8th St. and Harris Ave. Bioretention Basin

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8th St. and Harris Ave. Bioretention Basin

 site type is bioretention basin
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8th St. and Harris Ave. Bioretention Basin

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Where is this located? It’s at the corner of 8th Street where the hill on Harris Avenue levels out near the Padden Estuary.

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What’s special about this place? This is one of the most sophisticated stormwater facilities in Bellingham called a bioretention facility. Part of 8th Street was used to make room for this facility which is responsible for final treatment for most of Fairhaven’s stormwater. For its size, it cleans an enormous amount of water. This system has three chambers or basins filled with layers and layers of special material and topped with hardy native plants and perennials. The runoff carried under the roads in Fairhaven to the bioscape eventually ends up here. It enters the bottom of the chambers through pipes. Stormwater normally flows downhill, but here, the pressure of the water pushes it upwards through pipes and out through the green-domed bubblers you see on top. On the surface, you’ll see leaves and other things that were carried away in the stormwater runoff. The stormwater spreads out and then flows back down through a special formula of soil and other materials. The roots of the plants on top loosen the mulch and soil so the water can seep in. This process removes the remaining pollutants and any sediment from the stormwater. Below the surface, pipes then collect the cleaned water and channel it directly into Padden Creek. During a storm, some water may flow so quickly as to not have a chance to soak in. When that happens, the overflow goes down the drain through pipes and empties into Padden Creek. Even under these conditions, the water has by this time had some treatment before entering the bay. 

The raised maintenance access path along 8th Street next to the facility is made of pervious concrete. When it’s raining, you can watch the water soak right into the concrete and into the materials below where it’s filtered of any pollutants.

About Bioretention Basins

Bioretention basins are shallow depressions that use a special soil mixture and specific plants to collect, absorb, and filter stormwater pollutants flowing off hard surfaces. The soil mixture uses soil, compost, sand, and specific minerals to allow water to soak in rapidly, treat runoff, and support plant growth. Hardy, low-maintenance plants adapted to the local climate and soil moisture conditions are chosen including trees, shrubs, and grasses. These plants can have the added benefit of attracting pollinators, providing habitat for beneficial insects and birds, adding beauty, and improving neighboring property values.

Engineered rain gardens are one type of bioretention basin. Some other bioretention basins include proprietary devices such as the Filterra tree box media filter on Ohio and Ellis Street, and the Filterra BioScape on 8th Street.

Water Quality Benefit: Bioretention basins can capture sediment and bacteria, capture oil, pesticides, fertilizers, and dissolved metals. Plant roots also are host to diverse microbial and fungal populations that filter pollution using biological processes. Bioretention basins that have under-drains usually only filter out large sediment and can allow dissolved pollution to pass through.

Water Quantity Benefit: Bioretention basins reduce flooding by either holding rainwater and releasing it slowly, or by soaking it into the ground. Special soil mixtures are chosen to allow water to soak into the ground. Roots break up the soil so water can soak into the ground more easily. If they are built in an area where the existing soils drains well, then water will soak in and recharge the groundwater below. If the existing soil does not drain well, the bioretention basin will be built with an underdrain that lets water out slowly. In a large storm, if there is too much rainwater to fit in that bioretention basin, it will drain out an overflow pipe or bypass the basin.


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Drains 88 acres or 55 entire city blocks.

Where does this stormwater runoff come from? Stormwater at this site comes from a large area of Fairhaven and South Hill.

Where does this stormwater runoff flow next? Runoff from this facility flows into Padden Creek near Harris Avenue.

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