WSP01625 - Laserfiche WebLink

Home Browse Search

others for municipal and industrial purposes. The mountain streams in the Upper Colorado River Basin produce high-quality water with total dissolved solids ranging from 30 to 350 mg/L. Water quality in the Colorado River Basin has deteriorated as riverflows have been utilized for man's beneficial use and by return flows from irrigated areas to the Colorado River and its tributaries. Palo Verde Irrigation District unit area contributes about 152,000 tons of salt annually to the Colorado River. Irrigation return flows from irri- gated lands in the Palo Verde subarea of the District contribute an estimated 144,000 tons of this total annually to the Colorado River resulting in an increase of about 18 mg/L at Imperial Dam. The canal systems in the area were not designed for seepage control. Less than 2 miles of the 295 miles of canals and laterals in the District are concrete lined. Side slopes are generally covered with a bermuda-type grass for erosion prevention and weed control which attracts muskrats and gophers whose burrowing causes 10 to 20 canal bank failures each year. While the distribution system has been well maintained, most canals do not have modern diversion structures, measuring devices, or other control structures. The PVID is directly connected to the river system so virtually all inflow comes directly from the Colorado River, with the exception of minor overland runoff caused by rain, and all out-flow returns to the river. Agricul- tural drainage from the District contains salt that is present in the diverted water and salt that is picked up beneath the surface of the District. While some lands require pump lifts to deliver water, most irrigation deliv- eries are by gravity. Water is lost from the distribution system by canal breaks, evaporation, seepage, and operational spills. Operational spills occur as the result of fluctuating demands on the system and time lags up to 12 hours between diversions into the intake facilities and deliveries to farms. Excess water in the canals is spilled directly back to the river or to drainage ditches. Bookman-Edmonston Engineering, Inc., was retained by the Bureau of Reclamation, in 1975, to gather data on irrigation efficiency and agricultural drainage in the PVID. They were to make a preliminary analysis of whether irrigation systems improvements might reduce salt loading of the Colorado River. Using operational data from 1974, Bookman-Edmonston made an independent analysis of irrigation and drainage in the District. It was concluded that the river water diverted by the District contained 945,000 tons of salt, and that measured return flows plus net subsurface outflow to the river contained 1,097,000 tons of salt. The difference of 152,000 tons constituted the net salt discharge from the District. Bookman-Edmonston divided the irrigated flood plain land of the District into seven subareas and made water and salt budget analyses for each. The effect of irrigation on the Palo Verde Mesa was also considered. The subareas are 8 r ,., f' l l:;;;~v4