ROBUST HABITAT ESTIMATES FROM RIVER2D USING TWO WINTER HYDROMETRIC SURVEYS FIVE YEARS APART ON THE NORTHLANDS STUDY REACH OF THE ATHABASCA RIVER

摘要

The amount of aquatic habitat versus river discharge is a basic output of hydraulic and habitat simulations. The functional relationship between discharge and fish habitat indexes, such as WUA (weighted usable area), is used extensively to make instream flow recommendations. The accuracy of simulated hydraulic variables, such as water depth and velocity as well as habitat estimates, such as WUA for specific life stages of each species of interest, is rarely evaluated several years after first estimated. Water supply for oilsand extraction projects and ecological concerns led to habitat simulation studies in the lower Athabasca River, with particular emphasis in winter when flows are lowest. Two hydrometric surveys in the Northlands study reach were conducted in winter with ice-covered conditions in 2004 and 2009, representing river discharges of 148.0 m~3/s and 118.6 m~3/s, respectively. Athabasca River daily discharge ranges from 75 to 250 m~3/s (1957-2009) during ice covered conditions. The two surveys are used to compare hydraulic and habitat estimates in the critical winter season using the River2D model. The river reach Total Wetted Areas and the species specific life stage WUAs were comparable, in spite of the fact that the distribution of suitable habitat shifted between 2004 and 2009 as evidenced by changes in water depth and channel bed between the two surveys. Estimated measurement errors for river depths and velocities were within acceptable limits. The ratio of Wetted/Total Area based on contours of depth or velocity had estimated errors within 5.6% and 15.7%, respectively. For adult walleye (Sander vitreus), error estimates for the ratio of WUA/Total Wetted Area were within 3.4% or 7.6% based on previous depth or velocity contours. Similarly, the corresponding error estimates for the same ratio were 4.5% and 14.1% for adult longnose sucker (Catostomus catostomus) and 3.1% and 6.8% for northern pike [Esox lucius). Overall, hydraulic and habitat modeling provided robust functional relationships between WUA and river discharge.