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

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made on the main stem at base-flow periods in thespring and in late summer to better define groundwaterflow contributions to streams of the WillametteRiver Basin.Spatial data layers of land use, soils, geology,topography, and precipitation were used to define thebasic computational unit for PRMS—the uniquehydrologic response unit (HRU). The WillametteRiver Basin was partitioned into 21 major tributarybasins, each defining a major tributary inflow to themain stem or an intervening segment between majortributary inflows. The major tributary basins were furtherdivided into 253 subbasins. Each subbasin hadfrom 2 to 12 individual HRU’s, which collectivelynumbered approximately 1,000 basinwide.To obtain the most complete data set for modelcalibration and verification, time-series climate andstreamflow data were assembled for water years 1972–78. This period had the greatest number of operationalstream-gaging stations in the Willamette River Basin.Daily precipitation and air temperature data were compiledfor 52 weather stations, and daily streamflowdata were compiled for 31 streamflow stations. Hourlyhydrographs for 5 major storms for 22 of the streamgaging-stationlocations were also compiled for subsequentuse in storm modeling.A computer program was written to convertspatial-data coverage information into specific PRMSmodel parameter values. Spatial data were input to ageographic information system (GIS) that was used todefine average annual precipitation (and subsequently,to compute a precipitation weighting factor for eachHRU for application to observed data from a specificrain gage location) and physiographic parameters suchas elevation, slope, aspect, soil, vegetation, geology,and total drainage area for each HRU. Tables wereused to cross reference specific physical modelparametervalues related to interception, evapotranspiration,infiltration, and runoff to codes identified in theHRU data layer. For each subbasin or tributary basin,43 parameter values for each HRU were written to afile used by the runoff model.To determine PRMS parameter values forungaged areas, runoff models for 10 unregulatedbasins that have historic streamflow records were calibrated.The PRMS user’s manual (Leavesley and others,1983) should be used with this report documentationto fully understand the precipitation-runoffmodels used in the study. Most model parameters hadvalues that were assigned on the basis of geographicinformation and field and laboratory data; however, 11model parameters were optimized during model calibration.Five of the optimized parameters were givenregionally constant values, but values for five otherparameters describing subsurface and ground-waterflow were obtained by using values from the calibrationbasin having characteristics that best matched thecharacteristics of the ungaged basin. The remainingparameter value was an overall adjustment to rainfallto accommodate the water balance and was applied inaddition to the individual HRU precipitation adjustment.Equations that relate cross-sectional area andwidth to discharge were defined for stream-reachsegments located at approximately 3-mile intervals onthe main stem and all major tributaries of the WillametteRiver. The form of these equations is given inAppendix 1. Time-of-travel measurements definecross sections at low flow, when pools and riffles arethe hydraulic controls. Cross sections measured atstream-gaging-station locations and for flood reports(U.S. Army Corps of Engineers, 1968–1972) definehigh flow conditions when channel roughness is theprimary hydraulic control. Approximately 760 milesof main stem and tributary geometry was described atintervals of about 3 miles (Appendix 1).Streamflow-routing models were constructedusing the Diffusion Analogy Flow model (DAFLOW)(Jobson, 1989) to simulate the different stream networksin the Willamette River Basin. In runningDAFLOW, it was necessary to define inflow hydrographsat the upstream boundary of the network andall tributary and diversion hydrographs at intermediatepoints. Upstream boundary hydrographs were fromexisting stream-gaging-station data, and tributaryhydrographs were from runoff-model simulations oftributary basins. The user’s manual for DAFLOW(Jobson, 1989) should be used in conjunction with thisreport to fully understand the flow-routing system.Eleven network models, each consisting of severalprecipitation-runoff models linked to a streamflowroutingmodel, were constructed and verified.As an example application for water-quality simulation,the Branched Lagrangian Transport Model(BLTM) (Jobson and Schoellhamer, 1987) was calibratedand used to simulate dye concentrations. Dyeconcentration data were from time-of-travel studies.Flow hydrographs used in simulations were fromstreamflow-routing and precipitation-runoff models.4
