Stream Loss and Fragmentation Due to Impoundments in the Upper Oconee Watershed

Abstract

Loss of natural stream habitat and stream network fragmentation are two major ecological impacts of dams and their impoundments. We use geographic information system (GIS) analyses of the stream network and impoundments in the Upper Oconee watershed to assess the cumulative impacts of habitat loss and fragmentation due to existing impoundments and illustrate the analysis for assessing alternative reservoir projects. Based on publicly available GIS data, we found 5,467 impoundments cover 175 km² in the entire watershed (2.3% of the watershed area) with 3,489 occurring within the 1:24,000 scale stream network. The impoundments have converted 834 km of lotic habitat into lentic habitat, or 8% of the total stream length represented on 1:24,000 maps. We developed fragmentation indices based on ratios of length and number of streams interconnected prior to and after reservoir placement. Also, distances upstream and downstream to impoundments were calculated for all stream segments in the watershed. The impacts of alternative impoundment projects should be analyzed with respect to habitat loss and fragmentation at the watershed level. The cumulative effect of thousands of impoundments, both large and small should be examined more closely and we believe these analyses will aid in understanding these effects.