porous pavers, and

gravel bed for porous asphalt and (B) completely renovated parking lot...........................8

5. Map showing generalized groundwater-flow direction in the vicinity of Silver Lake,

Wilmington, MA ............................................................................................................................9

6. Photographs showing (A) U.S. Geological Survey well drillers installing multilevel

samplers. Markings on the white PVC pipe are locations of the sampling ports and

(B) color-coded sampling tubes that lead to intake ports in multilevel samplers ...........11

7. Map showing features of Silver Lake Beach parking lot, Wilmington, MA, and

generalized groundwater-flow direction................................................................................12

8. Graph showing altitudes of water table determined in multilevel samplers and of

Silver Lake, Wilmington, MA, July 2005 to June 2007...........................................................13

9. Graph showing minimum, median, and maximum specific conductance values in 

groundwater samples collected at multilevel-sampler well number 1 (MLS#1)

before (pre-low-impact development) and after (post-low-impact-development) 

installation of a porous parking lot at Silver Lake Beach, Wilmington, MA .....................24

10. Graph showing minimum, median, and maximum dissolved oxygen concentrations

in groundwater samples collected at multilevel-sampler well number 1 (MLS#1)

before (pre-low-impact development) and after (post-low-impact-development) 

installation of a porous parking lot at Silver Lake Beach, Wilmington, MA .....................25

11. Graph showing total ammonia plus organic nitrogen concentrations and

water-table altitudes in multilevel-sampler well number 1 (MLS#1) before and after

installation of a porous parking lot at Silver Lake Beach, Wilmington, MA .....................26

12. Graph showing dissolved nitrate plus nitrite nitrogen concentrations and

water-table altitudes in multilevel-sampler well number 1 (MLS#1) before and after

installation of a porous parking lot at Silver Lake Beach, Wilmington, MA .....................26

13. Graph showing dissolved orthophosphorus concentrations and water-table

altitudes in multilevel-sampler well number 1 (MLS#1) before and after installation

of a porous parking lot at Silver Lake Beach, Wilmington, MA..........................................27

14. Graph showing total phosphorus concentrations and water-table altitudes in

multilevel-sampler well number 1 (MLS#1) before and after installation of a porous

parking lot at Silver Lake Beach, Wilmington, MA ...............................................................27

15. Graph showing dissolved copper concentrations and water-table altitudes in

multilevel-sampler well number 1 (MLS#1) before and after installation of a porous

parking lot at Silver Lake Beach, Wilmington, MA ...............................................................28

16. Graph showing dissolved lead concentrations and water-table altitudes in

altitudes sampler well number 1 (MLS#1) before and after installation of a porous

parking lot at Silver Lake Beach, Wilmington, MA ...............................................................28

17. Graph showing dissolved nickel concentrations and water-table altitudes in

multilevel-sampler well number 1 (MLS#1) before and after installation of a porous

parking lot at Silver Lake Beach, Wilmington, MA ...............................................................29
viii

18. Graph showing dissolved zinc concentrations and water-table altitudes in

multilevel-sampler well number 1 (MLS#1) before and after installation of a porous

parking lot at Silver Lake Beach, Wilmington, MA ...............................................................29

19. Graph showing total petroleum hydrocarbon concentration and water-table

altitudes in multilevel-sampler well number 1 (MLS#1) before and after installation

of a porous parking lot at Silver Lake Beach, Wilmington, MA..........................................30

20. Map showing Silver Lake Avenue/Dexter Street neighborhood in Wilmington,

MA, with drainage features and low-impact-development enhancements.....................31

21. Photographs showing rain gardens along Dexter Street, Wilmington, MA. Cutouts

in curbs to direct runoff from road into rain garden.............................................................33

22. Photograph showing rain garden along Dexter Street, Wilmington, MA.........................34

23. Photograph showing storm drain at Silver Lake Avenue, Wilmington, MA......................35

24. Photograph showing runoff-monitoring equipment in a catch basin at Silver Lake

Avenue, Wilmington, MA...........................................................................................................35

25. Photograph showing water draining into a storm-drain grate on Silver Lake

Avenue, Wilmington, MA...........................................................................................................36

26. Boxplots showing rainfall-runoff coefficients determined before (Pre-LID, Aug.

2005–Feb. 2006) and after (Post-LID, Aug. 2006–Nov. 2007) installation of

low-impact-development features along Silver Lake Avenue, Wilmington, MA, for

(A) all storms monitored during the study period and (B) monitored storms

preceded by 100 hours or more of dry conditions.................................................................38

27. Boxplots showing rainfall-runoff coefficients determined before (Pre-LID, Aug.

2005–Feb. 2006) and after (Post-LID, Aug. 2006–Nov. 2007) installation of

low-impact-development features along Silver Lake Avenue, Wilmington, MA, for

groups of storms with different amounts of precipitation ...................................................39

28. Graph showing median rainfall-runoff coefficients determined before (Pre-LID,

Aug. 2005–Feb. 2006) and after (Post-LID, Aug. 2006–Nov. 2007) installation of

low-impact-development features along Silver Lake Avenue, Wilmington, MA, for

storms with greater than and less than or equal to 0.25 inch of precipitation.................40

29. Graph showing relations between total runoff and total precipitation for storms

with total precipitation less than 0.26 inch that occurred before (Pre-LID, Aug.

2005–Feb. 2006) and after (Post-LID, Aug. 2006–Nov. 2007) installation of

low-impact-development features along Silver Lake Avenue, Wilmington, MA.............40

30. Boxplot showing nitrogen analyte loads in runoff from storms that occurred before

(Pre-LID, Aug. 2005–Feb. 2006) and after (Post-LID, Aug. 2006–Nov. 2007) installation

of low-impact-development features along Silver Lake Avenue, Wilmington, MA ........44

31. Boxplot showing phosphorus analyte loads in runoff from storms that occurred

before (Pre-LID, Aug. 2005–Feb. 2006) and after (Post-LID, Aug. 2006–Nov. 2007)

installation of low-impact-development features along Silver Lake Avenue,

Wilmington, MA ..........................................................................................................................45

32. Boxplot showing cadmium, chromium, copper, lead, nickel, and zinc loads in runoff

from storms that occurred before (Pre-LID, Aug. 2005–Feb. 2006) and after

(Post-LID, Aug. 2006–Nov. 2007) installation of low-impact-development features

along Silver Lake Avenue, Wilmington, MA...........................................................................46

33. Photograph showing structural features of a typical green roof.......................................47

34. Photograph showing (A) partially developed vegetation in summer 2007 and

(B) well-developed vegetation in autumn 2008 on the Whipple Annex green roof, 

Ipswich, MA.................................................................................................................................48

35. Photograph showing rubber-membrane roof on the Ipswich, MA, Town Hall with

drains leading into the building and to the runoff-monitoring and sampling system......49
ix

36. Photograph showing roof-runoff flow-monitoring and sampling system in the

Ipswich Town Hall, Ipswich, MA..............................................................................................50

37. Photograph showing roof-runoff flow-monitoring and sampling system during

assembly at the Whipple Annex, Ipswich, MA......................................................................51

38. Graphs showing (A) precipitation on and runoff from conventional rubber and

green roofs in Ipswich, MA, for the storm of September 27, 2007, and

(B) cumulative percentages of total precipitation and total runoff from the roofs

for the same storm......................................................................................................................53

39. Graphs showing (A) precipitation on and runoff from conventional rubber and

green roofs in Ipswich, MA, for the storm of September 9, 2007, and (B) cumulative

percentages of total precipitation and total runoff from the roofs for the

same storm ..................................................................................................................................54

40. Graphs showing (A) precipitation on and runoff from conventional rubber and

green roofs in Ipswich, MA, for the storm of October 26, 2008, and (B) cumulative

percentages of total precipitation and total runoff from the roofs for the

same storm ..................................................................................................................................55

41. Graphs showing (A) precipitation on and runoff from conventional rubber and

green roofs in Ipswich, MA, for the storm of September 11, 2007, and (B) cumulative 

percentages of total precipitation and total runoff from the roofs for the

same storm ..................................................................................................................................56

42. Graphs showing (A) precipitation on and runoff from conventional rubber and

green roofs in Ipswich, MA, for the storm of September 26, 2008, and (B) cumulative 

percentages of total precipitation and total runoff from the roofs for the

same storm ..................................................................................................................................57

43. Graph showing percentage of precipitation retained by the Whipple Annex green

roof in Ipswich, MA, in relation to total precipitation depth for storms that were

monitored from June 2007 through November 2008 .............................................................59

44. Graph showing percentage of precipitation retained by the Whipple Annex green

roof in Ipswich, MA, in relation to the length of the antecedent dry period and the

total amount of precipitation for storms that were monitored from June 2007

through November 2008.............................................................................................................60

45. Boxplots showing concentrations of (A) total nitrogen, (B) total phosphorus,

(C) dissolved ammonia nitrogen, (D) dissolved phosphorus, and (E) nitrate plus nitrite

nitrogen in bulk precipitation and in runoff from the town hall rubber roof and the

Whipple Annex green roof, Ipswich, MA, June 2007 through November 2008................61

46. Boxplots showing concentrations of (A) total cadmium, (B) total copper, (C) total

nickel, (D) total lead, and (E) total zinc in bulk precipitation and in runoff from the

town hall rubber roof and the Whipple Annex green roof, Ipswich, MA, June 2007

through November 2008.............................................................................................................62

47. Boxplots showing loads of (A) total nitrogen, (B) total phosphorus, (C) dissolved

ammonia nitrogen, (D) dissolved phosphorus, and (E) nitrate plus nitrite nitrogen in

bulk precipitation and in runoff from the town hall rubber roof and the Whipple

Annex green roof, Ipswich, MA, June 2007 through November 2008................................66

48. Boxplots showing loads of (A) total cadmium, (B) total copper, (C) total nickel,

(D) total lead, and (E) total zinc in bulk precipitation and in runoff from the town hall

rubber roof and the Whipple Annex green roof, Ipswich, MA, June 2007 through

November 2008............................................................................................................................67

49. Map showing model reaches and subbasin boundaries in the Ipswich River

Basin, MA.....................................................................................................................................69

50. Map showing changes in groundwater withdrawals for Reading and Wilmington,

MA, for the updated baseline simulation relative to the original baseline simulation....72
x

51. Map showing land potentially available for development in the Ipswich River Basin,

MA, based on 1991 land use .....................................................................................................75

52. Map showing generalized land use in the Ipswich River Basin, MA, (A) in 1991 and

(B) at buildout..............................................................................................................................76

53. Map showing commercial, high-density residential, and low-density residential

land use in 1991 for the drainage area to the South Middleton streamgage, Ipswich,

MA 78

54. Map showing percent effective impervious area, by subbasin (1991 land use), for

subbasins upstream from the South Middleton streamgage, Ipswich, MA.....................79

55. Graphs showing flow-duration curves of daily mean streamflow at (A) reach 1,

Maple Meadow Brook at Route 38, Wilmington, (B) reach 8, Ipswich River at Mill

Street near Reading, (C) reach 5, Lubbers Brook above Route 38, Wilmington, (D)

reach 13, Martins Brook above mouth, North Reading, and (E) reach 19, Ipswich

River at South Middleton streamgage in the Ipswich River Basin developed from

long-term (1961–1995) simulations with 1989–1993 withdrawals (original baseline

withdrawals), updated withdrawals for the towns of Reading and Wilmington

(updated baseline withdrawals), and no withdrawals .........................................................85

56. Graphs showing flow-duration curves of daily mean streamflow at (A) reach 34,

Boston Brook above mouth, Middleton, (B) reach 35, Ipswich River above Nichols

Brook, Middleton, (C) reach 28, Ipswich River at Maple Street, Middleton, (D) reach

27, Middleton Pond Brook, Middleton, (E) reach 19, Ipswich River at South

Middleton streamgage, and (F) reach 56, Ipswich River at Ipswich streamgage in

the Ipswich River Basin developed from long-term (1961–1995) simulations with

1991 land use and potential land use at buildout ..................................................................88

57. Graphs showing flow-duration curves of daily mean streamflow at (A) reach 5,

Lubbers Brook above Route 38, Wilmington, (B) reach 2, Maple Meadow Brook

above mouth, Wilmington, (C) reach 2, Mapple Meadow Brook above mouth (no

flow from upstream reach), and (D) reach 19, Ipswich River at South Middleton 

streamgage in the Ipswich River Basin developed from long-term (1961–1995) 

simulations with 1991 land use and 1991 land use with effective impervious area 

for each urban land-use category reduced by 50 percent to simulate low-impactdevelopment retrofits.................................................................................................................91

58. Graphs showing flow-duration curves of daily mean streamflow at (A) reach 17,

Wills Brook, North Reading, (B) reach 49, Idlewild Brook, Hamilton, (C) reach 53, 

Howlett Brook, Topsfield, and (D) reach 19, Ipswich River at South Middleton 

streamgage in the Ipswich River Basin developed from long-term (1961–1995) 

simulations with updated baseline withdrawals, withdrawals reduced by scaled-up 

data from Massachusetts Department of Conservation and Recreation waterconservation pilot programs, withdrawals reduced by 20 percent, and no

withdrawals .................................................................................................................................94

59. Graphs showing flow-duration curves of daily mean streamflow and mean

daily-flow hydrographs from long-term (1961–1995) local-scale simulations of runoff 

from 100-acre parcels of undeveloped (forest) land and conventionally laid-out 

developed (low-density residential, high-density residential, and commercial) land 

(A) overlying till and (B) overlying sand and gravel with model-calibrated effective 

impervious area in the Ipswich River Basin, MA..................................................................95

60. Graph showing mean annual water budgets for forested and developed hydrologic

response units simulated in the Ipswich River Basin, MA..................................................99
xi

61. Graphs showing flow-duration curves of daily mean streamflow from long-term

(1961–1995) local-scale simulations of runoff from 100-acre parcels of conventionally 

laid-out (uniform) (A) commercial development, (B) high-density development 

overlying sand and gravel, (C) high-density residential development overlying till,

(D) low-density residential development overlying sand and gravel, and

(E) low-density residential development overlying till with various amounts of

effective impervious area (EIA) in the Ipswich River Basin, MA......................................100

62. Graphs showing (A) Median 1-day and 7-day high flows, (B) median 1-day low flows, 

and (C) median 7-day low flows from long-term (1961–1995) simulations of runoff 

from 100-acre parcels of conventionally laid out (uniform) development with various 

amounts of effective impervious area in the Ipswich River Basin, MA ..........................101

63. Graphs showing ratios of the magnitudes of simulated daily peak flows for

(A) commercial (developed) and forest overlying sand and gravel (undeveloped)

land use, and (B) commercial (developed) and forest overlying till (undeveloped)

land use as a function of recurrence interval and the amount of effective

impervious area in the Ipswich River Basin, MA................................................................102

64. Graphs showing flow-duration curves of daily-mean streamflow from long-term

(1961–1995) simulations of runoff from 100-acre parcels of conventionally laid out 

(uniform) and cluster development with varying amounts of EIA in the developed

part of the parcel for (A) high-density residential overlying sand and gravel,

(B) high-density residential overlying till, (C) low-density residential overlying

sand and gravel, and (D) low-density residential overlying till, Ipswich River

Basin, MA...................................................................................................................................104
xii

Tables

1. Concentrations of nutrients, dissolved metals, and total petroleum hydrocarbons in

samples collected at water-table elevations from three multilevel samplers

installed at the Silver Lake beach parking lot at Wilmington, MA, 2005–07 .....................14

2. Concentrations of nutrients, dissolved and total metals, and total petroleum

hydrocarbons in quality-control and corresponding environmental samples

collected at the Silver Lake beach parking lot and the Silver Lake Avenue runoff

site in Wilmington, MA, and Whipple Annex and Town Hall roof-runoff sites in

Ipswich, MA, 2005–07 ................................................................................................................18

3. Specific conductance, dissolved oxygen concentrations, and pH profiles in

samples from multilevel samplers #1, #2, and #3, in the Silver Lake beach parking

lot, Wilmington, MA, July 6, 2005, to June 19, 2007...............................................................20

4. Concentrations of nutrients, total metals, total petroleum hydrocarbons, total

coliform bacteria, and E. coli in samples collected at the Silver Lake Avenue runoff

site in Wilmington, MA, 2005–07 ..............................................................................................42

5. Estimated loads of nutrients, total metals, total petroleum hydrocarbons, total

coliform bacteria, and E. coli in samples collected at the Silver Lake Avenue runoff

site in Wilmington, MA, 2005–07 ..............................................................................................43

6. Characteristics of five selected storms and runoff from the rubber roof on Town

Hall and from the green roof on Whipple Annex, Ipswich, MA, 2007–08..........................59

7. Concentrations of nutrients, total metals, and total petroleum hydrocarbons in

runoff from the Town Hall and Whipple Annex roofs, and bulk precipitation,

Ipswich, MA, 2007–08 ................................................................................................................64

8. Description of scenarios simulated with the Hydrological Simulation

Program-FORTRAN precipitation runoff model of the Ipswich River Basin, Ipswich,

MA 71

9. Changes to the Wilmington, MA, water-supply system for the updated baseline

simulation.....................................................................................................................................73

10. Regionalized zoning codes for developable areas grouped by land-use categories

used to construct the land use at buildout data layer for the Hydrological

Simulation Program-FORTRAN model.....................................................................................74

11. Land use in 1991 and potential land use at buildout in the Ipswich River Basin, MA.....77

12. Hypothetical water-use reductions obtained by scaling up the results from four

water-conservation pilot projects conducted by the Massachusetts Department of

Conservation and Recreation for towns that withdraw water from the Ipswich River

Basin, MA. ...................................................................................................................................81

13. Land-use distribution used in local-scale simulations for 100-acre parcels,

conducted with the calibrated Hydrological Simulation Program-FORTRAN model

of the Ipswich River Basin, MA................................................................................................83

14. Flow statistics for long-term (1961–1995) simulations with original baseline

(1989–1993) withdrawals and updated baseline withdrawals for the towns of

Reading and Wilmington (scenario LID_LT-upDem) at selected subbasins in the

Ipswich River Basin, MA...........................................................................................................86

15. Flow statistics for long-term (1961–1995) simulations with 1991 land use and

potential land use at buildout (scenario LID_LT-build) at selected subbasins in the

Ipswich River Basin, MA...........................................................................................................89

16. Flow statistics for long-term (1961–1995) simulations with 1991 land use and 1991

land use with effective impervious area reduced by 50 percent to represent

low-impact-development retrofits (scenario LID_LT-retrofit) at selected subbasins

in the Ipswich River Basin, MA. ..............................................................................................92
xiii

Table 17. Flow statistics for long-term (1961–1995), local-scale simulations of runoff from 100-

acre parcels with various combinations of undeveloped and developed land uses and 

amounts of effective impervious area.....................................................................................96

Conversion Factors, Datum, and Abbreviations

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

yard (yd) 0.9144 meter (m)

Area

acre 4,047 square meter (m2)

acre 0.4047 hectare (ha)

acre 0.004047 square kilometer (km2)

square foot (ft2) 929.0 square centimeter (cm2)

square foot (ft2) 0.09290 square meter (m2)

square inch (in2) 6.452 square centimeter (cm2)

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2)

Volume

gallon (gal) 3.785 liter (L)

gallon (gal) 0.003785 cubic meter (m3)

cubic foot (ft3) 0.02832 cubic meter (m3)

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

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

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

Mass

ounce, avoirdupois (oz) 28.35 gram (g)

pound, avoirdupois (lb) 0.4536 kilogram (kg)

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

°F=(1.8×°C)+32 

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

(NAVD 88).

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

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

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25°C).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) 

or micrograms per liter (μg/L).
xiv

ABBREVIATIONS AND ACRONYMS

α Accepted statistical significance level

Cd Cadmium

Cr Chromium

Cu Copper

EIA Effective Impervious Area

HRU Hydrologic Response Unit

HSPF Hydrologic Simulation Program-FORTRAN

IMPLND HSPF Impervious-area Land Element

LID Low-impact development

MDCR Massachusetts Department of Conservation and Recreation

MLS Multilevel Sampler

MPN Most probable number

MWRA Massachusetts Water Resources Authority

NEIA Noneffective Impervious Area

Ni Nickel

Pb Lead

PERLND HSPF pervious-area Land Element

RCHRES HSPF stream or reservoir reach

RPD Relative percent difference

TPH Total petroleum hydrocarbons

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

Zn Zinc
Abstract

During the months of August and September, flows in the 

Ipswich River, Massachusetts, dramatically decrease largely 

due to groundwater withdrawals needed to meet increased 

residential and commercial water demands. In the summer, 

rates of groundwater recharge are lower than during the rest of 

the year, and water demands are higher. From 2005 to 2008, 

the U.S. Geological Survey, in a cooperative funding agreement with the Massachusetts Department of Conservation and 

Recreation, monitored small-scale installations of low-impactdevelopment (LID) enhancements designed to diminish the 

effects of storm runoff on the quantity and quality of surface 

water and groundwater. Funding for the studies also was contributed by the U.S. Environmental Protection Agency’s Targeted Watersheds Grant Program through a financial assistance 

agreement with Massachusetts Department of Conservation 

and Recreation. The monitoring studies examined the effects 

of (1) replacing an impervious parking lot surface with a 

porous surface on groundwater quality, (2) installing rain gardens and porous pavement in a neighborhood of 3 acres on the 

quantity and quality of stormwater runoff, and (3) installing a 

3,000-square foot (ft2) green roof on the quantity and quality 

of stormwater runoff. In addition, the effects of broad-scale 

implementation of LID techniques, reduced water withdrawals, and water-conservation measures on streamflow in large 

areas of the basin were simulated using the U.S. Geological 

Survey’s Ipswich River Basin model.

From June 2005 to 2007, groundwater quality was monitored at the Silver Lake town beach parking lot in Wilmington, 

MA, prior to and following the replacement of the conventional, impervious-asphalt surface with a porous surface consisting primarily of porous asphalt and porous pavers. Changes 

in the concentrations of the water-quality constituents, phosphorus, nitrogen, cadmium, chromium, copper, lead, nickel, 

zinc, and total petroleum hydrocarbons, were monitored. 

Increased infiltration of precipitation did not result in discernible increases in concentrations of these potential groundwater 

contaminants. Concentrations of dissolved oxygen increased 

slightly in groundwater profiles following the removal of the 

impervious asphalt parking lot surface.

In Wilmington, MA, in a 3-acre neighborhood, stormwater runoff volume and quality were monitored to determine the 

ability of selected LID enhancements (rain gardens and porous 

paving stones) to reduce flows and loads of the above constituents to Silver Lake. Flow-proportional water-quality samples 

were analyzed for nutrients, metals, total petroleum hydrocarbons, and total-coliform and Escherichia coli bacteria. In general, when all storms were considered, no substantial decreases 

were observed in runoff volume as a result of installing LID 

enhancements. However, the relation between rainfall and runoff did provide some insight into how the LID enhancements 

affected the effective impervious area for the neighborhood. 

A decrease in runoff was observed for storms of 0.2 inches 

(in.) or less of precipitation, which indicated a reduction in 

effective impervious area from approximately 10 percent to 

about 4.5 percent for the 3-acre area. Water-quality-monitoring 

results were inconclusive; there were no statistically significant differences in concentrations or loads when the pre- and 

post-installation-period samples were compared. Three factors 

were probably most important in minimizing differences: 

(1) the small decrease in effective impervious area, (2) the 

differences in the size of storms sampled for water-quality 

constituents before and after installation of the infiltration 

enhancing measures, and (3) small sample sizes.

In a third field study, the characteristics of runoff from a 

vegetated “green” roof and a conventional, rubber-membrane 

roof were compared. The amount of precipitation and the 

length of the antecedent dry period were the two primary 

factors affecting the green roof’s water-storage capacity. The 

green roof retained more than 50 percent of the precipitation from storms with 0.04 to 1.0 in. of rain. Approximately 

95 percent of the precipitation from one storm of nearly 2 in. 

was retained by the green roof. On the rubber-membrane roof, 

only a small, shallow puddle of insubstantial volume ever 

remained after a storm. Bulk precipitation from 10 storms 

was monitored for the same constituents (nutrients, metals, 

and total petroleum hydrocarbons) as the roof runoff, and the 

results were compared with those for roof-runoff samples. 

Effects of Selected Low-Impact-Development (LID) 

Techniques on Water Quality and Quantity in the Ipswich 

River Basin, Massachusetts: Field and Modeling Studies

By Marc J. Zimmerman, Jeffrey R. Barbaro, Jason R. Sorenson, and Marcus C. Waldron
2 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

The use of fertilizers to help establish the vegetation during 

the study probably distorted any effect the plants and growing 

medium may have had on the retention of target analytes. As a 

result of the fertilizer and growing medium chemistry, median 

concentrations of total nitrogen, total phosphorus, cadmium, 

copper, and nickel in runoff from the green roof were greater 

than in the runoff from the conventional roof or in bulk 

precipitation. Concentrations of lead and zinc were greater in 

runoff from the conventional roof, probably a result of passage 

through the old, metal drainpipes.

Simulations of the effects of LID on streamflow in the 

Ipswich River Basin were conducted with a previously calibrated Hydrological Simulation Program-FORTRAN (HSPF) 

precipitation-runoff model. Simulations were conducted at 

multiple spatial scales to evaluate the effects of (1) updated 

water withdrawals for the towns of Reading and Wilmington; (2) potential land-use changes at buildout (potential 

future development); (3) effective impervious area reductions 

upstream from the South Middleton streamgage to represent 

the effects of widespread implementation of LID retrofit 

techniques; (4) basin-scale water withdrawal reductions scaled 

up (expanded to the town level) from water-conservation pilot 

programs conducted by the Massachusetts Department of Conservation and Recreation; and (5) land-use change and LID 

techniques at a local scale, which is smaller than the HSPF 

subbasin. Effects on streamflow generally were evaluated 

by comparing results of two or more related simulations for 

selected reaches in the basin; thus, relative rather than absolute changes in simulated flow were the focus of the assessment. Simulations indicated that reduced withdrawals for the 

towns of Reading and Wilmington led to substantially higher 

medium and low flows in most of the reaches upstream from 

the South Middleton streamgage. Simulations of water-conservation measures resulted in negligible effects on streamflow.

Overall, simulations indicated that spatial scale is an 

important factor in determining the effects of land-use change 

and LID practices on streamflow. Potential land-use changes 

at buildout had modest (percent differences of less than 

20 percent) effects on streamflow in most subbasins because 

relatively little land in the basin was available for development (about 17 percent); moreover, most of the available open 

land is zoned for low-density residential development, and 

this land-use category was simulated to contain relatively little 

effective impervious area and to be similar hydrologically to 

the forested land in place prior to development. Results of 

the simulations conducted to evaluate widespread effective 

impervious area reductions upstream from the South Middleton streamgage indicated that the percentage of urban land 

use and associated effective impervious area was too small 

for a 50-percent reduction of effective impervious area to 

appreciably affect streamflow (percent differences of less than 

20 percent) in most subbasins. In contrast, the results of the 

hypothetical local-scale simulations indicated that for smaller 

streams, where the percentage of urban land use and associated effective impervious area in the drainage area may be 

substantially higher, land-use change, development patterns, 

and LID practices potentially have much greater effects on 

streamflow.

Modeling results also indicated that LID was potentially 

most beneficial for minimizing streamflow alteration when 

applied to dense urban development, largely because larger 

tracts of effective impervious area were available for reduction 

than were available for other land-use categories. For example, 

commercial-industrial-transportation land use is composed 

of 37 percent pervious area and 63 percent effective impervious area in the HSPF model, whereas low-density residential 

area is composed of 97.5 percent pervious area and only 

2.5 percent effective impervious area.

Field and modeling studies concurred in the assessment 

that LID enhancements would likely have the greatest effect 

on decreasing stormwater runoff when broadly applied to 

highly impervious urban areas. A measurable effect for small 

rainfall events (less than 0.25 inch) was determined in the 

small, highly pervious area that was monitored in this study, 

but the volume difference was not great.

Introduction

In 1997, the environmental organization, American Rivers, placed the Ipswich River, located in northeastern Massachusetts (fig. 1), on its list of 20 most-endangered rivers 

because of water withdrawals and development. American 

Rivers placed the Ipswich River on the list again in 2003 

because of the extent of groundwater withdrawals and expansive water use. The river has, on numerous occasions, run dry 

in several places during periods of maximum water withdrawals. In addition to use within the basin, water is exported for 

supply and wastewater treatment outside the basin, which contributes to stress on basin water resources. Short-term, stopgap 

measures such as mandatory water-use bans do not seem 

sufficient to guarantee adequate water supplies for human 

consumption and maintenance of aquatic habitat. Periods of 

extremely reduced flow have detrimental effects on streamwater quality, such as low concentrations of dissolved oxygen, 

elevated temperatures, algal blooms, and fish die-offs. Unless 

more effective means are implemented, further development 

in the Ipswich River Basin may continue to threaten this river. 

Recently, the towns of Wilmington and Reading have entered 

into water-supply agreements to have the Massachusetts Water 

Resources Authority (MWRA) provide water from sources 

outside of the Ipswich River Basin, thereby diminishing some 

of the demand from sources in the basin. The long-term effects 

on Ipswich River Basin streamflow of using this alternate 

water supply are not yet determined.

With increases in water demand for residential and commercial development in the Ipswich River Basin likely to 

continue for the foreseeable future, new approaches are called 

for to sustain the river’s flow throughout the year. Wide-scale 

application of water-conservation measures and redirecting runoff to infiltrate into the ground, rather than into storm 
Introduction 3

Figure 1. Location of streamgages, wells, and weather station in the Ipswich River Basin, MA.

ATLANTIC

OCEAN

ANDOVER

BOXFORD

ROWLEY

PEABODY

BEVERLY

SALEM

NORTH ANDOVER

ESSEX

DANVERS

HAMILTON

MIDDLETON

TOPSFIELD

READING

LYNNFIELD

GEORGETOWN

WENHAM

NORTH READING

TEWKSBURY

WOBURN

BURLINGTON

WAKEFIELD

GROVELAND

MANCHESTER

MARBLEHEAD

SWAMPSCOTT

LYNN

SAUGUS

IPSWICH

WILMINGTON

Maple Mead ow

Brook

Ipswich River

NORTH COASTAL

SHAWSHEEN

MERRIMACK

BOSTON HARBOR

PARKER

IPSWICH

MIDDLESEX

ESSEX COUNTY

 COUNTY

01101300

01101500

#01102000

Ipswich River Basin

Major drainage basin boundary

and name

Active streamgage and number 

Active streamgage with water-quality

data and number 

Discontinued streamgage and number 

Weather station 01100600

EXPLANATION

#

IPSWICH

01102000

01101500

01101300

Base from U.S. Geological Survey digital data, 1:25,000, 1991,

Lambert conformal conic projection, North American Datum of 1983

71°12' 71°03' 70°54'

42°30'

42°39'

0

0

2

2

4 MILES

4 KILOMETERS

CONNECTICUT RHODE

ISLAND

NEW YORK

VERMONT

MASSACHUSETTS

NEW HAMPSHIRE

Ipswich

River

Basin

Town Hall

study sites

Silver Lake 

study sites
4 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

drains and away from the area where the rain falls, are among 

potential means for relieving or decreasing the stress on the 

river. To this end, USGS, through a cooperative funding agreement with the Massachusetts Department of Conservation 

and Recreation (MDCR), conducted studies to (1) quantify 

LID benefits and water-conservation techniques for decreasing runoff, increasing stormwater infiltration to groundwater, 

and improving streamflow; and (2) quantify these benefits 

on a basin-wide scale using computer simulation. Funding 

for the studies also was contributed by the U.S. Environmental Protection Agency’s (USEPA) Targeted Watersheds 

Grant Program through a financial assistance agreement with 

MDCR. Additional funding for some of the infrastructural 

work described here came from the Town of Wilmington and 

in-kind support came from the Town of Ipswich, MA.

Applications of Low-Impact-Development (LID) 

Principles and Techniques

Conventional urban, suburban, commercial, and recreational development creates increased impervious surface 

areas through new roads, roofed structures, parking lots, driveways, and sidewalks.

Increasing amounts of impervious cover are generally associated with modifications to natural hydrology, 

such as increased runoff volume and rate (Leopold, 1968). 

Moreover, the increased imperviousness also contributes 

to increased loads of contaminants to waterways (Grimm 

and others, 2008). Conventional stormwater-runoff management aims to convey runoff quickly and efficiently to a 

holding facility or to a stream, thus minimizing infiltration 

into groundwater and altering surface-water hydrology. The 

goal of low-impact development (LID) is the maintenance 

or restoration of pre-development hydrology by increasing 

runoff times and infiltration. LID distributes small-scale controls throughout a developed site or a site proposed for new 

development. Features implemented in the studies presented in 

this report are swales, rain gardens, bioretention cells, porous 

pavements, and green roofs. Swales are graded, vegetated 

depressions, frequently installed along roadsides where they 

enhance road-runoff infiltration into the local groundwater; 

existing curbs may be cut to channel water to the swale. 

Rain gardens are landscaped, low-lying areas with soil mixes 

designed to absorb and filter water; rain gardens are planted 

with water- and drought-tolerant vegetation; curbs may also be 

cut to direct road runoff into rain gardens. Bioretention cells, 

similar to, but often more highly engineered than rain gardens, 

may be lined with filter fabric. Vegetated, or green, roofs also 

serve to attenuate stormwater-runoff peaks and provide some 

filtration of potential contaminants in stormwater. A green roof 

replaces a conventional, sealed roof of asphalt, shingles, or 

membranes with an absorbent plant-growing medium; greenroof soil media and plants attenuate runoff by absorbing and 

transpiring rainfall.

Previous Studies

Numerous reports document the propensity for the Ipswich River to run dry in the summer; many of these reports are 

summarized by Zarriello and Ries (2000), who also describe 

a basin-wide hydrologic model (the Ipswich River Basin 

Model). Since that report was published, the USGS has produced additional reports, including Zarriello (2004, 2002a, b) 

and Armstrong and others (2001). The first three works extend 

the modeling study (Zarriello and Ries, 2000), upon which 

part of the present study is based, to explore additional watermanagement options; Armstrong and others (2001) describe 

stream habitat and use standard streamflow-estimating methods to determine aquatic habitat requirements.

Additional studies examine the effects of stream discharge in the Ipswich River Basin. Williams and others (2005) 

indicate that land use accounts for about 50 percent of the 

variability of streamwater-solute concentrations; thus, other 

undefined factors are also important. Crump and Hobbie 

(2005) consider temperature and variations in discharge as the 

best predictors of bacterial diversity.

Filoso and others (2004) use the hydrologic component 

of the Ipswich River Basin model developed by Zarriello and 

Ries (2000) to model nitrogen transport in the basin under 

various land-use scenarios. They found that nitrogen concentrations in the river increased with increasing proportions of 

urban land use in the basin.

Selbig and Bannerman (2008) compare runoff and water 

quality in adjacent, conventional and LID-enhanced residential 

basins in Cross Plains, Wisconsin, from 1999 to 2005. They 

found that the conventional basin annually discharged 1.3 to 

9.2 times the volume discharged from the LID-enhanced basin. 

Selbig and Bannerman (2008) also determined that antecedent 

soil conditions (for example, percent saturation and freezing) 

and storm intensity affected the ability of the LID basin to 

retain runoff. A major feature of the LID basin was an infiltration basin that was the last feature used to treat runoff before 

it left the basin. Hood and others (2007) determined that LID 

techniques were most effective for small storms and dry antecedent conditions; they noted that, under all storm conditions 

that they studied, “LID [techniques] reduced [the] runoff depth 

and peak discharge.” Dietz and Clausen (2008) found that runoff and export of nitrogen and phosphorus from a conventional 

development increased logarithmically over time, whereas 

runoff and export from a comparable, adjacent, LID development did not change from pre-development conditions.

Purpose and Scope

This report describes the results of studies monitoring the 

effects of selected LID techniques on the volume and quality of storm runoff. The report also presents the results of a 

series of modeling scenarios based on the theoretical widescale implementation of LID enhancements or reductions of 

water withdrawals throughout the Ipswich River Basin, as 
Field Studies of Low-Impact-Development Techniques 5

well as some simulations designed to assess the effects of LID 

enhancements on 100-acre parcels of land.

In the first part of this report, the effects of selected LID 

techniques on runoff water quality and quantity are evaluated. In Wilmington, MA, nutrient, dissolved-metal, and total 

petroleum hydrocarbon (TPH) concentrations in groundwater 

samples were determined before and after the installation of 

a new porous-pavement parking lot and other LID enhancements at Silver Lake Beach. Groundwater levels also were 

monitored. On the opposite side of Silver Lake, LID enhancements, including rain gardens and porous pavers were retrofitted in the small (3-acre) Silver Lake Avenue/Dexter Street 

neighborhood; runoff volume and concentrations of waterquality constituents (nutrients, total metals, coliform bacteria, 

and TPH) were monitored prior to and following the installation of these LID enhancements. In Ipswich, MA, a 3,000-ft2

vegetated, green roof was installed on an existing building that 

was being converted into senior housing; the volume of, and 

water-quality constituents (nutrients, total metals, and TPH) 

in, runoff from the green roof and a neighboring conventional, 

rubber-membrane roof are discussed.

The second part of this report describes simulations conducted using the calibrated Ipswich River Basin Hydrologic 

Simulation Program-FORTRAN (HSPF) model to evaluate 

the effects of various LID practices, land-use changes, and 

water-management activities on streamflow at multiple spatial 

scales. The Ipswich River Basin HSPF model simulates only 

streamflow. This portion of the report includes descriptions 

of simulation scenarios developed to address the issues listed 

above, the accompanying modifications made to the calibrated 

model, and discussions of simulation results. Model limitations and applicability of simulation results to evaluate streamflow alteration in the Ipswich River Basin also are discussed.

Environmental Setting

The 155-mi2 Ipswich River Basin drains into the Atlantic 

Ocean in northeastern Massachusetts; the maximum altitude 

in the headwaters area is about 110 ft (NAVD 88). Wetlands 

account for about 21 percent of the basin’s area. Areas of 

sand and gravel or of glacial till dominate the basin’s surficial 

geology. Sand and gravel are concentrated most heavily in the 

headwaters and Coastal Plain reaches, and glacial till is present in the middle reaches of the basin. Land use upstream from 

the USGS South Middleton streamgage (01101500; fig. 1) is 

somewhat more residential (38 percent) than it is downstream 

(28 percent); upstream from the gage, forests and open space 

account for about 34 percent of the land use compared to 

44 percent downstream from the gage (Zarriello and Ries, 

2000; Sammel and others, 1964). The field studies in Wilmington took place in areas of sand and gravel, and the modeling study covered all geological settings within the study area.

The climate in the basin is humid. In general, precipitation is evenly distributed throughout the year with occasional 

extended dry periods in the middle to late summer. During 

summer and early fall of 2005, the basin had very little rain.

Field Studies of Low-ImpactDevelopment Techniques

Three field studies of varying duration were conducted 

from 2005 to 2008. The Silver Lake Avenue runoff study and 

green roof runoff study required extended sampling periods 

due to the difficulty of predicting storms of adequate magnitude for sampling; that is, (1) sufficiently large storms did not 

materialize as forecast, or (2) storms forecast as too small for 

sampling developed into large storms that were not sampled.

Porous Parking Lot Enhancements at

Silver Lake Beach

At Silver Lake Beach, Wilmington, MA, approximately 

one-half of the impervious-asphalt parking lot (figs. 2A, B), 

approximately 250 ft long and 135 ft wide, was replaced with 

a porous parking lot. The edge of the parking lot next to the 

sandy beach was approximately 135 ft from the lake. The 

porous-surfaced parking lot features rain gardens, bioretention 

cells, and other pervious cover. The porous parking areas, 120 

by 135 ft, consist of porous asphalt and pavers. The remaining 

half of the paved lot was replaced with impervious asphalt, 

bioretention cells, and rain gardens. The impervious section of 

the new parking lot was designed to drain toward the porous 

area and its bioretention cells. In the event that water volume 

should surpass the infiltration capability of the parking lot 

system, a drain pipe was installed to carry any surcharge to a 

grassy swale leading into the lake at the northwest corner of 

the beach.

The porous parking lot was not only intended to minimize runoff from the original, impervious parking lot into 

Silver Lake but also to serve as a demonstration and research 

project showing the lot’s effectiveness at enhancing infiltration 

(Roy and Braga, 2009). To address concerns about whether 

replacing part of the impervious parking lot with porous material would lead to groundwater contamination from infiltrating 

contaminants that had dropped or spilled onto the parking lot’s 

surface, the USGS analyzed the quality of the groundwater 

below the porous parking lot before and after installation.

