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<br />c:.-> <br />.) <br />N <br />t-"- <br />00 <br />tv <br /> <br />150 <br /> <br />Depletions corresponding to the last three terms in Equation <br /> <br />(5.2) take place within the basin at upstream locations exhibiting <br /> <br />lower dissolved solids concentrations than at the modeled location. <br /> <br />Removal of salts in each case is taken as the water depletion mu1ti- <br /> <br />plied by the average TDS concentration of diverted water for each use. <br /> <br />Water exported from the basin is assumed to have an average concen- <br /> <br />tration of 88 mg1 and water diverted for municipal and industrial <br /> <br />uses is assumed to have a concentration of 331 mgl (Weber et a1., <br /> <br />1971; pp. 13-14). <br /> <br />No return flow of TDS from municipal and industrial depletions <br /> <br />is provided, in accordance with recent policies for maintaining water <br /> <br />quality in the Colorado River Basin (Weber et al., 1975; p. 13). <br /> <br />Removal of TDS by agricultural diversions is made at the same <br /> <br />rate as for municipal depletions. Additional return flows of dissolved <br /> <br />solids from irrigation are estimated as a TDS pick-up per acre of <br /> <br />3 <br />additional irrigated acreage, at the rate of 1.0 ton/acre/yr (2.7*10 <br /> <br />kg/hectare/yr) (USBR, 1971a; p. 35). <br /> <br />5.3 Model Validation <br /> <br />The validation procedure is a method of checking to see if the <br /> <br />terms in the mass balance of water and salt at various points in the <br /> <br />river basin model correspond to mass flows or changes in mass storage <br /> <br />measured or estimated in the actual river basin. In this application, <br /> <br />measured monthly streamflows and estimates of side inflows for a given <br /> <br />historical period are input to each reservoir. Reservoir evaporation <br /> <br />is estimated as a function of storage for each reservoir. Measured <br />