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French Drains & Drainage Systems in Vashon Island, WA

Yards on the island often shed water toward the bluff edge, where concentrated flow can cut into the slope. A French drain can catch that flow, but only when its fall is right and its outlet is secure, and on Vashon the outlet question also involves the sole source aquifer.

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French drain cross-sectionA trench wrapped in filter fabric and filled with clean drain rock around a perforated pipe, collecting water from the surrounding soil. 12345
French drain section: fabric, clean rock, perforated pipe
  1. Filter fabric keeps silt out of the rock
  2. Clean drain rock gives water an easy path
  3. Perforated pipe carries the water away
  4. Soil cover over the trench
  5. Groundwater and runoff move toward the drain

Drainage & French drains in Vashon Island: what to know

Vashon-Maury Island was designated a Sole Source Aquifer by the EPA in June 1994. Because of that designation, we test the soil before choosing any infiltration outlet, and we do not put water into the ground in a way the county has not reviewed. Drains that stay on the parcel and empty into a planted or set-back area are the simplest route where the soil allows.

Outlets are where bluff drainage goes wrong. A discharge aimed over the bluff face invites slope failure, and a discharge onto a shoreline neighbor’s lot invites a dispute. Runs end in a set-back soakage bed or a grass-lined channel on the parcel, and any run that approaches a road or public ground goes to King County first.

Permits and rules in Vashon Island

Before we quote, we check each alignment against the lot edges, the road frontage, and any septic record found for the parcel. The disturbed area is totaled against the county’s 7,000 square foot line for land disturbing activity, and we confirm whether a trench counts toward it. Any outlet touching public or shoreline ground is referred to King County first, and the answer is attached to the drawing.

Rules change and vary by parcel, so we confirm the current requirements with the city before we start.

How we approach it

  • Survey the grade and fix the fall before the trench opens
  • Test the soil before any infiltration outlet is chosen
  • Check the septic record before digging near a drain field
  • Refer shoreline and road outlets to King County first

For the full process, see our Drainage Systems & French Drains page.

Questions from Vashon Island homeowners

Does a French drain on a Vashon Island lot need county review?

A drain kept inside the parcel line is handled as private work. A line reaching a road shoulder or shoreline ground goes to King County for written review before any trench is dug, and its disturbance is counted against the county’s land disturbing threshold.

Can a Vashon Island drain send water into the ground?

Only after a soil test and a check with King County, since the island was designated a sole source aquifer in June 1994. We do not place water in the ground in a way the county has not reviewed, and the decision is written on the plan.

Can a Vashon Island drain discharge over the bluff?

No. A discharge over the bluff face is ruled out, and the endpoint is recorded on the scope before the trench closes.

Other work in Vashon Island

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Call 206-483-5334
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Call 206-483-5334Get a quote