Dynamics of Whitcomb Flat

Whitcomb Flats is a sand flat located in the Grays Harbor estuary within one mile due east of the entrance to Westport Marina and immediately south of the present navigation channel. 

The Port of Grays Harbor and the Coastal Communities of Southwest Washington, supported an analysis of the dynamics of Whitcomb Flat, in Grays Harbor, Washington (see Figure at right; Click Map for larger version).  The work assisted the Port in addressing a request from Washington State Department of Natural Resources (WDNR) to examine the potential for adverse impacts on state-owned aquatic lands caused by the navigation channel of the Grays Harbor and Chehalis River Navigation Project.  WDNR raised concerns that increased wave energy stemming from the jetties or wave action from large vessels is exacerbating the migration of Whitcomb Flat and that ongoing navigation in the harbor could decrease the likelihood of the future formation of spits and shoals within the harbor.  The study included analysis of the geomorphic change and inlet processes at and adjacent to Whitcomb Flats in Grays Harbor since jetty construction. 

The study determined that recent sand flat migration is primarily caused by an increase in penetration of ocean storm waves and washover processes that in turn result from large-scale migration of the main ebb tidal channel.  The channel migration is a response to flood shoal accumulation on the north side of the inlet, a long-term response linked with jetty construction and rehabilitation.   Relocation of the navigation channel from Sand Island Reach to South Reach in the late 1970s, maintenance dredging at South Reach, and the widening and deepening project in the 1990s have also contributed to the overall increase in depth locally that has allowed larger waves to reach Whitcomb Flat.   

The results of the study were peer reviewed and the results published in the report:

P.D. Osborne. 2003.  Dynamics of Whitcomb Flats. PI Engineering Technical Report for Port of Grays Harbor in coordination with the Coastal Communities of Southwest Washington.  77p.

Acrobat PDF Document Available Here: Dynamics of Whitcomb Flats Report (Note:  Large File)