The primary concern faced at Silver Lake Beach was the 

frequent closing of the swimming area because of high counts 

of bacteria. During the summers of 1998 to 2005, the beach 

was closed for at least 1 week each year because of high bacteria counts; the beach was closed for 5 weeks in 2004. Waterfowl, such as ducks and geese (fig. 3), were thought to be the 

source of the bacterial contamination (Jamie Magaldi, Wilmington Department of Public Works, oral commun., 2005). 

The main attractions to the area for the waterfowl, the lake 

proper notwithstanding, were two grassy, stormwater outfall 

areas bordering and running perpendicular to the beach and 

the food offered by beachgoers, in spite of signs telling people 

not to feed the ducks and geese. To discourage waterfowl from 

staying near the beach and to treat some stormwater runoff 
6 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Figure 2. Views of Silver Lake Beach parking lot in Wilmington, MA, prior to renovation, (A) looking west and 

(B) looking north.

A

B
Field Studies of Low-Impact-Development Techniques 7

from the bordering neighborhood and the parking lot, the 

stormwater-outfall areas were converted into narrow swales 

with sufficient vegetation to prevent erosion and designed not 

to attract waterfowl. During the 2 years of this study that followed these changes, there were no beach closings due to high 

bacterial counts.

Design of Low-Impact-Development 

Enhancements to Increase Infiltration

The Massachusetts Department of Conservation and 

Recreation selected Geosyntec Consultants to design and oversee the installation of the porous parking lot at Silver Lake. 

Features of the U-shaped porous parking area include a central 

bioretention island, several rain gardens, porous paving stones 

in the parking spaces, and a porous asphalt drive (fig. 4). A 

12-in. layer of crushed stone was installed under all porous 

surfaces to enhance storage and infiltration. The soils in the 

bioretention cells and rain gardens were designed to promote 

infiltration of stormwater runoff and to filter out sediment 

and nutrients. On the basis of infiltration tests conducted by 

Geosyntec Consultants at Silver Lake, the porous asphalt and 

pavers allowed water to infiltrate at a rate of 78 and 57 in/h, 

respectively; water to the bioretention cells could infiltrate 

more than 20 in/h and to the rain gardens more than 12 in/h 

(Roy and Braga, 2009).

Monitoring Approach

To adequately monitor any changes in the concentrations of groundwater chemical constituents, it was necessary 

to understand the direction of regional and local groundwater movement. Therefore, surficial geology was studied and 

groundwater-flow direction determined to guide the design 

for monitoring water quality before installing water-qualitymonitoring wells on the site of the parking lot prior to its 

renovation.

Regional and Local Groundwater Flow

Silver Lake lies close to Lubbers Brook and near the 

topographic divide between the drainages to Lubbers Brook 

and the Shawsheen River. There is an intermittent surface outflow from the eastern side of the lake that runs under Rte. 38 

before entering Lubbers Brook. The regional groundwaterflow direction in the vicinity of the parking lot was estimated 

from surface topography and available information about the 

distribution of surficial deposits (Sammel and others, 1964). 

On this basis, regional groundwater flow is approximately 

from northwest to southeast (fig. 5).

In June 2005, wells were drilled in the parking lot to 

monitor water levels and water quality. First, four waterlevel-monitoring wells, also known as observation wells, 

were installed to determine the local direction of groundwater 

flow under the parking lot and, thus, to aid in the siting of 

water-quality-monitoring wells. Elevations of all wells were 

Figure 3. Water fowl feeding on Silver Lake Beach in Wilmington, MA, prior to installation of low-impactdevelopment features.
8 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Figure 4. Views of (A) partially completed porous parking lot at Silver Lake Beach, Wilmington, MA, showing 

bioretention cells, porous pavers, and gravel bed for porous asphalt and (B) completely renovated parking lot.

A

B

Porous pavers Gravel bed

Bioretention cell

Porous pavers

Bioretention cell

Porous asphalt
Field Studies of Low-Impact-Development Techniques 9

Figure 5. Generalized groundwater-flow direction in the vicinity of Silver Lake, Wilmington, MA.

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

Massachusetts state plane projection

Shawsheen River

Lubbers Brook

Parking

 lot

!(38

!(62

!(62

UV129

UV129

71°13' 71°12' 71°11' 

42°35'

42°34'

42°33'

Silver Lake

EXPLANATION

Ponds/lakes

Wetlands

Basin boundary

Major roads

Suburban roads

Area shown in figure 7

Area shown in figure 20

Generalized

 groundwater-

 flow direction

 within study area

NORTH COASTAL

MERRIMACK

SHAWSHEEN

BOSTON

 HARBOR

PARKER

IPSWICH

Area enlarged

0 0.5

0 0.5

1 MILE

1 KILOMETER
10 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

surveyed to enable comparisons of the water levels. The 

relatively flat water table indicated by the water-table altitudes 

in the observation wells resulted in some ambiguity about 

the precise direction of flow across the site. Two multilevel 

water-quality-sampling wells (MLSs) were originally planned, 

one upgradient and one downgradient from the parking lot 

with respect to groundwater-flow directions. Because of the 

relatively flat water table, a third MLS was added. Two of the 

three MLSs (MLS#1 and MLS#2) were installed at downgradient locations with the highest probability of observation of 

changes in water quality following installation of the porous 

pavement. The third MLS (MLS#3) was installed on the 

northwest edge of the parking lot, at an upgradient location, 

to serve as a reference well for monitoring the water-quality 

characteristics of groundwater that might enter the parking-lot 

area from offsite. Each MLS was assembled with 13 sampling 

ports, 6 in. apart from each other (fig. 6), extending downward, starting near the observed water table at the time of 

installation.

Water-Table Altitude and Water Quality

During each site visit, field parameters (temperature, dissolved oxygen, pH, and specific conductance) were measured 

with a QuantaTM multiparameter sonde from all ports in the 

multilevel samplers from which water could be drawn using 

a peristaltic pump. The sonde was calibrated using standard 

USGS protocols found in the National Field Manual for the 

Collection of Water-Quality Data (U.S. Geological Survey, 

variously dated). Starting at the highest sampling port and 

working downward into the well made it possible to identify, 

within approximately 6 in., the altitude of the water table—the 

altitude from which water-quality samples for nutrients (various chemical forms of nitrogen and phosphorus), dissolved 

metals (cadmium, copper, chromium, lead, nickel, and zinc), 

and total petroleum hydrocarbons were collected, also using 

methods described in the National Field Manual. After the 

samples were collected and processed, they were stored on ice 

at 4°C until they were shipped to the USGS National Water 

Quality Laboratory (NWQL) for analysis.

From July through October 2005, five samples were 

collected within a few days after storms. But, the initial 

sampling results indicated that substantially more frequent 

sampling would be required to determine whether the samples 

were actually capturing recent stormwater; however, budget 

constraints would not allow for frequent sampling following 

individual storms. After the porous parking lot installation 

was completed in June 2006, a monthly sampling schedule 

was followed during the rest of the study. This sampling frequency was adequate to ensure that water recharged through 

the replaced parking lot would be monitored within the study 

duration because unsaturated-zone calculations indicated that 

water infiltration through the parking lot to the water table 

should occur within weeks of precipitation.

Changes in Groundwater Quality Following 

the Installation of Low-Impact-Development 

Enhancements

Water-level data for the observation wells during the 

study period indicate that groundwater moves in the same 

general direction (toward Lubbers Brook) as the surface water, 

thus flowing under the parking lot approximately in a westnorthwest to east-southeast direction (fig. 7). In addition, the 

data indicate that groundwater flows toward Silver Lake in a 

manner that would make MLS#1, which is closer to the lake 

than MLS#2 (the other downgradient sampling well), the best 

well from which to assess changes in water quality that result 

from recharge through the parking lot. In the summer of 2005, 

drought conditions caused well elevations to drop below the 

lake surface elevation (fig. 8). On occasion, the lake outlet 

may become blocked, causing the lake elevation to exceed the 

water-table altitude at MLS#1, possibly slowing, but probably not reversing the flow of groundwater toward the lake; 

for example, in August 2006, the lake elevation exceeded the 

water table in the parking lot by about 1 ft. Other, more subtle, 

changes in flow direction may have gone undetected because 

of the monthly monitoring program.

The Wilcoxon rank-sum test was used to compare analyte 

concentrations (α = 0.05 was used to define the likelihood of 

differences in distributions of the sample concentrations) at 

the three MLSs before and after the parking lot installation 

(table 1). The small number of samples (5 before and 12 after 

installation), however, made it difficult to draw robust statistical inferences; changes in reporting levels also complicated 

statistical analysis. Some analytes were detected only rarely, 

if at all, in some wells; these include dissolved nitrite, dissolved cadmium, dissolved lead. Where appropriate, following 

a recommendation of Helsel (2005a, b), values of one-half 

the detection level were substituted for nondetects in order to 

make some of these statistical comparisons.

Quality-control samples (one blank and two field replicates) were collected (table 2) during the study. Concentrations 

in the replicates were consistent with those in the environmental samples. With the exception of ammonia, low-level detections (nitrite, nickel, and zinc) in the blank sample are insignificant relative to the concentrations detected in the associated 

well, MLS#3. Ammonia detections in the field samples were 

uncommon, indicating the blank may have been contaminated 

in the laboratory; moreover, both blank and environmental 

values were less than the reporting level. The occasional relative percent difference (RPD) value that exceeded 20 percent 

seems to have been random and not indicative of systematic 

excessive variability in the sample concentrations.

Specific Conductance, Dissolved Oxygen, and pH

The specific conductance profile data for MLS#1 and 

MLS#2 are similar in range (table 3). Most of the values range 

between 50 and 150 μS/cm. For 2005, a year with very dry 

conditions, some of the values exceed 200 μS/cm. In MLS#1, 
Field Studies of Low-Impact-Development Techniques 11

A

B

Figure 6. (A) U.S. Geological Survey well drillers installing multilevel samplers. Markings on the white PVC pipe are 

locations of the sampling ports and (B) color-coded sampling tubes that lead to intake ports in multilevel samplers.
12 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Bath House

BURNAP STREET

GROVE AVENUE

98

98

94

94

98

98

98

100

98

96

96

D

Y H

96.5

97.1

98.5

98.1

SWALE

SWALE

GRAVEL

PAVERS

POROUS

ASPHALT

IMPERVIOUS

ASPHALT

PAVED PARKING

PAVED WALKWAY TO FISHING PIER

EXISTING

OW#3

MLS#2

OW#1

MLS#1

MLS#3

OW#4

OW#2

USGS WELLS altitude approximately 93.5 feet 

Silver Lake

N

0 60 120 180 FEET

0 30 60 METERS

EXPLANATION

U.S. Geological Survey (USGS) observation well and identifier—Altitude on April 27, 2007

U.S. Geological Survey multi-level sampler and identifier 

Rain garden or bioretention cell

Water-table altitude—Contour interval is 0.2 foot 

Land-surface altitude—Contour interval is 2 feet

Parking lot drains and pipes

Generalized groundwater-flow direction

Street storm drains and pipes

94.64

94.8

OW#3

MLS#2

98

94.6

94.4

94.2

94.8

94.91

94.91

94.64

94.52

Basemap courtesy of Steven Roy, Geosyntec Consultants

Figure 7. Features of Silver Lake Beach parking lot, Wilmington, MA, and generalized groundwater-flow direction.
Field Studies of Low-Impact-Development Techniques 13

Figure 8. Altitudes of water table determined in multilevel samplers and of Silver Lake, Wilmington, MA, July 2005 to June 2007.

7/6/2005 12/31/2005 6/27/2006 12/22/2006 6/19/2007

DATE

91

92

93

94

95

ALTITUDE, IN FEET ABOVE NORTH AMERICAN VERTICAL DATUM OF 1988

Construction period

Observation well #4

Observation well #3

Observation well #2

Observation well #1

Lake level
14 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Table 1. Concentrations of nutrients, dissolved metals, and total petroleum hydrocarbons in samples collected at water-table 

elevations from three multilevel samplers installed at the Silver Lake beach parking lot at Wilmington, MA, 2005–07.—Continued

[E, estimated value less than the reporting level; MLS, multilevel sampler; <, less than; shading indicates samples collected prior to installation of porous

parking lot surface; L, sample lost during processing; --, not calculated]

Sampling 

date

Nutrients (concentrations in milligrams per liter)

Dissolved

ammonia plus

organic nitrogen,

as N

Total ammonia 

plus organic 

nitrogen,

as N

Dissolved 

ammonia,

as N

Dissolved 

nitrite plus 

nitrate,

as N

Dissolved 

nitrite,

as N

Orthophosphorus,

as P

Dissolved 

phosphorus,

as P

Total

phosphorus

MLS#1

7/6/2005 <.10 E.08 <.04 1.16 <.008 <.02 E.003 0.027

7/15/2005 0.27 0.12 <.04 1.13 <.008 <.02 E.003 E.003

9/9/2005 E.09 0.14 <.04 1.69 <.008 <.02 E.003 0.006

10/5/2005 E.08 0.12 <.04 2.2 <.008 <.09 E.004 0.022

10/19/2005 <.10 0.11 <.04 1.34 <.008 <.02 0.004 0.052

Median <.10 0.12 <.04 1.34 <.008 <.02 E.003 0.022

6/19/2006 0.11 E.09 <.010 0.67 <.002 0.008 0.006 0.023

7/26/2006 E.07 E.07 <.010 1.15 <.002 E.005 E.002 0.028

8/29/2006 E.08 0.16 E.006 1.61 <.002 0.006 E.004 0.022

9/18/2006 0.24 E.09 <.010 1.96 <.002 E.003 0.008 0.011

10/16/2006 <.10 <.10 <.020 1.61 <.002 E.005 <.006 0.009

11/20/2006 0.12 0.18 <.020 0.39 <.002 0.013 0.015 0.102

12/18/2006 <.10 <.10 E.015 0.36 <.002 E.005 <.006 E.008

1/23/2007 <.10 <.10 <.020 0.37 <.002 E.004 <.006 0.011

3/28/2007 <.10 <.10 <.020 0.65 <.002 E.004 <.006 0.019

4/27/2007 <.10 E.09 <.020 0.24 <.002 E.004 <.006 0.015

5/21/2007 E.09 0.1 <.020 1.27 E.001 0.007 0.007 0.049

6/19/2007 <.10 <.10 <.020 1.01 <.002 E.005 0.015 0.018

Median <.10 <.10 <.020 0.84 <.002 E.005 <.006 0.0185

MLS#2

7/6/2005 <.10 E.05 <.04 3.48 <.008 <.02 0.006 0.016

7/15/2005 E.10 E.07 <.04 3.02 <.008 <.02 0.007 0.013

9/9/2005 E.05 E.07 <.04 2.32 <.008 <.02 E.003 0.007

10/5/2005 0.14 0.13 <.04 4.19 <.008 <.09 0.007 0.015

10/19/2005 <.10 E.08 <.04 0.23 <.008 <.02 0.005 0.013

Median <.10 E.07 <.04 3.02 <.008 <.02 0.006 0.013

6/19/2006 0.17 0.19 <.010 0.12 <.002 0.008 0.006 0.034

7/26/2006 0.17 0.22 <.010 0.43 <.002 0.011 0.009 0.049

8/29/2006 0.11 0.13 E.005 1.01 <.002 0.01 0.006 0.012

9/18/2006 0.12 0.12 <.010 0.91 <.002 0.01 0.006 0.011

10/16/2006 0.11 0.11 <.020 2.51 <.002 0.009 0.006 0.011

11/20/2006 0.11 0.11 <.020 0.8 <.002 0.008 0.007 0.009

12/18/2006 E.07 <.10 E.014 0.14 <.002 0.007 E.004 0.012

1/23/2007 E.05 E.08 <.020 0.21 <.002 0.007 E.006 0.009

3/28/2007 E.07 <.10 <.020 0.84 <.002 E.006 0.006 0.009

4/27/2007 E.07 E.10 <.020 0.64 <.002 0.007 0.006 0.011

5/21/2007 E.09 0.11 <.020 1.58 <.002 0.016 0.008 0.016

6/19/2007 E.05 0.13 <.020 0.71 <.002 0.01 0.009 0.014

Median 0.1 0.11 <.020 0.755 <.002 0.0085 0.006 0.0125
Field Studies of Low-Impact-Development Techniques 15

Table 1. Concentrations of nutrients, dissolved metals, and total petroleum hydrocarbons in samples collected at water-table 

elevations from three multilevel samplers installed at the Silver Lake beach parking lot at Wilmington, MA, 2005–07.—Continued

[E, estimated value less than the reporting level; MLS, multilevel sampler; <, less than; shading indicates samples collected prior to installation of porous

parking lot surface; L, sample lost during processing; --, not calculated]

Sampling 

date

Nutrients (concentrations in milligrams per liter)

Dissolved

ammonia plus

organic nitrogen,

as N

Total ammonia 

plus organic 

nitrogen,

as N

Dissolved 

ammonia,

as N

Dissolved 

nitrite plus 

nitrate,

as N

Dissolved 

nitrite,

as N

Orthophosphorus,

as P

Dissolved 

phosphorus,

as P

Total

phosphorus

MLS#3

7/6/2005 <.10 E.06 <.04 <.06 <.008 <.02 E.003 0.054

7/15/2005 0.23 0.21 0.04 <.06 <.008 <.02 E.003 0.017

9/9/2005 0.15 0.23 <.04 1.28 0.028 <.02 E.004 0.043

10/5/2005 <.10 E.06 <.04 E.03 <.008 <.09 <.004 0.011

10/19/2005 E.07 0.22 <.04 0.09 <.008 <.02 <.004 0.114

Median <.10 0.21 <.04 <.06 <.008 <.02 <.004 0.043

6/19/2006 <.10 <.10 <.010 0.56 <.002 E.004 <.004 0.007

7/26/2006 <.10 <.10 <.010 E.04 <.002 <.006 <.004 0.005

8/29/2006 <.10 E.07 E.006 <.06 <.002 E.004 <.004 E.003

9/18/2006 <.10 <.10 <.010 <.06 <.002 E.005 <.004 E.003

10/16/2006 <.10 <.10 <.020 <.06 <.002 E.004 <.006 E.004

11/20/2006 0.17 0.18 <.020 <.06 <.002 E.004 E.004 0.02

12/18/2006 <.10 <.10 E.016 <.06 <.002 E.004 <.006 0.009

1/23/2007 <.10 <.10 <.020 <.06 <.002 E.004 <.006 E.006

3/28/2007 <.10 <.10 <.020 <.06 <.002 E.003 <.006 E.005

4/27/2007 <.10 <.10 <.020 E.03 <.002 E.003 <.006 E.004

5/21/2007 E.07 E.08 E.010 0.16 <.002 E.004 <.006 0.049

6/19/2007 <.10 <.10 <.020 <.06 <.002 E.004 <.006 <.008

Median <0.10 <0.10 <.020 <.06 <.002 E.004 <.006 0.005
16 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Table 1. Concentrations of nutrients, dissolved metals, and total petroleum hydrocarbons in samples collected at water-table 

elevations from three multilevel samplers installed at the Silver Lake beach parking lot at Wilmington, MA, 2005–07.—Continued

[E, estimated value less than the reporting level; MLS, multilevel sampler; <, less than; shading indicates samples collected prior to installation of porous parking lot surface; L, sample lost during processing; --, not calculated]

Sampling

date

Dissolved metals (concentrations in micrograms per liter) Total petroleum 

hydrocarbons

(concentrations in 

milligrams per liter)

Cadmium Chromium Copper Lead Nickel Zinc

MLS#1

7/6/2005 <.04 <2 1.5 0.12 0.96 1.6 <2

7/15/2005 E.04 <2 1.6 0.22 1.81 3.6 2

9/9/2005 E.03 <2 1 0.21 1.39 <.6 3

10/5/2005 E.02 <2 1.3 0.08 0.86 1.1 <2

10/19/2005 <.04 <2 0.5 <.08 0.49 E.4 2

Median <.04 <2 1.3 0.12 0.96 1.1 2

6/19/2006 <.04 <2 0.9 0.12 0.47 0.8 <2

7/26/2006 <.04 <2 0.51 0.08 0.12 E.31 L

8/29/2006 <.04 <2 0.66 E.05 0.12 E.36 2

9/18/2006 <.04 <2 0.66 0.14 0.11 E.50 4

10/16/2006 <.04 <2 1 E.07 0.13 <.60 3

11/20/2006 <.04 <2 1.6 0.12 0.17 <.60 <2

12/18/2006 E.02 <2 0.57 E.06 0.13 <.60 6

1/23/2007 <.04 <2 <.40 0.3 E.05 <.60 <2

3/28/2007 <.04 <2 E.38 <.12 0.09 <.60 5

4/27/2007 <.04 <2 0.41 <.12 0.09 <.60 2

5/21/2007 <.04 <2 1.1 E.11 0.17 0.98 <2

6/19/2007 <.04 <2 0.43 0.16 0.07 <.60 <2

Median <.04 <2 0.615 0.075 0.125 <.60 <2

MLS#2

7/6/2005 E.03 <2 1.5 0.18 1.71 3.7 <2

7/15/2005 E.03 <2 1.1 E.04 1.01 1.4 <2

9/9/2005 E.03 <2 E.2 <.08 0.47 E.5 <2

10/5/2005 0.04 <2 1 <.08 1.52 E.5 <2

10/19/2005 <.04 <2 0.6 <.08 0.73 E.4 <2

Median E.03 <2 1 1.01 E.5 <2

6/19/2006 0.07 <2 2.4 E.04 1.96 0.7 2

7/26/2006 <.04 <2 0.5 0.08 0.12 <.60 <2

8/29/2006 <.04 <2 0.83 <.08 0.15 <.60 3

9/18/2006 E.02 <2 0.67 <.08 0.17 <.60 3

10/16/2006 <.04 <2 0.74 <.12 0.18 E.30 6

11/20/2006 0.04 <2 1.4 <.12 0.91 0.74 4

12/18/2006 <.04 <2 1.2 <.12 0.14 E.31 <2

1/23/2007 <.04 <2 0.67 <.12 0.06 <.60 <2

3/28/2007 E.02 <2 1 <.12 0.38 0.8 2

4/27/2007 0.08 <2 1.3 <.12 0.44 1.9 3

5/21/2007 E.02 <2 1.1 <.12 0.42 0.82 <2

6/19/2007 <.04 <2 0.88 <.12 0.1 E.33 <2

Median <.04 <2 0.94 <.12 0.175 -- 2
Field Studies of Low-Impact-Development Techniques 17

Table 1. Concentrations of nutrients, dissolved metals, and total petroleum hydrocarbons in samples collected at water-table 

elevations from three multilevel samplers installed at the Silver Lake beach parking lot at Wilmington, MA, 2005–07.—Continued

[E, estimated value less than the reporting level; MLS, multilevel sampler; <, less than; shading indicates samples collected prior to installation of porous parking lot surface; L, sample lost during processing; --, not calculated]

Sampling

date

Dissolved metals (concentrations in micrograms per liter) Total petroleum 

hydrocarbons

(concentrations in 

milligrams per liter)

Cadmium Chromium Copper Lead Nickel Zinc

MLS#3

7/6/2005 0.16 <2 0.9 0.11 2.89 66.3 <2

7/15/2005 0.16 E1 4.8 0.81 2.72 8.5 <2

9/9/2005 0.16 E2 3.6 0.63 2.33 4.2 <2

10/5/2005 0.44 <2 1.4 0.13 8.94 157 <2

10/19/2005 0.12 <2 1.9 0.18 3.45 77.4 2

Median 0.16 1.9 0.18 2.89 66.3 <2

6/19/2006 0.32 <2 0.9 E.07 1.2 143 3

7/26/2006 0.31 <2 0.83 0.11 1.1 102 <2

8/29/2006 0.2 <2 0.61 E.05 0.71 90.4 <2

9/18/2006 0.28 <2 0.63 E.06 0.84 108 <2

10/16/2006 0.42 <2 0.8 E.11 1.1 143 2

11/20/2006 0.13 <2 4.9 0.6 1.7 16.6 3

12/18/2006 0.36 <2 0.92 E.11 1.2 120 3

1/23/2007 0.33 <2 0.63 E.09 0.76 123 <2

3/28/2007 0.32 <2 0.81 E.08 0.87 138 6

4/27/2007 0.26 <2 0.79 E.09 0.74 119 <2

5/21/2007 0.11 <2 1.9 0.34 0.86 16 L

6/19/2007 0.48 <2 0.76 0.18 1.1 206 6

Median 0.31 <2 0.805 0.1 0.985 120.5 2
18 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Table 2. Concentrations of nutrients, dissolved and total metals, and total petroleum hydrocarbons in quality-control and 

corresponding environmental samples collected at the Silver Lake beach parking lot and the Silver Lake Avenue runoff site in 

Wilmington, MA, and Whipple Annex and Town Hall roof-runoff sites in Ipswich, MA, 2005–07.—Continued

[Samples from Silver Lake beach parking lot were alalyzed for dissolved metals; samples from Lake Avenue runoff and roof runoff were analyzed for total 

metals. E, estimated value less than the reporting level; <, less than; shading indicates samples collected prior to installation of porous parking lot surface; total 

petroleum hydrocarbons values of detections in bold print, do not have unacceptably high laboratory blank contamination; L, sample lost during processing; 

M, detected, but not quantifiable; --, missing or not calculated; ns, sample not collected; ENV, environmental sample; REP, replicate sample; SOIL, green roof 

planting medium slurry sample; BLK, blank sample; RPD, relative percent difference; MLS, multilevel sampler; BP, bulk precipitation sample; TH, Town Hall; 

GR, Whipple Annex green roof; GS, USGS clean room]

Sampling 

date

Sample

type

Nutrients (concentrations in milligrams per liter)

Dissolved

ammonia plus 

organic

nitrogen,

as N

Total ammonia 

plus organic 

nitrogen,

as N

Dissolved 

ammonia, 

as N

Dissolved 

nitrate plus 

nitrite,

as N

Dissolved 

nitrite,

as N

Orthophosphate,

as P

Dissolved 

phosphorus,

as P

Total

phosphorus

Silver Lake beach parking lot

10/5/2005 ENV-MLS#1 E0.08 0.12 <0.04 2.2 <0.008 <0.09 E0.004 0.022

REP-MLS#1 E0.09 E0.10 <.04 1.66 <.008 <.02 E0.003 <.004

RPD 11.8 18.2 -- 28.0 -- -- 28.6 --

9/18/2006 ENV-MLS#2 0.12 0.12 <.010 0.91 <.002 0.01 0.006 0.011

REP-MLS#2 0.11 E.10 <.04 0.9 <.002 0.01 0.005 0.009

RPD 8.7 18.2 -- 1.1 -- 0.0 18.2 20.0

12/18/2006 BLK-MLS#3 ns ns ns ns ns ns ns ns

BLK <.10 <.10 E.018 <.06 E.001 <.006 <.006 <.008

Lake Avenue runoff

11/8/2006 ENV 1.1 1.3 <.020 0.28 0.003 0.395 0.675 0.71

REP 1 1.3 <.020 0.27 0.012 0.451 0.682 0.7

RPD 9.5 0.0 -- 3.6 120.0 13.2 1.0 1.4

BLK 0.11 <.10 0.026 <.06 <.002 <.006 <.006 <.008

8/6/2007 BLK <.10 <.10 0.022 <.06 E.001 <.006 <.006 <.008

Roof runoff

11/16/2007 BLK-BP <0.14 <0.14 E0.012 <.04 <.002 <.006 <.006 <.008

BLK-TH <0.14 <0.14 <.02 <.04 <.002 <.006 <.006 E0.005

7/9/2008 ENV-GR 3 3 0.092 0.41 0.015 0.73 0.83 0.88

REP-GR 3.2 3 0.165 0.41 0.016 0.76 0.82 0.92

RPD 6.5 0.0 56.8 0.0 6.5 4.0 1.2 4.4

7/22/2008 BLK-GS ns ns ns ns ns ns ns ns

7/23/2008 BLK-TH <.10 <.10 <.010 0.56 <.002 E.004 <.004 0.007

ENV-TH ns ns ns ns ns ns ns ns

REP-TH ns ns ns ns ns ns ns ns

10/21/2008 ENV-BP 0.77 0.81 0.673 1.59 0.004 <.008 0.006 0.008

ENV-TH ns ns ns ns ns ns ns ns

REP-BP 0.8 0.85 0.673 1.6 0.004 <.008 0.006 0.009

RPD 3.8 4.8 0.0 0.6 0.0 -- 0.0 11.8

10/23/2008 BLK-BP E0.05 <.10 E.016 <.06 <.002 E.004 <.006 0.009

BLK-TH ns ns ns ns ns ns ns ns

10/26/2008 ENV-GR 4 2.3 E0.015 0.6 0.005 1.33 1.51 1.57

REP-GR 2.3 2.2 0.011 0.6 0.004 1.47 1.45 1.57

RPD 54.0 4.4 30.8 0.0 22.2 10.0 4.1 0.0

11/5/2008 BLK-TH <.10 <.10 <.010 E.04 <.002 <.006 <.004 0.005

BLK-TH <.10 E.07 E.006 <.06 <.002 E.004 <.004 E.003

SOIL 1.2 3.5 <.02 0.21 0.004 0.318 0.38 1.14
Field Studies of Low-Impact-Development Techniques 19

Table 2. Concentrations of nutrients, dissolved and total metals, and total petroleum hydrocarbons in quality-control and 

corresponding environmental samples collected at the Silver Lake beach parking lot and the Silver Lake Avenue runoff site in 

Wilmington, MA, and Whipple Annex and Town Hall roof-runoff sites in Ipswich, MA, 2005–07.—Continued

[Samples from Silver Lake beach parking lot were alalyzed for dissolved metals; samples from Lake Avenue runoff and roof runoff were analyzed for total 

metals. E, estimated value less than the reporting level; <, less than; shading indicates samples collected prior to installation of porous parking lot surface; total 

petroleum hydrocarbons values of detections in bold print, do not have unacceptably high laboratory blank contamination; L, sample lost during processing; 

M, detected, but not quantifiable; --, missing or not calculated; ns, sample not collected; ENV, environmental sample; REP, replicate sample; SOIL, green roof 

planting medium slurry sample; BLK, blank sample; RPD, relative percent difference; MLS, multilevel sampler; BP, bulk precipitation sample; TH, Town Hall; 

GR, Whipple Annex green roof; GS, USGS clean room]

Sampling 

date

Sample

type

Metals (concentrations in micrograms per liter) Total

petroleum

hydrocarbons

(concentrations

in milligrams

per liter)

Cadmium Chromium Copper Lead Nickel Zinc

Silver Lake beach parking lot

10/5/2005 ENV-MLS#1 E0.02 <2 1.3 0.08 0.86 1.1 <2

REP-MLS#1 E0.04 <2 1 0.21 1.38 <.60 <2

RPD 66.7 -- 26.1 89.7 46.4 -- --

9/18/2006 ENV-MLS#2 <.04 <2 1 E.07 0.13 <.60 3

REP-MLS#2 E.02 <2 0.67 <.08 0.17 <.60 <2

RPD -- -- 39.5 -- 26.7 -- --

12/18/2006 BLK-MLS#3 <.04 <2 <.40 <.12 E.05 1.2 ns

BLK ns ns ns ns ns ns 2

Lake Avenue runoff

11/8/2006 ENV 0.04 M 6 1.4 1.57 37 <2

REP 0.05 M 6.1 1.4 1.59 37 <2

RPD 22.2 -- 1.7 0.0 1.3 0.0 --

BLK <.02 <.8 <1.2 <.06 <.16 <2 <2

8/6/2007 BLK <.02 <.8 <1.2 <.06 <.16 <2.0 L

Roof runoff

11/16/2007 BLK-BP <0.01 <1 <1.2 <0.06 0.45 <2 2

BLK-TH <0.01 <1 <1.2 <0.06 0.16 <2 E3

7/9/2008 ENV-GR 0.83 <1 590 1.59 3.5 384 E4.1

REP-GR 0.85 <1 589 1.67 3.6 389 E1.7

RPD 2.4 -- 0.2 4.9 2.8 1.3 ns

7/22/2008 BLK-GS ns ns ns ns ns ns E4.5

7/23/2008 BLK-TH 0.04 <1 <1.2 0.13 0.3 E1.3 ns

ENV-TH ns ns ns ns ns ns E3.7

REP-TH ns ns ns ns ns ns E2.4

10/21/2008 ENV-BP 0.19 <1 2.5 5.65 0.38 10.8 ns

ENV-TH ns ns ns ns ns ns E2.8

REP-BP 0.19 <1 2.4 5.49 0.47 11.6 ns

RPD 0.0 -- 4.1 2.9 21.2 7.1 ns

10/23/2008 BLK-BP <0.06 <1 <4 <0.1 <0.2 <2 ns

BLK-TH ns ns ns ns ns ns E2.7

10/26/2008 ENV-GR 0.46 <1 414 2.3 2.3 244 E4.9

REP-GR 0.45 <1 414 2.35 2.2 237 E3.7

RPD 2.2 -- 0.0 2.2 4.4 2.9 ns

11/5/2008 BLK-TH <0.06 <1 <4 <0.1 <0.2 <2 ns

BLK-TH <0.06 <1 <4 <0.1 <0.2 <2 ns

SOIL 0.14 5 51.7 13 8.2 86 ns
20 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin Table 3. Specific conductance, dissolved oxygen concentrations, and pH profiles in samples from multilevel samplers #1, #2, and #3, in the Silver Lake beach parking lot, Wilmington, MA, July 6, 2005, to June 19, 2007.—Continued [Elevations identify the height above NAV 88 of the sampling ports from which water may have been drawn. μS/cm, microsiemens per square centimeter at 25 degrees Celsius; mg/L, milligrams per liter; shading indicates samples collected prior to installation of porous parking lot surface; MLS, multilevel sampler; --, no data] Specific conductance, in μS/cm Elevation (feet) 7/6/2005 7/15/2005 9/9/2005 10/5/2005 10/19/2005 6/19/2006 7/26/2006 8/29/2006 9/18/2006 10/16/2006 11/20/2006 12/18/2006 1/23/2007 3/28/2007 4/27/2007 5/21/2007 6/19/2007 MLS#1 93.56 -- -- -- -- -- -- -- -- -- -- 124 -- -- -- -- 133 -- 93.06 -- -- -- -- -- 111 -- -- -- -- 122 106 85 128 107 98 -- 92.56 97 102 -- -- 164 107 108 129 123 152 127 111 96 122 105 94 90 92.06 86 90 -- -- 138 105 109 122 130 152 135 121 110 115 103 95 91 91.56 81 82 90 -- 121 102 104 121 131 150 140 129 114 109 98 93 89 91.06 76 77 92 100 123 98 98 121 130 150 142 130 107 96 93 94 90.56 76 75 113 123 145 86 81 112 119 140 133 111 115 99 88 87 84 90.06 102 83 126 173 210 83 64 101 141 156 112 90 96 88 77 79 77 89.56 161 99 143 176 282 101 55 108 137 174 112 81 82 79 75 72 71 89.06 254 166 184 148 273 98 55 95 118 168 123 76 97 96 79 66 68 MLS#2 93.38 -- -- -- -- -- 90 -- -- -- -- 74 -- -- 79 78 113 -- 92.88 -- -- 260 122 137 129 -- -- 82 62 58 56 73 80 90 92.38 109 115 -- -- 164 139 104 113 111 115 82 60 55 51 67 60 58 91.88 111 99 -- -- 136 149 95 106 106 101 84 70 61 56 63 56 52 91.38 96 98 124 -- 120 154 75 81 82 81 82 74 60 56 56 50 48 90.88 130 114 102 -- 122 107 64 73 75 68 74 77 60 56 52 49 49 90.38 164 149 101 -- 113 101 75 73 76 66 71 77 68 59 52 50 49 89.88 187 177 107 -- 110 100 88 72 75 67 65 75 78 63 52 51 49 89.38 194 188 113 100 124 98 98 84 85 70 67 72 77 55 52 51 49 88.88 191 186 119 110 130 101 101 94 105 87 66 72 72 52 51 49 49 88.38 201 192 131 115 136 116 106 102 123 129 79 78 72 54 49 49 49 MLS#3 93.88 -- -- -- -- -- -- -- -- -- -- 203 -- -- -- -- 78 -- 93.38 34 31 -- -- 99 35 46 68 -- -- 93 69 71 75 66 79 -- 92.88 135 169 -- -- 130 60 45 49 65 81 70 57 61 66 98 169 122 92.38 903 860 -- -- 272 51 66 133 84 66 59 74 65 78 353 362 369 91.88 1,374 927 410 -- 441 68 182 134 101 135 88 107 81 73 454 882 773 91.38 1,216 804 510 -- 446 279 562 205 217 268 123 143 124 201 682 1,090 1,071 90.88 1,074 950 443 477 472 393 820 660 610 462 213 172 162 256 788 944 1,013 90.38 968 966 470 486 490 593 808 678 680 517 427 298 239 200 929 853 875 89.88 667 628 534 545 473 793 838 552 471 522 484 336 314 326 1,045 837 827

89.38 596 580 579 578 471 937 789 666 662 616 450 396 338 416 904 634 88788.88 608 575 595 592 510 704 588 669 690 683 463 459 430 506 678 549 66088.38 603 572 599 592 548 612 571 679 690 685 491 477 498 606 630 631 665
Field Studies of Low-Impact-Development Techniques 21

Table 3. Specific conductance, dissolved oxygen concentrations, and pH profiles in samples from multilevel samplers #1, #2, and #3, in the Silver Lake beach parking lot, Wilmington, MA, July 6, 2005, to June 19, 2007.—Continued[Elevations identify the height above NAV 88 of the sampling ports from which water may have been drawn. μS/cm, microsiemens per square centimeter at 25 degrees Celsius; mg/L, milligrams per liter; shading indicates samples collected prior to installation of porous parking lot surface; MLS, multilevel sampler; --, no data]

Dissolved oxygen, in mg/L

Elevation 

(feet) 7/6/2005 7/15/2005 9/9/2005 10/5/2005 10/19/2005 6/19/2006 7/26/2006 8/29/2006 9/18/2006 10/16/2006 11/20/2006 12/18/2006 1/23/2007 3/28/2007 4/27/2007 5/21/2007 6/19/2007

MLS#1

93.56 -- -- -- -- -- -- -- -- -- -- 9.55 -- -- -- -- 7.99 --93.06 -- -- -- -- -- -- -- -- -- -- 7.70 9.06 10.80 10.90 8.41 7.39 --92.56 7.70 -- -- -- 5.18 -- 6.46 6.23 7.46 6.89 8.45 8.21 9.30 10.32 9.26 8.50 8.0192.06 6.40 -- -- -- 3.04 -- 5.61 5.08 6.07 6.49 8.06 6.95 8.10 9.10 8.40 8.11 6.9191.56 4.63 -- 4.20 -- 2.08 -- 5.80 4.75 5.04 5.91 7.04 6.89 8.00 9.64 9.05 8.34 7.7691.06 5.11 -- 1.65 7.60 1.84 7.30 5.49 4.58 4.49 5.77 7.41 6.50 -- 9.08 8.36 8.01 7.2190.56 5.12 -- 0.89 0.90 1.37 6.70 4.89 4.06 2.32 5.07 6.92 4.69 6.52 8.25 8.13 7.63 6.9390.06 3.70 -- 0.93 1.44 1.41 6.40 4.73 2.51 0.71 2.34 5.67 4.36 6.43 8.53 8.23 7.88 6.7589.56 1.95 -- 0.89 1.57 0.82 5.80 4.99 0.56 0.41 0.66 3.35 3.63 6.34 9.15 7.63 7.85 6.4389.06 1.30 -- 0.85 0.82 0.65 5.70 4.10 0.44 0.51 0.81 2.00 2.22 3.58 6.20 5.71 7.18 5.46

MLS#2

93.38 -- -- -- -- -- -- -- -- -- -- 7.60 -- -- 9.58 8.07 6.66 --92.88 -- -- -- -- 2.33 -- 4.29 4.23 -- -- 7.30 6.61 7.62 9.60 8.31 6.83 5.4892.38 3.11 -- -- -- 2.40 -- 4.32 3.56 3.47 4.61 6.06 5.16 6.22 6.45 7.76 6.66 5.0691.88 2.97 -- -- -- 2.33 -- 4.14 2.70 2.60 3.36 5.69 4.22 4.89 5.42 6.71 5.88 4.8191.38 2.42 -- 2.50 -- 1.35 -- 2.32 2.00 2.00 2.75 3.47 2.58 3.40 4.24 4.64 4.35 5.0790.88 1.52 -- 2.30 -- 0.88 -- 2.99 2.44 2.39 2.25 2.67 2.40 3.47 4.89 6.30 5.50 6.0190.38 1.30 -- 1.80 -- 0.64 -- 3.84 2.57 2.41 2.32 2.52 1.65 2.98 4.69 5.60 5.85 6.3089.88 0.53 -- 1.90 -- 0.64 -- 3.83 2.46 2.15 1.88 2.15 1.31 1.93 4.30 4.17 5.53 5.8689.38 0.48 -- 1.40 1.72 0.97 -- 4.20 2.43 2.28 2.04 2.15 1.55 1.77 5.16 4.59 6.25 6.6988.88 0.31 -- 0.90 1.28 1.30 -- 4.44 3.11 2.65 2.05 1.96 1.60 1.56 5.31 5.10 6.74 6.8488.38 0.39 -- 0.70 1.65 1.32 -- 4.87 3.64 2.51 1.97 2.08 1.89 1.53 4.97 5.49 6.95 7.30

