A depth-averaged two-dimensional water quality model as a research and management tool.

摘要

Sediments have been identified as one of the leading non-point source pollutants since 1980's. The contaminated sediments pose threats to human health, environment and ecosystems. Total Maximum Daily Load (TMDL) and Best Management Practice (BMP) are two major water quality management measures. To fully study the water quality problems and guide the design of TMDL and BMP, a comprehensive two-dimensional depth-averaged water quality model framework for freshwaters was developed.; The model framework comprises of three newly developed models: cohesive sediment transport model, water quality model (eutrophication model), and chemical fate and transport model. These three models were integrated with a robust hydrodynamic and non-cohesive sediment transport model, CCHE2D. The model development followed the steps of process formulation, model coding, model verification and validation.; These three models are based on the state-of-the-art mechanisms of major physical, chemical, bio-chemical processes of freshwater systems. Each model was constructed independently in a modular structure so that it is flexible to meet the needs of site-specific problems and is easy to be updated and improved. The models were first verified by analytical solutions and then validated using six lab and field cases.; Several empirical formulae for cohesive sediments were examined and found that there is a big uncertainty in the prediction of bed shear strength. A simple linear relationship for bed shear strength was found to fit well with the measurement for newly deposited cohesive sediment.; Incorporation of the impact of suspended sediments into the general water quality model extends its capability of simulating the sediment-laden water bodies with higher accuracy. The model can be used to carry out numerical sensitivity analysis to find out how the system responds to different levels of suspended sediment concentration.; The integrated flow, cohesive and non-cohesive sediment transport model, chemical fate and transport model was applied to the study of Upper Hudson River PCBs. The long term simulation of PCBs shows satisfactory agreement with the measurement.; The comprehensive model framework was demonstrated for its capabilities. The real world water quality problems associated with sediments are ready to be solved.