Modeling of runoff and chemical solute transport

The importance of non-point pollution has long been recognized for watersheds on claypan soils. The understanding of water movement for both surface and subsurface flow under the claypan soil conditions is significant for understanding the chemical solute transport.; A hybrid finite analytic method (HFAM) was used to solve lateral subsurface flow described by the extended Dupuit-Forchheimer equation. A program, VS2DT, was also used to investigate the two-dimensional variably saturated lateral subsurface flow. The HFAM numerical tests showed that this technique performs as well as the complete theory with little computational effort and time. This advantage will be significant in the modeling of a complex rainfall-runoff process when the kinematic wave approximation is inappropriate. The investigation conducted using VS2DT showed that the contribution of subsurface flow to the total runoff is insignificant.; A comprehensive runoff model for a field location in Goodwater Creek Watershed near Centralia, Missouri, without a subsurface component, consists of overland and stream flows and includes the effects of interception and infiltration. The finite difference method was used to discretize the diffusion wave flow equations. Interception was estimated using an empirical formula. Infiltration was calculated using the Green-Ampt model. Good agreement between observed and simulated hydrographs was obtained.; A chemical solute transport model without considering the influence of chemical kinetics and adsorption was developed based on the soil mixing zone theory and the runoff model. A comparison between simulated and observed discharge-averaged concentration for several events was made. Sensitivity analysis for the hydraulic and chemical parameters involved in this model was made. This analysis showed that if the infiltration is high the hydraulic conductivity will be significant for the solute transport. The initial concentration in the mixing zone and the depth of mixing zone have significant influence on the solute transport.