WSP07002 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I I I I I I I I I I I 5.4 migration has not been observed in the seepage from recent reservoir operations; however, the operations have been at restricted levels, so the effect of operation at full reservoir levels in unknown. We recommend that the current reservoir operational guidelines be continued until embankment modifications can be made. Daily monttoring of the reservoir and embankment should be continued during periods of reservoir operation Including a visual Inspection of the embankment, measurement of seepage in the flow weirs, and measurement of water levels in the downstream piezometers. In addition, water levels should be monttored and evaluated in the five piezometers installed for this investigation on a weekly basis during periods of reservoir operation, and on a monthly basis at other times during the year. We would be glad to assist you in evaluating piezometer measurements. HYDROLOGY AND HYDRAULICS 5.4.1 PROBABLE MAXIMUM FLOOD The Hourglass Reservoir drainage basin is just north of the Rocky Mountain National Park. Its headwaters are located along the north side of the 12,000 foot Mummy Range peaks. Hourglass Dam and Reservoir are located In a small tributary to Beaver Creek. Beaver Creek is a tributary to the south fork of the Cache Ia Poudre River. The drainage basin area Is 0.74 square miles and has an average slope of 600 feet per mile. The basin Is about 1.8 miles long with an average width of about 0.4 miles. The Soil Conservation Service dimensionless hydrograph was used, with a lag time of 1.46. The Hourglass Dam spillways are able to discharge the PMF with 2.8 feet of remaining freeboard on the dam. The usual refinements of determining drainage basin infiltration rates and incremental damage assessment were not needed and were not evaluated. Instead, all of the probable maximum precipitation PMP was assumed to flow into the reservoir. The resulting Inflow was routed through the reservoir. 5-13