effects of low-impact-development (lid) practices on ... · implementation of lid techniques may...

U.S. Department of the InteriorU.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


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 InteriorU.S. Geological Survey

7

U.S. Department of the InteriorKEN SALAZAR, Secretary

U.S. Geological SurveyMarcia 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 model-ing 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. Environ-mental 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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8

Contents

Abstract ...........................................................................................................................................................6Introduction.....................................................................................................................................................8Field 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 .....................20Simulation of the Effects of Land-Use and Water-Management Changes and Low-Impact

Development on Streamflow ........................................................................................................27Effects of Land Development on Streamflow in the Ipswich River Basin .................................30Simulation of Low-Impact-Development Retrofits in the Upper Ipswich River Basin ............32Simulation of Water Conservation Effects ......................................................................................32Simulations of Land-Use Change at the Local Scale ....................................................................33

Summary and Conclusions .........................................................................................................................36References Cited..........................................................................................................................................38Glossary 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 andgreen roofs in Ipswich, MA, for the storm of September 9, 2007, and (B) cumulativepercentages 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 andgreen roofs in Ipswich, MA, for the storm of September 11, 2007, and (B) cumulative percentages of total precipitation and total runoff from the roofsfor 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 inbulk 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 inbulk 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 bulkprecipitation 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 bulkprecipitation 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


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

• replacinganimperviousparking-lotsurfacewithaporoussurfaceongroundwaterquality,

• installingraingardensandporouspavementinaneighborhoodof3acresonthequantityandqualityofstormwaterrunoff,and

• installinga3,000-ft2(square-foot)greenroofonthequantityandqualityofrainfall-generatedroofrunoff.

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

• updatedwater-supplywithdrawalsforthetownsofReadingandWilmington(representingnewbaselineconditionsforallsimulations),

• potentialland-usechangesatbuildout(potentialfuturedevelopment),

• widespreadimplementationofretrofittingLIDtechniques,

• basin-scalewaterwithdrawalreductionsbasedonwater-conservationpilotprogramscon-ductedbytheMassachusettsDepartmentofConservationandRecreation,and

• land-usechangeandLIDapplicationsatalocalscale.

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.


IntroductionConventionalurbanandsuburbandevelopmentcanprofoundlyaffectthe

flowandqualityofstreamsandothernaturalwaterbodies.Urbandevelopmentincreasesthetotalareacoveredbyimpervioussurfaces(roofs,roads,side-walks,driveways,andparkinglots)andtypicallygenerateshigherratesoflocalstormwaterrunoff.Thegoaloftraditionalstormwatermanagementinurbanandsuburbanareasistominimizelocalfloodingofstreetsandotherimpervi-oussurfacesbyconveyingstormwaterrunoffasquicklyaspossibleawayfromdevelopedareas,usuallythroughnetworksofstormdrains,eithertolarge,offsitedetentionbasinsordirectlytotheneareststream,river,lake,orcoastalwaterbody.Whilereducingthehazardsassociatedwithlocalflooding,thetra-ditionalapproachoftenhasunintendedconsequences,includingthealterationofnaturalstreamflowandthedegradationofwaterqualityandaquatichabitatinreceivingwaterbodies.

Intheearly1990s,alandplanningandengineeringdesignapproachknownaslow-impact-development(LID)beganreceivingincreasedattentionasameanstoreducethegenerationofurbanrunoffatitssource.Incontrasttothetraditionaldevelopmentandstormwatermanagementapproach,LIDpracticesseektodevelopsitesinamannerthatmimicsthenaturalhydrologyoftheundevelopedsite(U.S.EnvironmentalProtectionAgency,2009).LIDdesignfeatures,suchasraingardens,permeablepavement,vegetated(orgreen)roofs,andnarrow,uncurbedstreets,wereintegratedintonewlydevelopedorexistingdevelopedareastominimizerunoffandmaximizetheinfiltrationofwaterintothesoiland(or)thetranspirationofwaterbyplants.

In1997,theIpswichRiverinnortheasternMassachusetts(fig.1)wasdesignated1ofthe20mostendangeredriversintheNationbytheenvironmentalorganizationAmericanRivers.Inrecentdecades,segmentsoftheupperriverhavegonedryforextendedperiodsduringthesummerwithseriousshort-andlong-termconsequencesforaquaticbiota(Armstrongandothers,2001).In2000,theU.S.GeologicalSurvey(USGS),incooperationwiththeMassachusettsDepartmentofEnvironmentalManagement(nowtheDepartmentofConservationandRecreation,MDCR),conductedamodelingstudytoevaluatethecausesofstreamflowdepletioninthebasin(ZarrielloandRies,2000).Thestudyconcludedthatgroundwaterwithdrawalsforpublicwatersupply,andsubsequentexportsofwatertousersoutsideofthebasin,werethelargestsinglefactorscausingflowdepletionintheriveranditstributaries.

In2005,USGSbeganastudyofselectedLIDpractices(vegetated“green”roof,raingardens,porouspavement,bioretentioncells)toevaluatetheireffectsongroundwaterqualityandrunoffvolumeandquality.ThisstudywasfundedthroughacooperativefundingagreementwiththeMDCR.Fund-ingforthestudywasalsocontributedbytheU.S.EnvironmentalProtectionAgency’sTargetedWatershedGrandProgramthroughafinancialassistanceagreementwithMDCR.Inaddition,thepreviouslydevelopedUSGSIpswichRiverBasinmodelwasusedtoquantifythepotentialrolesofLIDpracticesandwater-conservationstrategiesinrestoringnaturalstreamflowstourbanizedareas.Computersimulationswereconductedatboththebasinscale(155mi2)andatthescaleofindividualdevelopmentsites(100acres).ThepurposeofthiscircularistosummarizetheresultsofthesestudiesandtheirimplicationsforthewiderapplicationofLIDpracticesandwater-conservationstrategiesinurbanizingareasofthenortheasternUnitedStates.AmoredetaileddescriptionofthefieldstudiesandmodelingsimulationscanbefoundinthecompanionreportbyZimmermanandothers(2010).

Conventional urban and suburban development can profoundly affect the flow and quality of streams and

other natural water bodies.

Introduction 9

ATLANTICOCEAN

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

SWAMPSCOTTLYNN

SAUGUS

IPSWICH

WILMINGTON

Maple Mead o

w Br

ook

Ipswich River

NORTH COASTAL

SHAWSHEEN

MERRIMACK

BOSTON HARBOR

PARKER

IPSWICH

MIDDLESEXESSEX COUNTY

COUNTY

01101300

01101500

01102000

Ipswich River Basin

Major drainage basin boundaryand name

Active streamgage and number

Active streamgage with water-qualitydata 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 RHODEISLAND

NE

W Y

OR

K

VERMONT

MASSACHUSETTS

NEW HAMPSHIRE

IpswichRiverBasin

Town Hallstudy 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.


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 one-half 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

enhanceinfiltrationintothegroundwater,therebydecreasingrunoffvolumeanditsassociatedcontaminantloadenteringthestorm-drainsystemleadingdirectlyintoSilverLake.TheLIDfeaturesaccountedforlessthan2percentofthe3-acreneighborhoodareaorabout13percentofthepaved-roadarea.AlthoughthepercentageofporoussurfacecreatedorimprovedbytheLIDenhancementswasnotgreat,theenhancementswerenotdesignedjusttoreceiveandinfiltratedirectrainfall,buttoreceiverunofffromalargeportionoftheimpervioussurfacearea,potentiallyhavingagreatereffectonoverallrunoffthanmightbeexpectedonthebasisoftheLIDareaalone.

ThethirdLIDfeaturestudied,a3,000-ft2green(vegetated)roof,designedbyK.J.SavoieArchitecture,wasinstalledbyMagco,Inc.,aTectaAmericacompany,onWhippleAnnex,aformerindustrialbuildingrenovatedforseniorhousinginIpswich,MA,bytheNorthShoreHousingTrust.Thegreenroofwasdesignedtoretainasmuchas1in.ofrainfallandtoabsorbmaterialsfoundinprecipitation.Thevegetationonthegreenroofwasalsoexpectedtodiminishrunoffthroughevapotranspiration.Thegreenroofrunoffcharacteristicswerecomparedtothechemicalcharacteristicsofdirectprecipitationandtotherunoffcharacteristicsofa5,340-ft2sectionoftheconventional,rubber-membraneroofontheIpswichTownHall,locatedacrossasmallparkinglotfromtheWhippleAnnex.

WaterquantityandqualityweremonitoredtodeterminewhetheranychangesoccurredinassociationwiththeLIDapplications.Watersampleswerecollectedtodetermineconcentrationsofnutrients,metals,andtotalpetroleumhydrocarbonsatallofthestudysites.BacteriologicalsampleswerecollectedfromstormwaterrunoffinamanholeatSilverLakeAvenue.TheratesandvolumesofrunoffweremonitoredatSilverLakeAvenueinWilmingtonandatthegreenandrubber-membraneroofsinIpswich.

