Unraveling the Mystery of Lake Jackson Dam

In July 2011, open chambers were identified within the dam interior, beneath a sloping concrete shell at the upstream face of dam. A month later, the dam survived a 5.8 magnitude earthquake. In May 2012, flow was noted at two 9-inch (23 cm) diameter toe drains; and after a large precipitation event, flow from these toe drains increased dramatically. Interim risk reduction measures were implemented and a detailed investigation was performed to characterize the location/extent of internal chambers and flow within the dam interior. A combination of observation-hole penetrations, underwater sonar, soundings, and dye tracer tests were performed. The investigation revealed two penetrations through the upstream concrete shell, and active flow within the dam interior. In-the-wet construction generally entailed temporary seals, underwater-placement of self-consolidating concrete to fill fourteen hollow chambers, and toe scour repair. Temporary seals were an asset to effectively repair earthquake damage and return Lake Jackson Dam to service.