| Summary: | Fecal pollution is one of the major factors responsible for water quality impairments of rivers and streams, particularly organic-rich fine-grained lowland streams. While predicting fecal pollution is generally required in the development of water quality restoration plans like Total Maximum Daily Loads, no single model has been widely recognized as an efficient and effective tool for estimating fecal pollution.
This dissertation develops a simple yet effective modeling approach, called Hydrograph-based Approach, to bacterial fate and transport modeling in lowland rivers. The new hydrograph-based approach is simple and efficient in terms of its less data requirements as compared with other models. The new approach utilizes widely available hydrographs as the primary model input data. The new hydrograph-based approach is effective in terms of its capability in predicting bacterial concentrations for a wide range of flow conditions from low flow without sediment to flood events carrying high concentrations of sediment. The development of this new approach is based on the following major works: 1) a hydrograph-based method for determining bed shear velocity and other flow parameters was developed and tested using measured experimental data as well as simulated results from HEC-RAS for two river flood events; 2) a relatively simple hydrograph-based method for estimating sediment transport during unsteady flows was developed and tested using sediment concentration data collected during several flood events in two US rivers; 3) the solute transport process in rivers, in particular, the effect of channel size on residence time distribution, was investigated using a variable residence time model; and 4) a hydrograph-based approach for modeling bacterial fate and transport was developed, utilizing the variable residence time model for mass transport and hydrograph-based methods for flow and sediment transport, and tested through case studies using data observed in three rivers with distinct flow and sediment transport characteristics. This hydrograph-based approach includes most of the important bacterial transport and fate processes such as advection, dispersion, transient storage exchange, resuspension/deposition, and bacterial growth/decay. The modeling results using this approach appear to be better or at least comparable with the results from other more complicated models.
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