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Elwha nearshore, 27 September, 2019.

Rewilding Foundations of the Pacific Northwest: Ecosystem Restoration Following Large Scale Dam Removal: Elwha Nearshore

Featured Image: Elwha nearshore, 27 September 2019. Photo by Anne Shaffer and CWI.

By Shaffer J. Anne 1*, Dave Parks 1,  Jamie Michel 1, Kirsten Simonsen 1, and Bob Oxborrow 2

1Coastal Watershed Institute
PO Box 266
Port Angeles Washington 98362
*corresponding author anne.shaffer@coastalwatershedinstitute.org

2University of Washington School of Aquatic and Fishery Sciences
Seattle, Washington 98195

The nearshore is a foundation component of coastal systems of the northeast Pacific. Sediment starvation due to large-scale in-river dams has significant negative impacts to coastal hydrodynamic and ecosystem processes that form the nearshore. Removal of large-scale dams is assumed to restore these ecosystem processes but the details of nearshore response, particularly when shoreline impediments remain, is poorly understood.

Here we provide an overview of the importance of nearshore to wild systems, the roles that large scale dams play in impacting coastal systems, and the importance of nearshore for rewilding ecosystems through large scale dam removal. From 2011- 2014, two century-old large-scale dams in the Elwha River watershed in the Northwestern United States were removed as a course of the Elwha dam removal project. This is the largest dam removal project in the world that has occurred to date and was due to the decades long work by the Lower Elwha Klallam Tribe and Olympic National Park. Dam removals liberated upwards of 10 million m3 of previously detained silt, sand, and gravel to a sediment starved shoreline comprised of armored and unarmored shorelines. In 2016-2017 approximately 7,000 m3 of large riprap (shoreline armoring) was removed from 1,000 meters of this shoreline.

We use physical metrics of beach topography, grain size, and ecological metrics of large woody debris (LWD), beach wrack, and forage fish egg abundance as indicators of shoreline response to both dam removal and armor removal.  Within one year of the initiation of dam removal, unarmored shorelines in the drift cell broadened, flattened, and fined, and LWD volumes increased dramatically. Armored shorelines continued to be steep and coarse. Following subsequent armor removal, eroding shorelines broadened, fined, and LWD volumes increased significantly, beach wrack metrics echoed non-armored beaches, and forage fish spawn distribution increased. These responses were observed literally miles downdrift of the restoration project, illustrating the ecosystem scale of rewilding efforts.

We conclude that only partial nearshore ecosystem restoration occurs from large-scale dam removal when nearshore impediments remain, and that full ecosystem restoration/rewilding with large scale dam removals is achieved by restoring impaired shorelines preferably in advance of dam removals.

A link to a 20-minute video presentation of this overview of Elwha nearshore can be seen here.  

Learn more about the Elwha River Restoration Project.

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