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Show Although many data are available to guide water- shed management programs, additional information is needed to meet special problems. For example, more information is needed about the best rota- tion and tillage practices to conserve crop residues and reduce runoff and erosion on the dry-farm grain lands of the basin. Investigations of forest influences have been con- ducted on only a few of the combinations of climate, topography, and soil in the basin. These studies need to be extended and reinforced by studies of the effects of timber cutting and grazing on water re- sources. Studies also are needed to determine the best methods of converting brush lands to grazing. Basic information on fish and wildlife has been collected for a number of years by both State and Federal agencies, but much remains to be learned, particularly on such subjects as the life cycle of the salmon, and the possibilities of maintaining fish life in fluctuating reservoirs. If fish and wildlife are to be preserved, more information is needed. Conclusions Basic data are more adequate in the Central Valley than in many other basins of the country. However, present programs for collection and inter- pretation can be profitably increased, so as to meet the needs of future stages of development. Basic data on the extent of the underground storage available for irrigation and other uses are needed for planning extensions to the irrigation system, and replenishing the supply. Data should include the area and depth of the var- ious sub-basins for underground storage and their boundaries, the quality of water of each, the move- ment of water in them, as well as the location and depth of any subsurface control. Among the other data worthy of particular attention in this basin are those relating to methods of applying irrigation water, and economic data indicating needed water resources program adjustments to social and eco- nomic trends. Of prime importance in the Central Valley is more definite information on the loss of water through evaporation from various water surfaces- reservoirs, canals, and laterals. Such information is necessary for a sound approach to all problems of conserving the water. Also involved is the amount of transpiration from riparian water-consuming vegetation. These data are of critical concern in the valley. 2. The Proper Rate for Future Construction of Fa- cilities To Provide Water for Supplemental Irrigation, and New Land Development The Problem Factors to be considered in planning the rate of development of additional Federal irrigation works. The Situation There are important regional considerations in- volved in arriving at a desirable rate for irrigation developments in the Central Valley Basin. Agricul- ture in the basin is of an intensive character, is highly developed, and represents a very large capital investment. Because rainfall is limited, irrigation is the primary foundation of the agriculture of the valley. This foundation must be protected not only to sustain agriculture, but also because agriculture is the most important element in the economy of the region. To the extent that it is dependent on dimin- ishing supplies of ground water, the present agri- culture of the basin is in jeopardy. This dependence on ground water is extensive, particularly in the San Joaquin Valley, and supplemental supplies of surface water are a necessity. The regional situation justifies immediate de- velopments to provide additional quantities of water to relieve the pressure on ground water sup- plies, to make more efficient use of the land resources already developed, and thus to protect the agricul- tural economy of the basin. The need for bringing additional land under ir- rigation is less pressing than is the need for supple- mental water. There is a large demand for farms and farming opportunities which will need to be met, to the extent feasible, in the years ahead. This demand is more intense in or near the Central Valley than in most other parts of the country. The Cen- tral Valley supplies large quantities of specialty crops (fruits and vegetables) to other regions. Moreover, California is deficient in dairy and meat products, and any further expansion of the dairy and livestock industries within the region will be dependent on irrigation. The rate of additional irrigation development should not be based on agricultural considerations alone. Consideration should also be given to the fact that other uses for the water might result in greater benefits. 131 |