Hydraulic Impact of Flow Regulation on the Peace-Athabasca Delta

Abstract

In 1976 two notched-section overflow weirs were installed in the Rivière des Rochers and Revillon Coupe channels in an effort to mitigate the adverse effects of Bennett Dam regulation on the Peace-Athabasca Delta. In 1983, the Peace-Athabasca Delta Implementation Committee requested that the Environment Canada 1-Dimensional Hydrodynamic Model be employed to assess the performance of the weirs for the period 1960 to the present. Because the Bennett Dam was not constructed until 1967 and the resulting Williston Reservoir was not filled until 1971, it was necessary to simulate Bennett Dam regulation for the period 1960 to 1971. The simulated Bennett Dam flows were routed to the Peace Point gauge which represents one of the upstream boundary conditions for the model. The computer simulations displayed by graphics in this paper indicate that the weirs have been effective in maintaining mean natural levels on Lake Athabasca and the delta lakes. However, simulated peak and observed peak levels for lakes Clair, Mamawi and Baril for the weirs in place and Bennett Dam regulation are about 0.3 m lower than the simulated and observed natural levels. This observation suggests that supplies are not being replenished as often in the perched basins under this modified regime with even the weirs in place. The same hydrodynamic model was used to simulate the upstream hydraulic effects resulting from installation of the proposed Slave River Dam located about 4 km downstream of Mountain Rapids with a constant headpond elevation of 206 m. The simulations indicate that the proposed dam is equal in effectiveness to the present weirs installed in the Delta in restoring natural levels in the delta lakes. However, higher winter levels occur in the upstream reaches of the Slave River which would seriously affect the wintering habitat of the bison herds.