Multiphase distribution of cohesive sediments and heavy metals in estuarine systems

Characterization of the types and concentrations of heavy metals in their various phases is needed to assess potential adverse effects on the aquatic environment and its ecosystems, and thereby to assure cost-effective mitigation and waste-allocation strategies. A two-dimensional vertically averaged finite-element model was extended to predict the spatial and temporal distribution of cohesive sediments and associated toxic heavy metals as a result of a pollutant input into an estuarine system. Constitutive relationships for cohesive sediment deposition and erosion, heavy metal adsorption and desorption, and the governing hydromechanical transport mechanisms were incorporated in an existing sediment transport model. Formulation and validation of a new relationship for deposition was based on data derived from experiments carried out by previous investigators. The fate and transport of cohesive sediments and associated nickel was simulated for south San Francisco Bay. The comparison of model performance against field observations indicated that the model is capable of representing important phenomena governing the fate of cohesive sediments and associated nickel

Comparison of one- and two-dimensional models for simulation of hydrodynamics and water quality in shallow bays

A two-dimensional (2-D) vertically-averaged finite element model suite was adapted to investigate the hydrodynamics, water quality (WQ), and sediment-toxicant transport in San Diego Bay. The hydrodynamic model was calibrated and verified with two sets of observed data. Model predictions were also compared with the results from a previous study wherein a one-dimensional (1-D) finite difference approach was used. The 2-D model predictions of water surface elevations and velocities at specified locations in the bay were generally superior. The results of simulation of WQ constituents (temperature, nitrate-nitrogen, algae, and dissolved oxygen) using the 2-D WQ model compared well with the results from the I-D WQ model, both in the general trend as well as the specific distribution of constituent concentrations. Investigations were also carried out to determine the spatial and temporal distribution of sediments and a hypothetical sediment-borne toxicant in the bay. Results were found to be in general agreement with conclusions drawn from the hydrodynamic study