Presenter/s: Garrett Jackson
Symposium Session: 2022 - 04 Stream Restoration from the (WSDOT) Transportation Perspective
Topics covered: fish passage, fish-salmon, instream structure (culvert/bridge/dam), risk, stream, and wood
Although many aspects of wood behavior in streams are still being studied, the value of wood to habitat and geomorphic function has been understood for decades now. However, in past years, transportation agencies’ use of wood was limited to stream bank protection and mitigation projects. Stream crossing projects did not place wood below the 100-year water surface elevation. There really was no framework for evaluating infrastructure risk. Since then, what used to be viewed with great reservation has been embraced by WSDOT, resulting in agency-wide acceptance and a sea change in the approach to stream restoration design and construction.
WSDOT actually began using wood in the early 2000s, through the Chronic Environmental Deficiencies program. That program’s mission is to reduce maintenance and elevate habitat functions at problem sites. However, most of that work remained siloed from the rest of the agency for a long time.
A 2013 court injunction required the state of Washington to fix hundreds of fish passage barriers by the year 2030. As a portion of that effort, each project reach needs to be passable from day 1 after construction and remain passable into the future. With early fish passage projects, and little to no guidance, WSDOT staff developed large wood designs that reflected a background in highway engineering. Wood was over-anchored, placed far to the margins of the channel cross-sections, was quite sparse and very much like bank protection with little habitat value.
Through collaboration with the tribes, the WSDOT State Hydraulics Section incorporated more habitat complexity and features as part of the fish passage design process. One of the guidance documents is the leading paper on large wood quantities in streams in Washington State (Fox and Bolton, 2007). These recommendations – the target of the 75th percentile of key pieces and non-key pieces in undisturbed streams, have been adopted as the targeted starting point for conceptual large wood design. Once the length of the project reach is determined, the large wood targets are applied and the project specific targets are determined. There are often constraints, particularly in urbanized watersheds, that may make meeting the large wood targets difficult or impossible, but we work through those on a case by case basis. In addition, WSDOT has begun to embrace use of large wood for specific hydraulic and habitat objectives, such as restoration of alluvial fan processes, floodplain reconnection, and shear stress partitioning.
The WSDOT Hydraulics Manual was updated to include a chapter on large wood as well as a comprehensive water crossings chapter to achieve fish passage. WSDOT has also committed to following best available science and technology as we continue to learn with every crossing in this dynamic program. This includes participating in research opportunities that are state and nationally valued. The WSDOT Hydraulics Manual is being updated regularly as we learn new information and techniques through our detailed fish passage monitoring program.
Finally, use of large wood in emergency situations is now much more common. When site conditions allow, we now incorporate wood into embankment stabilization measures.