Erosion and sediment modeling of the Lake Sidney Lanier watershed
Sharma, Jitendra Bal
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Lake Sidney Lanier is the primary source of water for the metropolitan Atlanta area. Its watershed is critical to the economic well being of the region and the State of Georgia as highlighted by the recent drought and the impact of the consequent water shortage. This project is a study of spatially distributed Universal Soil Loss Equation (USLE) based erosion and sedimentation in the Lake Lanier watershed. The non-point source erosion study was performed for 1984, 1991, 1992, 1999, 2001 and 2005, using Landsat imagery, State Soil Geographic (SSURGO) soil data, State Soil Geographic (STATSGO) soil data, the National Land Cover Data (NLCD) and 30-m U.S. Geologic Survey (USGS) Digital Elevation Models (DEMs). The sedimentation modeling was done for 1984, 1991, 1999 and 2005. The time period of this study has seen a major change in land cover in the watershed, which has important implications for water quality. This remote sensing and GIS based modeling was done for 30-m x 30-m grid cells, and shows the erosion 'hot-spots' in the watershed, their proximity to streams and their time evolution over the period of this study. The erosion modeling also identified the regions where the erosion exceeds the soil loss tolerances, highlighting these locations for soil conservation efforts. The spatially distributed sedimentation model is based on an empirically derived µdrainage area vs. sediment delivery ratio (SDR)relationship. The erosion modeling provides the supply grid of eroded soil that is available to the sediment transport process. The sedimentation model provides a spatial distribution of the sediment deposition potential at every 30-m pixel, which is indicative of the highest upslope loading of sediment at that location. The querying of the sediment potential in the vicinity of the streams identifies the stream segments that are the most vulnerable to sediment input and associated pollutants. An index of impairment is proposed that helps determine the locations in the watershed most susceptible to sediment deposition. Viable comparisons of this spatially distributed erosion modeling with sediment discharge measurements of Faye et al. (1980) and Leigh (1998) lend confidence in the data and methods used in this study. Calibration of this model with more sediment discharge measurements can help in the effort to define and implement sediment Total Maximum Daily Loads (TMDL's). This study lays a foundation for more detailed spatially distributed erosion and sedimentation studies of the Lake Lanier watershed, conducted at higher spatial and temporal resolutions.