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~'J:.:t.,-__;c,;'::, "-_.,c_>...:._.-.~<~"-,,!<.,,,-,O'}, ,k j'; & t , ,.<, I -V ~~ f-' :~ 1 < J J :~ , I ~j :~~ ..;: " :~' , o ',0 ~ CJ t'::-" .. ~, ....-.', ,r :J oj ,- , ".,[2,."..""",,,",7 "'...'o''_. The area generally north of the Rio Grande River is a closed basin with no return of surface flCM to the Rio Grande River. Large anounts of water diverted into this area gradually percolate to the sump area in the eastern part of the Valley. If this water could retUIn to the river, TIU1Ch of the cJamstream shortages would be eased. 'fue Bureau of Reclamation 's prq:>esed Closed Basin project would perfom this function. Stream charmels through lIUlch of the San Luis Valley are small, not well entrenched, and as a result, crooked. 'fuis results in inadequate capacities for the streamE1CM, poor drainage outlets, and loss of water to phreatoprwtes. (Charmel irrproverrent needs are discussed under study Item 9.) Drainage problems of the San Luis Valley, particularly the closed basin, are discussed in a recent Geological Survey report y. "The depth to water in the valley is less than 12 feet except along the edges and in IlOSt of Costilla ColIDty... A large network of irrigation canals was built in 1880-90 to irrigate lands in the eastern and_ central parts of the closed basin. By 1915 llOSt of the area around M:lsca and Hooper became waterlogged because of this irrigation. Drainage systems ronstructed between 1911 and 1921 to reclaim waterlogged lands alleviated sone of the problems but created waterlogging in areas dcMngradient. Water- logging in other areas is caused by subirrigation because the water table is intentionally raised to the plant root zone. The practice rontinues because it is oonsidered locally to be essential to successful g~ of crops..." "Ground-water withdralllal for recent years (1962-1967) averaged about 1,100,000 acre-feet per year. withdralllal by large capacity irrigation wells was about 800,000 acre- feet per year.. . and withdralllal by small capacity wells tapping the ronfined aoquifer was 300,000 acre-feet per year. In 1967 the unconfined aoquifer acoounted for 71 percent of the ground-water withdrawn fran large capacity wells. A large nurrt>er of small capacity oonfined wells rontinue to flON throughout the year and an estimated 150,000 acre-feet per year might be ronsidered waste because it does not contribute to crop production. In fact it causes additional waterlogging... n "Surface water use has resulted in the waterlogging of a large part of the valley. The valley-fill deposits in the northern part of the valley are filled with water fran the tributaIy watersheds and f:rom the Rio Grande diversions. y See reference 27 6