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.,;' (. 2 3. '4. 5. 6. .,7. . DATA REOUIREMENTS FOR MODEL Physical characteristics at the basin .Operational criteria for the reservoirs Virgin water supply Imported water Delivery demands Reservoir evaporation . River water losses by section,s prime recreational seasons that It is virtually ImpossI- ble to maintain fishenes or use the reserVOtrS for recrealtonal purposes. Recrealton pressure on mountain areas during the summer could be partially relieved if 1\ could be shown that. under alternative management. water could be held longer In certain reservOirs while owners of reservoir water would continue to receive their legal water nghts wllhout damage. On the other hand, reservoirs on the plains are under somewhat less pressure for recreation Perhaps some of these could be drawn down belore the high-country reservoirs so that water remained stored longer in some of the high-mountain reser- voirs. Of course. dUllng pSlIods of severe drought the mountain reservoirs would necessarily be exhausted as the situation dictates. Would it be possible from a hydrologic and a legal standpoint to maintain high water levels in . . . the reservoirs through. . . the recreation season? To test the model on a real system where histoncal data are available, a set of SIX high-mountain reser- VOllS under Single ownership was selected. Five 01 these reservoirS. in conjunction With a system 01 plains reservoirs, constitute the water supply system for a major irrigation company Of the live high- mountain reservoirs, two were Judged by recreation specialists as possessing outstanding recreation potential. The question raised lor study was thiS: Would it be possible tram a hydrologic and a legal standpOint to maintain high water levels in one or more of these reservOirs through a greater part ollhe recreation season? Any alteration from traditional operating policy must occur In such a manner that historical water demands are satistied With no Injury to any water- light holders. It also IS desirable to know the Impact 01 any change upon Instream Ilow conditions. Using a three-year test periOd of past record including both a wet year and a dry year, It was found that three of the mountain storage reservoirs could be maintained at relatively high teveis throughout the three-year pellod The model. . . proves that improved recreational conditions on some high-mountain reservoirs could be achieved without injury to water-right owners. The other two reservoirs were drawn down to a greater degree and were essentially empty by the end of the test pellod. These two reservoirs in conjunclton with several plains reservoirs that were drawn upon more heaviiy than had been done hlstoricatly met the total demand. Figures 3, 4, 5, 6 and 7 show both Ihe historic water-levels in the live high-mountain reser- voirs (solid lines) together with the water levels resulting trom modilled operalton of the reservoirs in contunction With plains reservOirS (dotted lines). The model Simulation indicates that improved recreational conditions on some high-mountain reservoirs could be achieved in most years wllllout injury to water-rights owners. However, there are legal issues that must be deatt With before such a ptan of operation could be Implemented. In particular. storing water out of legal priority for certain reservoirs would need to be allowed. The foregOing changes in reservoir operation caused relatively small changes In monthly volumes of flow in the stream system A decrease In monthly Ilow of more than 1 percent was experienced In only two out of 12 months (August, 9 percent. September, 13 percent). Even with these decreases, the stream lIow remained higher during those two monfhs than it 4