Trends and Threats: Coastal Erosion and Flooding

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 wish to 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 led to increasing increased the numbers of more 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 awareness of the risks and consequences of shoreline development along dynamic shorelines has increased. They also Not only is there more understanding of better understand the natural hazards inherent in coastal areas but there is also recognition and some recognize that traditional engineering approaches to erosion and flooding may have unanticipated consequences in the longer term, 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.

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 more concerned about rapid beach accretion than erosion, but this situation has changed. But dDams on the Columbia River and large jetties at both the mouth of the Columbia and at Grays Harbor have altered patterns of sediment movement and deposition along the coast. As the reservoir of sediment at the mouth of the river disappeared, and erosion increased numerous erosion problems have emerged. Recent erosion engineering fixes at Ocean Shores, Westport, Cape Shoalwater, and Fort Canby State Park has led to controversial engineering fixes have been controversial, stirring and 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.

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.

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

Redwood Coast Tsunami Work Group

http://sorrel.humboldt.edu/~geodept/earthquakes/rctwg/RCTWG.html