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4. revealed ciencies Land classification surveys have a sizable area with drainage defi- which might be reclaimed. As return flows develop from the Colcrado- Big Thompson Project and as other transmountain diversion systems begin operation or increase their diversions, a reservoir below the area of N first use of the imported waters will becon:e W o increasingly important. A part of the return .... flows will occur during the irrigation season and be subject to use by holders of water rights. The remaining portion of the return flovs 'Jill occur in the winter or at times \/hen they cannot be used or stored by existing systems_ ~his water, which would otherwise remain unused, could De stored in Narrows. ,'. 5. A conservancy district was recently formed which encompasses land in counties around and to the north and east of Denver. The expressed purpose of the district is to supplement the 'Jater supply for irrigation and municipal uses by importations from the Colorado River Basin. Almost any combination of the preceding developments would have some effect on the water supply, design, or operation of the Narrows Unit. Additional st~dies would be required to evaluate the possible effects and to adjust the plan accordir.gly. POTENTIALITIES OF THE NARROWS UNIT Through the conservation of flood flmlS and otherwise unused waters, Narrows Reservoir could supplement the irrigation supplies for some 200,000 acres of land currently irrigated in the South Platte Valley. In addition, throug!1 exchange procedures it might be possible to pro- vide irrigation ,mter to users upstream from the Narrows Reservoir site. The reservoir would pro- vide substantial flood control benefits to the downstream valley' and important fish-wildlife and recreation benefits. .~.: A large onstream reservoir is needed on the South Platte River, preferably at the Narrows site, to utilize effectively all natural and imported waters. Under present conditions, large quantities of water pass the state line during high runoff years. An estimated 810,000 acre- feet left the state unused in 1942 and a similar quantity probably was lost during the high runoff year of 1957. Water shortages in the drought years 1954-1956 could have been alleviated if the estimated 200,000 acre-feet that passed the state line unused in 1952 had been stored. The Narrows Reservoir could capture these flows when.they occur and hold them over until such time as they could be used beneficially. FUTURE PLANS The Bureau of Reclamation contemplates no further studies of the Narrows Unit until stronger local interest is evidenced through a clearly defined position by the State of Colorado. -9- -8-