BC Hydro has announced it has received approval from the BC Utilities Commission (BCUC) and the Provincial Environmental Assessment Office to decommission Coursier dam, located near the outlet of Coursier lake about 30km south of Revelstoke, Canada.
Due to an ongoing history of dam safety deficiencies and various remedial works over the years, BC Hydro conducted a thorough review of options related to the future operation of Coursier dam and concluded that the dam should be decommissioned.
The water licence for Coursier lake reservoir permits a minimum elevation of 1263.7m and a maximum elevation of 1283.8m. To ensure public safety in the interim period prior to removal of the dam, BC Hydro has maintained a state of enhanced surveillance and has continued to operate the reservoir at a lower maximum reservoir elevation of 1274m.
‘With the key regulatory approvals in place, we have started site preparation and field office set-up while the final construction contracts are being tendered,’ said BC Hydro project manager Bill Seyers. ‘The decommissioning work will be done over the summer and fall of 2003, with revegetation work planned for 2004.’
Reservoir drawdown through Coursier dam’s low level outlet (LLO) started in April to prepare for freshet inflows. Additional pumping of about 1m3/sec of water over the spillway will start by late June to accelerate the drawdown and prepare for a mid-July start-up of excavation work, depending on freshet/inflow conditions.
The Coursier dam decommissioning project has an estimated cost of $4.6M, and will consist of dam removal/excavation, channel restoration, site cleanup, revegetation, and monitoring.
‘Dam removal will involve excavation of a notch through the centre of the existing earthfill dam,’ explained Seyers. ‘The slopes on the sides of the notch will be terraced and vegetated to create erosion resistant banks with a stream channel being constructed at the approximate location of the original creek bed. Coursier Lake will be returned to its original historic elevation of 1266m with a surface area of about 40ha.’
Revegetation including riparian planting and reforestation are planned to return the area to its natural vegetated condition. The existing concrete spillway will be broken up and buried and the low level outlet intake, pipe and valve house will be removed. All disturbed areas will be graded and left in a stable condition. Exposed soils including the previously inundated shoreline, spoil and borrow areas will be revegetated. During the past five years of lower reservoir operating levels, the Coursier lake shoreline above 1274m has started to revegetate naturally.
A comprehensive Environmental Management Plan (EMP) is being prepared for the project to ensure that all environmental conditions and permitting requirements are met, and environmental impacts are avoided or addressed in a timely way.
Coursier dam was built in 1963 by the City of Revelstoke. The height of the dam was raised in 1969, and the dam was purchased by BC Hydro in 1972. It is BC Hydro’s intention that the licence for storage at Coursier lake reservoir will be released after decommissioning.