Fragmentation By Dams: Spatial Measures of Dam Impacts On Streams of the Conterminous U.S

Dams constitute a complex and highly variable form of disturbance to fluvial habitats.  For example, a single dam may affect both upstream and downstream habitats in a network, and many dams vs. few within networks lead to differences in overall network fragmentation.  This complexity highlights the need for diverse spatial measures to account for dam impacts throughout aquatic landscapes.  While previous studies have characterized fragmentation by dams for individual river basins or through multi-state regions, efforts to represent fragmentation across very large spatial extents, like the conterminous U.S., are lacking.  Using GIS, we developed a set of fragmentation metrics for the conterminous U.S. in support of the National Fish Habitat Partnership using ~50,000 dams from the 2012 National Anthropogenic Barrier Dataset and 2.3 million stream reaches from the National Hydrography Dataset Plus V1.  Fragmentation metrics, summarized for every stream reach in the dataset, include density-based measures, distance-to-dam measures, cumulative upstream reservoir storage, and connectivity to oceans/Great Lakes.  Comparing metrics shows regional differences in degree and impacts of fragmentation across the Nation, emphasizing the importance of selecting metrics that capture regional variability in assessment.  Further, this work underscores the need to integrate multiple measures of dam impacts when prioritizing management actions.