MLS#3

93.88 -- -- -- -- -- -- -- -- -- -- 7.28 -- -- -- -- 7.47 --93.38 5.19 -- -- -- 4.06 -- 4.31 7.61 8.18 7.32 7.76 8.77 7.55 6.48 --92.88 4.38 -- -- -- 4.11 -- 4.63 4.28 5.45 5.70 6.54 5.92 5.50 4.88 4.98 4.88 5.4892.38 2.83 -- -- -- 3.88 -- 3.88 3.26 3.40 2.64 3.03 2.20 1.28 0.88 1.22 2.21 3.2091.88 1.40 -- 7.20 -- 1.35 -- 2.63 0.89 0.64 0.54 0.64 0.49 0.58 0.32 0.44 0.57 1.3891.38 0.70 -- 3.00 -- 1.40 -- 1.25 0.48 0.42 0.45 0.48 0.49 0.70 0.51 0.57 0.84 1.0590.88 0.40 -- 0.70 4.81 0.54 -- 0.68 0.27 0.69 0.44 0.43 0.36 0.39 0.28 0.27 0.63 0.5990.38 0.29 -- 0.50 1.45 2.98 -- 0.43 0.25 1.00 0.34 0.31 0.33 0.41 0.33 0.27 0.25 0.2889.88 0.35 -- 0.70 1.25 0.57 -- 0.39 0.32 0.62 0.40 0.34 0.29 0.41 0.37 0.24 0.30 0.2189.38 0.81 -- 0.90 1.53 0.31 -- 0.65 0.47 0.46 0.32 0.29 0.28 0.29 0.35 0.60 0.34 0.2888.88 0.71 -- 1.50 1.23 0.26 -- 0.37 0.65 0.83 0.54 0.31 0.22 0.25 0.43 0.62 0.38 0.5488.38 1.20 -- 1.50 1.23 0.55 -- 0.42 0.90 0.94 0.82 0.33 0.24 0.21 1.05 1.07 0.59 0.75
22 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin Table 3. Specific conductance, dissolved oxygen concentrations, and pH profiles in samples from multilevel samplers #1, #2, and #3, in the Silver Lake beach parking lot, Wilmington, MA, July 6, 2005, to June 19, 2007.—Continued [Elevations identify the height above NAV 88 of the sampling ports from which water may have been drawn. μS/cm, microsiemens per square centimeter at 25 degrees Celsius; mg/L, milligrams per liter; shading indicates samples collected prior to installation of porous parking lot surface; MLS, multilevel sampler; --, no data] pH, standard units Elevation (feet) 7/6/2005 7/15/2005 9/9/2005 10/5/2005 10/19/2005 6/19/2006 7/26/2006 8/29/2006 9/18/2006 10/16/2006 11/20/2006 12/18/2006 1/23/2007 3/28/2007 4/27/2007 5/21/2007 6/19/2007 MLS#1 93.56 -- -- -- -- -- -- -- -- -- -- 7.88 -- -- -- -- 6.76 -- 93.06 -- -- -- -- -- 6.16 -- -- -- -- 7.43 6.43 6.79 7.03 6.47 6.64 -- 92.56 5.64 5.64 -- -- 6.18 6.33 6.48 6.42 7.27 6.35 7.11 6.35 6.61 6.53 6.40 6.38 6.55 92.06 5.32 5.53 -- -- 5.85 6.29 6.43 6.27 6.82 6.41 6.92 6.29 6.53 6.50 6.40 6.37 6.38 91.56 5.34 5.36 5.30 -- 5.49 6.34 6.37 6.23 6.41 6.37 6.64 6.32 6.52 6.32 6.33 6.32 6.26 91.06 5.24 5.17 5.19 5.21 5.39 6.31 6.34 6.20 6.39 6.36 6.59 6.36 -- 6.32 6.43 6.40 6.31 90.56 5.11 5.10 5.28 5.29 5.47 6.05 6.15 6.00 6.13 6.07 6.12 6.01 6.25 5.98 6.17 6.20 6.08 90.06 5.12 5.03 5.36 5.27 5.44 5.78 6.07 5.87 6.00 5.92 5.85 5.78 6.00 5.78 5.80 5.82 5.80 89.56 4.87 4.86 5.32 5.27 5.32 5.43 5.83 5.50 5.75 5.70 5.61 5.63 5.84 5.57 5.56 5.59 5.50 89.06 4.85 4.82 5.29 5.32 5.32 5.35 5.75 5.50 5.71 5.70 5.51 5.51 5.71 5.44 5.47 5.52 5.42 MLS#2 93.38 -- -- -- -- -- 5.88 -- -- -- -- 6.05 -- -- 6.25 6.09 6.13 -- 92.88 -- -- -- -- 5.73 6.19 6.17 5.89 -- -- 6.39 6.08 6.65 6.20 6.22 6.16 6.00 92.38 5.26 5.21 -- -- 5.71 5.98 6.06 5.79 6.18 6.02 6.21 6.15 6.50 6.13 6.06 6.01 5.92 91.88 5.27 5.17 -- -- 5.68 5.85 5.98 5.88 6.15 6.05 6.16 6.06 6.45 6.05 6.00 5.97 5.90 91.38 5.22 5.11 5.55 -- 5.67 5.78 5.88 5.76 6.08 5.98 6.03 6.00 6.36 5.95 5.85 5.89 5.79 90.88 5.15 5.13 5.58 -- 5.69 5.72 5.83 5.74 6.02 5.93 6.02 5.83 6.32 5.92 5.84 5.84 5.79 90.38 5.09 5.04 5.48 -- 5.68 5.66 5.81 5.74 6.01 5.87 5.99 5.81 6.24 5.83 5.75 5.80 5.71 89.88 5.09 5.05 5.38 -- 5.62 5.62 5.76 5.70 5.99 5.83 5.81 5.82 6.14 5.76 5.74 5.76 5.69 89.38 5.08 5.09 5.37 5.48 5.52 5.57 5.69 5.64 5.90 5.80 5.77 5.71 6.06 5.73 5.67 5.75 5.66 88.88 5.06 5.01 5.33 5.37 5.49 5.52 5.64 5.58 5.82 5.66 5.72 5.68 6.00 5.70 5.65 5.71 5.65 88.38 5.04 4.96 5.27 5.30 5.47 5.47 5.61 5.53 5.76 5.55 5.66 5.65 5.98 5.70 5.62 5.69 5.62 MLS#3 93.88 -- -- -- -- -- -- -- -- -- -- 5.98 -- -- -- -- 5.80 -- 93.38 4.80 4.59 -- -- 5.19 5.22 5.29 5.48 -- -- 5.37 5.29 6.15 5.31 5.26 5.27 -- 92.88 4.65 4.59 -- -- 5.12 5.99 5.32 5.30 5.73 5.33 5.33 5.39 5.96 5.26 5.16 5.05 5.05 92.38 4.61 4.52 -- -- 5.27 5.44 5.46 5.28 5.82 5.58 5.55 5.58 6.12 5.43 5.01 5.01 4.97 91.88 4.83 4.86 5.55 -- 5.54 5.85 5.61 5.69 6.17 5.86 5.99 5.85 6.36 5.79 5.25 5.12 5.08 91.38 5.12 5.17 5.42 -- 5.61 5.79 5.60 6.03 6.26 5.88 6.07 6.00 6.44 5.79 5.44 5.32 5.27 90.88 5.19 5.22 5.43 5.58 5.63 5.79 5.53 5.79 6.12 5.97 6.13 6.02 6.48 5.80 5.51 5.41 5.43 90.38 5.17 5.15 5.43 5.47 5.66 5.68 5.54 5.70 6.04 5.85 5.99 6.00 6.39 5.76 5.49 5.55 5.51 89.88 5.26 5.24 5.33 5.36 5.54 5.56 5.51 5.65 6.00 5.82 5.92 5.97 6.30 5.82 5.49 5.58 5.51

89.38 5.28 5.28 5.26 5.30 5.53 5.56 5.53 5.55 5.84 5.74 5.86 5.91 6.23 5.72 5.60 5.70 5.4988.88 5.20 5.16 5.29 5.34 5.53 5.58 5.53 5.54 5.80 5.69 5.81 5.83 6.11 5.66 5.65 5.69 5.5588.38 5.18 5.11 5.31 5.35 5.51 5.53 5.50 5.54 5.81 5.70 5.74 5.78 6.04 5.59 5.55 5.57 5.48
Field Studies of Low-Impact-Development Techniques 23

the highest values were found in samples from the deepest 

port from which water could be drawn. In MLS#2, the single 

highest value was found in samples from the highest port 

yielding water (October 19, 2005), although, in July 2005, 

the deepest ports had the highest specific conductance values. 

A comparison of the mean and range of specific conductance 

profiles for MLS#1 indicates no substantial changes in data 

from the uppermost sampling ports after the porous parking lot 

was installed (fig. 9); the specific conductance values for the 

lowest ports seem to have declined, leaving median values that 

change little from the top to bottom ports after installation. 

The pre- to post-installation changes likely reflect differences 

between the relatively dry summer and autumn of 2005 and 

the wetter autumn of 2006. There may also be an effect from 

the direct infiltration of rain water after installation. Specific 

conductance data for MLS#3 (table 3) are higher than for 

MLS#1 or MSL#2; most of the measurements for MLS#3 are 

200 μS/cm or more with a high of 1,374 μS/cm.

Dissolved oxygen (DO) concentrations before and after 

installation of the porous parking lot also differ somewhat 

among the MLS wells (table 3). Median DO concentrations (fig. 10) in samples from all ports in MLS#1 increased, 

which may be a response to surficial disruption and increased 

aeration caused by the removal of the impervious asphalt; 

however, the range of values for MLS#1 overlap substantially, except at deepest levels, indicating no substantial 

changes overall. For MLS#2, the DO concentrations seem 

to have risen somewhat more between 2005 and 2006 than 

in MLS#1. The median DO concentrations at MLS#2 before 

installation ranged from 0.64 to 2.76 mg/L along the depth 

profile, and after installation concentrations ranged from 2.43 

to 7.835 mg/L (data not shown). The DO concentrations for 

MLS#3 have a wider range with many of the lowest ports 

yielding samples with less than 1 mg/L of DO in both years.

Values of pH seem to have risen slightly for all three 

wells (table 3) after installation of the porous parking lot. The 

profile data for MLS#1 and MLS#2 are similar to each other 

with highest to lowest pH values generally found in a gradient 

from the highest-elevation ports to the lowest. The pH values 

in MLS#3 do not follow such a pattern; the lowest pH values 

are generally associated with the highest-elevation ports.

Although some of the differences in field characteristic 

values may be due to the effects of recharge after replacing 

the parking lot surface, the hydrology of a relatively dry year 

(2005) versus that of a wetter one (2006) probably contributed 

to these values too. The differences in field characteristics 

between MLS#3 and the two downgradient wells, MLS#1 

and MLS#2, seem to indicate that MLS#1 and MLS#2, which 

were present before installation of the parking lot, may not 

actually be downgradient from MLS#3; in other words, 

groundwater flow from MLS#3 probably bypasses the two 

parking lot MLS sampling sites. Thus, differences in other 

chemical characteristics between MLS#3 and the two downgradient MLSs are unlikely to reflect changes that resulted 

from parking lot installation.

Nutrients, Dissolved Metals, and Total Petroleum 

Hydrocarbons

Differences in concentrations of all analytes also were 

examined in relation to month-to-month water levels; no 

consistent trends were determined (figs. 11 to 19). For MLS#1, 

the highest concentrations of several of the nutrient analytes 

and dissolved copper were detected on November 20, 2006, 

the date when the water table was closest to the land surface; 

however, this value is not part of a trend. Because of the inferences and observations cited in the previous paragraph, figures 

depicting the concentrations of water-quality constituents 

(figs. 11 to 19) are limited to data for MLS#1; data for MLS#2 

and MLS#3 are listed in table 1. Because estimated values less 

than the reporting level appear in the data tables, the detection 

limit, generally, one-half the value of the reporting level, is 

indicated on the figures, where appropriate.

Nutrients

Differences in concentrations of analytes of nitrogen and 

phosphorus in MLS#1 (figs. 11 to 14) and MLS#2 before and 

after installation of the porous parking lot (table 1) are not 

statistically significant (α = 0.05) when the Wilcoxon ranksum test is applied. However, more variability in concentrations is apparent after installation, probably resulting from the 

increase in the range of concentrations when more samples 

were collected after replacement of the old parking lot rather 

than resulting from the effects of the installation of the new 

parking lot surface.

For MLS#3, in spite of the low number of samples 

collected, there is a statistically significant decrease in total 

phosphorus concentrations after the parking lot installation. 

Nitrogen analytes and dissolved phosphorus were not detected 

in a sufficient number of samples from MLS#3 to enable statistical analysis (table 1). Orthophosphorus was not detected in 

any of the wells during the pre-installation period; the reporting level for orthophosphorus was lowered after that period, 

and orthophosphorus was detected in the wells after the porous 

parking lot was installed. Orthophosphorus concentrations in 

MLS#3 never exceeded the pre-installation reporting level or 

detection limit.

Dissolved Metals

As with some of the nutrient analytes, some of the dissolved metals were rarely detected in particular wells, rendering graphical statistical analyses, such as boxplot comparisons, 

not especially helpful: chromium was only detected twice 

(in MLS#3); cadmium was rarely detected in MLS#1 and 

frequently not detected in MLS#2; lead was detected only 

four times in MLS#2; and zinc was frequently not found in 

MLS#1. Bar charts depicting concentrations of the most commonly detected analytes, Cu, Pb, Ni, and Zn in MLS#1 are 

presented (figs. 15 to 18). In general, MLS#3 had the highest 

frequency of metal detections (table 1). Of the three MLSs, 

MLS#3 is closest to the bordering road, and its groundwater 
24 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Figure 9. Minimum, median, and maximum specific conductance values in groundwater 

samples collected at multilevel-sampler well number 1 (MLS#1) before (pre-low-impact 

development) and after (post-low-impact-development) installation of a porous parking lot at 

Silver Lake Beach, Wilmington, MA. The profiles are slightly offset to facilitate comparison. 

Pre-LID, pre-low-impact development; Post-LID, post-low-impact development. 

0 50 100 150 200 250 300

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER

88.5

89.0

89.5

90.0

90.5

91.0

91.5

92.0

92.5

93.0

ALTITUDE, IN FEET ABOVE NORTH AMERICAN VERTICAL DATUM OF 1988

minimum median maximum

RANGE SCHEMATIC

Post-LID Pre-LID
Field Studies of Low-Impact-Development Techniques 25

Figure 10. Minimum, median, and maximum dissolved oxygen concentrations in groundwater 

samples collected at multilevel-sampler well number 1 (MLS#1) before (pre-low-impact 

development) and after (post-low-impact-development) installation of a porous parking lot at 

Silver Lake Beach, Wilmington, MA. The profiles are slightly offset to facilitate comparison. 

Pre-LID, pre-low-impact development; Post-LID, post-low-impact development.

0.0 2.0 4.0 6.0 8.0 10.0

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

88.5

89.0

89.5

90.0

90.5

91.0

91.5

92.0

92.5

93.0

ALTITUDE, IN FEET ABOVE NORTH AMERICAN VERTICAL DATUM OF 1988

Post-LID

Pre-LID

minimum median maximum

RANGE SCHEMATIC
26 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Figure 11. Total ammonia plus organic nitrogen concentrations and water-table altitudes in multilevel-sampler 

well number 1 (MLS#1) before and after installation of a porous parking lot at Silver Lake Beach, Wilmington, MA. 

Empty bar indicates nondetect.

7/23/2005

7/6/2005

8/10/20058/28/2005 9/15/2005

10/3/2005

10/20/2005 11/7/2005

11/25/2005 12/13/2005

12/31/2005 1/18/2006 2/4/2006

2/22/2006

3/12/2006 3/30/20064/17/2006 5/5/2006

5/22/2006 6/9/2006

6/27/2006

7/15/2006 8/2/2006

8/19/2006 9/6/2006

9/24/2006

10/12/2006 10/30/2006 11/17/2006 12/4/2006

12/22/2006 1/9/2007

1/27/2007

2/14/2007 3/4/2007

3/21/2007 4/8/2007

4/26/2007

5/14/2007 6/1/20076/19/2007

DATE

WATER-TABLE ALTITUDE, IN FEET ABOVE

NORTH AMERICAN VERTICAL DATUM OF 1988

91.0

91.5

92.0

92.5

93.0

93.5

94.0

0

0.05

0.10

0.15

0.20

TOTAL AMMONIA PLUS ORGANIC NITROGEN,

IN MILLIGRAMS PER LITER AS NITROGEN

Detection limit=0.05 mg/L

Total ammonia plus organic nitrogen as nitrogen

Total ammonia plus organic nitrogen as nitrogen,

 below detection limit

Detection limit (as indicated)

Water-table altitude

Construction period

7/23/2005

7/6/2005

8/10/2005 8/28/2005 9/15/2005

10/3/2005

10/20/2005 11/7/2005

11/25/2005 12/13/2005

12/31/2005 1/18/2006 2/4/2006

2/22/2006

3/12/2006 3/30/20064/17/2006 5/5/2006

5/22/2006 6/9/2006

6/27/2006

7/15/2006 8/2/2006

8/19/2006 9/6/2006

9/24/2006

10/12/2006 10/30/2006 11/17/2006 12/4/2006

12/22/2006 1/9/2007

1/27/2007

2/14/2007 3/4/2007

3/21/2007 4/8/2007

4/26/2007

5/14/2007 6/1/20076/19/2007

DATE

91.0

91.5

92.0

92.5

93.0

93.5

94.0

WATER-TABLE ALTITUDE, IN FEET ABOVE

NORTH AMERICAN VERTICAL DATUM OF 1988

0

0.5

1.0

1.5

2.0

DISSOLVED NITRATE PLUS NITRATE,

IN MILLIGRA

MS PER LITER AS NITROGEN

Dissolved nitrate plus nitrite as nitrogen

Water-table altitude

Construction period

Figure 12. Dissolved nitrate plus nitrite nitrogen concentrations and water-table altitudes in multilevel-sampler 

well number 1 (MLS#1) before and after installation of a porous parking lot at Silver Lake Beach, Wilmington, MA.
Field Studies of Low-Impact-Development Techniques 27

Orthophosphorus as phosphorus

Orthophosphorus as phosphorus, below detection limit

Detection limit (as indicated)

Water-table altitude

7/23/2005

7/6/2005

8/10/20058/28/2005 9/15/2005

10/3/2005

10/20/2005 11/7/2005

11/25/2005 12/13/2005

12/31/2005 1/18/2006 2/4/2006

2/22/2006

3/12/2006 3/30/20064/17/2006 5/5/2006

5/22/2006 6/9/2006

6/27/2006

7/15/2006 8/2/2006

8/19/2006 9/6/2006

9/24/2006

10/12/2006 10/30/2006 11/17/2006 12/4/2006

12/22/2006 1/9/2007

1/27/2007

2/14/2007 3/4/2007

3/21/2007 4/8/2007

4/26/2007

5/14/2007 6/1/20076/19/2007

DATE

0

0.004

0.008

0.012

DISSOLVED ORTHOPHOSPHORUS,

IN MILLIGRAMS PER LITER AS PHOSPHORUS

91.0

91.5

92.0

92.5

93.0

93.5

WATER-TABLE ALTITUDE, IN FEET ABOVE

NORTH AMERICAN VERTICAL DATUM OF 1988

Detection limit=0.01 mg/L

Detection limit=0.003 mg/L

Construction period

Total phosphorus

Water-table altitude

7/23/2005

7/6/2005

8/10/2005 8/28/2005 9/15/2005

10/3/2005

10/20/2005 11/7/2005

11/25/2005 12/13/2005

12/31/2005 1/18/2006 2/4/2006

2/22/2006

3/12/2006 3/30/20064/17/2006 5/5/2006

5/22/2006 6/9/2006

6/27/2006

7/15/2006 8/2/2006

8/19/2006 9/6/2006

9/24/2006

10/12/2006 10/30/2006 11/17/2006 12/4/2006

12/22/2006 1/9/2007

1/27/2007

2/14/2007 3/4/2007

3/21/2007 4/8/2007

4/26/2007

5/14/2007 6/1/20076/19/2007

DATE

0

0.02

0.04

0.06

0.08

0.10

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

91.0

91.5

92.0

92.5

93.0

93.5

94.0

WATER-TABLE ALTITUDE, IN FEET ABOVE

NORTH AMERICAN VERTICAL DATUM OF 1988

Construction period

Figure 13. Dissolved orthophosphorus concentrations and water-table altitudes in multilevel-sampler well number 1 

(MLS#1) before and after installation of a porous parking lot at Silver Lake Beach, Wilmington, MA.

Figure 14. Total phosphorus concentrations and water-table altitudes in multilevel-sampler well number 1 (MLS#1) 

before and after installation of a porous parking lot at Silver Lake Beach, Wilmington, MA.
28 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

7/23/2005

7/6/2005

8/10/20058/28/2005 9/15/2005

10/3/2005

10/20/2005 11/7/2005

11/25/2005 12/13/2005

12/31/2005 1/18/2006 2/4/2006

2/22/2006

3/12/2006 3/30/20064/17/2006 5/5/2006

5/22/2006 6/9/2006

6/27/2006

7/15/2006 8/2/2006

8/19/2006 9/6/2006

9/24/2006

10/12/2006 10/30/2006 11/17/2006 12/4/2006

12/22/2006 1/9/2007

1/27/2007

2/14/2007 3/4/2007

3/21/2007 4/8/2007

4/26/2007

5/14/2007 6/1/20076/19/2007

DATE

91.0

91.5

92.0

92.5

93.0

93.5

94.0

WATER-TABLE ALTITUDE, IN FEET ABOVE

NORTH AMERICAN VERTICAL DATUM OF 1988

0

0.5

1.0

1.5

DISSOLVED COPPER, IN MICROGRAMS PER LITER

Detection limit=0.02 μg/L

Construction period

Dissolved copper

Dissolved copper, below detection limit

Detection limit (as indicated)

Water-table altitude

7/23/2005

7/6/2005

8/10/20058/28/2005 9/15/2005

10/3/2005

10/20/2005 11/7/2005

11/25/2005 12/13/2005

12/31/2005 1/18/2006 2/4/2006

2/22/2006

3/12/2006 3/30/20064/17/2006 5/5/2006

5/22/2006 6/9/2006

6/27/2006

7/15/2006 8/2/2006

8/19/2006 9/6/2006

9/24/2006

10/12/2006 10/30/2006 11/17/2006 12/4/2006

12/22/2006 1/9/2007

1/27/2007

2/14/2007 3/4/2007

3/21/2007 4/8/2007

4/26/2007

5/14/2007 6/1/20076/19/2007

DATE

0.05

0

0.10

0.15

0.20

0.25

0.30

DISSOLVED LEAD, IN MICROGRAMS PER LITER

91.0

91.5

92.0

92.5

93.0

93.5

94.0

WATER-TABLE ALTITUDE, IN FEET ABOVE

NORTH AMERICAN VERTICAL DATUM OF 1988

Detection limit=0.04 μg/L

Detection

limit=0.06 μg/L

Lead

Lead, below detection limit

Detection limit (as indicated)

Water-table altitude

Construction period

Figure 15. Dissolved copper concentrations and water-table altitudes in multilevel-sampler well number 1 

(MLS#1) before and after installation of a porous parking lot at Silver Lake Beach, Wilmington, MA.

Figure 16. Dissolved lead concentrations and water-table altitudes in multilevel-sampler well number 1 (MLS#1) 

before and after installation of a porous parking lot at Silver Lake Beach, Wilmington, MA. Empty bar indicates 

nondetect.
Field Studies of Low-Impact-Development Techniques 29

Dissolved nickel

Water-table altitude

7/23/2005

7/6/2005

8/10/20058/28/2005 9/15/2005

10/3/2005

10/20/2005 11/7/2005

11/25/2005 12/13/2005

12/31/2005 1/18/2006 2/4/2006

2/22/2006

3/12/2006 3/30/20064/17/2006 5/5/2006

5/22/2006 6/9/2006

6/27/2006

7/15/2006 8/2/2006

8/19/2006 9/6/2006

9/24/2006

10/12/2006 10/30/2006 11/17/2006 12/4/2006

12/22/2006 1/9/2007

1/27/2007

2/14/2007 3/4/2007

3/21/2007 4/8/2007

4/26/2007

5/14/2007 6/1/20076/19/2007

DATE

91.0

91.5

92.0

92.5

93.0

93.5

94.0

WATER-TABLE ALTITUDE, IN FEET ABOVE

NORTH AMERICAN VERTICAL DATUM OF 1988

0

0.5

1.0

1.5

2.0

DISSOLVED NICKEL, IN MICROGRAMS PER LITER

Construction period

7/23/2005

7/6/2005

8/10/2005 8/28/2005 9/15/2005

10/3/2005

10/20/2005 11/7/2005

11/25/2005 12/13/2005

12/31/2005 1/18/2006 2/4/2006

2/22/2006

3/12/2006 3/30/20064/17/2006 5/5/2006

5/22/2006 6/9/2006

6/27/2006

7/15/2006 8/2/2006

8/19/2006 9/6/2006

9/24/2006

10/12/2006 10/30/2006 11/17/2006 12/4/2006

12/22/2006 1/9/2007

1/27/2007

2/14/2007 3/4/2007

3/21/2007 4/8/2007

4/26/2007

5/14/2007 6/1/20076/19/2007

DATE

91.0

91.5

92.0

92.5

93.0

93.5

94.0

WATER-TABLE ALTITUDE, IN FEET ABOVE

NORTH AMERICAN VERTICAL DATUM OF 1988

1

0

2

3

4

DISSOLVED ZINC, IN MICROGRAMS PER LITER

Construction period

Dissolved zinc

Dissolved zinc, below detection limit

Detection limit (as indicated)

Water-table altitude

Detection limit=0.3 μg/L 

Figure 17. Dissolved nickel concentrations and water-table altitudes in multilevel-sampler well number 1 (MLS#1) 

before and after installation of a porous parking lot at Silver Lake Beach, Wilmington, MA.

Figure 18. Dissolved zinc concentrations and water-table altitudes in multilevel-sampler well number 1 (MLS#1) 

before and after installation of a porous parking lot at Silver Lake Beach, Wilmington, MA. Empty bar indicates 

nondetect.
30 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

7/23/2005 8/10/2005

8/28/2005 9/15/2005

10/3/2005

10/20/2005 11/7/2005

11/25/2005 12/13/2005

12/31/2005 1/18/2006 2/4/2006

2/22/2006

3/12/2006 3/30/2006

4/17/2006 5/5/2006

5/22/2006 6/9/2006

6/27/2006 7/15/2006 8/2/2006

8/19/2006 9/6/2006

9/24/2006

10/12/2006 10/30/2006

11/17/2006 12/4/2006

12/22/2006 1/9/2007

1/27/2007

2/14/2007 3/4/2007

3/21/2007 4/8/2007

4/26/2007

5/14/2007 6/1/2007

6/19/2007

DATE

91.0

91.5

92.0

92.5

93.0

93.5

94.0

WATER-TABLE ALTITUDE, IN FEET ABOVE

NORTH AMERICAN VERTICAL DATUM OF 1988

0

1

2

3

4

5

6

TOTAL PETROLEUM HYDROCARBONS,

IN MILLIGRAMS PER LITER 

Detection limit=1 mg/L

Total petroleum hydrocarbons

Total petroleum hydrocarbons, below detection limit

Detection limit (as indicated)

Water-table altitude

Construction period

Figure 19. Total petroleum hydrocarbon concentration and water-table altitudes in multilevel-sampler well 

number 1 (MLS#1) before and after installation of a porous parking lot at Silver Lake Beach, Wilmington, MA. Empty 

bars indicate nondetect.

quality may have been affected by contaminants infiltrating 

from street runoff.

For all three wells, the concentrations of dissolved nickel 

changed (declined) significantly (fig. 17). There is no clear, 

apparent cause for this change. Possible explanations are the 

removal of nickel from an upgradient source or from a source 

within the old parking lot during replacement. The Wilcoxon 

rank-sum test did not demonstrate any other significant 

changes in metal concentrations.

Total Petroleum Hydrocarbons

Prior to the installation of the porous parking lot, detections of total petroleum hydrocarbons (TPH) were not common; for the five sampling dates, TPH was only detected once 

in MLS#2 or MLS#3, and there were 3 detections in MLS#1 

(fig. 19, table 1). The TPH reporting level was 2 mg/L. After 

the porous parking lot installation, there were more frequent 

TPH detections, with the highest concentration of 6 mg/L 

occurring once in each well. These differences were not statistically significant, however, possibly because of the small 

sample size.

Low-Impact-Development Enhancements at the 

Silver Lake Avenue/Dexter Street Neighborhood 

and Water Quantity and Quality of Stormwater 

Runoff

The primary objective of LID is to create, retain, or 

restore a hydrologic landscape that mimics natural hydrological conditions. Therefore, minimizing the effects of human 

alterations on hydrology by removing obstacles to natural 

infiltration, such as impervious asphalt or effectively impervious surfaces, is an obvious approach to hydrologic restoration 

in previously developed residential areas, such as the Silver 

Lake Avenue/Dexter Street neighborhood in Wilmington, MA 

(fig. 20). The desired effects of these retrofits were to decrease 

and delay runoff into storm sewers and other conveyances, 

thus enhancing infiltration and decreasing the mass, or loads, 

of transported contaminants and bacteria to Silver Lake.

The LID features designed for this neighborhood were 

not expected to substantially decrease nitrogen and phosphorus analyte concentrations, but rather to decrease the volume 

of runoff and, thus, diminish loads of nutrients, total metals, 
Field Studies of Low-Impact-Development Techniques 31

Figure 20. Silver Lake Avenue/Dexter Street neighborhood in Wilmington, MA, with drainage features and low-impactdevelopment enhancements.

Silver Lake

LAKE STREET

SILVER LAKE AVENUE

DEXTER STREET

MAIN STREET

DAVIS ROAD

SILVERHURST AVENUE

Rain garden

Drains

Monitoring site

EXPLANATION

Basemap courtesy of Steven Roy, Geosyntec Consultants

N

0 30 60 90 METERS

0 60 120 180 240 300 FEET
32 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

TPH, and coliform bacteria, where load is defined as concentration multiplied by runoff volume. To measure such reductions accurately, the LID features would need to reduce runoff 

volumes by substantially more than measurement errors over 

a wide range of storm sizes. Additionally, runoff from an 

adequate number of storms of comparable precipitation before 

and after implementation would need to be sampled for water 

quality. Both of these conditions were difficult to meet within 

the field constraints and study length.

Design of Low-Impact-Development 

Enhancements to Increase Infiltration

The MDCR contracted with Geosyntec Consultants to 

design and install the LID enhancements in the Silver Lake 

Avenue/Dexter Street neighborhood; this work took place 

from December 2005 to June 2006, following approximately 

5 months of monitoring the pre-LID-modification conditions. The neighborhood’s total impervious area, including 

roads, driveways, and rooftops, accounted for 39 percent 

of the total 3.0-acre drainage area, as determined from the 

MassGIS 1-meter-resolution impervious surface datalayer 

(http://www.mass.gov/mgis/impervious_surface.htm, last 

accessed June 1, 2009).

LID enhancements, consisting of 12 pocket rain gardens 

along Dexter Street and Silver Lake Avenue and 2 strips of 

porous pavers along Silver Lake Avenue, were installed in the 

public right-of-way to increase stormwater infiltration from 

driveways and the street (figs. 21 to 23) and, hence, reduce the 

volume of direct stormwater runoff to Silver Lake. Underdrains from two of the porous-paved areas and overflow drains 

from rain gardens were connected to the existing storm-sewer 

system; stormwater entering these drains was monitored at the 

storm-sewer gage. The LID features roughly accounted for 

less than 2 percent of the 3-acre neighborhood. Although the 

percentage of pervious surface created or enhanced by the LID 

features was not great, the enhancements were not designed 

just to receive and infiltrate direct rainfall, but to have runoff 

routed to them from most of the impervious surfaces, thus 

resulting in a greater effect on overall runoff than would be 

expected for the area of new pervious surface.

Monitoring Approach

The Silver Lake Avenue monitoring site consists of a 

15-in. storm sewer that collects street runoff from the 3-acre 

residential development. The storm sewer was outfitted with 

a 15-in. Thel-Mar, v-notch, volumetric weir and a Teledyne 

ISCO 4120 pressure transducer and datalogger (fig. 24). The 

transducer and logger controlled the Teledyne ISCO sampler 

that collected flow-proportional water samples (Edwards 

and Glysson, 1999). The transducer, weir, and sample intake 

were installed 2 ft downstream from a manhole entry stormdrain grate (fig. 25) that was the most downstream location 

possible to monitor the runoff (refer to fig. 20 for location 

of monitoring site). A storage box containing the automated 

water sampler and datalogger was installed at the edge of the 

road, next to the catch basin; the autosampler was linked to the 

transducer that provided a signal to initiate sampling based on 

a preset volume of water that passed the weir. This trigger volume was determined from National Weather Service forecasts 

of precipitation and the calculated runoff expected to occur 

at the sampling site. Site visits were made monthly or during 

storm sampling to collect stormwater samples and to service 

the equipment.

Precipitation was monitored at a gage at Silver Lake 

beach and at the USGS Shawsheen River near Wilmington 

streamgage located 1.4 mi away (fig. 1). The Shawsheen River 

precipitation gage was primarily used for data analysis but was 

supplemented with the Silver Lake precipitation gage because 

of occasional data losses. The correlation between precipitation recorded at the gages is strong (R2

 = 0.97).

All stage and precipitation data were processed in the 

USGS National Water Information System (NWIS) database, 

and the stage-discharge relation from the rated volumetric weir 

was used to calculate flow. The period of record started on 

August 22, 2005, and ended on December 5, 2007. Because of 

equipment malfunctions, four gaps in the stage data occurred 

during the period of record: (1) September 14 to October 

2, 2006, (2) October 5 to October 25, 2006, (3) December 4 

to December 6, 2006, and (4) April 22 to May 16, 2007. In 

addition, unreasonably high stages and calculated flows not 

consistent with precipitation records are attributed to debris on 

the weir or ice effects and were not used for analyses.

As stated previously, coliform bacteria in Silver Lake 

had historically caused beach closings during the summer. 

Although runoff from the Silver Lake Avenue side of the lake 

was not likely to have been associated with those closings, 

runoff was sampled for Escherichia coli (E. coli) and total 

coliform bacteria to test the potential of LID enhancements for 

diminishing bacterial concentrations in runoff.

The short holding-time requirement for obtaining valid 

bacteria samples was considered in determining the approach 

to sample collection. Holding times of 3 hours for bacteria 

and uncertain storm durations often made it necessary to 

collect multiple samples, representing fractions of the predicted storm runoff, rather than a single composite sample 

for the entire storm. The short holding time also meant that 

staff were often present throughout the storm-sampling 

period. The bacteriological samples were processed with a 

Colilert Quanti-Tray system (http://www.idexx.com/water/

products/quantitray/, last accessed April 2, 2009). After a 

bacterial sample was collected, a 100-milliliter subsample 

was removed and mixed with a reagent. To make serial dilutions, aliquots from the container with media were removed 

and added to another container with media; this process was 

repeated until the estimated numbers of bacteria became 

quantifiable. In general, two 1:10 or 1:100 dilutions were 

prepared routinely. Samples were incubated for 24 hours 

at 35°C. Following incubation, the bacterial colonies were 

quantified using the Most Probable Number (MPN) model 
Field Studies of Low-Impact-Development Techniques 33

Figure 21. Rain gardens along Dexter Street, Wilmington, MA. Cutouts in curbs to direct runoff from road into 

rain garden.

Curb cutout

Curb cutout
34 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Figure 22. Rain garden along Dexter Street, Wilmington, MA.

Curb cutout
Field Studies of Low-Impact-Development Techniques 35

Figure 24. Runoff-monitoring equipment in a catch basin at Silver Lake Avenue, Wilmington, MA. A v-notch 

weir is mounted in the drain pipe behind a pressure transducer that lies on the bottom of the catch basin. An 

opaque Teflon sampling tube extends outward about 2 in. from the black, red-striped, protective tube. Water 

flows toward the pressure transducer and then over the weir.

Figure 23. Storm drain at Silver Lake Avenue, Wilmington, MA. Gravel fill covers a pipe leading from the 

underflow collector beneath the porous-pavement section at right of photograph.

Porous pavers

Gravel fill

Storm

drain

Weir

Pressure 

transducer

Sampling 

tube

Water-flow 

direction
36 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Figure 25. Water draining into a storm-drain grate on Silver Lake Avenue, Wilmington, MA. 

Cold-patch asphalt dams and sandbags were used to guide runoff to the grate.

Stormdrain

grate

Cold-patch

asphalt

Cold-patch

asphalt
Field Studies of Low-Impact-Development Techniques 37

(http://oh.water.usgs.gov/micro/tce3.html, last accessed 

April 2, 2009).

The USGS monitored the water quantity and quality of 

storm runoff (concentrations of nutrients, total metals, TPH, 

and coliform bacteria) starting in August 2005; water-quality 

monitoring was suspended during the installation phase of 

LID retrofits (December 2005 to June 2006), restarted in July 

2006, and completed in November 2007. Also, water-quality 

monitoring was not performed during the winter and early 

spring because of variable conditions associated with freezing, 

thawing, and snowfall. Changes in runoff volume and concentrations and loads of water-quality constituents were compared 

for the pre- and post-LID enhancement periods.

The Quality Assurance Project Plan (QAPP) called for 

the collection of six stormwater-quality samples during the 

8-month period preceding the installation of LID enhancements and six stormwater samples following the LID installation. The limited time available prior to the LID modifications and the lack of storms that met the minimal sampling 

criteria resulted in five pre-LID sampling events; only 6 

months were available for sampling during the pre-installation 

period (effectively, water-quality sampling was conducted 

for 3 months from August 30 to November 22). However, 10 

post-LID storm samples were collected. Of the 10 post-LID 

storms, irregularities in the flows invalidated the results for 

one sample set; bacteriological samples were not collected for 

all storms.

Four quality-control, replicate, and blank samples 

were collected (table 2). With the exceptions of the Cd 

(22.2 percent) and nitrite (120 percent) relative percent differences (RPDs), RPDs were within the measurement criterion 

of 20 percent; the high RPD samples were still low in concentration. Most blank samples were clean or detections were at 

concentrations close to the reporting level.

Changes in Runoff Quantity and Quality Following 

Installation of Low-Impact-Development 

Enhancements

At Silver Lake Avenue, changes in pre- and post-LID 

stormwater-runoff quantity and quality were small, subtle, 

and complicated by differences in climatic conditions and by 

changes in drainage infrastructure.

Runoff Quantity

To compare pre- and post-LID changes in runoff, the data 

were examined for all storms associated with measured runoff. 

For storms determined to have data acceptable for analysis, 

rainfall and runoff relations were determined. In addition 

to considering all storms, the storms were also sub-divided 

by time of year, storm size (inches of rainfall), and antecedent 

dry period.

Pre- and post-LID rainfall-runoff coefficients1 (RRs) were 

examined to assess the effectiveness of the LID installations; 

RRs were further examined by sorting storms by total precipitation and antecedent dry period. When all acceptable pre- and 

post-LID storms were considered, no significant differences 

between median RR values were detected, even for storms 

with antecedent dry period exceeding 100 hours (figs. 26A, B). 

Sorting storms into four size classes also did not reveal any 

statistically significant differences between pre- and post-LID 

RRs; however, median RRs did indicate a difference between 

pre- and post-LID storms, as the storm size decreased (fig. 27). 

Specifically, the differences in median runoff coefficients were 

greatest in the category of smallest storms (less than 0.25 in.), 

where the pre-LID median of the runoff coefficients was 

slightly greater than 0.1 and the post-LID median was about 

0.045. Using the median of the rainfall-runoff curve for the 

smallest class of storms as a surrogate for the effective impervious area (EIA) (Zarriello and Barlow, 2002; Jennings and 

Doyle, 1978), the pre-LID EIA was about 10 percent, and the 

post-LID EIA was approximately 4.5 percent (fig. 28).

