Debris Accumulation at Bridge Crossings: Laboratory and Field Studies

Extensive accumulation of large woody debris at bridge piers poses a chronic and sometimes quite severe problem at several bridge crossings in Indiana. This study, involving both laboratory and field components, examines the factors contributing to the initiation and development of such debris piles. The laboratory study, performed in a rectangular channel with a single model pier (and in some cases with an upstream vertical cylinder modeling a debris deflector, as well as a model sand bar) and both dowels and twigs as model logs, considered the effects of velocity and depth. The experiments point to a stronger than might be expected effect of local depth, with the potential for debris accumulation generally greater when the local depth is smaller. The field study consisted of video monitoring and recording of debris-transporting events at two sites, the SR59 south crossing of the Eel River (in operation since 9/2001), and the SR63 southbound bridge over the Big Vermillion River (in operation since 4/2003). Results (images) during significant flow events have only been obtained at the SR59 site during the 2001/2002 season, and some qualitative conclusions can be drawn regarding the initiation and growth of debris piles in relation to significant flow events.