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3.0 DETERMINATION OF DEPLETIONS FROM PUMPING WAS MEMBER WELLS <br />Three tasks aze nece,ssary to determine stream depletions from pumping WAS member wells: <br />1. Detennine the quantity, or volume, of depletions. <br />Z. Detemune the timing, or delay, of the depletions reaching the stream. <br />3. Detennine when these estimated depletions aze out of priority aad must be replaced. <br />3.1 Estimating Stream Deptetion Volume <br />For purposes af estimating ground water pumping from WAS member wells, ti�e consumptive <br />use of ground water and surface water is estimated using a Blaney-Criddle evapotranspiration <br />(E'I') methodology. Obtaining a WAS contract requires crop reporting for the period 1998 <br />through 2003 and an estimate of the crops and acreage to be planted in 2004. The alluvial <br />ground water consumptive use estimates for the Apri1 1, 2004 through March 31, 2005 period aze <br />based on these crop and acreage data. Actual reported irrigated acres and crop types were used <br />for the 1998 through 2003 period. From 1974 —1997, crop types and acreage were estimated <br />using the 1998 reported irrigated acreage. Crop history from 1974 - 2003 for each applicant's <br />crop and acreage was used to estimate the total irrigation requirement and the onsite alluvial <br />ground water consumptive use for each member well. Table 1 presents the 1998 - 2004 crop <br />distribution as reported to Central. Table 2 present the estimated total irrigated azea by reach for <br />2004. <br />The consumptive use for each member well was estimated based on (1) number of acres <br />irnigated, (2) number of acres of specific crops irrigated, (3) irrigation method used and (4) <br />surface water rights Iisted on each WAS application. Each member's application was treated as <br />a farm model unit with onsite alluvial ground water consumptive use esrimated for each of the <br />228 WAS irrigator applicanxs. There are five non-irrigation contracts that were handled on an <br />individual basis to determine consumptive use. <br />All irrigation contracts list the number of acres irrigated by flood or sprinkler. Surface water <br />volumes applied by flood irrigarion were multiplied by a 0.65 application efficiency factor to <br />obtain the surface w�ter available to meet crop imgation requirements. Surface water applied by <br />sprinkler was multiplied by a 0.80 application efficiency factor to obtain the surface water <br />available to meet crop irrigation requirements. <br />The consumptive use model (IDSCin developed by the Integrated Decision Support Group <br />(IDS) at Colorado State University was used to estimate the consumptive use of alluvial ground <br />water (via a water budget} for each WAS member well. The model used to estimate the onsite <br />alluvial depletions caa be obtained &om www.ids.colostate.edu. IDSCU uses the modified <br />Blaney-Criddle method to estimats ET and calculates a monthly water budget �at includes <br />effective precipitation, soil moisture, monthly surface water diversions, and estimated alluvial <br />ground water pumpage credited towards meeting the net crop irrigation water requirement <br />(NCIWR). The 2004 NCIWR was estimated using average mon�ly clima.te data from 1974 <br />21m3 from tfiree weather stations, Longrnont ESE (NOAA), Greeley iJNC (NOAA) and Fort <br />Morgan (NCWCD), loc�ted witl�in the WAS boundaries. <br />P:\Data\GEN\CCWCD\25087\SWSP WAS\2004 WAS SWSP (FINAL).doc �j <br />