| Popis: |
A study was conducted to determine the nature and rate of ongoing erosion of the upstream riverbank slope at the Pleasant Valley Dam. The dam is composed of compacted earth fill containing a mixture of gravel, sand, and silt; and the abutments are composed of Bishop Tuff. Geochemical, geotechnical, and wave run-up/wind-setup analyses were applied to provide mitigation recommendations regarding the continued erosion concerns along the western shoreline abutment and potential future damage to the dam and its structures from slope failure if the erosion continues. The geochemical and geotechnical investigation included core rock samples, bulk samples and reservoir water sample testing. The wave run-up/wind-setup analyses were completed as a desktop study used to simulate wave action and erosive forces. Geochemical analyses of the dam material and reservoir water indicated that chemical dissolution of the earth materials is insignificant, and that clay swelling is also not a factor. The wave set-up and run-up analyses indicated a wave height of 1.5 to 1.8 feet and strength testing along this zone did not indicate weakened rock. The freeze thaw mechanical weathering is considered one of primary causes for the erosion. The overall results indicated that mitigation should focus on controlling sequential wetting and drying near the air-water interface, and/or limiting the penetration of water in the erosion area to avoid mechanical weathering. |
