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2290 cannot oe made. 5. Elevation-Area-Capacity Taole: At each elevation level ~here is an associated surface area and water volume. The elevat~on- area-capacity relation (Figure 2-2) is unique to each reservoir oasin and is used as input to determine evaporation losses and elevation changes during the simulation. 6. Evaporation: Evaporation is computed as the average depth of evaporative loss per month multiplied oy the average monthly water surface area. o . 7. Water Quality: The quality of reservoir inflows are expressed in terms of total dissolved solids (TOS). Evaporation from the reservoir surface tends to concentrate dissolved solids in the reservoir - an important factor for fish and water supply. Ocean water has a total dissolved solids concentration of about 31,000 mg/l (milligrams per liter). Concentration of reservoir water is computed based on a mass balance of solids in accord with the following formula: Cs(t+l) = ( Cs(t)*S(t) + Ci(t)*I(t) ) / ( S(t+1) + R(t) ) where: Cs(t) = storage TOS concentration, beginning of period t. other terms are the same as defined for the storage mass balance. The method assumes complete mixing of inflows coming into the reservoir and does not consider possible chemical reactions and precipitation of salts. If a reservoir dries up, it is assumed that the salts remain, and will redissolve when water is added to the reservoir. 3.2 Reservoir Operations Policies An operations policy is a set of rules which govern the operation of the reservoir system. In GPSIM, an operations policy is defined as a schedule of factors and limits to be applied in a simulation run. Figure 3-1 shows GPSIM's Reservoir Operations Policy Schedule. The factors included in the schedule relate to water management options possible for each component of the mass balance equation - reservoir inflows, releases, and storage volumes. The factors presented in the operations Policy Schedule are summarized. 14