Use of Elcom and Caedym for Water Quality Simulation in Boulder Basin

The growth of the Las Vegas Metropolitan area may eventually lead to increased wastewater discharges into Boulder Basin of Lake Mead (Figure 1). Boulder Basin has experienced several algal blooms over the last few years. As a result, alternate discharge locations and strategies are being investigated. Thus, studying the water quality in Boulder Basin becomes imminent in order to assist various agencies in making decisions on operations within Boulder Basin.Due to its extremely irregular shoreline and large surface area, Lake Mead cannot be simulated adequately by one or two-dimensional models. Therefore, ELCOM (Estuary and Lake COmputer Model), an advanced three-dimensional hydrodynamic model coupled with CAEDYM (Computational Aquatic Ecosystem DYnamics Model) was chosen to simulate threedimensional transport and interactions of flow physics, biology, and chemistry in the reservoir.ELCOM was designed for practical numerical simulation of hydrodynamics and thermodynamics for inland and coastal waters. The code links seamlessly with the CAEDYM model undergoing development at the University of Western Australia Centre for Water Research. The combination of the two codes provides three-dimensional simulation capability for examination of detailed changes in water quality. Figure 2 shows the three-dimensional ELCOM grid used for the Lake Mead simulation.This work involves the set-up and application of the models for Boulder Basin. Comparisons between measurements and simulation results show that ELCOM can accurately simulate the temporal and spatial variations of physical (e.g., temperature and conductivity), biological (e.g., chlorophyll-a and total organic carbon), and chemical (e.g., nitrogen and phosphorus) parameters. This study indicates that the hydrodynamic patterns of Boulder Basin are mainly driven by the Colorado River inflow, the Hoover Dam outflow, and meteorological parameters (especially episodes of high wind speed). However, the water quality of Boulder Basin is also affected by the load of nutrients (mainly phosphorus) from the Las Vegas Wash, which carries the treated wastewater effluents from municipal wastewater treatment plants, surface runoff, and groundwater discharges into the basin. This presentation will show animations of the flow within the reservoir, as well as “movies” that depict tracer and contaminant concentrations and velocity vectors. For example, Figure 3 shows the model predictions for water velocity vectors at the level of the Hoover Dam Upper Intake (about 150 ft below the water surface) at different times.