Literature Review of Large Woody Debris (LWD) Guidelines and Implementation Strategies
* What guidelines are currently available for the potential use and implementation of LWD structures to improve riverine habitat, restore flood plain-river connectivity, modify patterns of sediment deposition and erosion, and provide bank stability?
* What information does each of the guidelines offer and in which environments are they applicable?
Need and Benefit
LWD structures, commonly referred to as Engineered Log Jams, are used in river restoration to form complex assemblages of hydraulics and substrates, stabilize streambanks, and provide fish cover and shade, all of which work in combination to create diverse habitat for use by various species of differing life stages. Various Federal and State agencies are advocating that Reclamation use these types of "soft" engineering approaches to meet endangered species requirements while maintaining water delivery needs. For example, bank stabilization techniques employed to maximize water delivery to downstream water users were historically comprised of rock or concrete structures. Due to competing needs of minimum flow and habitat requirements for endangered species, Reclamation is often directed to use LWD structures in place of hardened stabilization techniques.
An understanding of the importance of LWD in river systems has gained significant strength in the research and applied studies of eco-hydraulics within recent history. One major ecological benefit of the use of LWD within rivers is the improvement to flood plain connectivity and creation of habitat and cover for endangered fish species. These improvements to habitat may reduce instream flow requirements, thereby increasing the amount of water delivery to downstream water users. Design of LWD structures that can sustain habitat features and meet program objectives for water users are essential components of successful project implementations. A document that clearly defines existing resources for LWD design and implementation may lead to more effective and sustainable projects.
Failures of LWD structures are fairly common and may result from a lack of a complete set of guidelines, misapplication of existing guidelines, or poor implementation and design strategies. Reclamation is incorporating LWD structures into its project designs at a more frequent rate today than has previously occurred. An essential component of project success is a clear understanding of application limitations for each type of LWD structure and each scenario within which LWD structures are considered for use. A first step in development of a complete set of guidelines for LWD use is to evaluate the sufficiency of the current state of the art and identify information gaps. A literature review of the existing available information on the use of LWD in stream restoration is necessary to:
* Form a knowledge base of current guidelines and implementation methodologies
* Recognize possible reasons for failure
* Understand application limitations
* Identify the need for a more complete set of guidelines
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