Elwha Watershed Information Resource

In healthy rivers and streams, the natural accumulation of trees, branches, and root wads provides critical habitat for fish, amphibians, and invertebrates by forming pools and creating cover. These accumulated products are called large woody debris (LWD), and they can also help retain soil nutrients that are important to riparian vegetation (Pettit and Naiman 2005).

Today, logging practices and construction of roads and dams has reduced the amount of LWD in rivers and streams (Naiman, Decamps and McClain 2005). In the Elwha River watershed, transport of LWD to the lower river has been blocked by two dams since the early 1900s, and the LWD depletion has resulted in limited spawning and rearing habitat for salmon (McHenry 2004). In an effort to restore LWD in the lower Elwha River, engineers and biologists have constructed man-made versions of these collections called engineered log jams (ELJs).

Large Woody Debris (LWD)

Historically, LWD was thought to be bad for the environment and was removed from rivers and streams after logging (Dolloff 1994) and cleared from waterways to make transportation possible (Harmon and others 1986). As a result of these land use practices (and other factors), salmon populations have declined. For example, coho (Oncorhynchus kisutch) salmon populations in California have declined 70 percent since the 1960s (Brown, Moyle and Yoshiyama 1994).

In the Elwha watershed, there are two primary reasons for the decline of LWD:

Engineered log jam in the lower Elwha River in winter of 2004. Mike McHenry, Lower Elwha Klallam Tribe

• The construction of the Elwha Dam in 1914 and Glines Canyon Dam in 1927 on the Elwha River have blocked the transport of LWD and sediments to the lower river.

• Throughout the Olympic Peninsula, the accumulation in streams of LWD from old-growth forests has declined rapidly due to logging; the LWD from younger forests do not provide the same quality of habitat because they are smaller, more mobile, and decay faster (McHenry and others 1998).

Today, LWD is recognized as a key component of the ecosystem. Studies like the ones below have helped managers and biologists understand the importance of LWD:

• In Alaska, it is estimated that a 70 percent reduction in LWD would occur if areas continued to be clear-cut for 90 years without a streamside buffer--and recovery to the prelogging state would take more than 250 years (Murphy and Koski 1989).

• In Oregon, the Elk Creek watershed was degraded by logging and floods in the late 1980s; today, reconstructed areas have seen a five-fold increase in suitable coho salmon habitat (Crispin, House and Roberts 1993).

• The replacement of LWD has also improved habitat for non-salmonid fishes such as lamprey and sculpin (Roni 2003) and for invertebrates (Hilderbrand and others 1997).

In addition to replacing naturally accumulating LWD using ELJs, some states are taking steps to prevent the depletion of LWD in the first place. For example, Washington State requires streamside buffers during timber harvest to protect streams and ensure the presence of LWD (Forest Practices Rules - Title 222 WAC).

Engineered Log Jams (ELJs)

ELJs are designed to mimic the effects of naturally accumulating LWD, and the four ELJ categories are equivalent to log jams that naturally occur. A 2006 report by Herrera Environmental Consultants, Inc. describes the four categories as:

• Habitat enhancement: reestablish complex and diverse habitat by creating pools and cover.

• Bank protection: direct flows away from stream banks to prevent erosion.

• Bar apex: generally created in the middle of the channel in order to divide the stream into multiple channels, which leads to increased channel length, depth, cover, and number of pools.

• Grade control: retain sediment and provide bank stabilization by dissipating the energy of the water.

Selecting the type of ELJ to be used in a restoration project depends on the physical characteristics of the river (such as flow and geology), the desired type of habitat structure, and the budget of the project.

Engineered Log Jams in the Elwha River

Construction of engineered log jam in the lower ElwhaRiver. Mike McHenry, Lower Elwha Klallam Tribe

Since 1999, more than 20 ELJs have been installed in the lower Elwha River to restore the LWD blocked by the dams (McHenry 2004). A total of 645 pieces of wood have been used and, to date, all ELJs are intact and the results have been encouraging:

• Habitat has been restored at these sites: pools have developed at the majority of sites and sediment has changed from large cobble to gravel.

• Primary and secondary production on ELJ surfaces is significantly higher than in other habitats.

• Macroinvertebrate communities (such as mayflies) have changed significantly and more juvenile salmon have been observed at ELJ sites.

• The location of salmon redds (spawning nests) also appears to be related to the presence of ELJs.

Collaborators: George Pess (NOAA Northwest Fisheries Science Center), Mike McHenry (Lower Elwha Klallam Tribe), and Jeff Duda (United States Geological Survey)

Reference

Brown, L. R., P. B. Moyle, and R. M. Yoshiyama. 1994. "Historical decline and current status of coho salmon in California." North American Journal of Fisheries Management. Volume 14. Pages 237 to 261.

Crispin, V. R. House, and D. Roberts. 1993. "Changes in instream habitat, large woody debris, and salmon habitat after restructuring of coastal Oregon stream." North American Journal of Fisheries Management. Volume 13. Pages 96 to 102.

Dolloff, C. A. 1995. "Large Woody Debris - The common denominator for integrated environmental management of forest streams." Implementing Environmental Management. Edited by John Cairns, Jr., Todd V. Crawford, and Hal Salwasser. Virginia Polytechnic Institute and State University. Blacksburg, Virginia.

Harmon, M. E. and others. 1986. "Ecology of coarse woody debris in temperate ecosystems." Advances in Ecological Research. Volume 15. Pages 133 to 302.

Herrera Environmental Consultants, Inc. 2006. Conceptual design guidelines: application of engineered logjams. Prepared for Scottish Environmental Agency.

Hilderbrand, R. H. and others. 1997. "Effects of large woody debris placement on stream channels and benthic macroinvertebrates." Canadian Journal of Fisheries and Aquatic Sciences. Volume 54. Pages 931 to 939.

McHenry, M. 2004. Monitoring of Engineered logjams in the Elwha River, 1999-2003. Executive Summary prepared for Salmon Recovery Funding Board and Interagency Committee for Outdoor Recreation.

McHenry, M. L. and others. 1998. "Changes in the quantity and characteristics of large woody debris in streams of the Olympic Peninsula, Washington, U.S.A. (1982-1993)." Canadian Journal of Fisheries and Aquatic Sciences. Volume 55. Pages 1395 to 1407.

Murphy, M. L., and K. V. Koski. 1989. "Input and depletion of woody debris in Alaska steams and implications for streamside management." North American Journal of Fisheries Management. Volume 9. Pages 427 to 436.

Naiman, R. J., H. Decamps, and M. E. McClain. 2005. Ripararia: Ecology, conservation, and management of streamside communities. Elsevier Academic Press, Burlington, MA.

Pettit, N. E., and R. J. Naiman. 2005. "Flood-deposited wood debris and its contribution to heterogeneity and regeneration in a semi-arid riparian landscape." Oecologia. Volume 145. Pages 434 to 444.

Roni, P. 2003. "Responses of benthic fishes and giant salamanders to placement of large woody debris in small Pacific Northwest streams." North American Journal of Fisheries Management. Volume 123. Pages 1087 to 1097.