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Information gained through interviews with the Di vision 4 Engineer and wa ter users in the basin. <br />? <br /> <br />Studies in the Grand Valley of Colorado have f ound that the average irrigation efficiency ranges <br />? <br />from 40 to 50 percent. For purposes of this anal ysis, if the ratio of monthly consumptive use to <br />monthly ditch diversion is great er than 50 percent, it is assumed the water supply is limiting crop <br />consumptive use. <br />TABLE 1 <br />USBR?S 1981-85 CONSUMPTIVE USES AND LOSSES REPORT <br />CRITERIA FOR LIMITED WATER SUPPLY <br />(GUNNISON RIVER BASIN) <br />ALFALFAPASTURE GRASS <br />PERCENT PERCENT <br />OF 1981 OF 1981 <br />IRRIGATED IRRIGATED <br />AREA IN AREA IN <br />USGS CUTOFF UNIT CUTOFF UNIT <br />HYDROLOGIC FLOW ALFALFA- FLOW PASTURE- <br />UNITCOUNTYSTREAM GAGE RATE SHORT RATE SHORT <br />14020001GunnisonGunnison River near n/a087041.3 <br />Gunnison <br />14020002Gunnison""0"17.2 <br />Hinsdale""0"40.4 <br />Delta"73041.08009.0 <br />MontroseSmith Fork near 1232.5n/a0 <br />Crawford <br />14020003SaguacheGunnison River near n/a087030.5 <br />Gunnison <br />Gunnison"n/a087018.5 <br />14020004Gunnison"n/a087043.0 <br />DeltaSmith Fork near 1229.31313.3 <br />Crawford <br />14020005MontroseUncompahgre River n/a0n/a0 <br />near Colona <br />Delta"32012.6n/a0 <br />Mesa""9.6n/a0 <br />14020006Delta"n/a0n/a <br />Ouray"n/a065014.8 <br />Montrose"n/a0n/a <br />The monthly estimates of actual crop consumptive use were compared to monthl y ditch diversion amounts <br />to determine which ditches appeared to have a limiting water supply. For the ditches that had a limiting <br />water supply, daily diversion records were analyzed to determine the historical dates the ditch typically cut <br />back or reduced its rate of diversion and how we ll those dates matched the USBR cutoff dates. The <br />causation of the reduction in diversion rates is assume d to be caused by either (1) a senior call, (2) the <br />physical availability of water, or (3) an operational decision. <br />2 <br />A 275 01.09.95 1.14-24 Walter <br />