Safety upgrade of Elsie Dam near Port Alberni

May 17, 2000 - BC Hydro keeps water levels lower than normal in Elsie Lake Reservoir during seismic upgrade review

BC Hydro is keeping water levels in the Elsie Lake Reservoir lower than normal as it reviews seismic upgrade alternatives for Elsie Dam. The Elsie Lake Reservoir is currently eight metres (m) below the normal level for this time of year. Over the past winter BC Hydro has maintained the reservoir at lower than normal levels because of a dam safety concern. 

In October, 1999, as part of a dam safety investigation at the Elsie Dam, a horizontal layer of loose material was found by test-drilling in the main dam at an elevation of 326 m, about five metres below full pool level. Analysis confirmed that if the reservoir level is above this layer, and there should be a large earthquake, the dam would likely deform - which could lead to failure of the dam. 

BC Hydro is reviewing alternatives to improve the safety of the main dam that include: removing and replacing the loose layer near the top of the dam, combined with adding rock on the downstream slope of the dam; or placing a new upstream core and facing on the upstream slope. In considering the repair alternatives, BC Hydro staff will be looking at potential impacts on recreation, the environment, reservoir drawdown, risk during construction and estimated costs. The selected alternative will be reviewed by an independent advisory board of engineering experts in June.

The alternatives being considered require dry weather for construction, likely between June and September, and would include a method to keep the reservoir level lower than the work area. To keep the reservoir level below 326 m throughout the winter season to address safety concerns and to prepare for construction, BC Hydro is considering a plan to temporarily lower part of the spillway by excavating a slot in the rock. The work would likely to be carried out this fall, so work on the main dam could start in the spring, 2001. When the work on the main dam is complete, the slot would then be re-filled to return the reservoir to normal operating levels. 

The reservoir level is also currently drawn down in anticipation of the snow melt in the watershed this spring. The reservoir level will rise during the next few months but is not expected to rise above the layer of less compacted material. If an unexpected storm temporarily raises the reservoir level above an elevation of 326 m, BC Hydro will activate an enhanced response plan to monitor the dam 24 hours a day. The enhanced response plan, established last fall, was developed in cooperation with local emergency response organizations and is linked to the Port Alberni Emergency Preparedness Plan.

CONTACT: Dave Thomson
Vancouver Island Community Relations Manager
Phone: (250) 755-4773