U.S. Department of the Interior

U.S. Geological Survey

Circular 1361

Prepared in cooperation with the 

Massachusetts Department of Conservation and Recreation and the 

U.S. Environmental Protection Agency

Effects of Low-Impact-Development (LID) Practices 

on Streamflow, Runoff Quantity, and Runoff Quality 

in the Ipswich River Basin, Massachusetts: 

A Summary of Field and Modeling Studies
Front cover description: Vegetated green roof on the Whipple Annex, Ipswich, MA

Back cover description: Rain garden on Dexter Street, Wilmington, MA
6 

Effects of Low-Impact-Development (LID) 

Practices on Streamflow, Runoff Quantity, 

and Runoff Quality in the Ipswich River Basin, 

Massachusetts: A Summary of Field and 

Modeling Studies

By Marc J. Zimmerman, Marcus C. Waldron, Jeffrey R. Barbaro, and 

Jason R. Sorenson 

Prepared in cooperation with the 

Massachusetts Department of Conservation and Recreation and the 

U.S. Environmental Protection Agency

Circular 1361

U.S. Department of the Interior

U.S. Geological Survey
 7

U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director 

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

Suggested citation:

Zimmerman, M.J., Waldron, M.C., Barbaro, J.R., and Sorenson, J.R., 2010, Effects of low-impact-development (LID) practices 

on streamflow, runoff quantity, and runoff quality in the Ipswich River Basin, Massachusetts—A Summary of field and modeling studies: U.S. Geological Survey Circular 1361, 40 p. (Also available at http://pubs.usgs.gov/circ/circ1361.)

Library of Congress Cataloging-in-Publication Data

Effects of low-impact-development (LID) practices on streamflow, runoff quantity, and runoff quality in the Ipswich River basin, 

Massachusetts : a summary of field and modeling studies / by Marc J. Zimmerman ... [et al.] ; prepared in cooperation with 

the Massachusetts Department of Conservation and Recreation and the U.S. Environmental Protection Agency.

 p. cm. -- (Circular ; 1361)

 ISBN 978-1-4113-2959-1 (softcover : alk. paper)

 1. Runoff--Massachusetts--Ipswich River Watershed. 2. Streamflow--Massachusetts--Ipswich River Watershed. 3. Environmental engineering--Massachusetts--Ipswich River Watershed. 4. Water quality management--Massachusetts--Ipswich River 

Watershed. I. Zimmerman, Marc James, 1947- II. Massachusetts. Dept. of Conservation and Recreation. III. United States. 

Environmental Protection Agency. IV. Geological Survey (U.S.) V. Title: Effects of low impact development (LID) practices on 

streamflow, runoff quantity, and runoff quality in the Ipswich River basin, Massachusetts. VI. Series: U.S. Geological Survey 

circular ; 1361. 

 GB991.M4E35 2010

 551.48’809744--dc22

 2010037426

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U.S. Government.

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

reproduce any copyrighted materials contained within this report.
8 

Contents

Abstract...........................................................................................................................................................6

Introduction.....................................................................................................................................................8

Field Studies of the Effects of LID Practices...........................................................................................10

Changes in Groundwater Quality Following the Retrofit of a Conventional Parking Lot

with LID Features ..................................................................................................................12

Effects of LID Features on Stormwater Runoff Quantity and Quality from a Suburban

Neighborhood ........................................................................................................................16

Ability of a Green Roof to Alter the Quantity and Quality of Stormwater Runoff .....................20

Simulation of the Effects of Land-Use and Water-Management Changes and Low-Impact

Development on Streamflow........................................................................................................27

Effects of Land Development on Streamflow in the Ipswich River Basin.................................30

Simulation of Low-Impact-Development Retrofits in the Upper Ipswich River Basin ............32

Simulation of Water Conservation Effects......................................................................................32

Simulations of Land-Use Change at the Local Scale....................................................................33

Summary and Conclusions.........................................................................................................................36

References Cited..........................................................................................................................................38

Glossary of terms as commonly used in this circular............................................................................40

Figures

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

low-impact-development study sites in the Ipswich River drainage basin in eastern

Massachusetts..............................................................................................................................9

2. Photograph showing low-impact-development features installed in the parking lot

at Silver Lake Beach, Wilmington, MA ...................................................................................10

3. Schematic diagram of low-impact-development features of Silver Lake beach

parking lot and generalized groundwater-flow direction ....................................................12

4. Graph showing profiles of median dissolved oxygen concentrations in groundwater

at multilevel sampler #1 (MLS#1) beneath the Silver Lake beach parking lot in

Wilmington, MA, before (Pre-LID) and after (Post-LID) installation of

low-impact-development features, July–December 2005 and June 2006–June 2007,

respectively .................................................................................................................................13

5. Bar graph showing total nitrogen concentrations in samples from multilevel

sampler #1 (MLS#1) before and after installation of porous parking lot at Silver Lake

beach, Wilmington, MA.............................................................................................................14

6. Bar graph showing total phosphorus concentrations in samples from multilevel

sampler #1 (MLS#1) before and after installation of porous parking lot at Silver Lake

beach, Wilmington, MA.............................................................................................................14

7. Bar graph showing dissolved copper concentrations in samples from multilevel

sampler #1 (MLS#1) before and after installation of porous parking lot at Silver Lake

beach, Wilmington, MA.............................................................................................................15

8. Bar graph showing dissolved nickel concentrations in samples from multilevel

sampler #1 (MLS#1) before and after installation of porous parking lot at Silver Lake

beach, Wilmington, MA.............................................................................................................15
 9

9. Photograph showing low-impact-development (LID) features installed in the

LID-retrofit neighborhood along Dexter Street and Silver Lake Avenue, 

Wilmington, MA ..........................................................................................................................16

10. Box plot showing rainfall-runoff coefficients for storms that occurred before (PRE)

and after (POST) installation of low-impact-development (LID) features in the

LID-retrofit neighborhood along Silver Lake Avenue and Dexter Street, Wilmington,

MA. Rainfall-runoff coefficients are sorted by precipitation depth...................................17

11. Bar graph showing median rainfall-runoff coefficients for storms that occurred

before (Pre-LID) and after (Post-LID) installation of low-impact-development (LID)

features in the LID-retrofit neighborhood along Silver Lake Avenue and Dexter

Street, Wilmington, MA .............................................................................................................17

12. Graph showing total runoff in relation to total precipitation for storms of less than

0.26 in. in the LID-retrofit neighborhood along Silver Lake Avenue and Dexter

Street, Wilmington, MA .............................................................................................................18

13. Box plot showing estimated loads of selected nutrients from storms that occurred

before and after installation of low-impact-development (LID) features in the

LID-retrofit neighborhood along Silver Lake Avenue and Dexter Street, Wilmington,

MA ................................................................................................................................................19

14. Box plot showing estimated loads of selected metals from storms that occurred

before and after installation of low-impact-development (LID) features in the

LID-retrofit neighborhood along Silver Lake Avenue and Dexter Street, Wilmington,

MA ................................................................................................................................................19

15. Photograph showing the green roof installed on the Whipple Annex next to the

Ipswich, MA, Town Hall, summer 2007....................................................................................20

16. Photograph showing the conventional, rubberized-membrane roof on the Ipswich,

MA, Town Hall .............................................................................................................................20

17. Photograph showing the system, during construction, for collecting stormwater

runoff from the Whipple Annex green roof, Ipswich, MA....................................................21

18. 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 ..................................................................................................................................22

19. 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......................................................................................................................23

20. Scatter graph showing percentages of rainfall retained by the Whipple Annex

green roof in Ipswich, MA, in relation to the period of dry weather preceding the

storm.............................................................................................................................................24

21. Box plots showing concentrations of (A) total phosphorus and (B) total nitrogen in

bulk precipitation and rainfall runoff from the Town Hall conventional rubber roof

and from the Whipple Annex green roof, Ipswich, MA, from storms sampled during

2007 and 2008...............................................................................................................................24

22. Box plots showing estimated loads of (A) total phosphorus and (B) total nitrogen in

bulk precipitation and in rainfall runoff from the Town Hall conventional rubber roof

and from the Whipple Annex green roof, Ipswich, MA, from storms sampled in 2007

and 2008........................................................................................................................................25

24. Box plots showing estimated loads of (A) total copper and (B) total lead in bulk

precipitation and in rainfall runoff from the Town Hall conventional rubber roof and

from the Whipple Annex green roof, Ipswich, MA, from storms sampled in 2007 

and 2008........................................................................................................................................26
10 

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2

)

square foot (ft2

) 929.0 square centimeter (cm2)

square mile (mi2

) 2.590 square kilometer (km2) 

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)

Volume

gallon (gal) 0.003785 cubic meter (m3

)

Conversion Factors and Datums

23. Box plots showing concentrations of (A) total copper and (B) total lead in bulk

precipitation and in rainfall runoff from the Town Hall conventional rubber roof and

from the Whipple Annex green roof, Ipswich, MA, from storms sampled in 2007

and 2008........................................................................................................................................26

25. Map showing model reaches and subbasin boundaries in the Ipswich River Basin,

MA ................................................................................................................................................29

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

(1961–95) local-scale simulations of runoff from 100-acre parcels with variable

amounts of effective impervious area.....................................................................................34

Tables

1. Summary of Ipswich River Basin modeling scenarios and results....................................28

2. Simulated August median flows in the Ipswich River at the South Middleton

streamgage..................................................................................................................................30

3. Land use in 1991 and potential land use at buildout in the Ipswich River Basin, MA.....30

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.

