Simulation of Hydrodynamics, Temperature and dissolved oxygen in Beaver Lake

The tailwaters of Beaver Lake and other White River reservoirs support a cold-water trout fishery of significant economic yield in northwestern Arkansas. Proposed increases in minimum flows released from the dam have produced concerns about the sustainability of cold-water temperature and dissolved oxygen in the bottom water above the Beaver Lake Dam. There is concern that even slight warming of the release waters might decrease the length of the tailwaters thermally suitable for trout growth and sustainability, possibly adversely impacting the trout fishery. Thus, this study intended to assess the impact of additional minimum flows on the temperature and dissolved-oxygen qualities in Beaver Lake water above the dam and the released water. A two-dimensional laterally averaged hydrodynamic, thermal, and dissolved-oxygen model was developed for Beaver Lake, Arkansas. The model was calibrated and verified using hydrologic, meteorological, physicochemical and other water-quality data measured in or near Beaver Lake from January 1994 through December 1995. The model simulates surface-water elevation, currents, heat transport, and dissolved- oxygen dynamics. The model was developed to assess the impacts of proposed increases in minimum flows from 1.76 m3/s (the existing minimum flow) to 3.85 m3/s (the additional minimum flow). Simulations included (1) the impact of additional minimum flows on tailwater temperature and dissolved-oxygen qualities and (2) increasing initial water-surface elevation 0.5 m and assessing the impact of additional minimum flow on tailwater temperatures and dissolved-oxygen concentrations. With the increase in minimum flow, water temperatures appeared to increase (<0.9 C) and dissolved oxygen appeared to decrease (<2.2 mg/L) in the outflow discharge. Conversely, increasing minimum flow plus increasing initial pool elevation (0.5 m) apparently lowered the outflow water temperature (<0.5 C) and increased dissolved-oxygen concentrations (<1.2 mg/L). However, these results were within the boundaries or similar to the error between measured and simulated water-column profile values. This model provides the basis and framework for future water-quality modeling of Beaver Lake—as extensive data are collected in both the reservoirs and tributaries the existing model can be adjusted to assess the nutrient assimilative capacity of the reservoir, nutrient limitation, and the effect of increases in nutrient loading on reservoir trophic status.