Silt Fence & Inlet Protection in Seattle, WA

Silt fence and inlet protection in Seattle should be the first things installed on a building or grading site and the last things to come out. When bare soil gets rained on, runoff carries fine sediment toward sidewalks, gutters and catch basins. Silt fence along the low edge slows that water and lets the soil settle out, and inlet protection keeps what gets past it out of the storm drain. As silt fence contractors, we install both, along with the other basic sediment control measures a residential or small commercial site needs.

Why it matters in this city

Water covers about 41 percent of Seattle's area, between Puget Sound, Lake Washington, Lake Union and the Ship Canal, and storm drains on many streets lead toward one of them. Most of the year's rain arrives between October and March, so a site that is bare in the fall is a site that will produce muddy runoff for months. The city's Stormwater Code and Manual exist to protect those receiving waters, and Volume 2 of the manual covers construction stormwater control. Projects under 5,000 square feet of land disturbance can use the city's standard construction stormwater control and soil management plan; larger ones need a custom plan sheet that often shows exactly where fence and inlet protection go.

Doing silt fence installation right

Silt fence only works when its bottom edge is buried so water cannot run underneath it, the posts are on the downhill side, and the line follows the contour rather than running straight down a slope. Ends are turned uphill so runoff does not simply flow around the last post. Where heavier loads are expected, we use stabilized, wire-backed fence. A fence that is just stapled to stakes on top of the ground will not catch much.

Inlet protection

Catch basins downhill of the work get protected with filter fabric, sandbag rings, gravel and mesh, or insert devices. Which one we use comes down to where the basin sits: a back yard, a curb gutter or a lane cars drive over. Inserts in a street have to drain fast enough not to flood the road in a downpour, so we choose the device for the location.

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Upkeep and removal

Sediment control is not install-and-forget. After heavy rain, fence can bow, undercut or fill with silt, and inlet filters clog. We can check and repair controls on a schedule during your project, clean out built-up sediment, and remove everything once the site is seeded and the grass has taken hold. Pulling fence too early, before cover is established, is one of the most common ways a finished site still ends up shedding mud.

Fitting controls to small city lots

Most infill lots in Seattle have very little room between the excavation and the sidewalk. Silt fence still has to sit on the downhill side of the work with enough space for sediment to collect, so we lay it out with the builder before digging starts, leave gaps only where they are covered by other controls, and plan where equipment will cross. Where fence will not fit, compost socks or wattles on the hard surface can do the same job.

Stockpiles and exposed soil

A pile of excavated soil next to a foundation is one of the biggest sediment sources on a small site. We cover stockpiles with plastic or mulch, ring them with wattles, and keep them away from inlets and the street. Areas that will sit untouched for a while get hydromulch so they are not bare through the next storm.

Larger sites and state coverage

The City of Seattle notes that the Washington Department of Ecology's Construction Stormwater General Permit is required for projects disturbing one or more acres of land. On those sites, sediment controls are usually part of a detailed plan with regular inspections. We install and maintain fence, inlet protection and cover to the plan, and keep our work documented so your site inspector has what they need.

When fence is not the right tool

Silt fence is meant for sheet flow from small areas. It is not designed to hold back water in a ditch or channel, and placing it across concentrated flow usually ends with it blown out. In those spots we use check dams, rock or wattles in the channel, or route water around the disturbed area. Once the surrounding soil is covered with hydromulch or blankets, much less sediment reaches the perimeter in the first place, and that is the real goal.

Sediment that does get past the controls on a rainy day should be swept from the sidewalk and street, not hosed toward the nearest drain.

Typical sites

• Home additions and new single-family builds
• Townhome and backyard cottage projects on infill lots
• Side-sewer and utility trenching that crosses a slope
• Grading and landscape renovation jobs
• Commercial pads and parking lot expansions