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

or micrograms per liter (μg/L).
6 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts

Effects of Low-Impact-Development (LID) 

Practices on Streamflow, Runoff Quantity, 

and Runoff Quality in the Ipswich River Basin, 

Massachusetts: A Summary of Field and 

Modeling Studies

By Marc J. Zimmerman, Marcus C. Waldron, Jeffrey R. Barbaro, and 

Jason R. Sorenson 

Abstract

Low-impact-development (LID) approaches are intended to create, retain, or restore natural 

hydrologic and water-quality conditions that may be affected by human alterations. Wide-scale 

implementation of LID techniques may offer the possibility of improving conditions in river basins, 

such as the Ipswich River Basin in Massachusetts, that have run dry during the summer because of 

groundwater withdrawals and drought. 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 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 

•	 replacing an impervious parking-lot surface with a porous surface on groundwater quality,

•	 installing rain gardens and porous pavement in a neighborhood of 3 acres on the quantity and

quality of stormwater runoff, and

•	 installing a 3,000-ft2 (square-foot) green roof on the quantity and quality of rainfall-generated

roof runoff.

In addition to these small-scale installations, the U.S. Geological Survey’s Ipswich River Basin 

model was used to simulate the basin-wide effects on streamflow of several changes: broad-scale 

implementation of LID techniques, reduced water-supply withdrawals, and water-conservation 

measures. Water-supply and conservation scenarios for application in model simulations were 

developed with the assistance of two technical advisory committees that included representatives 

of State agencies responsible for water resources, the U.S. Environmental Protection Agency, the 

U.S. Geological Survey, water suppliers, and non-governmental organizations.

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

parking lot in Wilmington, Massachusetts, prior to and following the replacement of the conventional, 

impervious-asphalt surface with a porous surface consisting primarily of porous asphalt and 

porous pavers designed to enhance rainfall infiltration into the groundwater and to minimize runoff 

Silver Lake, Wilmington, Massachusetts
Abstract 7

to Silver Lake. Concentrations of phosphorus, nitrogen, cadmium, chromium, copper, lead, nickel, 

zinc, and total petroleum hydrocarbons in groundwater were monitored. Enhancing 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, Massachusetts, 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 selected constituents to Silver Lake. Water-quality 

samples were analyzed for nutrients, metals, total petroleum hydrocarbons, and total-coliform 

and E. coli bacteria. A decrease in runoff quantity was observed for storms of 0.25 inch or less 

of precipitation. 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. 

In a third field study, the characteristics of runoff from a vegetated "green" roof and a 

conventional, rubber-membrane roof were compared. The two primary factors affecting the green 

roof’s water-storage capacity were the amount of precipitation and antecedent dry period. Although 

concentrations of many of the chemicals in roof runoff were higher from the green roof than from 

the conventional roof, the ability of the green roof to retain water generally resulted in decreased 

differences between the total amounts (loads) of the chemicals that ran off the roofs.

Land-use and water-management changes associated with LID implementation were investigated 

at multiple spatial scales, using the U.S. Geological Survey’s Ipswich River Basin model, to evaluate 

the effects of

•	 updated water-supply withdrawals for the towns of Reading and Wilmington (representing new

baseline conditions for all simulations),

•	 potential land-use changes at buildout (potential future development),

•	 widespread implementation of retrofitting LID techniques,

•	 basin-scale water withdrawal reductions based on water-conservation pilot programs conducted by the Massachusetts Department of Conservation and Recreation, and

•	 land-use change and LID applications at a local scale.

The new baseline simulation indicated that reduced water-supply 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 in the upper Ipswich River basin. 

Overall, simulations pointed to the importance of spatial scale in determining the effects of 

land-use change and LID practices on streamflow. Potential land-use changes at buildout had modest 

effects on streamflow in most subbasins (percent differences of less than 20 percent) because 

relatively little land in the basin was available for development. Results of the simulations conducted 

to evaluate widespread effective-impervious-area reductions upstream from the South Middleton 

streamgage indicated that the percentages of urban land use and associated effective impervious 

area were too small for even a 50-percent reduction of effective impervious area to appreciably affect 

streamflow in most subbasins. In contrast, the results of the hypothetical local-scale simulations 

indicated that for smaller streams, with high percentages of urban land use and associated effective 

impervious area, land-use change, development patterns, and LID practices may have substantial 

effects on streamflow. Modeling studies concurred with the results of fieldwork in the assessment 

that LID enhancements would likely have the greatest effect on decreasing stormwater runoff when 

broadly applied to highly impervious urban areas. 
8 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts

Introduction

Conventional urban and suburban development can profoundly affect the

flow and quality of streams and other natural water bodies. Urban development

increases the total area covered by impervious surfaces (roofs, roads, sidewalks, driveways, and parking lots) and typically generates higher rates of local

stormwater runoff. The goal of traditional stormwater management in urban

and suburban areas is to minimize local flooding of streets and other impervious surfaces by conveying stormwater runoff as quickly as possible away from

developed areas, usually through networks of storm drains, either to large,

offsite detention basins or directly to the nearest stream, river, lake, or coastal

water body. While reducing the hazards associated with local flooding, the traditional approach often has unintended consequences, including the alteration

of natural streamflow and the degradation of water quality and aquatic habitat

in receiving water bodies.

In the early 1990s, a land planning and engineering design approach

known as low-impact-development (LID) began receiving increased attention

as a means to reduce the generation of urban runoff at its source. In contrast

to the traditional development and stormwater management approach, LID

practices seek to develop sites in a manner that mimics the natural hydrology

of the undeveloped site (U.S. Environmental Protection Agency, 2009). LID

design features, such as rain gardens, permeable pavement, vegetated (or green)

roofs, and narrow, uncurbed streets, were integrated into newly developed or

existing developed areas to minimize runoff and maximize the infiltration of

water into the soil and (or) the transpiration of water by plants.

In 1997, the Ipswich River in northeastern Massachusetts (fig. 1)

was designated 1 of the 20 most endangered rivers in the Nation by the

environmental organization American Rivers. In recent decades, segments of

the upper river have gone dry for extended periods during the summer with

serious short- and long-term consequences for aquatic biota (Armstrong and

others, 2001). In 2000, the U.S. Geological Survey (USGS), in cooperation

with the Massachusetts Department of Environmental Management (now the

Department of Conservation and Recreation, MDCR), conducted a modeling

study to evaluate the causes of streamflow depletion in the basin (Zarriello

and Ries, 2000). The study concluded that groundwater withdrawals for

public water supply, and subsequent exports of water to users outside of the

basin, were the largest single factors causing flow depletion in the river and

its tributaries.

In 2005, USGS began a study of selected LID practices (vegetated

“green” roof, rain gardens, porous pavement, bioretention cells) to evaluate

their effects on groundwater quality and runoff volume and quality. This study

was funded through a cooperative funding agreement with the MDCR. Funding for the study was also contributed by the U.S. Environmental Protection

Agency’s Targeted Watershed Grand Program through a financial assistance

agreement with MDCR. In addition, the previously developed USGS Ipswich

River Basin model was used to quantify the potential roles of LID practices

and water-conservation strategies in restoring natural streamflows to urbanized

areas. Computer simulations were conducted at both the basin scale (155 mi2)

and at the scale of individual development sites (100 acres). The purpose of

this circular is to summarize the results of these studies and their implications

for the wider application of LID practices and water-conservation strategies in

urbanizing areas of the northeastern United States. A more detailed description

of the field studies and modeling simulations can be found in the companion

report by Zimmerman and others (2010).

Conventional urban and suburban 

development can profoundly affect 

the flow and quality of streams and 

other natural water bodies.
Introduction 9

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

Figure 1. Location of streamgages, weather station, and the low-impact-development study sites in the Ipswich River 

drainage basin in eastern Massachusetts.
10 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts

Field Studies of the Effects of LID Practices

From 2005 through 2008, widely used LID practices were evaluated 

to determine their effects on hydrology and water chemistry at three sites in 

the Ipswich River Basin in northeastern Massachusetts (fig. 1). Two of the 

sites were in Wilmington, in the upper part of the basin, and the third was in 

Ipswich, not far from the mouth of the river.

At the town beach at Silver Lake, in Wilmington, approximately onehalf of the conventional, impervious-asphalt parking lot was replaced with 

a porous parking surface, primarily consisting of porous asphalt and porous 

pavers overlying a 12-in. layer of stone designed to enhance the infiltration 

of precipitation into the groundwater (fig. 2). The rest of the asphalt was 

replaced with a new impervious asphalt surface that was graded to drain to 

the porous asphalt, rather than to the pond, or drain toward the edges of the 

parking lot. Surface runoff from the impervious asphalt also drained toward 

rain gardens and bioretention islands that were installed in the porous and 

impervious areas of the parking lot to enhance infiltration and to filter out 

sediment and nutrients. Two stormwater-runoff drainpipes were partially 

daylighted to lessen bacteria loads to the lake near the beach.

