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. . USFWS - Palisade/Grand Junction Stream Flow Analyses - DRAFT May 12, 1995 'Page 17 Table 1 is a comparison of the precipitation recorded at the Grand Junction Airport station during the July through December period in 1991, 1992, 1993, and 1994 with long term. averages. This table general1y confirms that the 1991 and 1992 October and November period, and August 1993 was wetter than average as stated by the irrigation managers in the area. Also, in 1994 July and August were much drier than average and previous years. Jul Aug Sept Oct Nov Dec Total 1991 .40 .57 2.30 1.20 1.10 .54 6.11 1992 1.03 .84 .33 1.45 .76 .35 4.76 1993 .04 1.42 .41 1.34 .41 .57 4.19 1994 .01 .48 1.50 .58 .69 .64 3.90 Long Term Avg. ,65 .81 .82 .98 .71 .61 4.58 Table 1 Precipitation Comparison in Inches Grand Junction Airport Based on Figure 5 and interviews with local irrigation company officials, we believe that local precipitation can produce significant runoff spikes into the Colorado River, that are relatively short lived. In 1992, the large amount of precipitation at the end of October may have contributed to offsetting the characteristic drop in local inflows that was experienced in November of 1991, 1993, and 1994 after the local irrigation diversions ceased. V.3 Diversion Dam Operations vs Local Inflow Based on discussions in 1993 with Mr. Bil1 Klapwyck of the Grand Val1ey Water Users Association, we believe that the operation of the Cameo rol1er dam can significantly alter the calculations of local inflow to the critical reach. These operations are believed to affect the calculation of local inflow greatest when 1) irrigation diversions are ceased in the late fal1, and 2) when power generation is initiated in the late fal1 or early winter. In general, at the end of the irrigation season not only are diversions terminated but water stored behind the Cameo roller dam is released. -Then after maintenance activities are completed the rol1er dam gates are lowered and water is stored to develop the head necessary to make winter diversions on the order of 800 cfs for power generation. In 1991, 1993 and 1994 the characteristic drop in estimated local inflows coincides with the end of irrigation diversions as shown in Figure 8. In 1992, the abundance of precipitation at the end of October makes the interpretation more difficult. We believe what is happening is that when diversions end and water stored behind the rol1er dam is