Development of conjunctive management and soil pesticide transport models

Four different models have been developed in this report. The first two models are coupled simulation-optimization models that can be used to find the optimal joint operation of surface and groundwater supplies without addressing water quality issues. Among these two optimization models, the first one is a linear mathematical model formulated based exclusively on physical quantities of the hydrogeologic system. The second one is an extended version of the first model, which involves the operational costs of various components of a hydrogeologic system. Unlike the first one, the second optimization model is a nonlinear mathematical model, thus it is computationally more intensive. Surface and subsurface flow components in both models are coupled through numerically-generated response equations to account for system heterogeneities.; The third and fourth models are developed to simulate the transport and fate of agrochemicals in soils and streambeds. The third model focuses on the contaminant transport in radial coordinates across a soil particle by considering mass interaction between intra-particle and surrounding bulk concentrations. This model is solved using the Linear Driving Force (LDF) approximation for both volume-averaged and spatially-varying intra-particle concentrations. The performance of the LDF model is then compared against the numerical model coded based on the finite-difference approximation. In the fourth model, the transport and fate of agrochemicals across the root and vadose zones are formulated using a compartmental approach by drawing an analogy between a series of continuous-flow stirred rectors and a soil column with many sub-layers. A number of sorption kinetic models are linked to the newly developed soil-pesticide model. The compartmental approach used in the formulation allows: (1) the consideration of spatially-varying initial contaminant concentration across the soil horizons; and (2) various forms of pesticide loading through the top soil.; Because a dynamic linkage between the aforementioned optimization and contaminant simulation models in a single optimization framework is not computationally and practically efficient, those models are developed separately. However, they can be used interactively in the remediation decision-making that requires screening of various proposed alternatives on water- and pesticide-use policy when both hydrological and environmental criteria are of concern.