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

FS–2012–3085August 2012

Streamflow of 2011—Water Year Summary

U.S. Geological SurveyReston, Virginia

January 2012

• Introduction•NationalOverview•RegionalPatterns•SeasonalCharacteristics•HighandLowFlows

WetNormalDry

2011 statewide streamflow

Introduction

Themapsandgraphsinthissummarydescribestreamflowconditionsforwateryear2011(October1,2010,toSeptember30,2011)inthecontextofthe82-yearperiodfrom1930through2011,unlessotherwisenoted.TheillustrationsarebasedonobserveddatafromtheU.S.GeologicalSurvey’s(USGS)NationalStreamflowInformationProgram(http://water.usgs.gov/nsip/).Theperiod1930–2011wasusedbecause,priorto1930,thenumberofstreamgageswastoosmalltoproviderepresentativedataforcomputingstatisticsformostregionsofthecountry.

Inthesummary,referenceismadetotheterm“runoff,”whichisthedepthtowhichariverbasin,State,orothergeographicareawouldbecoveredwithwaterifallthestreamflowwithintheareaduringasingleyearwasuniformlydistributeduponit.RunoffquantifiesthemagnitudeofwaterflowingthroughtheNation’sriversandstreamsinmeasurementunitsthatcanbecomparedfromoneareatoanother.

Eachofthemapsandgraphsbelowcanbeexpandedtoalargerviewbyclickingontheimage.Inallthegraphics,arankof1indicatesthehighestflowofallyearsanalyzed.

National Overview

MeanrunoffintheNation’sriversandstreamsduring2011(10.50inches)washigherthanthelong-termannualmeanfortheUnitedStates(9.31inches).Nationwide,2011streamflowranked16thoutofthe82yearsinperiod1930–2011.Notethatinpreviouswateryearsummariesthemedianrunoff,notthemeanrunoff,wascomparedamongtimeperiods.

Streamflowwasatrecordhighlev-els(rankingfirstin82years)intheStatesofMontana,NorthDakota,SouthDakota,Minnesota,NewYork,andVermont.Above-normalandmuch-above-normalstreamflowcharacterizedtheremainingStatesintheNortheast,North,West,andPuertoRico.Incontrast,streamflowwasatrecordlowlevels(ranking82din82years)inTexasandAlaska.Below-normalandmuch-below-normalstreamflowwasprevalentcrosstheSoutheastandSouth.Only11Stateshadstreamflowinthenormalrange.

*ForPuertoRico,68yearsofavailabledatawereused.

1930 1940 1950 1960 1970 1980 1990 2000 2010

Year

0

5

10

15

Annu

al m

ean

runo

ff (in

ches

)

0

5

10

15

Annual mean U.S. runoff1930–2011

18

11

1 2119 81

8 133

12

1410

27

66 310 8

24 27 472365 11

6974

683462

82

46 80797272

8181

82

37

2*

1

2011 statewide streamflow ranks (1930–2011)

VTNH

MA (12)RI(43)

CT(6)NJ(2)DE(41)MD(22)DC(4)

AKHI

PR-VI

Explanation - Rank12–89–2063–7475–8182

HighestMuchabovenormal

AbovenormalNormalBelow

normal

Muchbelownormal

Lowest

21–62

Regional Patterns

TheUnitedStates(includingPuertoRico)isdividedinto21largedrain-ages,orwaterresourcesregions.Thesehydrologicareasarebasedonsurfacetopographyandcontaineitherthedrainageareaofamajorriver,suchastheColumbia,thecombineddrainageareasofaseriesofrivers,suchastheTexas-Gulfregion,whichincludesanumberofriversdrainingintotheGulfofMex-ico,ortheareaofanislandorislandgroup.Waterresourcesregionsprovideacoherent,watershed-basedframeworkfordepictingstreamflowvariations.

Water resources regions of the United States

Streamflowwasatrecordhighlevels(rankingfirstin82years)inthewaterresourceregionsintheSouris-Red-RainyandMid-Atlanticregions.Above-normalandmuch-above-normalstreamflowoccurredinallnortheastern,northern,andwesternregions,andintheCarib-bean.Incontrast,streamflowwasatrecordlowlevels(ranking82din82years)intheSouthAtlantic-Gulf,Texas-Gulf,andAlaskaregions,respectively.Below-normalandmuch-below-normalstreamflowswerereportedintheLowerMissis-sippi,andRioGranderegions.

