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001697 10. Salinity 10.1 General Salinity, or TDS (total dissolved solids), is computed at each point in the system as a concentration in the river, in units of mg/L. (The CRSS assumes mg/L and parts per million are equivalent.) The CIR (concen- tration in the river) can increase, decrease, or remain constant at each point depending on whether salt is being added or removed, whether water is being added or removed, and on the concentration of the inflow or diversion. 10.2 Concentration in the River At an inflow point, the CIR increases if the concentration of the inflow is greater than the CIR. The CIR decreases if the concentration of the inflow is less than the CIR. The concentration of the inflow is com- puted from the natural salt load in the hydrology input data file. At a diversion point, the CIR normally does not change. With the excep- tion of exports, diversions are made at the same concentration as the CIR, which, therefore, does not change the CIR. An export diverts water at the concentration specified in the demand input data file. This allows exports to divert water at a concentration that is less than the CIR if the export is physically diverted farther upstream than the CRSM models. The crR increases if the concentration of the export is less than the CIR. I ~ At a return flow point, the CIR increases if the concentration of the return flow is greater than the CIR. The CIR decreases if the con- centration of the return flow is less than the CIR. The concentration of the return flow is firstly dependent on the quantity of depletion of the diversion. All salt that is diverted is returned in the return flow. The greater the depletion the lesser the return flow and, there- fore, the greater the concentration of the return flow. The con- centration of the return flow is further altered by any salt pickup, which is specified in the demand input data file. A positive salt pickup will increase the concentration of the return flow. A negative salt pickup will decrease the concentration of the return flow. An irrigation project which is leaching salts, for example, will have a positive salt pickup. A water quality improvement project will have a negative salt pickup. At a reservoir, the CIR is the concentration of the release. The CIR increases if the concentration of the reservoir inflow is greater than the concentration of the reservoir. The CrR decreases if the concentra- tion of the reservoir inflow is less than the concentration of the reservoir. The CIR is further altered by the movement of water in and out of bank storage and by evaporation. The evaporation of water is a loss of water with no loss of salt. ~ I. 1 L The salt loading of natural point or natural diffuse sources of salinity are included in the natural salt values in the hydrology input data. These salt loads, therefore, enter the system at CRSS inflow points. 47