On the Olympic Peninsula in Northwest Washington, the Lower Dungeness River Floodplain Restoration project restores habitat and natural river processes that are confined by various levees and dikes constructed in the 1940s through 1960s. The lower reaches of the Dungeness River have been constricted on the right bank by an existing 2.4-mile-long levee built in the 1960s by the United States Army Corps of Engineers (USACE). However, the USACE levee is ‘under-designed’ for anticipated flood events to come.
Aerial view of the 2,600-foot setback levee
Photo credit: Jamestown S’Klallam Tribe (JST)
Twenty years ago, the Lower Dungeness River Floodplain Restoration project was conceived with the goal of building a new setback levee and reconnecting the Dungeness River with its historical floodplain; improving habitat conditions; and restoring riverine processes and functions. The project was split into two parts: the Clallam County (County) levee setback project from River Mile (RM) 0.8 to 1.75, and the River’s Edge Project between RM 1.75 to 2.7. The County project started in 2015, but then the floodplain restoration work hit a standstill – until the Jamestown S’Klallam Tribe (JST) brought the River’s Edge Levee Setback project to life.
Jamestown S’Klallam Tribe Rebuilds a Floodplain to Restore the Region
For thousands of years pre-colonialism, the JST nurtured the land and many saltwater bays and freshwater rivers. Today, the JST takes an active role in community environmental projects, including participating in the Dungeness River Management Team and implementing habitat restoration projects such as this levee project, which is a part of the Lower Dungeness River restoration efforts.
JST purchased farmland along this stretch of the Dungeness River (with a strong show of support from local community members) with the understanding that the purchased land would be used for conservation efforts. JST secured funding support from Washington state’s Floodplains by Design grant and brought on Engineering Services Association (ESA) to lead the project design. ESA in turn brought Aspect in to be the geotechnical lead, as well as several other key team members like WEST Consultants (hydrology and hydraulics) and Johnston Land Surveying.
The River’s Edge project will renew historical riparian habitat and boost the overall health of the ecosystem, including salmon recovery for key species like Chinook salmon, summer chum, bull trout, and steelhead. The new setback levee will also double as a walking path to be used by all members of the community.
Early Detective Work in a Floodplain Leads to Success
Rivers deposit soils in highly varied and complex ways. To set up the 2600-foot-long setback levee for success and understand the subsurface conditions, Aspect led a two-phase subsurface exploration program that included six soil borings (2 with vibrating wire piezometer installations), 11 test pit excavations, 13 hand-dug explorations, and 4 cone penetrometer explorations. Using this information we created a profile of subsurface conditions to power smart levee design.
Levees Need to Be Made of the ‘Right Stuff’
Nearby gravel pit that ‘fed’ the levee
Photo credit: Krazan & Associates
A key driver in any levee project is the availability of material. This levee was made up of over 37,000 cubic yards of gravel and sand. ESA identified a material source only two minutes away and Aspect and ESA tailored the levee design to make sure the material available from the gravel pit could be successfully used to build the levee to meet design standards. Having a material source so close to the Site helped save budget, time, and greenhouse gas emissions.
Finishing a 2,600-Foot Levee in Under Two Years: A Win !
Floodplain restoration without River's Edge Levee Setback project (on the left) and WITH River's Edge Levee Setback Project (on the right).
Photo credit: North Olympic Land Trust
Aspect collaborated with ESA, JST, and USACE to design the setback levee in just under one year, with construction of the project hot on the heels of the final design submittals. Construction then started and the new setback levee was built in just over 2 months!
In summer 2022, the existing levee will be removed to allow the Dungeness River to reclaim 56 acres of floodplain. The Clallam County project will eventually tie into the River’s Edge Setback Levee to open up an additional 87 acres for a combined 143 acres of reclaimed historical floodplain and habitat for salmon, birds, and wildlife.
The hard work and dedication of the River’s Edge project team helped realize the JST’s desire to create a quality setback levee that meets the latest and greatest safety standards, within their desired schedule – and underbudget!