The second LID application also took place in Wilmington in the 

Silver Lake Avenue and Dexter Street neighborhood (“LID retrofit 

neighborhood”) adjacent to Silver Lake. Initially, Dexter Street had curbs 

running along its length and several stormwater drains that joined and ran 

under Silver Lake Avenue and into Silver Lake. Silver Lake Avenue had 

neither curbs nor stormwater drains. LID retrofitting diverted stormwater 

through curb cutouts into and through rain gardens and over porous-paver 

parking areas. The rain gardens and porous paved areas were designed to 

Figure 2. Low-impact-development features installed in the parking lot at Silver Lake Beach, Wilmington, MA.

Porous pavers

Bioretention cell

Porous asphalt

Rain garden designed to enhance 

infiltration at Dexter Street, Wilmington, MA.
Field Studies of the Effects of LID Practices 11

enhance infiltration into the groundwater, thereby decreasing runoff volume

and its associated contaminant load entering the storm-drain system leading

directly into Silver Lake. The LID features accounted for less than 2 percent

of the 3-acre neighborhood area or about 13 percent of the paved-road area.

Although the percentage of porous surface created or improved by the LID

enhancements was not great, the enhancements were not designed just

to receive and infiltrate direct rainfall, but to receive runoff from a large

portion of the impervious surface area, potentially having a greater effect on

overall runoff than might be expected on the basis of the LID area alone.

The third LID feature studied, a 3,000-ft2 green (vegetated) roof,

designed by K.J. Savoie Architecture, was installed by Magco, Inc., a

Tecta America company, on Whipple Annex, a former industrial building

renovated for senior housing in Ipswich, MA, by the North Shore Housing

Trust. The green roof was designed to retain as much as 1 in. of rainfall and

to absorb materials found in precipitation. The vegetation on the green roof

was also expected to diminish runoff through evapotranspiration. The green

roof runoff characteristics were compared to the chemical characteristics of

direct precipitation and to the runoff characteristics of a 5,340-ft2 section of

the conventional, rubber-membrane roof on the Ipswich Town Hall, located

across a small parking lot from the Whipple Annex.

Water quantity and quality were monitored to determine whether any

changes occurred in association with the LID applications. Water samples

were collected to determine concentrations of nutrients, metals, and total

petroleum hydrocarbons at all of the study sites. Bacteriological samples

were collected from stormwater runoff in a manhole at Silver Lake Avenue.

The rates and volumes of runoff were monitored at Silver Lake Avenue in

Wilmington and at the green and rubber-membrane roofs in Ipswich.

Vegetated green roof, designed by K.J. Savoie Architecture and 

installed by Magco, Inc., on the Whipple Annex, 

Ipswich, MA. 
12 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts

Changes in Groundwater Quality Following the Retrofit of 

a Conventional Parking Lot with LID Features

A general concern with LID-enhanced infiltration at the Silver Lake

beach parking lot was the possibility of groundwater contamination from

materials on the parking-lot’s surface. The parking-lot retrofit provided

useful information about groundwater contaminant transport that could

eventually affect the groundwater-fed lake.

Prior to the parking-lot retrofit, four observation wells to monitor

water-table altitudes and three multilevel-port, sampling wells (MLSs) were

installed to collect groundwater samples in the parking lot (fig. 3). Samples

were collected from July 2005 to June 2007, except during the winter and

spring of 2006 when the new parking lot was being installed. On each

sampling date, routine field measurements of temperature, dissolved oxygen

concentration, specific conductance, and pH were made from each sampling

port from the top of the water table to the bottom port of the MLS. Waterquality samples for chemical analysis were collected from MLS ports

closest to the water table because this was considered the most likely place

where infiltrating contaminants could be detected.

Figure 3. Low-impact-development features of Silver Lake beach parking lot and generalized 

groundwater-flow direction.

RAIN GARDEN

RAIN GARDEN

RAIN GARDENS AND

BIORETENTION CELLS

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

STORM

DRAIN

STORM

DRAIN
Field Studies of the Effects of LID Practices 13

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

Figure 4. Profiles of median dissolved oxygen 

concentrations in groundwater at multilevel sampler 

#1 (MLS#1) beneath the Silver Lake beach parking 

lot in Wilmington, MA, before (Pre-LID) and after 

(Post-LID) installation of low-impact-development 

features, July–December 2005 and June 2006–June 

2007, respectively.

In general, no substantial changes in groundwater-quality conditions

were detected after the installation of the porous parking lot and other LID

features. Many of the constituent concentrations were at or below detection

limits both before and after the installation. Results from sampling well

MLS#1 illustrate the minimal changes in groundwater quality. Dissolved

oxygen concentrations increased after the LID installation, suggesting

a more direct recharge from oxygenated precipitation under the LIDenhanced parking lot than under the conventional impervious parking

lot, but the ranges of values before and after installation overlapped

considerably (fig. 4). The ranges of total nitrogen and total phosphorus

concentrations changed little following installation of the LID retrofits

(figs. 5, 6). The highest total nitrogen concentration was detected before

installation, and the highest total phosphorus concentration was detected

afterward; nevertheless, the overall differences were not great for either

constituent. Similarly, the range of concentrations of dissolved copper

(fig. 7) did not appear to change after installation. Among all the analytes

examined, only nickel concentrations decreased significantly (fig. 8),

suggesting that the source was removed during or shortly after the parkinglot construction period.
14 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts

Figure 6. Total phosphorus concentrations in samples from multilevel sampler #1 (MLS#1) before and after 

installation of porous parking lot at Silver Lake beach, Wilmington, MA.

Figure 5. Total nitrogen concentrations in samples from multilevel sampler #1 (MLS#1) before and after 

installation of porous parking lot at Silver Lake beach, Wilmington, MA.

Construction period

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

DATE

Total phosphorus

Water-table altitude

2005 2006 2007

8/10/2005

7/6/2005

7/23/2005

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

8/1/2005

8/28/20059/24/2005

10/20/200511/16/200512/13/2005

1/9/20062/4/20063/3/2006

3/30/20064/26/20065/22/20066/18/20067/15/20068/11/2006

9/6/2006

10/3/2006

10/30/200611/26/200612/22/2006

1/18/20072/14/20073/12/2007

4/8/2007

5/5/20076/1/2007

2005 2006

DATE

2007

0

0.5

1.0

1.5

2.0

TOTAL NITROGEN, IN MILLIGRAMS PER LITER 

2.5

Construction period 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

Total nitrogen

Water-table altitude
Field Studies of the Effects of LID Practices 15

Figure 7. Dissolved copper concentrations in samples from multilevel sampler #1 (MLS#1) before and after 

installation of porous parking lot at Silver Lake beach, Wilmington, MA.

Figure 8. Dissolved nickel concentrations in samples from multilevel sampler #1 (MLS#1) before and after 

installation of porous parking lot at Silver Lake beach, Wilmington, MA.

Detection limit = 0.02 μg/L

DATE

2005 2006 2007

Dissolved copper

Dissolved copper, below detection limit

Detection limit (as indicated)

Water-table altitude

Construction period

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

7/23/2005

8/10/2005

7/6/2005

8/28/2005

9/15/2005

10/3/2005

11/7/2005

10/20/2005

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

Dissolved nickel

Water-table altitude

DATE

7/6/2005

7/23/20058/10/20058/28/20059/15/200510/3/2005

10/20/2005

11/7/2005

11/25/2005

12/13/2005

12/31/2005

1/18/2006 2/4/2006

2/22/20063/12/20063/30/2006

4/17/2006 5/5/2006

5/22/2006 6/9/20066/27/2006

7/15/2006 8/2/20068/19/2006 9/6/2006

9/24/2006

10/12/200610/30/2006

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

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

2005 2006 2007
16 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts

Effects of LID Features on Stormwater Runoff Quantity and Quality from a 

Suburban Neighborhood

Twelve rain gardens and several areas of porous pavers installed in the LID-retrofit

neighborhood near Silver Lake (fig. 9) were designed to decrease and delay runoff into storm drains,

thus enhancing infiltration and decreasing the loads of nutrients, metals, total petroleum hydrocarbons

(TPH), and coliform bacteria transported to Silver Lake. Load is the amount, or mass, of a constituent

transported by stormwater (or a stream) during a specific period of time; load is calculated as the

constituent concentration multiplied by runoff volume. Runoff was sampled for E. coli and total

coliform bacteria to evaluate the effects of LID enhancements on bacterial loads to Silver Lake.

