| OCR Text |
Show added roads to open new areas, provision for con- centrating use, providing sanitary facilities, and adoption of various other measures to safeguard scenic and other public values. Recreation should also be provided in greater degree at reservoirs. Legislation is needed that would grant to the Bureau of Reclamation the authority to include recreation facilities in reservoir construction without special authorization. Such facilities should be planned so as to obtain maxi- mum benefit from the site, and the cost should not be repaid by irrigation water users or other non- recreational beneficiaries. Reservoirs in mountain areas should be so planned as to permit operation in a fashion that "would enhance rather than diminish recreation values. Adequate lands should be acquired at reservoir sites to meet public recreation needs. Beaver should be encouraged because of its recreational value and its value for fur as well as for its beneficial effect to sediment control and water regulation. Mining laws should be modified so as to prevent the loss of public recreation resources. 8. Effects on Available Water of Evaporation from Reservoir Surfaces The Problem Minimizing losses from evaporation insofar as consistent with beneficial uses. The Situation Evaporation from present reservoirs in the lower basin as estimated by the Bureau of Reclamation may amount to as much as 770,000 acre-feet a year.66 This is 10 percent of the flow of the river allotted to the lower basin States by the Colorado River Compact, or about one-sixth of the amount covered by the California Limitation Act6T on that State's share of the waters apportioned by the com- pact. Other estimates of evaporation from the same reservoir surfaces are even higher, amounting to 900,000 acre-feet a year or more. However, adequate information on the exact extent of these losses is lacking, in part because of the difficulty of measuring evaporation accurately. "Department of the Interior, The Colorado River (1947), H. Doc. 419, 80th Gong., 1st sess., p. 14. "Act of March 4, 1929, Ch. 16, 48th sess. Statutes and amendments to the Code, pp. 38-39 (1929). As additional reservoirs are built in the basin, evaporation will increase correspondingly. The Bureau of Reclamation estimated in 1946 that with all of 134 suggested potential projects in operation, evaporation losses would be 1.7 million acre-feet,68 or a little more than 11 percent of waters appor- tioned by the compact. While the Bureau of Rec- lamation estimate represents careful study, it is possible that it may be conservative. Reduction in rates of evaporation can be achieved by reducing reservoir surface through location in narrow and deep canyons, and by choosing higher and cooler sites. Storage of water underground, where possible, also will assist in reducing such losses. Conclusions (1) Effort should be made to determine as ac- curately as possible the potential evaporation losses under different combinations of projects in a full program for the basin. Such information should be given fully when programs are presented for authorization. (2) Where compatible with the most beneficial combination of water uses, water should be stored underground. 9. Water-Consuming Weeds The Problem Effect of water-consuming weeds on water supply, and means of their eradication. The Situation Weed vegetation growing in the stream courses of the basin wastes great quantities of water. Oc- cupying riparian areas underlain by shallow water tables, the willows, cottonwood, and salt cedar ex- tract on an areal basis as much as 6 acre-feet of water a year. In addition to wasting water, this vegetation creates flood hazards by choking chan- nels. Outside river bottoms, on semiarid uplands, steady invasion on overgrazed lands by mesquite, juniper, cactus, cheat-grass, foxtail, and other types of undesirable vegetation is also affecting water sup- plies, although not as directly as riparian vegetation. The total amount of water consumed by the valley-bottom vegetation has been variously esti- mated from 20 to 25 million acre-feet69 of water a ' Department of the Interior, op. cit., p. 14. ' U. S. Geological Survey, January 1950. 439 |
