| This thesis focuses on the transport of mobilized contaminants in riverine sediments. A two-dimensional numerical model which simulates contaminant flux through the water column-benthic sediment interface in the presence of sediment bed forms has been constructed. Characteristics of the model include: hydrodynamics in the porous sediment modeled using the Darcy's Law; a sinusoidal pressure distribution used to describe the stream flow-induced pressure distribution that over sand dunes and ripples of sediment bed surfaces; and use of the hydraulic gradient of the stream flow to generate longitudinal underflow in the porous sediment bed. Numerical simulation results show that, depending on a number of environmental factors including depth of the hotspot, hydraulic conductivity, height of the bedforms, and other factors, the stream velocity can significantly affect the vertical flux (the flux of mobilized contaminants from the benthic sediment bed into the water column). In addition, the model results indicate that under certain environmental conditions, a significant amount of mobilized contaminant may be released from the benthic sediment into the water column. The model also predicts the distance downstream of the hotspot where the maximum net vertical flux is expected to appear.; A 2.1 meter laboratory flume filled with 3 mm glass beads and injected with a non-sorbing tracer was constructed to test the model predictions. The numerical model was calibrated with the flume study data and two model parameters, related to bed was calibrated with the flume study data and two model parameters, related to bed surface pressure and hydraulic gradient of overlying flow, were adjusted to complete the model calibration. The numerical model after calibration showed close agreement with the flume-generated experimental data.; Results of this effort verify that the model used is valid for predicting the mass flux between the water column and the sediment bed in the laboratory flume. The model developed here can be used as a planning tool for water quality management or, with modification, used within other models, such as Water Quality Analysis Simulation Program (WASP). |
