Erosion Happens: And your favorite beach is the beneficiary
February 22, 2011 · 12:29 PM
By Tina Whitman
Special to the Journal
Have you ever wondered how popular sandy beaches such as Crescent Beach on Orcas, Jackson’s Beach on San Juan, South Beach on Shaw, or Odlin on Lopez came to exist amidst the many miles of rocky shoreline here?
Geologists explain that beaches are linked by a trail of gravel and sand back to “feeder bluffs” — a term coined in the 1970s by local engineer Wolf Bauer to describe the role that bluffs play in providing the materials that create and sustain beaches.
Because feeder bluffs play such a crucial role in shaping our shorelines, Friends of the San Juans and the Marine Resources Committee collaborated with Coastal Geologic Services of Bellingham to map current and pre-development feeder bluffs and beaches in San Juan County.
CGS completed similar maps in other Puget Sound counties, including Whatcom, King, Island, and partly mapped four other counties. In addition to mapping feeder bluffs through extensive field work, the surveys looked at the quality of feeder bluffs.
Surveys found that a considerable portion of bluffs were armored with bulkheads, severely limiting the ability of the bluff to provide beaches with essential gravel and sand.
Friends and CGS will explore opportunities to restore these bluffs and beaches.
The project also identified San Juan County’s remaining high-quality feeder bluff areas that warrant protection, including Waldron’s Point Hammond, Shaw’s Indian Cove and Ship Bay on Orcas.
Countywide, 22 miles of feeder bluffs have been mapped, representing current conditions. Historical analysis found an additional five miles of feeder bluffs have been lost to impacts from development, such as bulkheads, docks, roads, and marinas.
Lopez has the most feeder bluffs, with 33 percent of the county total. Other islands with more than five miles of the county total, by percent:
— Orcas 16
— San Juan 15
— Decatur 10
— Waldron 9
— Blakely 7
The greatest impact to feeder bluffs by development have been on Shaw, Orcas and Lopez islands, respectively, as well as several non-ferry served islands, like Pearl, Brown and Center.
Mapping for our county is now complete. Project results can be used by decision-makers to help protect property and preserve spawning beaches for surf smelt and sand lance, small fish which rely on beaches for incubating eggs and that are an important food source for salmon, rockfish and seabirds.
Maps and project reports and maps are being provided to coastal researchers, planners and managers to inform the local Shoreline Master Program update and salmon recovery efforts.
Maps of feeder bluffs and associated reports are also available to the public upon request.
Funding for the San Juan County Feeder Bluff Mapping Project was provided by the Puget Sound Partnership, the Northwest Straits Foundation and the Washington State Salmon Recovery Funding Board.
For more information on Friends projects please visit our website at www.sanjuans.org.
Tina Whitman is the science director for Friends of the San Juans. She can be recached at 378-2319.