city in the country: quantifying the effects of land … · 2018-09-28 · methods - u.s.g.s....

CITYINTHECOUNTRY:QUANTIFYINGTHEEFFECTSOFLANDUSECHANGEONTHEHYDROLOGYOFAWATERSUPPLYWATERSHED,SARATOGASPRINGS,NY

Wiles-Skeels,RobinH.1andNichols,KyleK.2,

1EnvironmentalStudiesand

2Geosciences,SkidmoreCollege,SaratogaSprings,NY12866

ABSTRACT

SignificantrecentandprojectedfuturegrowthinSaratogaCounty,NewYork,andinthe

13.7km2LoughberryLakewatershedinparticular,createsimpermeablesurfaces,suchas

roads,parkinglotsandroofs,thatincreaserunoffvolumeandpeakstormwaterdischarge.In

theLoughberryLakewatershed,mostlandusechangeisfromwell -drained,sandyforeststo

themixedimpermeableandgreenspacelandusesofcommercialandresidentialzones.

Suchlandusechangeincreasesthesurfacerunoffanddecreasesthegroundwaterrecharge

thatisimportanttosustainreservoirlevelsthroughthehigh-demandsummermonths.

Wequantifiedlandusechangefrom1980to2001,aperiodofrapiddevel opmentinthe

LakeLoughberrywatershed.WeusedGeographicInformationSystems(GIS)toquantifythe

1980datafromtheEarthResourcesObservationSystems(EROS)DataCenter(EDC)land

useclassificationthatonlyallowsforageneralizedestimateoflanduseareas.Wedigitized

the2001,usingGIS,from12”perpixelhigh-resolutionorthophotographicimages.Forthe

2001data,wedigitizedallimpermeablesurfacesincludinghouses,roads,andparkinglots,

greenspace,andforestedareas.Thus,the2001dataaremoreprecisethanthe1980data.

Basedona10-year24-hourstorm,andusingthecurvenumberapproach,thetotalrunoff

volumehasincreased304%fromundevelopedconditionsof100%forestcover,similartothe

conditionsinthe1870swhenthereservoirwasbuilt.Therunoffvolumefrom1980to2001

forthesamedesignstormhasincreased26%.Usingtherationalrunoffmodel,peak

dischargesin2001are160%overtheundevelopedconditionand54%higherthanthe1980

landusecover.

Suchtime-seriesmeasurementsoflandusechangeprovideusefulresearchexperience

forundergraduatestudentsandalsoprovidesvaluabledataontheexpansionofimpermeable

surfaceswithincriticalwatersheds.InSaratogaSprings,thisprojectisprovidingimportant

informationonlandusepracticesatatimewhenthecityislookingtoexpanditssummer

watersupply.

INTRODUCTION

-LoughberryLakesuppliesSaratogaSpringswithitsdrinkingwater

-Demandforwaterincreasesyearly,anddoublesduringthesummerhorseracing(tourist)

season

-DevelopmentintheLoughberryLakewatershedhasincreasedsignificantlyoverthepast

twodecades

-Developmentandimpervioussurfacesdecreasegroundwaterrechargeareas

-Groundwaterrechargeisessentialforthelaketomaintainreservoirlevelsduringhigh-

demandsummermonths

-GroundwatersustainsLoughberryLakereservoirlevelssuitableforSaratoga

Springsuse

METHODS

-U.S.G.S.1:24,000topographicmapsusedtodefinewatershedboundary

-EarthResourcesObservationSystems(EROS)datausedtoquantify1980landuse

-12''perpixelhigh-resolutionorthophotographicimagesusedtodelineate2001landuse(houses,

roads,parkinglots,greenspace,forestedareas)

-GISusedtoquantify2001landuseareas

-SoilnamesfromEngineeringHandbook4(1972)usedtoverifyhydrologicsoilconditions

-Rationalrunoffmodel(DunneandLeopold,1978)usedtoquantifypeakdischargesfrom1980and

2001landuses

-Curvenumberapproach(DunneandLeopold,1978)usedtoquantifyrunoffvolumefrom1980and

2001landuses

-Calculationsbasedon10-yrdesignstormsof24,6,1,and0.5hourdurations

REFERENCES

Dunne,ThomasandLeopold,LunaB.,1978.WaterInEnvironmentalPlanning:W.H.Freeman

andCo.,NewYork,718p.