Study Area DescriptionThe Willamette River Basin (fig. 1) has an areaof approximately 11,500 mi 2 (square miles) and containsthe State’s four largest cities, Portland, Eugene,Salem, and Gresham. About 2 million people, representing69 percent of the State’s population (1990 census),live in the basin. The basin supports an economybased on agriculture, manufacturing, timber, and recreationand contains extensive fish and wildlife habitat.The Willamette River Basin has a temperatemarine climate characterized by dry summers and wetwinters. About 80 percent of the normal precipitationfalls between October and May. Mean annual precipitationranges from about 40 inches in the WillametteValley to 175 inches at crests in the Coast and CascadeRanges (fig. 4). About 35 percent of the precipitationfalls as snow at the 4,000 ft (foot) elevation, and morethan 75 percent falls as snow at 7,000 ft. Because thebasin is largely dominated by maritime air, bothannual and diurnal temperature ranges are relativelysmall. In the Willamette River Basin, the averageannual temperature ranges between 40 o F (degreesFahrenheit) and 65 o F (primarily dependent on elevation),with an average daily minimum of 30 o F in Januaryand an average daily maximum of 80 o F in July atlower elevations in the valley.The basin is bounded on the west by the CoastRange, on the east by the Cascade Range, on the southby the Calapooya Mountains, and on the north by theColumbia River. Elevations range from less than 10 ftabove sea level near the Columbia River to more than10,000 ft in the Cascade Range. The slopes and foothillsof the Cascade Range account for more than50 percent of the basin area. The Willamette Valley,generally considered the part of the basin below 500 ft,is about 30 miles wide and 117 miles long and representsabout 30 percent of the basin area. The mountainsof the Coast Range, reaching elevations of about4,000 ft, make up the remaining 20 percent of thebasin area. About 20 percent of the basin is above4,000 ft, which is considered the lower limit of thetransient snow zone.On the basis of physiography (Fenneman, 1931)and geology (Baldwin, 1981), the Willamette RiverBasin can be divided into three north-south-trendingprovinces: the Cascade Range, the Coast Range, andthe Willamette Valley. The Cascade Range is composedof volcanic rocks, consisting of (1) Tertiarybasaltic and andesitic rocks together with volcanicdebris, primarily in the western part of the range, and(2) Quaternary basaltic and andesitic lava flows, primarilyin the high Cascade Range. The Coast Range iscomposed of Tertiary marine sandstone, shale, andmudstone interbedded with volcanic basalt flows andvolcanic debris. Much of the terrain in the WillametteValley up to an elevation of about 400 ft is covered bysandy to silty terrace deposits that settled from waterponded in a great glaciofluvial lake (Glenn, 1965; Allison,1978). Alluvial deposits that border existing riversand form alluvial fans near river mouths werederived from the surrounding mountains, and theyconsist of intermingled layers of clay, silt, sand, andgravel.The main stem of the Willamette River is formedby the confluence of the Coast and Middle Forks nearEugene and flows 187 miles to the Columbia River.The main stem can be divided into four distinctreaches whose physical characteristics govern thehydraulics of flow. The upper reach extends fromEugene to Albany, river mile (RM) 187 to 119, and ischaracterized by a meandering and braided channelwith many islands and sloughs. The river is shallowand the bed is composed almost entirely of cobblesand gravel which, during the summer, are covered withbiological growth. The middle reach extends fromAlbany to the mouth of the Yamhill River,RM 119 to 55, and is characterized by a meanderingchannel deeply incised into the valley. The river isdeeper and has fewer gravel bars exposed in the summercompared to the upper reach. The Newberg Poolreach extends from RM 55 to Willamette Falls at RM26.5. Hydraulically, the deep, slow-moving pool canbe characterized as a reservoir. The pool is a depositionalarea for small gravel- to silt-sized material.Gravels are regularly mined from the streambed, andabout 6.5 million cubic yards have been removed overthe last 20 years (USACE, Portland District, NavigationSection, written commun., 1992). WillametteFalls is a 50-ft high natural falls; flashboards are usedto control pool elevation during summer low flow. Thetidal reach, from RM 26.5 to the mouth, is affected bytides and, during spring and early summer, by backwaterfrom the Columbia River. The tidal reach was notmodeled in this study.The Willamette River Basin has 11 major reservoirs(fig. 1); their combined usable capacity is nearly1.9 million acre-feet. The reservoirs are designed formultipurpose use, but their primary, legally designatedfunction is the maintenance of a minimum navigable5
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 12 and 13: network-routing models where availa
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
Page 22 and 23: Table 2. Stream-gaging stations use
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
Page 48 and 49: stream network is shown on figure 1
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Page 56 and 57: YamhillRiver123˚45´ 30´ 15´123
Page 58 and 59: 123˚07´30´´ 123˚00´ 45´ 30´
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Page 62 and 63: 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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Precipitation-Runoff and Streamflow-Routing Models for the ...

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