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<br />oj ,..< Ol)123~ <br /> <br />An important feature is the inland Salton Sea into <br />which most of the drainage from Imperial and Coachella Valleys <br />flows. Since the major supply of water available to maintain <br />the level of the lake is irrigation drainage water and since the <br />only water loss from the lake is by evaporation, the mineral <br />quality has degraded over the years to approximately the same <br />degree as the ocean. <br />Seepage losses from the conveyance system serving the <br />Palo Verde area are not really losses at all because the drainage <br />system and underlying valley fill drain percolation water directly <br />to the river. Seepage losses from part of the unlined All- <br />American Canal drain bac~ to the river to help meet the Mexican <br />Water Treaty obligation. The major portion which drains into <br />the Salton Sea is needed for leaching purposes and for maintenance <br />of salt balance and also contributes to the regional economy as <br />a recreation benefit. <br />The 124-mile-long Coachella branch of the All-American <br />Canal is about one-third lined. It appears that appreciable <br />water could be salvaged by lining the remaining portion of the <br />Coachella branch; and plans are under study now to do this, <br />although the economic benefit has yet to be determined. Losses <br />from the unlined All-American Canal compare favorably with those <br />for unlined canals elsewhere. The economic benefit of lining <br />this canal has not been determined. The work of lining these <br />canals poses an expensive problem, since they must be kept in <br />continuous service all year. Conveyance losses within the <br /> <br />-9- <br />