A study was undertaken to better understand the hydrogeologic framework of the Delaware County, Indiana. Arc View GIS 3-D and Spatial Analysts along with VISUAL MODFLOW are used to study the flow patterns by developing a 3-D model of major aquifers in the county, both glacial and bedrock. The GIS platform facilitates the time consuming task of preparing data input and output. In addition, major recharge zones are also identified in GIS using soil and slope data.The bedrock of Delaware County is composed of Silurian bedrock, which is overlain by glacial drift. The drift is mostly till that is interbedded with eight sand and gravel layers which are horizontal and discontinuous. Both, bedrock and sand & gravel glacial aquifers are good sources of groundwater in the county. More than 3000 water wells are located in the area. It is very interesting to note that 50% of the water-wells in the area are in confined sand and gravel and the remaining wells are in carbonaceous bedrock. The bedrock contains numerous preglacial karsts valley systems which are areas of high transmissivity solution features, also adding further interest to modeling this region.The hydraulic conductivity of sand and gravel is assumed to be 0.0015 m/s whereas for bedrock 0.00025 m/s is used. The streambeds in the area are also the source of groundwater discharge. The hydraulic conductivity of streambed is equal to 0.00028 m/s. Recharge to the area occurs as net recharge, which varies spatially depending on the nature of soil.Several simplifying assumptions were made for the conceptualization and simulation of flow in the basins. The main assumptions are as follows: 1) groundwater is in steady-state, 2) pumping does not significantly affect the level of hydraulic heads; therefore only high capacity pumping wells are simulated, 3) Net recharge from precipitation varies spatially, 4) flow in the bedrock aquifer occurs in the uppermost 40 m and is horizontal 5) vertical flow is assumed to be controlled by intervening sand and gravel units. Ground-water flow in the basins was conceptualized as a three-dimensional flow system. The model boundaries selected to represent natural hydrologic boundaries include (1) river leakage boundaries along major rivers; (2) a constant head boundary around the aquifer boundaries; (3) a general head boundary along the major streams; (4) drain boundaries along major drains; and 5) Evapotranspiration losses.The simulated region is an area of 398 square miles. The model consists of over 3600 cells and employed a regular grid spacing of 6o x 60. A variable grid was designed to provide additional detail in areas of special interest and thus allowed these areas to be simulated more accurately in the model.The model was calibrated using a manual trial-and-error adjustment of parameters. Hydraulic conductivity values, and streambed conductance were adjusted during successive simulations until the flow pattern matches the regional flow direction as computed from the water-well derived (static water level) potentiometric surface. The computed potentiometric surface is an adequate or reasonable match on a regional scale, with the general trend of SE-NW. It is observed that the model is extremely sensitive to changes in horizontal hydraulic conductivity and recharge in the form of precipitation. The model is least sensitive to streambed vertical hydraulic conductivity.The water budget for the calibrated model represents the distribution of groundwater inflow and outflow during calibration. The data indicate that 16.5% of the inflow to the modeled groundwater system is flow across model boundaries and 83% from effective recharge from precipitation, and the rest from streams and rivers. Outflow consists of 2% pumpage, 5% seepage to streams and drains, and 93% is flow across boundaries.It is expected that this study will be beneficial to improve the understanding of groundwater in Delaware County, including both vertical and horizontal flow and interaction of flow between surface and groundwater. Also, the results of the modeling study can be used as a predictive tool for long-term management and monitoring of water resources in the region. / Department of Geology
| Identifer | oai:union.ndltd.org:BSU/oai:cardinalscholar.bsu.edu:handle/187772 |
| Date | January 2004 |
| Creators | Singhal, Alka |
| Contributors | Samuelson, Alan C. |
| Source Sets | Ball State University |
| Detected Language | English |
| Format | x, 81, [4] leaves : col. ill., col. maps ; 28 cm. + 1 CD-ROM (4 3/4 in.) |
| Source | Virtual Press |
| Coverage | n-us-in |
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