Lake Mead, the largest-volume man-made reservoir in the United States, faces a variety of challenges, including increasing demands for municipal water, 10 years of drought in the Colorado River system, lower water surface elevations, discharges of highly treated wastewater effluent, invasive mussels, and climate change. Lake Mead is an important source of water for 25 million people in the southwest U.S. and is also a National Recreation Area. Thus, it is imperative that the lake be adequately protected and managed to meet the often competing needs of the multiple users. A well-calibrated and validated three-dimensional hydrodynamic and water quality model of Lake Mead has been a key component of this management strategy, enabling hydrodynamics and water quality within the reservoir to be predicted and assessed for a wide range of anticipated conditions. The model was developed using the ELCOM and CAEDYM simulation codes, and has been calibrated and validated for the 2000-2008 period using measured field data for temperature, conductivity, perchlorate, bromide, chlorophyll a, nutrients (phosphorus and nitrogen), total organic carbon, pH, and dissolved oxygen. The model captured the hydrodynamics and water quality of this complex system well, and the standard errors of the model results for selected parameters were found to be larger than, but of the same order of magnitude, as the accuracy of the measured field data.
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 setup 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 3943 WEFTEC®.06
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