Designing Large Wood Structures to Improve Public Safety
Project ID: 8952
Principal Investigator: Connie Svoboda
Research Topic: Sediment Management and River Restoration
Funded Fiscal Years: 2014
Keywords: large woody debris, engineered log jams, river restoration, large wood safety, large wood design
Large wood installations are an important element of Reclamation's overall river restoration strategy due to the many benefits of large wood structures. However, large wood installations can pose a public safety hazard to recreational river users such as boaters, swimmers, fisherman, and children. Large wood in rivers can produce what are known in the boating community as "strainers". Flow through or underneath a structure can pin boaters or swimmers against the structure or pull them under water.
Large wood structures should be designed to minimize human interaction with the structure. Safe large wood should only partially span the width of the river to allow boaters and swimmers the ability to safely avoid the structure. Adequate sight distance should be provided so that recreationalists can either safely navigate around the structure by water or portage around the structure by land. Large wood should not be placed downstream of drops, in swift currents, or in tight radius river bends with limited sight distance. Signs on the river bank and in the river can alert people to the presence of large wood structures.
Even with a well-marked large wood structure installed in a safe location, humans may come in contact with the structure. The porosity of the large wood structure, the flow underneath of the structure, and the orientation of the wood can influence whether a boater or swimmer can be pinned against the structure or entrapped on or under the structure.
The primary research is question is: How can large wood structures be designed to minimize the risk of pinning or entrainment to river users while achieving project goals such as habitat production?
Need and Benefit
A technical workshop on Large Wood Applications and Research Needs in River Restoration was hosted jointly by Reclamation & U.S. Army Corps of Engineers in February 2012 (funded by S&T program). The primary goal of the workshop was to provide an opportunity for individuals and agencies actively working in the field of the engineered placement of large wood to collectively develop a road map for future large wood research needs and priorities. The road map and summary report from the workshop identified the need for design criteria to improve the safety of structures as high priority. Results from the workshop show that this is a topic of interest to many people in the field of river restoration within Reclamation, Corps of Engineers, other federal agencies, local agencies, and private firms.
S&T Program funded a scoping level proposal on "Improving Public Safety of Large Wood Installations". Because safety incorporates many different components – large wood design and placement, structure stability and mobility, risk analysis, and liability – each topic area was only addressed in a general sense to identify research gaps. One research gap relates to the safe design of the structure to improve public safety if human interaction with the structure occurs. This specific area should be researched more thoroughly so that a study plan can be developed to address this issue with a physical or numerical model.
Research conducted under this initial scoping level effort will be documented in a scoping paper. If a full research project is proposed, details about the research concept and methodology will be outlined.