Submitted to: American Geophysical Union
Publication Type: Monograph
Publication Acceptance Date: 5/15/2003
Publication Date: 5/15/2004
Citation: Alonso, C.V. 2004. Transport mechanics of stream-borne logs. In: Bennett, S.J., Simon, A., editors. Riparian Vegetation and Fluvial Geomorphology. American Geophysical Union, Washington, DC. p. 59-70. Interpretive Summary: Problem: Eroding banks of alluvial streams introduce into the stream channels large numbers of fallen trees (Large Woody Debris, LWD) that accumulate at specific locations along the streams causing upstream flooding and altering the direction and magnitude of the stream flow. The fluvial transport of LWD is being studied as for its long-term impact on stream stability and river restoration programs. Accomplishment: We developed a complete characterization of the mechanics of fluvial transport of single logs, and examined in detail how the hydraulic drag forces driving the logs are modified by their interaction with the stream. Contribution: This knowledge is an important step towards unraveling the dynamics of LWD transport because the later depends on the complex interaction of multiple logs among themselves and with the stream environs. As our knowledge of these processes grows, action agencies will be able to develop better tools for assessing the impact of LWD accumulations on river flow conveyance and flood risk potential.
Technical Abstract: Large woody debris is increasingly regarded as an integral component of stream stabilization and restoration programs. Unravelling the dynamics of complex interaction of multiple logs among themselves and with the stream environs must start with a correct specification of all the forces acting on individual logs. This paper presents a generalized model of log motion, and examines in detail the influence of roughness, high Reynolds number, proximity to plane streambeds, interaction with the free surface, and flow unsteadiness on the time-mean drag of submerged cylindrical logs.