Underdrains from the two porous-paved areas and overflow drains from rain gardens were

connected to the existing storm-drain system. Combined stormwater quantity and quality from Silver

Lake Avenue and Dexter Street were monitored in

a manhole on Silver Lake Avenue. The manhole

was equipped to monitor stormwater flows and

to trigger an automated water sampler to collect

flow-proportional samples. Runoff volume was

monitored at this location throughout the study to

obtain data on storms of all sizes. Water-qualitysample-collection efforts were focused on storms

that were likely to generate a sufficient volume

of runoff for sample analysis. When the National

Weather Service predicted storms of sufficient

magnitude for sampling, the automated sampler

was programmed manually to collect samples,

if enough runoff was measured. Samples for

chemical-water-quality analysis and for E. coli 

and total coliform testing were collected from

August to November 2005, before the LID

enhancements were installed, and from August

2006 to November 2007, the post-LID period.

Differences in pre- and post-LID stormwaterrunoff quantity and quality were generally small

and subtle. Rainfall-runoff (RR) coefficients

before and after LID installation were not

statistically different, even for storms with

antecedent dry periods exceeding 100 hours.

Sorting storms into four size classes (fig. 10) also

did not reveal statistically significant differences

between pre- and post-LID RRs. However,

median runoff coefficients for the small storms

(less than or equal to 0.25 in. of rain) did show

an appreciable difference: the pre-LID median

RR was slightly greater than 0.1 and greater than

the post-LID median RR of about 0.045 (fig. 11).

The median post-LID RR for storms with 0.26 in.

or more precipitation was about the same as the

pre-LID median RR. Thus, the estimated effective

impervious area (EIA), that is, the area that

transmits stormwater directly to Silver Lake with

no opportunity for infiltration, decreased from

about 10 percent of the drainage area to about

4.5 percent as a result of the LID retrofits.

Figure 9. Low-impact-development (LID) features installed in the LID-retrofit 

neighborhood along Dexter Street and Silver Lake Avenue, Wilmington, MA.

Curb cutout

Curb cutout
Field Studies of the Effects of LID Practices 17

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 INCHES

PRECIPITATION DEPTH

x

x

x

x

x

o

6 24 6 8 4 13 6 9

Figure 10. Rainfall-runoff coefficients for storms that occurred before (PRE) and after (POST) installation of low-impactdevelopment (LID) features in the LID-retrofit neighborhood along Silver Lake Avenue and Dexter Street, Wilmington, MA. 

Rainfall-runoff coefficients are sorted by precipitation depth.

Figure 11. Median rainfall-runoff coefficients for 

storms that occurred before (Pre-LID) and after 

(Post-LID) installation of low-impact-development 

(LID) features in the LID-retrofit neighborhood 

along Silver Lake Avenue and Dexter Street, 

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
18 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts

A notable difference between runoff conditions before and after the

LID-retrofit in the Silver Lake neighborhood was the absence of any runoff

from 7 of 21 post-LID storms (33 percent) with 0.25 in. or less precipitation

(fig. 12). Of the seven pre-LID storms of up to 0.26 in. of precipitation,

all had some measurable runoff. No specific factor, such as antecedent dry

period, storm duration, or storm intensity, seemed to be associated with the

absence or presence of runoff. These results indicate that even relatively

small reductions in EIA, in an area underlain by highly permeable, sandy

soils, such as the LID-retrofit neighborhood, can produce measurable

reductions in stormwater runoff for small storms. In the case of this study

site, that threshold was about 0.25 in. of precipitation.

Differences between estimated pre- and post-LID stormwater loads

of nutrients, metals, total petroleum hydrocarbons, and coliform bacteria

to Silver Lake were inconsistent. None of the differences between pre- and

post-LID median loads were statistically significant. The median loads of

nitrogen analytes increased after LID implementation, whereas median

phosphorus-analyte loads decreased (fig. 13). Among the metal analytes,

median loads of lead and zinc decreased and median loads of cadmium,

chromium, copper, and nickel increased (fig. 14). The median of total

coliform bacteria loads increased slightly, and the median of E. coli loads

decreased somewhat. However, none of the changes from pre- to post-LID

median loads for any of the chemical and biological constituents were

statistically significant.

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

Figure 12. Total runoff in relation to total precipitation for storms of less than 

0.26 in. in the LID-retrofit neighborhood along Silver Lake Avenue and Dexter 

Street, Wilmington, MA.

These results indicate that even relatively 

small reductions in EIA, in an area 

underlain by highly permeable, sandy soils, 

such as the LID-retrofit neighborhood, 

can produce measurable reductions in 

stormwater runoff for small storms.
Field Studies of the Effects of LID Practices 19

Figure 13. Estimated loads of selected nutrients from storms that occurred before (PRE) and after (POST)

installation of low-impact-development (LID) features in the LID-retrofit neighborhood along Silver Lake Avenue 

and Dexter Street, Wilmington, MA.

Figure 14. Estimated loads of selected metals from storms that occurred before (PRE) and after (POST) installation of 

low-impact-development (LID) features in the LID-retrofit neighborhood along Silver Lake Avenue and Dexter Street, 

Wilmington, MA.

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

CADMIUM CHROMIUM COPPER LEAD NICKEL ZINC

0.01

0.1

1

10

100

LOAD, IN MILLIGRAMS

1,000

10,000

PRE POST PRE POST PRE POST PRE POST PRE POST PRE POST

x

8595 959595 95

0.01

0.10

1.00

10.0

100

1,000

LOAD, IN GRAMS

EXPLANATION 

75th percentile

Median

25th percentile

10th percentile

Ammonia plus 

organic nitrogen

Ammonia 

nitrogen 

Nitrate 

nitrogen 

Total

nitrogen

OrthophosphorusDissolved 

phosphorus

Total 

phosphorus

PRE POST PRE POST PRE PRE PRE PRE PRE POST POST POST POST POST

5 9 5 9 5 9 5 9 5 9 5 9 5 9

90th percentile

9 Number of values
20 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts

Ability of a Green Roof to Alter 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 finding application for mitigating problems related to stormwater

runoff (Berghage and others, 2007). Green roofs are reported to substantially reduce runoff volume

and attenuate, or slow down, runoff when compared to standard roofs. The plants and growing

medium on the roof, through absorption and

evapotranspiration, make runoff reduction and

attenuation possible. The growing medium may

also neutralize acidic precipitation through its

inherent buffering capacity and retain atmospheric

pollutants that affect the quality of runoff.

The green roof on the Whipple Annex

building in Ipswich (fig. 15) consists of a

waterproof membrane, a plastic drainage layer,

filter fabric, a layer of growth medium (crushed

clay plus organic matter), and plants, including

Talinum calycinum (fameflower), Allium 

schoenoprasum (chive), and eight species of

Sedum (a drought-tolerant succulent). Ipswich

Town Hall has a rubberized membrane roof

(fig. 16). Both roofs were instrumented (fig. 17) so

that rates of stormwater runoff could be monitored

and samples of stormwater could be collected in

proportion to the volume of runoff and analyzed

chemically. A continuous precipitation gage and a

data recorder were installed on the Ipswich Town

Hall roof to monitor rainfall.

Rainfall on and runoff from the two roofs

were monitored for a period of 18 months in 2007

and 2008. Storms producing less than 0.04 in. of

rain were not included in the analysis, nor were

most winter storms or any runoff resulting from

snowmelt because of the uncertainties caused by

freezing, thawing, and snowfall. In all, 70 storms

provided data suitable for comparison of stormwater runoff from the green and conventional roofs.

The ability of a vegetated green roof to reduce

the volume of runoff from a particular storm

depends on the amount, duration, and intensity of

storm precipitation, and on the amount of water

present in the plants and growing medium at the

start of the storm (referred to as “antecedent”

conditions). Water retained from a previous storm

will slowly evaporate from the green roof surface

or transpire into the atmosphere through the

plants (hence the term “evapotranspiration”). As

the length of the antecedent dry period increases,

more of the previously retained water is removed

and the roof’s capacity to store new rainfall

increases. Conversely, if the antecedent dry period

is brief, less storage is available, likely resulting

in some runoff from the roof. However, the timing

Drain

Drain

Figure 15. The green roof installed on the Whipple Annex next to the Ipswich, 

MA, Town Hall, summer 2007.

Figure 16. The conventional, rubberizedmembrane roof on the Ipswich, MA, Town Hall.
Field Studies of the Effects of LID Practices 21

of the release of runoff from a green roof may be

different from that of a conventional roof.

The differences in the responses of the green

roof and rubber roof to antecedent conditions and

storm size are shown in graphs of precipitation

(hyetographs) and runoff (hydrographs) during

two storms in September 2007 (figs. 18, 19).

The September 9, 2007, storm (fig. 18) followed

an extended dry period of 22 days, lasted about

17 hours, and produced 0.61 in. of rainfall that

fell in two bursts about 11 hours apart. Runoff

from the conventional roof began almost as soon

as the rain began (fig. 18) and totaled 273 ft3. In

contrast, runoff from the green roof totaled only

13 ft3. One hundred percent of the rainfall on the

conventional roof became runoff, whereas more

than 85 percent of the rain on the green roof was

retained; that is, less than 15 percent of the rain

that fell on the green roof became runoff. There

was also a noticeable delay in the initial response

of runoff from the green roof relative to the start

of precipitation (fig. 18). Runoff from the green

roof did not increase appreciably until about

1 hour after the storm began.

