Washington: Dynamic revetment revealed as top choice for North Cove shoreline preservation
Dynamic revetment — the placement of cobble rock along coastal shorelines to protect them from erosion — is the official “preferred choice” to stave off the shoreline erosion that has been gobbling up property and houses in the North Cove area for decades.
The selection of the preferred design after a year-long demonstration project is a step toward a more permanent solution to the erosion problem that has cost the area more than 3 miles of coastline land since the late 1800s. North Cove is in Pacific County along Highway 105, near the northern entrance to Willapa Harbor but without much of the harbor’s protection. It’s been referred to as Washaway Beach.
Vladimir Shepsis, technical lead for the project’s engineering firm Mott MacDonald, told a packed house at the Shoalwater Community Center April 17 that revetment rose to the top of the list after considering factors ranging from construction and maintenance costs to environmental, shoreline and recreational impacts and, of course, effectiveness.
The options were considered by the engineering firm in conjunction with two advisory committees working together to come up with the preferred option: A technical committee, comprised of scientists and engineers from several agencies including the Army Corps and Engineers, the Department of Ecology, the Pacific County Drainage District, the Department of Transportation and the Pacific Conservation District; and a steering committee made up of policy, permitting and funding experts from many of those same agencies and the Shoalwater Bay Tribe.
“We are going to proceed with dynamic revetment and continue to evaluate the dynamic revetment plus groin option, which may become part of the master plan,” he said. A “groin” is basically a short jetty, said Shepsis, running perpendicular to the shoreline.
Shepsis showed a preliminary cost estimate, breaking down the five options. The preferred option has an initial capital cost of $6 million; the combination dynamic revetment and groin option $8 million. Maintenance costs for both run $13 million and $11 million respectively. The maintenance cost of the revetment itself is based on major maintenance performed every five years during the life cycle, said Shepsis.
The revetment runs from just north of the end of the Old State Route 105 south to the mouth of drainage ditch #1 — near where State Route 105 runs right alongside the shore — a total of about 3,500 feet of coastline. The “groin,” if implemented, would run south and west off the south end of the revetment.
Currently each linear foot of shoreline is protected by 1-5 cubic yards of cobble. Shepsis said the preferred design would call for 15 cubic yards of material for each linear foot.
Pacific County Administrator Kathy Spoor said now that the preferred design has been selected, funding for construction and maintenance of the revetment can be pursued.
“We will submit for construction permits this summer,” said Shane Phillips, Vice President of Mott MacDonald. “It’s hard to estimate how long that will take. It could take at least a year to get construction permits.”
A 2016 state capital budget item of $650,000 paid for the demonstration project and the work to this point, including the project design and recently-completed analysis, and the construction permit applications. Now it’s up to local stakeholders to go back to the table to find more money to fund the construction itself.
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