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1 ~` ~~ F-"" by either a minimum release rate, a flood space storage requirement, demands which draw from the reservoir, demands which draw from upstream reservoirs and move water through the reservoir, or the "Laws of the River." The operations of Lakes Powell and Mead are large- ly determined by the criteria and constraints relating to the "Laws of the River." All calcula- tions for reservoir operations aze based on another form of the continuity equation: Change in storage =Inflow -Outflow - Evaporation -Change in bank storage Evaporation, bank storage, and power produc- tion are calculated ea:h time water is moved through a reservoir. Evaporation is determined by a monthly coefficient and the surface area of the lake that month. Change in bank storage is calculates as a percentage of the change in surface storage each month. -This percentage ranges from 6.5 percent in Lake Mead to 15 percent in Lake Powell.. After the entire system is in hydrologic balance, salinities aze computed throughout the system by a mass balance accounting procedure. Initial salinities are read in from the hydrology file. Salt pickup or removal is read in from the de- mand file. The impact of the salt pickup or re- moval is brought into the river by the return flow of an associated diversion. To route salt through a reservoir, complete mixing is assumed. This approach, in a simpli- fied form, was verified by Dr. John Hendrick in his Ph.D. dissertation (1973), Colorado State University, as applicable to Lake Mead on a monthly basis. The concentration of salt in the outflow is assumed equal to a weighted average. of the beginning and ending concentra- tions of the salt in the reservoir. Operational Control Data Operational control data are input to the CRSM and include: reach identification and basin configuration; reach description data (location and identification of diversions, return flows, inflows, and reservoirs); reservoir and powerplant characteristics data; data con- trolling output options- and various run param- eters (i.e., starting and ending dates, etc.); and miscellaneous data which control the opera- tions and conditions specific to the Colorado River Basin. Reservoir operational characteristics data are entered in the form of polynomial equations for the following: 1. Reservoir elevation-area-capacity relationships 2. Turbine horsepower output at full gate versus head 3. Discharge versus head 4. Tailwater elevation versus flow Polynomials for the reservoir elevation-azea- capacity curves are selected to reproduce the tables used in the operations of the reservoirs. Manufacturer's rating curves are used for the power output of the powerplants. Other reser- voir operation data contained in the control file are listed below: 1. Tazget capacities for each month - rule curves 2. Bank storage coefficients 9