The September 11, 2007, storm

(fig. 19) followed an antecedent dry period

of only 10 hours, lasted about 7.5 hours, and

produced 1.27 in. of rainfall. In contrast to

the September 9, 2007 storm, only 2 days

earlier, this storm was about twice as large and

delivered more intense rainfall, with much

wetter antecedent conditions. Runoff from the

conventional roof was similar to that observed

in the previous storm, with a direct response

to rainfall that produced total runoff of 569 ft3.

All precipitation on the conventional roof

became runoff. The runoff response from the

green roof was appreciably different from the

previous, September 9, 2007, storm. In the first

hour of the storm, runoff from the green roof

was negligible, but then followed a more direct

response to rainfall, producing a total of 251 ft3,

about 80 percent of the total rainfall that fell on

the roof (20-percent retention). This response

indicates that the growing-medium layer was

already nearly saturated from the previous storm,

and the time between storms was insufficient

for evapotranspiration to allow more than

20 percent retention of rainfall from this storm.

This storm also draws attention to the limits of

the green roof’s design storage capacity of 1.0 in.

of precipitation that was exceeded by 0.27 in.

Total storm precipitation and the length

of the antecedent dry period determine the

Downspout

Downspout

Downspout

junction Field Box 

Field Box (containing 

automated water sampler)

Level spreader (perforated pipe)

Observation tube

Figure 17. The system, during construction, for collecting stormwater runoff 

from the Whipple Annex green roof, Ipswich, MA.

effectiveness of a green roof in retaining water. The finite capacity of

the green roof is a function of its design limits and the amount of water

still retained from previous storms; that amount is controlled by the

length of time since the previous storm and the overall potential for

evapotranspiration, which varies seasonally. For example, in winter, when

plants are dormant, evapotranspiration is minimal, and much precipitation

falls in the form of snow that does not immediately result in runoff.

A broad view of the green roof performance was obtained by relating

storm characteristics to runoff volume for the 70 storms analyzed. The

percentage of precipitation retained in relation to total precipitation varied

from nearly zero to 100 percent for storms less than 1 in., which was the

green roof’s design capacity. In general, the green roof retained more than

50 percent of the precipitation from 70 percent of the storms (49 of 70).

Of the remaining 21 storms, most had antecedent dry periods of less than

70 hours (fig. 20).
22 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts

Figure 18. (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-inch-per-hour intensity 

0.61-inch storm, 531.5-hour antecedent dry period, 16.75-hour duration, 

and 0.036-inch-per-hour intensity 
Field Studies of the Effects of LID Practices 23

Figure 19. (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 16:00

9/11/07 16:30

9/11/07 17:009/11/07 17:309/11/07 18:00

9/11/07 18:30

9/11/07 19:009/11/07 19:30

9/11/07 20:00

9/11/07 20:30

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 15:30

9/11/07 16:009/11/07 16:30

9/11/07 17:009/11/07 17:309/11/07 18:00

9/11/07 18:309/11/07 19:00

9/11/07 19:309/11/07 20:00

9/11/07 20:30

DATE AND TIME

0

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

PRECIPITATION, IN INCHES

0

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
24 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts

Adequate volumes of composite, flow-proportional runoff samples

and bulk (direct) precipitation samples were obtained from five

storms and analyzed for nutrients (nitrogen and phosphorus), metals

(cadmium, chromium, copper, lead, nickel, and zinc), and total petroleum

hydrocarbons. (For a compilation of all data, refer to the companion report,

Zimmerman and others, 2010.) Median concentrations of total phosphorus

and total nitrogen were higher in runoff from the green roof than they

were in runoff from the conventional roof, and median concentrations of

these constituents in both sets of runoff samples were significantly higher

than those in bulk precipitation (fig. 21). The relatively high nutrient

concentrations in runoff from the green roof were likely due to nitrogen

and phosphorus initially present in the growing medium and to subsequent

fertilization of the roof during establishment of the plants. Leaching of

nutrients from green roofs has been reported elsewhere (Oberndorfer and

others, 2007; Dietz, 2007). With the planned discontinuation of fertilization

as the vegetation becomes fully established, the concentrations of nutrients

in the green roof runoff should diminish. Likely sources of the constituents

found in runoff from the conventional roof include dryfall (particles

deposited on surfaces from dry air) between storms and fecal deposits left

by birds and insects, in addition to chemicals dissolved in precipitation.

Constituent loads (the total mass of a constituent in stormwater

runoff) were computed from concentration data and runoff volumes and

divided by roof surface area to account for the differences in area between

the two roofs. Estimated constituent loads indicate that the reduction in

0 100 200 300 400 500 600

PERIOD, IN HOURS

0

20

40

60

80

100

PERCENTAGE OF PRECIPITATION RETAINED

0.0 to less than 0.1

0.1 to less than 0.5

0.5 to less than 1.0

1.0 to less than 2.0

2.0 and above

Total precipitation, in inches

EXPLANATION

Figure 20. Scatter Percentages of rainfall 

retained by the Whipple Annex green roof in 

Ipswich, MA, in relation to the period of dry 

weather preceding the storm.

A Phosphorus

B Nitrogen

0.1

0.5

1

5

10

BULK

PRECIPITATION

CONVENTIONAL

RUBBER ROOF

GREEN ROOF

5 5 5

TOTAL NITROGEN CONCENTRATION,

 IN MILLIGRAMS PER LITER

0.01

0.1

1

10

BULK

PRECIPITATION

CONVENTIONAL

RUBBER ROOF

GREEN ROOF

5 5 5

TOTAL PHOSPHORUS CONCENTRATION,

 IN MILLIGRAMS PER LITER

5 Number of 

values

EXPLANATION 

90th percentile

75th percentile

Median

25th percentile

10th percentile

Figure 21. Concentrations of (A) total phosphorus 

and (B) total nitrogen in bulk precipitation and 

rainfall runoff from the Town Hall conventional 

rubber roof and from the Whipple Annex green 

roof, Ipswich, MA, from storms sampled during 

2007 and 2008.
Field Studies of the Effects of LID Practices 25

stormwater volume from the green roof effectively reduced the nutrient

loads, even though the constituent concentrations from green roof samples

were significantly higher than the constituent concentrations from the

conventional roof samples (fig. 22). For example, the median total

phosphorus concentration was almost 100 times greater in the green roof

runoff than in the conventional roof runoff, but the median total phosphorus

loads in runoff from the two roofs differed by only about a magnitude factor

of 10. The green roof’s median total nitrogen concentration was slightly

greater than that of the conventional roof, but the median load was slightly

smaller than the median load from the conventional roof. Differences

between median total nitrogen loads for the green roof and the conventional

roof were not statistically significant.

The median total copper concentration measured in runoff from the

green roof (414 micrograms per liter (μg/L)) was about 10 times greater

than that in runoff from the conventional roof (41.2 μg/L), and more than

100 times greater than that in bulk precipitation (2 μg/L, fig. 23A). In

contrast, the median total lead concentration in runoff from the green roof

(1.87 μg/L) was less than 1 percent of that from the conventional roof

(589 μg/L) and was not statistically different than the median total lead

concentration in bulk precipitation (fig. 23B). These differences in runoff

quality are attributed to differences in plumbing and roof-construction

materials. The gutters, downspouts, machinery, vents, and copper flashing

on the green roof likely all affect runoff water quality. Cast iron drain pipes

A Phosphorus

B Nitrogen

1

10

100

BULK

PRECIPITATION

CONVENTIONAL

RUBBER ROOF

GREEN ROOF

5 5 5

TOTAL NITROGEN LOAD, IN GRAMS

0.01

0.1

1

10

100

BULK

PRECIPITATION

CONVENTIONAL

RUBBER ROOF

GREEN ROOF

5 5 5

TOTAL PHOSPHORUS LOAD, IN GRAMS

5 Number of 

values

EXPLANATION 

90th percentile

75th percentile

Median

25th percentile

10th percentile

Figure 22. Estimated loads of (A) total phosphorus 

and (B) total nitrogen in bulk precipitation and in 

rainfall runoff from the Town Hall conventional 

rubber roof and from the Whipple Annex green roof, 

Ipswich, MA, from storms sampled in 2007 and 2008.
26 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts

5 Number of 

values

EXPLANATION 

90th percentile

75th percentile

Median

25th percentile

10th percentile

1

10

100

1,000

BULK

PRECIPITATION

CONVENTIONAL

RUBBER ROOF

GREEN ROOF

5 5 5

TOTAL LEAD CONCENTRATION,

 IN MICROGRAMS PER LITER

BULK

PRECIPITATION

CONVENTIONAL

RUBBER ROOF

GREEN ROOF

0.1

1

10

100

1,000 5 5 5

TOTAL COPPER CONCENTRATION,

 IN MICROGRAMS PER LITER

A Copper

B Lead

Figure 23. Concentrations of (A) total copper and 

(B) total lead in bulk precipitation and in rainfall 

runoff from the Town Hall conventional rubber roof 

and from the Whipple Annex green roof, Ipswich, 

MA, from storms sampled in 2007 and 2008.