Another difference was the occurrence of zero runoff 

from several post-installation storms; these storms were all 

of 0.20 in. or less of precipitation (fig. 29). Of the 21 postinstallation storms with 0.25 in. or less precipitation, 7, or 

33 percent, produced no measurable runoff. Of the seven preinstallation storms of 0.26 in. of rainfall or less, all had some 

measurable runoff. No specific factor, such as antecedent dry 

period or storm duration or intensity, seemed to be associated 

with the absence or presence of runoff. These results indicate 

that even relatively small-scale changes in EIA, in an area 

underlain by highly porous soils, can produce measurable 

changes in runoff, if the storms do not exceed a size threshold; 

in the case of this study site, that threshold was about 0.20 in. 

of precipitation, which included 56 percent of all pre- and 

post-LID storms,.

1

The unitless runoff coefficient is the depth, in inches, of the total volume of 

runoff distributed evenly over the drainage-area surface, divided by the depth 

of precipitation, in inches.
38 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Figure 26. Rainfall-runoff coefficients determined before (Pre-LID, Aug. 2005–Feb. 2006) and after (Post-LID, Aug. 2006–Nov. 2007) 

installation of low-impact-development features along Silver Lake Avenue, Wilmington, MA, for (A) all storms monitored during the 

study period and (B) monitored storms preceded by 100 hours or more of dry conditions. LID, low-impact development.

EXPLANATION

Number of samples

Data value greater than 3.0 times the

interquartile range above the box

Data value 1.5 to 3.0 times the interquartile

range above the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

22

x

o

0

0.1

0.2

0.3

0.4

0.5

RAINFALL-RUNOFF COEFFICIENT

0

0.1

0.2

0.3

0.4

0.5

RAINFALL-RUNOFF COEFFICIENT

PRE-LID POST-LID

PRE-LID POST-LID

o

x

x x

x

10 22

22 54

B

A
Field Studies of Low-Impact-Development Techniques 39

Figure 27. Rainfall-runoff coefficients determined before (Pre-LID, Aug. 2005–Feb. 2006) and after 

(Post-LID, Aug. 2006–Nov. 2007) installation of low-impact-development features along Silver Lake 

Avenue, Wilmington, MA, for groups of storms with different amounts of precipitation. LID, low-impact 

development.

EXPLANATION

Number of samples

Data value greater than 3.0 times the

interquartile range above the box

Data value 1.5 to 3.0 times the interquartile

range above the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Data value 1.5 to 3.0 times the interquartile

range below the box

24

x

x

o

0

0.1

0.2

0.3

0.4

0.5

RAINFALL-RUNOFF COEFFICIENT

PRE-LID POST-LID PRE-LID POST-LID PRE-LID POST-LID PRE-LID POST-LID

LESS THAN OR EQUAL TO

0.25 INCH 0.26 TO 0.50 INCH 0.51 TO 1.00 INCH 1.01 TO 4.00 INCH

PRECIPITATION DEPTH

x

x

x

x

x

o

6 24 6 8 4 13 6 9
40 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Figure 28. Median rainfall-runoff 

coefficients determined before (Pre-LID, 

Aug. 2005–Feb. 2006) and after (PostLID, Aug. 2006–Nov. 2007) installation of 

low-impact-development features along 

Silver Lake Avenue, Wilmington, MA, for 

storms with greater than and less than or 

equal to 0.25 inch of precipitation.

Figure 29. Relations between total 

runoff and total precipitation for 

storms with total precipitation less 

than 0.26 inch that occurred before 

(Pre-LID, Aug. 2005–Feb. 2006) and 

after (Post-LID, Aug. 2006–Nov. 

2007) installation of low-impactdevelopment features along Silver 

Lake Avenue, Wilmington, MA.

LESS THAN OR

EQUAL TO 0.25 INCH

GREATER THAN 0.25 INCH

PRECIPITATION DEPTH

0

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

MEDIAN RAINFALL-RUNOFF COEFFICIENT

Pre-LID

Post-LID

0 0.05 0.10 0.15 0.20 0.25 0.30

TOTAL PRECIPITATION, IN INCHES

0

0.01

0.02

0.03

0.04

0.05

TOTAL RUNOFF, IN INCHES

Pre-LID

Post-LID
Field Studies of Low-Impact-Development Techniques 41

Runoff Quality

Water-quality constituent concentrations were almost 

always greater than detection levels (table 4); the only exception was TPH with 50 percent nondetects (concentrations less 

than the 2 mg/L detection limit). For the creation of concentration boxplots and calculation of loads, rare non-detects were 

replaced with values equal to one-half of their respective 

detection limits; the resulting nutrient loads were the smallest 

calculated; the single metal non-detect replaced in this manner 

resulted in a load equal to the lower quartile.

The pre- and post-installation nutrient (nitrogen and 

phosphorus) and metal analyte concentrations were not statistically different when evaluated with the Wilcoxon rank-sum 

test; the small numbers of samples made it unlikely that the 

generally small differences would be significantly different. 

Post-installation median concentrations of nitrogen and metal 

analytes were larger or about the same as pre-installation 

concentrations. The median concentrations of orthophosphorus and dissolved phosphorus (0.180 and 0.280 mg/L as P, 

respectively, before installation) decreased after LID installation (0.128 and 0.243 mg/L as P, respectively), and the median 

total phosphorus concentration increased slightly (from 0.400 

to 0.47 mg/L as P). The MPN of total coliform bacteria in preand post-LID runoff ranged widely and was not significantly 

different when evaluated with the Wilcoxon rank-sum test.

Pre- and post-LID estimated loads of nutrients, metals, 

TPH, and coliform bacteria to Silver Lake did not change in 

a consistent manner (table 5); moreover, none of the changes 

in pre- and post-LID median loads for any of the chemical 

and biological constituents were statistically significant. The 

calculated median values of loads of all nitrogen-containing 

analytes increased (fig. 30). Median values of loads of phosphorus-containing analytes decreased (fig. 31). Among the 

metal analytes Pb and Zn, median values of loads decreased, 

and the median values of loads of other metals increased 

(fig. 32). The median value of the loads of total coliform bacteria increased slightly and the median value of the loads of 

E. coli decreased somewhat.

The differences, or lack thereof, in the chemical and biological properties of pre- and post-LID storms may be a result 

of the storm sizes sampled. The median precipitation of the 

storms sampled after installation of the LID features was more 

than twice the pre-LID median storm precipitation (0.77 and 

0.36 in., respectively). A larger decrease in EIA would have 

made it more likely that changes in loads would have been 

detected. Moreover, the non-point nature of the runoff and the 

potential sources of the material, such as seasonal or, perhaps 

random, vegetation fertilization and animal and automotiveassociated contamination make it difficult to detect the effects 

of small changes in EIA during a short study period.
42 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Table 4. Concentrations of nutrients, total metals, total petroleum hydrocarbons, total coliform bacteria, and E. coli in samples 

collected at the Silver Lake Avenue runoff site in Wilmington, MA, 2005–07.

[E, estimated value less than the reporting level; <, less than; shading indicates samples collected prior to installation of low impact development enhancements; L, sample lost during processing; MPN, most probable number; >, greater than; ns, sample not collected]

Sampling

date

Nutrients (concentrations in milligrams per liter)

Dissolved

ammonia plus 

organic nitrogen,

as N

Total ammonia 

plus organic 

nitrogen,

as N

Dissolved 

ammonia,

as N

Dissolved 

nitrate plus 

nitrite,

as N

Dissolved 

nitrite,

as N

Orthophosphorus,

as P

Dissolved 

phosphorus,

as P

Total

phosphorus

8/30/2005 0.88 1.3 0.27 0.44 0.014 0.230 0.280 0.400

9/15/2005 2.2 2.8 0.45 0.68 0.027 0.270 0.440 0.600

9/29/2005 0.79 1.7 0.17 0.33 E.007 0.180 0.230 0.400

10/8/2005 0.76 1.2 0.05 <.06 <.008 0.150 0.240 0.410

11/22/2005 0.23 0.56 <.04 0.14 E.005 0.070 0.108 0.186

Median 0.79 1.3 0.17 0.33 <.008 0.180 0.240 0.400

8/21/2006 0.46 0.6 0.071 0.19 0.006 0.128 0.170 0.220

11/8/2006 1.1 1.3 <.020 0.28 0.003 0.395 0.675 0.710

11/24/2006 0.22 0.27 0.051 1.86 0.007 0.021 0.028 0.046

12/1/2006 0.62 2.2 0.127 0.56 0.011 0.013 0.033 0.500

5/16/2007 1.9 2.2 0.399 0.97 0.008 0.031 0.301 0.339

6/9/2007 1.6 2.9 0.562 1.55 0.027 0.045 0.084 0.337

8/6/2007 1.8 2.7 0.653 1.06 0.02 0.177 0.243 0.470

9/28/2007 5.5 7.9 2.32 3.58 0.736 0.223 0.360 0.780

11/3/2007 0.59 1.2 <.020 <.04 0.003 0.349 0.410 0.550

Median 1.1 2.2 0.127 0.72 0.008 0.128 0.243 0.47

Sampling

date

Total metals (concentrations in micrograms per liter) Total petroleum

hydrocarbons

(concentrations 

in milligrams

per liter)

Total coliforms and E. coli

Cadmium Chromium Copper Lead Nickel Zinc

Total coliform 

bacteria

(MPN per

100 mL)

Total E. coli

(MPN per

100 mL)

8/30/2005 0.06 E2 8.1 6.51 2.24 31 <2 >242,000 48,700

9/15/2005 0.17 4 17.5 10 4.2 76 <2 630,000 10,400

9/29/2005 0.13 3 9.4 9.59 2.33 41 2 715,000 7,470

10/8/2005 0.11 E1 11.1 5.11 2.19 53 <2 1,320 67.0

11/22/2005 0.06 E1 4.5 5.15 1.3 24 2 19,700 15,000

Median 0.11 E2 9.4 6.51 2.24 41 <2 >242,000 10,400

8/21/2006 E0.03 <2 6.8 3.09 0.97 13 3 1,250 29.0

11/8/2006 0.04 L 6 1.4 1.57 37 <2 ns ns

11/24/2006 0.07 2 3.1 1.07 0.66 9 3 ns ns

12/1/2006 0.18 7 24.7 39.9 4.71 57 6 ns ns

5/16/2007 0.12 4 10.3 12.8 3 39.1 <2 51,100 28.0

6/9/2007 0.20 2 10.7 7.84 3.2 42.1 2 381,000 4,130

8/6/2007 0.13 3 12.6 8.34 3.5 60.6 L 690,000 17,000

9/28/2007 0.17 2 26.7 7.01 5.3 132 <2 1,860,000 2,550

11/3/2007 0.10 5 22.3 3.7 8.8 62.2 <2 ns ns

Median 0.11 2 10.7 7.01 3.2 42.1 2 381,000 2,550
Field Studies of Low-Impact-Development Techniques 43

Sampling

date

Total metals (milligrams) Total

petroleum 

hydrocarbons

(grams)

Total coliforms and E. coli

Cadmium Chromium Copper Lead Nickel Zinc

Total coliform 

bacteria

(MPN)

Total E. coli

(MPN)

8/30/2005 0.19 6.42 26.01 20.90 7.19 99.55 6.42 7,770,000,000 1,560,000,000

9/15/2005 2.66 62.58 273.77 156.44 65.70 1,188.95 31.29 98,500,000,000 1,620,000,000

9/29/2005 1.60 36.87 115.52 117.85 28.63 503.85 24.58 87,800,000,000 918,000,000

10/8/2005 0.05 0.46 5.11 2.35 1.01 24.41 0.92 6,090,000 309,000

11/22/2005 1.46 24.30 109.37 125.17 31.60 583.31 48.61 4,790,000,000 365,000,000

Median 1.46 24.30 109.37 117.85 28.63 301.70 24.58 7,770,000,000 918,000,000

8/21/2006 0.44 29.19 99.26 45.10 14.16 189.76 43.79 182,000,000 4,300,000

11/8/2006 1.80 -- 269.92 62.98 70.63 1,664.52 89.97 ns ns

11/24/2006 3.37 96.32 149.29 51.53 31.79 433.43 144.48 ns ns

12/1/2006 5.97 232.34 819.83 1,324.33 156.33 1,891.91 199.15 ns ns

5/16/2007 2.68 89.36 230.09 285.94 67.02 873.46 44.68 11,400,000,000 6,200,000

6/9/2007 1.50 14.98 80.13 58.71 23.96 315.28 14.98 28,600,000,000 310,000,000

8/6/2007 0.31 7.18 30.15 19.96 8.38 145.02 -- 16,500,000,000 407,000,000

9/28/2007 0.29 3.45 46.10 12.10 9.15 227.90 3.45 32,100,000,000 44,000,000

11/3/2007 5.96 298.22 1,330.08 223.67 524.87 3,709.90 119.29 ns ns

Median 1.80 59.28 124.28 55.12 31.79 271.59 67.33 16,500,000,000 44,000,000

Table 5. Estimated loads of nutrients, total metals, total petroleum hydrocarbons, total coliform bacteria, and E. coli in samples 

collected at the Silver Lake Avenue runoff site in Wilmington, MA, 2005–07.

[Shading indicates samples collected prior to installation of low-impact-development enhancements; --, sample lost during processing; MPN, most probable 

number; ns, sample not collected]

Sampling 

date

Nutrients (grams)

Dissolved

ammonia plus 

organic nitrogen,

as N

Total ammonia 

plus organic 

nitrogen,

as N

Dissolved 

ammonia, 

as N

Dissolved 

nitrate plus 

nitrite,

as N

Dissolved 

nitrite,

as N

Orthophosphorus, 

as P

Dissolved 

phosphorus,

as P

Total

phosphorus

8/30/2005 2.83 4.17 0.87 1.41 0.04 0.74 0.90 1.28

9/15/2005 34.42 43.80 7.04 10.64 0.42 4.22 6.88 9.39

9/29/2005 9.71 20.89 2.09 4.06 0.09 2.21 2.83 4.92

10/8/2005 0.35 0.55 0.02 0.03 0.00 0.07 0.11 0.19

11/22/2005 5.59 13.61 0.97 3.40 0.12 1.70 2.62 4.52

Median 5.59 13.61 0.97 3.40 0.09 1.70 2.62 4.52

8/21/2006 6.71 8.76 1.04 2.77 0.09 1.87 2.48 3.21

11/8/2006 49.49 58.48 0.90 12.60 0.13 17.77 30.37 31.94

11/24/2006 10.60 13.00 2.46 89.58 0.34 1.01 1.35 2.22

12/1/2006 20.58 73.02 4.22 18.59 0.37 0.43 1.10 16.60

5/16/2007 42.44 49.15 8.91 21.67 0.18 0.69 6.72 7.57

6/9/2007 11.98 21.72 4.21 11.61 0.20 0.34 0.63 2.52

8/6/2007 4.31 6.46 1.56 2.54 0.05 0.42 0.58 1.12

9/28/2007 9.50 13.64 4.01 6.18 1.27 0.39 0.62 1.35

11/3/2007 35.19 71.57 1.19 2.39 0.18 20.82 24.45 32.80

Median 11.98 21.72 2.46 11.61 0.18 0.69 1.35 3.21
44 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Figure 30. Nitrogen analyte loads in runoff from storms that occurred before (Pre-LID, Aug. 2005–Feb. 2006) and after

(Post-LID, Aug. 2006–Nov. 2007) installation of low-impact-development features along Silver Lake Avenue, Wilmington, MA. 

LID, low-impact development.

EXPLANATION

Number of samples

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Data value 1.5 to 3.0 times the interquartile

range below the box

Data value greater than 3.0 times the

interquartile range above the box

5

x

o

 DISSOLVED AMMONIA

PLUS ORGANIC

NITROGEN

TOTAL AMMONIA

PLUS

ORGANIC NITROGEN

DISSOLVED

AMMONIA

NITRATE

PLUS NITRITE

NITRITE TOTAL NITROGEN

PRE-LID POST-LID PRE-LID POST-LID PRE-LID POST-LID PRE-LID POST-LID PRE-LID POST-LID PRE-LID POST-LID

0.001

0.01

0.1

10

1

100

1,000

LOAD AS NITROGEN, IN GRAMS

5 9 5 9 5 9 5 9 5 9 5 9

x

o o

x

x
Field Studies of Low-Impact-Development Techniques 45

Figure 31. Phosphorus analyte loads in runoff from storms that occurred before (Pre-LID, Aug. 2005–Feb. 2006) and 

after (Post-LID, Aug. 2006–Nov. 2007) installation of low-impact-development features along Silver Lake Avenue, 

Wilmington, MA. LID, low-impact development. 

EXPLANATION

Number of samples

Data value 1.5 to 3.0 times the interquartile

range above the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Data value 1.5 to 3.0 times the interquartile

range below the box

5

x

x

PRE-LID POST-LID PRE-LID POST-LID PRE-LID POST-LID

0.1

0.01

1

10

100

LOAD AS PHOSPHORUS, IN GRAMS 

5 9 5 9 5 9

x

x

x

x

ORTHOPHOSPHORUS DISSOLVED PHOSPHORUS TOTAL PHOSPHORUS
46 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Figure 32. Cadmium, chromium, copper, lead, nickel, and zinc loads in runoff from storms that occurred before (Pre-LID, 

Aug. 2005–Feb. 2006) and after (Post-LID, Aug. 2006–Nov. 2007) installation of low-impact-development features along 

Silver Lake Avenue, Wilmington, MA. LID, low-impact development. 

5 9 5 8 5 9 5 9 5 9 5 9

x

PRE-LID POST-LID PRE-LID POST-LID PRE-LID POST-LID PRE-LID POST-LID PRE-LID POST-LID PRE-LID POST-LID

0.01

0.1

1

10

100

LOAD, IN MILLIGRAMS

1,000

10,000

CADMIUM CHROMIUM COPPER LEAD NICKEL ZINC

EXPLANATION

Number of samples

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Data value 1.5 to 3.0 times the interquartile

range below the box

5

x
Field Studies of Low-Impact-Development Techniques 47

Green and Conventional Roofs and the Quantity 

and Quality of Stormwater Runoff

Although green roofs have been used in Europe for 

some time, they are relatively new in North America, where 

they are, however, being applied to mitigate storm runoff 

(Berghage and others, 2007). A green roof generally consists 

of four parts or layers (fig. 33)—(1) an impervious material that serves to prevent roots and water from penetrating 

the building’s roof at the bottom; (2) a sturdy drainage layer 

that allows water to pass rapidly to rooftop discharge points; 

(3) a lightweight, but highly absorbent, growing medium that 

provides the substrate for plants; and (4) drought-resistant vegetation. Green roofs are reportedly able to substantially reduce 

stormwater runoff volume and attenuate flow when compared 

to conventional roofs. The roof’s plants and growing medium, 

through evapotranspiration and absorption, make runoff reduction and attenuation possible; the growing medium may also 

neutralize acidic precipitation through its inherent buffering 

capacity.

In Ipswich, MA, a 3,000-ft2 green roof was designed 

by K.J. Savoie Architecture and installed by Magco, Inc., a 

Tecta America company, on an existing building, the Whipple 

Annex, which was undergoing rehabilitation to serve as senior 

housing. Initial plantings on the green roof took place in 

September 2006; some additional material was added in 2007 

to replace plants that had died. The plants included eight species of Sedum, Talinum calycinum (fameflower), and Allium 

schoenoprasum (chive). The starting date for water-quality 

sampling was delayed until late summer of 2007, after the 

vegetation became established (fig. 34). However, because of 

an extended rain-free period, the first samples were collected 

in October 2007. In order for the vegetation on the green roof 

to become established, fertilizers were applied during the first 

2 years of development, which matched the period of this 

study. Detailed records of the specific types of fertilizers and 

their application schedules were not available for inclusion in 

this assessment. In general, the fertilizers were slow-release 

varieties. Six maintenance visits occurred during the first 2 

years, three each summer. Fertilizer was applied at least once 

each summer.

Runoff water quantity and quality from this green roof 

were compared with runoff from a 5,340-ft2 section of the 

neighboring Ipswich Town Hall roof that has a conventional 

rubber-membrane roof (fig. 35) and with water quality in bulk 

precipitation (rain) falling on the conventional roof. Waterquality constituents examined in this study included nutrients 

(nitrogen and phosphorus), total metals (Cd, Cr, Cu, Pb, Ni, 

and Zn), and TPH.

Monitoring Approach

Installation of the monitoring equipment took place 

in two stages. While the Whipple Annex was undergoing 

reconstruction and remodeling in autumn 2006, equipment 

was installed at the Ipswich Town Hall. The Town Hall had no 

outside drains from the roof so its indoor, 30-ft vertical downspout was modified to incorporate a short, nearly horizontal 

section of PVC pipe fitted with v-notch weir with a bubble line 

used to record stage for conversion to flow data (fig. 36). The 

Figure 33. Structural features of a typical green roof. Schematic (modified) courtesy of Angela Durhman, Tecta America 

Corp. 

PERFORATED DIVIDER

DROUGHT-RESISTANT

VEGETATION

GROWING MEDIUM (SOIL)

DRAINAGE BOARD

ROOFING MEMBRANE

INSULATION

WOOD 

BLOCKING

WALL

ROOF DECK

FILTER FABRIC

STONE BALLAST

12 to 18 inches

wide
48 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Figure 34. (A) Partially developed vegetation in summer 2007 and (B) well-developed vegetation in autumn 2008 on the 

Whipple Annex green roof, Ipswich, MA.

B

A
Field Studies of Low-Impact-Development Techniques 49

Figure 35. Rubber-membrane roof on the Ipswich, MA, Town Hall with drains leading into the building and to the 

runoff-monitoring and sampling system.

Drain

Drain
50 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Figure 36. Roof-runoff flow-monitoring and sampling system in the Ipswich Town Hall, Ipswich, MA.

Computer

Automated

water sampler

Sample

bottle Battery

Weir Sampling

tube

Piping from roof

small “pool” behind the weir provided a water-quality-sample 

collection point.

All runoff from the slightly pitched, 3,000-ft2 Whipple 

Annex green roof drained to a 100-ft-long gutter system 

attached to the eastern side of the building with three 4-in2, 

vertical, aluminum downspouts. Drainage from these three 

aluminum outlets was routed to a central junction using 4-in.-

diameter polyvinyl chloride (PVC) pipe (fig. 37). Total green 

roof drainage then passed through a 10-ft section of 6-in. PVC 

pipe to another 4-in. PVC section containing a v-notch weir 

and eventually discharged through a 4-in. PVC level spreader 

designed to reduce potential erosion (fig. 37). Preparatory 

work at the Whipple Annex was completed in December 2006.

Both rooftop monitoring systems were equipped with 

the bubble line and datalogger to measure and record water 

level. The level-to-flow relation from the volumetric weir 

allowed calculation of discharge to support flow-proportional 

sampling with a Teledyne ISCO 6700 autosampler. The automated samplers were programmed to collect a maximum of 

10 flow-proportional stormwater samples per storm based on 

forecasted precipitation amounts for each storm. Samples were 

collected in pre-cleaned 10-liter Teflon bags installed inside 

polyethylene containers. Containers were kept chilled throughout sampling period until they were retrieved. Site visits were 

made monthly or during storm sampling periods to check the 

condition of the weirs, the performance of instrumentation, 

and to prepare for water-quality sampling.

The Ipswich Town Hall stage and gymnasium complex was host to many different sporting events and social 

programs. Although precautions were taken to avoid it, the 

circuit breaker supplying power to the monitors and sampling 

equipment was occasionally shut down by other users of the 

complex, causing periodic power losses, until battery backup 

units were installed in autumn 2007.

The data record for the conventional-roof runoff began on 

January 31, 2007, and the Green roof drainage record began 

on June 21, 2007. Measurements were recorded at 15-min. 

intervals. Both roof runoff records end on November 17, 2008. 

Data losses occurred at the Whipple Annex site during the following periods: (1) July 8 to August 16, 2007, (2) October 6 

to 23, 2007, (3) November 14, 2007, to February 4, 2008, and 

(4) July 10 to 23, 2008. The first two data gaps were attributed 

to power losses. The third data gap was the result of the datalogger software failure requiring repair by the manufacturer, 

and the fourth data loss was attributed to user error. Extremely 

high stage values during February and March 2008 coincided 

with icing. Icing was also observed in December 2007. Only 

one period of data loss at the Ipswich Town Hall site occurred 

during the period of record from July 8 to August 9, 2007.

A continuous precipitation gage and logger also were 

installed on the Ipswich Town Hall next to the runoff section of the roof. Continuous measurements of precipitation 

and roof runoff from both roof types began in June 2007 

and were discontinued in October 2008. Three gaps in the 

Town Hall precipitation record occurred from (1) December 21, 2007, to February 2, 2008, (2) May 21 to 22, 2008, 

and (3) July 4 to 24, 2008. The first data gap was associated 

with a power loss in the heater funnel, the second resulted 

from a logger power loss, and the third was caused by a seed 

lodged in the precipitation gage’s tipping bucket mechanism. 
Field Studies of Low-Impact-Development Techniques 51

Gaps in the precipitation record were filled by substituting 

the precipitation record from the Ipswich Fire Department 

located approximately 0.38 mi east of Town Hall. Ten flowproportional, storm-runoff composite samples were collected. 

After water-quality samples were retrieved, they were stored 

on ice at 4°C for transportation and processing. After processing, the samples were shipped to the USGS National Water 

Quality Laboratory (NWQL) for analysis. The only exception 

to this procedure was for TPH samples collected after January 

1, 2008; starting at that time, all USGS samples were sent to 

a contract laboratory, TestAmerica Laboratories (TAL), Inc., 

in Arvada, CO, for analysis. TAL’s reporting level for TPH 

was 5.0 mg/L (versus 2.0 mg/L for the NWQL). Background 

TPH concentrations in TAL laboratory blanks associated with 

environmental samples were unacceptably high, with one 

exception—the green roof environmental sample collected on 

July 23, 2008; therefore, the data are reported in the tables but 

are not interpreted.

In this study, small storms tended to generate inadequate 

volumes of runoff for water-quality samples and, subsequently, there were no chemical analyses for small storms. 

Thus, the study did not account for the reduction in constituent load that occurred by virtue of the absence of runoff from 

small storms.

Comparison of Conventional and Green Roof 

Runoff Quantity and Quality

The growing medium installed on the green roof is capable of absorbing about 1 in. of precipitation (Angela Durhman, 

Green Roof Manager, Tecta America Corp., oral commun., 

2008). The actual amount absorbed for a given storm will 

depend on several factors, including antecedent conditions, 

total rainfall and its duration, and temperature. When considering roof runoff, the concept of storm intensity (rainfall 

divided by duration) may not be as important a factor as it is in 

natural landscape drainage. On a roof, all precipitation drains 

downward; it cannot become diffuse surface runoff when the 

intensity exceeds the infiltration capacity of the soil.

Runoff data were collected on a more-or-less continuous 

basis throughout the study period. Storms targeted for waterquality sampling were expected to produce runoff from the 

green roof to provide sample volumes sufficient for analyses of all target analytes because the absorption and storage 

capacity of the green roof soil medium during minor rainfall 

events with dry antecedent conditions should result in little or 

no runoff. Storms that were anticipated to produce runoff from 

the green roof did not always produce adequate volumes of 

water for analysis of the complete suite of nutrients, metals, 

Figure 37. Roof-runoff flow-monitoring and sampling system during assembly at the Whipple Annex, 

Ipswich, MA. Three downspouts were joined to create a single monitoring location next to the green 

equipment box. A level spreader with multiple drainage holes ensured that runoff passing through the 

collection system would not cause erosion.

Field Box (containing 

automated water sampler)

Level spreader (perforated pipe)

Observation tube
52 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

and TPH, resulting in additional storm sampling or incomplete 

suites of analytes for some storms.

Roof-Runoff Quantity

In all, roof runoff from 118 storms was examined. Storms 

producing less than 0.04 in. of rain were not included because 

they yielded minimal runoff that could not be measured with 

sufficient accuracy. Storms during freezing conditions and 

affected by snow melt also were not considered in this analysis. Storms that produced runoff from the rubber-membrane 

roof that was not within ±15 percent of the expected volume determined from the rainfall volume also were rejected 

because of the measurement error in the runoff or precipitation, or both. Of the remaining 70 storms, those with runoff 

volumes within 15 percent of the expected runoff volume from 

the rubber-membrane roof were used in these analyses, providing 30 storms for comparisons between the rubber-membrane 

and green roofs. Data from 40 other storms were of sufficient 

quality for use in examining runoff characteristics of the green 

roof alone.

The ability of a vegetated green roof to retain precipitation was the focus of this part of the study. Several factors 

can affect the volume retained and the attenuation of runoff; 

the amount and duration of precipitation and antecedent dry 

conditions are the most obvious. The effects of these factors 

were examined for five individual storms of varying precipitation totals, duration, and antecedent conditions. Storm runoff 

from the roofs was determined from the start of precipitation 

until runoff stopped or until 6 hours after precipitation ended, 

if runoff from the green roof had not stopped. In order to compare storm runoff from the rubber-membrane and green roofs 

and evaluate retention by the green roof, data are presented 

in pairs of graphs (figs. 38 to 42). The first graph of each pair 

depicts standard hydrographs for runoff from the two roofs 

and a hyetograph of the rainfall. The second graph presents 

double-mass curves for the same data. The double-mass 

curves represent the cumulative-percentage data over time for 

total precipitation and for total calculated, or potential, runoff 

that fell on each roof based on measured precipitation; that is, 

their differences are normalized by percentage of roof area. In 

theory, the runoff from the rubber-membrane roof would equal 

the total precipitation, but measurement error may cause slight 

deviations from expected values. Green roof runoff is normalized to the amount that was expected to fall on it, given its 

having about 45 percent less area than the rubber-membrane 

roof. The final percentage of runoff is the complement of the 

percentage retained.

Runoff from the rubber-membrane roof responds directly 

to the rate of precipitation and does not vary by antecedent 

conditions. The runoff response to precipitation on the green 

roof varies by the size of the storm and antecedent conditions, 

as exemplified in the five examples that follow.

The first storm under consideration here occurred on 

September 27, 2007. After an antecedent dry period of nearly 

300 hours, a storm of 1-hour duration and totaling 0.13 in. of 

precipitation resulted in a maximum runoff of about 0.02 ft3

from the rubber-membrane roof (fig. 38A). Runoff from the 

green roof generated by this storm started about 0.5 hours 

later, producing a maximum discharge of less than 0.001 ft3. 

A total of 61 ft3 ran off the rubber-membrane roof, and about 

3.3 ft3 ran off the green roof. The percentage of the total cumulative runoff from the rubber-membrane roof slightly exceeded 

the total cumulative precipitation because of some minor 

measurement errors, likely because the rate of flow exceeded 

the accuracy limits of the instruments or because of hysteresis 

effects, whereas the mass of runoff from the green roof was 

less than 10 percent of the total rainfall (fig. 38B).

Storms (figs. 39 and 40) on September 9, 2007, and 

October 26, 2008, were of moderate size—0.61 and 0.78 in. 

of total precipitation, and 16.75 and 7.25 hours in duration. 

The storms differed considerably in their antecedent conditions; the times since the previous precipitation were about 

532 and 87 hours for the September 29, 2007, and October 26, 

2008, storms, respectively. Both storms had two precipitation 

episodes reflected in the hydrographs and double-mass curves 

for each roof. Although the October 26 storm’s relatively short 

duration resulted in an average intensity about 3 times greater 

than that of the September 9 storm (0.108 and 0.036 in/h, 

respectively), differences in the green roof runoff responses 

are attributed mostly to antecedent conditions. The time since 

the last rainfall was about 6 times longer for the September 9 

storm than for the October 26 storm, which resulted in less 

available storage leading into the October 26 storm. Runoff 

from the green roof was delayed about 1 hour from the start 

of precipitation from both storms (figs. 39A, 40A). Runoff 

from the green roof’s first episode of precipitation was more 

pronounced for the October 26 storm than for the September 9 storm with respect to the amount of precipitation from 

each storm and during each part of the storm, a reflection of 

the greater intensity of early part of the October 26 storm. 

The September 9 storm produced a total of 273 ft3 of runoff 

from the rubber-membrane roof and about 13 ft3 of runoff 

from the green roof; overall, the green roof retained about 

85 percent of the precipitation that fell on it (fig. 39B). The 

October 26 storm produced 357 ft3 of runoff from the rubbermembrane roof and about 55 ft3

 from the green roof; overall, 

the green roof retained about 70 percent of the total precipitation (fig. 40B).

Two of the largest storms during the study period began 

on September 11, 2007, and September 26, 2008. The September 11, 2007, storm (fig. 41) left 1.27 in. of precipitation and lasted 7.5 hours; the storm was preceded by two 

smaller storms of 0.11 and 0.61 in. that occurred about 10 and 

32 hours earlier, respectively. The initial, light precipitation 

on September 11 did not generate runoff, but runoff increased 

rapidly about 2 hours into the storm because the available 

storage was likely filled from the recent preceding storms and 

initial rainfall from this storm. As a result of the depleted storage, the green roof was able to retain only about 20 percent of 

the total storm precipitation volume (fig. 41B).
Field Studies of Low-Impact-Development Techniques 53

Figure 38. (A) Precipitation on and runoff from conventional rubber and green roofs in Ipswich, MA, for the 

storm of September 27, 2007, and (B) cumulative percentages of total precipitation and total runoff from the 

roofs for the same storm.

9/28/07 02:30

9/28/07 03:15

9/28/07 04:00

9/28/07 04:45

9/28/07 05:309/27/07 22:00

9/27/07 22:45

9/27/07 22:30

9/28/07 00:15

9/28/07 01:00

9/28/07 01:45

9/28/07 02:30

9/28/07 03:15

9/28/07 04:00

9/28/07 04:45

9/28/07 05:30

9/27/07 22:00

9/27/07 22:45

9/27/07 22:30

9/28/07 00:15

9/28/07 01:00

9/28/07 01:45

DATE AND TIME

0

0.010

0.020

0.030

0.040

0.050

0.060

PRECIPITATION, IN INCHES

0

0.005

0.015

0.010

0.020

0.025

RAINFALL RUNOFF, IN CUBIC 

FEET PER SECOND

0

20

40

60

80

100

PERCENTAGE OF TOTAL

Precipitation, in inches

Town Hall runoff from rubber roof

Whipple Annex runoff from green roof

Precipitation

Town Hall runoff from rubber roof

Whipple Annex runoff from green roof

A

B

0.13-inch storm, 298.5-hour antecedent dry period, 1.00-hour duration, and 0.13-inch-per-hour intensity

0.13-inch storm, 298.5-hour antecedent dry period, 1.00-hour duration, and 0.13-inch-per-hour intensity
54 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Figure 39. (A) Precipitation on and runoff from conventional rubber and green roofs in Ipswich, MA, for the storm of 

September 9, 2007, and (B) cumulative percentages of total precipitation and total runoff from the roofs for the same 

storm.

9/9/07 5:45

9/9/07 6:30

9/9/07 7:15

9/9/07 8:00

9/9/07 8:45

9/9/07 9:30

9/9/07 10:15

9/9/07 11:00

9/9/07 11:45

9/9/07 12:30

9/9/07 13:15

9/9/07 14:00

9/9/07 14:45

9/9/07 15:30

9/9/07 16:15

9/9/07 17:00

9/9/07 17:45

9/9/0718:30

9/9/07 19:15

9/9/07 20:00

9/9/07 20:45

9/9/07 21:30

9/9/07 22:15

9/9/07 5:45

9/9/07 6:30

9/9/07 7:15

9/9/07 8:00

9/9/07 8:45

9/9/07 9:30

9/9/07 10:15

9/9/07 11:00

9/9/07 11:45

9/9/07 12:30

9/9/07 13:15

9/9/07 14:00

9/9/07 14:45

9/9/07 15:30

9/9/07 16:15

9/9/07 17:00

9/9/07 17:45

9/9/0718:30

9/9/07 19:15

9/9/07 20:00

9/9/07 20:45

9/9/07 21:30

9/9/07 22:15

DATE AND TIME

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

RAINFALL RUNOFF, IN CUBIC 

FEET PER SECOND

0

0.05

0.10

0.15

0.20

0.25

PRECIPITATION, IN INCHES

0

20

40

60

80

100

PERCENTAGE OF TOTAL

Precipitation, in inches

Town Hall runoff from rubber roof

Whipple Annex runoff from green roof

Precipitation

Town Hall runoff from rubber roof

Whipple Annex runoff from green roof

A

B

0.61-inch storm, 531.5-hour antecedent dry period, 16.75-hour duration, 

and 0.036-inches-per-hour intensity

0.61-inch storm, 531.5-hour antecedent dry period, 16.75-hour duration, 

and 0.036-inches-per-hour intensity
Field Studies of Low-Impact-Development Techniques 55

Figure 40. (A) Precipitation on and runoff from conventional rubber and green roofs in Ipswich, MA, for 

the storm of October 26, 2008, and (B) cumulative percentages of total precipitation and total runoff from the 

roofs for the same storm.

10/26/08 2:30

10/26/08 1:0010/26/08 1:4510/26/08 0:1510/26/08 5:3010/26/08 4:0010/26/08 4:4510/26/08 3:1510/26/08 13:00

10/26/08 13:45

10/26/08 12:15

10/26/08 8:3010/26/08 7:0010/26/08 7:4510/26/08 6:15

10/26/08 11:3010/26/08 10:0010/26/08 10:4510/26/08 9:15

DATE AND TIME

10/26/08 2:3010/26/08 1:0010/26/08 1:4510/26/08 0:1510/26/08 5:3010/26/08 4:0010/26/08 4:4510/26/08 3:1510/26/08 13:00

10/26/08 13:45

10/26/08 12:15

10/26/08 8:30

10/26/08 7:00

10/26/08 7:45

10/26/08 6:1510/26/08 11:3010/26/08 10:0010/26/08 10:45

10/26/08 9:15

0.00

0.01

0.02

0.03

0.04

0.05

0.06

RAINFALL RUNOFF, IN CUBIC 

FEET PER SECOND

0

20

40

60

80

100

PERCENTAGE OF TOTAL

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

PRECIPITATION, IN INCHES

Precipitation, in inches

Town Hall runoff from rubber roof

Whipple Annex runoff from green roof

Precipitation

Town Hall runoff from rubber roof

Whipple Annex runoff from green roof

A

B

0.78-inch storm, 87-hour antecedent dry period, 7.25-hour duration, and 0.108-inch-per-hour intensity

0.78-inch storm, 87-hour antecedent dry period, 7.25-hour duration, and 0.108-inch-per-hour intensity
56 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Figure 41. (A) Precipitation on and runoff from conventional rubber and green roofs in Ipswich, MA, for 

the storm of September 11, 2007, and (B) cumulative percentages of total precipitation and total runoff 

from the roofs for the same storm.

9/11/07 11:309/11/07 12:009/11/07 12:309/11/07 13:009/11/07 13:309/11/07 14:009/11/07 14:309/11/07 15:00

9/11/07 15:309/11/07 16:009/11/07 16:309/11/07 17:009/11/07 17:309/11/07 18:009/11/07 18:309/11/07 19:009/11/07 19:30

9/11/07 20:00

9/11/07 20:30

9/11/07 11:30

9/11/07 12:009/11/07 12:309/11/07 13:00

9/11/07 13:309/11/07 14:009/11/07 14:30

9/11/07 15:00

9/11/07 15:309/11/07 16:009/11/07 16:309/11/07 17:009/11/07 17:30

9/11/07 18:00

9/11/07 18:30

9/11/07 19:00

9/11/07 19:309/11/07 20:00

9/11/07 20:30

DATE AND TIME

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

PRECIPITATION, IN INCHES

0.00

0.09

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

RAINFALL RUNOFF, IN CUBIC 

FEET PER SECOND

0

20

40

60

80

100

PERCENTAGE OF TOTAL

Precipitation, in inches

Town Hall runoff from rubber roof

Whipple Annex runoff from green roof

Precipitation

Town Hall runoff from rubber roof

Whipple Annex runoff from green roof

A

B

1.27-inch storm, antecedent dry period 9.75 hours since 0.11-inch event and 32.25 hours since 

0.61-inch event, 7.5-hour duration and 0.169-inch-per-hour intensity

1.27-inch storm, antecedent dry period 9.75 hours since 0.11-inch event and 32.25 hours since 

0.61 inch event, 7.5-hour duration and 0.169-inch-per-hour intensity
Field Studies of Low-Impact-Development Techniques 57

Figure 42. (A) Precipitation on and runoff from conventional rubber and green roofs in Ipswich, MA, for the 

storm of September 26, 2008, and (B) cumulative percentages of total precipitation and total runoff from the 

roofs for the same storm.

