Integrated Hydrologic Modeling
Surface Water–Groundwater Interactions
Integrated hydrologic modeling leverages advanced knowledge of interactions within all aspects of the water cycle — atmospheric water, surface waters, and groundwater. The Illinois State Water Survey (ISWS) is able to leverage its robust expertise across the hydrologic sciences and its 130 years of data to use integrated hydrologic models to address the issues facing the state of Illinois today. This represents a major step forward from previous modeling at the survey, where hydrologic research and management were separated into spatially discrete domains — e.g., surface waters being simulated separately from groundwater. The advent of integrated hydrologic models allows for a deeper understanding of processes and more powerful forecasting tools that can be deployed to analyze both local and regional hydrologic systems.
Historically, our research group has used MODFLOW (a modeling software produced by the United States Geological Survey) to analyze Illinois’ groundwater resources. ISWS also developed its own groundwater modeling software, PLASM, that predates the development of MODFLOW. These software programs focus primarily on calculating saturated subsurface flow conditions. However, this neglects unsaturated near-surface conditions, which are especially important when analyzing the interaction between surface waters and nearby shallow aquifers.
A caveat – MODFLOW has developed packages to analyze these important dynamics – Unsaturated Zone Flow (UZF) and Soil-Water-Balance (SWB).
To expand the hydrologic analysis tools in our toolkit, our research team is utilizing the integrated hydrologic modeling software ParFlow. ParFlow is based on using the Richards Equation to calculate water flow in both unsaturated and saturated conditions. This facilitates analyzing areas near land surface that are regularly wet and dry due to both precipitation and fluctuating near-surface groundwater levels.
Which model is better?
To answer simply, it depends.
The modeling tool we employ depends on the research question we are answering. For example, if we are analyzing the dynamics of a deep aquifer (e.g., thousands of feet deep), we would use MODFLOW for our research simulations because we are primarily concerned about saturated hydrologic conditions.
Ultimately, there is no better or worse. Our research group is open to all tools and analysis techniques that help improve our understanding of hydrologic conditions in the state of Illinois and beyond.