Effects of Engineered Log Jams on Channel Morphology, Middle Fork of the John Day River, Oregon

Abstract:

Engineered log jams (ELJs) were constructed on the Middle Fork of the John Day River in eastern Oregon as part of a large river restoration project. These log structures were designed to address many of the restoration goals including creating scour pools, creating and maintaining a sinuous river planform, providing fish cover, and increasing complexity of fish habitat. This study uses geomorphic change detection techniques to monitor topographic change under and around the 26 log structures in two different river reaches over a six to seven year period. This study finds that the ELJs are remaining stable within the river, even following a large flood in 2011. While some pools are shallowing or shifting laterally slightly, in general they are maintaining deep pool habitat. The study provides insight into which log structure variables are most related to the patterns and amounts of aggradation and degradation. Analysis suggests that volume of aggradation is related to both porosity and volume of the log structures, while the area of aggradation was correlated with porosity, as well as, the proportion of logs within bankfull. Understanding the geomorphic changes to the riverbed in response to the placement of the ELJs can influence the design and future effectiveness of ELJs.