Comparison Of Base Flows To Selected Streamflow Statistics .
Prepared in cooperation with the West Virginia Department of Environmental Protection,Division of Water and Waste ManagementBase flow, in percent of mean annual base flowComparison of Base Flows to Selected Streamflow StatisticsRepresentative of 1930–2002 in West Virginia150SpringSummerFallWinter100500-50-100Apr. May June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar.MonthScientific Investigations Report 2012–5121U.S. Department of the InteriorU.S. Geological Survey
Cover. Mean seasonal and mean monthly base flows as percentage of mean annual base flows for 15 streamflow-gaging stations in WestVirginia, 1930–2002.
Comparison of Base Flows to SelectedStreamflow Statistics Representativeof 1930–2002 in West VirginiaBy Jeffrey B. WileyPrepared in cooperation withthe West Virginia Department of Environmental Protection,Division of Water and Waste ManagementScientific Investigations Report 2012–5121U.S. Department of the InteriorU.S. Geological Survey
U.S. Department of the InteriorKEN SALAZAR, SecretaryU.S. Geological SurveyMarcia K. McNutt, DirectorU.S. Geological Survey, Reston, Virginia: 2012For more information on the USGS—the Federal source for science about the Earth, its natural and livingresources, natural hazards, and the environment, visit http://www.usgs.gov or call 1–888–ASK–USGS.For an overview of USGS information products, including maps, imagery, and publications,visit http://www.usgs.gov/pubprodTo order this and other USGS information products, visit http://store.usgs.govAny use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by theU.S. Government.Although this report is in the public domain, permission must be secured from the individual copyright owners toreproduce any copyrighted materials contained within this report.Suggested citation:Wiley, J.B., 2012, Comparison of base flows to selected streamflow statistics representative of 1930–2002 in WestVirginia: U.S. Geological Survey Scientific Investigations Report 2012–5121, 18 p.
iiiAcknowledgmentsThe author thanks U.S. Geological Survey colleague Samuel H. Austin and U.S. Fishand Wildlife Service colleague Rachel A. Esralew for their technical reviews of this report.The technical assistance of colleagues Terence Messinger and Katherine S. Paybins andeditorial assistance of Ruth Larkins also are appreciated.
n.1Description of Study Area.2Previous Studies.2Computation of Base Flows.4Comparison of Base Flows to Streamflow Statistics.4Examples of Estimating Base Flows .8Limitations of Base-Flow Estimates.11Summary and Conclusions.12References Cited.12Appendix 1. Annual and seasonal base flows at 15 streamflow-gaging stationsin West Virginia, 1930–2002.16Figures1.2.3.4.5.Map showing Appalachian Plateaus, Valley and Ridge, and Blue RidgePhysiographic Provinces, and Climatic Divide in West Virginia.3Map showing location of selected U.S. Geological Survey streamflow-gagingstations in West Virginia.5Graph showing mean seasonal and mean monthly base flows as percentageof mean annual base flows for 15 streamflow-gaging stations in West Virginia,1930–2002.8Graph showing mean annual base flows in relation to annual 50-percent durationflows for 15 streamflow-gaging stations in West Virginia, 1930–2002.8Graphs showing mean seasonal and mean annual base flows in relation to selectedduration flows for 15 streamflow-gaging stations during A, spring, B, summer,C, fall, and D, winter in West Virginia, 1930–2002.9Tables1. The streamflow-gaging stations used to compare base flows and selectedstreamflow statistics in West Virginia.62. Average, minimum, and maximum differences between mean annual base flowsand selected annual statistics computed for 1930–2002, and those computed forthe indicated record periods for 15 streamflow-gaging stations in West Virginia.63. Average differences between base flows and selected seasonal statisticscomputed for 1930–2002, and those computed for the indicated record periodsfor 15 streamflow-gaging stations in West Virginia.7
vConversion Factors and DatumsMultiplyinch (in.)inch (in.)foot (ft)mile (mi)acresquare foot (ft2)square mile (mi2)cubic foot (ft3)cubic foot per second 2.590Volume0.02832Flow rate0.02832To obtaincentimeter (cm)millimeter (mm)meter (m)kilometer (km)square meter (m2)square meter (m2)square kilometer (km2)cubic meter (m3)cubic meter per second (m3/s)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.
