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Show gation. The extent to which these factors might increase the ultimate water requirements of the basin is difficult to foresee, but the total increase might amount to several million acre-feet of water annually. Should these larger demands materialize, there are several possibilities for obtaining the additional water. One method would be to make further use of the water within the Central Valley itself. Ad- ditional water would be available for conservation; however, since the previous estimates assumed all of the runoff during the 1927-34 period would be utilized, the only way to conserve additional water would be to provide additional storage and to carry the water from preceding wet years into the critical dry period. For a 7-year carry-over, it would take 7 acre-feet of additional storage capacity to obtain 1 acre-foot of additional yield. If large amounts of additional storage capacity were provided, the carry-over period might be extended to 12 or 17 years, which would require even greater amounts of storage capacity per acre-foot of yield. This storage might be obtained either by construction of additional surface reservoirs or by further use of ground water capacity. Either method would be quite costly and would be increasingly expensive as additional storage was provided. Another method of conserving water would be to construct a barrier across the northern end of the San Francisco Bay. This would prevent salt water intrusion into the delta area, and thereby reduce the required outflow of fresh water for salinity con- trol. This possibility has received much attention during the past 30 years. It was rejected as not being an economically feasible alternative for the salinity control outflows now being provided. The potentialities of water conservation by means of the salt water barrier depend on a number of factors. For example, it is certain that even with such a barrier, some fresh water releases would have to be made into San Francisco Bay to provide for the pas- sage of ships, to pass fish, and to permit outflows of saline irrigation return water. Furthermore, such a barrier would create a fresh-water lake, the evap- oration from which would be large. Thus the feas- ibility of a salt water barrier depends on comparing the cost of the barrier with the net amount of water which could be saved. A third possibility of additional water is through importations of surplus supplies from adjacent basins. The north coastal streams of California are the nearest and most likely source of such water. They include principally the Klamath, Trinity, Eel, and Russian Rivers. The runoff of the first three of these rivers, and to a lesser extent of the Rus- sian River, is far greater than the ultimate water needs within the basins for domestic, industrial, and irrigation purposes. However, these rivers are quite valuable for their fishery and recreational resources, and diversions would reduce their power potentialities. A diversion from the upper Trinity River was included in the California State Water Plan and also the Bureau of Reclamation's plan for the Cen- tral Valley. The California Legislature recently removed the Trinity Diversion from the State Water Plan. Other interests within the basin have at- tempted to restore it to the State Water Plan but so far have been unsuccessful. Under present tentative plans of the Bureau of Reclamation, approximately 700,000 acre-feet an- nually would be diverted from the upper Trinity River into the Central Valley Basin, in addition to which 120,000 acre-feet would be released down the channel of the Trinity River for fish, recreation, and other purposes. This downstream release, to- gether with the large tributary inflows below the diversion point, is considered by the Bureau of Reclamation to be more than sufficient to meet all conceivable ultimate demands in the Trinity River Basin. The Trinity Diversion is being considered by the Bureau because it offers a relatively inex- pensive source of both water and power. Another possible interbasin diversion is from the Russian River. Estimates by the Corps of Engineers indicate that 86,000 acre-feet over and above the needs of the Russian River Basin could be diverted to the northern San Francisco Bay area for irrigation and municipal and industrial de- mands. Such a diversion would reduce the re- quired diversions from Central Valley to the San Francisco Bay area. A number of other plans for diversion from the Klamath, lower Trinity, and Eel Rivers into the Central Valley or to the San Francisco Bay area have been considered by various agencies over a period of many years. The extent to which these might be undertaken is difficult to forecast. On the Klamath River, below the mouth of the Shasta 141 |