AMEC was retained by CEMA in February 2008 as the prime consultant on a team with Northwest Hydraulic Consultants to execute a detailed bathymetric and hydrometric survey at key locations in the Athabasca River delta. The summer survey was conducted in the 2008 open water season (AMEC-nhc, 2008a) while the winter survey was conducted in February 2008 (AMEC-nhc, 2008b). The surveys focused on four sites within the delta.
This report presents the results of a hydrodynamic and fish habitat modeling exercise for Site 2 and Site 4 using the River2D hydrodynamic model.
HYDRODYNAMIC MODELING
Model boundaries were selected which encompassed all the topographic data in each segment which typically included the top of bank line and one additional survey point taken approximately 10 m inland from the top of bank. The upstream boundary at Site 4 was extended about 400 m upstream of the survey data to allow the model to simulate the velocity distribution measured at Section 4-1Q. The final open water simulations were carried out with bed roughness values of 50, 80, 100 and 120 mm with a bed roughness of 80 mm providing the best overall fit to the observed water surface elevation data. The final under ice simulations were carried out for ice roughness values of 80, 120, 160, 200 and 240 mm with an ice roughness of 160 mm providing the best overall fit to the observed water surface elevation data. Under both open water and under ice conditions, the modeled water surface elevations were found to be insensitive to the roughness values selected but were sensitive to the water level assigned to the downstream boundary. The simulated velocities matched the measured velocities reasonably well under both open water and under ice conditions.
FISH HABITAT MODELING
Outflow boundary rating curves at Site 2 and Site 4 were developed using an average Lake Athabasca water level computed based on lake level records between 1998 and 2006. Using the open water outflow rating curves, a total of 116 different river discharges at Site 2 and 112 different river discharges at Site 4 were selected to represent both extreme low flow conditions and extreme high (but confined within the channel) flow conditions. Using the under ice outflow rating curves, a total of 20 different river discharges each at Site 2 and Site 4 were selected to represent both extreme low flow conditions and extreme high (but confined within the channel) flow conditions. River2D models were generated for each of the above open water and under ice modeling conditions. For each open water River2D model, the total available wetted area was computed as were the weighted useable area (WUA) values for a total of ten different fish species/life stage combinations. For each under ice River2D model, the total available wetted area was computed as were the weighted useable area (WUA) values for a total of three different fish species/life stage combinations.