vi
Comparison of Base Flows to Selected StreamflowStatistics Representative of 1930–2002in West VirginiaBy Jeffrey B. WileyAbstractIntroductionBase flows were compared with published streamflowstatistics to assess climate variability and to determine thepublished statistics that can be substituted for annual and seasonal base flows of unregulated streams in West Virginia. Thecomparison study was done by the U.S. Geological Survey, incooperation with the West Virginia Department of Environmental Protection, Division of Water and Waste Management.The seasons were defined as winter (January 1–March 31),spring (April 1–June 30), summer (July 1–September 30),and fall (October 1–December 31).Differences in mean annual base flows for five recordsub-periods (1930–42, 1943–62, 1963–69, 1970–79, and1980–2002) range from -14.9 to 14.6 percent when comparedto the values for the period 1930–2002. Differences betweenmean seasonal base flows and values for the period 1930–2002 are less variable for winter and spring, -11.2 to 11.0 percent, than for summer and fall, -47.0 to 43.6 percent. Meansummer base flows (July–September) and mean monthly baseflows for July, August, September, and October are approximately equal, within 7.4 percentage points of mean annualbase flow. The mean of each of annual, spring, summer, fall,and winter base flows are approximately equal to the annual50-percent (standard error of 10.3 percent), 45-percent (errorof 14.6 percent), 75-percent (error of 11.8 percent), 55-percent (error of 11.2 percent), and 35-percent duration flows(error of 11.1 percent), respectively. The mean seasonal baseflows for spring, summer, fall, and winter are approximatelyequal to the spring 50- to 55-percent (standard error of6.8 percent), summer 45- to 50-percent (error of 6.7 percent),fall 45-percent (error of 15.2 percent), and winter 60-percentduration flows (error of 8.5 percent), respectively.Annual and seasonal base flows representative ofthe period 1930–2002 at unregulated streamflow-gagingstations and ungaged locations in West Virginia can beestimated using previously published values of statisticsand procedures.Streamflow can be separated into discharge from overland runoff and discharge from groundwater. Base flow is theportion of streamflow contributed by groundwater discharge.Generally, base flows are greater in wetter seasons than indryer seasons because more water accumulates and is releasedfrom groundwater. Knowledge of climatic, seasonal, andmonthly differences in base flows can assist scientists andwater-resource managers in understanding the capacity ofgroundwater storage in watersheds and the ability of a streamto maintain flows during droughts.Streamflow statistics have been computed for streamflow-gaging stations, and equations have been determined toestimate streamflows at ungaged locations in West Virginiafor the period 1930 to 2002 (Wiley, 2006, 2008; Wiley andAtkins, 2010a). Equations for estimating base flows could bedetermined using similar methods, but a simpler and lowercost method for estimating base flows is already available ifpublished streamflow statistics can be used as surrogates forbase flows.This study, conducted in cooperation with the WestVirginia Department of Environmental Protection, Divisionof Waste and Water Management, investigated the climatic,seasonal, and monthly variability of base flows at 15 selectedlong-term streamflow-gaging stations, documented thedevelopment of relations between base flows and publishedstreamflow statistics, and determined surrogate statistics (thepublished statistics that can be substituted for base flows)to be used to estimate annual and seasonal base flows atother streamflow-gaging stations and at ungaged locations.The results of this study are representative of the period1930–2002 and are relevant only to West Virginia, but theprocedures presented in this report can be used to determinesubstitute streamflow statistics that can be used to estimatebase flows in other regions.This report presents the procedures used to estimate baseflows for 1930–2002. The climatic, seasonal, and monthly
