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Show The Situation Two studies have been made of the possible an- nual net use of water in the Central Valley: one by the State, included in the report on the State Water Plan; the other by the Bureau of Reclamation, presented in its report.19 They are abstracted as follows: the estimated ultimate Central Valley demands in the following manner: 20 Type of use Bureau of Reclamation State Irrigation. _................ Domestic, industrial, and miscellaneous uses............ Salinity control............. Export to S an Francisco Bay. . Acre-feet 16, 600, 000 550, 000 2, 400, 000 450, 000 Acre-feet 19,287,000 2, 390, 000 1, 075, 000 Total i................ 20, 000, 000 22, 752, 000 1 Totals do not include evaporation losses. The average annual runoff into the Central Val- ley Basin over the 40-year period 1904-43 was 33 million acre-feet. However, not all of this water can be conserved for beneficial purposes. Much of it occurs ixi occasional years of extremely large flow. It would 3iot be possible to provide sufficient stor- age capacity in the Central Valley, either surface or ground water storage, to hold over all of these large flows from wet periods to dry periods. The critical water supply period in the Central Valley was the 7-year pe*iod 1927-34, in which the average an- nual runoff was 18.4 million acre-feet. Rainfall data indicate this to be the driest period during the 100 years for which records are available. Most water sup*ply studies for the basin as a whole are predicated on meeting the assumed demands during a period smich as 1927-34, although in certain areas, other base periods are used. The Biareau of Reclamation on the one hand, and the State engineer on the other, propose to meet Annual averages in acre-feet Bureau of Reclamation* State of California > Estimated available supply Natural runoff.............. Draft from carry-over storage (surface and underground). . Trinity River importation..... 18, 400, 000 2, 400, 000 700, 000 20, 900, 000 2, 274, 000 700, 000 Total................. 21, 500, 000 23, 874, 000 Estimated use and losses Net use of water............. Evaporation losses........... Unavoidable waste to the ocean.................... 20, 000, 000 900, 000 600, 000 22, 752, 000 1,122, 000 Total................. 21, 500, 000 23, 874, 000 *Data from the Bureau of Reclamation are for 1927- 1934. The period covered by the State is not known. See discussion of California State Engineer in S. Doc. 113, 81st Cong., 1st sess. The foregoing figures would indicate that the ultimate demands of the Central Valley could be met with the available supply in the basin, plus the importation of 700,000 acre-feet. However, events and additional data gathered during the past few years suggest that the estimates of ultimate wa- ter needs presented above may be low. It now appears that more water will be required in the San Francisco Bay area than previously estimated,21 and the additional water will have to be obtained from either the Central Valley or the north coastal streams of California. Technical studies reveal that the requirement for outflow for salinity control also will be significantly greater. During recent years there has been suc- cessful development of irrigation on lands which previously were considered uneconomical for irri- 19 S. Doc. 113, 81st Cong., 1st sess. (1949). S. Doc. 113,81st Cong., 1st sess., pp. 326, 329. Particularly in the Bureau of Reclamation estimates. 140 |
