SWAT-Modflow: Hydrologic and Water Quality Modeling Tool for Coupled Land Surface / Groundwater Systems.

Hydrologic and water quality models frequently are used to assess groundwater and surface water resources, quantify groundwater-surface water interactions, assess levels of contamination in groundwater and surface water, and predict the impact of climate change and land management practices on water quantity and water quality. These models focus on a single system (aquifer, stream) or on the entire watershed system that includes land surface hydrology, groundwater hydrology, streamflow, and interactions between groundwater and surface water. This presentation provides an overview of the development and applications of a new hydrologic model that couples the Soil Water and Assessment Tool (SWAT) with the groundwater flow model MODFLOW. The SWAT-MODFLOW model accounts for land surface hydrology, in-stream hydrologic and bio-chemical processes, multi-dimensional groundwater flow and solute reactive transport, and groundwater-surface water interaction and solute mass exchange. Details of model applications to several watersheds, including the Upper Klamath River Basin (Oregon), the Middle Bosque watershed (central Texas), the South Platte River Basin (Colorado), and the Ogallala Aquifer Region in eastern Colorado and northwestern Kansas, are presented. Current topics of research that are being addressed through these applications include groundwater-surface water interactions, impact of climate change on groundwater resources, groundwater storage in arid climates, storage and transport of nutrients (nitrogen and phosphorus) in an irrigated agricultural watershed, and the effect of subsurface tile drains on nutrient mass loading to streams.