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<br />APPENDIX A
<br />Consumptive Use Analysis in the Upper Gunnison Basin
<br />
<br />Irrigation consumptive use accounts for about 115,000 acre-feet of the total
<br />annual Upper Gunnison Basin water use. Records of diversion and return flow are not /
<br />complete enough ',to allow the direct calculation of this volume, therefore, theoretical/
<br />methods are employed.
<br />
<br />Several eq~ations exist that estimate the amount of water used by growing plants.
<br />Each of these require differing amounts of input data, the equations vary from
<br />relatively simple to complex. While each equation has strengths and weaknesses, the
<br />Bureau of Reclamations's testing and experience suggest that the modified
<br />Blaney-Criddle formula accurately predicts irrigation consumptive use, with minimal
<br />data reuirements~ This formula has been eXClusively used on the Uper Gunnison River
<br />Basin, and throughout the Upper Colorado River Basins.
<br />
<br />This equation requires the input of irrigated acreage, type of crop, maximum
<br />length of crop'growing season, frost dates, mean monthly temperatures, monthly
<br />precipitation. mOnthly daylight hours, and a crop "Kc" curve which expresses the crop
<br />water requirements.
<br />
<br />Bistoricallt the Bureau has calculated irrigated acreages by sampling techniques. (
<br />such as the Type:I Study (a comprehensive acreage survey completed in the mid 1960's).
<br />state Agicultural Statistics published annually, and the National Censuses of
<br />Agriculture.
<br />
<br />This study compared the remote sensing with the
<br />the consumptive ~se in the Upper Gunnison Basin.
<br />results of applying these two methods.
<br />
<br />traditional method of calculating
<br />The fOllowing table shows the
<br />
<br /> Traditional Remote Sensing
<br /> ------------------- --------------------
<br /> TOTAL TOTAL
<br />HYDROLOGIC IRRIGATED e'ON-USE IRRIGATED CON-USE
<br />UNIT COl1l!lTY ACRES (AC-FT) ACRES (AC-FT)
<br /> ,
<br />---------- ---------- ---------- --------- ---------- ---------
<br />20001 GunniSon 9,510 7.423 7,823 6,107
<br />20002 Delta 10,280 24,599 7,836 18,751
<br />20002 Gunnililon 25,210 31.967 25,088 34,461
<br />20002 Hinsdale 670 603 1,402 1,165
<br />20002 Montrose 9,200 16,512 10,819 19,417
<br />20002 Saguache None 119 118
<br />20003 Gunnisdn 11,890 16,194 13,364 18,202
<br />20003 Saguache 13,680 16,956 6,730 8,342
<br />TOTAL 80,440 114,254 73,181 106,563
<br />20001 9,510 7,423 7,823 6.107
<br />20002 45,360 73,681 45,264 73,912
<br />20003 25,570 33,150 20,094 26,543
<br />TOTAL 80,440 +14,254 73,181 106,563
<br />Percent Change 9.0% 6.7%
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