2 Comparison of Base Flows to Selected Streamflow Statistics Representative of 1930–2002 in West Virginiavariability of base flows at 15 long-term streamflow-gagingstations is discussed. Relations between mean annual andmean seasonal base flows, and between mean annual and50-percent duration flows, are shown in illustrations. Relations between mean seasonal base flows and seasonalduration flows are also shown in illustrations. Differencesbetween mean annual base flows and annual streamflowstatistics are listed in tables. Base flows for the 15 long-termstreamflow-gaging stations are provided in an Appendix assupplementary information.Description of Study AreaWest Virginia can be differentiated into three physiographic provinces (fig. 1), the Appalachian Plateaus, Valleyand Ridge, and Blue Ridge (Fenneman, 1938). The movement of air masses across the State allows identification oftwo climatic regions (fig. 1), separated by a line defined asthe Climatic Divide (Wiley and others, 2000; Wiley andAtkins, 2010b).Generally, the part of the State west of the ClimaticDivide is in the Appalachian Plateaus Physiographic Province;altitudes in the Appalachian Plateaus range from about 2,500to 4,861 ft (NAVD 88) at Spruce Knob along the ClimaticDivide to about 550 to 650 ft along the Ohio River. The part ofWest Virginia east of the Climatic Divide is in the Valley andRidge Physiographic Province, except for the extreme easterntip of the State, which is in the Blue Ridge PhysiographicProvince. Altitudes decrease eastward from the ClimaticDivide to 274 ft at Harpers Ferry in the Eastern Panhandle(U.S. Geological Survey, 1990, 2006; National Oceanic andAtmospheric Administration, 2006a).The Appalachian Plateaus Physiographic Province consists of consolidated, mostly siliciclastic sedimentary rocksthat have a gentle slope from southeast to northwest near theClimatic Divide and are nearly flat-lying along the Ohio River.One exception is in the northeastern area of the province (westof the Climatic Divide), where the rocks are gently folded andsome carbonate rock crops out (Fenneman, 1938). The rocksin the Appalachian Plateaus Physiographic Province have beeneroded to form steep hills and deeply incised valleys. Drainagepatterns are dendritic.The Valley and Ridge Physiographic Province in WestVirginia consists of consolidated carbonate and siliciclasticsedimentary rocks that are folded sharply and extensivelyfaulted (Fenneman, 1938). Northeast-trending valleysand ridges parallel the Climatic Divide. Drainage patternsare trellis.The Blue Ridge Physiographic Province within West Virginia consists predominantly of metamorphosed sandstone andshale (Fenneman, 1938). The province has high relief betweenmountains and wide valleys that parallel the Climatic Divide.Drainage patterns are trellis.The climate of West Virginia is primarily continental,with mild summers and cold winters. Major weather systemsgenerally approach from the west and southwest, althoughpolar continental air masses of cold, dry air that approach fromthe north and northwest are not unusual. Air masses from theAtlantic Ocean sometimes affect the area east of the ClimaticDivide and less frequently affect the area west of the ClimaticDivide. Generally, tropical continental masses of hot, dry airfrom the southwest affect the climate west of the ClimaticDivide. Tropical maritime masses of warm, moist air from theGulf of Mexico affect the climate east of the Climatic Dividemore than west of the Climatic Divide. Evaporation from localand upwind land surfaces, lakes, and reservoirs also providesa source of moisture that affects the climate of the State (U.S.Geological Survey, 1991; National Oceanic and AtmosphericAdministration, 2006a).Annual precipitation averages about 42 to 45 in. statewide with about 60 percent received from March throughAugust. July is the wettest month, and September throughNovember are the driest months. Annual average precipitationin the State generally decreases northwestward from about 50to 60 in. along the Climatic Divide to about 40 in. along theOhio River; precipitation ranges from about 30 to 35 in. eastof the Climatic Divide to about 40 in. in the extreme easterntip of the State. Greater precipitation along and west of theClimatic Divide is a consequence of the higher elevationsalong the Divide and the orographic lifting of weather systemsgenerally approaching from the west and southwest. Annualaverage snowfall follows the general pattern of annual average precipitation, decreasing northwestward from about 36 to100 in. along the Climatic Divide to about 20 to 30 in. alongthe Ohio River. East of the Climatic Divide, annual averagesnowfall ranges from 24 to 36 in. (U.S. Geological Survey,1991; Natural Resources Conservation Service, 2006; NationalOceanic and Atmospheric Administration, 2006a, 2006b).Previous StudiesSelected statistics for U.S. Geological Survey (USGS)streamflow-gaging stations representative of conditions during1930–2002 were