Vegetated green roof, designed by K.J. Savoie Architecture and installed by Magco, Inc., on the Whipple Annex,

Ipswich, MA.


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

AgeneralconcernwithLID-enhancedinfiltrationattheSilverLakebeachparkinglotwasthepossibilityofgroundwatercontaminationfrommaterialsontheparking-lot’ssurface.Theparking-lotretrofitprovidedusefulinformationaboutgroundwatercontaminanttransportthatcouldeventuallyaffectthegroundwater-fedlake.

Priortotheparking-lotretrofit,fourobservationwellstomonitorwater-tablealtitudesandthreemultilevel-port,samplingwells(MLSs)wereinstalledtocollectgroundwatersamplesintheparkinglot(fig.3).SampleswerecollectedfromJuly2005toJune2007,exceptduringthewinterandspringof2006whenthenewparkinglotwasbeinginstalled.Oneachsamplingdate,routinefieldmeasurementsoftemperature,dissolvedoxygenconcentration,specificconductance,andpHweremadefromeachsamplingportfromthetopofthewatertabletothebottomportoftheMLS.Water-qualitysamplesforchemicalanalysiswerecollectedfromMLSportsclosesttothewatertablebecausethiswasconsideredthemostlikelyplacewhereinfiltratingcontaminantscouldbedetected.

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

RAIN GARDEN

RAIN GARDEN

RAIN GARDENS ANDBIORETENTION CELLS

Bath House

BURNAP STREET

GROVE AVENUE

98

98

94

94

98

9898

100

98

96

96

DYH

96.5

97.1

98.5

98.198.1

GRAVEL

PAVERS

POROUS

ASPHALT

IMPERVIOUS

ASPHALT

PAVED PARKING

PAVED WALKWAY TO FISHING PIER

EXISTING

SWALE

SWALE

RAIN GARDEN

RAIN GARDEN

RAIN GARDENS ANDBIORETENTION CELLSRAIN GARDENS ANDBIORETENTION 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

STORMDRAIN

STORMDRAIN


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

ALTI

TUDE

, IN

FEE

T AB

OVE

NOR

TH A

MER

ICAN

VER

TICA

L DA

TUM

OF

1988

Post-LID

Pre-LID

minimum maximummedian

RANGE SCHEMATICFigure 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.

Ingeneral,nosubstantialchangesingroundwater-qualityconditionsweredetectedaftertheinstallationoftheporousparkinglotandotherLIDfeatures.Manyoftheconstituentconcentrationswereatorbelowdetectionlimitsbothbeforeandaftertheinstallation.ResultsfromsamplingwellMLS#1illustratetheminimalchangesingroundwaterquality.DissolvedoxygenconcentrationsincreasedaftertheLIDinstallation,suggestingamoredirectrechargefromoxygenatedprecipitationundertheLID-enhancedparkinglotthanundertheconventionalimperviousparkinglot,buttherangesofvaluesbeforeandafterinstallationoverlappedconsiderably(fig.4).TherangesoftotalnitrogenandtotalphosphorusconcentrationschangedlittlefollowinginstallationoftheLIDretrofits(figs.5,6).Thehighesttotalnitrogenconcentrationwasdetectedbeforeinstallation,andthehighesttotalphosphorusconcentrationwasdetectedafterward;nevertheless,theoveralldifferenceswerenotgreatforeitherconstituent.Similarly,therangeofconcentrationsofdissolvedcopper(fig.7)didnotappeartochangeafterinstallation.Amongalltheanalytesexamined,onlynickelconcentrationsdecreasedsignificantly(fig.8),suggestingthatthesourcewasremovedduringorshortlyaftertheparking-lotconstructionperiod.


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

TOTA

L PH

OSPH

ORUS

, IN

MIL

LIGR

AMS

PER

LITE

R

91.0

91.5

92.0

92.5

93.0

93.5

94.0

WATER-TABLE ALTITUDE, IN

FEET ABOVEN

ORTH AMERICAN

VERTICAL DATUM OF 1988

DATE

Total phosphorusWater-table altitude

2005 2006 2007

8/10/2

005

7/6/20

05

7/23/2

005

8/28/2

005

9/15/2

005

10/3/

2005

10/20

/2005

11/7/

2005

11/25

/2005

12/13

/2005

12/31

/2005

1/18/2

006

2/4/20

06

2/22/2

006

3/12/2

006

3/30/2

006

4/17/2

006

5/5/20

06

5/22/2

006

6/9/20

06

6/27/2

006

7/15/2

006

8/2/20

06

8/19/2

006

9/6/20

06

9/24/2

006

10/12

/2006

10/30

/2006

11/17

/2006

12/4/

2006

12/22

/2006

1/9/20

07

1/27/2

007

2/14/2

007

3/4/20

07

3/21/2

007

4/8/20

07

4/26/2

007

5/14/2

007

6/1/20

07

6/19/2

007

8/1/20

05

8/28/2

005

9/24/2

005

10/20

/2005

11/16

/2005

12/13

/2005

1/9/20

06

2/4/20

06

3/3/20

06

3/30/2

006

4/26/2

006

5/22/2

006

6/18/2

006

7/15/2

006

8/11/2

006

9/6/20

06

10/3/

2006

10/30

/2006

11/26

/2006

12/22

/2006

1/18/2

007

2/14/2

007

3/12/2

007

4/8/20

07

5/5/20

07

6/1/20

07

2005 2006

DATE

2007

0

0.5

1.0

1.5

2.0

TOTA

L N

ITRO

GEN

, IN

MIL

LIGR

AMS

PER

LITE

R

2.5

Construction period 91.0

91.5

92.0

92.5

93.0

93.5

94.0W

ATER-TABLE ALTITUDE, IN FEET ABOVE

NORTH AM

ERICAN VERTICAL DATUM

OF 1988Total nitrogenWater-table altitude


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 copperDissolved copper, below detection limitDetection limit (as indicated)Water-table altitude

Construction period

91.0

91.5

92.0

92.5

93.0

93.5

94.0W

ATER-TABLE ALTITUDE, IN FEET ABOVE

NORTH AM

ERICAN VERTICAL DATUM

OF 1988

0

0.5

1.0

1.5

DISS

OLVE

D CO

PPER

, IN

MIC

ROGR

AMS

PER

LITE

R

8/10/2

005

7/23/2

005

7/6/20

05

8/28/2

005

11/7/

2005

9/15/2

005

10/3/

2005

10/20

/2005

11/25

/2005

12/13

/2005

12/31

/2005

1/18/2

006

2/4/20

06

2/22/2

006

3/12/2

006

3/30/2

006

4/17/2

006

5/5/20

06

5/22/2

006

6/9/20

06

6/27/2

006

7/15/2

006

8/2/20

06

8/19/2

006

9/6/20

06

9/24/2

006

10/12

/2006

10/30

/2006

11/17

/2006

12/4/

2006

12/22

/2006

1/9/20

07

1/27/2

007

2/14/2

007

3/4/20

07

3/21/2

007

4/8/20

07

4/26/2

007

5/14/2

007

6/1/20

07

6/19/2

007

Dissolved nickelWater-table altitude

DATE

7/6/20

05

7/23/2

005

8/10/2

005

8/28/2

005

9/15/2

005

10/3/

2005

10/20

/2005

11/7/

2005

11/25

/2005

12/13

/2005

12/31

/2005

1/18/2

006

2/4/20

06

2/22/2

006

3/12/2

006

3/30/2

006

4/17/2

006

5/5/20

06

5/22/2

006

6/9/20

06

6/27/2

006

7/15/2

006

8/2/20

06

8/19/2

006

9/6/20

06

9/24/2

006

10/12

/2006

10/30

/2006

11/17

/2006

12/4/

2006

12/22

/2006

1/9/20

07

1/27/2

007

2/14/2

007

3/4/20

07

3/21/2

007

4/8/20

07

4/26/2

007

5/14/2

007

6/1/20

07

6/19/2

007

91.0

91.5

92.0

92.5

93.0

93.5

94.0

WATER-TABLE ALTITUDE, IN

FEET ABOVEN

ORTH AMERICAN

VERTICAL DATUM OF 1988

0

0.5

1.0

1.5

2.0

DISS

OLVE

D N

ICKE

L, IN

MIC

ROGR

AMS

PER

LITE

R

Construction period

2005 2006 2007


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

TwelveraingardensandseveralareasofporouspaversinstalledintheLID-retrofitneighborhoodnearSilverLake(fig.9)weredesignedtodecreaseanddelayrunoffintostormdrains,thusenhancinginfiltrationanddecreasingtheloadsofnutrients,metals,totalpetroleumhydrocarbons(TPH),andcoliformbacteriatransportedtoSilverLake.Loadistheamount,ormass,ofaconstituenttransportedbystormwater(orastream)duringaspecificperiodoftime;loadiscalculatedastheconstituentconcentrationmultipliedbyrunoffvolume.RunoffwassampledforE.coliandtotalcoliformbacteriatoevaluatetheeffectsofLIDenhancementsonbacterialloadstoSilverLake.

