Numerical modeling of shock wave propagation and contaminant fate and transport in open channel networks

In this thesis, numerical methods and mathematical models for flow simulation and contaminant fate and transport in open-channel networks were investigated. A new-type shock-capturing relaxation scheme were proposed for simulation of flow and shock wave propagation in an open channel. The proposed relaxation scheme is based on the construction of relaxation system that approximates the original nonlinear system of conservation equations for a small relaxation time. This leads to a simple and efficient scheme when compared with other modern shock capturing methods. Then, by combining the relaxation scheme with the Method of Characteristics (MOC), a hybrid algorithm was proposed for flow and shock wave propagation simulation in open channel networks. Furthermore, a solute transport model which includes transient storage was proposed. This model, by coupling with the hydrodynamic model, can be easily applied to the solution of solute transport and fate in open-channel networks under an unsteady flow regime. A fractional-step algorithm which combines the relaxation scheme and a central difference of an implicit scheme was proposed for the solution of transport equation. The algorithm is valid even for transport process with dominant advection. Furthermore, a contaminant-sediment infraction model, which includes various physical and chemical processes and a transient storage mechanism was developed for modeling transport and fate of radionuclides, trace metals and toxic chemicals in the streams. Through application to several test and field problems, the usefulness, accuracy and efficiency of the proposed models and algorithms were demonstrated. Finally, a computer Modular Modeling System with a user-friendly graphic interface based on the proposed methods and models was developed for flow simulation and contaminant transport and fate analysis in open-channel networks.