AUGUST 6, 2009 ISSUE
everGREEN Tips
Rain Gardens
Many communities in North Carolina have seen their forest replaced with impervious development. The rooftops, parking lots and roads don’t allow water to slowly infiltrate into the ground to replenish our groundwater. Instead, that stormwater washes into the gutters and quickly into our streams causing a “flashy” rise in the water levels of the rivers. The excess stormwater that ends up in the stream can lead to pressure on the banks causing erosion, which can be very harmful to water quality. Stormwater is considered “non-point source pollution,” which is the leading remaining cause of water quality problems in the nation according to North Carolina Division of Water Quality reports. Non-point source pollution comes from many diffuse sources including; excess fertilizers from agricultural and residential lands, oil, grease and toxic chemicals from urban runoff, sediment, salt, bacteria and nutrients from faulty septics and livestock and pet wastes. Non-point source pollution is the main reason why 40 percent of our nation’s surveyed rivers, lakes and estuaries are not clean enough to meet basic uses such as swimming or fishing.
The environmental community has been recently encouraging homeowners and developers to install simple rain gardens to filter runoff and recharge aquifers. While most rain gardens are small, collectively they can have enormous environmental benefit. Rain gardens are shallow depressions designed to collect rain from impervious surfaces and lets plants, bacteria and soils cleanse the water as it seeps slowly back into the ground. Rain gardens are beneficial because they reduce the amount of stormwater that enters a local stream, river or lake.
Rain gardens can be a beautiful plant garden that can blend right into the landscape. The plants, shrubs and trees that are planted in this area should be water tolerant, not water loving. This area is not intended to be a wetland. The rain garden should be designed so that water regularly inundates the soil for short periods of time after a storm event.
Rain gardens remove pollutants using physical, chemical and biological mechanisms. They use absorption, microbial action, plant uptake, sedimentation and filtration. Plus the rain garden helps to replenish groundwater by allowing infiltration of stormwater runoff. The exact ability of rain gardens to remove pollutants has not yet fully been quantified. However, rain gardens do appear to be effective in removing the most critical pollutants found in stormwater runoff including most metals, total phosphorus and total nitrogen.
The Internet has numerous sites that will assist individuals with the location, construction and maintenance of a rain garden. Additionally, North Carolina Cooperative Extension Service has illustrated materials explaining how to construct and maintain rain gardens. Locally, a number of rain gardens have been installed on private and public properties, all of which are contributing to improving the water quality of our rivers and tributaries. On a larger scale many communities have constructed a number of wetlands, which have similar function and impact on water quality as rain gardens, but on a much larger scale, treating multi-acre drainage areas.
When next considering a new landscaping project, we hope that you will consider constructing a rain garden that will not only beautify your yard, but also protect the environment!
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