OCR Text |
Show nearly $Ul million annually, of which $22 million are agricultural and $19 million are nonagricultural damages. IRRIGATION AND DRAINAGE Irrigation In base year 19&5> there were approximately 1,530,000 acres of land developed for irrigation in the Lower Colorado Region. About 370,000 of these developed acres were out of production because of insufficient water supplies, poor water quality, high pumping costs, and other factors. Of the remaining 1,190,000 acres irrigated, a portion was plagued by simi- lar problems. About 125j000 acres were cropped more than once in 19&5. See map following page k2. Of the 1,315 ?000 acres planted in the Region in 1965, only about 280,000 acres depend entirely on surface waters. About 417,000 acres require supplemental ground water and 6l8,OOO acres depend entirely on a ground-water source of supply. Average annual irrigation withdrawal rates of over 6 acre-feet per acre are common and, in some cases, with- drawals greater than 10 acre-feet per acre are required. Seven crops, accounting for nearly 95 percent of the total harvested acreage under irrigation in the Region in 1965> are shown in the following tabulation: Crop Acreage Alfalfa 208,000 Barley 170,000 Citrus 39,000 Cotton 3^5,000 Pasture 92,000 Sorghum 186,000 Vegetables 75,000 There is a very intense recycling and reuse of irrigation runoff and percolating water which result in increased concentrations of dissolved salts in these waters. Consequently, damaging concentrations of salts are being built up in some soils, especially in the lower elevations of some areas of the Region. Ground-water quality is progressively deteriorating, making it increasingly more difficult to maintain an acceptable salt balance. In 1965, about 7.7 million acre-feet of water were withdrawn for irri- gation use, of which h.7 million acre-feet were pumped from underground sources and 3.0 million acre-feet were diverted from surface sources. 39 |