The amount of large woody debris that potentially could be transported to bridge sites was assessed in the basin of the West Harpeth River in Tennessee in the fall of 1992. The assessment was based on inspections of study sites at 12 bridges and examination of channel reaches between bridges. It involved estimating the amount of woody material at least 1.5 meters long, stored in the channel, and not rooted in soil. Study of multiple sites allowed estimation of the amount, characteristics, and sources of debris stored in the channel, and identification of geomorphic features of the channel associated with debris production. Woody debris is plentiful in the channel network, and much of the debris could be transported by a large flood.
Tree trunks with attached root masses are the dominant large debris type.
Death of these trees is primarily the result of bank erosion. Bank instability seems to be the basin characteristic most useful in identifying basins with a high potential for abundant production of debris. Introduction Accumulations of large woody debris at bridges have caused increased backwater and bank scour at bridges in the Harpeth River basin in middle Tennessee. Tree trunks with attached root masses play a key structural role in debris accumulations at these bridges. In the fall of 1992, the U.S. Geological Survey, in cooperation with the Tennessee Department of Transportation, assessed the potential supply of large woody debris in the basin of the West Harpeth River upstream from bridges at which debris has accumulated.