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Description of Existing Model 6 ODIZ33 releaSe '=. (forecast + contents -capacity)/monthsleft forecast is the projected inflow from the current date through July contents is the active Contents of-Ridgway at the beginning of the current month capacity is the active capacity of Ridgway (55,000 acre.feet) monthsleft is the number of months from the current date through July The storage targets are used to insure adequate drawdown pf the reservoir prior to forecasts becoming available. These targets were derived based on discussions with the USBR Salt Lake Regional office; they could not be verified during calibration since there was no historical record of Ridgway op- eration at the time the model was developed. The targets used in the model are as follows: March.July August September October 55,000 52,000 49,000 46,000 November December January February 44,000 41,000 40,000 40,000 Afier estimating the release calIed for by the storage targets, the forecast, or the various demands, the model checks to insure that the minimum release of 30 cfs or inflow (whichever is less) has been satisfied. If it has not, this release or bypass is imposed as the minimum value. Project 7 Water Authority The Project 7 Water Authority obtains water supplies from the Cimarron Canal and from the South Canal. The total Project 7 demand in the model is 10,194 afperyear. Deliveries from the Cimar- ron are limited to the average yield .of shares owned by the City of Montrose. Diversions from th.e UV. WUA's South Canal make up the remaining Project 7 raw water deliveries, with a like amount of water released for irrigation use from the M&I account in Ridgway. Storage of Cimarron Canal and South Canal water in Cerra and Fairview reservoirs is represented in the model; releases from these reservoirs are made on demand. MODEL CAuBRATION The model was calibrated against historical data for the years 1979 through 1983. This period was chosen because the gaged flow and storage records for this period reflect current operations rea. sonably well and because it did not require development of additional inflow data beyond that required for other study purposes. Graphical comparisons and correlations were made between historical gaged streamflows and reservoir contents and those predicted by the modeL Model parameters relating to simulation of operating procedures and to calculation of return flows were adjusted to achieve closer agreement between modeled and historical resultS. The calibration so achieved was quite good. CRITICAL REVIEW OF EXISTING MODEL The criticisms that have been made of the existing model relate mainly to the simplifying as- sumptions that were made to permit its development within a limited study budget or to the purposes to which it was put (the latter really being criticisms of the study rather than the model). The prinCipal simplifying assumptions in the model are the following: I) certain tributary areas of the basin were represented only as net inflows and systems in those areas were not modeled explicitly, 2) most water rights were aggregated and represented as depletions rather than diversions and return flows, 3) the model failed to show some shortages that local water users had been experiencing suggesting that in- flows for certain ungagcd basins should be refined, and 4) no user document or manual was produced to assist others in using the model. Each of these areas is discussed briefly below.