Underdrainsfromthetwoporous-pavedareasandoverflowdrainsfromraingardenswereconnectedtotheexistingstorm-drainsystem.CombinedstormwaterquantityandqualityfromSilver

LakeAvenueandDexterStreetweremonitoredinamanholeonSilverLakeAvenue.Themanholewasequippedtomonitorstormwaterflowsandtotriggeranautomatedwatersamplertocollectflow-proportionalsamples.Runoffvolumewasmonitoredatthislocationthroughoutthestudytoobtaindataonstormsofallsizes.Water-quality-sample-collectioneffortswerefocusedonstormsthatwerelikelytogenerateasufficientvolumeofrunoffforsampleanalysis.WhentheNationalWeatherServicepredictedstormsofsufficientmagnitudeforsampling,theautomatedsamplerwasprogrammedmanuallytocollectsamples,ifenoughrunoffwasmeasured.Samplesforchemical-water-qualityanalysisandforE. coli andtotalcoliformtestingwerecollectedfromAugusttoNovember2005,beforetheLIDenhancementswereinstalled,andfromAugust2006toNovember2007,thepost-LIDperiod.

Differencesinpre-andpost-LIDstormwater-runoffquantityandqualityweregenerallysmallandsubtle.Rainfall-runoff(RR)coefficientsbeforeandafterLIDinstallationwerenotstatisticallydifferent,evenforstormswithantecedentdryperiodsexceeding100hours.Sortingstormsintofoursizeclasses(fig.10)alsodidnotrevealstatisticallysignificantdifferencesbetweenpre-andpost-LIDRRs.However,medianrunoffcoefficientsforthesmallstorms(lessthanorequalto0.25in.ofrain)didshowanappreciabledifference:thepre-LIDmedianRRwasslightlygreaterthan0.1andgreaterthanthepost-LIDmedianRRofabout0.045(fig.11).Themedianpost-LIDRRforstormswith0.26in.ormoreprecipitationwasaboutthesameasthepre-LIDmedianRR.Thus,theestimatedeffectiveimperviousarea(EIA),thatis,theareathattransmitsstormwaterdirectlytoSilverLakewithnoopportunityforinfiltration,decreasedfromabout10percentofthedrainageareatoabout4.5percentasaresultoftheLIDretrofits.

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


EXPLANATION

Number of samples

Data value greater than 3.0 times theinterquartile range above the box

Data value 1.5 to 3.0 times the interquartilerange above the box

Largest data value within 1.5 times theinterquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times theinterquartile range below the box

Data value 1.5 to 3.0 times the interquartilerange below the box

24

x

x

o

0

0.1

0.2

0.3

0.4

0.5

RAIN

FALL

-RUN

OFF

COEF

FICI

ENT

PRE-LID POST-LID PRE-LID POST-LID PRE-LID POST-LID PRE-LID POST-LID

LESS THAN OR EQUAL TO0.25 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

13 66 24 6 8 4 9

Figure 10. 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.

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 OREQUAL 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

MED

IAN

RAI

NFA

LL-R

UNOF

F CO

EFFI

CIEN

T Pre-LIDPost-LID


AnotabledifferencebetweenrunoffconditionsbeforeandaftertheLID-retrofitintheSilverLakeneighborhoodwastheabsenceofanyrunofffrom7of21post-LIDstorms(33percent)with0.25in.orlessprecipitation(fig.12).Ofthesevenpre-LIDstormsofupto0.26in.ofprecipitation,allhadsomemeasurablerunoff.Nospecificfactor,suchasantecedentdryperiod,stormduration,orstormintensity,seemedtobeassociatedwiththeabsenceorpresenceofrunoff.TheseresultsindicatethatevenrelativelysmallreductionsinEIA,inanareaunderlainbyhighlypermeable,sandysoils,suchastheLID-retrofitneighborhood,canproducemeasurablereductionsinstormwaterrunoffforsmallstorms.Inthecaseofthisstudysite,thatthresholdwasabout0.25in.ofprecipitation.

Differencesbetweenestimatedpre-andpost-LIDstormwaterloadsofnutrients,metals,totalpetroleumhydrocarbons,andcoliformbacteriatoSilverLakewereinconsistent.Noneofthedifferencesbetweenpre-andpost-LIDmedianloadswerestatisticallysignificant.ThemedianloadsofnitrogenanalytesincreasedafterLIDimplementation,whereasmedianphosphorus-analyteloadsdecreased(fig.13).Amongthemetalanalytes,medianloadsofleadandzincdecreasedandmedianloadsofcadmium,chromium,copper,andnickelincreased(fig.14).Themedianoftotalcoliformbacterialoadsincreasedslightly,andthemedianofE.coliloadsdecreasedsomewhat.However,noneofthechangesfrompre-topost-LIDmedianloadsforanyofthechemicalandbiologicalconstituentswerestatisticallysignificant.

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

TOTA

L RU

NOF

F, IN

INCH

ES

Pre-LIDPost-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.


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 theinterquartile range above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times theinterquartile range below the box

Data value 1.5 to 3.0 times the interquartilerange below the box

5

x

CADMIUM CHROMIUM COPPER LEAD NICKEL ZINC

0.01

0.1

1

10

100

LOAD

, IN

MIL

LIGR

AMS

1,000

10,000

PRE POST PRE POSTPRE POST PRE POST PRE POST PRE POST

x

959595 958595

0.01

0.10

1.00

10.0

100

1,000

LOAD

, IN

GRA

MS

EXPLANATION

75th percentile

Median

25th percentile

10th percentile

Ammonia plus organic nitrogen

Ammonia nitrogen

Nitrate nitrogen

Totalnitrogen

Ortho-phosphorus

Dissolved phosphorus

Total phosphorus

PRE PREPOST POST PRE PRE PRE PRE PREPOST POST POST POST POST

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

90th percentile

Number of values9


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

AlthoughgreenroofshavebeenusedinEuropeforsometime,theyarerelativelynewinNorthAmericawheretheyarefindingapplicationformitigatingproblemsrelatedtostormwaterrunoff(Berghageandothers,2007).Greenroofsarereportedtosubstantiallyreducerunoffvolumeandattenuate,orslowdown,runoffwhencomparedtostandardroofs.Theplantsandgrowing

mediumontheroof,throughabsorptionandevapotranspiration,makerunoffreductionandattenuationpossible.Thegrowingmediummayalsoneutralizeacidicprecipitationthroughitsinherentbufferingcapacityandretainatmosphericpollutantsthataffectthequalityofrunoff.

ThegreenroofontheWhippleAnnexbuildinginIpswich(fig.15)consistsofawaterproofmembrane,aplasticdrainagelayer,filterfabric,alayerofgrowthmedium(crushedclayplusorganicmatter),andplants,includingTalinum calycinum(fameflower),Allium schoenoprasum(chive),andeightspeciesofSedum(adrought-tolerantsucculent).IpswichTownHallhasarubberizedmembraneroof(fig.16).Bothroofswereinstrumented(fig.17)sothatratesofstormwaterrunoffcouldbemonitoredandsamplesofstormwatercouldbecollectedinproportiontothevolumeofrunoffandanalyzedchemically.AcontinuousprecipitationgageandadatarecorderwereinstalledontheIpswichTownHallrooftomonitorrainfall.

Rainfallonandrunofffromthetworoofsweremonitoredforaperiodof18monthsin2007and2008.Stormsproducinglessthan0.04in.ofrainwerenotincludedintheanalysis,norweremostwinterstormsoranyrunoffresultingfromsnowmeltbecauseoftheuncertaintiescausedbyfreezing,thawing,andsnowfall.Inall,70stormsprovideddatasuitableforcomparisonofstormwa-terrunofffromthegreenandconventionalroofs.

Theabilityofavegetatedgreenrooftoreducethevolumeofrunofffromaparticularstormdependsontheamount,duration,andintensityofstormprecipitation,andontheamountofwaterpresentintheplantsandgrowingmediumatthestartofthestorm(referredtoas“antecedent”conditions).Waterretainedfromapreviousstormwillslowlyevaporatefromthegreenroofsurfaceortranspireintotheatmospherethroughtheplants(hencetheterm“evapotranspiration”).Asthelengthoftheantecedentdryperiodincreases,moreofthepreviouslyretainedwaterisremovedandtheroof’scapacitytostorenewrainfallincreases.Conversely,iftheantecedentdryperiodisbrief,lessstorageisavailable,likelyresultinginsomerunofffromtheroof.However,thetiming

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, rubberized-membrane roof on the Ipswich, MA, Town Hall.


ofthereleaseofrunofffromagreenroofmaybedifferentfromthatofaconventionalroof.

