Raingardens are an effective way for homeowners to treat and infiltrate stormwater or surface water runoff during rain events. Designing a rain garden can involve some basic math and a little bit of creativity.
Main features of a rain garden:
- Shallow (4” to 12” max. deep) depressions
- Surface should be dry in 48 hours or less after a rain event
- Planted with deep-rooting plants (natives work well)
- Design as a landscape feature (“natural," formal or in-between)
- Integrated into landscaping
- Selected plants attract wildlife for multiple benefits
Prior to designing a raingarden, it is recommended that homeowners call in a utility locate, determine the general location and surface water flow, measure the drainage area, and determine the soils in the location of the raingarden. These factors will help you determine the size, shape, and depth of the rain garden.
Raingardens should be designed to drain water from the basin into the soil within 24 to 48 hours. The following depths are recommended for each soil type to ensure water will drain into the soil quickly.
- Sand: 9 – 12” depth
- Loam: 6 – 9” depth
- Clay: 2 – 4” depth
Once you determine the area from which the raingarden will collect water, the size of the raingarden can be calculated. The basic method is to take the square footage of the area you will be receiving water from and multiply that by a factor, which is determined by your soil type. Generally, the raingarden should be sized about 5 – 15% of the area you will be receiving water from. See the chart and example below.
In summary, once the rain garden location is chosen, determine the soil type and measure the surface area to be collected, and next multiply the square footage area by the recommended percentage to get your raingarden size. Then it’s time to start digging and planting!