Y--Mouth of the Columbia River (MCR), South Jetty Dune Stabilization

Construct a dynamic revetment to an elevation +22 feet NAVD88. The crest width of the dynamic revetment will be approximately 65 feet. The oceanside face of the dynamic revetment will be constructed at a slope aspect of 1v:5h, from the crest breakpoint to where the slope intersects the foundation grade (toe). The landside face of the dynamic revetment will abut with the existing foredune face. The base (foundation toe) of the dynamic revetment will be constructed at +9 to +11.6 feet NAVD88 as shown on the drawings. The depth of sand excavation needed to achieve the dynamic revetment foundation grade is expected to be 5- to 8-feet. Replace the excavated sand along the oceanside face of the dynamic revetment, after the final grade line of the revetment has been approved by the COR. Construction shall meet all environmental restrictions. Construct incrementally in 100- to 200-foot long segments or as needed to accommodate sequencing with high tides, storms and affected groundwater levels along the presently degraded foredune. Each segment shall be completed before significant work on the next adjoining segment is initiated. BACKGROUND The foredune south of the South Jetty is in a condition of advanced deterioration. The initial foredune (1970's) had a crest elevation of 30-40 feet NAVD, and 50-100 foot crest width. The foredune, as a result of erosion by winter storms, is now a relatively narrow feature on an otherwise flat, low-elevation area adjacent to a tidal marsh. The high-crested foredune prevents storm-induced overtopping and protects the narrow strip of low-lying land that is separating the ocean from the jetty lagoon called Trestle Bay. Between 2003 and 2007, the concave shoreline area receded approximately 40 feet, further reducing the protective ability of the foredune. Presently, the foredune crest has been reduced to less than 25 feet NAVD along much of the project's 1,100 foot reach. LOCATION This work is located on Clatsop Spit on the north end of Ft. Stevens State Park, in Clatsop County, Oregon, near the cities of Warrenton, Hammond, and Astoria.