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

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flow can become a significant component of the totalflow.Estimation of Parameters in Ungaged BasinsOf the many PRMS parameter values requiredfor modeling, only 4 snow-related values, 6 subsurface-and ground-water-reservoir-related values, and 1rainfall-related parameter value had to be specified forungaged basins (table 9). Most of the PRMS parameterswere assigned values in tables related to the HRUdata layer because field and laboratory values could berelated to mapped basin features. Of the 11 parametersthat were optimized, 5 of those could be given a constantregional value for use in modeling in the WillametteRiver Basin. In modeling ungaged basins, fiveof the remaining parameters, RSEP, RESMX, REXP,RCP, and RCB, can be assigned values from thoseobtained in basin calibration based on their proximityto the calibration basin and (or) their similarity inwatershed characteristics. For example, runoff modelsfor ungaged basin tributary inflow in the McKenzieRiver network simulation used the five parameter valuescalibrated in the Mohawk River Basin in the lowerpart of the network and the parameter values fromLookout Creek Basin in the upper part of the network.Parameter values from Lookout Creek could be usedfor parameter estimates for all high elevation HRU’s.Parameter values from Johnson Creek were used forurban HRU’s. Parameter values from the MohawkRiver, and Butte, Rickreall, and Thomas Creeks wereused to represent varying states of agricultural development.The most important correction factor applied,however, was to the daily precipitation correctionfactor for rain (DRCOR), which ranged from 0.50 to2.07 and was applied to ensure that total water volumesbetween simulations and observations matchedwithin +5 percent. The DRCOR values were initiallyset using the ratio of the historical mean annual precipitationfor the precipitation record used as model inputto the mean annual precipitation value for the HRUclass. DRCOR provides adjustment weights toaccount for elevation and orographic differencesbetween the input precipitation record(s) and theHRU. In calibration, the DRCOR values are adjustedupward or downward (as a unit, to preserve the originaldistribution) to optimize the match between thesimulated and observed streamflows (bias in percent,tables 11 and 12). The application of this factor yieldsthe greatest uncertainty in streamflow prediction inungaged basins. For the network-routing models, anadjustment to DRCOR was uniformly applied in allprecipitation-runoff models of ungaged basins inorder to match total volume at the observed calibrationlocation.STREAMFLOW-ROUTING MODELSThe DAFLOW model was selected for use in thisstudy because it allows for the routing of flows overhundreds of river miles with an adequate amount ofspatial discretization and a fast computing time.Description of Diffusion Analogy FlowModelThe DAFLOW model (Jobson, 1989) is a onedimensional,unsteady-state (dynamic) streamflowroutingmodel that solves the energy equation anda simplified version of the momentum equation(acceleration terms of the momentum equation areneglected). The model is designed to be used in conjunctionwith the flow-transport model, BLTM. Themodel can be easily calibrated with time-of-travel dataand requires minimal cross-section data.“One dimensional” refers to flow that is modeledin one plane. In the case of DAFLOW, flow directionis limited to downstream only, because accelerationterms are neglected. Other one-dimensional modelsthat use the complete momentum equation are able tomodel flows in both upstream and downstream directions.One-dimensional models based on theLagrangian reference frame have been found to bevery accurate and stable. Lagrangian refers to a computationalx-coordinate reference frame, where computationsare performed for a parcel of water as itmoves downstream, rather than at a fixed grid location.The simplicity of solving the diffusion analogy in aLagrangian reference frame greatly reduces computationtime.“Unsteady state” or “dynamic” refers to flowcomputations that are made at prescribed time intervals;time-varying input is allowed, and time-varyingoutput is produced. Flood waves (which include evensmall perturbations) are routed downstream by usinginputs of channel geometry and conveyance (abilityof the stream channel to convey flow) to controlattenuation.For many situations, the DAFLOW modelrequires only a starting and ending cross section in ariver reach of 10 to 20 miles to obtain acceptable cali-30
