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00 CO ". -' Operation - Colorado Division .-- '- Under present conditions Colorado ditch diversions conform to seasonal flows of La Plata River and, as a consequence, are unbalanced as to crop needs, late summer water shortages being of major concern. Since the maximum irrigation requirements occur in June, July, and Au,gust, the function of Long Hollow Reservoir is to store the excess waters of April and May and to furnish a dependable water supply for the late summer qtonths. Since the 12,000 acre-feet of capacity which would be ava:i.lable at Long Hollow Reservoir is inadequate for both seasonal regulation and yearly carry-over storage, complete regulation of water available to Colorado users could not be provided. Peak run-off of high-water years would continue to pass to New Mexico. Analytical studies of water supply indicate that seasonal regula- tion of water in Long Hollow Reservoir would yield annual amounts of supplemental water in accordance with crop needs, primarily for June to September irrigation requirements, as shown in table 1. These reser- voir yields would be secur~d partly by reducing the present excessive April-May diversions and by storing such excess water in Long Hollow Reservoir, along with peak river flows, for late summer use in accord- ance with crop needs. Crop production studies disclose that Red Mesa farm production can be doubled by the use of 'supplemental water, and be well sustained in all years oxcept during years of extreme low run- off, such as 1931, 1934, and 1939, when the available water was about one-half of the anticipated average yearly usable supplies with Long Hollow Reservoir in operation. Limited exchange benefits from Long Hollow Reservoir would provide a small additional water supply during the summer months for the upper land. Under the adopted plan tho upper ditches would divert all avail- able river flow, and any compact deficiencies for New Mexico would be made up from Long Hollow Reservoir storage; whereas, under the present practice of rotation between the two states, the upper ditches are v closed for 10-day periods. The graph of reservoir operations (drawing No. 56-D-323) shows the theoretical monthly contents of the Long Hollow and State Line Reser- voirs for the period of 1938-1940, a period containing the critical dry years of record, and portrays storage conditions on the La Plata River under minimum conditions of run-off. The graph also shows his- torically the monthly ditch diversions of the Colorado and New Mexico ditches togother with possible future diversions when supplemental reservoir water is made available from Long Hollow and State Line Reser- voirs. La Plata River at the State Line State l.ine gaging station is 25 miles downstream from the Hesperus station and 300 feet bolow tho Colorado-New Mexico "tate li.ne, near the head of the New Moxico ditches. Two small interstate ditches divert above the station, in Colorado. La Plata River flow at sltate l,ine 21