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Forcing of large-scale cycles of coastal change at the entrance to Willapa Bay, Washington

Marine Geology

By:
, , , , and
DOI: 10.1016/j.margeo.2007.07.008

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Abstract

Anomalous morphological features within large estuaries may be: (1) recorders of external forces that periodically overwhelm the normal morphodynamic responses to estuarine energy fluxes, and (2) possible predictors of cycles of future coastal change. At the entrance to Willapa Bay, Washington, chronic beach erosion and frequent coastal flooding are related to the historical northward channel migration that destroyed the protective sand spits of Cape Shoalwater. Northward channel migration since the late 1800s conforms to the long-term net sediment transport direction. What requires explanation is periodic southward relocation of the trunk channel by as much as 5 km, and attendant construction of moderately large sand spits on the north side of the bay such as Kindred Island, Tokeland Peninsula, and Cape Shoalwater.


Both autocyclic and allocyclic processes may have been responsible for trunk channel realignment and associated spit deposition. Channel recycling may occur when the main channel becomes overextended to the north and the tidal flow is inefficient because of its decreased gradient and increased susceptibility to shoaling by the growth and migration of tidal sand ridges. Under those conditions trunk channel relocation would be facilitated by increased wave heights and water levels of El Niño winter storms. However, co-seismic subsidence is the most likely mechanism for abruptly increasing sand supply and longshore transport that would favor discrete periods of channel relocation and spit deposition. Unless external forcing changes sand supply and predominant sediment transport directions in the future, the relative rise in sea level, frequent winter storms, and local deficit in the sand budget assure that beach erosion will continue at the mouth of this large estuary.

Geospatial Extents

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Forcing of large-scale cycles of coastal change at the entrance to Willapa Bay, Washington
Series title:
Marine Geology
DOI:
10.1016/j.margeo.2007.07.008
Volume
246
Issue:
1
Year Published:
2007
Language:
English
Publisher:
Elsevier
Contributing office(s):
Coastal and Marine Geology Program
Description:
18 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Marine Geology
First page:
24
Last page:
41
Country:
United States
State:
Washington
Other Geospatial:
Willapa Bay