Paper No. 8
Presentation Time: 10:05 AM
A LEGACY OF ABSENCE: WOOD REMOVAL IN U.S. RIVERS
The historical removal of large masses of wood on medium to large rivers in the continental United States caused a fundamental change in riverine systems that has been largely neglected by the geomorphic community. Although geomorphologists know of the log rafts present on the Red or the Atchafalaya Rivers in the southeastern U.S., there is little recognition that similar extensive masses of wood are documented in the historical record from forested river catchments as diverse and widespread as those in the northeast, southeast, Texas Gulf Coast, Pacific Northwest, and upper Great Lakes regions of the country. While present, these log rafts decreased channel conveyance, increased channel-floodplain connectivity, and facilitated multithread channels and floodplain lakes. Removal of the log rafts began in the 17th century in the eastern US and proceeded westward with the movement of European settlers, accelerating during the 19th century era of steamboats and rafts of cut timber. Removal of the log rafts forced many rivers into an alternative stable state of single-thread channels with substantially reduced overbank flow, sedimentation, and avulsions. The magnitude of wood removal and associated geomorphic effects are illustrated by case studies from the St. Croix River of Wisconsin and the Congaree River of South Carolina. There is now widespread recognition among the geomorphic community of how upland clearance increased sediment yields and floodplain aggradation. I propose that widespread removal of instream wood for steamboat routes, timber rafts and flood control was equally significant in decreasing floodplain sedimentation and riverine complexity, and in causing a fundamental, extensive and intensive change in forested riverine systems throughout the country.