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PRESENTATION BY LARRY D. STEPHENS Reservoir Operation Studies The purpose of this report is to explain the project reservoir operations. The reservoir operation studies were made to show conditions at two time levels with two or three alternates. The two levels are adjusted historic and 1990, and the alternates for adjusted historic are with and without replacement. For the 1990 time level studies, we have "with" and "without replacement" with Two Forks, and "with replacement" and " with added tributary facilities." The reservoir supply consists of historically unused river flows inclUding return flows, inundated land water supply generation, and evaporation and seepage loss savings through offstream reservoir replacement. The storable flow at the project reservoir is the minimum flow not diverted historically or used in the without project routing study. Water supply generation from inundated lands is the consumptive use of historically irrigated lands only. It was assumed that the ' canal and farm losses returned to the river and were reused histori- cally; therefore, they were not included in the reservoir water supply. Water supply generation from reservoir replacement: In the adjusted historic study the water supply generated from reservoir replacement WaS the historic evaporation of the replaced offstream reservoirs. !J:'he 1990 study savings from reservoir replacement includes the additional evaporation and seepage loss savings on the 1990 increased diversion to offstream replaced reservoirs. During the 1952 through 1957 study period there was a great deal of unused existing reservoir capacity. It Was estimated that Riverside, Empire and Bijou Reservoirs could more fully utilize approximately 36,000 acre-feet annuslly in 1990. Of this 36,000 acre-feet diversion only 14,000 acre-feet were released from Riverside, Empire and Bijou storage. If these reservoirs are abandoned in the future, the 22,000 acre-feet lost could be stored in Weld Oounty and is an additional supply for the project. Only 500 acre-feet annually is realized by the transfer of Jackson Lake 'into Narrows Reservoir. With Narrows Reservoir, however, the reservoir seepage losses from Riverside, Empire and Bijou would accrue as new project water. Therefore, of the 30,000 acre-feet realized by Weld Oounty through reservoir replacement (8,000 acre-feet of which is evaporation savings on historically stored water and the 22,000 acre-feet mentioned above) about 15,000 is of benefit to Narrows too. See Exhibit 11 for the supply generated by each project reservoir. 35 ,