Swale… Doesn’t it sound elegant to say, “The iris are growing next to the swale?” Well, it certainly sounds classier than saying, “Those flowers, over by the ditch,” but swales and ditches are very similar.
The joy of ditches
Traditionally, a ditch is a V-shaped or U-shaped channel that is cut next to roads that redirect melted snow water downhill, without flooding the road. When I was a kid in Upstate New York, hammering open rocks in the dried out ditch in front of our house was great fun. You never knew what they were going to look like on the inside until you cracked them open! You couldn’t play in the ditch in spring, though. In spring, the ditch held water that was moving too rapidly to be absorbed and too cold to be any fun.
Swales are swell
Unlike a ditch, swales are low places that collect water. They can occur naturally or be manmade. You see them all the time next to freeway on-ramps and off-ramps. These particular swales, or contour bands, act as infiltration basins. They are called contour bands because a trench is dug along the natural contour, and then that dug out soil is used to create a berm on the downhill side. Swales collect water that may contain pollutants and filter the toxins out naturally. Since the water in a swale is in a low place, it doesn’t run off. Instead, it is slowly absorbed. Often, ornamental plants that can tolerate pollutants and wet soil are planted around swales. Also, microorganisms in the soil begin breaking those pollutants down into less toxic materials.
Rainwater as resource
We all know that, in nature, rain falls down, is absorbed by the soil, and is then used by plants to grow. Simple. But we have now paved much of that soil. In the United States alone, by 2004, more than 43,000 square miles of land was covered with concrete. That’s about the size of Ohio, and I’m pretty sure that number is higher today. When rain falls on concrete, or other impermeable surfaces, the water runs off and away, carrying topsoil, fertilizers, pollutants, and small bits of trash and plastic with it. We call that run-off urban drool and all of it the ends up in our rivers, lakes, and oceans. The California Native Plant Society tells us that urban drool is the #1 source of ocean pollution. The average 2700 sq. ft. roof in the Bay Area can collect more than 25,000 gallons of water each year. Rather than allowing that water to go to waste, you can harness it for your garden with a swale.
Swales in your backyard
Swales help retain and filter water three ways: slow, spread, sink. First, the flow of water is slowed down because it has a low place to collect. Then, rather than running off, it has a chance to slowly spread and expand through the nearby soil. Finally, the water sinks, naturally, into the soil where it feeds aquifers and underground creeks. All this water attracts the root systems of many of your larger and medium sized trees and shrubs. These nearby plants tap into this resource, which means they need less irrigation water.
Swales as damage reduction
Swales are an effective way to redirect water away from your home, without letting all that water go to waste. Most homes are built with a slightly sloping grade that should take rain water away from your home. This design really helps prevent foundations from shifting, but where does that water go once it’s away from your house? If the slope isn’t steep enough, very often, you will still end up with a muddy yard. Instead, you can redirect water from your downspouts into swales that draw the water away from your house and out into the yard, where it will nurture your plants.
Swales can be beautiful
Swales don’t have to look like a ditch. Instead, they can be made beautiful with river rocks, and plants that can handle the periodic moisture. This would include sedge, mosses, birch, iris, white cedar, azalea, rhododendron, hydrangea, hosta, Peace lily, japonica, ferns, pussywillow, coreopsis, geranium, and scarlet monkey. Heck, if you had a way to filter out the first flush of rain, you might even be able to grow rice! First flush refers to the first 1/2 inch or so of rain that contains higher levels of dust, debris, and pollutants. Before you install any plants, though, make sure that they are not invasive in your area.
Swales can be an attractive part of your landscape. They make the soil healthier, which makes your plants healthier. Plus, there’s less mud in your yard with a swale. Swales can be one part of a rain garden.
Creating areas where rain water can be slowed down and prevented from running off is called watershed design.
You can grow a surprising amount of food in your own yard. Ask me how!