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'Oct-31-Z00Z 11 :33am From- T-599 P.006/008 F-9TZ Mr, Jim Norfl~et, P.E. Mr. Jack Byers, P.E. Page 5 July", 2002 road. A drainage ditch will be constructed along the top of the downstream embankment with a high point in the center and the ditch draining to the east and west. The road will be constructed In accordance with Delta County and US Forest Service criteria. INSTRUMENTATION Survey monuments will be installed on the crest of the dam to monitor any movement of the embankment. A benchmark monument will be set on the right abutment and protected by a jersey barrier. Piezometers will be located on the upstream portion of the crest and just off of the crest on the downstream embankment. One set of piezometers will measure foundation seepage and the other will measure embankment seepage upstream and downstream of the foundation drain. SPILLWAY Hydrology The drainage basin tributary to Hotel Lake includes approximately 1,180 acres (1.84 square miles). The basin Is undeveloped except for 25 to 30 structures and a ,road around the lake, The basin Is heavily forested except for talus slope areas and three other lakes, The soils are gravels, sands, silts and clays derived from the Basalt flows which covered the area, Infiltration Is relatively high espeCially in the forest and talus slope areas. The draft soil survey completed by the NRCS and the USFS Indicates that approximately 35 percent of the soils are Hydrologic Group A and 66 percent are Hydrologic Group B. The probable maximum precipitation for the basin was estimated using HMR No. 49. The 6 hour precipitation is 5.2 Inches, the 24 hour precipitation is 10.9 inches, and the 72 hour precipitation la 17 inches. The 6 hour local storm precipitation Is 6.92 inches. The dam is a Class I small structure and must adequately pass the inflow design flood from the 0.75 PMP. The inflow and routed outflow were modeled using the HEC-HMS program and the SCS Unit Hydrograph method. The e hour PMP local storm produced the largest peak flow. The reservoir inflow is estimated at 3,075 efs and the routed outflow Is estimated at 840 ofs. The overflow spillway conveys 840 cfa with 0.16 feet of freeboard. Since the overflow spillway is across a CounWfForest Service road, it was discussed with the SEO that the service spillway should be capable of passing at least the 100 year inflow design flood. The 100 year 24 hour precipitation is 3.1 inches based on the NOAA Atlas, Volume III, Colorado. The 100 year storm was also modeled using the HEC-HMS program. The reservoir Inflow is estimated at 745 cfs and the' routed ._....-._-._...__w________ !!!!!! C) C C ,...... I I C) f"\ E::