Barrier Island Restoration for Storm Damage Reduction: Willapa Bay, Washington, Usa

Abstract

The U.S. Army Corps of Engineers, Seattle District has completed a feasibility study and determined barrier island restoration to be the most appropriate long-term coastal flood and storm damage reduction measure for the Shoalwater Indian Reservation. Over the last century, Cape Shoalwater has receded more than 2.8 miles. By 1990, the Shoalwater Reservation’s only remaining protection from storm wave attack was a series of barrier islands fronting Tokeland Peninsula. Extreme water levels coincident with strong winter storms have historically inundated this low lying topography and are responsible for the erosion and overwash of the protective barrier island known as Graveyard Spit. Here a simple risk assessment tool is presented for identifying flood risk to the Shoalwater Reservation infrastructure. Statistical analysis of extreme water levels and numerical modeling is utilized to determine the extent of inundation. From the analysis it was determined 54% of the inventoried infrastructure is at risk during a storm event equivalent to the observed event on March 3, 1999. With the barrier island restoration it was found that this risk is reduced to 7%.

The signature of accumulated permanent uplift, northern Cascadia subduction zone

“…In an estuary, erosion may occur from both waves and tidal current. Willapa Bay, a macrotidal estuary, has a tidal range between 1.25 and 3 m (Emmett et al, 2000; Banas and Hickey, 2005), and we use the modern mean tidal range for Willapa Bay of ±2 m (6.8 ft; Michalsen et al, 2010) as a minimum error for inner-edge elevation based on tidal fluctuation. Therefore, the uncertainty in the assigned elevation of the inner edge (e. g., shoreline angle) is ±2 m.…”

“…Wave-cut benches mark mean sea level, which varies with tides and storms. We use the tidal fluctuation for Willapa Bay of ±2 m (Michalsen et al, 2010).…”

Framework geology of Cape Shoalwater and northwest Willapa Bay, Washington : assessing potential geologic impacts on recent shoreline change

“…More recently, repeated bathymetric surveys by NWS indicate that over the last several years, migration of the channel thalweg has temporarily slowed, and anecdotal observations suggests that the associated shoreline erosion has also been reduced. After the completion of the ERDC research referenced above, and in collaboration with the ERDC, the US Geological Survey, and the University of Washington's Department of Ecology, NWS examined the shoreline erosion along Tokeland Peninsula and Cape Shoalwater with a Flood and Coastal Storm Damage Water Resources Development Study (e.g., NWS 2007;Michalsen et al 2010). During this effort, it was noted that if no action were taken, the relocation of the coastal community component of the Shoalwater Reservation would be unavoidable.…”