Thedifferencesintheresponsesofthegreenroofandrubberrooftoantecedentconditionsandstormsizeareshowningraphsofprecipitation(hyetographs)andrunoff(hydrographs)duringtwostormsinSeptember2007(figs.18,19).TheSeptember9,2007,storm(fig.18)followedanextendeddryperiodof22days,lastedabout17hours,andproduced0.61in.ofrainfallthatfellintwoburstsabout11hoursapart.Runofffromtheconventionalroofbeganalmostassoonastherainbegan(fig.18)andtotaled273ft3.Incontrast,runofffromthegreenrooftotaledonly13ft3.Onehundredpercentoftherainfallontheconventionalroofbecamerunoff,whereasmorethan85percentoftherainonthegreenroofwasretained;thatis,lessthan15percentoftherainthatfellonthegreenroofbecamerunoff.Therewasalsoanoticeabledelayintheinitialresponseofrunofffromthegreenroofrelativetothestartofprecipitation(fig.18).Runofffromthegreenroofdidnotincreaseappreciablyuntilabout1hourafterthestormbegan.

TheSeptember11,2007,storm(fig.19)followedanantecedentdryperiodofonly10hours,lastedabout7.5hours,andproduced1.27in.ofrainfall.IncontrasttotheSeptember9,2007storm,only2daysearlier,thisstormwasabouttwiceaslargeanddeliveredmoreintenserainfall,withmuchwetterantecedentconditions.Runofffromtheconventionalroofwassimilartothatobservedinthepreviousstorm,withadirectresponsetorainfallthatproducedtotalrunoffof569ft3.Allprecipitationontheconventionalroofbecamerunoff.Therunoffresponsefromthegreenroofwasappreciablydifferentfromtheprevious,September9,2007,storm.Inthefirsthourofthestorm,runofffromthegreenroofwasnegligible,butthenfollowedamoredirectresponsetorainfall,producingatotalof251ft3,about80percentofthetotalrainfallthatfellontheroof(20-percentretention).Thisresponseindicatesthatthegrowing-mediumlayerwasalreadynearlysaturatedfromthepreviousstorm,andthetimebetweenstormswasinsufficientforevapotranspirationtoallowmorethan20percentretentionofrainfallfromthisstorm.Thisstormalsodrawsattentiontothelimitsofthegreenroof’sdesignstoragecapacityof1.0in.ofprecipitationthatwasexceededby0.27in.

Totalstormprecipitationandthelengthoftheantecedentdryperioddeterminethe

Dow

nspo

ut

Dow

nspo

ut

Dow

nspo

ut

Downspoutjunction 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.

effectivenessofagreenroofinretainingwater.Thefinitecapacityofthegreenroofisafunctionofitsdesignlimitsandtheamountofwaterstillretainedfrompreviousstorms;thatamountiscontrolledbythelengthoftimesincethepreviousstormandtheoverallpotentialforevapotranspiration,whichvariesseasonally.Forexample,inwinter,whenplantsaredormant,evapotranspirationisminimal,andmuchprecipitationfallsintheformofsnowthatdoesnotimmediatelyresultinrunoff.

Abroadviewofthegreenroofperformancewasobtainedbyrelatingstormcharacteristicstorunoffvolumeforthe70stormsanalyzed.Thepercentageofprecipitationretainedinrelationtototalprecipitationvariedfromnearlyzeroto100percentforstormslessthan1in.,whichwasthegreenroof’sdesigncapacity.Ingeneral,thegreenroofretainedmorethan50percentoftheprecipitationfrom70percentofthestorms(49of70).Oftheremaining21storms,mosthadantecedentdryperiodsoflessthan70hours(fig.20).


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

9/9/07

18:30

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

9/9/07

18:30

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 RUN

OFF, IN CUBIC

FEET PER SECOND

0

0.05

0.10

0.15

0.20

0.25

PREC

IPIT

ATIO

N, I

N IN

CHES

0

20

40

60

80

100

PERC

ENTA

GE

OF

TOTA

L

Precipitation, in inches

Town Hall runoff from rubber roof

Whipple Annex runoff from green roof

Precipitation



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


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.

9/11/0

7 13:0

0

9/11/0

7 12:0

0

9/11/0

7 12:3

0

9/11/0

7 11:3

0

9/11/0

7 15:0

0

9/11/0

7 14:0

0

9/11/0

7 14:3

0

9/11/0

7 13:3

0

9/11/0

7 20:0

0

9/11/0

7 20:3

0

9/11/0

7 19:3

0

9/11/0

7 17:0

0

9/11/0

7 16:0

0

9/11/0

7 16:3

0

9/11/0

7 15:3

0

9/11/0

7 19:0

0

9/11/0

7 18:0

0

9/11/0

7 18:3

0

9/11/0

7 17:3

0

9/11/0

7 13:0

0

9/11/0

7 12:0

0

9/11/0

7 12:3

0

9/11/0

7 11:3

0

9/11/0

7 15:0

0

9/11/0

7 14:0

0

9/11/0

7 14:3

0

9/11/0

7 13:3

0

9/11/0

7 20:0

0

9/11/0

7 20:3

0

9/11/0

7 19:3

0

9/11/0

7 17:0

0

9/11/0

7 16:0

0

9/11/0

7 16:3

0

9/11/0

7 15:3

0

9/11/0

7 19:0

0

9/11/0

7 18:0

0

9/11/0

7 18:3

0

9/11/0

7 17:3

0

DATE AND TIME

0

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

PREC

IPIT

ATI

ON

, IN

INCH

ES

0

0.09

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

RAINFALL RUN

OFF, IN CUBIC

FEET PER SECOND

0

20

40

60

80

100

PERC

ENTA

GE

OF

TOTA

L

Precipitation, in inches



Precipitation



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


Adequatevolumesofcomposite,flow-proportionalrunoffsamplesandbulk(direct)precipitationsampleswereobtainedfromfivestormsandanalyzedfornutrients(nitrogenandphosphorus),metals(cadmium,chromium,copper,lead,nickel,andzinc),andtotalpetroleumhydrocarbons.(Foracompilationofalldata,refertothecompanionreport,Zimmermanandothers,2010.)Medianconcentrationsoftotalphosphorusandtotalnitrogenwerehigherinrunofffromthegreenroofthantheywereinrunofffromtheconventionalroof,andmedianconcentrationsoftheseconstituentsinbothsetsofrunoffsamplesweresignificantlyhigherthanthoseinbulkprecipitation(fig.21).Therelativelyhighnutrientconcentrationsinrunofffromthegreenroofwerelikelyduetonitrogenandphosphorusinitiallypresentinthegrowingmediumandtosubsequentfertilizationoftheroofduringestablishmentoftheplants.Leachingofnutrientsfromgreenroofshasbeenreportedelsewhere(Oberndorferandothers,2007;Dietz,2007).Withtheplanneddiscontinuationoffertilizationasthevegetationbecomesfullyestablished,theconcentrationsofnutrientsinthegreenroofrunoffshoulddiminish.Likelysourcesoftheconstituentsfoundinrunofffromtheconventionalroofincludedryfall(particlesdepositedonsurfacesfromdryair)betweenstormsandfecaldepositsleftbybirdsandinsects,inadditiontochemicalsdissolvedinprecipitation.

Constituentloads(thetotalmassofaconstituentinstormwaterrunoff)werecomputedfromconcentrationdataandrunoffvolumesanddividedbyroofsurfaceareatoaccountforthedifferencesinareabetweenthetworoofs.Estimatedconstituentloadsindicatethatthereductionin

0 100 200 300 400 500 600

PERIOD, IN HOURS

0

20

40

60

80

100

PERC

ENTA

GE O

F PR

ECIP

ITAT

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RET

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0.0 to less than 0.1




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

BULKPRECIPITATION

CONVENTIONALRUBBER ROOF

GREEN ROOF

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5 5 5

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, IN

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LIGR

AMS

PER

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R 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.


stormwatervolumefromthegreenroofeffectivelyreducedthenutrientloads,eventhoughtheconstituentconcentrationsfromgreenroofsamplesweresignificantlyhigherthantheconstituentconcentrationsfromtheconventionalroofsamples(fig.22).Forexample,themediantotalphosphorusconcentrationwasalmost100timesgreaterinthegreenroofrunoffthanintheconventionalroofrunoff,butthemediantotalphosphorusloadsinrunofffromthetworoofsdifferedbyonlyaboutamagnitudefactorof10.Thegreenroof’smediantotalnitrogenconcentrationwasslightlygreaterthanthatoftheconventionalroof,butthemedianloadwasslightlysmallerthanthemedianloadfromtheconventionalroof.Differencesbetweenmediantotalnitrogenloadsforthegreenroofandtheconventionalroofwerenotstatisticallysignificant.