DATE AND TIME

9/26/08 6:309/26/08 7:309/26/08 8:309/26/08 9:309/27/08 0:309/27/08 1:309/27/08 2:30

9/27/08 3:309/27/08 4:309/27/08 5:30

9/27/08 6:30

9/26/08 10:309/26/08 11:309/26/08 12:309/26/08 13:30

9/26/08 14:309/26/08 15:309/26/08 16:309/26/08 17:309/26/08 18:309/26/08 19:309/26/08 20:309/26/08 21:309/26/08 22:309/26/08 23:30

9/26/08 6:309/26/08 7:309/26/08 8:30

9/26/08 9:30

9/27/08 0:30

9/27/08 1:309/27/08 2:309/27/08 3:30

9/27/08 4:30

9/27/08 5:309/27/08 6:30

9/26/08 10:30

9/26/08 11:30

9/26/08 12:30

9/26/08 13:30

9/26/08 14:30

9/26/08 15:30

9/26/08 16:30

9/26/08 17:30

9/26/08 18:30

9/26/08 19:30

9/26/08 20:30

9/26/08 21:30

9/26/08 22:309/26/08 23:30

PRECIPITATION, IN INCHES

0

0.05

0.10

0.15

0.20

0.25

PERCENTAGE OF TOTAL

0

20

40

60

80

100

RAINFALL RUNOFF, IN CUBIC 

FEET PER SECOND

0.00

0.02

0.04

0.06

0.08

0.10

0.12

Precipitation

Town Hall runoff from rubber roof

Whipple Annex runoff from green roof

Precipitation, in inches

Town Hall runoff from rubber roof

Whipple Annex runoff from green roof

B 2.79-inch storm, 105-hour antecedent dry period, 17.5-hour duration, and 0.17-inch-per-hour intensity

A 2.79-inch storm, 105-hour antecedent dry period, 17.5-hour duration, and 0.17-inch-per-hour intensity
58 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

The September 26, 2008, storm was about twice as large 

in terms of total precipitation (2.97 in.) as the September 11, 

2007, storm. The September 26, 2008, storm was characterized by 17.5 hours of duration and intensity of about 0.17 in/h 

(fig. 42), about the same intensity as the September 11, 2007, 

storm. The antecedent dry period of the September 26, 2008, 

storm (105 hours) was distinctly longer than that of the September 11, 2007, storm, producing a much different runoff 

response from the green roof. The initial rain on September 

26, 2008, did not produce a measurable runoff response from 

the green roof for about 4 hours; whereas, the initial precipitation on September 11, 2007, which was considerably less 

than the precipitation on September 26, produced a more 

marked response about 1.5 hours after the start of the storm. 

Even though the September 26, 2008, storm had about 2.5 

times the amount of precipitation, the green roof retained 

about 60 percent of the total precipitation (fig. 42B), or about 

20 percent more than the September 11, 2007, storm.

The five example storms indicate how general characteristics yield differing runoff responses from the green roof over 

a wide range of storms (table 6). Clearly, total precipitation 

and antecedent dry period play the most important roles in 

water retention on the green roof. There is a finite amount of 

precipitation that the soil medium can retain, and this amount 

is affected by the amount of water that may remain from previous storms, which is a function of the time since and amount 

of previous precipitation. Retention is also a function of potential evapotranspiration during the antecedent dry period that 

changes seasonally. Thus, the green roof retained about 70 to 

90 percent of the precipitation from the September 27, 2007, 

September 9, 2007, and October 26, 2008, storms. About 

60 percent of the precipitation in the largest storm (September 

26, 2008) was retained by the green roof, but in a storm with 

less than half that precipitation (September 11, 2007), the 

green roof retained only about 20 percent of the precipitation 

because of wet antecedent conditions.

A broader view of the green roof performance was 

obtained by comparing general storm characteristics to runoff 

volume from the 70 storms used for analysis. The percentage 

of runoff retained is directly related to the available volume 

that can be stored in the green roof growing medium (and 

its associated vegetation). The percentage of precipitation 

retained in relation to total precipitation (fig. 43) varies from 

nearly zero to 100 percent for storms less than 1 in., which 

is the green roof’s design capacity. Oddly, for a storm with 

nearly 2.0 in. of precipitation, with an antecedent dry period 

of about 376 hours, nearly all the precipitation was retained by 

the green roof, indicating that the roof may have nearly twice 

the storage capacity of the design. Other possible explanations are precipitation or runoff measurement errors, or both. 

For other large storms, the roof did not exhibit similar runoff retention, which is consistent with the green roof design 

capacity.

In general, the green roof retained less than 50 percent 

of the precipitation from relatively few storms (21 of 70); 

most of those storms had short antecedent dry periods (less 

than 70 hours since last precipitation; fig. 44). For the most 

part, more than 50 percent of the rainfall from storms of less 

than 0.10 in. of precipitation was retained by the green roof, 

regardless of the antecedent dry period. Nearly half (34) of the 

storms fell in the category of 0.10 to 0.49 in. of precipitation; 

the green roof retained more than 50 percent of the precipitation in all but nine of these storms. Antecedent dry periods and 

total storm precipitation do not explain all of the variability in 

retention. The discrepancy indicates that neither the precipitation volume nor the potential evapotranspiration that largely 

control the available storage during the antecedent period are 

fully accounted for.

Roof-Runoff Quality

Unlike the examination of stormwater-runoff water 

quality at Silver Lake Avenue, the major considerations for 

roof-runoff water quality are not differences in constituent 

loads between a green roof and a conventional roof, but in 

the ability of a green roof to retain the chemical constituents 

of precipitation. Runoff water quality from the green roof 

was characterized by higher median concentrations of several 

nutrient constituents (total organic nitrogen, total phosphorus, 

and dissolved phosphorus) and metals (Cd and Cu) than were 

detected in either runoff from the rubber-membrane roof or 

from bulk precipitation (figs. 45, 46); the bulk precipitation 

samples generally had the lowest concentrations of the nutrients and metal analytes. Leaching of phosphorus and nitrogen 

from green roofs has been reported elsewhere (Oberndorfer 

and others, 2007; Dietz, 2007). More germane to this study 

than nutrient leaching is the documentation that the green roof 

vegetation was fertilized at least once each summer, although 

complete records of the summer fertilization schedule were 

not kept. While it may be possible to evaluate the composition 

of the fertilizers used and even the recommended application 

rate, the actual quantities of fertilizer applied cannot be determined. Thus, any water-quality results reported for this part of 

the study refer to the differences among the rubber-membrane 

roof, bulk precipitation, and the fertilized green roof.

The chemical composition of the growing medium on the 

green roof is likely to have affected the chemical composition 

of runoff. The green roof growing medium is composed of 

crushed clay (70 to 80 percent by volume) and 20 to 30 percent organic matter (Angela Durhman, Green Roof Manager, 

Tecta America Corp., written commun., 2008). The chemical composition is not known, but this growing medium and 

the plants themselves compose sources of nutrients required 

for growth. In addition to the standard blank and replicate 

samples, a sample of the growing medium was collected and 

brought to the laboratory at the USGS Massachusetts-Rhode 

Island Water Science Center; 18.01 g of material were placed 

in a beaker containing 3 L of deionized water for 13 days. 

Samples of this water were collected and shipped to the 

NWQL or TAL for analysis of nutrients, metals, and TPH. The 

analyses of these samples reveal the growing medium to be 

a potential source of nutrients, phosphorus in particular, and 
Field Studies of Low-Impact-Development Techniques 59

Table 6. Characteristics of five selected storms and runoff from the rubber roof on Town Hall and from the green roof on Whipple 

Annex, Ipswich, MA, 2007–08.

[in/hr, inches per hour; >, greater than]

Storm date

Total

precipitation

(inches)

Antecedent

dry period

(hours)

Storm

intensity

(in/hr)

Percent 

retention

Town Hall

runoff

(cubic feet)

Whipple Annex

runoff

(cubic feet)

September 27, 2007 0.13 298.5 0.13 >90 61 3.3

September 9, 2007 0.61 531.5 0.036 85 273 13

October 26, 2008 0.78 87 0.108 70 357 55

September 11, 2007 1.27 9.75 0.169 20 569 251

September 26, 2008 2.97 105 0.17 60 1,274 295

Figure 43. Percentage of precipitation retained by the Whipple Annex green roof in Ipswich, MA, in relation to total 

precipitation depth for storms that were monitored from June 2007 through November 2008. Grey-shaded area indicates 

storms that produced precipitation of less than 1 in. 

TOTAL PRECIPITATION DEPTH, IN INCHES

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

PERCENTAGE OF PRECIPITATION RETAINED

0

40

60

80

100

20
60 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Figure 44. Percentage of precipitation retained by the Whipple Annex green roof in Ipswich, MA, in relation to the 

length of the antecedent dry period and the total amount of precipitation for storms that were monitored from June 

2007 through November 2008.

0 100 200 300 400 500 600

PERIOD, IN HOURS

0

20

40

60

80

100

PERCENTAGE OF PRECIPITATION RETAINED

0.0 to 0.09

0.1 to 0.49

0.5 to 0.99

1.0 to 1.99

greater than 1.99

Total precipitation, in inches

EXPLANATION
Field Studies of Low-Impact-Development Techniques 61

EXPLANATION

Number of samples

Data value greater than 3.0 times the

interquartile range above the box

Data value 1.5 to 3.0 times the interquartile

range above the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Data value 1.5 to 3.0 times the interquartile

range below the box

5

x

x

o

BULK

PRECIPITATION

WHIPPLE ANNEX

GREEN ROOF

TOWN HALL

RUBBER ROOF

BULK

PRECIPITATION

WHIPPLE ANNEX

GREEN ROOF

TOWN HALL

RUBBER ROOF

BULK

PRECIPITATION

WHIPPLE ANNEX

GREEN ROOF

TOWN HALL

RUBBER ROOF

BULK

PRECIPITATION

WHIPPLE ANNEX

GREEN ROOF

TOWN HALL

RUBBER ROOF

BULK

PRECIPITATION

WHIPPLE ANNEX

GREEN ROOF

TOWN HALL

RUBBER ROOF

0.05

0.1

0.5

1

NITRATE PLUS NITRITE, IN MILLIGRAMS

PER LITER AS NITROGEN

0.001

0.01

0.1

1

10

DISSOLVED PHOSPHORUS, IN MILLIGRAMS

PER LITER AS PHOSPHORUS

0.01

0.05

0.5

0.1

1

5

DISSOLVED AMMONIA, IN MILLIGRAMS

PER LITER AS NITROGEN

0.01

0.1

1

10

TOTAL PHOSPHORUS, IN MILLIGRAMS

PER LITER

0.1

0.5

1

5

10

TOTAL NITROGEN, IN MILLIGRAMS

 PER LITER

o

x

x

x

x

x

o

x

x

x

o

x

5 5 5 5 5 5

5 5 5 5 5 5

5 5 5 E

C D

A B

Figure 45. Concentrations of (A) total nitrogen, (B) total phosphorus, (C) dissolved ammonia nitrogen, (D) dissolved phosphorus, and 

(E) nitrate plus nitrite nitrogen in bulk precipitation and in runoff from the town hall rubber roof and the Whipple Annex green roof, 

Ipswich, MA, June 2007 through November 2008.
62 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

EXPLANATION

Number of samples

Data value greater than 3.0 times the

interquartile range above the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Data value 1.5 to 3.0 times the interquartile

range below the box

5

x

o

BULK

PRECIPITATION

WHIPPLE ANNEX

GREEN ROOF

TOWN HALL

RUBBER ROOF

BULK

PRECIPITATION

WHIPPLE ANNEX

GREEN ROOF

TOWN HALL

RUBBER ROOF

BULK

PRECIPITATION

WHIPPLE ANNEX

GREEN ROOF

TOWN HALL

RUBBER ROOF

BULK

PRECIPITATION

WHIPPLE ANNEX

GREEN ROOF

TOWN HALL

RUBBER ROOF

BULK

PRECIPITATION

WHIPPLE ANNEX

GREEN ROOF

TOWN HALL

RUBBER ROOF

1

10

100

1,000

TOTAL LEAD, IN MICROGRAMS

PER LITER

0.1

1

10

100

1,000

TOTAL COPPER, IN MICROGRAMS

PER LITER

0.1

1

10

100

1,000

10,000

TOTAL ZINC, IN MICROGRAMS

PER LITER

0.05

0.1

0.5

1

TOTAL NICKEL, IN MICROGRAMS

PER LITER

0.005

0.05

0.5

TOTAL CADMIUM, IN MICROGRAMS

PER LITER

o

x

x

5 5 5 5 5 5

5 5 5

5 5 5 5 5 5

E

C D

A B

Figure 46. Concentrations of (A) total cadmium, (B) total copper, (C) total nickel, (D) total lead, and (E) total zinc in bulk precipitation and 

in runoff from the town hall rubber roof and the Whipple Annex green roof, Ipswich, MA, June 2007 through November 2008.
Field Studies of Low-Impact-Development Techniques 63

metals, with copper and zinc having the highest concentrations 

among the metals (table 2).

Results of analyses of quality-control replicate samples 

(6 blanks and 3 field replicates) collected during the roof study 

(table 2) were consistent with results from the environmental 

samples. Two analytes in separate environmental samples and 

their replicates, dissolved ammonia on July 9, 2008, and total 

nickel on October 21, 2008, had high relative percent difference (RPD) values (56.8 and 21.1 percent, respectively); other 

RPDs were less than 10 percent or could not be calculated 

because at least one value was less than the reporting level and 

(or) detection limit. The rare high RPD values do not detract 

from the overall consistency and quality of the data.

As in the calculations for Silver Lake runoff concentration boxplots and loads, the rare non-detects were replaced 

with values equal to half of their respective detection limits. 

This substitution had little effect on the nutrient calculations 

(the estimated loads were generally among the lowest values 

calculated). Cu in the bulk precipitation was the only metal 

affected, and the loads were small.

Median total and dissolved phosphorus concentrations in 

the green roof runoff were approximately one to two orders 

of magnitude greater than in either the rubber-membrane 

roof runoff or the bulk precipitation (figs. 45B, D). Median 

concentrations of most nitrogen analytes in runoff from the 

green roof were generally greater than in bulk precipitation 

or in runoff from the rubber-membrane roof (table 7); most of 

these differences were not statistically significant. Exceptions 

to this observation were the concentrations of total nitrogen, 

dissolved ammonia, and nitrate plus nitrite (figs. 45A, C, 

E). Median concentrations of total nitrogen from the green 

roof, rubber-membrane roof, and bulk precipitation were 

all statistically different from each other; the relatively high 

concentrations in green roof runoff could be due to breakdown 

of plant matter or release from the growing medium. Median 

concentrations of dissolved ammonia in runoff from the green 

roof were smaller than in either rubber-membrane roof runoff 

or bulk precipitation (fig. 45C); the relatively low concentrations may result from rapid absorption by the growing medium 

or by the vegetation. Dissolved nitrate plus nitrite median 

concentrations in green roof and rubber-membrane roof runoff 

were approximately equal, and both medians were greater 

than the median for bulk precipitation (fig. 45E). Differences 

among the median ammonia and nitrate plus nitrite concentrations were not statistically significant.

Median concentrations of Cd, Cu, and Ni were all substantially greater in runoff from the green roof than in rubbermembrane roof runoff or in bulk precipitation; however, only 

the Cd and Cu differences were statistically significant. On 

the other hand, the median concentration of Pb in the rubbermembrane roof runoff was two or more orders of magnitude 

greater than in bulk precipitation or in green roof runoff 

(fig. 46D); these differences were statistically significant. 

Median concentrations of Zn from the green and rubbermembrane roofs were about the same (fig. 46E), but both 

were more than an order of magnitude greater than in the bulk 

precipitation; the latter differences were statistically significant. The ranges of TPH concentrations were approximately 

equal (table 7) among collection sites.

For making comparisons among estimated loads of 

nutrients and metals in runoff and bulk precipitation, the 

calculated loads in the rubber-membrane roof runoff and bulk 

precipitation were normalized to the area of the green roof. 

That is, to account for differences in surface area, the rubbermembrane roof runoff load was multiplied by the ratio of the 

green roof area to the area of the rubber-membrane roof, and 

the concentrations in bulk precipitation were multiplied by 

the volume of precipitation that fell on the green roof (using 

appropriate unit conversion factors). Estimated median loads 

of total and dissolved phosphorus were greatest from the green 

roof (fig. 47); the load of total phosphorus in green roof runoff 

was statistically greater than the load in bulk precipitation, and 

the load of dissolved phosphorus was statistically greater than 

the load in either bulk precipitation or rubber-membrane-roof 

runoff. Estimated median loads of ammonia were smaller for 

the green roof than for the rubber-membrane roof or the bulk 

precipitation; the estimated median nitrate plus nitrite loads 

were greatest for the rubber-membrane roof runoff and about 

equal for bulk precipitation and green-roof runoff. Among the 

median nitrogen-analyte loads, only the difference between the 

rubber-membrane roof and green roof runoff of ammonia was 

statistically significant.

Green roof runoff had the greatest estimated median 

loads of Cd, Cu, and Ni (fig. 48). Estimated median loads of 

Pb and Zn were greatest in runoff from the rubber-membrane 

roof. Median loads of Cu and Zn in runoff from the green roof 

and the rubber-membrane roof were statistically greater than 

those in bulk precipitation. Median loads of Pb in rubbermembrane roof runoff and bulk precipitation were statistically 

greater than that in green roof runoff; loads of Pb in rubbermembrane roof runoff, in turn, were statistically greater than 

those in bulk precipitation.

Likely sources of the nutrients, metals, and TPH found 

in runoff from the rubber-membrane roof consist of dry fall 

between storms, deposits left by flying animals (birds and 

insects), and precipitation, the latter as determined in the bulk 

precipitation analyses. These differences in the source of materials account for the differences between rubber-membrane 

roof runoff and bulk precipitation as evidenced by the previously discussed data.

Considering the orders-of-magnitude differences among 

the constituent concentrations in runoff and in bulk precipitation, and the differences among the estimated loads, it is 

apparent that the soil medium, including any fertilizer that 

may have been applied, is the likely source of the nutrients 

in the runoff, a finding also reported by Emilsson and others 

(2007). If, as expected, fertilization does not continue indefinitely, with future maturation of the vegetation, it is possible 

that the original nutrients in the medium will diminish, and the 

concentrations and loads in the runoff will decline. However, 

decaying plant matter may contribute to the water quality of 

roof runoff in the future. In addition, the concentrations of 
64 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Table 7. Concentrations of nutrients, total metals, and total petroleum hydrocarbons in runoff from the Town Hall and Whipple Annex 

roofs, and bulk precipitation, Ipswich, MA, 2007–08.—Continued

[E, estimated value less than the reporting level; <, less than; M, detected but not quantifiable; --, missing or not calculated (median); ns, sample not collected]

Sampling 

date

Nutrients (concentrations in milligrams per liter)

Dissolved

ammonia plus 

organic nitrogen,

as N

Total ammonia 

plus organic 

nitrogen,

as N

Dissolved 

ammonia,

as N

Dissolved 

nitrate plus 

nitrite,

as N

Dissolved 

nitrite,

as N

Orthophosphorus,

as P

Dissolved 

phosphorus,

as P

Total

phosphorus

Whipple Annex green roof

5/9/2008 1.5 1.8 0.093 0.35 0.022 0.541 0.6 0.63

7/9/2008 3 3 0.092 0.41 0.015 0.73 0.83 0.88

7/23/2008 ns ns ns ns ns ns ns ns

9/6/2008 2 2.9 0.04 0.39 0.022 1.3 1.32 1.5

9/26/2008 11 12 8.66 0.51 0.056 9.71 8.96 9.59

10/21/2008 3.2 5.5 0.907 2.48 0.043 1.57 1.6 1.91

10/26/2008 4 2.3 E0.015 0.6 0.005 1.33 1.51 1.57

10/28/2008 1.9 1.7 <0.02 0.19 0.006 1.64 1.65 1.65

Median 3 2.9 0.092 0.41 0.022 1.33 1.51 1.57

Ipswich Town Hall rubber roof

10/23/2007 ns ns ns ns ns ns ns ns

11/162007 0.25 0.34 0.199 0.32 0.002 <0.006 <0.006 0.01

5/9/2008 1.6 3.3 0.849 0.9 <0.002 0.057 0.115 0.46

7/9/2008 ns ns ns ns ns ns ns ns

7/23/2008 ns ns ns ns ns ns ns ns

9/6/2008 2.8 2.9 1.32 0.62 E0.002 0.097 0.138 0.155

9/26/2008 1.1 1.3 0.869 0.43 <0.002 <0.006 E0.003 0.032

10/21/2008 1.3 1.5 0.968 1.91 0.007 0.01 0.021 0.064

10/26/2008 1.4 0.74 0.402 0.27 0.002 0.01 0.022 0.037

10/28/2008 2.1 0.17 0.088 0.26 0.005 E0.006 0.007 E0.011

Median 1.4 1.3 0.849 0.43 0.002 0.01 0.021 0.037

Bulk precipitation

10/23/2007 0.69 0.84 0.593 0.87 0.006 0.008 0.015 0.021

11/16/2007 0.22 0.26 0.187 0.3 E0.002 E0.005 E0.004 0.008

5/9/2008 -- 19 -- -- -- -- -- 1.66

7/9/2008 0.15 0.15 0.1 0.17 0.002 <0.006 <0.006 <0.008

7/23/2008 0.35 0.37 0.296 0.29 <0.002 <0.006 <0.006 0.009

9/6/2008 <0.14 E0.08 0.037 0.05 <0.002 <0.006 <0.006 0.01

9/26/2008 <0.1 E0.08 0.038 E0.04 E0.001 <0.006 <0.006 <0.012

10/21/2008 0.77 0.81 0.673 1.59 0.004 <0.008 0.006 E0.008

10/26/2008 4.2 0.1 0.067 0.06 0.006 E0.006 0.009 E0.009

10/28/2008 2.8 0.16 0.094 0.12 0.003 0.01 0.019 0.019

Median 0.35 0.26 0.1 0.17 0.002 -- -- 0.009
Field Studies of Low-Impact-Development Techniques 65

Table 7. Concentrations of nutrients, total metals, and total petroleum hydrocarbons in runoff from the Town Hall and Whipple Annex 

roofs, and bulk precipitation, Ipswich, MA, 2007–08.—Continued

[E, estimated value less than the reporting level; <, less than; M, detected but not quantifiable; --, missing or not calculated (median); ns, sample not collected]

Sampling

date

Total metals (concentrations in micrograms per liter) Total

petroleum

hydrocarbons

(concentrations in 

milligrams per liter)

Cadmium Chromium Copper Lead Nickel Zinc

Whipple Annex green roof

5/9/2008 0.17 <1 303 1.87 1.3 65.6 --

7/9/2008 0.83 <1 590 1.59 3.5 384 E4.1

7/23/2008 ns ns ns ns ns ns 5

9/6/2008 0.52 <1 479 5.05 2.8 369 E2

9/26/2008 0.27 1 405 1.46 2.3 133 E2.1

10/21/2008 0.32 1 611 8.2 2.4 365 --

10/26/2008 0.46 <1 414 2.3 2.3 244 E4.9

10/28/2008 0.41 <1 402 0.48 2.2 114 E1.5

Median 0.41 <1 414 1.87 2.3 244 E3.1

Ipswich Town Hall rubber roof

10/23/2007 ns ns ns ns ns ns --

11/16/2007 0.02 <1 12.6 331 0.8 47.9 5

5/9/2008 0.1 5 57.9 1,020 2.5 200 --

7/9/2008 ns ns ns ns ns ns --

7/23/2008 ns ns ns ns ns ns E3.7

9/6/2008 0.28 2 175 1,180 2.4 2610 <5

9/26/2008 0.07 10 41.2 589 0.87 513 E2.8

10/21/2008 0.21 M 60.6 1,190 0.93 293 E2.8

10/26/2008 0.06 <1 26 311 0.48 148 E4.1

10/28/2008 E0.04 <1 7.2 197 E0.17 100 <5

Median 0.07 -- 41.2 321 0.8 200 --

Bulk precipitation

10/23/2007 2.38 M 5.9 9.64 3.8 36.6 --

11/16/2007 0.08 <1 3.9 9.2 4 3.9 <2

5/9/2008 -- -- -- -- -- -- --

7/9/2008 E0.01 <1 <1.2 12.1 E0.12 8.1 E4.6

7/23/2008 E0.01 <1 <1.2 7.36 E0.1 2.6 E2.3

9/6/2008 0.01 <1 <1.2 0.51 E0.12 E1.4 E2.6

9/26/2008 0.01 <1 <1.2 0.59 E0.06 <2 E3.2

10/21/2008 0.19 <1 E2.5 5.65 0.38 10.8 --

10/26/2008 0.06 <1 <4 5.46 <0.2 5 E7.3

10/28/2008 0.06 <1 <4 3.38 0.58 4.3 <5

Median 0.06 <1 -- 5.65 E0.12 4.3 --
66 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

5 5 5

5 5 5 5 5 5

5 5 5 5 5 5

x

x

x

E

C D

A B

BULK

PRECIPITATION

WHIPPLE ANNEX

GREEN ROOF

TOWN HALL

RUBBER ROOF

BULK

PRECIPITATION

WHIPPLE ANNEX

GREEN ROOF

TOWN HALL

RUBBER ROOF

BULK

PRECIPITATION

WHIPPLE ANNEX

GREEN ROOF

TOWN HALL

RUBBER ROOF

BULK

PRECIPITATION

WHIPPLE ANNEX

GREEN ROOF

TOWN HALL

RUBBER ROOF

BULK

PRECIPITATION

WHIPPLE ANNEX

GREEN ROOF

TOWN HALL

RUBBER ROOF

0.1

0.5

1

5

10

NITRATE PLUS NITRITE,

IN GRAMS AS NITROGEN

0.01

0.1

1

10

100

TOTAL PHOSPHORUS,

IN GRAMS

0.01

0.1

1

10

100

DISSOLVED PHOSPHORUS,

IN GRAMS

0.01

0.1

1

10

100

DISSOLVED AMMONIA,

IN GRAMS AS NITROGEN

1

10

100

TOTAL NITROGEN,

IN GRAMS

EXPLANATION

Number of samples

Data value 1.5 to 3.0 times the interquartile

range above the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Data value 1.5 to 3.0 times the interquartile

range below the box

5

x

x

Figure 47. Loads of (A) total nitrogen, (B) total phosphorus, (C) dissolved ammonia nitrogen, (D) dissolved phosphorus, and (E) nitrate 

plus nitrite nitrogen in bulk precipitation and in runoff from the town hall rubber roof and the Whipple Annex green roof, Ipswich, MA, 

June 2007 through November 2008.
Field Studies of Low-Impact-Development Techniques 67

EXPLANATION

Number of samples

Data value greater than 3.0 times the

interquartile range above the box

Data value 1.5 to 3.0 times the interquartile

range above the box

Largest data value within 1.5 times the

interquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times the

interquartile range below the box

Data value 1.5 to 3.0 times the interquartile

range below the box

5

x

x

o

o

x

x

5 5 5

5 5 5

5 5 5

5 5 5 5 5 5

E

C D

A B

10

100

1,000

10,000

100,000

ZINC, IN MILLIGRAMS

0.1

1

10

100

1,000

10,000

100,000

LEAD, IN MILLIGRAMS

0.1

0.5

1

5

10

50

NICKEL, IN MILLIGRAMS

10

100

1,000

10,000

COPPER, IN MILLIGRAMS

0.01

0.1

0.05

0.5

1

5

CADMIUM, IN MILLIGRAMS

BULK

PRECIPITATION

WHIPPLE ANNEX

GREEN ROOF

TOWN HALL

RUBBER ROOF

BULK

PRECIPITATION

WHIPPLE ANNEX

GREEN ROOF

TOWN HALL

RUBBER ROOF

BULK

PRECIPITATION

WHIPPLE ANNEX

GREEN ROOF

TOWN HALL

RUBBER ROOF

BULK

PRECIPITATION

WHIPPLE ANNEX

GREEN ROOF

TOWN HALL

RUBBER ROOF

BULK

PRECIPITATION

WHIPPLE ANNEX

GREEN ROOF

TOWN HALL

RUBBER ROOF

Figure 48. Loads of (A) total cadmium, (B) total copper, (C) total nickel, (D) total lead, and (E) total zinc in bulk precipitation and in 

runoff from the town hall rubber roof and the Whipple Annex green roof, Ipswich, MA, June 2007 through November 2008.
68 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

copper and zinc in the soil slurry sample also are probably 

related to the concentrations and loads in runoff. Furthermore, 

the gutters, downspouts, machinery, vents, and copper flashing on the green roof all probably contribute to the chemical 

makeup of the runoff (fig. 33). Of the metals in the rubbermembrane roof runoff, lead and zinc are most notable for the 

high concentrations and estimated loads; these two metals are 

commonly found in the old pipes that drain the roof.

One of the features claimed for green roofs is the ability 

to sequester some atmospheric pollutants. With the exception 

of ammonia and nitrate plus nitrite, the concentrations of the 

nutrient analytes in bulk precipitation and rubber-membrane 

roof runoff samples are generally small fractions of the 

concentrations detected in the green roof runoff. Therefore, 

in general, the sequestration of atmospheric contaminants 

appears to be offset by the release of these constituents from 

the growing medium and plants, and from fertilization.

Simulation of the Effects of Land-Use 

Change and Low-Impact Development 

on Streamflow at Multiple Spatial 

Scales

The USGS, in cooperation with the MDCR and the 

USEPA, used the calibrated Ipswich River Basin Hydrological 

Simulation Program-FORTRAN (HSPF) precipitation-runoff 

model (Zarriello and Ries, 2000) to simulate the effects of 

various LID and water-conservation practices on streamflow 

at multiple spatial scales. Urbanization produces changes in 

land use and stormwater routing that have significant effects 

on the processes that generate streamflow. Loss of vegetation, increased imperviousness, and large-scale water infrastructure (water withdrawals and wastewater return flows) 

affect the entire flow regime from flood peaks to summer low 

flows maintained by groundwater discharge. To evaluate the 

effects of LID and water-conservation practices on streamflow 

using HSPF, the original model of Zarriello and Ries (2000) 

was modified to simulate hypothetical land-use changes and 

water-management scenarios developed by the USGS in 

consultation with MDCR, USEPA, and a Technical Advisory 

Committee created for the project. Specific LID practices, 

such as installation of porous pavement, rain gardens, bioretention areas, or green roofs, could not be represented explicitly in the HSPF model; rather, surrogates for these practices 

were simulated by changing patterns of land use and the 

amount of EIA in the basin.

Two types of simulations were conducted for this study. 

The first type simulated the effects of land-use change, LID 

practices, and water-conservation efforts in subbasins with 

heterogeneous land use, as structured to represent the basin 

in the original HSPF model. These simulations (referred to 

hereafter as basin-scale simulations) generally were conducted 

for the entire basin or for the drainage area above the USGS 

South Middleton streamgage (station 01101500), also referred 

to as the upper basin. Results for these simulations represent 

hydrologic processes in drainage areas ranging from about 0.5 

to 125 mi2 in size (fig. 49). The second type simulated small 

drainage areas consisting of mainly homogeneous land uses 

to evaluate the potential effects on streamflow of land-use 

change, LID practices such as clustered housing developments, and the amount of EIA. These simulations (referred 

to hereafter as local-scale simulations) represent hydrologic 

processes in hypothetical 100-acre (0.16 mi2) drainage areas. 

The local-scale simulations do not represent actual drainage 

areas in the basin, but because model-calibrated parameter 

values were used in the simulations, simulation results represent potential streamflow response in the Ipswich River Basin. 

Overall, the two types of simulations show the hydrologic 

responses to land-use change, water-management activities, 

and various LID practices over a wide range of spatial and 

temporal scales and patterns of land use.

The Ipswich River Basin HSPF model simulates the 

magnitude of streamflow only. The effects of urbanization and 

the potential mitigating effects of LID on other stream characteristics such as water quality (for example, concentrations of 

nutrients, metals, bacteria, and sediment), water temperature, 

channel stability, and aquatic ecology were not evaluated with 

the model.

Description of Original Baseline Model

The original baseline model refers to the calibrated 

Ipswich River Basin HSPF model2 described by Zarriello and 

Ries (2000) that consists of 15 pervious (PERLND) and 2 

impervious (IMPLND) hydrologic response units (HRUs) that 

have unique combinations of land use and surficial geology 

(table 7 in Zarriello and Ries, 2000). A surficial geology data 

layer consisting of two categories (1) till and (2) sand and 

gravel) and a 1991 land-use data layer were used to develop 

the HRUs for the original baseline model. IMPLNDs do not 

allow infiltration and are defined as impervious surfaces that 

are directly connected to the stream network. Thus, IMPLNDs 

hydrologically represent EIAs. PERLNDs allow infiltration 

and are assigned HSPF parameter values to represent the 

specific land-use and subsurface characteristics of the land 

segment. Surface flow from IMPLNDs and surface and subsurface flows from PERLNDs are directed to 67 river reaches 

or reservoir segments (RCHRES) that represent the hydraulic 

network of the basin (fig. 49; table 8 in Zarriello and Ries, 

2000). The original baseline model was calibrated to streamflow data from the USGS streamgage at South Middleton and 

at Ipswich (station 01102000) for the period 1989 to 1993. 

Climate data for the period 1961 to 1995 were provided by the 

Marine Biological Laboratory in Woods Hole, MA (Zarriello 

and Ries, 2000).

2

Bicknell and others (2000) provide a detailed description of the structure 

and capabilities of the HSPF model.
Simulation of the Effects of Land-Use Change and Low-Impact Development on Streamflow at Multiple Spatial Scales 69 HAMILTON DANVERS PEABODY LYNNFIELD WOBURN BURLINGTON TEWKSBURYWILMINGTON ANDOVER NORTH ANDOVER BOXFORD MIDDLETON NORTH READING READING TOPSFIELD ROWLEY IPSWICH WENHAMBEVERLY SALEM LYNN ESSEX

BILLERICA

MANCHESTER

GLOUCESTER

WAKEFIELD

GEORGETOWN

MARBLEHEAD

ATLANTIC OCEAN

01102000

01101500

42°40'

42°30'

71°10' 70°50'

EXPLANATION

IPSWICH

01101500

15

Open water

Model subbasin

Basin boundary and name

Streamgage subbasin  boundary

Reach and number  within model subbasin

Town boundary

Streamgage and number 

0 2 4

0 2 4 6 MILES

6 KILOMETERS

ATLANTIC

OCEAN

NORTH COASTAL

SHAWSHEEN

MERRIMACK

BOSTON HARBOR

PARKER

IPSWICH

PutnamvilleReservoir Swan

Pond

EmersonBrookReservoir

WinonaPond

SuntaugLake

Wenham

Lake Longham

Reservoir

MiddletonPond

Lowell Pond

Cleveland Brook

Salem-Beverly Canal

Pye Brook

Howlett Brook

Nichols Brook

Fish Brook

Lubbers Brook

Ipswich

R vi

er

Black Brook

Miles River

Idlewild Brook

Emerson Brook

Boston Brook

Wills Brook

Norris Brook

River

Bear Meadow Brook

Martins Brook

a M

wodae Mel p r B oo k

Mil Bl oor k

Ip

ws

ich

9

3

1

8

5

38

32

12

6

51

7

39

58

30

65

36

61

2

53

13

49

52

31

11

42

40

50

64

14

20

66

33

41

46

15

48

62

54

34

4

28

35

16

23

27

29

55

67

59

18

24

60

10

26

45

57

25

21

37

44

63

22

17

19

43

Base from U.S. Geological Survey digital data, 1:25,000, 1991,Lambert conformal conic projection, North American Datum of 1983

Figure 49. Model reaches and subbasin boundaries in the Ipswich River Basin, MA (from Zarriello and Ries, 2000).
70 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Time series of total groundwater and surface-water withdrawals were developed for reaches with municipal withdrawals during the calibration period. By quantifying withdrawals 

during the calibration period, the effects of withdrawals were 

included in the simulation so that the hydrologic parameters were not skewed. Daily withdrawals were obtained or 

estimated from monthly records for all major groundwater 

and surface-water withdrawals in the basin for the calibration period (or longer, when available). The original baseline 

model contained a total of 73 withdrawals, most of which 

were municipal groundwater withdrawals (table 3 in Zarriello 

and Ries, 2000). For time-varying groundwater withdrawals, 

the analytical program STRMDEPL (Barlow, 2000) was used 

to calculate rates of streamflow depletion. The streamflowdepletion rate reflected the time-delayed response to changes 

in the rate of withdrawal; the response was a function of the 

distance to the well from the stream and the hydraulic properties of the aquifer. Surface-water withdrawals and streamflowdepletion rates from individual wells were combined to obtain 

the total streamflow-depletion rate for each reach affected by 

withdrawals.

For the long-term (1961–1995) simulations conducted 

for this study, withdrawals for periods during which actual 

withdrawals were not obtained (generally from January 1961 

through December 1988 and January 1994 through December 

1995) were estimated from the average monthly streamflowdepletion rates for a period when withdrawals were available 

(generally 1989–1993). Thus, the long-term simulations compute streamflow for average 1989–1993 withdrawal conditions, constant land-use conditions (1991 land use), and actual, 

long-term climatic conditions.

Modifications to the Original Baseline Model

In this study, the calibrated HSPF model was modified 

to simulate five newly defined basin-scale scenarios. For each 

scenario, a new model control file (uci) was created. For the 

scenarios that incorporate withdrawal changes, new time series 

of streamflow-depletion rates were computed and stored in 

unique data-set numbers in the associated Water Data Management file for the Ipswich River Basin HSPF model. For 

the scenarios that incorporate land-use and EIA changes, new 

HRUs were created and copied into the schematic block of the 

uci file, as appropriate. For the hypothetical local-scale simulations, selected existing HRUs were re-sized to 100 acres to 

simulate runoff from small drainage areas with uniform land 

use. HRU and stream reach parameter values and climatic data 

from the original baseline model of Zarriello and Ries (2000) 

were not altered for this study. Specific modifications made to 

the calibrated model for each scenario are described in greater 

detail in the “Description of Basin-Scale and Local-Scale 

Simulations” section of the report.

Model Limitations

Because of limits on data availability and computational 

efficiency, numerical watershed models such as HSPF simplify 

the complex processes and physical characteristics of a drainage basin. Consequently, there are limitations to the types of 

questions that can be addressed by the model. The assumptions, information used to develop and calibrate the model, 

spatial resolution of the model, and the possible applicability 

of alternative model structures and parameter values need to 

be considered when evaluating the model results for waterresources management decisions. Limitations and uncertainties of the Ipswich River Basin HSPF model are described in 

greater detail in Zarriello and Ries (2000).

Model calibration reflects the combined effects of HRUs 

(PERLNDs and IMPLNDs) and reach characteristics. Hydrologic judgment was used to determine parameter values for the 

PERLNDs and IMPLNDs, but information was not available 

to calibrate the response for individual HRUs. In addition, the 

EIA associated with each developed land-use category was 

determined through model calibration. Calibrated EIA values 

in the original baseline model are 63 percent for commercialindustrial-transportation land use (hereafter referred to as 

commercial land use), 14 percent for high-density residential 

(< 0.5-acre lots) land use, and 2.5 percent for low-density 

residential (> 0.5-acre lots) land use. These values represent 

average subbasin-scale EIA; however, the local variability of 

EIA for a given type of development in the basin (for example, 

Roy and Shuster, 2009) could not be represented in the model. 

Despite the uncertainties associated with estimating EIA 

through model calibration, the model-calibrated values for 

commercial and residential areas in the Ipswich River Basin 

are consistent with values for similar broad land-use categories 

computed from rainfall-runoff relations in the Charles River 

Basin (Zarriello and Barlow, 2002) and values in the literature 

(Alley and Veenhuis, 1983). To evaluate the sensitivity of 

simulated streamflow to EIA, this basin property was varied in 

many of the simulations conducted for this study. The use of 

EIA as a surrogate for LID was considered reasonable given 

the number of different LID practices that would need to be 

explicitly represented in the model and the large scale of most 

of the simulations. One consequence of using EIA as a surrogate for LID is that specific LID practices designed to improve 

infiltration capacity in the pervious areas (for example, adding 

permeable soil to improve subsurface storage, re-grading the 

site, or installing detention structures) were not represented. 

Therefore, the model may underestimate the effects of LID on 

streamflow in the few simulations where enhanced infiltration 

from LID affects a large fraction of the drainage area and the 

underlying soil is not already permeable (that is, areas underlain by till).

Lastly, when the original baseline model was calibrated, 

the degree to which simulated flows were in agreement with 

actual flows could not be determined at most locations because 

most of the reaches in the basin were ungaged. Therefore, simulation results from ungaged areas or magnitudes of changes 
Simulation of the Effects of Land-Use Change and Low-Impact Development on Streamflow at Multiple Spatial Scales 71

Table 8. Description of scenarios simulated with the Hydrological Simulation Program-FORTRAN precipitation runoff model of the 

Ipswich River Basin, Ipswich, MA.

