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Engineered Log Jams Post Project Appraisal for Streambank Erosion and Salmonid Habitat in Washington State

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  International Symposium on Erosion and Landscape Evolution (ISELE), 18-21 September 2011, Anchorage, Alaska  711P0311cd Paper #11073.(doi:10.13031/2013.39267)
Authors:   W Barry Southerland, Frank R Reckendorf, Dean Michael Renner
Keywords:   KEYWORDS: Fluvial geomorphology, ELJ, Engineered log jams, Wood structures, Cowlitz River, Fish habitat, Tightness of radius of curvature, USDA National Engineering Handbook, Floods

In 2005 the Engineered Log Jam (ELJ) Handbook titled, Bank Protection and Habitat Enhancement using Engineered Log Jams: An Experimental Approach Developed in the Pacific Northwest was submitted to USDA-NRCS as part of the National Engineering Handbook 654. Concurrently, in 2006 the Washington-NRCS and the WNTSC-NRCS assembled an interdisciplinary team including two fluvial geomorphologists, fish biologist and a stream mechanics engineer and began to study the results and effects of ELJs implemented since the mid-1990s in the State of Washington. This paper discusses the preliminary results of the evaluation of 43 log jams utilizing in-part or completely the ELJ Technique and Design Criteria developed as part of a dissertation at the University of Washington. All of the log jams studied were installed with, minimally, the two primary objectives: streambank protection and fish habitat improvement. Reponses of these stream channel structural practices have ranged from successful habitat restoration to complete structural loss in attempts to incorporate wood. In the mid-1990s research on natural log jams characteristics, patterns, and benefits lead to the technology that is currently referred to as engineered log jams. One of the first sites for log jams (three) implemented with the new ELJ technology was on the Cowlitz River at river mile 121, three km north of Packwood, WA. These ELJs were designed to treat streambank erosion and instability and provide salmonid habitat along 430 meters located on private property. The three ELJs installed are no longer there. Since 1998, over one hundred million dollars of Washington State monies have been spent on ELJs. All sites assessed included both stream bank protection and adult salmon refugia as primary objectives were designated on permits. One of the unique characteristics of the specific ELJ design used on the Cowlitz and various other streams such as the Cispus, North Fork of the Stillaguamish, and others, is the exclusion of rock and other inert material such as cable to add stability to the structure and counter-act the buoyant properties of wood. Within the past several years several practitioners have begun to incorporate substantial amounts of cable, metals pins, and other appurtenances to similar kinds of engineered log jams. The results of ELJs implemented since the mid-1990s has shown that out of 43 ELJs visited 9 were completely lost and another 22 were partially lost and presently flanking and annually losing some log members. As of 2009, on the Elwha River, six of eight cabled log jams (averaging 250 feet of half inch cable per jam) have been meeting both streambank protection and fish habitat objectives since their 1999 installation. The other two are no longer present. Scalloping and flanking has been observed on numerous ELJs. As of 2009 twenty one percent of the installed ELJs still have summer refugia adult salmonid pools remaining. This presentation will provide a qualitative evaluation garnered from site visits, field observation, and some field morphometry. The team dove some log jams to observe salmonids. Other log jams had clear and visible pools to observe fish in the late summer. Additional information was added to the evaluation from remote sensing (aerial photography). August of 2011, the five year Stage I site visitations and data collection will end. A stage II data collection involving a more in-depth field morphometry has been proposed for 2012-2014.

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