determined by Wiley (2006). In that study, acriterion-based sample of the record period was used to determine statistics representative of 1930–2002 rather than usingthe entire record period and (or) using record-extension techniques. The selected statistics included annual and seasonalhydrologically and biologically based low-flow frequencyvalues, harmonic means, and flow-duration values (includingvariability index).Wiley (2008) developed estimating procedures for theannual 1-, 3-, 7-, 14-, and 30-day 2-year; 1-, 3-, 7-, 14-, and30-day 5-year; and 1-, 3-, 7-, 14-, and 30-day 10-year hydrologically based low-flow frequency values for unregulatedstreams in West Virginia. Equations and procedures for theannual 1-day 3-year and 4-day 3-year biologically basedlow-flow frequency values; the annual U.S. EnvironmentalProtection Agency (USEPA) harmonic mean flows; and theannual 10-, 25-, 50-, 75-, and 90-percent flow-duration values
Introduction 381 W78 WEXPLANATIONState boundaryGeographic locationPENNSYLVANIAWheeling40 NOHIOm nsVAIANPLATESpruceKnobCharleston38 NCKENTUCKYmliactiDivideVIRGINIABeckley00Base from U.S. Geological Survey 1:100,000 digital line graphics.Universal Transverse Mercator projection, zone 17, NAD 020404060 MILES60 KILOMETERSPhysiographic provinces from Fenneman, 1938Figure 1. Appalachian Plateaus, Valley and Ridge, and Blue Ridge Physiographic Provinces, and Climatic Divide in West Virginia.(From Wiley and Atkins, 2010b, figure 2)
4 Comparison of Base Flows to Selected Streamflow Statistics Representative of 1930–2002 in West Virginiaalso were developed. Regional equations were developedusing ordinary least squares regression with flow statisticsfrom USGS streamflow-gaging stations as dependent variablesand basin characteristics for these streamflow-gaging stationsas independent variables.Methods for estimating seasonal flow statistics atungaged locations were developed by Wiley and Atkins(2010a) using data from Wiley (2006). The seasons weredefined as winter (January 1–March 31), spring (April 1–June 30), summer (July 1–September 30), and fall (October1–December 31). Regional equations for the seasonal 1-day10-year, 7-day 10-year, and 30-day 5-year hydrologicallybased low-flow frequency values; the seasonal USEPA harmonic mean flows; and the seasonal 50-percent flow-durationvalues were developed using the same methods and regionalboundaries used by Wiley (2006).Computation of Base FlowsBase flow can be determined hydrographically usingbase-flow-recession methods (Olmsted and Hely, 1962; Riggs,1964; Rorabaugh, 1964), curve-fitting methods (Pettyjohnand Henning, 1979; Linsley and others, 1982), and computermethods (Sloto and Crouse, 1996; Rutledge, 1998). A computer method is desired because computation time is substantially reduced, and a method that excludes individual biases ofmanipulation allows for reproducible results.Daily mean discharge records for 14 USGS streamflowgaging stations in West Virginia that have no more than4 years of missing record during 1930–2002 were used tocompute base flows. A combination of two nearby stationswas used to supplement the 14 stations and provide information near the southern border of the State, but no stations wereavailable along the western border that met the record-lengthcriterion. Fifteen stations (counting the combination of the twoTug Fork stations as one) are identical to those used by Wiley(2006) to study the variability of selected annual and seasonalflow statistics (fig. 2, table 1).Base flows were computed for the 15 streamflow-gagingstations using the PART (streamflow PARTitioning) computer program developed by Rutledge (1998). Base flows forthe 15 streamflow-gaging stations were computed annually,seasonally, and monthly for the period of record 1930 to 2002and annually for five periods of record found by Wiley (2006)to have similar characteristics in annual minimum daily meanflows: 1930–42, 1943–62, 1963–69, 1970–79, and 1980–2002.The period 1930 to 2002 includes periods of droughts duringthe 1930s and 1960s and a wet period during the 1970s. Baseflows were computed for climatic years (April 1 to March 31of the indicated year) and for winter (January 1–March 31),spring (April 1–June 30), summer (July 1–September 30), andfall (October 1–December 31) for comparison with streamflowstatistics computed by Wiley (2006).The combined stations are Tug Fork near Kermit (stationnumber, 03214000; drainage area, 1,188 mi2) and Tug Fork atKermit (03214500; 1,280 mi2). Most annual, and all seasonaland monthly, base-flow