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This engineered rain garden treats water flowing off the parking lot. The pipe on the left allows the water to flow from catch basins to here.

Large Parking Lot Rain Garden

Where is this located? The four rain gardens lie next to the loop trail between the parking lot and the baseball field.

What’s special about this place? Next to the parking lot drain, you’ll see a series of wide and shallow, interconnected depressions known as rain gardens. Runoff from the majority of the parking lot passes through these engineered rain gardens – one after another. In each one, plants slow down the flow which gives the particles in the stormwater time to seep into the soil. Through biological processes, nutrients and other contaminants are removed by the vegetation and roots.

About Rain Gardens

rain garden is a bowl-shaped garden that collects, absorbs, and filters the rainwater that runs off hard surfaces including parking lots, driveways, sidewalks, lawns, and roofs. They provide on-site cleaning of stormwater by using special soil mixtures and low-maintenance plants that soak up runoff. The soil mixes used in rain gardens are selected to allow water to soak in rapidly, treat runoff, and support plant growth. Hardy, often native, plants are carefully selected for each site, including wildflowers, grasses, rushes, ferns, shrubs, and even small trees. These plants can have the added benefit of attracting pollinators, providing habitat for beneficial insects and birds, adding beauty, and improving neighboring property values.

Rain gardens can be small and home-made, or they can be engineered with specific materials to be highly effective. Home-made rain gardens are usually applied in smaller, residential systems working to intercept runoff that would otherwise flow onto streets. Engineered rain gardens are a type of bioretention basin and are sized for specific water quality treatment and flow control capacity that includes designed soil mixes and, often, under-drains and control structures. All the rain gardens highlighted on these tours are engineered bioretention facilities.

Water Quality Benefit: Rain gardens can capture sediment and bacteria, capture oil, pesticides, and fertilizers, and use their mulch layer to bind-up dissolved metals. Plant roots also are host to diverse microbial and fungal populations that filter pollution using biological processes.

Water Quantity Benefit: 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. By absorbing runoff from hard surfaces, rain gardens reduce flooding on neighboring property, reduce erosion in streams, and may recharge local groundwater.

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Drains 2.1 acres.

Where does this stormwater runoff come from? Runoff comes from most of the parking lot and the basketball court.

Where does this stormwater runoff flow next? Most of the runoff infiltrates into the ground. Some may flow into Squalicum Creek.