Figure 24. Estimated loads of (A) total copper and 

(B) total lead in bulk precipitation and in rainfall 

runoff from the Town Hall conventional rubber roof 

and from the Whipple Annex green roof, Ipswich, 

MA, from storms sampled in 2007 and 2008.

A Copper

B Lead

5 Number of 

values

EXPLANATION 

90th percentile

75th percentile

Median

25th percentile

10th percentile

1

10

100

1,000

10,000

100,000

BULK

PRECIPITATION

CONVENTIONAL

RUBBER ROOF

GREEN ROOF

5 5 5

TOTAL LEAD LOAD, IN MILLIGRAMS

10

100

1,000

10,000

BULK

PRECIPITATION

CONVENTIONAL

RUBBER ROOF

GREEN ROOF

5 5 5

TOTAL COPPER LOAD, IN MILLIGRAMS
Simulation of the Effects of Land-Use and Water-Management Changes and Low-Impact Development on Streamflow 27

with lead seals likely contribute to the chemical makeup of the conventional

roof runoff. In a similar manner to nitrogen, the reduced stormwater volume

from the green roof, relative to the conventional roof, resulted in copper

loads that were not significantly different from those estimated for the

conventional roof (fig. 24A). Lead loads from the conventional roof were

much greater than those from the green roof (fig. 24B).

Simulation of the Effects of Land-Use and 

Water-Management Changes and Low-Impact 

Development on Streamflow

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 water use (water withdrawals,

wastewater return flows, and water transfers) affect the entire flow regime,

from flood peaks to summer low flows maintained by groundwater

discharge. Storm drainage systems, such as catch basins and storm sewers,

concentrate and distribute runoff from impervious areas. A computer model

of the Ipswich River Basin, called the Ipswich River Basin Hydrological

Simulation Program-FORTRAN (HSPF) precipitation-runoff model

(Zarriello and Ries, 2000), was modified to simulate the effects of changes

in land-use and LID practices on streamflow. To better reflect current

conditions, recent changes in public water-supply withdrawals by the towns

of Wilmington and Reading were incorporated into the model primarily

to bring the model up to date with current water-supply conditions.

Several water-withdrawal scenarios representing widespread application

of water-conservation strategies were then developed in consultation with

MDCR, U.S. Environmental Protection Agency, and the project’s technical

advisory committees.

Watershed computer models, such as HSPF, simplify the complex

processes and physical characteristics of a drainage basin. This

simplification consequently limits the types of questions that can be

addressed with the model. The assumptions, information used to develop

and calibrate the model, spatial resolution (degree of detail) of the model,

and alternative model structures and parameters (characteristics such as

precipitation and housing density) need to be considered when evaluating

model results for use in water-resources management decisions. For

example, specific LID practices, such as installation of porous pavement,

rain gardens, bioretention areas, and green roofs, could not be represented

explicitly in the basin-scale Ipswich River Basin HSPF model; instead,

substitutes for these practices were simulated by varying the amount of EIA

over the entire basin. For more detailed elaboration of the Ipswich River

Basin model assumptions and limitations, see Zarriello and Ries (2000).

Simulations were conducted at two different geographic scales for

this study (table 1). The first set of simulations examined the effects of

land-use change, LID practices, and water-conservation efforts at basin and

subbasin scales. The basin-scale simulations generally generally focused

on the upper Ipswich River Basin, an area of 44.5 mi2, upstream from the

USGS South Middleton streamgage ((01101500) in fig. 25). However,

model simulations represented hydrologic processes in drainage areas

ranging from about 0.5 to 125 mi2 in size. To better represent hydrologic

Loss of vegetation, increased 

imperviousness, and water use 

(water withdrawals, wastewater return 

flows, and water transfers) affect the 

entire flow regime, from flood peaks 

to summer low flows maintained by 

groundwater discharge.
28 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts

Table 1. Summary of Ipswich River Basin modeling scenarios and results. (For complete details, see Zimmerman and others, 2010.)

[LID, low-impact development]

Simulation scenario Area covered Brief description of selected results of effects of 

modifying original baseline model

Basin-scale simulations

Original baseline simulation (Zarriello

and Ries, 2000)—average 1989 to 1993

withdrawals (also referred to as original

baseline withdrawals), 1991 land use

Entire basin

(155 mi2)

Original baseline model

Updated baseline simulation—average 1989 to

1993 withdrawals with updated withdrawals

for Reading and Wilmington (also referred

to as updated baseline withdrawals), 1991

land use

Entire basin

(155 mi2)

Increases in low and medium flows upstream from the South

Middleton streamgage.

Buildout simulation—updated baseline

withdrawals, potential land use at buildout

Entire basin

(155 mi2)

Minor effects on streamflow: 0 to 20 percent change at

subbasin scale.

Simulation of LID retrofits upstream from the

South Middleton streamgage (station no.

01101500)—updated baseline withdrawals,

1991 land use with effective impervious area

reduced by 50 percent

Upper basin

(44.5 mi2)

Minor effects on streamflow: 0 to 20 percent change

Water-conservation simulation—updated

baseline withdrawals with rates reduced by 1

to 20 percent to represent water-conservation

programs, 1991 land use

Entire basin

(155 mi2)

With 5 percent reduction in withdrawals, effects were minor. With

20 percent reduction in withdrawals, low flows increased slightly.

Local-scale simulations

Local-scale simulations—no water

withdrawals, varying combinations of

developed and undeveloped land-use types

and amounts of effective impervious area

Hypothetical,

100-acre parcels

Conventional development:

(A) Conversion of forested land use to commercial: increased

median 1-day high flow 1,250 percent; decreased median 1-day

low flow 33 percent;

(B) Conversion of forested land use to high-density residential: 

increased high or medium and low flows, depending on

underlying geology;

(C) Sensitivity of streamflow to effective impervious area: 

Implementing LID in commercial and high-density

residential land-use areas reduced flow alteration more than

implementation in low-density residential land-use areas.

Cluster development:

Clustering tended to reduce high flows.
Simulation of the Effects of Land-Use and Water-Management Changes and Low-Impact Development on Streamflow 29

Figure 25. Model reaches and subbasin boundaries in the Ipswich River Basin, MA. (From Zarriello and Ries, 2000)

responses at a local scale, the second set of simulations examined the potential effects of changes in land use, amount of EIA,

and incorporation of LID practices, such as clustering development and preserving open space, on streamflow in hypothetical

100-acre (0.16 mi2) parcels of land. The local-scale simulations were based on homogeneous land uses with different mixes of

development density and EIA. Collectively, the simulations represented a wide range of spatial scales and time periods as well

as a range of hydrologic responses to land-use change, water-management activities, and various LID practices. (For a complete

description of the modeling study, see Zimmerman and others, 2010.)

The baseline simulation in the original Ipswich River Basin modeling study was used to evaluate the effects of average

1989–93 groundwater withdrawals on streamflow over long-term (1961–95) climatic conditions (Zarriello and Ries, 2000).

This baseline simulation was updated to incorporate recent changes in groundwater withdrawals for the towns of Reading

and Wilmington that had relied on withdrawals from wells in the upper part of the basin. In 2006, the town of Reading began

purchasing water from the Massachusetts Water Resources Authority (MWRA) to meet its water needs. To simulate current

withdrawals, the 10 well withdrawals by Reading wells were discontinued—a decrease of 2.2 Mgal/d from reach 8 (fig. 25).

In anticipation of the town of Wilmington purchasing water from the MWRA in 2008, daily summer withdrawal rates from four

active wells were decreased by a total of 1 Mgal/d from reaches 5, 12, and 13 (fig. 25) in the updated baseline simulation.

Total annual withdrawals upstream from the South Middleton streamgage averaged 6.7 Mgal/d in the original baseline

simulation (Zarriello and Ries, 2000) and dropped to 3.5 Mgal/d in the updated baseline simulation for the present study.

HAMILTON

DANVERS

PEABODY

LYNNFIELD

BURLINGTON WOBURN

TEWKSBURY

WILMINGTON

ANDOVER

NORTH

ANDOVER

BOXFORD

MIDDLETON

NORTH READING

READING 

TOPSFIELD

ROWLEY

IPSWICH

WENHAM

BEVERLY

SALEM

LYNN

ESSEX

BILLERICA

MANCHESTER

GLOUCESTER

WAKEFIELD

GEORGETOWN

MARBLEHEAD

ATLANTIC OCEAN

42°40'

42°30'

71°10' 70°50'

EXPLANATION

IPSWICH

15 Stream reach and number 

 within model subbasin

Basin boundary and name

Streamgage subbasin 

 boundary

Town boundary

Model subbasin

Open water

01101500 Streamgage and number 

0 2 4

0 2 4 6 MILES

6 KILOMETERS

ATLANTIC

OCEAN

NORTH COASTAL

SHAWSHEEN

MERRIMACK

BOSTON HARBOR

PARKER

IPSWICH

Putnamville

Reservoir Swan

Pond

Emerson

Brook

Reservoir

Winona

Pond

Suntaug

Lake

Wenham

Lake

Longham

Reservoir Middleton

Pond

Lowell 

Pond

Cleveland Brook

Salem-Beverly Canal

Pye Brook

Howlett Brook

Nichols Brook

Fish Brook

Lubbe rs Bro ok

Ipswich

River

Black Brook

Miles Rive r

Idlewild Brook

Emerson Brook

Boston Brook

Wills Brook

Norris Brook

River

Bear Meadow Brook

Martins Brook

Ma ple Meadow Brook

Mill Brook

Ipswich

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

01102000

01101500

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

Lambert conformal conic projection, North American Datum of 1983
30 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts

The decrease in withdrawal led to substantial

simulated increases in low and median flows

in the Ipswich River at the South Middleton

streamgage (table 2).

