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ERIE Research Projects

Evaluating engineered log jam designs for stream restoration

Participants:

ERIE Fellow: Michael Gallisdorfer, Department of Geography

Faculty: Sean Bennett, Department of Geography

Summary:

Stream restoration and river engineering projects are employing engineered log jams (ELJs) increasingly for stabilization and in-stream improvements. To advance the design of these structures and their morphodynamic effects on corridors, scaled ELJ models are deployed in Froude-scaled physical models of the Big Sioux River, SD, where they will be used to mitigate excessive bank erosion. First, flow forces acting on an ELJ deployed in single and multi-structure configurations were measured in the fixed-bed model. Scour patterns resulting from similar ELJ configurations deployed in the movable-bed model will next be evaluated using digital close-range photogrammetry. The scaling ratios for the movable-bed model sediment are relaxed, allowing for the use of typical experimental flows, facilities, and materials. Proposed ELJ designs are based on proven field installations, and these structures also are scaled to natural timber dimensions to be used in the prototype. Preliminary results for the fixed-bed model show that (1) ELJs greatly decelerate flow near the structure and accelerate flow in the main portion of the channel, yet spatially-averaged flow velocity and depth remain unchanged, and (2) derived drag coefficients for the ELJs based on force measurements vary from 0.3 to 0.7 depending on the scaling velocity employed. While physical experimentation using wood is not uncommon, the use of physical scaling theory appears to be employed infrequently, which potentially could limit 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.

Lidar imaging of a fixed bed flume

Close-range photogrammetry of ELJ flow structure influence on fixed bed sediment.

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