11

3

51

761

1310

15 9

59 56

8182

42

708282

52

2*

PR-VI

HIAK

Explanation - Rank12–89–2063–7475–8182

HighestMuchabovenormal

AbovenormalNormalBelow

normal

Muchbelownormal

Lowest

21–62

Seasonal Characteristics

Autumnseason(October–Decem-ber)streamflowwasatrecordshighlevels(rankingfirstin82years)intheStatesofNorthDakota,SouthDakota,andMinnesota.Above-andmuch-above-normalflowswerereportedinnortheastern,northern,andsouthwesternStates.Floridahadrecordlowflow(ranking82din82years).Mostoftheothersouth-easternandsouthernStates,aswellasAlaska,hadbelow-andmuch-below-normalstreamflows.Nation-wide,autumnseasonstreamflowranked44thoutof82years.

*ForPuertoRico,68yearsofavailabledatawereused.

30

40

46 31

128 114

12 752148

14

92014

3217 5148 6245 64 545154 53

5041

565774

74

76 79747472

8082

74

20

Autumn (October–December 2010) statewide ranks

12*

VTNH

MA (31)RI(43)

CT(40)NJ(52)DE(40)MD(46)DC(40)

AKHI

PR-VI

Winterseason(January–March)streamflowwasabovetomuchabove-normalinmanynorthernandnortheasternStates.Recordlowflow(ranking82din82years)occurredinAlaska.Below-normalandmuch-below-normalstreamflowoccurredinthemostsouthernandsouth-easternStates.Nationwide,winterseasonstreamflowranked31stoutof82years.

*ForPuertoRico,68yearsofavailabledatawereused.

15

18

8 6316

34 2218

10 1146

419

2416

121218

26 1528 2840 34 612841 42

6174

625576

79

75 8174677378

7882

42

Winter (January–March 2011) statewide ranks

39*

41

VTNH

MA (20)RI(57)

CT(17)NJ(20)DE(59)MD(52)DC(40)

AKHI

PR-VI

Explanation - Rank12–89–2063–7475–8182

HighestMuchabovenormal

AbovenormalNormalBelow

normal

Muchbelownormal

Lowest

21–62

Springseason(April–June)stream-flowwasatrecordhighlevels(rank-ing1stin82years)intheStatesofMontana,SouthDakota,NorthDakota,Illinois,Indiana,Ohio,Kentucky,andVermont.Stream-flowwasaboveormuchabovenormalinthenorthernandwesternStates,Missouri,Arkansas,Tennes-see,Hawaii,andPuertoRico.Incontrast,southeasternandsouthernStatesreportedbelow-ormuch-below-normalflows;streamflowinTexaswasatrecordlowlevels.Onanationwidebasis,springseasonstreamflowwasmuchabovenormal,rankingfifthin82years.

*ForPuertoRico,68yearsofavailabledatawereused.

14

8

1 18314 13

6 1

10 2614

1517

21410

20 11 126 9 29856 1

6668

68 337

82

6 71715657

7980

71

19

5*

Spring (April–June 2011) statewide ranks

VTNH

MA (36)RI(43)

CT(13)NJ(15)DE(57)MD(26)DC(44)

AKHI

PR-VI

Summerseason(July–September)streamflowwasatrecordhighlevels(ranking1stin82years)intheStatesofMontana,NorthDakota,Wyoming,Idaho,NewJersey,NewYork,andVermont.ThiswasthethirdseasonoutoffourthatNorthDakotaexperiencedrecordhighlev-els.Streamflowwasaboveormuchabovenormalinthenortheastern,northern,northwesternandwesternStates,andPuertoRico.Incontrast,southeasternandsouthernStatesandAlaskareportedbelow-ormuch-below-normalflows.StreamflowinGeorgiawasatrecordlowlevels.Onanationwidebasis,summerseasonstreamflowwasmuchabovenormal,ranking13thin82years.

*ForPuertoRico,68yearsofavailabledatawereused.

