Elwha River Delta
Coastal Engineering with Nature
Between 2011 and 2014 the Elwha River was site of the largest dam removal in the world thus far, releasing more than 14 million cubic yards (cy) of sediment downstream. In 2015, Lally Consulting LLC was requested to provide engineering services in support of a long-term coastal resiliency design development for a private property located on the Elwha River Delta.
The site is subject to erosion and flooding due to severe wave forces and ocean swell along the Strait of Juan de Fuca. To combat these effects, the site shoreline had been modified by previous owners to include a timber and rubble-mound seawall that was later determined to be in violation of federal law under U.S. Army Corps of Engineers (USACE) authority.
Services included conducting field reconnaissance to assess and document current conditions, shoreline survey coordination, research and review of property information, permits, existing and historical photography, topography and bathymetry, and other data review. Lally LLC analyzed geomorphological processes associated with the recent dam removal on the Upper Elwha River, shoreline change rates, water levels, tides, wave regime and numerical modeling (SWAN) results, sediment transport conditions, and compiled findings in a coastal processes evaluation report.
Using this basis for design information, several shoreline erosion control alternatives were developed, including engineering drawings, quantity takeoffs, and cost estimates. Each alternative involved the removal of the existing timber and quarry stone seawall and proposed a nature-based engineering approach to promote properly functioning sediment transport conditions within the deltaic littoral cell through incorporation of endemic habitat elements and foreshore geometries and components representative of neighboring shorelines.
The erosion control designs sought to reduce costs and better balance stakeholder needs, by recycling armor stone on site, set at proper offsets, crest elevations and slopes, incorporating curvilinear alignments, anchoring large woody debris to promote sediment and driftwood recruitment, installation of seagrasses above OHWL and rounded gravel along the foreshore intertidal zone to serve as a feeder beach for surf smelt spawning. Removal of hard armoring elements altogether with movement of existing residential structures landward (retreat) was also evaluated, and ultimately implemented to allow the shoreline to return to a completely natural condition.
Services Provided
Field Investigations
Coastal Processes Analyses
Shoreline Erosion Control Engineering
Nature-based Engineering
Production and Cost Estimates
Location
Elwha River Delta – Strait of Juan de Fuca, Washington, USA
Period
2015 – 2016
The project site is located on the Elwha River Delta, downstream of the largest dam removal project in U.S. History, completed in 2014 to restore the river ecosystem and native anadromous fisheries it historically supported.