[DSN, dataset number in the Watershed Data Management (WDM) database; long-term (1961–1995) simulations conducted for all scenarios]

Scenario identifier Description Output DSN

Basin-scale scenarios simulated

LT-Demd Original baseline simulation (Zarriello and Ries, 2000)—1989–1993 withdrawals (also 

referred to as original baseline withdrawals), 1991 land use.

6501–6567

LID-LT-upDem Updated baseline simulation—1989–1993 withdrawals with updated withdrawals for

Reading and Wilmington (also referred to as updated baseline withdrawals), 1991 land use.

7501–7567, 8501–8567

LID_LT-build Buildout simulation—updated baseline withdrawals, potential land use at buildout. 7601–7667, 8601–8667

LID_LT-imperv Simulation of LID retrofits above South Middleton streamgage (station 01101500)—updated 

baseline withdrawals, 1991 land use with effective impervious area reduced by 50 percent.

7701–7767, 8701–8767

LID_LT-conserv Water-conservation simulation—updated baseline withdrawals with rates reduced by 1 to

20 percent to represent water-conservation programs, 1991 land use.

7801–7867, 8801–8867

Local-scale scenarios simulated

LID_LT-local Local-scale simulations (100-acre parcels)—no water withdrawals, varying combinations of 

developed and undeveloped land-use types and amounts of effective impervious area.

3001–3031

in flows produced by altering the distribution of HRUs were 

uncertain. Overall, simulated streamflow responses were 

viewed as relative rather than absolute.

Description of Basin-Scale and Local-Scale 

Simulations

This section describes the simulations developed by 

the USGS in consultation with MDCR, USEPA, and the 

Technical Advisory Committee (table 8). Two types of simulations, basin-scale simulations and local-scale simulations, 

were conducted.

Basin-Scale Simulations

The basin-scale simulations were conducted for either 

the entire basin (original baseline simulation, updated baseline simulation, buildout simulation, and water-conservation 

simulation) or the upper basin above the South Middleton 

streamgage (LID retrofit simulation). Specific LID practices 

involving land-use change were not represented explicitly 

in the HSPF model; rather, surrogates for these practices 

were simulated by changing patterns of land use and the 

amount of model-calibrated EIA. Other practices, such as 

hypothetical reductions in withdrawal rates through water conservation and major changes in groundwater withdrawals by 

the towns of Reading and Wilmington, were simulated directly 

with the model.

Original Baseline Simulation

The original long-term baseline simulation was conducted previously with the original baseline model to evaluate 

the effects of average 1989–1993 withdrawals on streamflow 

over long-term (1961–1995) climatic conditions (Zarriello and 

Ries, 2000). For simulations incorporating updated withdrawals for Reading and Wilmington, discussed in the following 

section, withdrawal amounts were altered from the average 

1989–1993 rates.

Updated Baseline Simulation

The original, long-term, baseline simulation was updated 

to incorporate major changes in the withdrawals for the towns 

of Reading and Wilmington that have occurred since the original baseline model was developed. In the original baseline 

simulation, both towns relied entirely on groundwater withdrawals from wells in the upper part of the basin.

In 2006, the town of Reading began purchasing water 

from the MWRA to meet its water needs. To simulate current 

conditions for Reading, withdrawals for the 10 Reading Water 

Department wells in reach 8 (fig. 50) that were in service 

for the original baseline simulation were removed from the 

updated baseline simulation. This change resulted in Reading 

withdrawals decreasing from an average of 2.2 Mgal/d in the 

original baseline simulation to 0.037 Mgal/d in the updated 

baseline simulation (minor withdrawals for Meadow Brook 

Golf Club remained in the model).

In 2008, the town of Wilmington anticipated satisfying 

some of its summer demand with purchases from the MWRA 

(Michael Wood, Town of Wilmington, written commun., 

2008), but because changes to the water-supply system had 

not yet been implemented, only projected changes provided 

by the town were simulated. At the time of this study, Wilmington obtained water from four wells: Shawsheen Avenue in 

reach 5, Browns Crossing in reach 12, and Barrows wellfield 

and Salem Street in reach 13 (fig. 50). To represent current 

(2008) withdrawals from each well, daily withdrawal rates for 

2006 to 2007 were averaged to produce a single year of daily 
72 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

8 9

1

12

3 5

6

13

11

15

7

17

2

16

14

4

18 19

10

01101500

71°12' 71°06' 71°00'

42°36'

42°33'

42°30'

Base from U.S. Geological Survey digital data,

Massachusetts state plane projection, North American Datum of 1983

EXPLANATION

Hydrology

 Open water

 Model subbasin

 Reach and number within model subbasin

 Ipswich River Basin boundary

 Streamgage subbasin boundary

Streamgage and number

Updated baseline simulation withdrawals

 Unchanged—1989–93 withdrawal rates

 Updated—No withdrawals

 Updated—Projected future withdrawal rates

 based on 2006–07 data

01101500

6

0 2 4

0 2 4 6 MILES

6 KILOMETERS

Area enlarged

IPSWICH RIVER BASIN

ANDOVER

BOXFORD

PEABODY

NORTH ANDOVER

MIDDLETON

READING

LYNNFIELD

NORTH READING

TEWKSBURY

WOBURN

BURLINGTON

WAKEFIELD

WILMINGTON

Shawsheen Avenue

Browns Crossing

Barrows wellfield

Salem Street

Figure 50. Changes in groundwater withdrawals for Reading and Wilmington, MA, for the updated baseline simulation relative 

to the original baseline simulation.
Simulation of the Effects of Land-Use Change and Low-Impact Development on Streamflow at Multiple Spatial Scales 73

flows. Average withdrawal rates for 2006 to 2007 ranged from 

0.392 Mgal/d (Barrows) to 0.569 Mgal/d (Browns Crossing); 

the total rate from the four wells was 1.94 Mgal/d (table 9). 

Wilmington also purchased 0.2 to 0.5 Mgal/d from MWRA 

during the summer and anticipated purchasing an additional 

1 Mgal/d to supplement summer supplies (Michael Wood, 

Town of Wilmington, written commun., 2008). The anticipated additional purchases from the MWRA were incorporated 

into the updated baseline simulation by reducing average 

2006–2007 summer (May through September) withdrawal 

rates. On the basis of information provided by the town, rates 

were reduced by 0.551 Mgal/d at the Shawsheen Avenue well, 

0.300 Mgal/d at the Browns Crossing well, and 0.150 Mgal/d 

at Barrows well. Rates were unchanged at the Salem Street 

well (table 9). These changes resulted in a total reduction for 

the town of about 1 Mgal/d (from 2.04 Mgal/d in 2006 to 2007 

to 1.04 Mgal/d in the updated baseline simulation) during the 

summer months. For each well, streamflow depletion then 

was computed from the modified annual time series of daily 

withdrawals, and long-term time series for 1961 to 1995 was 

developed as described in the Model Development section of 

this report. All other aspects of the original baseline simulation by Zarriello and Ries (2000) remained unchanged in the 

updated baseline simulation.

Changes to Wilmington withdrawals directly affected 

simulated streamflow (fig. 50) in reaches 1, 5, 12, and 13 as 

described below.

Reach 1. Average streamflow depletion from Maple 

Meadow Brook at Route 38 in Wilmington (reach 1) decreased 

from 1.08 Mgal/d in the original baseline simulation (five 

wells) to 0 Mgal/d in the updated baseline simulation (no 

wells). Five Wilmington wells that were in operation during 

the 1989–1993 calibration period were no longer in service.

Reach 5. Average streamflow depletion from Lubbers 

Brook above Route 38 in Wilmington (reach 5) increased 

from 0.16 Mgal/d in the baseline simulation (two wells) to 

0.27 Mgal/d in the updated baseline simulation (one well). 

The average streamflow depletion rate increased because the 

Shawsheen Avenue well was pumped at a higher rate than 

the combined rate of the two wells in operation during the 

1989–1993 calibration period; however, summer streamflow 

depletion was lower for the updated baseline simulation than 

for original baseline simulation because of the anticipated 

purchases from the MWRA.

Reach 12. Average streamflow depletion from Martins 

Brook at Route 62 in North Reading (reach 12) decreased 

from 1.23 Mgal/d in the original baseline simulation (three 

wells) to 1.06 Mgal/d in the updated baseline simulation (three 

wells). The simulations had the same number of withdrawals, 

but the updated baseline simulation reflected lower average 

and summer pumping rates from the Browns Crossing well.

Reach 13. Average streamflow depletion from Martins 

Brook upstream from the mouth in North Reading (reach 13) 

increased slightly from 0.91 Mgal/d in the original baseline 

simulation (two wells) to 1.03 Mgal/d in the updated baseline 

simulation (three wells). The overall rate increased because the 

Salem Street well was not in operation during the 1989–1993 

calibration period. As for the other reaches affected by MWRA 

purchases, summer streamflow depletion in reach 13 in the 

updated simulation was lower during the summer months. 

The updated baseline withdrawals for the towns of Reading and Wilmington were used in all subsequent basin-scale 

simulations.

Buildout Simulation

Information from a state-wide buildout analysis conducted by the Massachusetts Executive Office of Energy and 

Environmental Affairs (EOEEA) in 2001 (Massachusetts 

Executive Office of Energy and Environmental Affairs, 2008) 

was used to simulate the effects of potential future development (also referred to as buildout) on streamflow in the 

Ipswich River Basin. The main objective of this analysis was 

to simulate the effects of potential future development when 

it takes place as conventional land-use change (that is, LID 

practices were not applied to the new development). Because 

simulating buildout involved converting an undeveloped 

HRU (for example, forest overlying till) to a developed HRU 

(for example, low-density residential development overlying till), the simulated effects of land-use change resulting 

Table 9. Changes to the Wilmington, MA, water-supply system for the updated baseline simulation.

[Mgal/d, million gallons per day; MWRA, Massachusetts Water Resources Authority; Updated 2006–2007 withdrawal rates represent projected future withdrawals and are referred to as updated baseline withdrawals in the model simulations.]

Model 

reach Well name

Average

1989–1993

withdrawal

rate

(Mgal/d)

Average 

2006–2007 

withdrawal 

rate

(Mgal/d)

Average 

2006–2007 

May–September 

withdrawal rate

(Mgal/d)

Projected 

May–September 

change due to 

MWRA purchases

(Mgal/d)

Updated average 

2006–2007

withdrawal

rate

(Mgal/d)

Updated 

2006–2007 

May–September 

withdrawal rate

(Mgal/d)

5 Shawsheen Avenue 0.161 0.511 0.551 -0.551 0.280 0

12 Browns Crossing 1.47 0.569 0.572 -0.300 0.443 0.272

13 Barrows 0.656 0.392 0.391 -0.150 0.330 0.241

13 Salem Street 0 0.471 0.522 0 0.471 0.522

Total: 2.29 1.94 2.04 1.00 1.52 1.04
74 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

from development were determined by the parameterization 

and consequent precipitation-runoff response of the modelcalibrated HRUs.

The buildout analysis shows how a community might 

develop if all remaining developable areas were fully built out 

in accordance with current local zoning codes (Massachusetts 

Executive Office of Energy and Environmental Affairs, 2008). 

Land that is not considered developable includes permanently 

protected open space, such as conservation land and riparian 

buffers, open water, and land that is already developed; for this 

study, forested and non-forested wetlands also are considered 

unavailable for development. The drainage area upstream 

from the South Middleton streamgage is relatively urban and 

contains less developable land than other parts of the basin. 

On a subbasin scale, drainage areas to reaches 27, 28, 31, and 

35 have the highest percentages of developable land (35 to 

50 percent) in the basin (fig. 51).

To simulate the effects of potential future development on 

streamflow, a new land-use data layer was created by combining the EOEEA buildout information with the 1991 land-use 

data used to develop the original baseline model. To develop 

a new land-use data layer, the zoning codes in the developable areas were related to the land-use categories used for 

model HRU development (table 10). Using 1991 land use as a 

baseline, the buildout analysis indicated that about 17 percent 

of the entire Ipswich River Basin was developable (fig. 51). 

The major change in the basin was the loss of forest and gain 

of low-density residential development (fig. 52; table 11). Forest cover decreased from 38.6 percent in 1991 to 24.2 percent 

at buildout, and low-density residential development increased 

from 15.2 to 31.4 percent. Other developed land-use categories, including high-density residential and commercial, 

increased slightly at buildout.

After modifying the land-use data layer, the areas of 

HRUs for 1991 land use were modified to represent HRUs 

at buildout. All other aspects of the updated baseline model, 

such as parameter values, updated water withdrawals, and the 

amount of residential area using public water and on-site septic systems (PERLNDs 4, 6, 11, and 13), were held constant. 

To isolate the effects of land-use change on streamflow, results 

from a long-term simulation incorporating land use at buildout 

were compared to the results from the updated baseline simulation (LID-LT_upDem) incorporating 1991 land use; the only 

difference between these two simulations is the land-use data 

layer used to compute the HRUs in the basin.

The original intent was to simulate buildout with conventional development and LID to determine the extent to which 

buildout with LID practices reduced streamflow alteration 

Table 10. Regionalized zoning codes for developable areas grouped by land-use categories used to construct 

the land use at buildout data layer for the Hydrological Simulation Program-FORTRAN model.

[Letters and numbers in parentheses represent abbreviations and codes; >, greater than; sq. ft., square feet]

Regionalized zoning codes Land-use categories

Limited business (LB) Commercial-industrial-transportation

General business (GB)

Central business (CB)

Highway business (HB)

Office park (OP)

Mixed use (MU)

Light industrial (LI)

General Industrial (GI)

Institutional (IN)

Health care (HC)

Multifamily, medium density (MM) High-density residential

Multifamily, low density (ML)

Residential, 5,000–15,000 sq. ft. (R5)

Residential, 15,000–20,000 sq. ft. (R4)

Residential, 20,000–40,000 sq. ft. (R3) Low-density residential

Residential, 40,000–80,000 sq. ft. (R2)

Residential, >80,000 sq. ft. (R1)

Residential/agricultural, >2 acre (RA)
Simulation of the Effects of Land-Use Change and Low-Impact Development on Streamflow at Multiple Spatial Scales 75

Area enlarged

IPSWICH RIVER BASIN

38

9 8

1

12

5 3

32

30

53

39

40

65

52

6

61

66

58

36

13

51

46

34

23

11

49

33

50

67 54

62

64

15

25

7

63

17

31

28

35

26

41

2

20

59

16

42

48

14

4

22

45

44

18

37

29

55

27

43

19

21

57

60

24 10

47

56

42°42'

42°36'

42°30'

71°12' 71°06' 71°00' 70°54'

Base from U.S. Geological Survey digital data

Buildout information from Massachusetts Executive Office of Environmental Affairs, 2001

Massachusetts state plane projection, North American Datum of 1983

EXPLANATION

Model subbasin and number

Developed or permanently protected

Available for development

6

0 2 4

0 2 4 6 MILES

6 KILOMETERS

Figure 51. Land potentially available for development in the Ipswich River Basin, MA, based on 1991 land use.
76 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Figure 52. Generalized land use in the Ipswich River Basin, MA, (A) in 1991 and (B) at buildout.

71°12' 71°06' 71°00' 70°54'

42°42'

42°36'

42°30'

71°12' 71°06' 71°00' 70°54'

42°42'

42°36'

42°30'

1991

Buildout

A

B

EXPLANATION

Forest

Open area

Open water

Nonforested wetland

Low-density residential

High-density

 residential

Commercial-

 industrial-

 transportation

Forested

 wetland

Base from U.S. Geological Survey digital data

Land-use data from Massachusetts GIS, 1991

Buidldout information from Massachusetts Executive Office of Environmental Affairs, 2001

Massachusetts state plane projection, North American Datum of 1983

0 2 4

0 2 4 6 MILES

6 KILOMETERS

0 2 4

0 2 4 6 MILES

6 KILOMETERS

Area

enlarged

IPSWICH RIVER BASIN
Simulation of the Effects of Land-Use Change and Low-Impact Development on Streamflow at Multiple Spatial Scales 77

Table 11. Land use in 1991 and potential land use at buildout in the Ipswich River Basin, MA.

[Percent change expressed as area at buildout minus area in 1991 over area in 1991]

Land use description

1991 land use Buildout land use

Percent

change Area

(acres)

Percentage of 

total area

Area

(acres)

Percentage of 

total area

Forest 36,854.0 38.6 23,113.6 24.2 -37.3

Open 6,675.2 7.0 3,407.0 3.6 -49.0

Open water 2,384.4 2.5 2,384.4 2.5 0.0

Nonforested wetland 6,750.1 7.1 6,750.1 7.1 0.0

Low-density residential 14,471.3 15.2 30,005.4 31.4 107.3

High-density residential 11,486.0 12.0 11,696.3 12.2 1.8

Commercial-industrial-transportation 3,583.5 3.8 4,847.7 5.1 35.3

Forested wetland 13,284.0 13.9 13,284.0 13.9 0.0

Total: 95,488.5 95,488.5

relative to conventional buildout. However, because there was 

relatively little difference between streamflow for buildout 

using conventional development and streamflow using 1991 

land use (discussed in the “Results and Discussion” section 

of this report), buildout incorporating LID practices, such as 

cluster development, was not evaluated in this study.

Simulation of Low-Impact-Development Retrofits 

Upstream from the South Middleton Streamgage

EIA upstream from the South Middleton streamgage 

was reduced by 50 percent as a surrogate for the implementation of LID practices that decrease EIA (for example, porous 

pavement, green roofs, and re-direction of surface runoff 

from some percentage of the EIA to natural or constructed 

recharge areas). In 1991, about 42.5 percent of the 28,416-acre 

(44.4 mi2) drainage area to the South Middleton streamgage 

was developed land use (fig. 53). Of the 12,070 acres of 

developed land, 1,929 acres (16.0 percent of developed area 

and 6.8 percent of total area) were designated as IMPLNDs 

(Zarriello and Ries, 2000). EIA ranged from 1.6 percent 

(reach 4) to 21.9 percent (reach 2), with a median value of 

5.9 percent for the 19 subbasins representing the area upstream 

from the South Middleton streamgage (fig. 54). A reduction 

of 50 percent, which would correspond to re-directing surface 

runoff from about 965 acres of highly discontinuous impervious surface with direct discharge to streams, was selected as 

a substantial, but reasonable, level of EIA reduction in the 

44.4 mi2 drainage area. Thus, this simulation was considered 

to represent widespread implementation of various LID practices achieved by retrofitting existing commercial, high-density residential, and low-density residential development. The 

response of simulated streamflow to a 50-percent reduction in 

EIA provided insight into the magnitude of response that could 

be expected from higher or lower percentage EIA reductions.

To simulate the LID retrofits using the HSPF model, the 

percentage of total area apportioned to IMPLNDs was reduced 

from 63 percent to 31.5 percent for commercial land use, 

14 percent to 7 percent for high-density residential land use, 

and 2.5 percent to 1.25 percent for low-density residential land 

use. These changes resulted in a uniform 50-percent reduction 

in EIA while maintaining the spatial distribution of HRUs in 

the subbasins upstream from the South Middleton streamgage. 

To isolate the effects on streamflow of reducing EIA, the 

results of the long-term simulation incorporating reduced EIA 

was compared to the results of the updated baseline simulation 

(LID-LT_upDem); the only difference between these two simulations was the amount of EIA and associated pervious urban 

land use upstream from the South Middleton streamgage.

Water Conservation Simulation

Five water-conservation pilot projects were conducted 

in the Ipswich River Basin by MDCR, in collaboration with 

researchers at Tufts University. Results from the following 

four of the five pilot projects were used in the water-conservation simulation: (1) installation of weather-sensitive “smart” 

irrigation controller switches on automated sprinkler systems 

at municipal athletic fields; (2) application of soil amendments 

at a municipal athletic field to improve soil moisture and nutrient retention; (3) installation of 800-gallon rainwater harvesting systems for the collection and reuse of rainwater for irrigation; and (4) implementation of two concurrent municipal 

programs offering homeowners free indoor water-use audits, 

water-reducing retrofit kits, and rebates for low-flow toilets 

and washing machines. Features in the first three of these pilot 

projects were designed to reduce irrigation demands that affect 

summer withdrawals in the basin, and the fourth was designed 

to reduce indoor water use that affects withdrawals year round.
78 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

01101500

Base from U.S. Geological Survey digital data

Land-use data from Massachusetts GIS, 1991

Massachusetts state plane projection, North American Datum of 1983

0 2 4

0 2 4 6 MILES

6 KILOMETERS

71°12' 71°06' 71°00'

42°36'

42°30'

01101500

Developed land use categories

 Low-density residential

 High-density residential

 Commercial-industrial-transportation

Hydrology

 Ipswich River Basin boundary

 Streamgage subbasin boundary

Streamgage and number

EXPLANATION

Area enlarged

IPSWICH RIVER BASIN

Figure 53. Commercial, high-density residential, and low-density residential land use in 1991 for the drainage area to the South 

Middleton streamgage, Ipswich, MA.
Simulation of the Effects of Land-Use Change and Low-Impact Development on Streamflow at Multiple Spatial Scales 79

9

01101500

Hydrology

 Open water

 Reach and number within model subbasin

 Ipswich River Basin boundary

 Streamgage subbasin boundary

 Streamgage, and number

Percent effective impervious

 area by subbasin

 1.6 to 2.9

 3.0 to 4.0

 4.1 to 6.4

 6.5 to 12.2

 12.3 to 21.9

EXPLANATION

0 2 4

0 2 4 6 MILES

6 KILOMETERS

9

8

1

12

3 5

6

13

11

15

7

17

2

16

14

4

18

19

10 01101500

5.6

2.9

8.8

8.8

12.2

9.6

5.2

3.9

2.9

3.3

4.0

5.9

9.1

6.4

11.5

1.6

5.5

21.9

10.9

71°12' 71°06' 71°00'

42°36'

42°30'

Base from U.S. Geological Survey digital data

Massachusetts state plane projection, North American Datum of 1983

Area enlarged

IPSWICH RIVER BASIN

Figure 54. Percent effective impervious area, by subbasin (1991 land use), for subbasins upstream from the South Middleton 

streamgage, Ipswich, MA.
80 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

To simulate the hydrologic effects of basin-wide application of the water-conservation pilot projects, MDCR estimated 

hypothetical reductions in monthly withdrawals for each 

town that withdraws water from the basin (as represented by 

the withdrawals in the updated baseline simulation). Reductions were calculated by MDCR by scaling up the water-use 

reductions computed for each pilot project using the appropriate data for each town (for example, the number of acres of 

athletic field irrigated with water withdrawn from the basin, 

the number of single-family homes, and the total number 

of households). Details of the calculations and assumptions 

used by MDCR to scale up the data from the pilot-scale water 

conservation programs to the town level are provided in 

tables 1–1 and 1–2 in Appendix 1. Although some reductions 

would only occur seasonally (irrigation demands), reductions 

were applied year round to simulate the effects of a best-case 

reduction in water use. Water-use reductions ranged from 

about 0.27 million gallons per month (Mgal/month) for the 

town of Ipswich to 4.43 Mgal/month for the Salem-Beverly 

water-supply system, which correspond to 3.3 and 1.4 percent of average 1989–1993 withdrawal rates, respectively, for 

these communities (table 12). The largest percentage reductions were for the town of Hamilton (8.5 percent of average 

1989–1993 withdrawals).

Monthly water-use reductions were converted to daily 

rates and then used to adjust the updated baseline simulation 

withdrawals by use of multiplication factors. To compute 

the multiplication factors, the average streamflow-depletion 

rate or direct surface-water withdrawal rate, as appropriate, 

(collectively referred to as withdrawals in this section) was 

computed for each source for the period 1989 to 1993 (with 

the exception of the Reading and Wilmington withdrawals, for which the updated withdrawals were used). Sources 

were then grouped by town, and a total average withdrawal 

rate for each town was calculated (table 12). The multiplication factor for each town was then computed as one minus 

the ratio of the average water savings rate to the total average updated baseline withdrawal rate (data not shown). This 

multiplication factor was then applied to the withdrawal time 

series for each source, resulting in reductions proportional to 

average updated baseline withdrawals. Long-term time series 

for 1961 to 1995 then were computed as described in the 

“Model Description” section of the report, and withdrawals 

were regrouped and totaled by subbasin. To isolate the effects 

of the reductions from the scaled up water-conservation pilot 

projects, the long-term simulation with reduced withdrawals (LID_LT_conserv) was compared to the updated baseline 

simulation (LID-LT_upDem); the only differences between 

these two simulations were the withdrawal rates.

Local-Scale Simulations

At the scale of model subbasins (hundreds to thousands 

of acres), drainage areas in the Ipswich River Basin are characterized as a heterogeneous mixture of land use and surficial 

geology. As indicated by the results from the basin-scale 

simulations (discussed below), the percentage of urban land 

use generally was found to be too low to induce large changes 

in simulated streamflow in response to reducing EIA to represent LID practices. On smaller spatial scales, however, larger 

percentages of drainage areas are likely to be developed (in the 

Ipswich River Basin and elsewhere), and LID could be implemented in the developed areas, with a resulting larger effect 

on flow in small streams. To address this issue of spatial scale, 

hypothetical local-scale simulations were conducted to show 

the potential effects of land-use change, surficial geology, and 

management practices on a local scale (100 acres). By simulating streamflow on a local scale, effects that may not be evident 

on the subbasin scale, such as responses to land-use change 

and development patterns, were evaluated. Consequently, 

simulations at this scale provided a better understanding of the 

geologic and land-use settings for which LID may have the 

greatest potential benefits. Similar to the basin-scale simulations, reduced EIA was used as a surrogate measure of the net 

effect of specific LID practices.

To conduct the local-scale simulations with the calibrated HSPF model, selected existing HRUs were re-scaled 

to 100 acres to simulate runoff from small drainage areas 

with uniform land use. Although drainage areas in eastern 

Massachusetts smaller than about 1 mi2 (640 acres) have a 

low probability of producing perennial streamflow (Bent and 

Steeves, 2006), the model is capable of simulating continuous 

runoff from 100-acre parcels (at low flows below measureable 

values); consequently, it was possible to compare differences 

in simulated flows to evaluate local-scale effects. Streamflow 

was simulated as total surface runoff, interflow, and base flow 

from the parcel (that is, there was no spatially variable flow to 

a channel adjacent to the parcel). As in the basin-scale simulations, EIA represented the fraction of the total impervious area 

from which precipitation discharged directly to streams with 

no infiltration. Runoff from the remaining impervious surfaces 

within the pervious areas (noneffective impervious surface 

(NEIA)) was assumed to discharge directly to ground surface; 

stormwater-control structures for the NEIA, such as detention 

basins, were not explicitly represented in the model. Simulations were conducted for conventional development and 

cluster development scenarios.

Conventional Development

A set of simulations was conducted to evaluate the effects 

of uniform land-use change on streamflow. One example of 

such a change was the conversion of 100 acres of forest to a 

commercial development. Simulations also were conducted 

to evaluate the sensitivity of streamflow to the amount of EIA 

associated with developed land use. In this study, conventional 

development refers to development consisting of uniform lot 

sizes with no preservation of open space. In the Ipswich River 

Basin HSPF model, high-density residential areas contain lot 

sizes of less than or equal to 0.5 acre, whereas low-density 

residential areas contain lot sizes of greater than 0.5 acre 

(Zarriello and Ries, 2000). Therefore, representative housing 
Simulation of the Effects of Land-Use Change and Low-Impact Development on Streamflow at Multiple Spatial Scales 81

Table 12. Hypothetical water-use reductions obtained by scaling up the results from four water-conservation pilot projects conducted by the Massachusetts Department of Conservation and Recreation for towns that withdraw water from the Ipswich River Basin, MA.[gal/month, gallons per month; ft3/s, cubic feet per second]

Town or supplier

Water-use reductions 

from installation of 

800-gallon rainwater 

harvesting systems 

(summer)

(gal/month)

Water-use

reductions from 

installation of lowflow indoor fixtures 

and appliances

(year round)

(gal/month)

Water-use

reductions from 

application of 

soil amendments 

at athletic fields 

(summer)

(gal/month)

Water-use reductions 

from installation of 

weather-sensitive 

irrigation systems 

on athletic fields 

(summer)

(gal/month)

Total wateruse reductions 

(summer savings 

plus year-round 

savings)

(gal/month)

Total water-use

reductions 

(summer 

savings plus 

year-round 

savings)

(ft3/s)

Average 

town withdrawal rate 

for 1989–1993 

calibration 

period

(ft3/s)

Percentage 

of average 

town withdrawal rate

Wilmington 919,100 249,500 253,400 923,000 2,345,000 0.119 2.31* 5.2Danvers Water Supply 1,157,300 422,100 130,100 473,800 2,183,300 0.111 5.32 2.1North Reading 581,500 169,800 93,400 340,200 1,184,900 0.0603 1.33 4.5Peabody 790,900 329,400 200,100 728,900 2,049,300 0.104 5.44 1.9Hamilton 340,300 994,300 89,100 324,400 1,748,100 0.0889 1.05 8.5Ipswich 134,300 48,800 18,500 67,500 269,100 0.0137 0.42 3.3Topsfield 265,900 74,700 89,900 327,300 757,800 0.0385 0.78 5.0Wenham 150,100 46,000 30,000 109,300 335,400 0.0171 0.52 3.3Salem Beverly Water Supply 1,929,000 1,200,800 280,200 1,020,500 4,430,500 0.225 15.8 1.4Lynnfield 202,100 56,300 6,700 24,300 289,400 0.0147 0.47 3.1Lynn 337,000 241,800 29,400 106,900 715,100 0.0364 1.08 3.4

* Updated Wilmington withdrawal rate (refer to “Updated Baseline Withdrawal Simulation” section of text).
82 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

densities would be about 400 houses on 100 acres (1/4-acre 

lots) for conventional high-density residential development 

and about 100 houses on 100 acres (1-acre lots) for low-density residential development.

Four land-use types were defined for the local-scale 

scenario. Within each land-use type, additional simulations 

were made at the local scale to represent various combinations 

of EIA, NEIA, and pervious areas overlying surficial geology 

types (table 13).

1. Forested (undeveloped) land use (no EIA).

2. Commercial land use. One simulation was conducted 

with the model-calibrated EIA for commercial land use of 

63 percent. Thus, 100 acres of commercial development 

were represented by 37 acres of the pervious commercial 

HRU and 63 acres of EIA. Two additional simulations 

were conducted to evaluate the effects of varying EIA. 

The model-calibrated EIA was reduced by 25 and 50 percent (to 47 acres and 31.5 acres, respectively) to simulate 

the hydrologic effects of incorporating LID practices that 

reduce EIA. The model variables for the pervious commercial HRU were adjusted slightly during calibration to 

respond faster to precipitation than otherwise would be 

the case based only on underlying geology to account for 

NEIA that contributed water to the pervious area and for 

disturbances to the underlying soil from compaction and 

land filling (Zarriello and Ries, 2000). However, because 

the commercial HRU was not differentiated by underlying geology (commercial areas overlying till and sand 

and gravel were grouped into a single HRU), and because 

most of the commercial land use in the basin overlies sand 

and gravel, calibrated parameter values for the pervious 

commercial HRU allowed more infiltration and less interflow and surface runoff than the residential HRUs overlying till, which represented the least pervious PERLNDs in 

the model.

3. High-density residential land use. One simulation was 

conducted with the model-calibrated EIA for high-density 

residential land use of 14 percent. Thus, 100 acres of 

high-density residential development were represented by 

86 acres of the high-density residential HRU (overlying 

till or sand and gravel) and 14 acres of EIA. Two additional simulations were conducted to evaluate the effect 

of varying EIA. The model-calibrated EIA (14 acres) was 

reduced by 50 percent (to 7 acres) to evaluate the effects 

of implementing LID to reduce EIA and increased by 

100 percent (to 28 acres) to simulate a reasonable upper 

boundary for EIA in high-density residential areas (Alley 

and Veenhuis, 1983). An EIA higher than the model-calibrated value could be representative of local conditions in 

the basin. Similar to the model variables for the pervious 

commercial HRU, model variables for the pervious highdensity residential HRUs were adjusted slightly during 

calibration to account for NEIA and disturbance of the 

soil, but after adjustment the model variables more closely 

represented the characteristics of undisturbed soil than 

disturbed soil.

4. Low-density residential land use. One simulation was 

conducted with the model-calibrated EIA for low-density 

residential land use of 2.5 percent. Thus, 100 acres of 

low-density residential development were represented by 

97.5 pervious acres of the low-density residential HRU 

(overlying till or sand and gravel) and 2.5 acres of EIA. 

As above, two additional simulations were conducted to 

evaluate the effect of varying EIA. The model-calibrated 

EIA (2.5 acres) was reduced by 50 percent (to 1.25 acres) 

to simulate the effects of implementing LID to reduce 

EIA, and increased by 100 percent (to 5 acres) to simulate a reasonable upper boundary for EIA in low-density 

residential areas (Alley and Veenhuis, 1983). As for 

high-density residential land use, an EIA higher than the 

model-calibrated value for low-density residential land 

use could be representative of local conditions in the 

basin. The model variables for the pervious low-density 

residential HRUs were adjusted the least during calibration to account for NEIA and disturbance of the soil, and 

thus were most representative of the undisturbed soil. 

Because the percentage of imperviousness associated with 

low-density residential development is low, EIA changes 

can be expected to have minor effects on simulated 

streamflow; however, the simulation was conducted to 

show the types of development for which implementation of LID techniques would likely have the largest and 

smallest hydrologic effects.

Cluster Development

Simulations were conducted to evaluate the effects of 

high- and low-density residential clustered-housing practices, 

with and without LID features, on streamflow (table 13). 

Cluster developments preserve open, undeveloped space and 

potentially reduce the overall amount of EIA compared to conventional developments. To simulate clustering, the 100-acre 

parcel was divided into an undeveloped (forested) part and a 

developed part containing the houses. Forested HRUs were 

used to represent the undeveloped part of the parcel because 

most developable areas in the basin were forested at the time 

of the study. Additional simulations were conducted to evaluate the effects of varying the amount of EIA in the developed 

part of the parcel.

Clustering Practices for High-Density Residential Development

Housing for a conventional 100-acre high-density 

residential development (400 houses on 1/4-acre lots) was 

clustered onto 40 acres (400 houses on 0.1-acre lots) of the 

100-acre parcel to evaluate the effects of open-space preservation for a high-density residential development. The remaining 

60 acres were assumed to be forested. The spatial distribution 

of runoff from the 100-acre parcel was not represented in the 

model.
Simulation of the Effects of Land-Use Change and Low-Impact Development on Streamflow at Multiple Spatial Scales 83

Table 13. Land-use distribution used in local-scale simulations for 100-acre parcels, conducted with the calibrated Hydrological 

Simulation Program-FORTRAN model of the Ipswich River Basin, MA.

[EIA, effective impervious area; SG, sand and gravel; %, percent; HRU, hydrologic response unit; l-d res, pervious low-density residential area; h-d res, 

pervious high-density residential area; In contrast to forested and residential HRUs, the pervious commercial HRU is not differentiated by underlying surfical 

geology]

Simulation (LID_LT-local) description Percent 

EIA Land-use distribution

Undeveloped

Forest over SG 0 100 acres forest over SG

Forest over till 0 100 acres forest over till

Conventionally laid out (uniform) development

Commercial, model-calibrated EIA 63 37 acres commercial; 63 acres EIA

Commercial, 25% reduction in EIA 47 53 acres commercial; 47 acres EIA

Commercial, 50% reduction in EIA 31.5 68.5 acres commercial; 31.5 acres EIA

High-density residential over SG, model-calibrated EIA 14 86 acres h-d res over SG; 14 acres EIA

High-density residential over SG, 50% decrease in EIA 7 93 acres h-d res over SG; 7 acres EIA

High-density residential over SG, 100% increase in EIA 28 72 acres h-d res over SG; 28 acres EIA

Low-density residential over SG, model-calibrated EIA 2.5 97.5 acres l-d res over SG; 2.5 acres EIA

Low-density residential over SG, 50% decrease in EIA 1.25 98.75 acres l-d res over SG; 1.25 acres EIA

Low-density residential over SG, 100% increase in EIA 5 95 acres l-d res over SG; 5 acres EIA

High-density residential over till, model-calibrated EIA 14 86 acres h-d res over SG; 14 acres EIA

High-density residential over till, 50% decrease in EIA 7 93 acres h-d res over SG; 7 acres EIA

High-density residential over till, 100% increase in EIA 28 72 acres h-d res over SG; 28 acres EIA

Low-density residential over till, model-calibrated EIA 2.5 97.5 acres l-d res over SG; 2.5 acres EIA

Low-density residential over till, 50% decrease in EIA 1.25 98.75 acres l-d res over SG; 1.25 acres EIA

Low-density residential over till, 100% increase in EIA 5 95 acres l-d res over SG; 5 acres EIA

Cluster development1

High-density residential over SG, 14% EIA in developed area 5.6 60 acres forest over SG; 34.4 acres commercial; 5.6 acres EIA

High-density residential over SG, 28% EIA in developed area 11.2 60 acres forest over SG; 28.8 acres commercial; 11.2 acres EIA

High-density residential over SG, 56% EIA in developed area 22.4 60 acres forest over SG; 17.6 acres commercial; 22.4 acres EIA

Low-density residential over SG, 7% EIA in developed area 1.8 75 acres forest over SG; 23.5 acres h-d res over SG; 1.8 acres EIA

Low-density residential over SG, 14% EIA in developed area 3.5 75 acres forest over SG; 21.5 acres h-d res over SG; 3.5 acres EIA

Low-density residential over SG, 28% EIA in developed area 7.0 75 acres forest over SG; 18.0 acres h-d res over SG; 7.0 acres EIA

High-density residential over till, 14% EIA in developed area 5.6 60 acres forest over till; 34.4 acres commercial; 5.6 acres EIA

High-density residential over till, 28% EIA in developed area 11.2 61 acres forest over till; 28.8 acres commercial; 11.2 acres EIA

High-density residential over till, 56% EIA in developed area 22.4 60 acres forest over SG; 17.6 acres commercial; 22.4 acres EIA

Low-density residential over till, 7% EIA in developed area 1.8 75 acres forest over SG; 23.5 acres h-d res over SG; 1.8 acres EIA

Low-density residential over till, 14% EIA in developed area 3.5 75 acres forest over SG; 21.5 acres h-d res over SG; 3.5 acres EIA

Low-density residential over till, 28% EIA in developed area 7.0 75 acres forest over SG; 18.0 acres h-d res over SG; 7.0 acres EIA

1

The low-density cluster development was represented by the high-density residential HRU.
84 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

For each surficial geology type, three simulations were 

conducted to simulate a reasonable range of EIA for the 

40-acre developed part of the parcel: 56 percent (22.4 acres) 

EIA, 28 percent (11.2 acres) EIA, and 14 percent (5.6 acres) 

EIA, leaving 17.6, 28.8, and 34.4 acres, respectively, as pervious area in the developed part of the parcel. The spread in EIA 

values represents a reasonable range for high-density residential development on 0.1-acre lots, with 28 percent representing a typical value (Alley and Veenhuis, 1983), 56 percent 

representing a potential upper boundary (Alley and Veenhuis, 

1983), and 14 percent representing a potential lower boundary 

if LID practices such as porous pavement were applied to the 

development. Despite reducing lot sizes to 0.1 acre, the pervious areas in the developed part of the parcel still were represented by the high-density residential HRUs because, of all the 

HRUs in the Ipswich River Basin HSPF model, the high-density residential HRUs best represent the intensity of residential 

development. The 60-acre undeveloped part of the parcel, 

represented by the forested HRUs, remained unchanged for all 

simulations.

Clustering Practices for Low-Density Residential Development

Housing for a conventional 100-acre low-density residential development (100 houses on 1-acre lots) was clustered 

onto 25 acres (100 houses on 0.25 acre lots) of the 100-acre 

parcel to evaluate the effects of open-space preservation for a 

low-density residential development. The remaining 75 acres 

were assumed to be forested. The spatial distribution of runoff 

from the 100-acre parcel was not represented in the model.

For each surficial geology type, three simulations were 

conducted to simulate a reasonable range of EIA values for the 

25-acre developed part of the parcel: 28 percent (7.0 acres) 

EIA, 14 percent (3.5 acres) EIA, and 7 percent (1.8 acres) 

EIA, leaving 18.0 acres, 21.5 acres, and 23.2 acres, respectively, as pervious area in the developed part of the parcel. The 

spread in EIA values represents a reasonable range for highdensity residential development on 1/4-acre lots, with 14 percent representing the model-calibrated value for high-density 

residential development, 28 percent representing a potential 

upper boundary (Alley and Veenhuis, 1983), and 7 percent 

representing a potential lower boundary if LID practices such 

as porous pavement were applied to the development. The pervious area in the developed part of the parcel was represented 

by the high-density residential HRU, rather than the lowdensity residential HRU, because the high-density residential 

HRU parameter values better represent the higher density of 

development (1/4-acre lots). The 75-acre undeveloped part 

of the parcel, represented by the forested HRUs, remained 

unchanged for all of the simulations.

