Rain Gardens are small basins that collect rain from sump pumps, driveways, lawns and downspouts. The idea is to correctly landscape a subtle "well" shaped basin to catch flowing rainwater. These rain gardens typically utilize native grasses and flowers that thrive in a wet environment.
Advantages of a Rain Garden
Rain gardens are designed with the Low Impact Development (LID) concept. A rain garden can be used as an alternative fix (cheaper/faster) to help alleviate water problems closer to the source, unlike traditional draining methods. By installing a rain garden, the property owner will not only have a sufficient low cost/low impact aesthetically pleasing functional piece of landscaping but the amount of water pollutants will decrease because of the filtration properties of the garden. However, because of the relatively small volume of stormwater that a rain garden can detain, there should not be the unrealistic expectation that a rain garden will solve a major flooding problem.
Sizing & Sitting of a Rain Garden
Rain gardens are commonly located in two places: near the house to catch roof runoff and sump pump discharge or farther out on the lawn to collect water from the sump pump discharge, lawn and roof.
- Keep garden at least 10 feet from house so infiltrating water doesn’t seep back towards the foundation.
- Rain garden should not be installed over septic system.
- Putting the rain garden in a flatter part of the yard will allow for easier excavation.
- Locating in sunny area is best.
- Water should be channeled using a natural drainage way, constructed swale or a 4-inch PVC pipe placed in a backfilled trench that connects down spouts to the garden.
- Mulch should be used 3 to 4 inches deep throughout the garden (provides weed protection)
- A berm should be built on the edge of the garden facing the street or nearest catch basin in case of overflow
Size of a rain garden will depend on three important factors:
- How deep the garden will be. A typical rain garden is between 6 and 8 inches deep. These dimensions maintain a balance so as to prevent tripping hazards, visual appearance, and water storage. The depth also depends on the slope of the lawn.
- If slope is less than 4%, build the garden 3 to 5 inches deep
- If slope is between 5 and 7%, build one 6 to 7 inches deep.
- If the slope is between 8 and 12%, build one about 8 inches deep.
- The type of soils the garden will be placed in. Before installation begins, identify the type of soil that the garden will be placed over. The most typical soil in Palatine is a heavy clay which do not drain very well. Therefore a deeper garden with a course gravel layer on the bottom followed by a sandy topsoil mix with a loose topsoil layer on the top should work best. Otherwise the
- Clay soils suitable for rain gardens should be able to drain about 6 inches of water within 24 hours. Dig a hole about 6 inches deep where the rain garden will go and fill the hole with water. If it takes more than 24-hours to soak in, the soil or location is not suitable for a rain garden.
- Gravel, sand and peat moss can be used in the rain garden to improve infiltration.
- How much roof/lawn will drain to garden. The last important factor to consider in determining the size of a rain garden is the area that will drain into the rain garden. The bigger the area of the lawn/roof being drained, the bigger the area of the rain garden should be.
- To calculate the amount of water that needs to drain from roof or watershed area, measure the roof area that will be facing the rain garden
- The total rain garden area should be at least 60% the area of the contributing roof watershed to enable proper infiltration