DESIGN AND CONSTRUCTION OF LOG-BEDDED SALMON STREAMS IN FOOTHILLS OF THE CASCADE AND OLYMPIC RANGES, WA

I design and build natural-appearing channels patterned after “reference reaches.” The ideal reference reach is a stable stream, not aggrading or degrading, and with a productive ecosystem. It should have similar flow, soil and slope as the proposed enhancement area, and should support abundant salmonid spawning and/or rearing habitats. Meander radii, entrenchment, floodplain shapes, wood placement and pool formation of the reference reach are emulated in the restoration design to create natural shapes and functioning. Usually the intent is to create a stream that is stable, and not prone to avulsion, but this is not always the case. My primary goal is to create salmon habitat, but other goals such as protection of roadways and houses are often important parts of the plan. Low gradient streams (< 2% slope) in western Washington tend to be bedded in logs, not rock, with about one large piece per 10 feet of creek bed. To re-create such conditions, I specify logs and whole trees of any local species, in any stage of decay, and with branches and roots intact as possible. Logs are installed for various purposes. Deeply buried logs provide a foundation to control downcutting of the stream bed. Others, installed higher, influence channel roughness, creating local scour holes and gravel deposits. All installed wood influences water surface elevations and aquatic habitat. One design objective is to install wood so that relatively stable gravel bars develop, minimizing the washout of redds during storms. Most installed logs create a scour hole and a gravel deposit; both are desired outcomes. Proper installation of large wood is the primary method to consistently create spawning and rearing habitats. The wood is installed by direct burial into the soil without artificial anchors. I have installed a few thousand pieces in this fashion within a few miles of newly created streams, with virtually no washout except for in one system where about 20% washout occurred. In some instances spawning gravel is installed to create spawning habitat, but it is not the gravel so much as proper wood installation that leads to the dependable creation of spawning areas. The talk will focus on specific design features from numerous stream, culvert and bridge projects designed and constructed by the author.