Precipitation-Runoff and Streamflow-Routing Models for the ...

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network-routing models where available, andsimulated streamflows from runoff model resultswere used for ungaged areas. Absolute error forthe network-routing models ranged from about 21percent for the Molalla River model, for which 70percent of the subbasin was ungaged, to about 4percent for the Willamette main-stem model(Albany to Salem), for which only 9 percent ofthe subbasin was ungaged.With an input of current streamflow,precipitation, and air temperature data thecombined runoff and routing models can providecurrent estimates of streamflow at almost 500locations on the main stem and major tributariesof the Willamette River with a high degree ofaccuracy. Relative contributions of surface runoff,subsurface flow, and ground-water flow can beassessed for 1 to 10 HRU classes in each of 253subbasins identified for precipitation-runoffmodeling. Model outputs were used with a waterqualitymodel to simulate the movement of dye inthe Pudding River as an example application inthe Willamette River Basin.INTRODUCTIONIn 1991, the U.S. Geological Survey (USGS)began a cooperative program with the Oregon Departmentof Environmental Quality (ODEQ) to studywater quality in the main stem and major tributaries ofthe Willamette River. The program was part of a largerstudy that included participation by ODEQ, USGS, aprivate consultant, and Oregon State University. Thelarger ODEQ study (Tetra Tech, Inc., 1993) isintended to provide information on dissolved oxygen,nutrients, algae, toxics, bacteria, point and nonpointpollution sources, sediments, river ecology, and riverflow. The information from the ODEQ study, in turn,will provide a foundation for future long-term workand management decisions on water-quality issues inthe basin.The USGS cooperative program with ODEQconsisted of three parts: (1) a streamflow simulationusing precipitation-runoff and streamflow-routingmodels, (2) an analysis of sediment transport (Laenen,1995), and (3) a reconnaissance-level determination ofcontaminants. This report describes the developmentof models for streamflow simulation. The existingmodels have not been fully calibrated for use in waterqualityassessment; however, they can be used to supplythe required hydrologic inputs for future waterqualitymodeling.The USGS program was also designed to complementthe USGS Willamette National Water-QualityAssessment (NAWQA) study that began in fiscal year1993. The Willamette Basin is one of 60 basins in theNation that will be studied by NAWQA. NAWQA isdesigned to describe the status of and trends in theNation’s ground- and surface-water resources and toprovide a sound understanding of the natural andhuman factors that affect the quality of these resources.The NAWQA intends to integrate information at differentspatial scales—local, study unit, regional, andnational—and will focus on water-quality conditionsthat affect large areas or are recurrent on the localscale.BackgroundA large quantity of streamflow data is availablefor the Willamette River Basin, and two previouslydeveloped streamflow-simulation models are regularlyused to simulate flows in the basin. Most streamflowrouting in the basin has been done by the NationalWeather Service (NWS) and the U.S. Army Corps ofEngineers (USACE). The NWS uses the StreamflowSynthesis and Reservoir Regulation (SSARR) model(U.S. Army Corps of Engineers, 1975) for flood predictionpurposes. The USACE primarily uses HydrologicEngineering Center—Fifth Model (HEC–5)(U.S. Army Corps of Engineers, 1982) for throughreservoirstreamflow routing and testing.The existing models are intended for flood routingand are satisfactory for this purpose, but they areless satisfactory for water-quality applications. Theexisting models do not adequately define the complexhydrology of the basin or identify effects of humanactivities other than reservoir regulation, do not havehydraulic-flow equations, they do not link precipitationrunoff to physical properties in the basin, and have notbeen calibrated to low-streamflow conditions becauselow-flow data are missing for critical locations.Current SSARR and HEC models provide veryusable high-flow simulations but cannot provide a conceptualunderstanding of the physical flow system. Theprecipitation-runoff component of the SSARR modelsimulates the streamflow response to precipitation bymeans of simple equations that represent surface flow2
y using hypothetical reservoirs that do not accountfor surface topology and represent subsurface andground-water flow by using hypothetical reservoirsthat do not account for soil infiltration. These equationsare empirically fit to observed peak flows. Flowsources can be empirically simulated by the equations,but the equations do not adequately represent thephysical environment. For example, soil characteristicschange due to freezing or extreme drying conditions,and the hydrologic response varies markedly.Models based entirely on empirical fitting require differentcalibrations for different soil conditions. Thus,the precipitation-runoff component of the SSARRmodel cannot simulate variations of hydrologicresponse in a basin and, for most situations, cannot beused to predict changes in hydrology caused by eithernatural or anthropogenic changes. Stream and reservoirrouting in the currently calibrated SSARR andHEC models is done by Muskingum (McCarthy, 1938)or other storage-routing techniques, which treat a riversegment as a reservoir (using inflow and outflow relations);this technique limits the model’s capability torelate streamflow to physical changes of the channel.Routing of sediment and contaminant fluxes cannot beaccomplished by this simplified streamflow-routingscheme, because particle transport is not described bya physically based model component such as watervelocity.The Precipitation-Runoff Modeling System(PRMS) (Leavesley and others, 1983) was used in thestudy for simulation of runoff, and the Diffusion AnalogyFLOW model (DAFLOW) (Jobson, 1980) wasused for in-channel streamflow routing. In contrast tothe precipitation-runoff component of SSARR, aphysical-process model such as PRMS can be usedto answer questions regarding