Large Woody Debris Effects on Channel Friction Factor

by F. Douglas Shields, Jr., U.S. Dep of Agriculture, Oxford, United States,
Roger H. Smith, U.S. Dep of Agriculture, Oxford, United States,

Document Type: Proceeding Paper

Part of: Hydraulic Engineering


A simple method for quantifying large woody debris (LWD) density and computing associated friction factors was developed and tested using data from the South Fork Obion River in western Tennessee. Data were collected at a range of stages. The study site included three adjacent straight, sand-bed channel reaches about 1,500-2,000 m long, 20 m wide and 4-5 m deep from top bank to thalweg. Aside from the presence of LWD, the channel was fairly uniform. Emergent bars and riffles were not observed during data collection. Hydrologic variations were dampened due to ponding behind major LWD jams upstream of study reaches. Bed material was sand (approximately 0.3-0.6 mm). LWD formations blocking more than a fifth of the cross section were common, and LWD density varied from reach to reach due to natural factors and due to a selective clearing and snagging project underway concurrent with this study.

Subject Headings: Friction | Wood and wood products | Debris | Channels (waterway) | Flow measurement | Fluid flow | Bed materials | River flow | Tennessee | United States

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