Groundwater Flow Models of Northeastern Illinois a case study
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Groundwater Flow Models of Northeastern Illinois a case study for building MODFLOW models with GIS PROJECT FRAMEWORK Abstract The Chicago metropolitan area of northeastern Illinois is experiencing rapid population growth, particularly in the suburban counties surrounding the city of Chicago. The population of one of these suburban counties, Kane County, is predicted to increase by as much as 36 percent by the year 2020. At this growth rate, five townships within Kane County are projected to experience local water shortages by 2020, prompting Kane County to fund a joint study by the Illinois State Water Survey and Illinois State Geological Survey of the water resources of Kane County. Managers and policy makers require a study that organizes the data, evaluates the system, improves understanding, and establishes a framework for follow-up analyses. This effort is assisted by the use of GIS and database technologies, which provide efficient tools for building a knowledge base for this study and translating geohydrological data into model-ready formats. Examples are provided for several procedures to efficiently manage, interpolate, and reformat MODFLOW data using ArcGIS 8.X. Figure 1. The model domain includes the active regional aquifer model (light gray) and local deep aquifer model (dark gray). The management of water resources in northeastern Illinois is complicated by international and interstate agreements, hydraulically coupled aquifer systems, natural and anthropogenic contamination, surface water – groundwater interaction, and conjunctive use of multiple resources. The net effect of these complications is that withdrawals from Lake Michigan cannot be increased beyond current rates, and the withdrawals from the deep bedrock Figure 2. Conceptual geological model of aquifers in northeastern Illinois aquifers may already be at their maximum. Urban planners have concluded that the region’s Flux & Head Watershed Withdrawal Surface Water Existing Non- Existing Digital Measurements Climate Data Boundaries Data Properties digital Maps Maps growing population will need to investigate the shallow aquifers as a source of water to meet Digitizing & Assembling Mass Balance Models USGS Stream Well Cell & Transient Stream to River Cell Interpolation & Smoothing growing demands Coding System Data Conversion Pattern Recognition* K/T/S Pattern & Rates The initial efforts of the project have focused on Recharge (R) Boundary Conditions Model Grid Structure assembling the data and information of previous Pattern & Rates studies in a unified format to provide the Groundwater Flow Model: MODFLOW 2000 framework for analyses. A series of databases Using GIS Platform and GIS files are being created for storage, (ArcGIS 8.x) Calibration Processing: UCODE No retrieval, and processing of these data (Figure 3). The end product of this initial step is a geologic Calibration Targets Head and Flux Optimum Parameter Values (R/K/T/S) and hydrologic data set extensive enough to permit modeling on an interstate basis, while Yes detailed enough to support site-scale models. Optimum GW Flow Model Parameter Sensitivity Rather than commit to a single model code or * Lin, Y-F., and M.P. Anderson, 2003. A Digital Procedure for Ground Water Recharge and Discharge Pattern Recognition and grid, this study has emphasized the use of GIS in Rate Estimation, Ground Water 41(3), p.306-315 cataloging, analyzing, and adapting the data, as Figure 3. Flow chart of the regional modeling process: 1) gray boxes well as procedures and scripts for translating indicate the processing applications; 2) The dashed box contains processes and data in a GIS compatible format. geohydrological data into model-ready formats. Yu-Feng Lin, Doug Walker, Scott Meyer firstname.lastname@example.org, email@example.com, firstname.lastname@example.org DATABASE INTEGRATION Several procedures have been developed to efficiently manage, interpolate, and reformat hydrogeological data using ArcGIS 8.2 and 8.3. Figure 4 illustrates the process employed for integrating geologic information collected from various states in different formats. We then apply procedures and scripts for translating geohydrological data into digital and model-ready formats (e.g., Figure 5). Silurian Maquoketa St. Peter Prairie du Chien St. Lawrence Ironton-Galesville Eau Claire Mt. Simon Precambrian Figure 4. An example of information unified under a GIS platform for re-interpolation based on MODFLOW grids. The bedrock elevation information includes GIS contours in different coordinate systems (IL and IN), contours manually digitized from paper maps (MI), USGS DEM data (SW WI) and interpolated point elevations from previous studies (SE WI and Lake Michigan). Figure 5. SURFER interpolation of nine major bedrock