SoilConservationService,1972.Nationalengineeringhandbooksection4:Hydrology.

Washington,D.C.,USA:UnitedStatesDepartmentofAgriculture.

curvenumbersfromDunneandLeopold,1978

1980EarthResourcesObservationSystems

DataCenterlanduseclassificationfor

LoughberryLakewatershed

LoughberryLakewatershedsoiltypes

HydrologygroupA:loamysand(mud,silt,clay

andsandmixture)-lowrunoffpotential

HydrologyGroupC:rolling,rocky-highrunoff

potential

2001aerialphotoofLoughberryLake

watershed

2001landcoverdelineationin

LoughberryLakewatershed

A

C

NewYorkState

SaratogaCounty

UnitedStates

ACKNOWLEDGMENTS

WethankBobJonesforGISexpertise.Fundingforthisproject

wasprovidedbytheRathmannFoundationandSkidmore

College.

NEXTSTEP

-SaratogaSpringsislookingtouseSaratogaLakeor

theUpperHudsonRiverasanewwater

source

-Wewillperform

similarhydrologicanalysesforthe

SaratogaLakewatershed

-Wewillevaluateprojecteddevelopmentinthe

SaratogaLakewatershedforthenext20to30years

(basedonzoningandpopulationdata)toseehow

runoffandpeakdischargewillchangeandinfluence

SaratogaLakewaterquantityandwaterquality

IMPLICATIONS

-Bestresults,forsmallbasins,areobtainedfromhighresolutionaerialphotographscompared

to"generalized"EROSlandusedata(tradetimeforaccuracy)

-DevelopmentintheneighboringtownofWiltonsignificantlyincreasesrunoffvolume(26

to58%)andpeakdischarge(54%)for10-yearstorms

-Greatersurfacerunoffvolumesandpeakdischargesincreasepollutanttransporttothelake

-Morerunoffandlessinfiltrationexasperateswatershortageduringdroughtduetoless

groundwaterrechargeintoLoughberryLake

-Continueddevelopmentwillfurtherdiminishwaterquantityandquality

-EffectsofdevelopmentonLoughberryLakenecessitateeither1)waterconservationand

betterwatershedmanagementor2)anewwatersupplyforSaratogaSprings

24hr

6hr

1hr

30min

187050,000

25,000

00

1980161,000

101,000

39,000

31,000

2001203,000

140,000

60,000

49,000

%increase

1980-2001

26

38

53

58

10-yrSTORMRUNOFFVOLUME(m

3)

24hr

6hr

1hr

30min

1870

2.2

6.6

22

37

1980

3.7

11

38

62

2001

5.7

17

58

96

%increase

1980-2001

54

54

54

54

10-yrSTORMPEAKDISCHARGE(m

3/s)

Landuse

Curve#

HydrologicCondition

MixedForest

30

goodcondition

CroplandandPasture

60

goodcondition

Commercial

70

<70%impervious

Builtupareas

40

<25%impervious

Residential

54

goodcondition

Roads

98

paved

soilgroupsfromSoilConservationService,1972

curvenumbersfromDunneandLeopold,1978

CURVENUMBERSUSEDFOR1980DATA

Landuse

Curve#

HydrologicCondition

Forest(sandy)

30

goodcondition

Forest(notsandy)

60

goodcondition,low

infiltration

Greenspace

40

goodcondition

Roads

98

paved

Roofs

98

impervious

soilgroupsfromSoilConservationService,1972

curvenumbersfromDunneandLeopold,1978

CURVENUMBERSUSEDFOR2001DATA

Rainfall(in)

02

46

810

12

StormRunoff(in) 2468

1968aerialphotoofLoughberryLake

Noticeminimaldevelopmentnorthoflake

October2003developmentinLoughberry

Lakewatershed

Cropland

Residential

Builtup

Commercial

Roads

MixedForest

Loughberry

Forestnotsandy

Forestsandy

Roads

Greenspace

Roofs

Loughberry

*Northistothetopoftheposterineachmap,LoughberryLakeis~1.5kmlong