Themediantotalcopperconcentrationmeasuredinrunofffromthegreenroof(414microgramsperliter(μg/L))wasabout10timesgreaterthanthatinrunofffromtheconventionalroof(41.2μg/L),andmorethan100timesgreaterthanthatinbulkprecipitation(2μg/L,fig.23A).Incontrast,themediantotalleadconcentrationinrunofffromthegreenroof(1.87μg/L)waslessthan1percentofthatfromtheconventionalroof(589μg/L)andwasnotstatisticallydifferentthanthemediantotalleadconcentrationinbulkprecipitation(fig.23B).Thesedifferencesinrunoffqualityareattributedtodifferencesinplumbingandroof-constructionmaterials.Thegutters,downspouts,machinery,vents,andcopperflashingonthegreenrooflikelyallaffectrunoffwaterquality.Castirondrainpipes

A Phosphorus

B Nitrogen

1

10

100

BULKPRECIPITATION


GREEN ROOF

5 5 5

TOTA

L N

ITRO

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BULKPRECIPITATION


GREEN ROOF

5 5 5

TOTA

L PH

OSPH

ORUS

LOA

D, IN

GRA

MS

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.


5 Number of values

EXPLANATION

90th percentile

75th percentile

Median

25th percentile

10th percentile

1

10

100

1,000

BULKPRECIPITATION


GREEN ROOF

5 5 5

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L LE

AD C

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IN M

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TOTA

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PPER

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, IN

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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

LeadB

5 Number of values

EXPLANATION

90th percentile

75th percentile

Median

25th percentile

10th percentile

1

10

100

1,000

10,000

100,000

BULKPRECIPITATION


GREEN ROOF

5 5 5

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L LE

AD L

OAD,

IN M

ILLI

GRAM

S

10

100

1,000

10,000

BULKPRECIPITATION


GREEN ROOF

5 5 5

TOTA

L CO

PPER

LOA

D, IN

MIL

LIGR

AMS

Simulation of the Effects of Land-Use and Water-Management Changes and Low-Impact Development on Streamflow 27

withleadsealslikelycontributetothechemicalmakeupoftheconventionalroofrunoff.Inasimilarmannertonitrogen,thereducedstormwatervolumefromthegreenroof,relativetotheconventionalroof,resultedincopperloadsthatwerenotsignificantlydifferentfromthoseestimatedfortheconventionalroof(fig.24A).Leadloadsfromtheconventionalroofweremuchgreaterthanthosefromthegreenroof(fig.24B).

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

Urbanizationproduceschangesinlanduseandstormwaterroutingthathavesignificanteffectsontheprocessesthatgeneratestreamflow.Lossofvegetation,increasedimperviousness,andwateruse(waterwithdrawals,wastewaterreturnflows,andwatertransfers)affecttheentireflowregime,fromfloodpeakstosummerlowflowsmaintainedbygroundwaterdischarge.Stormdrainagesystems,suchascatchbasinsandstormsewers,concentrateanddistributerunofffromimperviousareas.AcomputermodeloftheIpswichRiverBasin,calledtheIpswichRiverBasinHydrologicalSimulationProgram-FORTRAN(HSPF)precipitation-runoffmodel(ZarrielloandRies,2000),wasmodifiedtosimulatetheeffectsofchangesinland-useandLIDpracticesonstreamflow.Tobetterreflectcurrentconditions,recentchangesinpublicwater-supplywithdrawalsbythetownsofWilmingtonandReadingwereincorporatedintothemodelprimarilytobringthemodeluptodatewithcurrentwater-supplyconditions.Severalwater-withdrawalscenariosrepresentingwidespreadapplicationofwater-conservationstrategieswerethendevelopedinconsultationwithMDCR,U.S.EnvironmentalProtectionAgency,andtheproject’stechnicaladvisorycommittees.

Watershedcomputermodels,suchasHSPF,simplifythecomplexprocessesandphysicalcharacteristicsofadrainagebasin.Thissimplificationconsequentlylimitsthetypesofquestionsthatcanbeaddressedwiththemodel.Theassumptions,informationusedtodevelopandcalibratethemodel,spatialresolution(degreeofdetail)ofthemodel,andalternativemodelstructuresandparameters(characteristicssuchasprecipitationandhousingdensity)needtobeconsideredwhenevaluatingmodelresultsforuseinwater-resourcesmanagementdecisions.Forexample,specificLIDpractices,suchasinstallationofporouspavement,raingardens,bioretentionareas,andgreenroofs,couldnotberepresentedexplicitlyinthebasin-scaleIpswichRiverBasinHSPFmodel;instead,substitutesforthesepracticesweresimulatedbyvaryingtheamountofEIAovertheentirebasin.FormoredetailedelaborationoftheIpswichRiverBasinmodelassumptionsandlimitations,seeZarrielloandRies(2000).

Simulationswereconductedattwodifferentgeographicscalesforthisstudy(table1).Thefirstsetofsimulationsexaminedtheeffectsofland-usechange,LIDpractices,andwater-conservationeffortsatbasinandsubbasinscales.Thebasin-scalesimulationsgenerallygenerallyfocusedontheupperIpswichRiverBasin,anareaof44.5mi2,upstreamfromtheUSGSSouthMiddletonstreamgage((01101500)infig.25).However,modelsimulationsrepresentedhydrologicprocessesindrainageareasrangingfromabout0.5to125mi2insize.Tobetterrepresenthydrologic

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.


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

[LID,low-impactdevelopment]

Simulation scenario Area coveredBrief description of selected results of effects of

modifying original baseline model

Basin-scale simulations

Originalbaselinesimulation(ZarrielloandRies,2000)—average1989to1993withdrawals(alsoreferredtoasoriginalbaselinewithdrawals),1991landuse

Entirebasin(155mi2)

Originalbaselinemodel

Updatedbaselinesimulation—average1989to1993withdrawalswithupdatedwithdrawalsforReadingandWilmington(alsoreferredtoasupdatedbaselinewithdrawals),1991landuse

Entirebasin(155mi2)

IncreasesinlowandmediumflowsupstreamfromtheSouthMiddletonstreamgage.

Buildoutsimulation—updatedbaselinewithdrawals,potentiallanduseatbuildout

Entirebasin(155mi2)

Minoreffectsonstreamflow:0to20percentchangeatsubbasinscale.

SimulationofLIDretrofitsupstreamfromtheSouthMiddletonstreamgage(stationno.01101500)—updatedbaselinewithdrawals,1991landusewitheffectiveimperviousareareducedby50percent

Upperbasin(44.5mi2)

Minoreffectsonstreamflow:0to20percentchange

Water-conservationsimulation—updatedbaselinewithdrawalswithratesreducedby1to20percenttorepresentwater-conservationprograms,1991landuse

Entirebasin(155mi2)

With5percentreductioninwithdrawals,effectswereminor.With20percentreductioninwithdrawals,lowflowsincreasedslightly.

Local-scale simulations

Local-scalesimulations—nowaterwithdrawals,varyingcombinationsofdevelopedandundevelopedland-usetypesandamountsofeffectiveimperviousarea

Hypothetical,100-acreparcels

Conventional development:(A)Conversionofforestedlandusetocommercial:increased

median1-dayhighflow1,250percent;decreasedmedian1-daylowflow33percent;

(B)Conversionofforestedlandusetohigh-densityresidential:increasedhighormediumandlowflows,dependingonunderlyinggeology;

(C)Sensitivityofstreamflowtoeffectiveimperviousarea:ImplementingLIDincommercialandhigh-densityresidentialland-useareasreducedflowalterationmorethanimplementationinlow-densityresidentialland-useareas.

Cluster development:Clusteringtendedtoreducehighflows.


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

responsesatalocalscale,thesecondsetofsimulationsexaminedthepotentialeffectsofchangesinlanduse,amountofEIA,andincorporationofLIDpractices,suchasclusteringdevelopmentandpreservingopenspace,onstreamflowinhypothetical100-acre(0.16mi2)parcelsofland.Thelocal-scalesimulationswerebasedonhomogeneouslanduseswithdifferentmixesofdevelopmentdensityandEIA.Collectively,thesimulationsrepresentedawiderangeofspatialscalesandtimeperiodsaswellasarangeofhydrologicresponsestoland-usechange,water-managementactivities,andvariousLIDpractices.(Foracompletedescriptionofthemodelingstudy,seeZimmermanandothers,2010.)

ThebaselinesimulationintheoriginalIpswichRiverBasinmodelingstudywasusedtoevaluatetheeffectsofaverage1989–93groundwaterwithdrawalsonstreamflowoverlong-term(1961–95)climaticconditions(ZarrielloandRies,2000).ThisbaselinesimulationwasupdatedtoincorporaterecentchangesingroundwaterwithdrawalsforthetownsofReadingandWilmingtonthathadreliedonwithdrawalsfromwellsintheupperpartofthebasin.In2006,thetownofReadingbeganpurchasingwaterfromtheMassachusettsWaterResourcesAuthority(MWRA)tomeetitswaterneeds.Tosimulatecurrentwithdrawals,the10wellwithdrawalsbyReadingwellswerediscontinued—adecreaseof2.2Mgal/dfromreach8(fig.25).InanticipationofthetownofWilmingtonpurchasingwaterfromtheMWRAin2008,dailysummerwithdrawalratesfromfouractivewellsweredecreasedbyatotalof1Mgal/dfromreaches5,12,and13(fig.25)intheupdatedbaselinesimulation.

