C150063 Feasibility Study - Laserfiche WebLink

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I I I I I I compacted lifts to build a flattened upstream slope. An erosion resistant surface would be placed on the upstream surface to assist in stabilizing the sands. The existing concrete slabs would remain in place, and no program of void investigation would be made, due to the overall stability of the flattened slope. The theory behind the beaching concept is to replicate a natural beach slope that is stable under wave action. Wave energy dissipation is accomplished through the wave travel (runup) up the relatively flat surface. The parapet wall could be abandoned/removed under this option. The design concept for these options is shown in Figure 8. I I I I I I I I I I I I I Option 5A - Beach the Upstream Slope at a 10(H):1(V) Slope and Armor with Gravel This option would flatten the upstream slope to a 10.0 (horizontal) to 1.0 (vertical) slope to replicate the design utilized by the Bureau of Reclamation on several dams and on Vancil Dam constructed by Riverside Irrigation District in about 1990. A layer of imported coarse sand and gravel would be placed' on the surface to protect underlying fine sands from movement. This option is untested in a large reservoir with significant fetch, wind-induced currents and fine sand materials for embankment construction. Vancil Dam, constructed around 1990 under the Riverside system, shows signs of benching at the waterline. The Vancil Dam embankment was constructed with coarser materials than is available at Jackson Lake Reservoir, and has only half the fetch of Jackson lake Reservoir. Empirical evidence suggests that the wind-induced lake circulation moves and redistributes significant amounts of the fine lakebed sand and sediments in the large South Platte River irrigation reservoirs. Examination of the Jackson lake Reservoir lake bed survey data indicates that natural beach slope for these lakebed materials may be more on. the order of three percent to five percent, or flatter. It would be economically and practically unfeasible to construct a dam slope at five percent. The beaching option has an unknown life span, but is estimated to be approximately ten years between major, maintenance, with minor maintenance possibly required on an annual basis. On a historic basis, the Company beached the upstream dam slope with lakebed materials in the 1950s and 1960s. There has been very little evidence of the breaching remains in the recent years. This historic beaching effort did not armor the 29