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Rain Gardens – Managing your Water Resources Naturally

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Rain Gardens – Managing your Water Resources Naturally

Making a Rain Garden

A Rain GardenA developed urban environment – even a rural or suburban residential environment – is comprised of many impervious surfaces that rain hits and quickly runs off, such as driveways, roofs and sidewalks. Instead of percolating gradually into soil and recharging groundwater, the rainfall becomes stormwater runoff, a concentrated torrent that picks up and transports everything in its path to surface water bodies like lakes and streams. As the Wisconsin Department of Natural Resources puts it, “When people build houses they design them to get rid of water as quickly as possible. Builders and developers use the principle of collecting water, concentrating the flow, and conveying it quickly off the property.”

If there is not enough vegetation to anchor the soil in the path of that runoff flow, the water will cause erosion, picking up soil, fertilizers, heavy metals, and other contaminants as it travels. Along with many other problems, the nutrients concentrated in this runoff cause eutrophication in the lakes and streams it dumps into, supporting massive algae blooms that deplete dissolved oxygen and choke out other forms of vegetation and the diverse life that feeds on it. Excess sediment washing into the stream or lake blankets the bottom and chokes off crucial bottom habitats and increases turbidity.

Rain gardens can work in many environments to naturally capture and filter stormwater runoff and reduce the resulting nonpoint source pollution. They are a natural or dug depression to provide needed drainage to an area where runoff is a problem. Rain gardens are usually comprised of native perennial flowering plants and grasses that can tolerate extremes of flooding and droughts. Riparian edge species that are adapted to extremes of temperature and moisture are good plants to use. Plants in the most low-lying areas of the basin should be particularly adapted to floodplain conditions. These species will of course be extremely variable by area. In the Midwest, for example, many native prairie grasses can be used. Native plants tend to have root systems extending at least twice as deep as they are tall, whereas typical turfgrass roots are only the depth of the vegetation’s height.

Deep, fibrous root systems absorb excess nutrients that wash into the basin, and help aerate soil and increase porosity so that pollutants can be filtered out. Organic matter hosts a rich array of microbial life in the soil, which breaks down pollutants and other chemicals, while heavy metals bind to clay particles. A diverse rain garden provides a habitat for wildlife and beneficial insects. Winter seedheads of these crops are food for songbirds.

The area should be very well-drained, to the point where it can drain within four hours after a one inch rain event. Soil can be amended with porous material, such as peat, if needed, and mixing in the material to a depth of at least 2-3 feet is ideal. If soil is too sandy, compost can be dug in as well. It can be more wild, or more managed and formal, depending on the desired aesthetic appeal. The garden can be treated much like any other garden, but only has to be watered frequently during the first year, as the plants become established. The area can also be weeded until the garden plants are big enough to outcompete them (but keep in mind, weeds are native plants, and can be kept selectively if they are able to endure the conditions without taking over.) Most plants have more success when they are planted young, since this gives them time to adapt to the local conditions. Avoid walking in the garden to minimize compaction. The lighter and fluffier the soil, the better it will drain. Sediment accumulation is a sign of success, that the garden is arresting erosion, but can be removed with a flat shovel if it gets excessive.

A well-established rain garden ultimately needs little management, since it is ideally made up of the hardiest, most adaptable native species available in the area. It should become a self-contained ecosystem, establishing its own balance in response to the conditions, mimicking the hydrologic cycle of a prairie or forest, which is based on the critical ecological function of groundwater management and filtration.

Genevieve Slocum is a Contributor to The Free George.

The Free George is the online magazine and visitors’ guide of Upstate NY, covering things from Albany to Lake Placid, including Saratoga, the Lake George region and the Adirondacks. Check out our City Blogs section for our extended coverage areas as well.

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