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Engineered Rain Gardens

Engineered rain gardens are large, landscaped features planted with beautiful, hardy, low-maintenance, water-wise plants. They are designed with amended soils and drainage layers of gravel and sand, which absorb and naturally filter stormwater before it enters our storm systems and eventually our rivers. Properly constructed rain gardens are designed to allow overflow in a large rain event and hold standing water for no more than 48 hours.

Rain gardens are a low impact development practice and are a part of ourStormwater Management Strategy to help manage the level of sediment going into rivers from Calgary's stormwater drainage system.

Information about rain gardens, including specification requirements can be found in the following documents:

How do engineered rain gardens work?

When it rains, stormwater from the surrounding area is directed into the rain garden. Plants and layers of soil and gravel filter and absorb the stormwater. The silt and other natural solids (like leaves) are collected on top of the gardens. Other pollutants (chemicals and bacteria) are filtered and used by the soil and plant root systems.

Excess water not absorbed by the plants, seeps into the native soil below or collects in the drainage pipe located under the drainage layers. This drainage pipe connects to the stormwater system to carry excess filtered water back to the river.

Calgary Rain Garden Design Example 

What about mosquitos?

Rain gardens are not good breeding areas because the water will drain within 72 hours (but usually within 48 hours). Mosquitos take 10 to 14 days to develop depending on the air temperature (it takes 24-48 hours to hatch and the mosquito larva must live in water for 7 to 12 days). Additionally, the Culex mosquito (the kind that transmits West Nile Virus) prefers breeding in small, stagnant containers of water.