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DRAFT DRAFT DRAFT <br />Total annual inflow from 1928-2004 into the McPhee Reservoir site is presented <br />below, and it should be clear that inflows to the Dolores River at McPhee is <br />highly variable. The standard deviation of these 76 years of data is nearly <br />160,000 AF, meaning that for approximately 2/3 of the years, the `expected <br />variability of inflow' is ± 44% of the average total inflow. The other 1 /3 of the <br />years lie outside the `expected variability', suggesting that outside of the monthly <br />precipitation and snowpack forecasts, it is difficult to predict inflow to McPhee <br />with any certainty. <br />A hydrologic analysis of the differences in total flows at Bedrock and Dolores was <br />done to assess how the total flows varied at these locations in the pre-MVIC <br />period. The analysis used daily flow data between 1974 and 1985 to assess how <br />total flow, mean peak daily flow, and the timing of peak flows may have compared <br />at these two gage locations absent any significant diversions. For total flow <br />analyses, daily diversion records at the MVIC Canals Nos. 1 and 2, available from <br />the State's Colorado Decision Support System (CDSS) hydrologic database, were <br />added back into the gage record to determine the relationship of these variables <br />over this 12-year period, which encompassed very dry (1977), very wet (1983) <br />and average (1974) water years. <br />This analysis showed that even during dry years, total flow at Bedrock was greater <br />than that at Dolores (Figure 6). This would be expected due to the nearly 4-fold <br />difference in watershed area at these two gages. What is notable from this <br />comparison is the insignificant flow contribution of tributary watersheds <br />downstream of Dolores during dry periods, when flow at Dolores is nearly the <br />same as that at Bedrock. During wet years, (e.g., 1979, 1980, 1983) total flow <br />downstream is 50-60% greater than upstream at Dolores, indicating that <br />contributions from downstream watershed increase proportionally to total moisture <br />in the watershed. <br />Peak flows are an important ecological variable, as they perform the work <br />necessary to flush sediments, rejuvenate floodplain habitats, and maintain <br />channel form in alluvial reaches. In the geomorphic literature, the `bankfull flow' is <br />often related to the peak flow with a recurrence interval of approximately 1.5 <br />years. Also called the `effective flow' or `dominant discharge', it is that flow which <br />because of a relatively high frequency of occurrence combined with high stream <br />power, does the most physical work on the channel over time. It is especially <br />important in alluvial rivers (rivers with mobile bed and bank sediments), where the <br />instream and floodplain habitats become a reflection of the balance between the <br />dominant discharge, sediment flux, and vegetation. Cottonwoods are a species <br />that is particularly dependent on periodic very high flows to scour near-channel <br />and floodplain sites so that seeds can deposit on moist, bare surfaces in order to <br />germinate and survive absent competition from other species. <br />9/5/06 14 <br />