Watershed Modeling for Surface-Groundwater Interactionby Wayne E. Woldt, P.E., Ph.D.,
George Yeh, P.E., Ph.D.,
Abstract: Groundwater use has increased rapidly due to irrigation development in the Great Plains. This is especially true in the Republican Basin that intersects the three states of Nebraska, Kansas and Colorado. The significant increase in groundwater utilization for irrigation is suspected of inducing changes to the surface water system, due to the highly connected nature of these water resources. Therefore, a greater understanding of the complex surface-groundwater system is very important for better management of water resources in this region. The Frenchman watershed is a sub-basin of the Republican Basin that extends from northeast Colorado to south-west Nebraska with an east-west length of about 246 km. It is a semi-arid region with land surface sloping from west to east; and currently exhibiting impacts of drought with an increase in irrigation wells, leading to stream depletion. Various surface water modeling and groundwater modeling programs are used for the study of the interaction between subsurface and stream flow. The interaction analyses are developed using fairly simplistic assumptions, and do not represent an integrated system, such as during the simultaneous simulation of both stream and subsurface flow. This is not likely to represent the real situation of the complex interaction processes. WASH123D is a complex integrated watershed modeling system capable of simulating subsurface, overland, and stream flow in a fully integrated manner, which considers various hydrogeologic properties of the study area, providing a more in-depth conceptualization of groundwater and surface water flow patterns and connections of the region. One of the challenges of employing fully integrated models is the computational demand that stems from the complex systems and numerical schemes. The objective of this research is to implement a complex model, and study the interaction processes of groundwater and surface water flow in an integrated simulation framework. Analysis of the resultant recharge and discharge zones of aquifers and streams of the study region from an integrated watershed perspective, along with the interaction of surface and subsurface flow will be discussed.
Subject Headings: Groundwater | Watersheds | Subsurface flow | Model analysis | Flow simulation | Streamflow | Surface water | Water flow | Terrain models | Water resources | North America | United States | Nebraska | Colorado | Kansas
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