11. Flood control.-The mountain streams in the basin debouch from their canyons upon extensive debris cones, over which they flow during flood stages in numerous unstable channels. With the occurrence of a major flood these channels are liable to change their location and cause loss of life and damage to property in the foothill communities. This danger is further aggravated by debris flow from the foothills. On the valley floors, and in the Coastal Plain, the tributaries and the main stream ride upon ridges, built up by past debris deposits, and in former times wandered widely. Under present conditions of development such channel changes would damage rich agricultural areas and highly developed communities. 12. Data on flood damages in the basin are meager. The largest flood of record, with a peak discharge of 50,000 second-feet at Santa Ana, occurred in 1916. The damage from this storm, not all chargeable to flood flow, was estimated at about $1,500,000. The damage to public works, mostly highways and bridges, was estimated at about $365,000. The assessed valuation in the area has about trebled since that time and with the recurrence of a similar flood much greater damage would result. 13. Some flood-protection works have been constructed to give partial protection, at the lower ends of Lytle and San Timateo Creeks, at Cucomingo Cone, on the south side of the main stream north of Redlands and on the lower reaches of the Santa Ana River in the Coastal Plain. About $800,000 has been expended by local interests and the State of California for the construction of spreading grounds, which have been partially completed by Civil Conservation Corps and Civil Works Administration labor, on San Antonio, Cucomingo, Deer, Day, Lytle, Devils, Waterman, and Twin Creeks Cones and on the Santa Ana River Cone. 14. There are no problems of navigation or power development. PROPOSED IMPROVEMENTS 15. Flood control and conservation programs have been worked out by local interests and by the State of California. The floodcontrol features of the proposed plan contemplate protection from a flood having a discharge of twice the 1916 flood, the largest flood of record, and the conservation of from 40,000 to 45,000 acre-feet of water that now goes to waste. The works proposed for flood control and conservation in the upper valley and those proposed for the lower basin are largely independent of each other as each project solves a local problem and has a negligible effect on other sections of the stream. 16. The major works proposed consist of large reservoirs in or immediately above lower Santa Ana Canyon and in Brea, Fullerton, Carbon, and Santiago Canyons. Three reservoir sites have been investigated in Santa Ana Canyon and the upper site has been tentatively selected as the most favorable. Debris dams above the canyon mouths and spreading works on the cones are proposed for San Antonio, Cucomingo, Deer, Day, Lytle, Devil, Waterman, Twin, and Mill Creeks and on Santa Ana River. Conservation of about 17,000 acre-feet of rising water annually, which is now lost by transpiration and evaporation along the river from San Bernardino to the lower Santa Ana Narrows, is contemplated by its diversion into a lined conduit from which it could be used directly. Channel improvements are proposed for all the streams to carry the regulated flows across the upper valleys and the Coastal Plain. The proposed improvements in the various sections of the watershed, in the order of merit, and their estimates of cost by the State and local interests, based upon 1929 and 1931 price levels, are as follows: A COMPREHENSIVE PLAN FOR THE IMPROVEMENT AND THE ARID AND SEMIARID SECTION COMMENTS ON THE REPORTS OF THE REGIONAL TECHNICAL ADVISORY SUBCOMMITTEES THE ARID AND SEMIARID SECTION COMMENTS ON THE REPORTS OF THE REGIONAL (Submitted by George O. Sanford, Chief, Engineering Division, Bureau of Reclamation) GENERAL In the western third of the United States where rainfall is insufficient for profitable crop production, the conservation and utilization of the waters of streams is an entirely different problem than that in the humid section. On many of the streams the consumptive use of water in irrigation and to supply the domestic and industrial needs of cities and towns, will absorb the entire flow, and on some streams this limit has already been reached. The importance of long-time planning in the use of streams is far greater in the arid section than in the humid section, because what is done now may vitally affect the development, comfort, and well-being of the inhabitants of this region a century hence. This fact has influenced the selection for development of the six projects in the arid section of the country. These projects are as follows: The interior valley of California, comprising the Sacramento and San Joaquin Basins, has the most acute water shortage of any part of the United States. Disregarding the warnings of engineers and irrigators, the irrigated area of the San Joaquin Valley has been extended far beyond what the available water supply will serve. This is especially true of that section of the basin that is irrigated from wells. Large tracts of citrus orchards and vineyards have been destroyed by 65854-34-25 379 |