|Shields Jr, Fletcher|
Submitted to: Congress of International Association for Hydraulic Research Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/1/2009
Publication Date: 8/9/2009
Citation: Alonso, C.V., Shields Jr, F.D., Temple, D.M. 2009. Dynamics of Large Wood: A Prototype-Scale Flume Experiment. Water Engineering for a Sustainable Environment. Proceedings, International Association for Hydraulic Research 33rd Congress, IAHR, Madrid, CD-ROM. Interpretive Summary: Trees and logs in streams are important components of aquatic ecosystems and influence sedimentation, erosion and river channel migration, but prediction of how this large wood moves through channel systems is difficult due to a lack of information about flow forces on the wood. Flow forces were measured on three logs with complicated geometries (e.g., branches) fixed in a large, outdoor flume as a second phase of similar work with uniform, cylindrical logs. Flow forces varied rather widely from log to log and with the angle the center of the log made with the flow direction. This information will be useful to engineers and scientists who wish to compute the forces on large wood used for managing and restoring stream ecosystems.
Technical Abstract: Knowledge of hydrodynamic forces on single bodies is applied to the problem of measuring drag and lift of large wood (LW) in the form of branching logs and root wads submerged in steady, uniform flows representative of conditions encountered in natural streams. Flow forces were measured on two branching logs and a rootwad in a straight, grassed channel with steady discharge. Drag and lift were characterized using drag and lift coefficients that are not known a priori due to the complexity of the flow and LW geometry. Parametric charts are presented detailing the dependence of time-mean drag and lift coefficients on LW geometry and orientation. The results exhibit lack of scaling similarity, and they also suggest assumed drag and lift coefficients for large wood in rivers may be misleading when based on coefficients measured for single cylindrical logs.