Evaluation of constructed wood jams in a forest, gravelbed stream

Whole tree materials that include trees with attached rootwads, logs, and branches are recognized as important components of streams flowing through coastal redwood forests of Northern California. As the understanding of the importance of large wood materials has emerged, they have been recognized as key physical elements missing from many streams due to the historic and systematic removal associated with timber harvest and stream cleaning practices. The recognition of the ecological importance of wood materials within stream and floodplain ecosystems has led scientists and managers to advocate for the re-introduction of large wood directly into these environments. However, common applications of instream wood restoration can fall short of producing features capable of inducing the physical changes necessary to achieve desired restoration objectives, such as the formation of deep pools and cover. Current research shows that natural wood jams, with increased wood piece counts and volumes, are more effective at producing the hydraulic and geomorphic conditions necessary for creating and sustaining complex habitat. This study hypothesized that wood jams constructed with whole tree materials, increased wood piece counts, and greater wood volumes would be more effective than simple structures at creating the hydraulic conditions necessary for increasing instream complexity, geomorphic function, and aquatic habitat quality. Results were based on an evaluation of changes to surface sediment textures and channel morphology at ten constructed wood features built with varying complexity and wood volumes. Eight of these features were complex wood jams constructed with whole tree materials including large diameter trees with attached rootwad, logs, and branches. Each complex jam was individually designed to interact with seasonal variations in stream flow, floodplain morphology, and the dominant sediment transport regime. Two of the studied features were "simple structures" constructed in 1995 and comprised of one or two logs anchored to imported boulders with cable. The simple structures were designed following a standard California restoration protocol. Results indicate that complex wood jams were more effective than simple fish habitat structures in achieving common restoration objectives that include: (1) increasing percentage pool cover; (2) increasing scour pool habitat; (3) metering and sorting salmon spawning gravels; and (4) improving habitat heterogeneity. In addition, the effectiveness of an individual constructed jam improved as the overall wood piece count and volume within the jam increased. The increase in pool depths demonstrate that complex wood jams were effective at improving over summering and overwintering pool habitats for steelhead trout, coho salmon, and Chinook salmon.