Table 12. Statistical analyses of combined Precipitation-Runoff Modeling System and Diffusion Analogy Flow model calibrationand verification for 11 Willamette River Basin, Oregon, stream-network applications (modeling was done for a daily time step)[--, data not available]_________________________________________________________________________________________________________PercentData-set number 1 Period of record 2 of basin Bias (in percent) 4 Absolute error (in percent) 5Network Observed Simulated Calibration Verification simulated 3 Calibration Verification Calibration Verification_________________________________________________________________________________________________________Clackamas River 1715 1120 1972–75 1976–78 28 2.53 0.26 7.13 7.09Molalla Riverto Canby 8706 8210 1972–75 1976–78 70 -1.28 7.46 16.34 20.69Tualatin River 13720 13050 1972–75 1976–78 82 -.14 .21 16.65 18.73Johnson Creek 6 15720 15050 1989–92 -- 49 .04 .-- 9.43 .--McKenzie River 2720 2050 1972 -- 17 4.68 .-- 8.31 .--Yamhill River -- -- -- -- 35 .-- .-- .-- .--Santiam River 3710 3200 1972–75 1976–78 27 3.62 3.17 7.43 6.51Willamette River—Jasper to Harrisburg 18710 20800 1972–75 1976–78 3 4.57 4.64 7.99 7.43Willamette River—Harrisburg to Albany 710 20400 1972–75 1976–78 21 -1.38 -1.89 5.38 5.30Willamette River—Albany to Salem 17710 20200 1972–75 1976–78 9 -.26 1.50 3.20 3.90Willamette River—Salem toWillamette Falls 7 16710 20600 1972 -- 4 -1.51 .-- 3.32 .--______________________________________________________________________________________________________________________________________________________1 Data set number corresponds to the location of the observed and simulated flow time series in the Water Data Management file.2 All period of records are water years, except for Johnson Creek, which was from May 1, 1989 to August 31, 1992.3 Percent of basin simulated with precipitation-runoff modeling, other part of basin uses observed inflow hydrograph that is routed.4 Bias, as a percent of mean observed runoff, = 100 × Σ e / Σ O5 Absolute error, = 100 × |S - O| / OΣ6 Johnson Creek is part of the Portland Basin.7 Simulations and observations are made at Wilsonville at river mile 38.5.Σbration results. Geometry requirements of the modelinclude a cross-sectional area relative to dischargerelation, and a width relative to discharge relation.Channel roughness is therefore not a required input forthe model. Instead, velocity information from dyetracerstudies made at various discharges are used todefine cross-sectional area relative to discharge relations.These data yield true velocity information forlow-flow situations, so channels that have pool-andrifflemorphology can be adequately quantified.Channel Reach DelineationApproximately 760 miles of stream channelwere defined for the DAFLOW model for this study.At intervals of about every 1 to 3 miles, channelgeometry was described by width and cross-sectionalareaequations. The resulting channel-network descriptioncorresponded to changes in channel geomorphology,stream-gaging-station locations, tributary inflows,and canal outflows. This stream information can befound in Appendix 1. Stream geometry was defined ingeneral for (1) the Willamette River main stem fromRM 187.0 to the mouth (fig. 1); (2) major tributarieswith reservoirs, from the most downstream reservoir tothe mouth; (3) major tributaries without reservoirs,from an existing or discontinued USGS stream-gagingstation to the mouth, and (4) a few important urbanstreams, through the urban areas.Model ParameterizationThe DAFLOW model requires channel input valuesfor effective area, average width, and average wave31
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
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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 32 and 33: tion value of the HRU class by the
Page 34 and 35: Table 8. Selected monthly basinwide
Page 36 and 37: Figure 9. Location of Precipitation
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Page 42 and 43: diffusion at selected grid interval
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Page 46 and 47: 3,0002,500June 21-30, 1993September
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Page 56 and 57: YamhillRiver123˚45´ 30´ 15´123
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Page 72 and 73: 20DYE CONCENTRATION, IN MICROGRAMS
Page 74 and 75: ARC-INFO and Geographic Information
Page 76 and 77: WILL.WDMData-base file(Observed pre
Page 78 and 79: WILL.WDMData-base fileSWSTATSFreque
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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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