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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
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Effects of Low-Impact-Development (LID) Practices on Streamflow, Runoff Quantity, and Runoff Quality in the Ipswich River Basin, Massachusetts: A Summary of Field and Modeling Studies
By Marc J. Zimmerman, Marcus C. Waldron, Jeffrey R. Barbaro, and Jason R. Sorenson
Prepared in cooperation with the Massachusetts Department of Conservation and Recreation and the U.S. Environmental Protection Agency
Circular 1361
U.S. Department of the InteriorU.S. Geological Survey
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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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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
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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
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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
Effects of Low-Impact-Development (LID) Practices on Streamflow, Runoff Quantity, and Runoff Quality in the Ipswich River Basin, Massachusetts: A Summary of Field and Modeling Studies
By Marc J. Zimmerman, Marcus C. Waldron, Jeffrey R. Barbaro, and Jason R. Sorenson
Abstract
Low-impact-development (LID) approaches are intended to create, retain, or restore natural hydrologic and water-quality conditions that may be affected by human alterations. Wide-scale implementation of LID techniques may offer the possibility of improving conditions in river basins, such as the Ipswich River Basin in Massachusetts, that have run dry during the summer because of groundwater withdrawals and drought. From 2005 to 2008, the U.S. Geological Survey, in a cooperative funding agreement with the Massachusetts Department of Conservation and Recreation, monitored small-scale installations of LID enhancements designed to diminish the effects of storm runoff on the quantity and quality of surface water and groundwater. Funding for the studies also was contributed by the U.S. Environmental Protection Agency’s Targeted Watersheds Grant Program through a financial assistance agreement with Massachusetts Department of Conservation and Recreation. The monitoring studies examined the effects of
• 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.
8 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts
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.
10 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts
Field Studies of the Effects of LID Practices
From 2005 through 2008, widely used LID practices were evaluated to determine their effects on hydrology and water chemistry at three sites in the Ipswich River Basin in northeastern Massachusetts (fig. 1). Two of the sites were in Wilmington, in the upper part of the basin, and the third was in Ipswich, not far from the mouth of the river.
At the town beach at Silver Lake, in Wilmington, approximately 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.
12 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts
Changes in Groundwater Quality Following the Retrofit of a Conventional Parking Lot with LID Features
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
Field Studies of the Effects of LID Practices 13
0 2.0 4.0 6.0 8.0 10.0
DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER
88.5
89.0
89.5
90.0
90.5
91.0
91.5
92.0
92.5
93.0
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.
14 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts
Figure 6. Total phosphorus concentrations in samples from multilevel sampler #1 (MLS#1) before and after installation of porous parking lot at Silver Lake beach, Wilmington, MA.
Figure 5. Total nitrogen concentrations in samples from multilevel sampler #1 (MLS#1) before and after installation of porous parking lot at Silver Lake beach, Wilmington, MA.
Construction period
0
0.02
0.04
0.06
0.08
0.10
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
Field Studies of the Effects of LID Practices 15
Figure 7. Dissolved copper concentrations in samples from multilevel sampler #1 (MLS#1) before and after installation of porous parking lot at Silver Lake beach, Wilmington, MA.
Figure 8. Dissolved nickel concentrations in samples from multilevel sampler #1 (MLS#1) before and after installation of porous parking lot at Silver Lake beach, Wilmington, MA.
Detection limit = 0.02 µg/L
DATE
2005 2006 2007
Dissolved 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
16 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts
Effects of LID Features on Stormwater Runoff Quantity and Quality from a Suburban Neighborhood
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
Field Studies of the Effects of LID Practices 17
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
18 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts
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.
Field Studies of the Effects of LID Practices 19
Figure 13. Estimated loads of selected nutrients from storms that occurred before (PRE) and after (POST) installation of low-impact-development (LID) features in the LID-retrofit neighborhood along Silver Lake Avenue and Dexter Street, Wilmington, MA.
