Rain Gardens: Grass Roots Projects for Storm Water Management

Civic infrastructure – roads, bridges, sewer systems—is the purview of government. Individuals wouldn’t think of throwing up a new Tappan Zee Bridge, or even filling potholes in a local road. But individual homeowners and neighborhood groups, in the United States and elsewhere, are taking the lead in building storm water management systems. How can this be? They’re building rain gardens.

Rain garden in Seattle, WA. Image credit: Sightline Institute

A rain garden, more formally known as a bio-retention cell, is a planted area designed specifically to collect storm water runoff, or snow melt-off, and return the water to the local ground water, without causing soil erosion or overburdening storm sewers. Rain gardens on home sites – single family homes or apartment buildings – collect potential runoff before it has a chance to flow into storm sewers or cause soil erosion. The garden can be a few square feet or a large swath around a building or along a sidewalk as long as it serves these purposes. A typical rain garden absorbs 600 gallons of water during a one-inch rainfall. And a five-year study by the US Geological Survey proved that these small residential gardens can collect 100 per cent of roof runoff. Other hard surfaces, like paved roads, also prevent water from soaking into the soil. So it runs off into a storm drain, or it erodes a yard.

History of the Rain Garden Concept

The first residential rain gardens were part of Somerset, a 1990’s residential development in Prince George’s County, Maryland. The developer, Dick Brinker, proposed replacing the standard retention ponds, curbs, gutters, and sidewalks with open drainage swales and plantings that resembled the land’s original topography and plant cover. Larry Coffman, who was director of the Prince George’s County Dept. of Natural Resources, concurred; he earned the title of “father of the rain garden.” This approach, called Low Impact Design or LID, cost substantially less ($100K instead of $400K) than curbs, gutters and sidewalks, and resulted in a 75-85 per cent reduction in storm water flow during small storms.

Since this auspicious beginning, many local governments, county cooperative extension services, and conservation organizations have popularized rain garden development for homeowners. Many people have the skills to complete these projects; they can draw upon countless free design and construction guidelines available online (see References at the end of this post for a few examples). In some places, such as Prince George’s County, homeowners are eligible for rebates when they install these gardens, or financial assistance to purchase plants.

Garden Design

The intent of a rain garden is to soak up storm water, allowing water to pond up, seep through the prepared ground, and penetrate deeply enough to spread through lower soil layers. The rule of thumb for drainage is for the garden to return to normal -- no ponded water -- within 24 hours after a rain.

Constructing a garden includes:

• Calculating the size needed based on the estimated runoff from nearby hardscapes
• Selecting a site that can catch the runoff, such as downstream from a rain gutter
• Testing water percolation through the existing soil at the site
• Preparing the garden location, which can include mixing existing soil with compost, mulch, sand, or other amendments to increase permeability
• Adding pipes or other methods to guide runoff towards the garden

Rain Garden Construction. Image credit: H2O Designs

The best plant choices – other than ensuring that the plants selected don’t mind wet feet – are those that are native to the locality. Natives are best adapted to the climate and soil conditions, and they’re attractive to indigenous wildlife and to migrants who depend on a particular local plant – like monarch butterflies and milkweed – for survival. Nonnative species that have adapted to local conditions can also play a role, particularly if natives are difficult to find or expensive.

Other benefits

These gardens offer benefits in addition to preventing storm water runoff. As mentioned above, homeowners can receive tax rebates or other monetary incentives to create rain gardens. Gardens can reduce by up to 30 per cent the levels of pollutants such as pesticides, volatile organic compounds (VOCs), and trace metals that would otherwise flow into natural waterways. These gardens enhance a property’s natural beauty and, as noted, attract and support local wildlife.

Rain garden in Hilton Head, SC, after a 4 inch early spring rainfall (left) and in full summer bloom (right).

Image credits: The Liquid Letter

Although this post focuses on residential gardens, large-scale installations exist and are performing quite well. This recent article from Engineering 360 discusses the importance of a rain garden in one Queens neighborhood. The city estimates that the 321 gardens will collect 38 million gallons of storm water each year. This is one neighborhood in one large city. Imagine the difference a larger network of rain gardens would make in storm water runoff in New York City. Individuals can’t build a Tappan Zee bridge, but we can help out by constructing our own little bits of infrastructure by installing rain gardens, whether around the house or in a local park … making our corner of the world a little better.

References

http://www.raingardennetwork.com/blog/about-rain-garden-network/

http://www.ewashtenaw.org/government/drain_commissioner/dc_webWaterQuality/rain-gardens

https://youtu.be/JlScj9yN6Jw

http://www.princegeorgescountymd.gov/sites/stormwatermanagement/Services/CleanWaterActFees/BMP/RainGardens/Pages/default.aspx

https://www.epa.gov/soakuptherain/rain-gardens

http://www.sustainablecitynetwork.com/topic_channels/water/article_b65fe518-3de0-11e0-82aa-00127992bc8b.html?utm_source=SCN+InBox+e-Newsletter&utm_campaign=2c869b70df-Newsletter_2-23-11_Tech&utm_medium=email