Responses of Experimental River Corridors to Engineered Log Jams

Abstract

Physical models of the Big Sioux River, SD, were constructed to assess the impact on flow, drag, and bed erosion and deposition in response to the installation of two different types of engineered log jams (ELJs). A fixed-bed model focused on flow velocity and forces acting on an instrumented ELJ, and a movable-bed model focused on channel morphodynamics. The results show that: (1) downstream flow velocity, as expected, can be markedly affected by the presence of the ELJs, (2) both ELJ types afforded relatively large regions of bank protection, and (3) the relatively larger ELJ had a higher drag coefficient, relatively larger areas of bed deformation, and greater impact on the opposite stream bank as compared to the relatively smaller ELJ. These modeling results show that the style and size of ELJs can have a significant impact on flow resistance, bank protection, and stream channel responses, which should facilitate practitioners in the effective design of ELJs for natural rivers.