Location: Watershed Physical Processes ResearchTitle: Physical-scale models of engineered log jams in rivers Author
Submitted to: Journal of Hydro-environment Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2013
Publication Date: 6/1/2014
Publication URL: http://handle.nal.usda.gov/10113/59414
Citation: Gallisdorfer, M.S., Bennett, S.J., Atkinson, J.F., Ghaneeizad, S.M., Brooks, A.P., Simon, A., Langendoen, E.J. 2014. Physical-scale models of engineered log jams in rivers. Journal of Hydro-environment Research. 8(2):115-128. doi:10.1016lj.jher.2013.10.002. Interpretive Summary: Historically, the design of stable stream bank protection measures have relied on materials such as rock and concrete. While such measures ensure protecting adjacent floodplain uses, they typically do not improve in-stream, aquatic habitat. Therefore, stream restoration and river engineering projects are increasingly employing engineered log jams to provide both bank protection and new habitat. However, design guidelines that characterize the forces acting on the whole engineered log jam as well as its individual members are lacking. The impact of engineered log jams on open channel hydraulics and morphology can be studied using physical scale models in the laboratory. The proper scaling laws were derived for fixed and movable-bed models. This information will enable hydraulics experimentalists to develop improved design guidelines for engineered log jams.
Technical Abstract: Stream restoration and river engineering projects are employing engineered log jams increasingly for stabilization and in-stream improvements. To further advance the design of these structures and their morphodynamic effects on corridors, the basis for physical-scale models of rivers with engineered log jams is presented and discussed. The prototype selected is the Big Sioux River, SD, chosen because engineered log jams will be used to mitigate excessive bank erosion. The underlying theory of physical-scale modeling and all primary and secondary scaling ratios are derived for two boundary conditions, a fixed- and movable-bed, given the experimental constraints of the intended facility. All model hydraulic parameters are scaled to represent approximately the 1.5-year return interval flow in the Big Sioux River, which corresponds to the design discharge. The scaling ratios for the movable-bed model sediment are relaxed, allowing for the use of typical experimental flows, facilities, and materials. Proposed engineered log jam designs are based on proven field installations, and these structures also are scaled to natural timber dimensions to be used in the prototype. While physical experimentation using wood is not uncommon, the use of physical scaling theory appears to be employed infrequently, thereby restricting the applicability of the results obtained. It is envisioned that the procedures outlined here would become more widely used in experimental research of rivers and in river restoration design.