Effects of Land Development on 

Streamflow in the Ipswich River Basin

A statewide buildout analysis was conducted

by the Massachusetts Executive Office of

Energy and Environmental Affairs (EOEEA)

in 2001 (Massachusetts Executive Office of

Energy and Environmental Affairs, 2008).

This analysis provided information to simulate

the effects of potential future development,

referred to as buildout, on streamflow in the

Ipswich River Basin. A buildout analysis

determines how a community might develop if

all remaining developable areas were fully built

out in accordance with current local zoning and

other development constraints. 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.

Table 3. 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

Table 2. Simulated August median flows in the Ipswich River at the South 

Middleton streamgage.

Original baseline,

cubic feet per second

Updated baseline,

cubic feet per second Percent change

August median flows

3.42 8.36 144

Median 1-day low flows

0.74 2.8 278

Median 7-day low flows

0.983 3.65 271
Simulation of the Effects of Land-Use and Water-Management Changes and Low-Impact Development on Streamflow 31

To develop new land-use data to simulate future conditions, the zoning

codes in the developable areas were related to the land-use categories used

for model development. Using 1991 land use as a baseline, the buildout

analysis indicated that about 17 percent of the entire Ipswich River Basin

was developable. The major changes in the basin were the decline in forested areas from 39 to 24 percent, and the increase in low-density residential development (lot sizes greater than 0.5 acre) from 15 to 31 percent.

Other developed land-use categories, including high-density residential (lot

sizes less than or equal to 0.5 acre) and commercial, increased slightly at

buildout (table 3).

To isolate the effects of land-use change on streamflow, the updated

baseline simulation, reflecting 1991 land use, was modified to account for

land-use change at buildout. Land-use change associated with buildout

generally had minor effects (0 to 20 percent change) on streamflow at the

subbasin scale because most of the developable land in the basin was forested or open and zoned for low-density residential development. The EIA

associated with low-density residential development was relatively small

(2.5 percent in the calibrated Ipswich River Basin HSPF model); therefore,

increases in this type of land use were not expected to appreciably change

the runoff response to precipitation because the runoff characteristics are

similar for forest and low-density-residential land use for a given type

of underlying surficial geology. The major difference between simulated

forests and low-density residential development was the amount of water

lost to evapotranspiration. 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

lower the soil-moisture content, reduce recharge, and lower water tables,

thus reducing the base-flow (groundwater) contribution to streamflow.

Consequently, although low-density residential areas received slightly less

infiltration per unit area than forested areas because of EIA, the comparatively small evapotranspiration losses from low-density residential areas are

believed to have resulted in slight increases in summer low flows, relative

to forested areas with the same surficial geology.

By comparison, conversion of forest to commercial land use in this

analysis had a pronounced effect on simulated streamflow, producing

increases in peak flows, because the relatively large increases in EIA

increased surface runoff. Although this effect of urbanization on flood peaks

was relatively clear, the effect of increasing urbanization on low flows

showed conflicting results, as also noted by Brandes and others (2005) and

Rose and Peters (2001). The lack of clear effects may result 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).

Overall, the buildout simulation assuming conventional styles of

development demonstrated only minor effects on streamflow in the basin.

Therefore, buildout incorporating LID practices, which would only show

subtle effects of development, was not evaluated.

The major difference between simulated 

forests and low-density residential 

development was the amount of water lost 

to evapotranspiration. 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). 
32 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts

Simulation of Low-Impact-Development Retrofits in the 

Upper Ipswich River Basin

The drainage area of the upper Ipswich River Basin, upstream from

the South Middleton streamgage (fig. 25), is relatively urban and has less

developable land than the rest of the basin. Therefore, this subbasin was

used to evaluate the effects of retrofitting existing development with LID

features to increase stormwater recharge and decrease surface runoff.

In the LID-retrofit simulation, 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

EIA to natural or constructed recharge areas). The simulated 50-percent

reduction in EIA was considered a substantial, but reasonable, maximum

amount of EIA reduction that could be achieved through the widespread

implementation of various LID practices. The 50-percent reduction

of EIA upstream from the South Middleton streamgage generally had

modest effects on subbasin streamflows (percent differences of less than

20 percent). (Specific details of these differences may be found in the

companion report, Zimmerman and others, 2010). Even in this relatively

urban part of the Ipswich River Basin, the heterogeneous mix of land uses

resulted in changes in the total EIA that were small percentages of the total

areas of the 19 subbasins. Thus, the results may indicate that widespread

LID practices may not substantially affect flows in large rivers and tributary

streams that are characterized by heterogeneous land use and an EIA lower

than 50 percent. On the other hand, LID practices that reduce EIA on a local

scale may have substantial effects on flows because the EIA as a percentage

of the drainage area may be large and a large decrease in EIA may be

attainable. This concept is examined further in the section, “Simulations of

Land-Use Change at the Local Scale.”

Simulation of Water Conservation Effects

Data from four water-conservation pilot projects conducted by MDCR

were used to simulate the effects of widespread application of conservation

practices on streamflow. Pilot projects included:

•	 installation of weather-sensitive “smart” irrigation controller

switches on automated sprinkler systems at municipal athletic fields;

•	 application of soil amendments at a municipal athletic field to

improve soil moisture and nutrient retention;

•	 installation of 800-gallon rainwater harvesting systems for the collection and reuse of rainwater for irrigation; and

•	 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 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.

Based on per-unit savings calculated by MDCR from the pilot projects and

from specific information about each town, for example, acres of irrigated

LID features to increase stormwater 

recharge and decrease surface runoff.
Simulation of the Effects of Land-Use and Water-Management Changes and Low-Impact Development on Streamflow 33

athletic fields and number of households, water suppliers were assigned

hypothetical, potentially achievable, town-wide water-withdrawal reductions. (For a detailed description of the assumptions used for these simulations, see Zimmerman and others, 2010.)

Reductions in water use were expected to have their greatest effects

on low flows in subbasins in which streamflow depletion was high, relative

to the rate of streamflow in the absence of withdrawals (Barbaro, 2007).

Hypothetical water-use reductions from the pilot projects in the basin

ranged from 1.4 percent (Salem-Beverly water supply) to 8.5 percent

(Hamilton) of average 1989–93 withdrawals. Withdrawal reductions

of 5 percent had little effect on simulated low flows, and a 20-percent

withdrawal reduction resulted in slightly higher low flows. In general,

however, the conservation scenarios examined did not indicate appreciable

changes from current (1989–93) simulations. This result is consistent with

previous reduced-withdrawal simulations for the Ipswich River upstream

from the South Middleton streamgage that were conducted with the original

baseline withdrawals (Zarriello, 2002). The effects of withdrawal reductions

on small streams would likely be more pronounced.

Simulations of Land-Use Change at the Local Scale

Local-scale simulations were conducted to evaluate the hydrologic

effects of land-use change, development patterns, and surficial geology

on 100-acre parcels of land. The results of these simulations are depicted

with flow-duration curves (fig. 26). (See box for explanation of flowduration curves.) These simulations of the effects of land-use change

provided valuable information for assessing the conditions under which

LID practices may have the greatest benefits. Specifically, simulations were

conducted to evaluate the effect on streamflow of

•	 uniform land-use change for conventional development (that is,

uniform lot sizes);

•	 cluster development;

•	 changes in the amount of EIA that represent LID applications; and

•	 surficial geology. (See Zimmerman and others (2010) for additional

simulation details.)

Converting a 100-acre parcel from forested land to developed land

increased simulated median 1-day high flows (median of 1-day annual high

flows for 1961–95 simulation) by as much as 1,250 percent, depending on

the underlying surficial geology and the type of development. Conversion

of forested land overlying sand and gravel deposits to commercial

development produced the maximum increase in the simulated median

1-day high flow, from 0.49 to 6.60 ft3/s (1,250 percent.) Converting forest

to low-density or high-density residential development resulted in modest

increases in the median 1-day high flow and also increased simulated

medium and low flows (fig. 26). Medium and low flows increased because

both residential densities were simulated to have lower evapotranspiration

losses than forested drainage areas, producing more subsurface discharge

to streams. Simulations of runoff from a 100-acre parcel with variable

amounts of EIA indicate that LID provided the greatest benefit in

LID practices that reduce EIA on a local 

scale may have substantial effects 

on flows.
34 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts

commercial and high-density residential land-use parcels because of their

high proportion of EIA relative to other land uses.

