Effects of land use on recharge potential of surficial and shallow bedrock aquifers in the upper Illinois River basin

Abstract

The upper Illinois River Basin (UIRB) is the 10,949-square-mile drainage area upstream from Ottawa, Illinois on the Illinois River and is one of the U.S. Geological Survey’s National WaterQuality Assessment (NAWQA) program study units. To assist in the interpretation of groundwater data that will be collected during the course of the UIRB study, the study-unit team designed a spatial model to describe recharge potential of surficial and shallow bedrock aquifers. The following factors, identified as having an effect on recharge potential, were incorporated into the model: land use, soil permeability, type and thickness of surficial deposits, and uppermost bedrock geology. Other models designed to simulate recharge potential and the potential for contamination that were examined during the preparation of this model included factors similar to those included in this model, with the exception of land use. Land use and changes in land use over time, however, can affect recharge potential. The UIRB model was used to simulate recharge potential with and without incorporating land use. A comparison of the simulation results showed that recharge potential was overestimated in some areas and underestimated in other areas when land use was not included in the model. Comparisons of simulations that used 1970 and estimated 1990 land use showed changes in recharge potential over time. INTRODUCTION The National Water-Quality Assessment (NAWQA) program of the U.S. Geological Survey was designed to provide a national view of the status and trends of the Nation’s water resources (Hirsch and others, 1988). This national design facilitates a comparison of water-quality conditions across the country and provides consistent monitoring of water-quality conditions over time. The NAWQA program utilizes an interdisciplinary approach, which integrates groundand surface-water hydrology and biology, to study basin ecosystems. The NAWQA program is designed around approximately 60 major surface-water drainage basins, called study units. These study units include about one-half the area of the conterminous United States and supply water to approximately 65 percent of the population that relies on public-water supply (Gilliom and others, 1995). The upper Illinois River Basin (UIRB) is one such study unit in the NAWQA program (Friedel, 1998). The UIRB covers 10,949 mi 2 upstream from Ottawa, Illinois, on the Illinois River in parts of northeastern Illinois, northwestern Indiana, and southeastern Wisconsin. Some of the major water-quality issues in the UIRB are related to urban and agricultural land use: municipal and industrial wastewater releases, urban and agricultural runoff, and atmospheric deposition of pesticides and trace metals (Friedel, 1998). In 1990, most land use in the basin was agricultural (75 percent of the area), followed by urban (17 percent of the area) (Hitt, 1994; Hitt, 1992; Arnold and others, 1999). The human populations and activities within these two principal land-use areas make large demands on the water resources of the basin. Chicago is the largest urban area in the UIRB. In the northern part of the basin, particularly along the Fox and Des Plaines Rivers, suburban expansion