How to improve stormwater management in your yard : Designing a rain garden

Whether it’s melting snow in the spring or rainfall all year round, stormwater runoff from your roof, driveway and other hard surfaces in your yard can tax municipal sewer systems, pollute lakes and streams, and harm aquatic habitats.

One relatively easy and inexpensive way to reduce runoff is with a rain garden — a planted or stone-covered bed specifically designed to receive stormwater and allow it to be absorbed into the soil.

To help you let your stormwater runoff soak in, Canada Mortgage and Housing Corporation (CMHC) has a series of tips on how to design and build an attractive rain garden for your yard, including:

– First, find a suitable location. Observe where stormwater normally accumulates in your yard, and place your rain garden at a low point along that natural flow.

– Make sure your rain garden is as level as possible, to prevent water from simply flowing over the lower edge. If possible, avoid slopes greater than 12% to minimize the amount of soil you need to build up on the lower edge.

– To avoid moisture problems, place your rain garden at least four metres away from vulnerable areas, such as your house foundation, septic beds or neighbouring homes.

– Look for soil that is sandy, gravelly, loam or a mix of soils that drain easily so that you don’t have standing water for more than two days. Avoid clay soil, because it can substantially slow the drainage process.

– Direct your roof downspout extension into your rain garden to absorb runoff from your roof..

– Loosen compacted soils in the rain garden to a depth of between 0.6-1.2 metres, to ensure that the soil drains easily. You can amend your soil to this depth by working in sand, fine gravel and organic matter to improve drainage.

– Make certain the surface of the depression is at least one metre above the seasonally high shallow groundwater table.

– Consider locating your rain garden in a sunny or partially shady area, to allow you the greatest selection of plant varieties and species.

– Make sure the rain garden is at least 1.5 times longer than it is wide, to capture as much stormwater as possible.

– Finally, select perennials, shrubs and grasses that can tolerate both wet and dry conditions. Or, for an attractive alternative, cover the rain garden with loose, hard materials such as pebbles or river stone or combine pebbles and river stone with plants.

For more information or a free copy of the ‘About Your House’ fact sheet on Rain Gardens: Improve Stormwater Management in Your Yard or other fact sheets on virtually every facet of owning, maintaining or renovating your home, ask CMHC at 1 800 668-2642 or visit www.cmhc.ca . Canada Mortgage and Housing Corporation (CMHC) is Canada’s national housing agency and a source of objective, reliable housing expertise.

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