A bioswale is a ditch with vegetation and a porous bottom. The top layer consists of enhanced soil with plants. Below that layer is a layer of gravel, scoria or baked clay pellets packed in geotextile. These materials have large empty spaces, allowing the rainwater to drain off. The layer is packed in geotextile to prevent the layer from becoming clogged by sludge or roots. An infiltration pipe/drainpipe is situated below the second layer. To prevent the bioswale from overflowing its banks during heavy rainfall, overflows are added that are connected directly to the infiltration pipe/drainpipe. Rainfall infiltrates into the ground via the ditch and the packed layer. If the water rises above the level of the overflow, the water runs through it to the drainpipe. The bioswale’s dimensions should be sufficient to ensure that this occurs no more than once every two years. If the drain and the overflow both fill up, the bioswale acts as an above-ground drainage system and leads the water directly to surface water.
Also see this article, which seems to be a different design:
Also see this article, which seems to be a different design:
Bioswales are vegetated, shallow, landscaped depressions designed to capture, treat, and infiltrate stormwater runoff as it moves downstream. They are typically sized to treat the water quality event, also known as the “first flush,” which is the first and often most polluted volume of water resulting from a storm event. Bioswales are the most effective type of green infrastructure facility in slowing runoff velocity and cleansing water while recharging the underlying groundwater table. They have flexible siting requirements, allowing them to be integrated with medians, cul-de-sacs, bulb outs, and other public space or traffic calming strategies.
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Also see this article, which seems to be a different design: