Large Wood Design Guidelines - National Manual
Project ID: 2754
Principal Investigator: David DJ Bandrowski
Research Topic: Water Operation Models and Decision Support Systems
Funded Fiscal Years: 2013
Keywords: large wood, lwd, egineering, ecosystem, restoration, river management, hydraulics, geomorphology, habitat, fisheries
The historical legacy of anthropogenic removal of large wood (LW) from river valleys is commonly cited as a contributor for the disruption of river environments and decline of their dependent native species. As a result, regulatory agencies and the fisheries community often recommend the reintroduction of large wood, including the use of engineered logjams, for reestablishment of fluvial processes, habitat enhancement, and species recovery. Bureau of Reclamation (Reclamation) and United States Army Corps of Engineers' (USACE) roles in protecting native and listed species while meeting water delivery and managing flood risk and navigational needs has become increasingly apparent over the past few decades. The importance of large wood in fluvial environments had until recent decades been largely overlooked (Bisson et al, 1987). Various federal and state agencies are increasingly advocating that more wood be used as a "soft", cost-effective, and ecologically beneficial engineering approach in restoration and mitigation projects to meet environmental mandates and endangered species requirements while maintaining traditional agency missions.
Reclamation and USACE have missions that span the United States. Staff tasked with developing designs for projects, or providing technical design assistance and reviews must ensure projects will meet habitat improvement goals, and in some cases population improvement metrics. As public stewards, Reclamation and USACE are also tasked with ensuring due diligence with design of these projects to prevent unanticipated harm to private landowners, infrastructure, or recreationalists on the river. Based on Reclamation and USACE's shared missions, mandates, and broad geographic focus, it was recognized that a cooperative effort to better understand existing practice, develop collaborative research opportunities, and improve design standards for wood-based restoration engineering was needed.
Need and Benefit
In recent decades ecosystem ecology and restoration science have exponentially increased attention paid to effects of large woody debris in aquatic ecosystems, with an emphasis on lotic systems. This work has revealed an array of significant roles that wood plays in many stream and river systems. Physical, hydraulic, hydrologic, chemical, processual, and biological roles have been shown to be significant individually and collectively.
As federal agencies and their partners seek to restore aquatic ecosystems and the populations, water supply, water quality, recreation, aesthetics, and other values that they support in the most ecologically effective and cost-efficient manner that current states of science and practice can support, the promising restoration opportunities and the challenging engineering, safety, and liability issues that the use of large wood creates must all be addressed with rigor and transparency. Up to this point, utilization of large wood and realization of its benefits have been severely limited due to the absence of the standards, specifications, design rigor, accepted construction techniques, and monitoring practices common in other forms of engineering. This void creates serious issues of liability for engineers who must stamp designs and agencies that review, fund, and implement them. Furthermore, poorly designed restoration projects pose risks to transportation and water management infrastructure in which federal agencies have very large investments. This proposed design guide is an initial attempt to address these needs and to improve standards of practice for wood-based restoration. (The authors and editors acknowledge that this is a highly dynamic field and look forward to criticism, advice, and suggested refinements from the community of practice, stakeholders, and academia for this seminal effort.)
Science on the roles of wood in lotic ecosystems and its utilization in river restoration is currently in a state of exponential growth. While the same can be said for river restoration science more broadly, wood-focused efforts have lagged the general field. There are multiple possible reasons for this delay, including broad land use patterns (wood removal), stream crossing designs, and reservoir placements and operations that have severely limited historic or "normative" rates and patterns of wood recruitment and transport through river systems; explicit or implicit foci on channel and bank stabilization rather than restoration of dynamic forms and processes; the influence of zero-risk engineering standards; an early focus and familiarity with rock and its suitability for engineering specifications and standards; and the overall roles of precedent and inertia.
That has changed, beginning in areas of the U.S. Pacific Northwest where relatively wild and narrow valley, steep sideslope headwater sub-basins continue to deliver large wood supplies, often through colluvial processes, to their drainage networks. Current foci for basic and applied wood research include the following areas:
• Hydraulic and hydrologic effects of wood
• Effects on hyporheic exchange
• Geomorphic roles of wood at site, reach, and system scales
• Effects on stream and river biochemistry and metabolism
• Habitat formation and maintenance roles
• Habitat utilization by varying age cohorts, species, and guilds
• Cumulative effects
• Interactions between engineered, active restoration and background sediment, wood, and ice regimes
• Roles for assisted and passive restoration techniques
• Implications for riparian restoration and management
• Recreational and safety issues
• Implications for stream crossing design and reservoir operations
• Roles in estuarine, intertidal, and near-shore zones
A large wood workshop noted that the rate of scientific advance will continue to be rapid, but that there are clear needs at present for robust and more standardized assessment protocols and design guidelines.
National Manual for Large Wood Design Guidelines: "Guidlines for Planning, Design, Placement, and Maintenance of Large Wood in River: Restoring Process and Function"