structural surfaces as a preliminary step in compiling a geologic regional model. GIS and other database tools have been used in organizing data and information of various types to create a knowledge base for this study and future studies. These data include an extensive database of groundwater withdrawals in Illinois, complete for the period from 1980 to present, presently being augmented with data for the pre-1980 period for the Kane County area (Figure 6). Low-flow data for 20 streams within the regional model domain have been assembled to assure that the calibrated regional model predicts reasonable rates of natural groundwater discharge to streams. Two hundred and two sets of shallow aquifer pumping test data in the Kane County area have been identified. High-quality pumping test data will be reinterpreted in later stages of the project to determine aquifer and aquitard hydraulic properties for use in local-scale groundwater flow modeling of the shallow aquifers. The above data will be in GIS and Microsoft Access compatible formats. (a) (b) Figure 6. Groundwater withdrawal database integration using GIS application: (a) deep aquifer withdrawal locations, and (b) shallow aquifer withdrawal locations. The data sources were from various state agencies. The shallow aquifer accounting region was selected by the watershed areas contributing to Kane county and the adjacent watersheds to those areas. Kane County Deep Aquifer Accounting Region Shallow Aquifer Accounting Region Illinois State Water Survey 2204 Griffith Drive, Champaign, IL 61820, USA GROUNDWATER MODEL The groundwater flow models for this study will use a nested modeling strategy, with a regional-scale model of the entire set of aquifers; a local-scale model of only the deep bedrock aquifer system (Figure 3); and local- scale models of the shallow aquifer system in selected areas of interest. The regional model provides the boundary conditions for constructing local-scale models in three dimensions, including local-scale models of shallow aquifers in Kane County. The regional model will be a multilayer groundwater flow model of the entire aquifer system from the Precambrian crystalline basement to ground surface. A local-scale, multilayer groundwater flow model will be constructed of the deep bedrock aquifer system. Local-scale shallow aquifer models will be constructed on an as-needed basis to support water resources planning at the county level. The models generally will consist of the unconsolidated glacial drift and the upper 50 to 100 feet of the fractured dolomite and shale bedrock; model domains will extend to natural hydrologic divides around Kane County. (a) Model Approximate Dimension • Regional deep aquifer model: • approximately 360 miles by 360 miles • grid spacing varies from 16 miles to 1/2 mile. N N • model size is approximately 44,000 cells for each layer or 880,000 cells for all 20 layers. Z • Local deep aquifer model Y X • approximately 60 miles by 90 miles (6 counties) X:Y:Z = 1:1:100 • grid spacing varying from 1/2 to 1/4 mile. Figure 7. Grid structure of regional • Local shallow aquifer models: groundwater flow model in (a) whole (b) domain, and (b) near field with finer • grid density of approximately 1/2 to 1/16 mile. grid resolution. Key elements of database for surface water - groundwater (SW-GW) interaction • Length, perimeter from USGS National Hydrography Dataset (NHD) • Stream width inferred from drainage area using GIS scripts. • Streambed conductivity from published estimates, and from well tests near streams • Determination of river type or drain type using stream seasonality from Q7,10 • Discharge from baseflow analysis of streams (flux targets for calibration) Figure 8. Surface water features from NHD in shallow • Database of predevelopment head aquifer accounting region (Figure 6). Conclusion This project will provide a framework for managing groundwater resources in Kane County, Illinois through collection, management, and analysis of data; conceptual and numerical modeling of aquifers; and evaluation of aquifer yield. Evaluation of the consequences of management options will also be examined based on this framework. The studies will produce a series of models and databases that will be maintained for use in assessing management options and will provide a framework for model updates and additional studies. ArcGIS 8.X and MODFLOW were chosen as the data management platform and groundwater flow modeling package, respectively, to optimize the research process in different stages and to amalgamate data from various sources. Acknowledgment U.S. Geological Survey - Wisconsin District Office, Wisconsin Geological and Natural History Survey, Indiana Geological Survey, Indiana Department of Natural Resources, Michigan Department of Environmental Quality, Illinois State Geological Survey, and Kane County Water Resources Department.