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<br /> <br />OJ2G71 <br /> <br />. <br /> <br />impossible physical situation. The positive sign indicates com- <br />puted salts would have been carried downstream if flows existed <br />while the negative sign denotes an attempt to remove an exceSS <br />of salt from the river. <br /> <br />. <br /> <br />Inputs specify either the concentration or mass of salts for <br />upstream boundaries. This mass is routed downstream with the <br />output from one element acting as input to the next. At junctions, <br />the salinity outflow is equal to the sum of salt inputs. Only <br />river reaches and reservoirs can contain element inputs to account <br />for imports, exports, and irrigation projects. Treatment of <br />river reaches has already been discussed and attention is now <br />turned to reservoirs. <br /> <br />A number of situations may arise in operating a reservoir. As <br />described below, each situation requires a different method of <br />computing salinities: <br /> <br />. <br /> <br />a. Normal procedure. - When reservoir releases for the month <br />are less than 2S percent of the total water in storage at the <br />beginning of the month (bank plus surface storage) and the <br />reservoir does not go dry during the month, normal procedures <br />are followed. The concentration at the start of the month is <br />used to compute salt removed by releases and exports from the <br />reservoir during the month. At the end of the month, the <br />mass of salts stored in the reservoir is equal to the algebraic <br />sum of the starting mass, export salts, downstream release <br />salts, and the net effect of import/export and irrigation <br />inputs. If the mass is negative, it indicates an attempt to <br />remove more salt than exists. The salt content is set to <br />zero and the negative value retained as a delta salt. A linear <br />mix of all salts is assumed, resulting in a uniform concen- <br />tration of salts throughout the surface and bank storage volumes. <br /> <br />b. Excessive releases. - When reservoir releases for the month <br />are equal to or greater than 2S percent of the total water <br />in storage at the beginning of the month and the reservoir does <br />not go dry during the month, use of the initial concentration <br />may be inappropriate. In particular, as the releases approach <br />100 percent of the initial content, outflow concentrations <br />would be expected to show some effect of the inflows. To <br />include the weight of present inflows, concentrations for <br />exports and releases are based on a linear mix of the starting <br />salt mass and volume with the inflow of salt and water. At <br />the end of the month the reservoir salinity is updated and <br />checked as it is under normal procedures. <br /> <br />. <br /> <br />3-8 <br /> <br />