SOIL EROSION SUSCEPTIBILITY WITHIN THE SNAKE CREEK RESERVOIR WATERSHED – A CHANGE ANALYSIS, 2000-2006

The management of drinking water reservoirs requires the identification of areas of excessive soil erosion within the watershed. The continuous monitoring and quantitative assessment of patterns of erosion susceptibility is also necessary. Increased concentrations of sediment in surface water increases the cost of drinking water treatment and negatively impacts the life of the reservoir. This study models changing patterns of soil erosion over a period of six years in a reservoir-watershed in west Georgia.

Factors controlling the susceptibility of soils to erosion include soil type, rainfall, slope length and angle, agricultural conservation practices, and land cover. Among these factors, the one most likely to change over time is land cover, particularly in areas of suburban development or where forest resources are regularly harvested. Monitoring land cover change at the watershed scale is an important element of any reservoir management program.

The Revised Universal Soil Loss Equation (RUSLE) calculates potential soil erosion rates using soil type, historic rainfall data, topography and land cover. Land cover maps were generated through supervised classification of Landsat TM imagery for three different years (2000, 2003, and 2006). Within a GIS, numeric values were assigned to each land cover type and were combined with values for the other RUSLE factors to generate soil-erosion susceptibility maps, identifying high-risk areas within the Snake Creek Watershed including new construction, harvesting of forests, poorly managed commercial facilities, and unauthorized roads and ATV trails. A change analysis was then performed to determine changing patterns of soil erosion susceptibility within the watershed over the six-year study period.

Satellite imagery is ideally suited to monitoring changing soil erosion conditions within reservoir-watersheds – it is timely, cost-effective, and provides data on the most changeable factor affecting soil erosion rates. The technique applied in this study is not only applicable to reservoir management, but is also more widely applicable to water-quality management throughout the watershed.