TotalannualwithdrawalsupstreamfromtheSouthMiddletonstreamgageaveraged6.7Mgal/dintheoriginalbaselinesimulation(ZarrielloandRies,2000)anddroppedto3.5Mgal/dintheupdatedbaselinesimulationforthepresentstudy.

HAMILTON

DANVERS

PEABODY

LYNNFIELD

WOBURNBURLINGTON

TEWKSBURY

WILMINGTON

ANDOVER

NORTHANDOVER

BOXFORD

MIDDLETON

NORTH READING

READING

TOPSFIELD

ROWLEY

IPSWICH

WENHAM

BEVERLY

SALEM

LYNN

ESSEX

BILL

ERIC

A

MANCHESTER

GLOU

CEST

ER

WAKEFIELD

GEORGETOWN

MARB

LEHEA

D

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

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6 KILOMETERS

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SHAWSHEEN

MERRIMACK

BOSTON HARBOR

PARKER

IPSWICH

PutnamvilleReservoir

SwanPond

EmersonBrookReservoir

WinonaPond

SuntaugLake

WenhamLake

LonghamReservoir

MiddletonPond

Lowell Pond

Cleveland Brook

Salem-Beverly Canal

Pye Brook

Howlett Brook

Nichols Brook

Fish Brook

Lubbe rs Brook

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

Mea

dow

Broo

k

Mill

Bro

ok

Ipswich

93

1

85

38

32

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6

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7

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61

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2835

16

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55

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1824

60

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45

57

25

21

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44

63

22

17

19

43

0110200001102000

0110150001101500

Base from U.S. Geological Survey digital data, 1:25,000, 1991,Lambert conformal conic projection, North American Datum of 1983


ThedecreaseinwithdrawalledtosubstantialsimulatedincreasesinlowandmedianflowsintheIpswichRiverattheSouthMiddletonstreamgage(table2).

Effects of Land Development on Streamflow in the Ipswich River Basin

AstatewidebuildoutanalysiswasconductedbytheMassachusettsExecutiveOfficeofEnergyandEnvironmentalAffairs(EOEEA)in2001(MassachusettsExecutiveOfficeofEnergyandEnvironmentalAffairs,2008).Thisanalysisprovidedinformationtosimulatetheeffectsofpotentialfuturedevelopment,referredtoasbuildout,onstreamflowintheIpswichRiverBasin.Abuildoutanalysisdetermineshowacommunitymightdevelopifallremainingdevelopableareaswerefullybuiltoutinaccordancewithcurrentlocalzoningandotherdevelopmentconstraints.Landthatisnotconsidereddevelopableincludespermanentlyprotectedopenspacesuchasconservationlandandriparianbuffers,openwater,andlandthatisalreadydeveloped.Forthisstudy,forestedandnon-forestedwetlandsalsoareconsideredunavailablefordevelopment.ThedrainageareaupstreamfromtheSouthMiddletonstreamgageisrelativelyurbanandcontainslessdevelopablelandthanotherpartsofthebasin.

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

[Percentchangeexpressedasareaatbuildoutminusareain1991overareain1991.]

Land-use description1991 land use Buildout land use

Percent changeArea

(acres)Percentage of

total areaArea

(acres)Percentage of

total area

Forest 36,854.0 38.6 23,113.6 24.2 -37.3Open 6,675.2 7.0 3,407.0 3.6 -49.0Openwater 2,384.4 2.5 2,384.4 2.5 0.0Nonforestedwetland 6,750.1 7.1 6,750.1 7.1 0.0Low-densityresidential 14,471.3 15.2 30,005.4 31.4 107.3High-densityresidential 11,486.0 12.0 11,696.3 12.2 1.8Commercial-industrial-transportation 3,583.5 3.8 4,847.7 5.1 35.3Forestedwetland 13,284.0 13.9 13,284.0 13.9 0.0Total: 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


Todevelopnewland-usedatatosimulatefutureconditions,thezoningcodesinthedevelopableareaswererelatedtotheland-usecategoriesusedformodeldevelopment.Using1991landuseasabaseline,thebuildoutanalysisindicatedthatabout17percentoftheentireIpswichRiverBasinwasdevelopable.Themajorchangesinthebasinwerethedeclineinfor-estedareasfrom39to24percent,andtheincreaseinlow-densityresiden-tialdevelopment(lotsizesgreaterthan0.5acre)from15to31percent.Otherdevelopedland-usecategories,includinghigh-densityresidential(lotsizeslessthanorequalto0.5acre)andcommercial,increasedslightlyatbuildout(table3).

Toisolatetheeffectsofland-usechangeonstreamflow,theupdatedbaselinesimulation,reflecting1991landuse,wasmodifiedtoaccountforland-usechangeatbuildout.Land-usechangeassociatedwithbuildoutgenerallyhadminoreffects(0to20percentchange)onstreamflowatthesubbasinscale becausemostofthedevelopablelandinthebasinwasfor-estedoropenandzonedforlow-densityresidentialdevelopment.TheEIAassociatedwithlow-densityresidentialdevelopmentwasrelativelysmall(2.5percentinthecalibratedIpswichRiverBasinHSPFmodel);therefore,increasesinthistypeoflandusewerenotexpectedtoappreciablychangetherunoffresponsetoprecipitationbecausetherunoffcharacteristicsaresimilarforforestandlow-density-residentiallanduseforagiventypeofunderlyingsurficialgeology.Themajordifferencebetweensimulatedforestsandlow-densityresidentialdevelopmentwastheamountofwaterlosttoevapotranspiration.Inhumidclimates,lowwateryieldsinforestedwatershedshavebeenattributedtoincreasedcanopy-interceptedevapora-tionandmoreintensiveroot-zonetranspirationduringthegrowingseason(Bent,2001;Calder,1993;Robinsonandothers,1991).Theseprocesseslowerthesoil-moisturecontent,reducerecharge,andlowerwatertables,thusreducingthebase-flow(groundwater)contributiontostreamflow.Consequently,althoughlow-densityresidentialareasreceivedslightlylessinfiltrationperunitareathanforestedareasbecauseofEIA,thecompara-tivelysmallevapotranspirationlossesfromlow-densityresidentialareasarebelievedtohaveresultedinslightincreasesinsummerlowflows,relativetoforestedareaswiththesamesurficialgeology.

Bycomparison,conversionofforesttocommerciallanduseinthisanalysishadapronouncedeffectonsimulatedstreamflow,producingincreasesinpeakflows,becausetherelativelylargeincreasesinEIAincreasedsurfacerunoff.Althoughthiseffectofurbanizationonfloodpeakswasrelativelyclear,theeffectofincreasingurbanizationonlowflowsshowedconflictingresults,asalsonotedbyBrandesandothers(2005)andRoseandPeters(2001).Thelackofcleareffectsmayresultbecauselowflowsaredeterminedbythenetresponsetocomplexinteractionsamongclimate,landuse,wateruse,andwaterinfrastructure(Claessensandothers,2006;Lerner,2002;DowandDeWalle,2000).

Overall,thebuildoutsimulationassumingconventionalstylesofdevelopmentdemonstratedonlyminoreffectsonstreamflowinthebasin.Therefore,buildoutincorporatingLIDpractices,whichwouldonlyshowsubtleeffectsofdevelopment,wasnotevaluated.

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).


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

ThedrainageareaoftheupperIpswichRiverBasin,upstreamfromtheSouthMiddletonstreamgage(fig.25),isrelativelyurbanandhaslessdevelopablelandthantherestofthebasin.Therefore,thissubbasinwasusedtoevaluatetheeffectsofretrofittingexistingdevelopmentwithLIDfeaturestoincreasestormwaterrechargeanddecreasesurfacerunoff.

IntheLID-retrofitsimulation,EIAupstreamfromtheSouthMiddletonstreamgagewasreducedby50percentasasurrogatefortheimplementationofLIDpracticesthatdecreaseEIA(forexample,porouspavement,greenroofs,andre-directionofsurfacerunofffromEIAtonaturalorconstructedrechargeareas).Thesimulated50-percentreductioninEIAwasconsideredasubstantial,butreasonable,maximumamountofEIAreductionthatcouldbeachievedthroughthewidespreadimplementationofvariousLIDpractices.The50-percentreductionofEIAupstreamfromtheSouthMiddletonstreamgagegenerallyhadmodesteffectsonsubbasinstreamflows(percentdifferencesoflessthan20percent).(Specificdetailsofthesedifferencesmaybefoundinthecompanionreport,Zimmermanandothers,2010).EveninthisrelativelyurbanpartoftheIpswichRiverBasin,theheterogeneousmixoflandusesresultedinchangesinthetotalEIAthatweresmallpercentagesofthetotalareasofthe19subbasins.Thus,theresultsmayindicatethatwidespreadLIDpracticesmaynotsubstantiallyaffectflowsinlargeriversandtributarystreamsthatarecharacterizedbyheterogeneouslanduseandanEIAlowerthan50percent.Ontheotherhand,LIDpracticesthatreduceEIAonalocalscalemayhavesubstantialeffectsonflowsbecausetheEIAasapercentageofthedrainageareamaybelargeandalargedecreaseinEIAmaybeattainable.Thisconceptisexaminedfurtherinthesection,“SimulationsofLand-UseChangeattheLocalScale.”

