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Grays Harbor Navigation and South Jetty Sediment Processes Study
In December 1993,
persistent shoreline erosion near the South Jetty culminated in the
formation of a
In 1999, construction began on a wave diffraction mound, and about one-third of a recommended design for a transition gravel beach with cobble material was placed on a subsequent fill of the breach. This greatly reduced scope of a transition beach was required to alleviate environmental concerns regarding impacts of placing gravel and cobble on a sandy beach.
The Coastal Communities of Southwest Washington continues to provide ongoing technical support to the project to evaluate alternative design modifications to the South Jetty eastern terminus and transition beach to address the ongoing erosion of the Half Moon Bay shoreline, and breaching of the South Beach shoreline at South Jetty, Grays Harbor.
References
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The
development of the channels and facilities at Grays Harbor has been a
continuing process since the Rivers and Harbors Act of June 1896
authorized the construction of the South Jetty. Maintenance dredging by
the US Army Corps has been required after the 1990 Grays Harbor Navigation
Improvement Project was completed. Erosion on South Beach and Half Moon
Bay prompted the disposal of a portion of this dredged material in these
areas. 
breach
between the jetty and the adjacent South Beach. The U.S. Army Engineer
District, Seattle (NWS) filled the breach in 1994 with 600,000 cu yd of
sand dredged from the navigation channel as a temporary measure to protect
the Grays Harbor Navigation Project and alleviate concerns raised by the
City of Westport. During the seventh winter that the fill was in place
(2001-2002), a series of storms damaged the South Beach and modified the
Half Moon Bay shoreline, re-emphasizing the temporary nature of the sand
fill. 
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Technical
studies are being conducted by the US Army Corps of Engineers, Engineer
Research and Development Center, Coastal Hydraulics Laboratory with
support from the Coastal Communities of Southwest Washington on behalf of
the City of Westport and the Port of Grays Harbor. A report completed in
February 2003 concludes that the transition zone in the lee of the
diffraction mound needs to be modified and evaluated over the long term to
provide sustained fill protection. The report also recommends that
consideration be given to modifications to the wave diffraction mound and
south jetty terminus to increase dissipation of the large waves that occur
at high water levels during storms and that are correlated with erosion.
