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<br />I <br />! I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />inches. The estimated monthly distribution of evaporation is based on evapo- <br /> <br /> <br />ration measurements taken at Montrose, the nearest evaporation station with a <br /> <br /> <br />similar elevation to that of the reservoir. The average monthly precipitation <br /> <br /> <br />at Grand Junction, the closest precipitation station, was used to calculate <br /> <br /> <br />the net water loss from the surface of the reservoir as shown in Table II-5. <br /> <br /> <br />The reservoir was assumed to be maintained at its normal maximum level of <br /> <br />El 5070. <br /> <br />F. PROBABLE MAXIMUM FLOOD <br /> <br />1. Introduction <br /> <br />The PMF at the Una dam site was developed on a feasibility-level <br />basis which did not include use of a mathematical model of the watershed. <br />Detailed studies, including mathematical modeling, should be conducted in the <br />future prior to final design of the Project. <br /> <br />I <br />I <br />I <br /> <br />The PMF estimate for the Una Reservoir Project is based on a 1981 <br /> <br /> <br />detailed watershed calibration and PMF analysis conducted by Beck for the <br /> <br />(6) <br />TM-County Reservoir Project on the Gunnison River near Lazear. The <br /> <br />Upper Colorado River Basin has watershed characteristics similar to the ad- <br /> <br /> <br />jacent Gunnison River Basin. The locations of the two basins are shown in <br /> <br /> <br />Fig. II-2. By considering differences between the two basins in terms of <br /> <br /> <br />drainage area, area-elevation distributions, snowpack depths, and the Probable <br /> <br /> <br />Maximum Precipitation (PMP), the results from the Tri-County Reservoir Project <br /> <br /> <br />investigl.tion were adjusted to reflect the PMF at the Una dam site. Design <br /> <br /> <br />nood estimates performed by the USER for the Dominguez and Curecanti Proj- <br /> <br />(20) <br />ects on the Gunnison River and flood frequency curves on the two rivers <br /> <br /> <br />were also utilized. The resulting Project PMF is estimated to have a peak <br /> <br /> <br />flow of 130,000 cfs. The volume was not estimated since it would be over 4 <br /> <br /> <br />million ac-ft for the period between May and August. The reservoir would have <br /> <br /> <br />essentially no effect in reducing the inflow peak and the spillway will have <br /> <br /> <br />to be designed for the inflClW peak discharge. <br /> <br />I <br /> <br />I <br />I <br />I <br />I <br />I <br /> <br />II-11 <br />