Simulation of Water Conservation Effects

Datafromfourwater-conservationpilotprojectsconductedbyMDCRwereusedtosimulatetheeffectsofwidespreadapplicationofconservationpracticesonstreamflow.Pilotprojectsincluded:

• installationofweather-sensitive“smart”irrigationcontrollerswitchesonautomatedsprinklersystemsatmunicipalathleticfields;

• applicationofsoilamendmentsatamunicipalathleticfieldtoimprovesoilmoistureandnutrientretention;

• installationof800-gallonrainwaterharvestingsystemsforthecol-lectionandreuseofrainwaterforirrigation;and

• implementationoftwoconcurrentmunicipalprogramsofferinghomeownersfreeindoorwater-useaudits,water-reducingretrofitkits,andrebatesforlow-flowtoiletsandwashingmachines.

Featuresinthefirstthreeprojectsweredesignedtoreduceirrigationdemandsthataffectsummerwithdrawalsinthebasin,andthefourthwasdesignedtoreduceindoorwaterusethataffectswithdrawalsyearround.Basedonper-unitsavingscalculatedbyMDCRfromthepilotprojectsandfromspecificinformationabouteachtown,forexample,acresofirrigated

LID features to increase stormwater recharge and decrease surface runoff.


athleticfieldsandnumberofhouseholds,watersupplierswereassignedhypothetical,potentiallyachievable,town-widewater-withdrawalreduc-tions.(Foradetaileddescriptionoftheassumptionsusedforthesesimula-tions,seeZimmermanandothers,2010.)

Reductionsinwaterusewereexpectedtohavetheirgreatesteffectsonlowflowsinsubbasinsinwhichstreamflowdepletionwashigh,relativetotherateofstreamflowintheabsenceofwithdrawals(Barbaro,2007).Hypotheticalwater-usereductionsfromthepilotprojectsinthebasinrangedfrom1.4percent(Salem-Beverlywatersupply)to8.5percent(Hamilton)ofaverage1989–93withdrawals.Withdrawalreductionsof5percenthadlittleeffectonsimulatedlowflows,anda20-percentwithdrawalreductionresultedinslightlyhigherlowflows.Ingeneral,however,theconservationscenariosexamineddidnotindicateappreciablechangesfromcurrent(1989–93)simulations.Thisresultisconsistentwithpreviousreduced-withdrawalsimulationsfortheIpswichRiverupstreamfromtheSouthMiddletonstreamgagethatwereconductedwiththeoriginalbaselinewithdrawals(Zarriello,2002).Theeffectsofwithdrawalreductionsonsmallstreamswouldlikelybemorepronounced.

Simulations of Land-Use Change at the Local Scale

Local-scalesimulationswereconductedtoevaluatethehydrologiceffectsofland-usechange,developmentpatterns,andsurficialgeologyon100-acreparcelsofland.Theresultsofthesesimulationsaredepictedwithflow-durationcurves(fig.26).(Seeboxforexplanationofflow-durationcurves.)Thesesimulationsoftheeffectsofland-usechangeprovidedvaluableinformationforassessingtheconditionsunderwhichLIDpracticesmayhavethegreatestbenefits.Specifically,simulationswereconductedtoevaluatetheeffectonstreamflowof

• uniformland-usechangeforconventionaldevelopment(thatis,uniformlotsizes);

• clusterdevelopment;

• changesintheamountofEIAthatrepresentLIDapplications;and

• surficialgeology.(SeeZimmermanandothers(2010)foradditionalsimulationdetails.)

Convertinga100-acreparcelfromforestedlandtodevelopedlandincreasedsimulatedmedian1-dayhighflows(medianof1-dayannualhighflowsfor1961–95simulation)byasmuchas1,250percent,dependingontheunderlyingsurficialgeologyandthetypeofdevelopment.Conversionofforestedlandoverlyingsandandgraveldepositstocommercialdevelopmentproducedthemaximumincreaseinthesimulatedmedian1-dayhighflow,from0.49to6.60ft3/s(1,250percent.)Convertingforesttolow-densityorhigh-densityresidentialdevelopmentresultedinmodestincreasesinthemedian1-dayhighflowandalsoincreasedsimulatedmediumandlowflows(fig.26).Mediumandlowflowsincreasedbecausebothresidentialdensitiesweresimulatedtohavelowerevapotranspirationlossesthanforesteddrainageareas,producingmoresubsurfacedischargetostreams.Simulationsofrunofffroma100-acreparcelwithvariableamountsofEIAindicatethatLIDprovidedthegreatestbenefitin

LID practices that reduce EIA on a local scale may have substantial effects

on flows.


commercialandhigh-densityresidentialland-useparcelsbecauseoftheirhighproportionofEIArelativetootherlanduses.

Simulationsofclusterdevelopment,inwhichapercentageoftheparcelremainsforested,orasopenspace,indicatedthatthispracticereducedhighflowsandhadvariableeffectsonlowflowswhencomparedtoconventionaldevelopmentwiththesamenumberofhouses.Forlow-densityclusterdevelopments,leavingalargepartofthelandforestedresultedinslightlylowerlowflowsthanforaconventionallow-densitydevelopmentwithuniformlotsizesbecauseagreaterpercentageofdeep-rootedvegetatedarearemainedundisturbed.Flowsfromaclusterdevelopmentmorecloselyapproximatedflowsfromforestedareasthanflowsfromconventionallow-densitydevelopmentonthe100-acreparcel.However,intheabsenceofLIDenhancements,flowsfromtheclusterdevelopmentitselfwouldcloselyapproximateahigh-densitydevelopment.SimulatedstreamflowdidnotvarysubstantiallywithvariationsintheamountofEIAintheclusterdevelopment,becausethetotalEIAovertheparcelwasarelativelylowpercentageofthearea.

PERCENTAGE OF TIMEFLOW 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

STRE

AMFL

OW, I

N C

UBIC

FEE

T PE

R SE

CON

DST

REAM

FLOW

, IN

CUB

IC F

EET

PER

SECO

ND

10

1

0.1

0.01

10

1

0.1

0.01

10

1

0.1

0.01

2.5% EIA5% EIA

1.25% EIA

14% EIA7% EIA

28% EIA

63% EIA47% EIA31.5% EIA

Commercial

High-density residentialoverlying sand and gravel

Low-density residentialoverlying 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.


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

STRE

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UBIC

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D


FLOW-DURATION CURVE


Summary and ConclusionsTheU.S.GeologicalSurvey,incooperationwiththeMassachusettsDepartmentofConservation

andRecreationandtheU.S.EnvironmentalProtectionAgency,examinedtheeffectsofimplementingselectedlow-impact-development(LID)techniquesonwaterquantityandqualityinseveralfieldstudiesandacomputer-modelingstudyintheIpswichRiverBasin,inMassachusetts,whichisadverselyaffectedbylowstreamflowsinthesummerseason.Thefieldstudiesmonitored

• possiblechangesingroundwaterqualitycausedbyreplacingaconventionalimperviousparking-lotsurfacewithaporousasphaltandpaversurface,

• effectsonrunoffquantityandqualitybydirectingrunofffromthestreetanddrivewaysintoacombinationofraingardensandporousparkingsurfacesina3-acreneighborhood,and

• differencesinrunoffquantityandqualityfromaconventionalrubberized-membraneroofandaneighboringvegetated“green”roof.

ThestudyalsoexaminedthepotentialeffectsofLIDpracticesandwater-withdrawalreductionsbymodifyingapreviouslydevelopedprecipitation-runoffmodelofthebasin.