calculations were computed usingrecords for Tug Fork near Kermit from 1936 to 1985 (climaticyears). The record period 1936–85 was representative of theperiod 1930–2002 (Wiley, 2006, table 13, page 190). Theannual base flows for the period 1980–2002 were computedfor Tug Fork at Kermit (1986–2002) and were estimated forTug Fork near Kermit by multiplying the base flows by theratio of drainage areas (1,188 mi2/1,280 mi2).Comparison of Base Flows toStreamflow StatisticsMean annual base flow was computed for each of the15 streamflow-gaging stations for the five characteristicallysimilar record periods and for the period 1930–2002. Thepercent differences between mean annual base flow for thefive record periods and the mean annual base flow for theperiod 1930–2002 were computed and compared to percentdifferences in streamflow statistics previously selected andcomputed by Wiley (2006, tables 2 and 3) to assess climatevariability (table 2). The streamflow statistics previouslyselected by Wiley (2006) are the annual 1-day 10-year (1Q10),7-day 10-year (7Q10), and 30-day 5-year (30Q5) hydrologically based low-flow frequency values; the 1-day 3-year (1B3)and 4-day 3-year (4B3) biologically based low-flow frequencyvalues; and the annual USEPA harmonic mean flow. Differences between mean annual base flows computed for the fiverecord periods and the values computed for 1930–2002 varyfrom -14.9 to 14.6 percent. Generally, differences betweenmean annual base flows computed for the five periods andthe values computed for the period 1930–2002 vary less thanpercent differences between the selected streamflow statisticscomputed for the five sub-periods and the values computed forthe period 1930–2002, particularly for the wet period 1970–79when differences for mean annual base flow were 14.6 percentgreater, and the differences between selected statistics wereapproximately 100 to 200 percent greater. The differencebetween mean annual base flow computed for the period1963–69 and the value computed for the period 1930–2002,‑14.9 percent, is slightly greater than that for the period1930–42, -12.6 percent.Mean seasonal base flows computed for 1930–2002 andpreviously selected seasonal streamflow statistics (Wiley,2006, table 4) were compared to base flows for the five recordperiods to assess seasonal variability (table 3). Differencesbetween base flows for the five record periods and mean seasonal base flows were less variable in the winter and spring,from -11.2 to 11.0 percent, than in summer and fall, from -47.0to 43.6 percent. The difference for base flows for the summerof 1963–69, -47.0 percent, was less than the difference for fallof 1930–42, -24.2 percent, and was the most negative seasonalpercentage for all base flows, including those for all selectedstreamflow statistics for the five record periods.
Comparison of Base Flows to Streamflow Statistics 581 W78 WEXPLANATIONState boundaryMajor stream03069500Streamflow-gaging stationand identifierPENNSYLVANIAerVal l e y R i vew h a ve 70500heat R i v ervOHIOonoRiv ngahelaer40 Nottie RverTu gorFKENTUCKYk03182500verRi v e RiBi gGu38 Nerivy RG a ulern b r ieR ivaS a n dyRiverwheeKaElknaGr0318350000Base from U.S. Geological Survey 1:100,000 digital line graphics.Universal Transverse Mercator projection, zone 17, NAD 83.Figure 2. Location of selected U.S. Geological Survey streamflow-gaging stations in West Virginia.2020404060 MILES60 KILOMETERS
6 Comparison of Base Flows to Selected Streamflow Statistics Representative of 1930–2002 in West VirginiaTable 1. The streamflow-gaging stations used to compare base flows andselected streamflow statistics in West Virginia.[Records for stations 03214000 and 03214500 were combined and counted as one station]StationnumberStation nameDrainage area,in square miles01606500South Branch Potomac River near Petersburg65101608500South Branch Potomac River near Springfield1,46101611500Cacapon River near Great Cacapon01636500Shenandoah River at Millville03051000Tygart Valley River at Belington40603053500Buckhannon River at Hall27703061500Buffalo Creek at Barrackville11603066000Blackwater River at Davis03069500Cheat River near Parsons72203070500Big Sandy Creek at Rockville20003182500Greenbrier River at Buckeye54003183500Greenbrier River at Alderson1,36403186500Williams River at Dyer03198500Big Coal River at Ashford03214000Tug Fork near Kermit1,18803214500Tug Fork at Kermit1,2806753,04185.9128391Table 2. Average, minimum, and maximum differences between mean annual base flows and selected annual statistics computed for1930–2002, and those computed for the indicated record periods for 15 streamflow-gaging stations in West Virginia.