Effects of Water-Withdrawal Changes and LowImpact-Development Practices on Streamflow

The effects of water-withdrawal changes and LID practices on streamflow were evaluated by comparing two or more 

scenarios at selected locations in the basin to each other; thus, 

relative rather than absolute changes in simulated streamflow 

were the focus of the assessment.

Basin-Scale Simulations

The reaches selected for analysis generally were chosen 

to show the maximum effect of a land-use or water-use change 

on an individual reach (for example, reach 27 with a direct 

drainage area of 0.66 mi2) or the integrated effect of a change 

over a larger area (for example, reach 19 with a total drainage 

area of 44.4 mi2).

Updated Baseline Simulation

The updated withdrawals for the towns of Reading and 

Wilmington generally led to substantially higher low and 

medium simulated flows in the reaches upstream from and at 

the South Middleton streamgage (fig. 55; table 14). Reducing ground-water withdrawals from the upper basin had a 

greater effect on simulated flows than any of the LID practices 

discussed in the following sections. Flow-duration plots from 

long-term simulations show that differences are evident for 

flows greater than the 30 percent exceedance probability at 

most locations (fig. 55). The largest increases in low flows 

occurred in reach 1 (Maple Meadow Brook at Route 38, 

Wilmington) and reach 8 (Ipswich River at Mill Street, near 

Reading) because multiple wells were taken out of service. 

Streamflow depletion rates fell to zero in headwater reach 1 

and to nearly zero in reach 8, causing the updated-baseline 

simulation flows to nearly equal the no-withdrawal-simulation 

flows (figs. 55A, B).

August median flows (median of August median flows for 

the period 1961–1995) rose from 0 to 1.34 ft3/s in reach 1 and 

from 0.539 to 6.12 ft3/s in reach 8. Similarly, median 1-day, 

7-day, and 30-day low flows rose from no-flow conditions 

to flows similar to the no-withdrawal simulation. Changes in 

withdrawal patterns and effects on flow are less pronounced 

in reach 5 (Lubbers Brook above Route 38, Wilmington) 

and reach 13 (Martins Brook above mouth, North Reading) 

(figs. 55C, D). For example, August median flows rose from 

0.917 to 1.01 ft3/s in reach 5 (about 10 percent) and from 

0.032 to 0.274 ft3/s in reach 13 (about 756 percent).

The combined changes in withdrawal patterns upstream 

from reach 19 (Ipswich River at South Middleton streamgage) 

led to substantially increased low and median flows in the 

Ipswich River at this location (fig. 55E). Total withdrawals 

upstream from reach 19 averaged 6.7 Mgal/d in the original 

baseline simulation and 3.5 Mgal/d in the updated baseline 

simulation. The original baseline model simulated August 

median flow was 3.42 ft3/s, the median 1-day low flow was 

0.740 ft3/s, and the median 7-day low flow was 0.983 ft3/s. 

The updated baseline model simulated August median flow 

was 8.36 ft3/s, the median 1-day low flow was 2.80 ft3/s, and 

the median 7-day low flow was 3.65 ft3/s. Thus, the August 
Simulation of the Effects of Land-Use Change and Low-Impact Development on Streamflow at Multiple Spatial Scales 85

Figure 55. Flow-duration curves of daily mean streamflow at (A) reach 1, Maple Meadow Brook at Route 38, 

Wilmington, (B) reach 8, Ipswich River at Mill Street near Reading, (C) reach 5, Lubbers Brook above Route 38, 

Wilmington, (D) reach 13, Martins Brook above mouth, North Reading, and (E) reach 19, Ipswich River at South Middleton 

streamgage in the Ipswich River Basin developed from long-term (1961–1995) simulations with 1989–1993 withdrawals 

(original baseline withdrawals), updated withdrawals for the towns of Reading and Wilmington (updated baseline 

withdrawals), and no withdrawals. Reach locations are shown in fig. 49.

Original baseline withdrawals

Updated baseline withdrawals

No withdrawals

D

100

1,000

10

 1

0.1

STREAMFLOW, IN CUBIC FEET PER SECOND

0.5 2 5 10 30 50 70 90 95 99 99.8

E

Original baseline withdrawals

Updated baseline withdrawals

No withdrawals

100

1,000

10

 1

0.1

PERCENTAGE OF TIME

FLOW WAS EQUALED OR EXCEEDED

0.5 2 5 10 30 50 70 90 95 99 99.8

Original Baseline Withdrawals

Updated Baseline Withdrawals

No Withdrawals

C

100

10

 1

0.1

0.5 2 5 10 30 50 70 90 95 99 99.8

Original baseline withdrawals

Updated baseline withdrawals

No withdrawals

A

100

10

 1

0.1

0.5 2 5 10 30 50 70 90 95 99 99.8

Original baseline withdrawals

Updated baseline withdrawals

No withdrawals

B

100

1,000

10

 1

0.1

0.5 2 5 10 30 50 70 90 95 99 99.8

PERCENTAGE OF TIME

FLOW WAS EQUALED OR EXCEEDED
86 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin Table 14. Flow statistics for long-term (1961–1995) simulations with original baseline (1989–1993) withdrawals and updated baseline withdrawals for the towns of Reading and Wilmington (scenario LID_LT-upDem) at selected subbasins in the Ipswich River Basin, MA. [DSN, dataset number in the Watershed Data Management database. Original baseline withdrawals refers to average 1989–1993 withdrawals simulated by Zarriello and Ries (2000). Updated baseline with- drawals reflect updated withdrawal rates for the towns of Reading and Wilmington as described in the text (scenario LID_LT-upDem). All other aspects of the model are identical. Indicators of Hydrologic Alteration, version 7, was used to compute flow statistics. January, April, August, and October median flows are medians of monthly medians for the period 1961–1995. Median 1-day, 7-day, and 30-day flows are medians of annual 1-day, 7-day, and 30-day means, respectively, for the period 1961–1995. Percent change defined as streamflow for updated baseline withdrawals minus streamflow for original baseline withdrawals over streamflow for original baseline withdrawals. --, no value; ft3/s, cubic feet per second] DSN Scenario description Statistics for simulated daily mean flow, 1961–1995, in ft3/s Mean annual January median April median August median October median Median 1-day low flow Median 7-day low flow Median 30-day low flow Median 1-day high flow Median 7-day high flow Median 30-day high flow Reach 1. Maple Meadow Brook at Route 38, Wilmington 6501 Original baseline withdrawals 5.76 5.29 8.00 0 0.247 0 0 0 37.7 29.8 17.8 7501 Updated baseline withdrawals 7.43 7.04 9.70 1.34 2.19 0.462 0.602 0.920 39.4 31.5 19.6 7901 No withdrawals 7.43 7.04 9.70 1.34 2.19 0.462 0.602 0.920 39.4 31.5 19.6 Percent change: 29 33 21 -- 788 -- -- -- 4 6 10 Reach 5. Lubbers Brook above Route 38, Wilmington 6505 Original baseline withdrawals 5.01 5.31 6.79 0.917 2.03 0.259 0.341 0.625 22.3 16.8 12.1 7505 Updated baseline withdrawals 4.69 4.98 6.01 1.01 1.43 0.247 0.352 0.672 21.7 16.1 11.5 7905 No withdrawals 5.12 5.44 6.89 1.04 2.11 0.381 0.472 0.742 22.4 16.9 12.2 Percent change: -6 -6 -11 10 -30 -5 3 7 -3 -4 -5 Reach 8. Ipswich River at Mill Street, near Reading 6508 Original baseline withdrawals 28.3 29.5 39.9 0.539 7.02 0 0 0.381 160 123 80.1 7508 Updated baseline withdrawals 33.0 33.8 44.0 6.12 11.7 2.14 2.63 4.19 165 128 83.9 7908 No withdrawals 33.5 34.2 44.8 6.35 12.3 2.25 2.79 4.33 165 128 84.6 Percent change: 16 14 10 1,036 67 -- -- 1,000 3 4 5 Reach 13. Martins Brook above mouth, North Reading 6513 Original baseline withdrawals 18.9 20.3 25.6 0.0320 4.52 0 0 0.0367 96.3 78.5 54.5 7513 Updated baseline withdrawals 19.0 19.8 25.4 0.274 4.60 0 0 0.115 96.1 78.3 54.3 7913 No withdrawals 22.2 23.3 28.8 3.65 8.11 1.56 1.79 2.68 99.5 81.8 57.7 Percent change: 0 -2 -1 756 2 -- -- 213 -0 -0 -0 Reach 19. Ipswich River at South Middleton streamgage 6519 Original baseline withdrawals 66.2 72.5 89.6 3.42 17.1 0.740 0.983 1.98 348 274 187 7519 Updated baseline withdrawals 70.9 76.9 93.4 8.36 22.3 2.80 3.65 5.89 351 279 191 7919 No withdrawals 76.3 81.0 105 12.5 26.8 5.13 6.11 8.96 360 284 198

Percent change: 7 6 4 144 30 279 271 197 1 2 2
Simulation of the Effects of Land-Use Change and Low-Impact Development on Streamflow at Multiple Spatial Scales 87

median flow rose 144 percent, the median 1-day low flow rose 

279 percent, and the median 7-day low flow rose 271 percent.

Current and anticipated reductions in water withdrawals for the towns of Reading and Wilmington have the largest 

effects on simulated flows in the upper Ipswich River and 

Maple Meadow Brook, and more modest effects on simulated 

flows in Lubbers Brook and Martins Brook. Local effects on 

small streams in the immediate vicinity of withdrawal wells 

could be more pronounced, but these effects were not specifically evaluated with the model.

Buildout Simulation

Land-use change associated with buildout generally had 

minor effects on simulated streamflow in the Ipswich River 

Basin. Flow-duration plots were compared with the updated 

baseline simulation (1991 land use). These plots (fig. 56) show 

(1) long-term buildout simulation results for one reach with a 

percentage of developable area in its drainage area similar to 

the basin average percentage (reach 34, Boston Brook above 

mouth, Middleton), (2) three reaches with greater than average percentages of developable area (reach 35, Ipswich River 

above Nichols Brook, Middleton; reach 28, Ipswich River at 

Maple Street, Middleton; reach 27, Middleton Pond Brook, 

Middleton), and (3) two reaches that show the effects of 

land-use change over large drainage areas (reach 19, Ipswich 

River at South Middleton streamgage; reach 56, Ipswich River 

at Ipswich streamgage). The total drainage areas to reaches 

19 and 56 are 44.4 and 125 mi2, respectively. For the three 

reaches with large percentages of developable area, upstream 

flows were omitted so that the effects of land-use change in the 

direct drainage area (that is, the subbasin area) that contributes 

streamflow to the reach could be evaluated.

In reach 34, about 24.5 percent (1,713 acres) of the 

6,980-acre (10.9 mi2) drainage area to Boston Brook was 

developable. Of the 1,713 developable acres, only 106 acres 

was apportioned to IMPLNDs because most of the developable land was zoned for low-density residential development. 

The EIA in the drainage area increased from 2.7 percent in 

1991 to 4.2 percent at buildout. These land-use changes had 

modest effects on streamflow in Boston Brook (fig. 56A; 

table 15). For example, the median 1-day high flow (annual 

flood flow) increased only about 13 percent from 104 to 

118 ft3/s, and the median August flow and other low-flow 

statistics increased by less than 5 percent.

In reach 35, about 52 percent (512 acres) of the 989-acre 

subbasin area was developable, of which only 13 acres 

(2.5 percent of the developable area) was apportioned to 

IMPLNDs because most of the developable area is zoned for 

low-density residential development. Thus, the EIA in the 

direct drainage area to reach 35 increased from 1.9 percent in 

1991 to 3.2 percent at buildout. Consequently, although almost 

52 percent of the subbasin was developable, land-use changes 

due to buildout had modest effects on streamflow (fig. 56B) 

for the same reasons as those for Boston Brook (reach 34). 

In reach 35, the 1-day high flow increased about 19 percent, 

from 14.4 ft3/s in 1991 to 17.2 ft3/s at buildout, and low flows 

decreased about 3 percent (table 15).

In reach 28, about 36 percent (382 acres) of the 

1,052-acre subbasin area was developable, of which 71 acres 

(about 19 percent of the developable area) were apportioned 

to IMPLNDs, reflecting a greater amount of land zoned for 

commercial and high-density residential use. The EIA in the 

subbasin increased from 3.8 percent in 1991 to 10.5 percent 

at buildout. Despite a larger percentage increase in EIA in 

reach 28 than in reaches 34 and 35, buildout still had a modest effect on streamflow in this reach (fig. 56C). In reach 28, 

the 1-day high flow increased from 14.7 ft3/s for 1991 land 

use to 16.5 ft3/s at buildout (about 12 percent), and low flows 

were slightly lower (about 4 percent) at buildout (table 15). 

A prevalence of sand and gravel in this subbasin may account 

for the lack of response to increased EIA compared to reaches 

34 and 35.

In reach 27, about 40 percent (169 acres) of the 421-acre 

subbasin was developable, of which 85 acres (about 50 percent 

of the developable area) was apportioned to IMPLNDs. This 

increased the EIA in the subbasin from 8.6 percent in 1991 to 

28.9 percent at buildout. The large percentage increase in EIA 

relative to the other reaches discussed in this section indicates 

that most of the developable land in this subbasin was zoned 

for one or more commercial and industrial uses (table 10). 

A change in EIA of this magnitude and large percentage 

increases in the amount of pervious commercial area resulted 

in more pronounced effects on both high and low flows 

(fig. 56D). The median 1-day and 7-day high flows increased 

by 67 percent and 33 percent, respectively, whereas the 

median 1-day and 7-day low flows at buildout decreased by 

28 percent and 26 percent, respectively (table 15). Simulation 

results for this subbasin indicate that a relatively large increase 

in EIA (percent increase of over 200 percent) is needed to substantially alter simulated flows; alterations in flow ranged from 

near zero percent to 20 percent in other areas of the Ipswich 

River Basin. Notably, changes of this magnitude occurred in a 

small subbasin, in which land-use change affected a relatively 

large percentage of the drainage area.

In reaches 19 and 56, which show land-use-change 

effects over large drainage areas (44.4 and 125 mi2, respectively), differences in streamflow for 1991 land use and land 

use at buildout generally were small (figs. 56E, F); percent 

changes ranged from zero to 10 percent (table 15). This result 

is consistent with the relatively small percentage increases in 

EIA in these large drainage areas. For example, the EIA in the 

reach 19 drainage area increased 0.9 percent, from 6.8 percent 

in 1991 to 7.7 percent at buildout. Similarly, the EIA in the 

reach 56 drainage area increased 1.2 percent, from 4.7 percent 

in 1991 to 5.9 percent at buildout.

These examples demonstrate that land-use change associated with buildout generally had modest (percent change in 

the range of 0 to 20 percent) effects on simulated streamflow 

because most of the developable land in the basin in 1991 

was forested or open and zoned for low-density residential development (table 11). Because there was a relatively 
88 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Figure 56. Flow-duration curves of daily mean streamflow at (A) reach 34, Boston Brook above mouth, Middleton, 

(B) reach 35, Ipswich River above Nichols Brook, Middleton, (C) reach 28, Ipswich River at Maple Street, Middleton, 

(D) reach 27, Middleton Pond Brook, Middleton, (E) reach 19, Ipswich River at South Middleton streamgage, and (F) 

reach 56, Ipswich River at Ipswich streamgage in the Ipswich River Basin developed from long-term (1961–1995) 

simulations with 1991 land use and potential land use at buildout. Simulations incorporate updated baseline 

withdrawals. Reach locations are shown in fig. 49.

0.5 2 5 10 30 50 70 90 95 99 99.8

PERCENTAGE OF TIME

FLOW WAS EQUALED OR EXCEEDED

PERCENTAGE OF TIME

FLOW WAS EQUALED OR EXCEEDED

0.5 2 5 10 30 50 70 90 95 99 99.8

0.5 2 5 10 30 50 70 90 95 99 99.8

0.5 2 5 10 30 50 70 90 95 99 99.8 0.5 2 5 10 30 50 70 90 95 99 99.8

0.5 2 5 10 30 50 70 90 95 99 99.8

100

1,000

10

 1

0.1

1,000

100

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1

STREAMFLOW, IN CUBIC FEET PER SECOND

100

10

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0.1

100

10

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0.1

100

10

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0.1

1,000

10,000

100

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1

A B

D

E F

C

Buildout land use

1991 land use

Buildout land use

1991 land use

Buildout land use

1991 land use

Buildout land use

1991 land use

Buildout land use

1991 land use

Buildout land use

1991 land use
Simulation of the Effects of Land-Use Change and Low-Impact Development on Streamflow at Multiple Spatial Scales 89

Table 15. Flow statistics for long-term (1961–1995) simulations with 1991 land use and potential land use at buildout (scenario LID_LT-build) at selected subbasins in the Ipswich River Basin, MA.[DSN, dataset number in the Watershed Data Management database; 1991 land use refers to the land-use data used by Zarriello and Ries (2000) for the original baseline model. Buildout land use refers to potential future land use at buildout (scenario LID_LT-build). All other aspects of the simulations are identical. Both simulations incorporate the updated Reading and Wilmington withdrawals. To evaluate the effects of land-use change in the direct drainage area to the reach, streamflow from upstream reaches was omitted for reaches 27, 28, and 35. Indicators of Hydrologic Alteration, version 7, was used to compute flow statistics. January, April, August, and October median flows are medians of monthly medians for the period 1961–1995. Median 1-day, 7-day, and 30-day flows are medians of annual 1-day, 7-day, and 30-day means, respectively, for the period 1961–1995. Percent change defined as streamflow at buildout minus streamflow in 1991 over streamflow in 1991. ft3/s, cubic feet per second]

DSN Scenario description

Statistics for simulated daily mean flow, 1961–1995, in ft3/s

Mean

annual

January 

median

April

median

August 

median

October 

median

Median 

1-day

low flow

Median

7-day

low flow

Median

30-day

low flow

Median 

1-day

high flow

Median 

7-day

high flow

Median 

30-day

high flow

Reach 34. Boston Brook above mouth, Middleton

7534 1991 land use 16.6 17.8 26.5 0.861 1.93 0.515 0.560 0.685 104 68.7 48.47634 Buildout land use 17.6 19.1 26.4 0.896 2.79 0.514 0.576 0.718 118 77.4 52.7

Percent change: 6 7 -0 4 44 -0 3 5 13 13 9

Reach 35. Ipswich River above Nichols Brook, Middleton (no flow from upstream reaches)

8535 1991 land use 2.37 2.37 3.74 0.282 0.462 0.210 0.221 0.248 14.4 9.66 6.818635 Buildout land use 2.59 2.92 3.56 0.277 0.567 0.201 0.215 0.248 17.2 11.8 7.34

Percent change: 9 23 -5 -2 23 -4 -3 -0 19 22 8

Reach 28. Ipswich River at Maple Street, Middleton (no flow from upstream reaches)

8528 1991 land use 2.97 3.23 3.97 0.414 1.16 0.253 0.272 0.348 14.7 11.1 7.448628 Buildout land use 3.17 3.52 4.02 0.414 1.23 0.243 0.253 0.330 16.5 13.1 7.86

Percent change: 7 9 1 0 6 -4 -7 -5 12 18 6

Reach 27. Middleton Pond Brook, Middleton (no flow from upstream reaches)

8527 1991 land use 1.28 1.15 1.50 0.416 0.587 0.279 0.292 0.332 8.45 4.73 2.968627 Buildout land use 1.46 1.22 1.14 0.391 0.637 0.202 0.216 0.304 14.1 6.30 3.91

Percent change: 14 6 -24 -6 9 -28 -26 -8 67 33 32

Reach 19. Ipswich River at South Middleton streamgage

7519 1991 land use 70.9 76.9 93.4 8.36 22.3 2.80 3.65 5.89 351 279 1917619 Buildout land use 72.8 78.9 95.3 8.37 23.7 2.71 3.47 6.04 378 299 194

Percent change: 3 3 2 0 6 -3 -5 2 8 7 2

Reach 56. Ipswich River at Ipswich streamgage

7556 1991 land use 183 199 250 17.6 45.5 7.44 8.12 12.2 904 740 5157656 Buildout land use 190 212 255 17.6 47.6 7.21 7.98 11.8 977 813 525

Percent change: 4 6 2 -0 5 -3 -2 -3 8 10 2
90 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

small amount of EIA associated with low-density residential 

development (2.5 percent in the calibrated Ipswich River 

Basin HSPF model), increases in this type of land use could 

not result in large changes in the amount of EIA in the basin. 

In addition, for a given type of underlying surficial geology, 

the runoff characteristics for forest and pervious low-density 

residential land use were similar.

The most significant difference between forest and lowdensity residential development was the amount of water lost 

to evapotranspiration and consequent reductions in runoff. 

Previous studies have shown that deforestation increases both 

peak flows and base-flow runoff (Bent, 2001; Hornbeck and 

others, 1993; Bosch and Hewlett, 1982). In humid climates, 

low water yields in forested watersheds have been attributed to increased canopy-intercepted evaporation and more 

intensive root-zone transpiration during the growing season 

(Bent, 2001; Calder, 1993; Robinson and others, 1991). These 

processes reduce soil moisture, reduce recharge, and lower 

water tables, and, thus, reduce the base-flow contribution to 

streamflow. Consequently, although low-density residential 

areas received slightly less infiltration per unit area because of 

EIA, the comparatively large evapotranspiration losses from 

forested areas resulted in slight increases in summer low flows 

in low-density residential areas. In the Ipswich River Basin 

HSPF model, forest and low-density residential HRUs were 

assigned parameter values that reflect these differences in the 

magnitude of evapotranspiration losses (Zarriello and Ries, 

2000). Other aspects of the effects of buildout on streamflow 

were not evaluated in this study. For example, although forests 

may produce lower water yields relative to residential areas 

with less deep-rooted vegetation, land-use studies have indicated that the quality of groundwater underlying forested areas 

typically was less affected by human activities than other land 

uses, and was considered to represent background conditions 

(Grady, 1994). Coles and others (2004) found that changes in 

water chemistry in coastal New England streams were strongly 

associated with the intensity of urban development.

Conversion of forest to low-density residential land 

use had only a modest effect on simulated streamflow; by 

comparison, conversion of forest to commercial land use had 

a much more pronounced effect on simulated streamflow 

because of the relatively large increases in EIA which resulted 

in increased surface runoff. Although the effect of urbanization 

on flood peaks was relatively clear, the effect of increasing 

urbanization on low flows showed conflicting results (Brandes 

and others, 2005; Rose and Peters, 2001), probably because 

low flows are determined by the net response to complex 

interactions among climate, land use, water use, and water 

infrastructure (Claessens and others, 2006; Lerner, 2002; Dow 

and DeWalle, 2000). Because of the uncertainty associated 

with assigning parameter values to individual HRUs (see the 

“Model Limitations” section of the report) and the lack of 

representation of specific basin features, such as urban water 

infrastructure, these simulation results were more representative of relative rather than absolute change in streamflow 

in response to land-use change. In addition, the effects of 

increased water withdrawals and wastewater return flows 

needed to serve a larger population at buildout (for example, 

Barbaro, 2007) were not evaluated in this study.

Simulation of Low-Impact-Development Retrofits 

Upstream from the South Middleton Streamgage

A 50-percent reduction of EIA upstream from the South 

Middleton streamgage (reach 19) generally had modest effects 

on streamflow at the subbasin scale (fig. 57; table 16). In 

reach 5 (Lubbers Brook above Route 38, Wilmington), EIA 

decreased from 5.2 percent (updated baseline simulation with 

1991 land use) to 2.6 percent after the EIA was reduced to 

simulate LID retrofits. The EIA for this reach is similar to the 

median value of 5.9 percent for the 19 subbasins upstream 

from the streamgage at South Middleton, and thus, the 

response of streamflow to reduced EIA is representative of a 

typical subbasin upstream from reach 19. The flow-duration 

curve (fig. 57A) and the flow statistics (table 16) indicate that 

reducing EIA by 50 percent had a small effect on high and low 

flows compared to the baseline simulation; for example, the 

median 1-day high flow decreased about 4 percent, from 21.7 

to 20.8 ft3/s. The decrease was small because only a small percentage of the subbasin area (47 of 1,811 acres) was subtracted 

from IMPLNDs and added to the various urban PERLNDs.

The direct reach 2 drainage area (Maple Meadow Brook 

above mouth, Wilmington) had the highest EIA of all the 

subbasins above the Middleton streamgage. The EIA was 

10.6 percent of the entire drainage area and 21.9 percent of 

the direct drainage area to the reach. Although in 1991 the 

entire drainage area to reach 2 had nearly double the EIA 

of reach 5, the flow-duration curve and flow statistics indicate that the decrease from 10.6 to 5.3 percent EIA still had 

a modest effect on simulated low and high flows (fig. 57B; 

table 16). For example, the median 1-day high flow at this 

location decreased 6 percent, from 49.7 to 46.8 ft3/s), whereas 

the median 1-day low flow increased 7 percent, from 0.590 to 

0.634 ft3/s. In the highly urban direct drainage area of reach 2, 

a 50-percent reduction in EIA corresponded to a reduction in 

EIA of 46 acres in a drainage area of 422 acres. Consequently, 

decreases in high flows were pronounced (the median 1-day 

high flow decreased about 20 percent), but low flows were 

largely unaffected (fig. 57C), presumably because increased 

evapotranspiration from the expanded PERLND area reduced 

base flow. Simulation results for reach 19, which reflect the 

integrated effects of LID retrofits for the entire drainage area, 

were similar to results for reach 5 (fig. 57D).

Overall, simulation of widespread reduction of EIA to 

50 percent of values in the updated baseline model (1991 land 

use) resulted in modest effects (percent differences of less than 

20 percent) on simulated streamflow upstream from the South 

Middleton streamgage. Even in this relatively urban part of 

the Ipswich River Basin, the heterogeneous mix of land uses 

resulted in total EIAs that were small percentages of subbasin 

areas. Consequently, reducing these areas by 50 percent did 

not have a pronounced effect on simulated streamflow at the 
Simulation of the Effects of Land-Use Change and Low-Impact Development on Streamflow at Multiple Spatial Scales 91

Figure 57. Flow-duration curves of daily mean streamflow at (A) reach 5, Lubbers Brook above Route 38, Wilmington,

(B) reach 2, Maple Meadow Brook above mouth, Wilmington, (C) reach 2, Mapple Meadow Brook above mouth (no 

flow from upstream reach), and (D) reach 19, Ipswich River at South Middleton streamgage in the Ipswich River Basin 

developed from long-term (1961–1995) simulations with 1991 land use and 1991 land use with effective impervious area for 

each urban land-use category reduced by 50 percent to simulate low-impact-development retrofits. Reach locations are 

shown in fig. 49. EIA, effective imperious area. STREAMFLOW, IN CUBIC FEET PER SECOND

0.5 2 5 10 30 50 70 90 95 99 99.8 0.5 2 5 10 30 50 70 90 95 99 99.8

0.5 2 5 10 30 50 70 90 95 99 99.8

PERCENTAGE OF TIME

FLOW WAS EQUALED OR EXCEEDED

PERCENTAGE OF TIME

FLOW WAS EQUALED OR EXCEEDED

0.5 2 5 10 30 50 70 90 95 99 99.8

1,000

100

 10

1

100

10

 1

0.1

100

10

 1

0.1

100

10

0.1

 1

1991 land use

1991 land use with EIA 

reduced by 50 percent

1991 land use

1991 land use with EIA 

reduced by 50 percent

1991 land use

1991 land use with EIA

reduced by 50 percent

1991 land use

1991 land use with EIA

reduced by 50 percent

A B

C D
92 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin Table 16. Flow statistics for long-term (1961–1995) simulations with 1991 land use and 1991 land use with effective impervious area reduced by 50 percent to represent low- impact-development retrofits (scenario LID_LT-retrofit) at selected subbasins in the Ipswich River Basin, MA. [DSN, dataset number in the Watershed Data Management file; EIA, effective impervious area. Both simulations incorporate the updated Reading and Wilmington withdrawals. To evaluate the effects of land- use change in the direct drainage area to the reach, streamflow from upstream reaches was omitted for reach 2 (scenario LID_LT-retrofit). Indicators of Hydrologic Alteration, version 7, was used to compute flow statistics. January, April, August, and October median flows are medians of monthly medians for the period 1961–1995. Median 1-day, 7-day, and 30-day flows are medians of annual 1-day, 7-day, and 30-day means, respectively, for the period 1961–1995. ft3/s, cubic feet per second] DSN Scenario description Statistics for simulated daily mean flow, 1961–1995, in ft3/s Mean annual January median April median August median October median Median 1-day low flow Median 7-day low flow Median 30-day low flow Median 1-day high flow Median 7-day high flow Median 30-day high flow Reach 5. Lubbers Brook above route 38, Wilmington 7505 1991 land use 4.69 4.98 6.01 1.01 1.43 0.247 0.352 0.672 21.7 16.1 11.5 7705 1991 land use with EIA reduced by 50 percent 4.58 4.81 5.94 0.962 1.37 0.254 0.366 0.645 20.8 15.3 11.3 Percent change: -2 -3 -1 -5 -4 3 4 -4 -4 -5 -1 Reach 2. Maple Meadow Brook above mouth, Wilmington 7502 1991 land use 8.74 8.26 11.1 1.75 2.57 0.590 0.748 1.20 49.7 36.9 22.7 7702 1991 land use with EIA reduced by 50 percent 8.35 8.20 11.1 1.56 2.51 0.634 0.780 1.13 46.8 35.2 21.8 Percent change: -4 -1 0 -11 -2 7 4 -6 -6 -5 -4 Reach 2. Maple Meadow Brook above mouth, Wilmington (no flow from upstream reach) 8502 1991 land use 1.31 1.16 1.21 0.292 0.404 0.125 0.145 0.238 10.6 5.78 3.37 8702 1991 land use with EIA reduced by 50 percent 1.20 1.09 1.28 0.309 0.408 0.138 0.164 0.231 8.49 5.00 2.90 Percent change: -8 -6 6 6 1 10 13 -3 -20 -14 -14 Reach 19. Ipswich River at South Middleton streamgage 7519 1991 land use 70.9 76.9 93.4 8.36 22.3 2.80 3.65 5.89 351 279 191 7719 1991 land use with EIA reduced by 50 percent 68.6 75.1 92.2 7.90 18.9 2.93 3.71 5.65 339 260 184 Percent change: -3 -2 -1 -6 -15 4 2 -4 -4 -7 -4
Simulation of the Effects of Land-Use Change and Low-Impact Development on Streamflow at Multiple Spatial Scales 93

subbasin scale. These results may have general significance 

for other drainage basins. If, because of heterogeneous land 

use, low total EIA is a general characteristic of large drainage 

areas, then widespread LID practices that reduce EIA may not 

substantially affect flows in large rivers and tributary streams. 

On the other hand, LID practices that reduce EIA on a local 

scale may have substantial effects on flows in small streams 

because (1) EIA as a percentage of the drainage area may be 

large and (2) a large percentage decrease in EIA may be attainable. The effect of scale and sensitivity to variable amounts of 

EIA are discussed in greater detail in the “Local-Scale Simulation” section of the report.

Water Conservation Simulation

Reductions in water use were expected to have their 

greatest effects on low flows in subbasins in which the 

streamflow-depletion rate was high relative to the rate of 

streamflow in the absence of withdrawals (Barbaro, 2007). 

Small tributaries affected by municipal withdrawals (Wills 

Brook (reach 17), Idlewild Brook (reach 49), and Howlett 

Brook (reach 53)) were chosen to illustrate the effects of 

hypothetical water-use reductions from widespread application 

of results from the water-conservation pilot programs (appendixes A1, A2) in the Ipswich River Basin (fig. 49). Streamflow 

depletion from time-varying groundwater withdrawals and 

direct surface-water withdrawals are collectively referred to as 

“withdrawals” in this section.

Reach 17 (Wills Brook, North Reading) is a 1,126 acre 

headwaters subbasin containing five municipal withdrawals 

for the town of Lynnfield and additional withdrawals for the 

Sagamore Springs Golf Club; the withdrawals for the golf 

club were not altered for this analysis. The average 1989–1993 

withdrawals for the town were 0.47 ft3/s (0.30 Mgal/d). The 

town-wide application of hypothetical water-use reductions 

from the water-conservation pilot programs reduced withdrawals by 0.015 ft3

/s, or 3.1 percent (table 12). The total withdrawals from the reach decreased from 0.56 to 0.55 ft3

/s. Reach 49 

(Idlewild Brook, Hamilton) is a 1,664-acre headwater subbasin dominated by Wenham swamp (43 percent of subbasin 

area). The subbasin contains three municipal withdrawals for 

the town of Hamilton and two municipal withdrawals for the 

town of Wenham. The average 1989–1993 withdrawal from 

reach 49 was 1.36 ft3/s (0.88 Mgal/d). The average reduced 

rate applied to the individual wells in the subbasin, accounting for the hypothetical water-use reductions for the towns of 

Hamilton and Wenham, was 1.27 ft3/s (0.82 Mgal/d), a reduction of 6.6 percent. Reach 53 (Howlett Brook, Topsfield) is a 

6,976-acre subbasin containing one municipal withdrawal for 

the town of Topsfield. The average 1989–1993 withdrawal rate 

from the subbasin was 0.61 ft3/s (0.39 Mgal/d). The average 

reduced withdrawal rate was 0.58 ft3/s (0.37 Mgal/d), a reduction of 5.0 percent.

Flow-duration curves indicate that withdrawal reductions on the order of 5 percent had a small effect on simulated 

low flows in these reaches (figs. 58A, B, C). Hypothetical 

20-percent reductions in withdrawal rates resulted in slightly 

higher simulated low flows, but flows for all withdrawal 

scenarios were more similar to each other than to flows for 

the no-withdrawal scenario. Flow-duration curves for reach 

19 (Ipswich River at South Middleton streamgage) indicate 

that the hypothetical water-use reductions from the waterconservation pilot programs had negligible effects on simulated low flows in the Ipswich River at this location (fig. 58D). 

This result is consistent with previous reduced-withdrawal 

simulations for this reach conducted with the original baseline 

withdrawals (Zarriello, 2002a). Local effects of withdrawal 

reductions on small streams in the immediate vicinity of withdrawal wells would likely be more pronounced, but they could 

not be evaluated with the HSPF model in its current form.3

Local-Scale Simulations

Simulated streamflow arising from combinations of land 

use, underlying surficial geology, percentage of EIA, and 

development patterns (conventional versus cluster) were compared to each other at a local (100-acre) scale (table 13).

Conventional Development

To evaluate the effects of uniform land-use change on 

streamflow, long-term (1961–1995) simulations were conducted for 100-acre parcels represented as undeveloped 

(forest) or as developed (low-density residential, high-density 

residential, or commercial) land uses (fig. 59). To facilitate 

comparison with the basin-scale results described above, the 

local-scale simulations of uniform land uses were conducted 

with model-calibrated EIA values. Converting 100 acres of 

forest overlying till to commercial development (63 acres 

EIA; 37 acres pervious commercial area) increased the 

simulated median 1-day high flow about 307 percent, from 

1.62 to 6.60 ft3/s, and decreased the median 1-day low flow 

about 33 percent, from 0.024 to 0.016 ft3/s (fig. 59A; table 17). 

Conversion of 100 acres of forest overlying till to high-density 

residential development overlying till (14 acres EIA; 86 acres 

pervious high-density residential area) had less of an effect 

on high flows; the median 1-day high flow increased about 

120 percent, from 1.62 to 3.58 ft3/s. For HRUs overlying sand 

and gravel (fig. 59B), the relative differences among land-use 

types were the same as for HRUs overlying till; however, 

the absolute differences among land-use types were more 

pronounced. For example, conversion of 100 acres of forest 

3

Subsequent to this analysis, DCR provided an updated average per-acre 

savings for the weather-based irrigation systems on athletic fields. The peracre savings increased from 16,241 to 21,128 gallons per acre per month 

(appendix A2). Simulations were not updated because the water-conservation 

savings as a percentage of average town pumping rate for the calibration 

period increased only by 0.3 percent on average for the 11 towns and water 

suppliers considered in the study (table 12). The average percentage for the 

11 towns increased from 3.8 to 4.1 percent, with the maximum percentage increase (0.6 percent) for Wilmington and Topsfield and the minimum 

percentage increase (0.1 percent) for Danvers Water Supply, Salem-Beverly 

water supply, Lynnfield, and Lynn.
94 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Figure 58. Flow-duration curves of daily mean streamflow at (A) reach 17, Wills Brook, North Reading, (B) reach 

49, Idlewild Brook, Hamilton, (C) reach 53, Howlett Brook, Topsfield, and (D) reach 19, Ipswich River at South 

Middleton streamgage in the Ipswich River Basin developed from long-term (1961–1995) simulations with updated 

baseline withdrawals, withdrawals reduced by scaled-up data from Massachusetts Department of Conservation 

and Recreation water-conservation pilot programs, withdrawals reduced by 20 percent, and no withdrawals. Reach 

locations are shown in fig. 49. DCR, Department of Conservation and Recreation. STREAMFLOW, IN CUBIC FEET PER SECOND

0.5 2 5 10 30 50 70 90 95 99 99.8 0.5 2 5 10 30 50 70 90 95 99 99.8

PERCENTAGE OF TIME

FLOW WAS EQUALED OR EXCEEDED

PERCENTAGE OF TIME

FLOW WAS EQUALED OR EXCEEDED

0.5 2 5 10 30 50 70 90 95 99 99.8 0.5 2 5 10 30 50 70 90 95 99 99.8

100

1,000

10

 1

0.1

100

10

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0.1

100

10

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0.1

1,000

100

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Updated baseline withdrawals

DCR-program reduced withdrawals

20-percent reduced withdrawals

No withdrawals

Updated baseline withdrawals

DCR-program reduced withdrawals

20-percent reduced withdrawals

No withdrawals

Updated baseline withdrawals

DCR-program reduced withdrawals

20-percent reduced withdrawals

No withdrawals

Updated baseline withdrawals

DCR-program reduced withdrawals

20-percent reduced withdrawals

No withdrawals

A B

C D
Simulation of the Effects of Land-Use Change and Low-Impact Development on Streamflow at Multiple Spatial Scales 95

Figure 59. Flow-duration curves of daily mean streamflow and mean daily-flow hydrographs from long-term (1961–1995) 

local-scale simulations of runoff from 100-acre parcels of undeveloped (forest) land and conventionally laid-out developed 

(low-density residential, high-density residential, and commercial) land (A) overlying till and (B) overlying sand and gravel 

with model-calibrated effective impervious area in the Ipswich River Basin, MA. %, percent; EIA, effective impervious 

area. 