Enhancedinfiltration,particularlyfromparkinglots,hasthepotentialtotransportcontaminantstothewatertable.ThefirstLIDfieldsite,aparkinglotforSilverLakeBeachinWilmington,MA,indicatednodetrimentaleffectsongroundwaterqualityaftertheparkinglotwasretrofittedwithporousasphalt,porouspavers,raingardens,andbioretentioncells.Atthesecondfieldsite,inaresidentialneighborhoodadjacenttoSilverLake,installationofLIDfeatures(raingardensandporouspavers)hadthemostpronouncedeffectonrunofffromsmallstorms(0.25in.orlessofprecipitation);themedianrunofffromsuchstormswasreducedbyabout50percent,consistentwiththedecreaseineffectiveimperviousareafrom10to4.5percentafterLIDimplementation.Inaddition,theseLIDfeaturesdecreasedthenumberofsmallstormsproducingmeasurablerunoff.Atthethirdfieldsite,therunofffromagreenroofretainedatleast50percentoftherainfallfromabout70percentofthestorms,relativetoaconventionalrubber-membraneroofthatdoesnotreducerunoffatall.Thelengthoftheantecedentdryperiodandstormsizewerethecontrollingfactorsaffectingthegreenroof’scapacityforwaterretentionandrunoffattenuation;long,dryantecedentperiodsincreasedavailablestorageforthegreenroof,thusattenuatingstormrunoff.Therelativelyhighconcentrationsofnutrientsingreenroofrunoff,affectedbyfertilizerapplicationduringestablishmentofthevegetation,

Summary and Conclusions 37

weresomewhatoffsetbythedecreaseinrunoffvolume.Extendingthestudydurationwoulddemonstratewhethernutrientloadswoulddecreaseasthevegetationfurthermaturedandfertilizerswerenolongerapplied.Contaminants,suchasmetals,intheroofrunoffwereattributedtospecificroofandgutterstructures.

ThemodelingstudiesusedthecalibratedHydrologicSimulationProgram-FORTRANIpswichRiverBasinprecipitation-runoffmodeltosimulatetheeffectsofwater-managementscenariosandLIDpracticesonstreamflowatscalesrangingfromthelocalscale(100acres,or0.16mi2)tothesubbasinandbasinscale(0.5to125mi2).SpecificLIDpracticeswerenotsimulated;rather,land-usechangeandassociatedchangesineffectiveimperviousareawereusedassurrogatesforLIDpractices.

Simulationsindicatedthat,atthebasinandsubbasinscale,thepotentialeffectiveimperviousareareductionfromtheapplicationofLIDpracticeswasgenerallytoolowtoappreciablyaffectstreamflow.Incontrast,thelocal-scalesimulationsofa100-acreparcelindicatedthat,wherethepercentageofurbanlanduseandassociatedeffectiveimperviousareawasrelativelyhigh,developmentpatternsandLIDpracticescouldhavesubstantialeffectsonstreamflow.

InLID-retrofitsimulations,reducingeffectiveimperviousareaby50percentminimallyaffectedstreamflowinmostsubbasinsanalyzed,becausetheeffectiveimperviousareainthesubbasinwasarelativelysmallpercentageoftheoverallarea.Indrainagebasinsthatarecharacterizedbyheterogeneouslanduse,widespreaduseofLIDpracticesmaynothaveapronouncedeffectonstreamflow.Ontheotherhand,LIDpracticesthatreduceeffectiveimperviousareaonalocalscalemayaffectstreamflowbecauseeffectiveimperviousarea,asapercentageofthedrainagearea,maybelarge,andarelativelylargepercentagedecreaseineffectiveimperviousareamaybeattainable.

Datafromwater-conservationpilotprojectswerescaleduptothetownlevelandusedtosimulatetheeffectsofwidespreadapplicationoftheseprogramsonstreamflow.Forcommunitieswithwaterwithdrawalsfromthebasin,theeffectsonsimulatedlowflowsinmostoftheriversandstreamsinthebasinwereminor.

Insummary,thefieldstudiesandmodelsimulationsdemonstratethatimplementationofLIDpracticescandemonstrablyaffectstormwaterrunoffquantityandquality;however,theireffectsmaybedifficulttodiscernwhenthechangesineffective-imperviousarea,asapercentageoftotalbasinarea,aresmall.ThebenefitsofLIDpracticesaregreatestwhenthepercentageofeffectiveimperviousareaislargeandtheLIDenhancementscansubstantiallyredirectstormrunoffawayfromconveyancesleadingtostreamsorlakes.


References Cited

Armstrong,D.S.,Richards,T.A.,andParker,G.W.,2001,Assessmentofhabitat,fishcommunities,andstreamflowrequirementsforhabitatprotection,IpswichRiver,Massachusetts,1998–99:U.S.GeologicalSurveyWater-ResourcesInvestigationsReport01–4161,72p.

Barbaro,J.R.,2007,Simulationoftheeffectsofwaterwithdrawals,wastewater-returnflows,andland-usechangeonstreamflowintheBlackstoneRiverBasin,MassachusettsandRhodeIsland:U.S.GeologicalSurveyScientificInvestigationsReport2007–5183,93p.

Bent,G.C.,2001,Effectsofforest-managementactivitiesonrunoffcomponentsandgroundwaterrechargetoQuabbinReservoir,centralMassachusetts:ForestEcologyandManagement,v.143,p.115–129.

Berghage,R.,Jarrett,A.,Beattie,D.,Kelley,K.,Husain,S.,Farzaneh,N.,Cameron,R.,andHunt,W.,2007,Transpirationalwaterlossesfromgreenroofsandgreenroofmediacapacityforneutralizingacidrain:StateCollege,PA,PennsylvaniaStateUniversity,variouslypaged.

Brandes,D.,Cavallo,G.J.,andNilson,M.L.,2005,BaseflowtrendsinurbanizingwatershedsoftheDelawareRiverBasin:JournaloftheAmericanWaterResourcesAssociation,v.41,no.6,p.1377–1391.

Calder,I.R.,1993,Hydrologiceffectsofland-usechange,inMaidment,D.R.,ed.,HandbookofHydrology:NewYork,McGraw-Hill,Inc.,p.13.1–13.50.

Claessens,L.,Hopkinson,C.,Rastetter,E.,andVallino,J.,2006,Effectofhistoricalchangesinlanduseandclimateonthewaterbudgetofanurbanizingwatershed:WaterResourcesResearch,v.42,WO3426,doi:10.1029/2005WR004131.

Dietz,M.E.,2007,Lowimpactdevelopmentpractices—Areviewofcurrentresearchandrecommendationsforfuturedirections:Water,Air,andSoilPollution,v.186,no.1–4,p.351–63.

References Cited 39

Dow,C.L.,andDeWalle,D.R.,2000,TrendsinevaporationandBowenratioonurbanizingwatershedsineasternUnitedStates:WaterResourcesResearch,v.36,no.7,p.1835–1843.

Lerner,D.N.,2002,Identifyingandquantifyingurbanrecharge—Areview:HydrogeologyJournal,v.10,p.143–152.

MassachusettsExecutiveOfficeofEnergyandEnvironmentalAffairs,2008,Buildoutmapsandanalyses:accessedApril7,2008,athttp://commpres.env.state.ma.us/content/buildout.asp.

Oberndorfer,E.,Lundholn,J.,Bass,B.,Coffman,R.R.,Doshi,H.,Dunnett,N.,Gaffin,S.,Köhler,M.,Liu,K.K.Y.,andRowe,B.,2007,Greenroofsasurbanecosystems—Ecologicalstructures,functions,andservices:Bioscience,v.57,no.10,p.823–33.

Robinson,M.,Gannon,B.,andSchuch,M.,1991,Acomparisonofthehydrologyofmoorlandundernaturalconditions,agriculturaluse,andforestry:HydrologicalSciences,v.36,p.565–577.

Rose,S.,andPeters,N.E.,2001,EffectsofurbanizationonstreamflowintheAtlantaarea(Georgia,USA)—Acomparativehydrologicalapproach:HydrologicalProcesses,v.15,p.1441–1457.

U.S.EnvironmentalProtectionAgency,2009,Lowimpactdevelopment(LID),accessedAugust27,2009,athttp://www/epa.gov/nps/lid.

Zarriello,P.J.,2002,Simulationofreservoirstorageandfirmyieldsofthreesurface-watersupplies:U.S.GeologicalSurveyWater-ResourcesInvestigationsReport02–4278,50p.

Zarriello,P.J.,andRies,K.G.,III,2000,Aprecipitation-runoffmodelforanalysisoftheeffectsofwaterwithdrawalsonstreamflow,IpswichRiverBasin,Massachusetts:U.S.GeologicalSurveyWater-ResourcesInvestigationsReport00–4029,99p.,availableonlineathttp://pubs.usgs.gov/wri/wri004029/.

Zimmerman,M.J.,Barbaro,J.R.,Sorenson,J.R.,andWaldron,M.C.,2010,Effectsoflow-impact-developmentonwaterqualityandquantityintheIpswichRiverBasin,Massachusetts—Fieldandmodelingstudies:U.S.GeologicalSurveyScientificInvestigationsReport2010–5007,113p.


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 Water-quality 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:

DirectorU.S. Geological SurveyMassachusetts-Rhode Island Water Science Center10 Bearfoot RoadNorthborough, MA [email protected]

or visit our Web site at:http://ma.water.usgs.gov

Zimm

erman and others—

Effects of Low-Im

pact-Developm

ent Practices on Streamflow

and Runoff in the Ipswich River B

asin, Massachusetts—

Circular 1361

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