Rain Gardens and Urban Stormwater Management Education in Nebraska

By
Steven N. Rodie, Ph.D.,
Landscape Horticulture Specialist
UNL Department of Agronomy/Horticulture

Thomas G. Franti, Ph.D., PE,
Surface Water Management Engineer
UNL Department of Biological Systems Engineering

Even smaller rain gardens can have a pleasing effect, like this 80 square-foot residential rain garden in Omaha (photo courtesy of Steve Rodie).

This rain garden figures prominently in the landscape of a Kansas City, Mo. Church (photo courtesy Steve Rodie).

Rain gardens are currently in the stormwater management spotlight.

Landscape lovers, stormwater managers and native plant enthusiasts are in mutual support of this relatively new stormwater management practice that both controls urban pollution and adds an aesthetic feature to lawns and landscapes.

Rain gardens have a proven track record across the country as an effective stormwater management tool that can benefit urban water quality and reduce runoff.

Their popularity is growing in Nebraska, and many people want to know more about rain garden aesthetics and function.

A rain garden is designed as a small depression in the landscape with mounded soil (soil berm) around three sides that captures rainwater and allows it to infiltrate into the soil.

The garden is typically planted with flowering shrubs, forbs and grasses. The rainwater can be directed from any hard or vegetated surface where runoff tends to collect, such as a rooftop, driveway, patio, or turf area. The garden is sized based upon the amount of surface where runoff is collected (for example, the area of a roof) and the type of soil in the garden. Gardens are designed to hold the water from 90 percent of all rainfalls that occur in a given location.  In Western Nebraska, 90 percent of rain events produce a half-inch or less of precipitation; in Eastern Nebraska, this amount is approximately 0.85 inches or less.

For these amounts of rain, the rain garden holds the entire storm run-off and allows the water to drain into the soil in 24 to 48 hours. For the 10 percent of storms that exceed rain garden capacity, the water overflows to a predetermined location.

On average, rain gardens sized to capture roof runoff from one roof downspout on a typical residential lot with adequate soil infiltration range from 100 to 300 square feet.

General rules-of-thumb for successful rain garden design and implementation include:

• Ponded water should drain away in less than 48 hours (for plant health as well as elimination of mosquito potential)
• The average depth should be 4-8 inches, with a level bottom
• Build only if soil infiltration tests indicate a minimum infiltration rate of one-quarter inch per hour; if not then soil drainage improvement methods will be needed or an alternative site will be required
• Locate rain gardens at least 10 feet from house foundations, 25 feet from wellheads or septic systems, and down slope from homes or other buildings
• Plant only deep-rooted native and adapted plants that tolerate swings of wet and dry soils, provide seasonal interest and habitat value, and stay relatively short so as not to flop over and appear weedy
• Include an overflow point in the soil berm so that when the garden fills from a heavy rainfall, excess water is properly released without causing soil erosion
• Use organic mulch to minimize weed growth and moisture loss during dry periods; wood mulch with a shredded, not blocky texture, will tend to lock together and will not float when water fills the garden
• Establish plants with supplemental water to help young plantings during dry periods, and provide regular maintenance to renew mulch and inventory plant health

UNL Extension has recently formed an urban stormwater management group. The group, co-led by Kelly Feehan, Extension Educator and Steven Rodie, Landscape Horticulture Specialist, is leading efforts to expand Nebraska stormwater educational materials and programs on rain gardens and other best management practices.

Audiences include homeowners, green industry designers and managers, communities across Nebraska as required by federal and state regulations (under Phase II of the National Pollutant Discharge Elimination System (NPDES) permit program), and land managers and developers.

Additionally, curriculum is being developed for students, ranging from 4-H lessons for middle school programs, to studio projects for landscape architecture students at UNL.

To-date, the work group has held two rain garden design workshops and two extension in-service site tours; produced eight publications on rain gardens and other best management practices; developed three major sections on the UNL Water Website (Lawns, Landscapes and Gardens; Lawn and Landscape Irrigation; and Property Design and Management); produced a five-minute segment on residential best management practices for a Nebraska Educational Television documentary on stormwater issues in Omaha; constructed a working rain garden model of a residential site to illustrate rain garden concepts at public events; and scheduled numerous presentations across the state and region on rain gardens and urban stormwater best management practices.

More specific information on rain garden design, construction and plant selection, together with additional materials on topics such as home and yard water pollutants, soil management, and best management practices for large-scale land development, can be found online at water.unl.edu/landscapes.