15

1

1 851

5 5123 1

402

1

4

5326

411 1

1422 376 46 214067 25

6958

79 5173

81

21 79826127

68

7779

29

Summer (July–September 2011) statewide ranks

3*

VTNH

MA (2)RI(5)

CT(2)NJ(1)DE(6)MD(5)DC(5)

AKHI

PR-VI

Explanation - Rank12–89–2063–7475–8182

HighestMuchabovenormal

AbovenormalNormalBelow

normal

Muchbelownormal

Lowest

21–62

High and Low Flows

10

20

30

0

10

20

30

2000 2002 2004 2006 2008 2010

Year

30

20

10

0

30

20

10

0

Perc

enta

ge o

f stre

amga

ges

Percentage of streamgages with very high and very low monthly streamflowOctober 1999–September 2011

>95th percentile for month <5th percentile for month

Inanygivenmonth,onaverage,itisexpectedthat5percentofthestreamgageswillexperienceveryhigh(>95thpercentile)andverylow(<5thpercentile)averagestreamflow.Duringwateryear2011,9months(October,December,March,April,May,June,July,August,andSeptember)hadagreaterthanexpectedpercentageofstreamgagesreportingveryhighstreamflow(6,6,12,16,15,11,14,14,and15percentrespec-tively).Incontrast,therewere5months(May,June,July,August,andSeptember)withagreaterthanexpectedpercentageofstreamgageswithverylowflows(6,9,7,7,and6percent,respectively).

Thebankfullstreamflowisdefinedasthehighestdailymeanstream-flowvalueexpectedtooccur,onaverage,onceinevery2.3years.In2011,50percentofstreamgageshadadailymeanstreamflowvalueabovethebankfulllevel.Thisvalueisgreaterthantheexpectednumber(43percent)tooccurinanygivenyear.Since1950,thelargestnumberofstreamgagesreportinghigherthanbankfullstreamflowinany1yearwas68percent,whichoccurredin1996.

1950 1960 1970 1980 1990 2000 2010

Year

0102030405060708090

100

Perc

enta

ge o

f stre

amga

ges

0102030405060708090100

Percentage of streamgages above bankfull streamflow1950−2011

The10thpercentile7-daylowflowisdefinedasthelowest7-dayaver-agestreamflowexpectedtooccur,onceevery10years.Inwateryear2011,17percentofthestreamgagesreporteda7-daylowflowlessthanthe10thpercentile7-daylowflow.Theexpectednumbertooccurinanygivenyearis10percent.Since1950,thelargestpercentageofstreamgagesreportinga7-daylowflowlessthanthe10thpercentile7-daylowflowwas25percentin1954.

1950 1960 1970 1980 1990 2000 2010

Year

0

5

10

15

20

25

30

Perc

enta

ge o

f stre

amga

ges

0

5

10

15

20

25

30

Percentage of streamgages below 10th percentile ofannual 7-day minimum streamflow

1950–2011

Additional Information

TheUSGSoperatesanetworkofnearly10,000streamgagesnationwide,manyinrealtime.Currentinformationderivedfromthesestationsisavailableathttp://waterwatch.usgs.gov.TablesofdatathatsummarizehistoricalstreamflowconditionsbyState,beginningin1900,canbeaccessedathttp://waterwatch.usgs.gov/?m=statesum.Thesetablesareupdatedeveryfewmonthstoreflectthemostcurrentstreamflowdata.

Thestreamflowinformationusedtopreparethissummaryisalsousedforwatermanagement,monitoringfloodsanddroughts,bridgedesign,andformanyrecreationalactivities.Toobtainreal-timeandarchivedstreamflowdataandinformation,visithttp://water.usgs.gov/nwis.Althoughthenationalstreamgagenet-workisoperatedprimarilybytheUSGS,itisfundedbyapartner-shipof850agenciesattheFederal,State,tribal,andlocallevels.Formoreinformationaboutthestreamgagenetwork,visithttp://water.usgs.gov/nsip/.

By Xiaodong Jian, David M. Wolock, Harry F. Lins, and Steve Brady

For additional information, contact: HarryLins U.S.GeologicalSurvey 415NationalCenter Reston,VA20192 Email:hlins@usgs.gov

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