C153644 Final Report - Laserfiche WebLink

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A 20 foot deep, 20 foot wide core trench would be excavated most of the length of the and upstream of the centerline of the embankment. Figure 4 shows the cross section of the dam at the outlet pipe. Figure 5 shows the front elevation view of the embankment looking upstream from below the dam. There is assumed to be adequate impermeable material for the embankment available in the reservoir basin. If there is any unsuitable material, e.g. excess rocks or humus, the material would be wasted near the reservoir. Table 3 shows the estimated volume of material required to construct the embankment. The material would be placed in lifts and compacted to at Least 95~ Standard Proctor. Adequate testing will be required to monitor the compaction. Rip rap is expected to be available in the immediate area. A toe drain is included to control seepage through the embankment. The drain would probably be a sand filter (ASTM C-33 sand) with a slotted drain pipe to convey water out of the filter. The drain is estimated to be 5 feet deep, 2 feet wide and about 350 feet long. The reservoir would be on private .land which will require the purchase of about 100 acres for the dam, reservoir, and needed access. OUTLET PIPE: The outlet pipe size is suggested to be 36 inch. diameter which is significantly larger than the size required by the Rules and Regulations but provides easier operation and maintenance and if a liner is needed in 50 years or so, it can be installed without impacting the ability to drain the top 5 feet of the reservoir in 5 days. The pipe material should be thick walled steel, possibly lined with mortar or another material, reinforced concrete pipe is also a possibility; CMP is not recommended. SPILLWAY: The spillway will be sized to pass 50$ of the PMF (probable maximum flood). Since the drainage basin is 25 square miles the size of the flood will be significant, estimated to be about 15,000 using Bureau of Reclamation reconnaissance study criteria. One half of the flood would be 7500 cfs which the spillway should pass in combination with the reservoir surcharge. A spillway width of 90 feet with l:l side slopes, excavated on the east abutment is assumed herein. The freeboard of 10 feet is included in the design. Based upon the equation: flow is equal to the length (90 feet) times a flow factor "C" (2.7) times the water depth ( 10 feet) to the 1.5 power, the spillway would pass about 7600 cfs. This is a conservative estimate because the reservoir surcharge would reduce the flood peak. Beaver Creek Dam 11