There are various devices designed to direct water over and through the landscape. French drains vs. There are two main types of drainage in the landscape: surface drainage and subsurface drainage.
As a general rule we use surface drainage to deal with rainwater, especially heavy rain. A good example of a surface drainage mechanism is a ditch on the side of a highway. Swales, flumes and trench drains are also used in various situations to convey water over grass, concrete or other media. In contrast, subsurface drainage deals with groundwater. This can be water that percolates down into the soil from above or bubbles up on your property.
Here in the South you might have seen groundwater entering a basement that contains a nasty orange colored substance called bacterial iron. We normally use French drains to deal with that kind of saturation. It was actually named for its inventor, Henry Flagg French. French was an American who practically invented the fine art of farmland drainage, mainly to remove waste-contaminated water from feedlots and help prevent disease. The French drain is a true subsurface structure meant to address water that saturates the soil.
Water is insidious, and will always seek the path of least resistance. Often there will be a harder layer of soil or even rock under the top layer of soil. The World Permaculture Organization advises property owners to consider building swales when accumulated rainwater is causing erosion.
Swales are also helpful for directing water to trees in arid and semi-arid areas. Swales can be built in most areas, if proper planning occurs. Though property owners can build small swales, longer and wider ones should be dug out by landscaping contractors. If the property is located near a septic tank, a bluff or a steep slope, This Old House recommends consulting with a civil engineer.
The swale should be built to carry water to a spot where it will be safely released. This could be a buried dry well or a garden bed that has adequate drainage. The swale must slope downhill, and has to gradually get deeper, ideally sloping 1 inch for every 10 feet in length. It is best to map out the swale first on paper, and then to mark it on the ground with its runoff point at the end.
Dig out the trench with a sturdy shovel. When digging the swale, the sides should be three to four times wider than tall. The top 8 inches of soil should be well-draining, so be sure to check it after every rainfall. Addendum 3. Full Report Drainage System Selection Tool 0. Join our eNewsletter Privacy Policy : Subscribe. Treat it like a no-dig garden — start with a layer of cardboard and newspaper as a sheet mulch to inhibit weeds, then add layers of compostable materials, before the top soil from the swale is added.
Swales are commonly used in food forests where fruit trees and other edibles are planted into the berms. Small swales in an urban garden are often filled with pebbles, rocks, bits of old brick, and topped with wood mulch — materials that still will allow water to flow in, help keep the shape of the swale, and stop people falling in!
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