Figure 14. Estimated loads of selected metals from storms that occurred before (PRE) and after (POST) installation of low-impact-development (LID) features in the LID-retrofit neighborhood along Silver Lake Avenue and Dexter Street, Wilmington, MA.
EXPLANATION
Number of samples
Largest data value within 1.5 times 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
20 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts
Ability of a Green Roof to Alter the Quantity and Quality of Stormwater Runoff
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.
Field Studies of the Effects of LID Practices 21
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).
22 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts
Figure 18. (A) Precipitation on and runoff from conventional rubber and green roofs in Ipswich, MA, for the storm of September 9, 2007, and (B) cumulative percentages of total precipitation and total runoff from the roofs for the same storm.
9/9/07
5:45
9/9/07
6:30
9/9/07
7:15
9/9/07
8:00
9/9/07
8:45
9/9/07
9:30
9/9/07
10:15
9/9/07
11:00
9/9/07
11:45
9/9/07
12:30
9/9/07
13:15
9/9/07
14:00
9/9/07
14:45
9/9/07
15:30
9/9/07
16:15
9/9/07
17:00
9/9/07
17:45
9/9/07
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
Town Hall runoff from rubber roof
Whipple Annex runoff from green roof
A
B
0.61-inch storm, 531.5-hour antecedent dry period, 16.75-hour duration, and 0.036-inch-per-hour intensity
0.61-inch storm, 531.5-hour antecedent dry period, 16.75-hour duration, and 0.036-inch-per-hour intensity
Field Studies of the Effects of LID Practices 23
Figure 19. (A) Precipitation on and runoff from conventional rubber and green roofs in Ipswich, MA, for the storm of September 11, 2007, and (B) cumulative percentages of total precipitation and total runoff from the roofs for the same storm.
9/11/0
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
Town Hall runoff from rubber roof
Whipple Annex runoff from green roof
Precipitation
Town Hall runoff from rubber roof
Whipple Annex runoff from green roof
A
B
1.27-inch storm, antecedent dry period 9.75 hours since 0.11-inch event and 32.25 hours since 0.61-inch event, 7.5-hour duration and 0.169-inch-per-hour intensity
1.27-inch storm, antecedent dry period 9.75 hours since 0.11-inch event and 32.25 hours since 0.61 inch event, 7.5-hour duration and 0.169-inch-per-hour intensity
24 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts
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
ION
RET
AIN
ED
0.0 to less than 0.1
0.1 to less than 0.5
0.5 to less than 1.0
1.0 to less than 2.0
2.0 and above
Total precipitation, in inches
EXPLANATION
Figure 20. Scatter Percentages of rainfall retained by the Whipple Annex green roof in Ipswich, MA, in relation to the period of dry weather preceding the storm.
A Phosphorus
B Nitrogen
0.1
0.5
1
5
10
BULKPRECIPITATION
CONVENTIONALRUBBER ROOF
GREEN ROOF
5 5 5
TOTA
L N
ITRO
GEN
CON
CEN
TRAT
ION
, IN
MIL
LIGR
AMS
PER
LITE
R
0.01
0.1
1
10
BULKPRECIPITATION
CONVENTIONALRUBBER ROOF
GREEN ROOF
5 5 5
TOTA
L PH
OSPH
ORUS
CON
CEN
TRAT
ION
, IN
MIL
LIGR
AMS
PER
LITE
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.
Field Studies of the Effects of LID Practices 25
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
CONVENTIONALRUBBER ROOF
GREEN ROOF
5 5 5
TOTA
L N
ITRO
GEN
LOA
D, IN
GRA
MS
0.01
0.1
1
10
100
BULKPRECIPITATION
CONVENTIONALRUBBER ROOF
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.