PERCENTAGE OF TIME

FLOW WAS EQUALED OR EXCEEDED

0.5 2 5 10 30 50 70 90 95 99 99.8

0.5 2 5 10 30 50 70 90 95 99 99.8

PERCENTAGE OF TIME

FLOW WAS EQUALED OR EXCEEDED

JAN

FEB

MAR

APR

MAY

JUNE

JULY

AUG

SEPT

OCT

NOV

DEC

MONTH

JAN

FEB

MAR

APR

MAY

JUNE

JULY

AUG

SEPT

OCT

NOV

DEC

MONTH

10

1

0.1

0.01

STREAMFLOW, IN CUBIC FEET PER SECOND STREAMFLOW, IN CUBIC FEET PER SECOND

10

0.1

0.01 0.01

0.1

1

10

MEDIAN DAILY FLOW, IN CUBIC 

FEET PER SECOND

0.01

0.1

1

10

MEDIAN DAILY FLOW, IN CUBIC 

FEET PER SECOND

1

Forest (0% EIA)

Low-density residential (2.5% EIA)

High-density residential (14% EIA)

Commercial (63% EIA)

A Uniform undeveloped and developed land uses overlying till

B Uniform undeveloped and developed land uses overyling sand and gravel
96 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin Table 17. Flow statistics for long-term (1961–1995), local-scale simulations of runoff from 100-acre parcels with various combinations of undeveloped and developed land uses and amounts of effective impervious area.—Continued [SG, sand and gravel; EIA, effective impervious area. In contrast to forested and residential land uses, commercial areas are not differentiated by underlying surfical geology. Undeveleoped is forested and developed is low-density residential, high-density residential, and commercial. LID_LT-local, long-term, local-scale simulations. Indicators of Hydrologic Alteration, version 7, was used to compute flow statis- tics. January, April, August, and October median flows are medians of monthly medians for the period 1961–1995. Median 1-day, 7-day, and 30-day flows are medians of annual 1-day, 7-day, and 30-day means, respectively, for the period 1961–1995. ft3/s, cubic feet per second] DSN Scenario (LID_LT-local) description Percent EIA Statistics for simulated daily mean flow, 1961–1995, in ft3/s Mean annual January median April median August median October median Median 1-day low flow Median 7-day low flow Median 30-day low flow Median 1-day high flow Median 7-day high flow Median 30-day high flow Undeveloped 3001 Forest over SG 0 0.210 0.152 0.342 0.129 0.096 0.081 0.083 0.087 0.490 0.467 0.403 3005 Forest over till 0 0.230 0.160 0.374 0.0490 0.031 0.024 0.025 0.027 1.62 1.05 0.743 Conventionally laid out (uniform) development 3004 Commercial, model-calibrated EIA 63 0.430 0.179 0.144 0.039 0.037 0.016 0.018 0.056 6.60 2.44 1.26 3008 Commercial, 25% reduction in EIA 47 0.390 0.215 0.196 0.056 0.053 0.023 0.025 0.061 5.27 2.08 1.13 3009 Commercial, 50% reduction in EIA 31.5 0.360 0.274 0.244 0.070 0.067 0.030 0.033 0.064 3.92 1.81 1.01 3003 High-density residential over SG, model-calibrated EIA 14 0.320 0.253 0.322 0.125 0.096 0.065 0.069 0.095 1.95 1.00 0.739 3014 High-density residential over SG, 50% decrease in EIA 7 0.300 0.265 0.338 0.129 0.102 0.070 0.074 0.092 1.45 0.86 0.702 3015 High-density residential over SG, 100% increase in EIA 28 0.350 0.248 0.283 0.108 0.081 0.054 0.059 0.097 3.13 1.37 0.820 3002 Low-density residential over SG, model-calibrated EIA 2.5 0.290 0.264 0.368 0.149 0.115 0.085 0.089 0.102 1.01 0.75 0.635 3016 Low-density residential over SG, 50% decrease in EIA 1.25 0.290 0.267 0.365 0.151 0.116 0.086 0.090 0.101 0.90 0.74 0.621 3017 Low-density residential over SG, 100% increase in EIA 5 0.300 0.257 0.362 0.145 0.114 0.083 0.088 0.105 1.18 0.79 0.649 3007 high-density residential over till, model-calibrated EIA 14 0.310 0.284 0.288 0.049 0.045 0.023 0.025 0.044 3.58 1.60 0.859 3010 High-density residential over till, 50% decrease in EIA 7 0.290 0.288 0.292 0.051 0.045 0.025 0.027 0.040 3.23 1.57 0.820 3011 High-density residential over till, 100% increase in EIA 28 0.350 0.265 0.260 0.044 0.039 0.019 0.021 0.051 4.20 1.77 0.964 3006 Low-density residential over till, model-calibrated EIA 2.5 0.280 0.283 0.316 0.062 0.052 0.032 0.035 0.043 2.56 1.41 0.764 3012 Low-density residential over till, 50% decrease in EIA 1.25 0.280 0.286 0.318 0.061 0.051 0.032 0.035 0.041 2.54 1.40 0.760 3013 Low-density residential over till, 100% increase in EIA 5 0.290 0.276 0.314 0.061 0.050 0.031 0.034 0.045 2.62 1.42 0.772
Simulation of the Effects of Land-Use Change and Low-Impact Development on Streamflow at Multiple Spatial Scales 97

Table 17. Flow statistics for long-term (1961–1995), local-scale simulations of runoff from 100-acre parcels with various combinations of undeveloped and developed land uses and amounts of effective impervious area.—Continued[SG, sand and gravel; EIA, effective impervious area. In contrast to forested and residential land uses, commercial areas are not differentiated by underlying surfical geology. Undeveleoped is forested and developed is low-density residential, high-density residential, and commercial. LID_LT-local, long-term, local-scale simulations. Indicators of Hydrologic Alteration, version 7, was used to compute flow statistics. January, April, August, and October median flows are medians of monthly medians for the period 1961–1995. Median 1-day, 7-day, and 30-day flows are medians of annual 1-day, 7-day, and 30-day means, respectively, for the period 1961–1995. ft3/s, cubic feet per second]

DSN Scenario (LID_LT-local) description Percent EIA

Statistics for simulated daily mean flow, 1961–1995, in ft3/s

Mean 

annual

January 

median

April 

median

August 

median

October 

median

Median 

1-day

low flow

Median 

7-day

low flow

Median 

30-day

low flow

Median 

1-day

high flow

Median 

7-day

high flow

Median 

30-day

high flow

Cluster development

3026 High-density residential over SG, 14% EIA in developed area 5.6 0.260 0.216 0.334 0.122 0.094 0.069 0.073 0.087 1.28 0.80 0.5923027 High-density residential over SG, 28% EIA in developed area 11.2 0.270 0.200 0.323 0.116 0.093 0.067 0.073 0.089 1.57 0.87 0.6173028 High-density residential over SG, 56% EIA in developed area 22.4 0.300 0.174 0.284 0.102 0.076 0.059 0.064 0.094 2.81 1.15 0.6853029 Low-density residential over SG, 7% EIA in developed area 1.8 0.230 0.177 0.344 0.131 0.099 0.081 0.084 0.091 0.63 0.54 0.4503030 Low-density residential over SG, 14% EIA in developed area 3.5 0.230 0.182 0.344 0.133 0.098 0.080 0.083 0.094 0.72 0.54 0.4543031 Low-density residential over SG, 28% EIA in developed area 7 0.240 0.179 0.338 0.130 0.096 0.079 0.081 0.096 0.89 0.56 0.4623019 High-density residential over till, 14% EIA in developed area 5.6 0.270 0.221 0.355 0.069 0.050 0.032 0.034 0.048 1.98 1.13 0.7943020 High-density residential over till, 28% EIA in developed area 11.2 0.280 0.225 0.376 0.065 0.045 0.030 0.033 0.052 2.26 1.20 0.8223021 High-density residential over till, 58% EIA in developed area 22.4 0.310 0.223 0.341 0.052 0.032 0.023 0.025 0.055 3.11 1.46 0.8903022 Low-density residential over till, 7% EIA in developed area 1.8 0.240 0.178 0.372 0.051 0.033 0.025 0.026 0.032 1.85 1.08 0.7493023 Low-density residential over till, 14% EIA in developed area 3.5 0.250 0.183 0.372 0.051 0.032 0.024 0.026 0.033 1.95 1.09 0.7533024 Low-density residential over till, 28% EIA in developed area 7 0.250 0.180 0.384 0.051 0.032 0.024 0.026 0.035 2.04 1.13 0.763
98 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

overlying sand and gravel to commercial land use increased 

the simulated median 1-day high flow about 1,250 percent, 

from 0.49 to 6.60 ft3/s. This difference occurred because the 

pervious HRUs overlying sand and gravel allowed for more 

infiltration and produced lower peak flows compared to the 

pervious HRUs overlying till. The pervious commercial HRU 

was not differentiated by underlying geology.

Converting forest to low-density or high-density residential land use increased simulated high flows but notably also 

increased most of the simulated medium and low flows for 

HRUs overlying both till and sand and gravel (figs. 59A, B). 

As discussed previously, both residential HRUs had less simulated evapotranspiration losses than forested HRUs, producing 

more discharge to streams as interflow or base flow. Relative 

differences in runoff and evapotranspiration for the developed 

and undeveloped HRUs involved in the local-scale simulations are shown by the mean annual water budgets (fig. 60). 

Because of the uncertainty associated with model parameter 

values for the individual HRUs, the water-budget results were 

more representative of relative rather than absolute differences 

in the amount of runoff and evapotranspiration among HRUs.

The hydrographs of median daily streamflow show 

that flows for commercial land use are relatively flashy and 

vary more on a seasonal basis than flows for other land-use 

types (figs. 59A, B). This occurs mainly because of the large 

percentage of EIA (63 percent) associated with commercial 

development. Hydrographs for the forest, low-density residential, and high-density residential land uses overlying till 

generally follow the hydrograph for commercial land use, 

whereas hydrographs for the same land uses overlying sand 

and gravel generally vary less than those for commercial land 

use throughout the year, and flows are higher in the summer as 

a result of higher base flows.

Simulations conducted to evaluate the sensitivity of 

streamflow to the amount of EIA for conventional (that is, 

spatially uniform) development indicated that streamflow 

changed in proportion to changes in EIA (fig. 61). Reducing 

EIA associated with commercial land use to 50 percent of 

model-calibrated values had the largest effects on simulated 

flows because a percentage reduction of this magnitude corresponded to converting 31.5 percent of the drainage area 

from effective impervious to pervious surface (fig. 61A). For 

example, a 50-percent reduction in EIA decreased the median 

1-day high flow by about 41 percent, from 6.60 to 3.92 ft3/s 

(table 17), whereas the median 1-day low flow increased by 

about 88 percent, from 0.016 to 0.030 ft3/s. In contrast, the 

effects of reducing EIA by 50 percent for high-density and 

low-density residential land uses were less pronounced than 

for commercial land use because less of the drainage area was 

converted from effective impervious to pervious surface; the 

effect of reduced EIA on flows was larger for high-density 

residential land use than for low-density residential land use 

because more EIA was available for reduction (figs. 61B–E). 

Overall, these simulation results indicate that the largest reduction in streamflow alteration could potentially be achieved by 

implementing LID in areas with commercial land use followed 

by high-density residential land use. Only modest changes in 

simulated streamflow were observed for low-density residential land use.

For a given change in the percentage of EIA in a 100-acre 

parcel, the effect on simulated high flows was similar for all 

of the developed HRUs (fig. 62A). Differences in streamflow 

become less pronounced as the percentage of EIA increases. 

Flows were most similar for high EIA values because impervious surface constituted a larger proportion of the drainage 

area than pervious surface, and differences in the infiltration 

characteristics among the pervious HRUs decreased in influence. When the percentage of EIA was relatively low, surficial 

geology differences had a greater effect on simulated high 

flows (fig. 62A). For example, for EIA values less than about 

10 percent, median 1-day high flows for HRUs overlying till 

were about double those for HRUs overlying sand and gravel. 

Overall, median 1-day high flows were more sensitive than 

median 7-day high flows to changes in EIA. Over the range of 

EIA values simulated (zero to 100 percent EIA), median 1-day 

high flows increased by a factor of about 5, whereas median 

7-day high flows increased by a factor of about 2.

In contrast to the high flows, simulated low flows were 

affected to a much greater degree by the infiltration characteristics of the pervious, developed HRUs, and the effect of a 

given change in the amount of EIA was more dependent on the 

type of HRU (that is, there were larger differences in slope), 

although for a given HRU median 1-day and 7-day low flows 

were similar (figs. 62B, C). For relatively low EIA, subsurface 

geology and evapotranspiration losses greatly affected the 

amount of base flow to streams. Consequently, differences in 

the HRU characteristics that controlled these factors resulted 

in simulated streamflows varying by a factor of about five 

for low EIA values. The maximum median 1-day low flow 

occurred for the low-density residential overlying sand and 

gravel HRU (0.00087 ft3/s/acre) simulation, and the minimum 

median 1-day low flow was from the high-density residential 

HRU overlying till (0.00027 ft3/s/acre) simulation. As EIA 

increased, median 1-day and 7-day low flows approached 

zero. Such high EIAs are likely uncommon, and the simulation 

results for individual HRUs are not representative of a basin 

that is becoming urbanized because the interactions among 

processes, such as reduced evaporation caused by land-use 

changes (Dow and Dewalle, 2000) and increased recharge 

caused by urban water infrastructure (Lerner, 2002), could 

cause low flows to increase at the watershed scale.

The vertical lines in figure 62 are the model-calibrated EIA values for low-density residential development (2.5 percent), high-density residential development 

(14 percent), and commercial development (63 percent). As 

indicated by the model-calibrated value, EIA for low-density 

developments typically would be low; thus, streamflow 

would be relatively insensitive to EIA reduction for this type 

of development, regardless of the physical properties of the 

underlying surficial geology and the magnitude of the flow. 

Similarly, for mixed urban development that has low total 

EIA as a percentage of the drainage area, reductions in EIA 
Simulation of the Effects of Land-Use Change and Low-Impact Development on Streamflow at Multiple Spatial Scales 99

Figure 60. Mean annual water budgets for forested and developed hydrologic response units simulated in the Ipswich 

River Basin, MA.

Runoff to

streams

Losses from

evapotranspiration

Overlying till Overlying sand 

and gravel

Effective 

Impervious area

 -40

 -30

 -20

 -10

0

 10

 20

 30

 40

 50

ANNUAL WATER BUDGET, IN INCHES PER ACRE

FORESTED

LOW-DENSITY RESIDENTIAL

HIGH-DENSITY RESIDENTIAL 

FORESTED 

LOW-DENSITY RESIDENTIAL

HIGH-DENSITY RESIDENTIAL 

COMMERCIAL-INDUSTRIAL-TRANSPORTATION

IMPERVIOUS COMMERCIAL

IMPERVIOUS RESIDENTIAL

Evapotranspiration from

AGWET—Active groundwater

UZET—Upper soil zone

CEPE—Interception

LZET—Lower soil zone 

Runoff from

AGWO—Active groundwater

IFWO—Interflow

SURO—Surface

EXPLANATION
100 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Figure 61. Flow-duration curves of daily mean streamflow from long-term (1961–1995) local-scale 

simulations of runoff from 100-acre parcels of conventionally laid-out (uniform) (A) commercial 

development, (B) high-density development overlying sand and gravel, (C) high-density residential 

development overlying till, (D) low-density residential development overlying sand and gravel, and 

(E) low-density residential development overlying till with various amounts of effective impervious area 

(EIA) in the Ipswich River Basin, MA. Blue curves represent model-calibrated EIA values.

0.5 2 5 10 30 50 70 90 95 99 99.8

PERCENTAGE OF TIME

FLOW WAS EQUALED OR EXCEEDED

PERCENTAGE OF TIME

FLOW WAS EQUALED OR EXCEEDED

0.5 2 5 10 30 50 70 90 95 99 99.8

0.5 2 5 10 30 50 70 90 95 99 99.8 0.5 2 5 10 30 50 70 90 95 99 99.8

0.5 2 5 10 30 50 70 90 95 99 99.8

STREAMFLOW, IN CUBIC FEET PER SECOND

10

1

0.1

0.01

10

1

0.1

0.01

10

1

0.1

0.01

10

1

0.1

0.01

10

1

0.1

0.01

2.5% EIA

5% EIA

1.25% EIA

2.5% EIA

5% EIA

1.25% EIA

14% EIA

7% EIA

28% EIA

14% EIA

7% EIA

28% EIA

63% EIA

47% EIA

31.5% EIA

A

B C

D E
Simulation of the Effects of Land-Use Change and Low-Impact Development on Streamflow at Multiple Spatial Scales 101

Figure 62. (A) Median 1-day and 7-day high flows, (B) median 1-day low flows, and (C) median 7-day low flows from long-term (1961–

1995) simulations of runoff from 100-acre parcels of conventionally laid out (uniform) development with various amounts of effective 

impervious area in the Ipswich River Basin, MA. HRU, hydrologic response unit; HSPF, Hydrologic Simulation Program FORTRAN. STREAMFLOW, IN CUBIC FEET PER SECOND PER ACRE

Commercial

High-density residential over till

Low-density residential over till

High-density residential over sand and gravel

Low-density residential over sand and gravel

Effective impervious area values for

 commercial (63%), high-density 

 residential (14%), and low-density 

 residential (2.5%) HRUs in the Ipswich 

 River Basin HSPF model

EXPLANATION

0 20 40 60 80 100

0 20 40 60 80 100 0 20 40 60 80 100

PERCENT EFFECTIVE IMPERVIOUS AREA

0

0.02

0.04

0.06

0.08

0.10

0

0.0002

0.0004

0.0006

0.0008

0.0010

0

0.0002

0.0004

0.0006

0.0008

0.0010

A

B C

Median 1-day

high flow

Median 7-day

high flow
102 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

likely would have modest effects on streamflow. This result is 

consistent with the results for the basin-scale simulations, particularly the LID retrofit and buildout simulations. Although 

the EIA values, parameter values for individual land-use 

types, and resulting simulated streamflows are specific to 

this study, there could be general significance to the conclusion that relatively modest changes in streamflow would be 

realized by reducing EIA for uniform or mixed land uses that 

have low initial EIA values. Small changes in EIA could have 

substantial effects on water quality and stream ecology (for 

example, fish assemblages in eastern Massachusetts streams 

(David Armstrong, U.S. Geological Survey, written commun., 

2008)), but evaluating these effects was beyond the scope of 

this study.

Flood-Peak Ratios

To evaluate the magnitude of flood-peak differences 

produced by the long-term (1961–1995) local-scale simulations of runoff from 100-acre parcels with uniform land use, 

1-day high flow (daily peak flow) frequency probabilities were 

computed by fitting annual series of daily high flows to the 

log-Pearson Type III distribution by use of SWSTAT, a program that computes surface-water statistics (Lumb and others, 

U.S. Geological Survey, written commun., 1994).

Previous studies have shown that urbanization affects 

the magnitude and frequency of flood flows (Beighley and 

Moglen, 2003; Booth and Jackson, 1997; Moscrip and Montgomery, 1997; Hollis, 1975; Leopold, 1968). For example, on 

the basis of a compilation of existing studies, Hollis (1975) 

showed that small floods (recurrence intervals of 1 year or 

less) can increase by a factor of 10 or more, depending on the 

degree of urbanization, and that the effects of urbanization 

decrease as flood recurrence intervals increase. A common 

explanation for the decreased effect of urbanization on larger 

floods is that undeveloped watersheds become so saturated 

during prolonged storms that the importance of infiltration is 

reduced and the channel network is extended in size, producing a hydrologic response like that of an impervious watershed 

(Hollis, 1975). Consequently, an undeveloped watershed could 

produce large floods similar in magnitude to a comparable 

developed watershed.

Ratios of the flood peaks after development (based on 

the commercial HRU) to those before development (based 

on the forest overlying till HRU or the forest overlying sand 

and gravel HRU) were plotted as a function of the recurrence interval of the flood, and the amount of EIA associated 

with commercial land use showed that simulated daily peak 

flows declined with increasing recurrence interval and with 

the amount of EIA associated with commercial development 

(fig. 63). For the contrast in infiltration characteristics between 

commercial development and forest overlying sand and gravel 

(fig. 63A), flood peaks after development were as much as 30 

times higher than before development for small floods with a 

return period on the order of 1 year or less. For the contrast in 

infiltration characteristics between commercial development 

and forest overlying till (fig. 63B), flood peaks after development were as much as 10 times higher for small floods than 

before development. For large floods, ratios decreased but 

generally remained greater than one. For example, daily peak 

flows for 100-year floods were about 10 times higher after 

forest overlying sand and gravel was converted to commercial 

Figure 63. Ratios of the magnitudes of simulated daily peak flows for (A) commercial (developed) and forest overlying sand 

and gravel (undeveloped) land use, and (B) commercial (developed) and forest overlying till (undeveloped) land use as a 

function of recurrence interval and the amount of effective impervious area in the Ipswich River Basin, MA.

RECURRENCE INTERVAL, IN YEARS RECURRENCE INTERVAL, IN YEARS

1 10 100 1,000 1 10 100 1,000

0

2

4

6

8

10

0

5

10

15

20

25

30

RATIO OF DAILY PEAK FLOW FOR DEVELOPED LAND 

USE TO DAILY PEAK FLOW FOR UNDEVELOPED 

LAND USE

Ratio=1

25 percent

10 percent

50 percent

75 percent

Effective impervious area associated

with commercial land use

A Commercial (developed); forest overlying B Commercial (developed); forest overlying till (undeveloped)

 sand and gravel (undeveloped)
Simulation of the Effects of Land-Use Change and Low-Impact Development on Streamflow at Multiple Spatial Scales 103

development with 75 percent EIA (fig. 63A) than before the 

conversion. On the other extreme, simulated daily peak flows 

for 100-year floods were about the same after forest overlying 

till was converted to commercial development with 10 percent 

EIA (fig. 63B).

Simulated flood-peak-ratio curves are not applicable 

to all spatial scales. For example, it is unlikely that a large 

watershed would undergo such intensive urbanization as 

to achieve EIAs of 50 or 75 percent (the top two curves in 

figs. 63A, B). HSPF-model-calibrated EIAs for large drainage 

basins in eastern Massachusetts and Rhode Island are in the 5 

to 8 percent range (Barbaro and Zarriello, 2006; Zarriello and 

Ries, 2000). Moreover, uniform land-use change to commercial development and uniform underlying geology are clearly 

not representative of larger basins. Therefore, the flood-peak 

ratios are most representative of the response in small, undeveloped catchments that may undergo uniform commercial 

development with varying amounts of EIA. In addition, these 

simulations assume the same infiltration capacity in pervious 

areas, regardless of the percentage of EIA associated with the 

development. Finally, the Ipswich River Basin HSPF model 

was less rigorously calibrated to high flows than to low flows, 

and model performance for large floods is relatively uncertain. 

For these reasons, the daily flood-peak ratios are best viewed 

as showing only relative effects of land-use change, as determined by the model parameter values assigned to individual 

HRUs, and are not representative of actual flood-peak changes 

in the basin.

Cluster Development

Simulations were conducted to evaluate the effects of 

cluster development on streamflow (fig. 64; table 17). For 

high-density residential development, clustering (60 acres 

undeveloped and 40 acres developed) generally reduced simulated high flows (defined here as flows equaled or exceeded 

less than 25 percent of the time) for HRUs overlying both 

sand and gravel and till compared to conventionally laid out 

development (figs. 64A, B). Clustering did not substantially 

change low flows (defined here as flows equaled or exceeded 

greater than 75 percent of the time) for HRUs overlying sand 

and gravel or till. Varying the EIA within the developed part 

of the parcel typically had less of an effect on simulated flows 

than clustering had. The exception was for the simulation with 

the highest EIA (56 percent EIA in the developed area), which 

produced high and low flows similar to the conventional 

development.

For low-density residential development, clustering 

(75 acres undeveloped and 25 acres developed) reduced 

high flows but also slightly reduced low flows compared to 

conventionally laid out development for both surficial geology types (figs. 64C, D). As discussed previously, simulated 

reductions in low flows were due to increased interception and 

evapotranspiration losses from the forested HRUs compared 

to the low-density residential HRUs. For low-density residential development, varying the EIA within the developed part 

of the parcel had a negligible effect on simulated streamflow. 

Simulated streamflow for a cluster development with a larger 

developed area (for example, 50 acres developed with 100 

houses on 0.5-acre lots and 50 acres undeveloped) would fall 

between the simulated flows for the conventional and clustered 

developments (simulations not shown).

Overall, clustering reduced simulated high flows and had 

variable effects on simulated low flows compared to conventional developments with the same number of houses. Lowdensity cluster developments, in particular, left a large part of 

the parcel forested, resulting in slightly lower low flows than 

conventional low-density developments with uniform lot sizes 

(figs. 64C, D). Simulated streamflow was relatively insensitive to the amount of EIA in the developed part of the parcel, 

particularly for cluster developments in which the developed 

area composed a relatively small fraction of the parcel. For 

example, for the low-density cluster development simulations 

conducted for this study, only 25 percent of the parcel was 

developed, and a reasonable EIA range of 7 to 28 percent in 

the developed area corresponded to an EIA range for the entire 

parcel of only 1.8 to 7 percent. In contrast, for the high-density 

cluster development simulations, more of the parcel was 

developed than for the low-density simulations; consequently, 

the EIA in the developed area of the high-density development had a larger effect on simulated streamflow than the 

low-density development had. Evaluation of other aspects of 

open-space preservation, such as possible beneficial effects on 

water quality, was beyond the scope of this study.
104 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Figure 64. Flow-duration curves of daily-mean streamflow from long-term (1961–1995) simulations of runoff from 100-acre 

parcels of conventionally laid out (uniform) and cluster development with varying amounts of EIA in the developed part of 

the parcel for (A) high-density residential overlying sand and gravel, (B) high-density residential overlying till, (C) low-density 

residential overlying sand and gravel, and (D) low-density residential overlying till, Ipswich River Basin, MA. The highdensity residential cluster development consists of 60 acres of undeveloped land and 40 acres of developed land, and the 

low-density residential cluster development consists of 75 acres of undeveloped land and 25 acres of developed land. Conv., 

conventionally laid out development; Clust., cluster development; EIA, effective impervious area. STREAMFLOW, IN CUBIC FEET PER SECOND

0.5 2 5 10 30 50 70 90 95 99 99.8 0.5 2 5 10 30 50 70 90 95 99 99.8

0.5 2 5 10 30 50 70 90 95 99 99.8 0.5 2 5 10 30 50 70 90 95 99 99.8

PERCENTAGE OF TIME

FLOW WAS EQUALED OR EXCEEDED

PERCENTAGE OF TIME

FLOW WAS EQUALED OR EXCEEDED

10

1

0.1

0.01

10

1

0.1

0.01

10

1

0.1

0.01

10

1

0.1

0.01

Conv. 2.5% EIA

Clust. 1.8% EIA (7% of developed area)

Clust. 3.5% EIA (14% of developed area)

Clust. 7.0% EIA (28% of developed area)

Conv. 2.5% EIA

Clust. 1.8% EIA (7% of developed area)

Clust. 3.5% EIA (14% of developed area)

Clust. 7.0% EIA (28% of developed area)

Conv. 14% EIA

Clust. 5.6% EIA (14% of developed area)

Clust. 11.2% EIA (28% of developed area)

Clust. 22.4% EIA (56% of developed area)

Conv. 14% EIA

Clust. 5.6% EIA (14% of developed area)

Clust. 11.2% EIA (28% of developed area)

Clust. 22.4% EIA (56% of developed area)

A B

C D
Summary and Conclusions 105

the inconsequential differences in water-quality constituent 

concentrations and loads were not surprising; in particular, 

storms sampled after the installation of the LID enhancements 

were characterized as having substantially more rainfall than 

those sampled prior to the enhancement installations. Small 

storms were sampled less frequently than large storms for 

water-quality analyses because small storms did not generate sufficient runoff for water-quality sampling. The design 

features were probably inadequate to reduce discharge sufficiently in order to achieve measurable results for large storms.

The roof runoff study clearly demonstrated the ability of 

the green roof to attenuate runoff, retaining at least 50 percent of the rainfall from most storms, and to store substantial 

amounts of precipitation. Both of these characteristics of green 

roofs depend on the amount of precipitation and antecedent 

dry periods associated with a given storm. The effects of the 

green roof on the water quality of runoff were less clear. Small 

storms tended to generate inadequate volumes of runoff for 

water-quality samples, and subsequently, there were no chemical analyses for small storms. Thus, the study did not account 

for the reduction in constituent load that occurred by virtue of 

the absence of runoff from small storms. The application of 

fertilizers, the composition of the growing medium, and the 

possible effects of metallic roof structures probably obscured 

the capacity of the medium to retain nutrients and metals from 

dryfall and rainfall.

Simulation Findings

The USGS, in consultation with the MDCR, USEPA, and 

a Technical Advisory Committee, created a set of hypothetical 

land-use change and water-management scenarios to investigate the effects on streamflow of implementing low-impactdevelopment practices in the Ipswich River Basin using the 

USGS Ipswich River Basin HSPF model. An updated baseline 

simulation was conducted to incorporate major changes in 

water-supply withdrawals from the upper basin that have 

taken place since the original baseline model was developed with 1989 to 1993 withdrawals. The incorporation of 

reduced groundwater withdrawals led to increases in simulated 

medium and low flows in the reaches above the South Middleton streamgage. Local effects on small streams in the immediate vicinity of wells with reduced withdrawals could be more 

pronounced, but these effects were not specifically evaluated 

with the model.

Information from a 2001 state-wide buildout analysis 

(Massachusetts Executive Office of Energy and Environmental 

Affairs, 2008) was used to simulate the effects of potential 

future development on streamflow in the Ipswich River Basin. 

Using 1991 land use as a baseline, the buildout analysis indicated that about 17 percent of the entire Ipswich River Basin 

was developable. Land-use change associated with buildout 

generally had modest effects (percent differences of less than 

20 percent) on simulated streamflow in the Ipswich River 

Basin because most of the developable land in the basin in 

Summary and Conclusions

The USGS, in cooperation with the MDCR and the 

USEPA, used field and modeling studies to examine the 

effects of implementing selected LID techniques and waterdemand-reduction strategies on water quantity and quality in 

the Ipswich River Basin, which is stressed by residential and 

commercial water demands. The field studies and computer 

simulations demonstrate that implementation of LID practices 

can demonstrably affect stormwater runoff, even in small, 

highly pervious drainage areas. However, the effects may be 

difficult to discern when the changes in EIA and in the volume of runoff are small. The benefits of implementing these 

practices are likely greatest when they are either extensively 

incorporated into the original design for a development or 

when a substantially urbanized area is retrofitted with LID 

enhancements that redirect runoff away from storm sewers and 

into groundwater.

Field-Study Findings

Three field studies were designed to monitor the effects 

of LID practices on water quantity and quality. The first compared the changes in groundwater quality that occurred after a 

porous parking lot surface replaced a conventional, impervious 

one. The second examined the changes in stormwater flow and 

quality after a system of rain gardens, swales, and porous pavers was retrofitted in a 3-acre neighborhood to divert runoff 

from the streets into the groundwater rather than into storm 

sewers leading to Silver Lake. The third field study simultaneously monitored and sampled stormwater runoff from a conventional, rubber-membrane roof and from a vegetated green 

roof to compare their differences.

Results from the monitoring of water quality in the Silver 

Lake parking-lot wells indicate little change over the period 

of study. The changes that did occur are more likely associated with the physical process of parking-lot replacement, as 

reflected in the field characteristics, than with any effects of 

chemical contaminants entering the water table after infiltrating from the porous surfaces of the parking lot. Within the 

scope of this study, it seems reasonable to infer that installing 

the porous parking lot had no observable deleterious effects on 

groundwater quality.

The results of the Silver Lake Avenue runoff study 

indicated some modest gains in reducing runoff: the rainfallrunoff relation decreased somewhat, primarily for storms of 

less than 0.25 in. of rainfall, although not in a statistically 

significant amount. The decrease in EIA was not sufficient 

to bring about significant change in this small neighborhood 

with highly porous soils. Decreasing the amount of EIA in a 

study site with a greater proportion of impervious area than 

that in the Silver Lake Avenue/Dexter Street neighborhood 

might have had a more substantial effect that would have been 

reflected in changes to the rainfall-runoff ratio. Given the 

ambiguous results of the runoff volume aspects of the study, 
106 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

1991 was forested or open and zoned for low-density residential development, and model-calibrated EIA associated with 

low-density residential development was 2.5 percent. Consequently, increases in this type of land use did not result in 

large changes in the amount of EIA in a drainage area. In areas 

with relatively substantial amounts of land zoned for commercial use (for example, in reach 27 where EIA in the subbasin 

increased from 8.6 percent in 1991 to 28.9 percent at buildout), effects on simulated flows were more pronounced.

EIA upstream from the South Middleton streamgage 

was reduced by 50 percent as a surrogate for LID retrofits 

that decrease EIA. Widespread reduction of EIA to 50 percent 

of values in the updated baseline model (1991 land use) had 

modest effects (percent differences of less than 20 percent) on 

simulated streamflow above the South Middleton station. Even 

in this relatively urban part of the Ipswich River Basin, the 

heterogeneous mix of land uses results in EIAs that are small 

percentages (1 to 22 percent) of subbasin areas.

Data from water-conservation pilot projects were scaled 

up to the town level and used to simulate the effects of 

widespread application of these programs on streamflow. For 

communities with water withdrawals from the basin, hypothetical water-use reductions from broad application of the 

pilot project data ranged from 1.4 percent (Salem-Beverly 

water supply) to 8.5 percent (Hamilton) of average 1989–1993 

withdrawals. Withdrawal reductions in this range (less than 

10 percent) had very minor effects on simulated low flows in 

most of the rivers and streams in the basin affected by groundwater withdrawals. Impacts of reduced water withdrawals may 

have more significant impacts at a local scale in the vicinity 

of the withdrawal locations, but a local-scale analysis of the 

impact of reduced water withdrawals was beyond the scope of 

this study.

Hypothetical local-scale simulations conducted to 

evaluate the hydrologic effects of land-use change, surficial 

geology, and development patterns on a local scale (100 acres) 

provide valuable understanding of the conditions for which 

LID practices have the greatest potential benefits. Specifically, simulations were conducted to evaluate the effect on 

streamflow of (1) uniform land-use change for conventionally laid out development (that is, uniform lot sizes in the 

development); (2) the amount of EIA, with EIA less than 

model-calibrated values representing an application of LID, 

and EIA greater than model-calibrated values representing an 

upper limit for a given land-use category; (3) surficial geology; and (4) cluster developments. Converting undeveloped, 

forested land to developed land increased simulated median 

1-day high flows (median of 1-day annual high flows for 

1961–1995 simulation) by up to 1,250 percent, depending on 

the underlying surficial geology and the type of development. 

Conversion of forest overlying sand and gravel to commercial 

development produced the maximum increase in the simulated 

median 1-day high flow, from 0.49 to 6.60 ft3/s. Converting 

forest to low-density or high-density residential development also increased simulated high flows, but these changes 

also increased most simulated medium and low flows for 

HRUs underlain by till, and sand and gravel. Flows increased 

because both residential HRUs were simulated to have less 

evapotranspiration losses than forested HRUs, producing more 

discharge to streams as interflow or base flow.

Simulations of runoff from 100-acre parcels with uniform 

land use were conducted to evaluate the sensitivity of streamflow to EIA. Results indicate that the largest reduction in 

streamflow alteration could potentially be achieved by implementing LID in areas with commercial land use and highdensity residential land use because more EIA was available 

for reduction in commercial areas and high-density residential 

areas than in other land-use areas. Only modest changes in 

simulated streamflow were observed for low-density residential land use.

To evaluate the magnitude of flood-peak differences 

produced by development, 1-day high flow (daily peak flow) 

frequency probabilities were computed for selected 100-acre 

developed and undeveloped HRUs. Ratios of simulated flood 

peaks after development (the commercial HRU) to those 

before development (the forest overlying till HRU or the forest overlying sand and gravel HRU) indicated that simulated 

daily peak flows declined with increasing recurrence interval 

and the amount of EIA associated with commercial development. Simulated flood peaks after development were as 

much as 30 times higher than before development for small 

floods with a recurrence interval on the order of 1 year or 

less. Simulated daily peak flows for larger floods, for example 

100-year floods, were 10 times higher after forest overlying 

sand and gravel was converted to commercial development 

with 75 percent EIA. On the other extreme, simulated daily 

peak flows for 100-year floods were about the same after forest overlying till was converted to commercial development 

with 10 percent EIA. The flood-peak ratios are most representative of the response in small, undeveloped subbasins that 

may undergo uniform commercial development with varying 

amounts of EIA.

Results of simulations conducted to evaluate cluster 

development indicate that clustering practices reduce high 

flows and have variable effects on low flows when compared 

to conventional development with the same number of houses. 

For low-density cluster developments, leaving a large part of 

the area forested resulted in slightly lower low flows than for a 

conventional low-density development with uniform lot sizes. 

Flows from a cluster development more closely approximated 

pre-development flows than did flows from conventional lowdensity development. Simulated streamflow was found to be 

relatively insensitive to the amount of EIA in the developed 

part of the parcel, particularly for cluster developments in 

which the developed area was relatively small.

Because of data limitations and computational efficiency, 

numerical watershed models such as HSPF simplify the 

complex processes and physical characteristics of a drainage 

basin. Of particular relevance for the present study, model 

calibration reflected the combined effects of the HRUs (both 

PERLNDs and IMPLNDs) and reach characteristics. Hydrologic judgment was used to determine the response of different 
References Cited 107

PERLNDs and IMPLNDs, but information was not available 

to calibrate the individual HRUs. In addition, the amount of 

EIA associated with each developed land-use category was 

determined through model calibration and represents average 

subbasin-scale EIA. Consequently, the magnitudes of changes 

produced by altering the distribution of HRUs are uncertain 

and simulated changes are best viewed as relative rather than 

absolute.

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110 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

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Appendix 111

Appendix 1
112 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

Table 1–1. Town data used to scale up results of water-conservation pilot projects conducted in the Ipswich River Basin, MA, for 

calculating hypothetical water savings for towns with municipal water supplies in the Basin.

[Information compiled by the Massachusetts Department of Conservation and Recreation.]

Town

Number of 

single family 

detached homes

Total 

number of 

households

Percent of water 

supply from

sources in the

Ipswich River 

Basin

Total area of athletic 

fields irrigated with 

public water supplies 

(acres)

Total area of athletic 

fields irrigated with 

onsite wells located in 

the Ipswich River Basin 

(acres)

Wilmington 6,368 7,158 42 (Summer only) 3.2 35

Danvers Water Supply

Middleton1 1,719 2,347 100 3.3 1.8

Danvers 6,299 9,762 100 15 0

North Reading 4,029 4,870 40 (Summer only) 0 14

Peabody 10,959 18,898 50 34 13

Hamilton 2,358 28,525 100 1.5 12

Ipswich 3,723 5,601 25 11 0

Topsfield1 1,842 2,144 100 2.8 11

Wenham 1,040 1,320 100 4.5

Salem Beverly Water Supply

Salem 4,915 18,175 100 19 0

Beverly 8,450 16,275 100 23 0

Lynnfield 3,705 4,273 54 0 1

Lynn 11,673 34,690 20 22 0

1

50–60 percent of Middleton residents and 15 percent of Topsfield residents use private wells, but all are located within the Ipswich River Basin. For 

Hydrological Simulation Program-FORTRAN simulations, the hypothetical savings at these private wells were attributed to the respective public water 

supply sources for each town.
Appendix 113

Table 1–2. Calculations and assumptions used to scale up data to the town level from the water-conservation pilot study conducted 

in the Ipswich River Basin, MA.

[Information compiled by the Massachusetts Department of Conservation and Recreation. Reductions were scaled up to the town level for towns with municipal water supplies in the Ipswich River Basin, so that the effects of reductions on streamflow could be simulated with the Hydrological Simulation ProgramFORTRAN (HSPF) model previously developed for the Basin.1

]

Water-conservation 

pilot project

Description of per unit savings and assumptions 

used to scale results up to town level

Per unit savings based 

on water-conservation 

pilot projects 

(gallons/month)

800-gallon rainwater 

harvesting systems

Average savings per participating single family household: 433

Assumption that 1/3 of the single-family homes in all Ipswich towns participate.

Reduction in withdrawals at Ipswich water-supply sources = 433 gallons/month 

* 1/3 * number of single family homes * percent of water supply pumped from 

Ipswich sources.

Low-flow indoor fixtures 

and appliances

Average savings per participating household: 450

Assumption that participation rates in other Ipswich towns would resemble those 

observed in town with the pilot program (approximately 9 percent).

Average savings per household town-wide: 35

Reduction in withdrawals at Ipswich water-supply sources = 35 gallons/month * 

number of households * percent of water supply from Ipswich sources.

Soil amendments at athletic 

fields

Average per-acre savings resulting from zeolite soil amendment: 6,671

Assumption that all athletic fields are treated similarly to pilot-study field.

Reduction in withdrawals for all athletic fields currently irrigated by public water 

= 6,671 gallons/month * acreage * percent of water supply from Ipswich 

sources.

Reduction in withdrawals for all athletic fields irrigated by on-site wells within 

the Ipswich River Basin = 6,671 gallons/month * acreage.

Weather-sensitive irrigation 

systems on athletic fields

Average per-acre savings resulting from weather-based irrigation systems: 16,2412

Assumption that all athletic fields irrigated were equipped with weather-sensitive 

irrigation systems.

Reduction in withdrawals for all athletic fields currently irrigated by public water 

= 16,241 gallons/month * acreage * percent of water supply from Ipswich 

sources.

Reduction in withdrawals for all athletic fields irrigated by onsite wells within the 

Ipswich River Basin = 16,241 gallons/month * acreage.

1

 For HSPF simulations, reductions in non-public groundwater supply sources were attributed to the public-water supply sources in the same town.

2

 Subsequent to the HSPF simulation, DCR provided a revised per-acre water savings for the weather-sensitive irrigation systems of 21,128 gal/month. 

See text for discussion of the effects of this revision.
114 Effects of Selected Low-Impact-Development Techniques on Water Quality and Quantity in the Ipswich River Basin

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Zimmerman and others—Effects of Selected Low-Impact-Development (LID) Techniques, Ipswich River Basin, MA—Scientific Investigations Report 2010–5007