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05/04/2007: "SJ Conservation Dist. & PW Improve Lagoon & Beach"

(Juan Islands Conservation District Photo by Danna Nicole Kinsey)

San Juan Islands Conservation District (SJICD), in conjunction with San Juan County Public Works (PW), has completed a three-year effort to improve water quality in the Port Stanley Lagoon on Lopez Island. Installation of a new, hydraulically-operated tide gate at the lagoon outlet in June 2006 restored daily tidal flow into the lagoon for the first time since the early 1960s. With the completion of the project, SJICD and PW expect to see not only improvement in the lagoon water quality, but also improved wildlife habitat and a reduction in flooding during severe winter storms.

The project replaced an existing tide gate and replanting of vegetation on the disturbed beach. The original flood gate to the lagoon was installed in the 1960s to block tidal flow into the lagoon, but as a result, the lagoon gradually filled with sediment so that it became so shallow that by late summer only a stagnant puddle remained.

In addition, without continuous tidal flushing, the tide gate’s outfall pipe on the beach sometimes filled with sand, preventing winter storm runoff from draining properly. At the request of the lagoon owners, the Mattson Family, SJICD received a US Fish and Wildlife Service (DFW) grant in 2003 to complete an engineering study to evaluate ways to restore some degree of tidal exchange while improving the winter drainage and flooding situation.


After completing a hydraulic modeling study and field-testing, SJICD presented several options to local community members. The Mattsons and other neighbors favored a plan to allow partial tidal exchange into the lagoon, but only up to a level that would not impact lawns, drain fields, and other property.

SJICD next won a grant from the DFW to design and implement this plan.The plan’s first task included dredging the outlet channel and modifying the beach outfall pipe, which were completed in August 2005.The second task involved fabricating and installing a new type of tide gate that would open and close at pre-set tidal elevations.

This type of tide gate, which is only the third installation of its kind in Washington State, works like a screen door. The force of water draining from the lagoon on a falling tide opens the “door.” The resistance in the door’s hydraulic piston keeps it open as salt water flows back into the lagoon on the next rising tide. When the tide reaches a specified height, it trips a float valve, which releases the pressure in the piston and allows the door to close again.

PW’s Lopez Island road crew installed the new tide gate in June 2006, during which the upland portion of the beach was disturbed and compacted by heavy machinery. Tom Slocum, the Conservation District Engineer, suggested planting dune grass to restore the original beach vegetation and complete the project.

The SJICD staff along with PW Island Road Crew on Lopez spent April 19, 2007 planting 700 plants to cover the 2500 square foot site. 500 Dune Wild Rye (Leymus mollis) and 200 Beach Pea (Lathyrus maritimus) (from 4th Corner Nursery in Bellingham) were planted. Plant choice was based on species currently present along undisturbed areas of the beach and from suggestions by beach restoration specialist Jim Johannessen of Coastal Geologic Services Inc.

Funding for this project was provided by Ducks Unlimited as well as the San Juan Islands Conservation District and San Juan County Public Works. The tide gate is managed by the PW Lopez Road Crew, and can be viewed inside a grated vault along Port Stanley Road, Lopez Island.