WSP05700 - Laserfiche WebLink

Home Browse Search

"I 1. PHYSICAL'CO~~ITIONS The delta of the Colorado Rivcrextends across thc long structural trough that contains the Gulf of California and the Sal ton Sea, l"hich is more than 230 feet belO1" mean sea level (Pigure A-l). The delta lias gradually risen to about 40 feet above mean sea level (msl) forming a divide l>llich prevents waters of the gulf from reaching the Salton Sea basin. Levees along the north side of the river and the numerous storage reservoirs in the Colorado River basin nOlI' prevent any uncontrolled Colorado River water to flow into the Salton Sea basin. A large part of the delta and other areas in the Salton Sea basin are irrigable by gravity diversion from the river. Drainage watcrs in the Salton Sea basin flol" into the Salton Sea and are dissi- pated by evaporation. Imperial Valley, the area between the Salton Sea and inter- national boundary, consists of a central part underlain by fine sediments and a terrace at each side (East and Vest Hesa) under- lain by coarser sediments. The central part includes nearly half a million acres of irrigated land, the principal cities of El Centro and Brawley, and seve'ral smaller towns. Tho area south of the international boundary is generally kn01ffi as 1-te:?;:i cal i VaU_~y-._Tlle_c,i.ty_o.LHexi,cali_i s_the-pJ.:incipal-city_of Baja California. About half a million acres are irrigated ldth water from the Colorado River or from groundlmter reservoirs that are recharged either by irrigation water or by seepage from thc river canals. The initial ora of irrigation development from 1900-193~ was charaeterizod by a wide fluctuation of the lower Colorado River flO1-r, from disastrously high peal_ fl01l's during flood seasons to insufficient flO1, during dry seasons in tho YUlUa area. Prior to completion of Hoovor D"tn and thc All-American Canal, there ,,'ore constant opcration and irrigation difficulties due to recurring floods and peri,ods of tlrought. The extremes of these concU tiOllS \ ! -I I , I I !