BC Hydro has now completed work on stage 1 of the Elsie dam upgrade in Vancouver Island, Canada. The dam, part of the 27MW Ash river hydroelectric facility built in 1958, is being upgraded to resist major seismic events. Dam safety investigations had shown that a thin layer of saturated loose material in the main dam at approximately el 326m would liquefy during a major earthquake.
Stage 1 of the upgrade included excavation of a 100m wide slot in the spillway, to keep the reservoir level below el 326m, and thereby prevent the saturation of the loose material layer.
The second stage of the upgrade work will see the replacement of the loose layer in the main dam, as well as placing a rock berm on the downstream side of the dam. This work is planned for April to October 2001. Once the second stage work is complete the temporary spillway channel will be plugged with concrete to re-establish normal reservoir levels.