Erosion Analysis of the Upstream Riverbank Slope at Pleasant Valley Dam

摘要

A study was conducted to evaluate ongoing erosion of the upstream riverbank slope at the Pleasant Valley Dam. There is continued erosion concerns along the western shoreline abutment and potential future damage to dam structures due to slope failure caused by erosion. The dam is composed of compacted earth fill containing a mixture of gravel, sand, and si and the abutments are composed of Bishop Tuff. A geotechnical and geochemical investigation was performed consisting of core rock sampling, bulk sampling, and reservoir water sample testing. Geotechnical, geochemical, and wave runup and wind setup analyses were performed to provide mitigation recommendations. Geochemical analyses indicated that chemical dissolution of the earth materials is insignificant, and that clay swelling is also not a factor. The wave runup and wind setup analyses simulated wave action and erosive forces; indicating wave heights 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 indicate that mitigation should focus on controlling sequential wetting and drying near the air-water interface, and/or limit the penetration of water in the erosion area to avoid mechanical weathering.