Erosion and Channel Migration at the Shoalwater Bay Reservation, Willapa Bay, Washington

Cape Shoalwater, at the north side of the mouth of Willapa Bay, Washington, has experienced some of the most severe erosion in the United States, exceeding 30 m per year during most of the 20th century. Morphological studies have documented that the rate of shore retreat near the Shoalwater Reservation has slowed to almost zero since the mid- to late-1980's. The reason is the presence of outcropping hard strata, a very dense, brown Pleistocene Terrace unit. This finding was unexpected because previous studies suggested that the shoreline would continue to retreat and that there were unlikely to be any practical engineering solutions to help stabilize the remnants of North Cove. Water diversion structures, such as dikes are impractical because they would need to be massive to have any effect in controlling the ebb-and flood-currents. Wave analysis verified that the waves causing local flooding in the reservation were generated in the fetch of the bay and that Pacific Ocean waves are effectively dampened as they pass over the Willapa ebb shoal.