Groundwater recharge estimation in an urbanizing watershed using GIS and groundwater modeling, Dekalb County, Illinois

This study addressed a problem which is increasing worldwide-impact of urbanization on groundwater recharge. The groundwater recharge estimation has been a poorly understood process and well-recognized as a difficult scientific problem. The problem becomes more complex when the area is urbanizing. This study is a significant contribution towards the better analysis of recharge in shallow aquifers beneath the urban areas. This study combines an older technique (mass-balance equation) with new advanced and sophisticated tools of Geographical Information System (GIS) to determine recharge over the rapidly urbanizing Upper South Branch Kishwaukee Watershed in DeKalb County, Illinois. The two main sources of urban leakages, in the study area, water mains distribution and sewerage leakage are evaluated for final recharge estimations. The method is automated using ArcGIS model-building tool that makes the calculations more reliable and efficient and can be replicated into different areas due to its simplicity.;The estimated recharge values for example years 1996, 2000 and 2005 are then included in a MODFLOW based groundwater flow model of the area by developing a new tool which is unique and can be used with any other groundwater model with different grid size. The model was calibrated without altering the recharge values for verification and simulation of estimated recharge rates. The modeling results show a good correlation between computed and observed head and streamflow values. However, the model is very sensitive to the values of hydraulic conductivity of aquifer layers.;This study developed an urbanization model to predict future urban land cover and resulting recharge rates. The predicted recharge rates were simulated through the developed groundwater flow model to better understand the long-term impact of urbanization on groundwater recharge to the shallow aquifers. The study predicts that urbanization results in decrease of 7-10 feet in groundwater levels of shallow system by 2020.