the physical effects ofhuman activities on basin hydrology. In contrast tothe streamflow-routing component of SSARR andHEC–5, DAFLOW can be used to determine localvelocity information and to simulate both the attenuationof a flood wave and the dispersion of a waterqualityconstituent needed to describe transport forwater-quality models.Purpose and ScopeThe purpose of this study was to construct flowrouting(routing) models capable of driving a waterqualitytransport model for the Willamette River Basinand to construct precipitation-runoff (runoff) modelsbased on physical properties of the basin that wouldsimulate runoff from ungaged areas and would becapable of helping assess natural and anthropogenicprocesses that affect streamflow and stream waterquality. As part of the overall purpose, this report(1) describes the construction and verification of therunoff and routing models specifically developed as aprecursor for water-quality modeling, (2) presents anexample of model use in a water-quality application,and (3) provides a guide to creating and using files formodeling.This study was the beginning of a larger effort tobuild a comprehensive understanding of water qualityin the Willamette River Basin. The study was designedto be open-ended, providing only the hydrologyneeded to drive a water-quality model. No work wasdone to collect data from or to model the 26.5-milestidal reach of the Willamette River from WillametteFalls to the mouth, although tributary streams to thisreach of the river were modeled.ApproachStudy elements were as follows: (1) collection ofdata to supplement existing low streamflow information,(2) assembly of spatial data defining hydrologicresponse units for runoff models, (3) assembly oftime-series climate and streamflow data to calibrateand verify the model parameter values, (4) definitionof uncalibrated runoff-model parameters from digitalspatial data layers, (5) calibration of other parametervalues using data from unregulated basins—the resultingvalues to be used for flow simulation in ungagedbasins, (6) development of stream channel crosssectional-areaand width relations from time-of-travelmeasurements and other flow information, (7) divisionof the Willamette River Basin into 21 major basins andcorresponding stream-routing networks, (8) constructionand verification of selected routing-network models,and (9) application of a water-quality model usingoutput from one of the networks.The following low streamflow data were collectedto determine spatial and temporal hydraulicproperties and their relation to the stream system: (1)time-of-travel measurements, made by using dyetracingtechniques on seven tributary reaches of theWillamette River previously unmeasured by Harris(1968) and on the main stem of the Willamette Riverbetween Harrisburg and Peoria to verify the work ofHarris, and (2) gain-loss (seepage) measurements,3
Page 1: Precipitation-Runoff and Streamflow
Page 4 and 5: U.S. DEPARTMENT OF THE INTERIORBRUC
Page 6 and 7: Determining Travel Time and Dilutio
Page 8 and 9: 2. Stream-gaging stations used to c
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Page 14 and 15: made on the main stem at base-flow
Page 16 and 17: Figure 1. Willamette River Basin, O
Page 18 and 19: EvapotranspirationINPUTSAirtemperat
Page 20 and 21: Table 1. Climate stations used to c
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Page 24 and 25: Figure 4. Mean annual precipitation
Page 26 and 27: Major Land Use MapHydrologic Soil G
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Page 34 and 35: Table 8. Selected monthly basinwide
Page 36 and 37: Figure 9. Location of Precipitation
Page 38 and 39: Table 11. Statistical analyses of P
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Page 46 and 47: 3,0002,500June 21-30, 1993September
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44˚15´14166000122˚07´30´´Will
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122˚15´ 122˚00´121˚52´30´´4
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44˚52´30´´45´122˚15´ 122˚00
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observed flow at the Willamette Riv
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DAFLOW model, and peak amplitude is
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20DYE CONCENTRATION, IN MICROGRAMS
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ARC-INFO and Geographic Information
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WILL.WDMData-base file(Observed pre
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WILL.WDMData-base fileSWSTATSFreque
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Jobson, H.E., 1980, Comment on A ne
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APPENDIX 1. STREAM GEOMETRY FOR MAI
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APPENDIX 2. ARC MACRO LANGUAGE (AML
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APPENDIX 3. DEFINITIONS OF PARAMETE
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APPENDIX 3. DEFINITIONS OF PARAMETE
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APPENDIX 4. MEASUREMENTS USED TO DE
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APPENDIX 5. EXAMPLE PRECIPITATION-R
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APPENDIX 5. EXAMPLE PRECIPITATION-R
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APPENDIX 6. DIFFUSION ANALOGY FLOW
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APPENDIX 7. PROGRAMMING STEPS TO IN
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APPENDIX 8. PROGRAMMING STEPS TO DE
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150Climatemaxtempmintempprecipitati
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APPENDIX 10. DIRECTORY TREE AND DES
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APPENDIX 11. DIRECTORY TREES AND DE
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APPENDIX 11. DIRECTORY TREES AND DE
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APPENDIX 12. DIRECTORY FOR will.wdm
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APPENDIX 13. PROGRAMMING STEPS FOR
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APPENDIX 14. INPUT FILES FOR BRANCH
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