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<br />. <br /> <br />nn~t~f')c;, <br />u 0 dO';,; u <br /> <br /> APR MAY JUN JUL AUG SEP OCT <br /> - <br /> Fort Lewis 1.12 1.05 0.65 1.94 2.12 1.45 2.10 <br /> Precip. (inches) <br />. Irrigated* 0.76 0.71 0.44 1.32 1.44 <br /> 0,99 1.44 <br /> Areas {inches} <br /> * Based on 12/17.64 or 68% of Fort Lewis average monthly precipitation. <br /> <br />. <br /> <br />Average temperatures in the irrigated area are affected by elevation <br /> <br /> <br />and topography. Temperatures at the Fort Lewis weather station at elevation <br /> <br />7610 are considerably cooler than in most of the irrigated areas within the <br /> <br />La Plata basin. The Durango (elevation 6550) and Ignacio (elevation 6420) weather <br /> <br /> <br />stations are at lower elevations than the Fort Lewis station and temperatures <br /> <br /> <br />at these stations are considered more representative of average conditions <br /> <br /> <br />in the La Plata irrigated areas. Average mean monthly temperatures for the <br /> <br /> <br />irrigation season are summarized as follows: <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br /> APR MAY JUN JUL AUG SEP OCT <br />Fort Lewis 40.5 48.9 56.7 63.9 62.1 55.3 45.6 <br />Ignacio 44.5 53.0 61.2 68.2 66.2 58.7 48.6 <br />Durango 45. I 52.9 60.2 67.5 66.0 58.6 48.8 <br />Irrigated * 44.8 53.0 60.7 67.9 66.1 58.6 48.7 <br />Areas <br />* Based on the average of Ignacio and Durango temperatures. <br /> <br />. <br /> <br />. <br /> <br />A portion of the precipitation occWTing during the irrigation season was estimated <br /> <br /> <br />to be effective in reducing irrigation requirements, based on use of the modified <br /> <br /> <br />Blaney-Criddle procedure for calculating effective precipitation. Using these <br /> <br /> <br />data, the average annual potential consumptive use of irrigation water was <br /> <br /> <br />estimated to be about 2.44 acre-feet per acre, provided that the irrigation water <br /> <br /> <br />supply is sufficient in time and quantity. Since the irrigated area in the La <br /> <br /> <br />Plata basin is about 15,300 acres, the total potential consumptive use requirement <br /> <br /> <br />for full irrigation is about 37,000 acre-feet. <br /> <br />. <br /> <br />. <br /> <br />Operation Study <br /> <br /> <br />The irrigation water supply (Table 5) in the La Plata River basin is inade- <br /> <br /> <br />quate to meet the full crop water requirements. An operation study was per- <br /> <br /> <br />formed in which the average monthly ditch diversions were compared to the <br /> <br />-11- <br /> <br />. <br /> <br />t '" <br />