EXAMINING HYDROLOGIC CONNECTIONS OF BASINS IN CENTRAL GEORGIA WITH RESPECT TO OVERTOPPING OF SIDEWALKS DURING RAINFALL EVENTS

The Oconee River Greenway (ORG) is a beautiful community park adjacent to the Oconee River in Milledgeville, GA. The Greenway is located at the confluence of the Oconee River and Fishing Creek. It comprises recreational areas, a historic industrial site, wetlands and an abandoned channel. To ensure that future developments meet the needs of the residents as well as maintain the ecological functions of this park, we conducted research on the hydrologic connections among surface water, groundwater, and sidewalk overtopping at the Greenway. One of the goals of the research was to investigate the source of water in the wetlands and potential for flooding of the sidewalks during rainfall events. This project also investigated the usefulness of ArcGIS Spatial Analyst tool box in predicting sources of overland flow into the wetlands and locating sites for needed culverts. A Total Station, Global Positioning System receivers, and other Geographic Information Systems’ sources were utilized to create a fine resolution topographic grid and a map of all low lying areas (basins). We then conducted a detailed analysis of the basins so as to understand overtopping of sidewalks and determine the best location for flood control measures. Potential sources of water in these basins were determined using both GIS analyses and field observations. While the abandoned channel gets most of its water from river flooding, the other basins receive their water from overland flow. These basins, with the exception of the abandoned channel, do not have well established outlets and, therefore, mostly lose water through subsurface flow and/or evapotranspiration. Water loss via the subsurface was determined using Darcy’s law and the Phi index infiltration method. Preliminary results indicate the presence of a significant clay layer with low permeability that causes evapotranspiration to account for most of the water loss in the wetlands. This research provides models of the hydrologic connections in the area and estimates of the amount of water needed to overtop the sidewalks. We also provide recommendations for the best location of the next culvert in respect to existing hydrologic conditions, which is valuable information for the ORG Authorities. The usefulness of the Spatial Analyst tool, even though still under investigation, shows great promise.