Morphodynamic responses of physical-scale experimental river channels to engineered log jams for stream restoration design

Engineered Log Jams (ELJs) reflect the structure and function of naturally occurring large wood jams, providing multifunctional benefits to degraded stream corridors by protecting infrastructure, enhancing habitat, and improving aesthetic qualities. A two-part experimental campaign was conducted using Froude-scale river models to evaluate in-stream hydraulic and morphodynamic effects for two ELJ types (ELJ-1 and ELJ-2) deployed in single-and multi-structure configurations. Morphodynamic responses of a movable-bed experimental channel is reported here, with channel response varying with ELJ type and spacing interval between paired ELJs. The extent of channel impacted by the introduction of ELJs is similar in most cases, while the length of opposite bank eroded ELJs is consistently greater for ELJ-1 vs. ELJ-2. An intensity score aggregating ELJ effects is also used to facilitate a comparison of ELJ effects between design-types and across the experimental configurations examined. Overall channel-bed response was amplified when ELJs were deployed at shorter spacing intervals, with adverse opposite-bank impacts increasing through the greatest interval between ELJs evaluated. Outcomes of this investigation are intended to guide the design and deployment of ELJs in rivers, including highly-constrained urban restoration scenarios requiring careful consideration of the extent, intensity, and pattern of ELJ effects before deployment.