TIDAL INLET MORPHOLOGY CHANGE IN RESPONSE TO NAVIGATION IMPROVEMENT

This paper describes accelerating morphology change within a confined tidal inlet responding to navigation channel improvement/maintenance and related hydrodynamic effects. The extent of morphology change is profound and compromises the inlet’s stability, shore-based assets, and navigation features. The Ilwaco Inlet is located within the Mouth of the Columbia River (MCR), bordering the states of Washington and Oregon along the Pacific Northwest Coast of the United States. (46015’25’’N,124002’10”W). The Ilwaco inlet supports a regionally important waterway servicing the Port of Ilwaco (greater than $20 million/yr commerce) and a US Coast Guard station (regional SAR activity and national motor lifeboat training school). The US Army Corps of Engineers is responsible for maintaining the inlet’s 5 km-long federal navigation channel (45-60 m wide and -4.9 m MLLW depth) and four hydraulic control structures to support the Ilwaco FNC (pile dikes). The downstream-southern 2.5 km of the inlet interacts directly with the Mouth of the Columbia River.