Simulations of cluster development, in which a percentage of the

parcel remains forested, or as open space, indicated that this practice

reduced high flows and had variable effects on low flows when compared

to conventional development with the same number of houses. For lowdensity cluster developments, leaving a large part of the land forested

resulted in slightly lower low flows than for a conventional low-density

development with uniform lot sizes because a greater percentage of

deep-rooted vegetated area remained undisturbed. Flows from a cluster

development more closely approximated flows from forested areas than

flows from conventional low-density development on the 100-acre parcel.

However, in the absence of LID enhancements, flows from the cluster

development itself would closely approximate a high-density development.

Simulated streamflow did not vary substantially with variations in the

amount of EIA in the cluster development, because the total EIA over the

parcel was a relatively low percentage of the area.

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

STREAMFLOW, IN CUBIC FEET PER SECOND STREAMFLOW, IN CUBIC FEET PER SECOND

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

14% EIA

7% EIA

28% EIA

63% EIA

47% EIA

31.5% EIA

Commercial

High-density residential

overlying sand and gravel

Low-density residential

overlying sand and gravel

Figure 26. Flow-duration curves of daily mean 

streamflow from long term (1961–95) local-scale 

simulations of runoff from 100-acre parcels with 

variable amounts of effective impervious area.
Simulation of the Effects of Land-Use and Water-Management Changes and Low-Impact Development on Streamflow 35

What is a Flow Duration Curve?

Simply stated, a flow-duration curve shows the 

percentage of time that a given streamflow is 

equaled or exceeded. For example, see the solid 

horizontal line extending from the y axis at 100 cubic 

feet per second to the point where it meets the 

curve. A vertical line extended downward from this 

point meets the x axis at approximately 25 percent. 

This means that the streamflow of cubic feet per 

second is met or surpassed about 25 percent of the 

time. In order to derive the median streamflow (the 

amount equaled or exceeded 50 percent of the time), 

see the dashed vertical line extending upward from 

the x axis at 50 percent to where it meets the curve. 

A horizontal line extended from this point meets the y 

axis at 10 cubic feet per second. This means that the 

median streamflow is 10 cubic feet per second. 

2 5 10 30 50 70 90 95 99 99.8

1,000

100

10

1

STREAMFLOW, IN CUBIC FEET PER SECOND

PERCENTAGE OF TIME

FLOW WAS EQUALED OR EXCEEDED

FLOW-DURATION CURVE
36 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts

Summary and Conclusions

The U.S. Geological Survey, in cooperation with the Massachusetts Department of Conservation

and Recreation and the U.S. Environmental Protection Agency, examined the effects of implementing

selected low-impact-development (LID) techniques on water quantity and quality in several field

studies and a computer-modeling study in the Ipswich River Basin, in Massachusetts, which is

adversely affected by low streamflows in the summer season. The field studies monitored

•	 possible changes in groundwater quality caused by replacing a conventional impervious

parking-lot surface with a porous asphalt and paver surface,

•	 effects on runoff quantity and quality by directing runoff from the street and driveways into a

combination of rain gardens and porous parking surfaces in a 3-acre neighborhood, and

•	 differences in runoff quantity and quality from a conventional rubberized-membrane roof and a

neighboring vegetated “green” roof.

The study also examined the potential effects of LID practices and water-withdrawal reductions by

modifying a previously developed precipitation-runoff model of the basin.

Enhanced infiltration, particularly from parking lots, has the potential to transport contaminants

to the water table. The first LID field site, a parking lot for Silver Lake Beach in Wilmington, MA,

indicated no detrimental effects on groundwater quality after the parking lot was retrofitted with

porous asphalt, porous pavers, rain gardens, and bioretention cells. At the second field site, in a

residential neighborhood adjacent to Silver Lake, installation of LID features (rain gardens and porous

pavers) had the most pronounced effect on runoff from small storms (0.25 in. or less of precipitation);

the median runoff from such storms was reduced by about 50 percent, consistent with the decrease

in effective impervious area from 10 to 4.5 percent after LID implementation. In addition, these LID

features decreased the number of small storms producing measurable runoff. At the third field site,

the runoff from a green roof retained at least 50 percent of the rainfall from about 70 percent of the

storms, relative to a conventional rubber-membrane roof that does not reduce runoff at all. The length

of the antecedent dry period and storm size were the controlling factors affecting the green roof’s

capacity for water retention and runoff attenuation; long, dry antecedent periods increased available

storage for the green roof, thus attenuating storm runoff. The relatively high concentrations of

nutrients in green roof runoff, affected by fertilizer application during establishment of the vegetation,
Summary and Conclusions 37

were somewhat offset by the decrease in runoff volume. Extending the study duration would

demonstrate whether nutrient loads would decrease as the vegetation further matured and fertilizers

were no longer applied. Contaminants, such as metals, in the roof runoff were attributed to specific

roof and gutter structures.

The modeling studies used the calibrated Hydrologic Simulation Program-FORTRAN Ipswich

River Basin precipitation-runoff model to simulate the effects of water-management scenarios and

LID practices on streamflow at scales ranging from the local scale (100 acres, or 0.16 mi2) to the

subbasin and basin scale (0.5 to 125 mi2). Specific LID practices were not simulated; rather, land-use

change and associated changes in effective impervious area were used as surrogates for LID practices.

Simulations indicated that, at the basin and subbasin scale, the potential effective impervious

area reduction from the application of LID practices was generally too low to appreciably affect

streamflow. In contrast, the local-scale simulations of a 100-acre parcel indicated that, where

the percentage of urban land use and associated effective impervious area was relatively high,

development patterns and LID practices could have substantial effects on streamflow.

In LID-retrofit simulations, reducing effective impervious area by 50 percent minimally affected

streamflow in most subbasins analyzed, because the effective impervious area in the subbasin

was a relatively small percentage of the overall area. In drainage basins that are characterized by

heterogeneous land use, widespread use of LID practices may not have a pronounced effect on

streamflow. On the other hand, LID practices that reduce effective impervious area on a local scale

may affect streamflow because effective impervious area, as a percentage of the drainage area, may be

large, and a relatively large percentage decrease in effective impervious area may be attainable.

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, the effects on simulated low flows in most of the rivers and streams in the

basin were minor.

In summary, the field studies and model simulations demonstrate that implementation of LID

practices can demonstrably affect stormwater runoff quantity and quality; however, their effects

may be difficult to discern when the changes in effective-impervious area, as a percentage of total

basin area, are small. The benefits of LID practices are greatest when the percentage of effective

impervious area is large and the LID enhancements can substantially redirect storm runoff away from

conveyances leading to streams or lakes.
38 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts

References Cited

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40 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts

Analyte The subject of a chemical analysis

Antecedent conditions Conditions 

preceding a particular storm

Base flow Streamflow that originates from 

groundwater

Bioretention cell A man-made feature, 

containing soil and plants, that functions to 

remove pollutants from runoff

Bulk-precipitation samples Precipitation 

samples that directly captured in open 

containers

Calibrate Modify computer program 

parameters so the results of a simulation 

closely match a set of known conditions

Composite, flow-proportional Waterquality subsamples collected and combined 

at a frequency sampled in proportion to 

the amount of water that has passed the 

collection point

EIA Effective impervious area—surface 

area that does not contribute runoff to 

groundwater or base flow

Evapotranspiration The sum of evaporation 

and plant transpiration from a surface to the 

atmosphere

Flow-duration curve A graph showing the 

percentage of time that streamflow is likely to 

equal or exceed a specific value

Hydrograph A graph showing the amount of 

streamflow over a period of time

Hyetograph A graph showing the amount of 

rainfall over a period of time

Impervious Incapable of being penetrated 

by water

Infiltration The process by which water on 

the surface enters the ground

LID Low-impact development—a planning 

or design approach to development intended 

to reduce runoff by enhancing infiltration, 

thereby retaining or restoring natural 

hydrological characteristics

Load The total amount of a particular 

analyte or subject of analysis, such as 

bacteria

Median In a group of numbers, the middle 

value above and below which there is an 

equal number of values

Parameters Characteristic values that can 

be manipulated in a computer model

Post-LID The time period after the 

installation of LID features

Pre-LID The time period before the 

installation of LID feature

Rainfall-Runoff Coefficient (RR) The ratio 

of the amount of runoff to the amount of 

precipitation

Scenario A condition, or set of conditions, 

to be simulated using a computer program

Simulation The implementation of a 

scenario by running a computer program

Glossary of terms as commonly used in this circular
Prepared by the Pembroke Publishing Service Center.

For more information concerning this report, contact:

Director

U.S. Geological Survey

Massachusetts-Rhode Island Water Science Center

10 Bearfoot Road

Northborough, MA 01532

dc_ma@usgs.gov

or visit our Web site at:

http://ma.water.usgs.gov
Zimmerman and others—Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts—Circular 1361

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