INVESTIGATING THE HYDROLOGIC CONNECTION IN A COMPLEX RIVER FLOODPLAIN SYSTEM IN MIDDLE GA

In this study, we examine the surface water flow system of an area in Milledgeville and its hydrologic connection to the Oconee River. The site of the study is an area locally known as the Oconee River Greenway, which is at the confluence of the Oconee River and a major tributary, Fishing Creek. In addition to providing space for recreation, the Greenway also provides an esthetically pleasing environment and benefits of wetland functions for the city. As the greenway expands and becomes more developed an advanced knowledge of surface and subsurface hydrology is required to achieve the management and educational goals brought forth by the greenway authority. The working hypothesis for this study was that a wetland of interest is being fed by ground water instead of overland flow from precipitation or flood events. Surface water flow paths were created using an elevation grid developed from data collected using a total station and topographic maps. Hydrogeologic data were collected using hand augers, piezometers and electrical resistivity. To investigate the connections between the wetland and ground water, infiltration and hydraulic conductivity of the sediments underlying the wetland and the abandoned channel were determined using slug tests, in-situ and laboratory permeameters. All data, including resistivity results, were incorporated in the GIS system to produce 3-D visualizations of both the surface and subsurface systems at the Greenway. Results of this research revealed the presence of an approximately one-foot clay layer, with very low hydraulic conductivity, underlying the wetland. The depth of the water table and the presences of this low conductivity layer convinces us that the water in the wetland is not generated by groundwater discharge. We concluded that groundwater development in this area would not have much impact on the functioning and aesthetic value of the wetland. Periodic flood events are crucial in supplying the wetland with water and therefore, future development should ensure that flood waters continue to reach the wetland.