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<br />. <br /> <br />in 1910, prior to construction of the dam. According to this docu- <br />ment, the reservoir capacity is 52,192 are-feet. The latter fjgure <br />has been used in administration of the reservoir. <br />To verify the actual stor.age capacity, Falcon Air Maps prepared <br />a contour map of the reservoir area in June, 1981 with a scale of <br />1:2,400 and a four-foot contour interval. Ground control was provided <br />by Davis Engineering Company of Del Norte, Colorado. Vertical control <br />was based upon the elevation of USGS Bench Mark 9321 Duray, located at <br />Thirtymile Campground. The reservoir water level at the time of the <br />aerial survey was 9402.2 feet, corresponding to 10,451 acre-feet in <br />storage from the SLVID elevation-capacity table. <br />Based on this initial storage content, the reservoir storage <br />capacity at the spillway crest was calculated to be 52,248 acre-feet. <br />The new elevation-capacity curve and area-capacity curve based on the <br />1981 survey are shown in Figure 5. The newly calculated storage <br />capacity is within 0.1 percent of the value previously used by the <br />SLVID. However, sediment accumulation below elevation 9402.2 may have <br />reduced the storage capacity by an unknown amount. The new elevation- <br />capacity curve almost exactly matches the old table values. The vari- <br />ation is within the accuracy of the new survey. Therefore, continued <br />use of the old elevation-capacity table is recommended. <br /> <br />. <br /> <br />Cl imatological Information <br /> <br /> <br />Weather conditions at Rio Grande Reservoir are strongly affected <br /> <br /> <br />by the mountainous terrain and high elevation. Summers are generally <br /> <br /> <br />cool, with occasional thunderstorms and general rainstorms. Frost can <br /> <br /> <br />occur at any time during summer except perhaps in July. Winters are <br /> <br /> <br />long, snowy, and cold at the reservoir, with snow accumulations of <br /> <br /> <br />several feet being common. A westerly wind often blows at high velocity <br /> <br /> <br />across the dam crest. Based on the existing four years of climato- <br /> <br /> <br />logical data at the dam, precipitation averages about 18 inches per <br /> <br /> <br />year. As shown in Table 1, the monthly distribution of precipitation <br /> <br /> <br />is fairly even. Winter low temperatures can reach -4DoF, and tempera- <br /> <br /> <br />tures below zero are normal during winter months of December through <br /> <br />. <br /> <br />-17- <br />