WAVES
STORMS
 
EROSION
What's
happening

Ocean Shores
Cape Disappointment
Washaway Beach
Westport
Leadbetter Point
dams
jetties
Grand Coulee Dam, Columbia River
Dams have reduced the sand supply
to coastal beaches

 
Over 219 dams in the Columbia River basin have reduced the amount of sand and sediment reaching beaches on the coast.
Dams in the Columbia River watershed
  • Before dams were constructed, sand moved freely
    Before dams were built on the Columbia River, floods carried sand to the delta, where it gathered in shoals. Longshore currents picked up the sand from the shoals, moved it along shore, and deposited it on beaches. The Columbia River carried about 12 million cubic yards of sediment to the coast per year.
  • Dams have restricted the flow of sand by two-thirds
    Beginning in the 1930's, dams were constructed over most of the U.S. part of the Columbia River. Dams restricted sediment supply from 90 percent of the watershed, a quarter of a million square miles. As a result, the Columbia River delta has been starved of critical beach building sand.
  • Delayed effects
    Peacock Spit, a huge shoal north of the mouth of the Columbia, supplied sand to coastal beaches for decades. Peacock Spit is now gone. The spit may have been scoured away by jetty-influenced currents. With sand in short supply, Washington's southwest coast may be entering a long-term period of erosion.

Source: The Southwest Washington Coastal Erosion Study.
 
Images courtesy of: Brian Voigt; Dam Safety Office, Water Resources Program, Washington State Department of Ecology.

Southwest Washington Coastal Erosion Study. A recent study of Washington's coastal processes and shoreline changes.
 
Our Disappearing Shores, The Tacoma News Tribune. An analysis of the erosion issue on Washington's coast.

Home | Sights | Hazards