If you live in a region with excessive rain and flooding, you can make rain gardens to alleviate the flooding.
The purpose of a rain garden
A rain garden is a landscaped area planted with native plants and flowers that soaks up rainwater. The garden fills with a few inches of rain water that come off of the roof of a house or building during a storm. After the storm, the water slowly soaks into the ground instead of running off the land into a storm sewer or waterway. Compared with a grassed lawn area, a rain garden may allow 30% more water to be absorbed. Native plants are suggested for use in the rain garden because of their deep roots, water uptake and their ability to tolerate conditions ranging from wet to dry and hot to freezing.
Where to place rain gardens
A rain garden can work virtually anywhere. The size, location and effectiveness depend on things like the amount of rain water runoff that is directed into the garden, the rate at which water soaks into the soil and the plants that are selected. Areas along driveways or sidewalks may also be ideal spots for a rain garden.
Locate your rain garden where it will collect the maximum amount of rain water runoff -- but at least 10 feet away from the foundation of your house. Look first for a natural depression in your yard where water from a downspout may already naturally flow. Alternately you may have to plan to route water from the downspout to the garden through a grassy depression called a swale or through a burried plastic pipe. Placing your rain garden "down hill" from a driveway will maximize its ability to collect rain water that runs off the driveway. Your garden will grow best in an area with partial or full sun, but Fort Wayne's How To Manual also includes some ideas for shady gardens.
The size of the rain garden
The size of your garden depends on how much rain water runoff will be going into it. You'll need to measure or approximate the area that will drain into the garden. You'll perform an infiltration test to find out how fast the water will soak into the ground. In general, for an area that has primarily clay soil, you can make the garden about 3" deep. Divide the area that will drain into the garden by 3 (the depth) to determine how large the garden should be.
Selecting plants for the rain garden
When selecting plants, remember that your rain garden will be an attractive part of your existing landscaping that also helps to protect water quality.
You want the plants to help soak rainwater into the ground. So look for plants that have deep root masses. Native grasses and wildflowers typically have roots that go several feet deep. Native plants are low maintenance. Many can tolerate drought or short periods of standing water. Most of the plants are perennials and will survive the winter. Native plants are also less prone to insect damage and disease.