TCS – Cascadia Chapter Website
Coastal Erosion and Flooding
Hugh Shipman
Trends and Threats: Coastal Erosion and Flooding
(for Cascadia Chapter of the Coastal Society)
Trends
Erosion, landslides, and floods have occurred for millennia along the coast of Cascadia and
continue to shape the shoreline today. Although these geologic processes only affect a narrow
band of coastline, it is the same narrow band in which increasing numbers of people live, work,
and play.
High cliffs and coastal bluffs, small estuary floodplains, and exposed beaches, when combined
with severe Pacific storms and periodic earthquakes, form a natural setting for geologic hazards
in the Northwest. Storms and waves erode beaches, redistribute sediment, and undermine
bluffs. Heavy rainstorms weaken slopes and send torrents down coastal watersheds.
Earthquakes trigger landslides and tsunamis and may lead to significant changes in coastal
elevations.
WA Dept of Ecology
Rapid population growth in the region has greatly increased development pressure in coastal
areas. Rising real estate values and greater affluence have increased the numbers of expensive
homes along the region’s shorelines. Tourism brings more people and more demand for high
density development and for amenities, while at the same time placing a premium on natural
shorelines, beach access, and on recreational experiences. Increasing investment in hazardous
shoreline areas leads to greater losses when disaster strikes, more elaborate and expensive
efforts to reduce risks, and more pressure on politicians to respond to short-term crises.
During the last decade, the public has become more aware of the risks and consequences of
shoreline development . They also better understand the natural hazards inherent in coastal
areas and some recognize that traditional engineering approaches to erosion and flooding may
have unanticipated consequences, reducing recreational access and harming biological
resources.
Issues
Northern California. California’s northern coast includes the rugged headlands of Mendocino
County, the spits and dunes of Humboldt Bay, and the beaches and rocky promontories of the
Crescent City region. Cliff erosion and landsliding pose serious problems along the Mendocino
coastline, whereas flooding, river mouth erosion, and dune management are major issues in the
Eureka area. Damage in Crescent City from tsunamis in 1960 and 1964 has underscored
concerns along low portions of the coast about the threat of future earthquakes and tsunamis.
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TCS – Cascadia Chapter Website
Coastal Erosion and Flooding
Hugh Shipman
Oregon Coast. The Oregon Coast is characterized by high rocky headlands, broad beaches, and
large river-mouth estuaries. Beach erosion, driven by severe storms and intensified during
periodic El Ninos, affects development on sand spits, on the marine bluffs, and adjacent to tidal
inlets. Landslides, ranging from small to very large, are common along the coast, affecting
residences, communities, and Highway 101.
Oregon DLCD
Southwest Washington. Prior to the 1990s, most communities along the broad sandy beaches
of Washington’s southwest coast were concerned about rapid beach accretion But dams on
the Columbia River and large jetties at both the mouth of the Columbia and at Grays Harbor
altered patterns of sediment movement and deposition along the coast. As the reservoir of
sediment at the mouth of the river disappeared, erosion increased Recent engineering fixes at
Ocean Shores, Westport, Cape Shoalwater, and Fort Canby State Park have been controversial,
stirring vigorous public debate.
WA Dept of Ecology
Puget Sound. Puget Sound is an inland sea with over 2100 miles of shoreline, much of it high
bluffs subject to periodic erosion and landsliding. Heavy rainfalls in 1996 and 1997 led to
widespread landslide damage and two federal disaster declarations. In addition, floods,
erosion, and storm damage frequently impact residential communities built on sand spits and
other low lying shorelines. Problems within the region are exacerbated by rapid population
growth in the Tacoma-Seattle-Everett urban corridor and by growing recognition of the need to
balance the needs to protect private property from erosion with a desire to maintain beaches
and a biologically rich nearshore environment.
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TCS – Cascadia Chapter Website
Coastal Erosion and Flooding
Hugh Shipman
WA Dept of Ecology
British Columbia. British Columbia has witnessed enormous population growth in the lower
Fraser valley and on southern Vancouver Island in recent years. Erosion and flooding are
significant issues along the shoreline of the Strait of Georgia, not unlike the geologically similar
Puget Sound region to the south. Erosion, flooding, and earthquake hazards are major
concerns on the Fraser River delta, where much of the Vancouver area’s industrial base is
located.
Solutions
Finding better ways to address erosion and flooding problems requires good science, informed
coastal management, and an educated public. Each of these components is reflected in efforts
currently underway in the Pacific Northwest.
California. Tsunami inundation studies and maps, hazard planning, and education have better
prepared northern California communities to deal with the threat of tsunamis, leading to
Crescent City being designated the first tsunami-ready community in the state in Fall, 2002.
Oregon. A decade of commitment by Oregon Sea Grant, the state’s Coastal Management
Program and the Department of Geology and Mineral Industries has greatly improved
understanding of coastal processes and natural hazards. Local communities and the general
public have been actively engaged in the discussion and have begun to develop planning tools
for managing development in erosion and flood-prone coastal areas. Research at Oregon State
University and elsewhere has complemented these efforts with important studies of geologic
and oceanographic processes.
Southwest Washington. For over six years, the Department of Ecology and the USGS have
carried out detailed studies of the beaches of southwest Washington, with the goal of better
understanding the complex relationships between storms, Columbia River sediment supply,
dredging and jetty construction, and beach erosion and accretion. This work has begun to
inform discussions at the state and local levels about long term approaches to this dynamic
segment of coastline.
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TCS – Cascadia Chapter Website
Coastal Erosion and Flooding
Hugh Shipman
WA Dept of Ecology
Puget Sound. Under the state’s Shoreline Management and Growth Management Acts, local
governments are developing improved policies, based on good science, for guiding development
of hazardous coastal areas. The Washington Coastal Planner’s Group, jointly led by Washington
Sea Grant and the Department of Ecology, provides a popular forum for state and local
shoreline officials to discuss a wide variety of issues, including erosion and flood hazards. The
U.S. Geological Survey and the University of Washington are beginning to collect critical
shoreline data to support scientific understanding of coastal geological processes.
Links
Oregon Coastal Management Program
http://www.lcd.state.or.us/coast/hazards.html
Oregon Department of Geology and Mineral Industries
http://www.oregongeology.com/earthquakes/Coastal/CoastalHazardsMain.htm
United States Geological Survey – El Nino
http://coastal.er.usgs.gov/response/
Washington Coast
http://www.ecy.wa.gov/programs/sea/coast/index.html
Puget Sound Landslides
http://www.ecy.wa.gov/programs/sea/landslides/index.html
British Columbia
http://sts.gsc.nrcan.gc.ca/geoscape/vancouver/home.asp
Washington Division of Geology and Earth Resources
http://www.wa.gov/dnr/htdocs/ger/landslid.htm
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TCS – Cascadia Chapter Website
Coastal Erosion and Flooding
Hugh Shipman
Redwood Coast Tsunami Work Group
http://sorrel.humboldt.edu/~geodept/earthquakes/rctwg/RCTWG.html
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