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Green Stormwater Infrastructure Project: Township of Perth South Office – Bioswale and Rain Garden

Green stormwater infrastructure (GSI) mimics the natural movement of water in order to manage stormwater (rainwater) close to its source. It seeks to lessen the impacts of increased stormwater runoff and pollution by using designs and landscape features to infiltrate, filter, retain, and slow down runoff.

The 95 m² rain garden and 35 m bioswale along edge of the Township of Perth South parking lot are designed to reduce the flooding of the parking lot, septic bed, and sidewalk leading to the staff entrance of the building caused by stormwater runoff.

The kidney-shaped rain garden is a shallow depression containing approximately 1 m of amended soil (mix of sand, silt, and gravel) that absorbs and naturally filters the runoff. It receives water from 1) the south side of the workshop building roof – the downspout connected to a pipe under the sidewalk and overland flow from the drain pop up, 2) the office building roof – overland flow from downspout, and 3) the parking lot and the bioswale.

The  bioswale is a u-shaped channel containing approximately 1 m of amended soil (mix of sand, silt, trace of gravel, and trace of clay) that absorbs and naturally filters the runoff from the parking lot. It also receives water from the downspout on the north side of the workshop roof through underground pipes and overland flow.

The rain garden and bioswale are designed to infiltrate (absorb) 25 mm (1 inch) of stormwater per hour. The amended soil used here can infiltrate (absorb) 40 mm (1.5 inches) of stormwater per hour!

Native Plants

Students from the grade 4/5 class at Downie Central Public School planted 900 native wildflowers in the rain garden and bioswale. Native plants are very important as they attract pollinator species; grow naturally in our area and are suited to our local conditions; have deeper root systems that absorb more water than grass; and are easier to maintain once established.

Species planted include BeeBalm, Tickseed, Black-Eyed Susan, Blanket Flower (yellow, red, Goblin), Stonecrop, Coneflower (purple, white) and Balloon Flower (blue, pink).