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Impact of Reservoirs on Stream Gaging Stations <br />Two of the three stream gaging sta tions are affected by releases from upstream reservoirs. The Gunnison <br />River gaging station near Gunnison is impacted by the operations of Tayl or Park Reservoir. Using daily <br />streamflow records of inflows (Texas Creek at Taylor Park and Taylor River at Taylor Park) and outflow <br />(Taylor River below Taylor Park Reservoir) to reser voir, the daily streamflow of the Gunnison River at <br />Gunnison was adjusted (e.g., if the inflow minus out flow equaled 100 cfs, 100 cfs was added to the daily <br />streamflow at Gunni son). Based upon an analysis of the in flow/outflow in 1988 and 1989, the impact upon <br />the cutoff dates was determined to be minimal. In 1988, the cutoff dates would shift 1 to 3 days later. In <br />1989, the cutoff dates would shift 3 to 4 days early. The Uncompahgre River at Colona gaging station is <br />affected by Ridgway Reservoir, which is located upstream 7.7 miles. Ridgway Reservoir is recently <br />constructed and has affected stream flow at this gage only since 1986. The reservoir has storage allocations <br />of 28,000 acre-feet for municipal and industrial use and 11,300 acre-feet for supplemental irrigation use. As <br />this reservoir becomes utilized more in the future, its impact upon the cutoff dates could be significant. <br />USGS Hydrologic Un its/County Units <br />The analysis was somewhat restricted because the ditc hes identified by the State for which crop distribution <br />and irrigated acreage were available are located in only 3 of the 6 USGS hydrol ogic units and 5 of the 15 <br />HCUs. Each of these HCUs is discussed in the following text. <br />H U 1 4 0 2 0 0 0 4 , G u n n i s o n C o u n t y <br />Only one structure, Fire Mountain Canal, was located in this HCU. This canal was excluded from the <br />analysis because it diverts considerable amounts of project water (Paonia Rese rvoir), and a portion of its <br />irrigated area is also irrigate d with water from Leroux Creek. <br />H U 1 4 0 2 0 0 0 4 , D e l t a C o u n t y <br />Five of the identified structures were located in this HCU. One of the ditches is the Leroux Creek Ditch. <br />Three of the five divert reservoir water. The re maining ditch irrigates no alfalfa or pasture grass. <br />H U 1 4 0 2 0 0 0 5 , D e l t a C o u n t y <br />Eleven of the identified structures we re located in this HCU. Four of these ditches were considered for <br />further analysis. A comparison of the monthly consumptive use values to the historic ditch diversions <br />revealed that three of the ditches have a full water supply. The monthly ratios of consumptive use to ditch <br />diversion for the remaining ditch, the Obergfell Bald win Ditch, indicated either (1) the ditch was always <br />limited by physical water supply, (2) the irrigated area fo r the ditch (289 acres) might be overstated, or (3) <br />not all of the diversions at this st ructure were included in the data base. In June, the ratio of consumptive <br />use demand to diversion ranged from 1.2 to 4.3. In July, the ratio ranged from 1.4 to 10.7. The data is <br />questionable because June is typically the month of highest st ream flows and even the most junior of water <br />rights can generally meet demand. <br />H U 1 4 0 2 0 0 0 6 , D e l t a C o u n t y <br />Six ditches were located in this HCU. The USBR Colorado River System C onsumptive Uses and Losses <br />Report, 1981-1985 indicates no pasture-short or alfalfa-short acreage in this HCU. However, comparisons <br />of monthly consumptive use values to historic ditch diversion for three of the ditches (Beach Nos. 1, 2, and <br />4 <br />A 275 01.09.95 1.14-24 Walter <br />