26 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts
5 Number of values
EXPLANATION
90th percentile
75th percentile
Median
25th percentile
10th percentile
1
10
100
1,000
BULKPRECIPITATION
CONVENTIONALRUBBER ROOF
GREEN ROOF
5 5 5
TOTA
L LE
AD C
ONCE
NTR
ATIO
N,
IN M
ICRO
GRAM
S PE
R LI
TER
BULKPRECIPITATION
CONVENTIONALRUBBER ROOF
GREEN ROOF0.1
1
10
100
1,0005 5 5
TOTA
L CO
PPER
CON
CEN
TRAT
ION
, IN
MIC
ROGR
AMS
PER
LITE
R
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
CONVENTIONALRUBBER ROOF
GREEN ROOF
5 5 5
TOTA
L LE
AD L
OAD,
IN M
ILLI
GRAM
S
10
100
1,000
10,000
BULKPRECIPITATION
CONVENTIONALRUBBER ROOF
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.
28 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts
Table 1. Summary of Ipswich River Basin modeling scenarios and results. (For complete details, see Zimmerman and others, 2010.)
[LID,low-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.
Simulation of the Effects of Land-Use and Water-Management Changes and Low-Impact Development on Streamflow 29
Figure 25. Model reaches and subbasin boundaries in the Ipswich River Basin, MA. (From Zarriello and Ries, 2000)
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
0 2 4
0 2 4 6 MILES
6 KILOMETERS
ATLANTICOCEAN
NORTH COASTAL
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
12
6
51
7
39
58
30
65
36
61
2
53
13
49
52
31
11
42
40
50
64
1420
66
33
41
46
15
48
62
54
34
4
2835
16
23
27
29
55
67
59
1824
60
10
26
45
57
25
21
37
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
30 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts
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
Simulation of the Effects of Land-Use and Water-Management Changes and Low-Impact Development on Streamflow 31
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).
32 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts
Simulation of Low-Impact-Development Retrofits in the Upper Ipswich River Basin
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.
Simulation of the Effects of Land-Use and Water-Management Changes and Low-Impact Development on Streamflow 33
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.
34 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts
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
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
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, IN
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EET
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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.
Simulation of the Effects of Land-Use and Water-Management Changes and Low-Impact Development on Streamflow 35
What is a Flow Duration Curve?
Simply stated, a flow-duration curve shows the percentage of time that a given streamflow is equaled or exceeded. For example, see the solid horizontal line extending from the y axis at 100 cubic feet per second to the point where it meets the curve. A vertical line extended downward from this point meets the x axis at approximately 25 percent. This means that the streamflow of cubic feet per second is met or surpassed about 25 percent of the time. In order to derive the median streamflow (the amount equaled or exceeded 50 percent of the time), see the dashed vertical line extending upward from the x axis at 50 percent to where it meets the curve. A horizontal line extended from this point meets the y axis at 10 cubic feet per second. This means that the median streamflow is 10 cubic feet per second.
2 5 10 30 50 70 90 95 99 99.8
1,000
100
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PERCENTAGE OF TIMEFLOW WAS EQUALED OR EXCEEDED
FLOW-DURATION CURVE
36 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts
Summary and 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.
38 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts
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.
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Zimmerman,M.J.,Barbaro,J.R.,Sorenson,J.R.,andWaldron,M.C.,2010,Effectsoflow-impact-developmentonwaterqualityandquantityintheIpswichRiverBasin,Massachusetts—Fieldandmodelingstudies:U.S.GeologicalSurveyScientificInvestigationsReport2010–5007,113p.
40 Effects of Low-Impact-Development Practices on Streamflow and Runoff in the Ipswich River Basin, Massachusetts
Analyte The subject of a chemical analysis
Antecedent conditions Conditions preceding a particular storm
Base flow Streamflow that originates from groundwater
Bioretention cell A man-made feature, containing soil and plants, that functions to remove pollutants from runoff
Bulk-precipitation samples Precipitation samples that directly captured in open containers
Calibrate Modify computer program parameters so the results of a simulation closely match a set of known conditions
Composite, flow-proportional 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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