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Modeling surface water and groundwater interactions in agricultural areas
In this dissertation research, three modeling tools have been developed to help quantify the complex processes of integrated surface- and ground-water systems in an area under significant agricultural development of Nebraska. To evaluate irrigation effect on stream depletion for the Lower Platte River (LPR) basin, a regional three-dimensional, transient groundwater-flow model is established with MODFLOW. A simplified and more efficient solution has been developed to estimate the stream depletion rate by re-using the flow coefficients of the baseline run. The flow equation is linearized because the head coefficients become constant between solver iterations. The tool has been successfully applied to the LPR model. The results show that the stream depletion analysis tool can reduce the numerical errors produced in the conventional method and improve the computational efficiency. The second modeling tool is a cross-section based streamflow routing (CSR) package for MODFLOW to simulate the streamflow and the interaction between streams and aquifers for the stream with a width larger than the MODFLOW grid size. In the CSR package, streams are divided into stream segments which are formed by two consecutive cross-sections. A rapid algorithm is used to compute the submerged area of the MODFLOW grid. Stream-aquifer seepage is treated as lateral flow in the streamflow routing computation with the Muskingum-Cunge method or mass conservation method. A hypothetical problem was established to test the capabilities of the CSR package with steady- and transient-state models. The third part of this dissertation aims to quantify the impacts of natural processes and human activities on ground-water dynamics in highly agricultural areas by developing an integrated surface-ground water model (ISGWM). In ISGWM, SWAT and MODFLOW are linked by a soil water module (SWM), which is developed based on a non-iterative solution of the 1D Richards equation. SWM explicitly represents infiltration, soil evaporation, unsaturated water flow, root water update, and lateral drainage. Taking advantage of the simulation capacities of these SWAT, MODFLOW and SWM, ISGWM can simulate the physical hydrologic processes in three domains and their interactions. The model has been successfully applied to the Johnson Creek watershed, which is located within the Lower Platte Basin.
Hydrologic sciences|Civil engineering|Water Resource Management
Ou, Gengxin, "Modeling surface water and groundwater interactions in agricultural areas" (2015). ETD collection for University of Nebraska - Lincoln. AAI3718063.