[Modified from Wiley, 2006, tables 2 and 3. Top number in each group is the average difference. Minimum difference followed by maximum difference inparentheses. Station numbers are 01606500, 01608500, 01611500, 01636500, 03051000, 03053500, 03061500, 03066000, 03069500, 03070500, 03182500,03183500, 03186500, 03198500, and combined stations 03214000 and 03214500. A negative value means the average for the indicated record period is lessthan the average for 1930–2002; a positive value means the average for the indicated record period is greater than the average for 1930–2002. USEPA, U.S.Environmental Protection Agency]Streamflow statisticDifference for the indicated period, in 2002Base flow-12.6(-24.6, -4.3)-1.1(-5.8, 2.0)-14.9(-25.8, -4.3)14.6(8.7, 24.5)5.5(1.3, 10.3)1-day 10-year hydrologically based low flow (1Q10)-23.7(-66.7, 4.6)-11.2(-56.3, 16.0)5.4(-31.4, 74.6)187.0(19.9, 524.4)52.3(-6.3, 250.0)7-day 10-year hydrologically based low flow (7Q10)-20.6(-59.0, 12.0)-13.6(-56.2, 14.0)2.4(-29.4, 55.7)182.8(14.0, 582.5)47.7(-3.1, 217.5)30-day 5-year hydrologically based low flow (30Q5)-9.8(-50.6, 11.1)-12.7(-35.4, 6.9)-19.2(-37.2, 3.2)115.1(13.9, 281.2)24.1(-2.1, 97.3)1-day 3-year biologically based low flow (1B3)-36.9(-93.9, 21.2)-10.7(-42.6, 21.4)9.2(-30.0, 75.0)200.7(18.6, 541.9)67.4(-20.6, 367.6)4-day 3-year biologically based low flow (4B3)-32.1(-91.3, 16.8)-13.5(-52.3, 17.2)8.9(-35.1, 66.6)190.3(13.4, 580.0)58.9(-20.0, 305.7)USEPA harmonic mean flow-21.0(-62.3, 17.4)-7.1(-45.4, 16.4)-15.2(-30.1, 30.4)90.7(22.3, 244.3)31.6(3.5, 97.2)
Comparison of Base Flows to Streamflow Statistics 7Table 3. Average differences between base flows and selected seasonal statistics computed for1930–2002, and those computed for the indicated record periods for 15 streamflow-gaging stationsin West Virginia. (Modified from Wiley, 2006, table 4)[Modified from Wiley, 2006, table 4. Winter, January 1–March 31; spring, April 1–June 30; summer, July 1–September 30; fall, October 1–December 31; station numbers are 01606500, 01608500, 01611500, 01636500, 03051000,03053500, 03061500, 03066000, 03069500, 03070500, 03182500, 03183500, 03186500, 03198500, and combinedstations 03214000 and 03214500. A negative value means the average for the indicated record period is less than theaverage for 1930–2002; a positive value means the average for the indicated record period is greater than the averagefor 1930–2002]SeasonDifference for the indicated period, in 200211.01.2Base ll1-day 10-year hydrologically based low flow 86.3167.262.27-day 10-year hydrologically based low flow .410.6140.455.330-day 5-year hydrologically based low flow -16.5104.622.91-day 3-year biologically based low flow 07.772.259.15.14-day 3-year biologically based low flow 4.1U.S. Environmental Protection Agency harmonic-mean 142.541.0
8 Comparison of Base Flows to Selected Streamflow Statistics Representative of 1930–2002 in West VirginiaExamples of Estimating Base FlowsBase flows at streamflow-gaging stations and ungagedlocations can be estimated using the surrogate statistics, whichcan be determined using procedures described by Wiley(2008). Mean annual base flows at ungaged locations can beinterpolated from duration flows determined from previouslygenerated equations when equations for the desired durationflows are not available. Mean seasonal base flows can bedetermined only from flows at the streamflow-gaging stationsbecause only equations for the seasonal 50-percent durationflows are available from Wiley and Atkins (2010a). Base-flowestimates determined using more than one surrogate statisticSeasonBase flow, in percent of mean annual base flowSpringSummerFallWinter150EXPLANATIONBase flowMean seasonalMean monthly100500-50-100Apr. May June July A
2 Comparison of Base Flows to Selected Streamflow Statistics Representative of 1930-2002 in West Virginia variability of base flows at 15 long-term streamflow-gaging stations is discussed. Relations between mean annual and mean seasonal base flows, and between mean annual and 50-percent duration flows, are shown in illustrations. Rela-
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Comparison table descriptions 8 Water bill comparison summary (table 3) 10 Wastewater bill comparison summary (table 4) 11 Combined bill comparison summary (table 5) 12 Water bill comparison – Phoenix Metro chart 13 Water bill comparison – Southwest Region chart 14
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