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.
Hydraulic modeling will eventually displace most field testing and bench modeling for the evaluation of clearwells.
The Safe Drinking Water Act and its amendments impose stringent guidelines on all plants that treat surface water. Virtually all such plants use clearwells to increase the duration of disinfection. A challenge in the design of these facilities is maximizing disinfection while limiting the formation of disinfection by‐products. These competing objectives can best be attained by optimizing the hydraulic performance and efficiency of clearwells.
Many researchers have had difficulty interpreting sediment data collected from the Palos Verdes Shelf, southern California. Factors that have been difficult to reconcile include the distribution of 210 Pb and metals, the depth and extent of bioturbation, and the rate of sedimentation. This paper presents a simple model that includes these elements and simulates the flux of 210 Pb, sediment, and metals to the sea floor near the Whites Point wastewater outfalls. The model uses known particle and metals emission rates from the outfalls and 210 Pb fluxes to the sediments that vary in proportion to the flux of sediment mass to the sea floor. Model-predicted metals and 210 Pb concentration profiles in the sediments agree well with data from cores collected at three locations on the Palos Verdes Shelf between 1972 and 1997. The implication of the model results is that 210 Pb fluxes to the sediments in this area have varied greatly over the past 60 years. The model suggests that subsurface 210 Pb maxima and uniform 210 Pb concentrations to depths within the sediments of roughly 30 cm have resulted from time-variable 210 Pb fluxes to the sediments and relatively shallow bioturbation and that natural sedimentation rates are relatively high (roughly 500-1000 mg cm -2 yr -1 , or about 0.7-1.3 cm yr -1 of unconsolidated sediment).
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