Laserfiche WebLink
Attachment 4 - Dolores River Instream Flow Recommendation <br /> Water Availability <br /> The BLM and CPW staff cooperated with the CWCB staff to conduct an initial evaluation of the <br /> stream hydrology to determine if water was physically available for the instream flow <br /> recommendation. The hydrograph below was derived from data collected by the USGS stream <br /> gage for the San Miguel River at Uravan, CO (#09177000), which has a drainage area of 1500 <br /> square miles and from the USGS stream gage for the Dolores River at Bedrock, CO, which has a <br /> drainage area of 2,025 square miles. The period of record for the San Miguel River at Uravan <br /> gage was 1954 to 2004, and he period of record for the Dolores River at Bedrock gage is 1917 to <br /> 2013. The analysis focused on an overlapping period of record between 1973 and 2012, or 40 <br /> years. <br /> The BLM and CPW staff determined that combining the mean monthly flow from these two <br /> gages would provide a conservative estimate of water availability. The reason the estimate is <br /> conservative is that there is some limited tributary inflow to the Dolores River from Mesa Creek, <br /> Roc Creek, and Blue Creek below these two gages. In addition,the estimate is believed to be <br /> accurate because there are no known diversions between the two gages and the upper terminus of <br /> the proposed instream flow reach at the confluence of the Dolores River and San Miguel River. <br /> Water availability for the lowest six miles of the proposed instream flow reach may have to be <br /> slightly adjusted for a handful of irrigation diversions that divert water upstream from Gateway. <br /> The initial water availability analysis may also have to be adjusted for channel losses or gains <br /> that occur through the 34-mile reach. <br /> The cooperative analysis also examined subsets of the 40-year data set. In 1984,the Dolores <br /> Project on the Dolores River came on line and substantially altered the hydrology of the river. In <br /> 2000, two major events occurred. First, additional water delivery service areas were brought on <br /> line under the Dolores Project, increasing demand for project water. Second, a period of <br /> extended drought began. In the Dolores River watershed that feeds the Dolores Project, 11 of 13 <br /> years between 2000 and 2012 were below average water yield years. In the San Miguel River <br /> basin, 10 of 13 years between 2000 and 2012 were below average water yield years. The <br /> hydrograph below displays the results of the cooperative analysis. <br />