Larrabee Ave. and 10th St. Gravel Filter - Stormwater Discovery Tours

Where is this located? It’s in a grassy area at the southeast (uphill) corner of 10th Street and Larrabee Avenue. Look for a bed of rocks and gravel in a grassy area.

What’s special about this place? This is the only filter of its kind in Bellingham using gravel as the cleaning medium. This unassuming section of rocks and gravel is actually a stormwater filter and captures polluted runoff from the buildings, streets, and parking lots along Larrabee Avenue. Gravel is particularly effective at holding back sediment, small particles, and pollution so that cleaner water comes out the other end. The gravel slows the flow of runoff giving sediment, small particles, and pollutants time to settle out in the gravel. The runoff is not yet clean enough, so to complete the job, the runoff is taken downhill via pipes to the stormwater facility at the 8th Street Bioscape for final cleaning. It then flows into Padden Creek.

There are several types of stormwater filters, including cartridge filters, media filter drains, sand filters, and gravel filters.

Water Quality Benefit: As water soaks through filter materials, pollutants are physically trapped, chemically neutralized, or biologically recycled back into the environment. Filters prevent particles of dirt and other pollutants, including hydrocarbons, fertilizers, and metals like zinc and copper (which are toxic to fish), from being released into creeks and lakes.

Cartridge filters are cylinder-shaped containers filled with special material that traps particles and absorbs pollutants. Cartridges are used in vaults or tanks. Just like an air filter in a car, cartridge filter materials need to be replaced to remove pollutants and maintain their ability to treat runoff.

Sand and gravel filters use layers of sand, gravel, and/or rock to trap and strain particles out of the water. By slowing the water down, most of the sediment, small particles, and some of the pollution can settle out into the crevices of the sand and gravel. Sand filters are better at removing pollution than gravel filters because they have more surface area to collect pollutants. The smaller the gravel size, the smaller the particles that are removed. Pollutants stick to the sand particles where chemical and biological processes break them down.

Media filter drains (MFDs) use special materials, or media, that target tough-to-capture pollutants, such as dissolved metals and nutrients. MFD media can be used inside a trench or vault, or along a shoreline. The media is made of tiny washed rocks, slightly larger than grains of sand, with perlite, dolomite, and gypsum added to it. The perlite absorbs water and expands, physically trapping particles of pollution. Next, dolomite and gypsum chemically react with water to trap nutrients including phosphorus, nitrogen, and potassium. Then, with the help of naturally occurring microbes, nutrients are recycled back into the environment.

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drainage area

Drains 2.4 acres.

Where does this stormwater runoff come from? Stormwater at this site comes from Larrabee Avenue below 12th Street and the nearby parking lots.

Where does this stormwater runoff flow next? Runoff from this facility flows through pipes under 10th Street and Harris Avenue where most of the water is sent to the 8th Street Bioretention Basin. During high flows some water goes directly to Padden Creek.

From here, it’s easy to access the Padden Creek Trail system from 10th Street and Donovan Avenue. If you follow the trail upstream, you’ll see extensive habitat work which restored Padden Creek’s stream channel and banks, so salmon and other creatures can thrive. Follow the Lower Padden Creek trail all the way to Bellingham Bay.

See the Fairhaven Discovery Tour map for routes and additional information.

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