Illinois River Basin Investigation

River with choppy water, surrounded by rocks and trees.

Illinois River Basin Investigation

Overview

The Illinois State Water Survey has partnered with the United States Geological Survey for an in-depth investigation into groundwater flow conditions in the Illinois River Basin. This basin was selected as the third watershed to be studied in the USGS’s Next Generation Water Observing System investigation. The ongoing project (June 2023 – June 2025) is the first part of a 10-year study. While the overarching goal is to understand the fate and transport of nutrients and the potential drivers of harmful algal blooms, the study also has sought to evaluate water availability, urban flooding, and emerging contaminants.  

ISWS is currently investigating four aspects of groundwater conditions in Illinois: 
Two model plots — upper shows the outlines of Illinois, Lake Michigan, and the Illinois River Basin. Lower plots shows a cross-section of the upper 200 meters of geology.
Groundwater Flow Modeling
Map of groundwater nitrate concentrations throughout the Illinois River Basin.
Nitrate
Map of bedrock elevations throughout the Illinois River Basin.
HTEM Analysis
An installed irrigation flow meter that measures the water used during irrigation.
Irrigation Meters

Groundwater Flow Modeling

The groundwater flow model of the Illinois River Basin streamlines data sources from Illinois, Wisconsin, and Indiana within a highly flexible framework using the USGS code Modflow-Setup. This Python code allows a user to modify the model to meet the needs of the user.

By changing just a few lines of code, the model can be modified to run steady state at a regional scale to answer broad questions related to water availability. This allows a user to evaluate water availability questions, such as regional drawdown.

Plot outlines the state of Illinois, and the Illinois River Basin being modeled. Map depicts the nature of the connection between surface waters in the Illinois River Basin and the nearby groundwater. Red line segments denote where the stream is discharging water to the groundwater, while blue lines show were groundwater is discharging into nearby rivers. Most river segments throughout the Illinois River Basin are blue (i.e., receiving water from nearby aquifers).
Steady-state model of the Illinois River Basin’s groundwater contributions to nearby surface waters.

Similarly, the framework can be modified to create a local scale model capable of investigating groundwater-surface water conditions at a monthly time scale. This flexibility is essential to evaluating drought conditions in an aquifer.

A time-series plot of groundwater observations compared against modeled groundwater elevations at the same site (pnumber 4413385). The modeled groundwater levels extend from years 2000 to 2020, while empirical observations a recorded only after 2016. From 2016 to 2020, the model results overlap the observed results fairly well.
Local Scale Transient Model

The model framework also allows users to zoom in to a specific area of Illinois for more detailed modeling and analyses. In the below example, the parent and child models are dynamically linked using local grid refinement.

Map of the model domain of the Illinois River Basin, with specific inset models outlined.
Regional Model – Illinois River Basin (blue) model domain outline, with smaller inset models outlined, including the Imperial Valley Water Authority (dashed black) model area, and the Mason City (solid black) model area.
A map of the Imperial Valley Water Authority model area boundary (dashed line), and the Mason City model area boundary (solid line). These areas are at higher resolution and have greater detail than the surrounding Illinois River Basin model.
Parent Insert Model (LGR)
A map of a portion of the Illinois River Basin. The Mason City model area is outlined in a solid black line. This model area is a subset of greater resolution and detail than the rest of Illinois River Basin model.
Child Insert Model (LGR)

The initial framework is currently undergoing review and report preparation. In late 2025, the report will be released, and the model will be made publicly available on GitHub. You can learn more by reviewing the following poster presentation abstracts from 2024:

Nitrate

Analysis is ongoing, results to come.

HTEM Analysis

Analysis is ongoing, results to come.

Irrigation Meters

Analysis is ongoing, results to come.

Computational Hydrology for Decision Support
2204 Griffith Dr.
MC-674
Champaign, IL 61820
217-333-2210
Prairie Research Institute

Illinois State Water Survey (link opens in new window)

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