Terracing and retaining walls are an effective way to control erosion
One of the most effective actions you can take to mitigate the problem of an eroding slope is to break up the rate of water decent by constructing terraces or retaining walls. It’s also what allows someone to have a garden on an otherwise challenging if not impossible location.
Use a terrace or walls to slow the flow
I get a lot of questions from gardeners of every level. One of the most common is how to plant a garden on a slope. I’m always happy to answer this frequent inquiry because it gives me the opportunity to talk about the more important issue first. Knowing how to plant on a slope is important but of even greater significance is why to plant on a slope.
Soil erosion and surface runoff occurs as water moves across the ground. The more exposed the soil and the faster the rate of flow, the greater the damage and the bigger the problem. The fact that I’m being asked this question tells me it’s not too late for those asking…I think. But it is imperative to make sure a slope is covered or planted so that erosion is minimized.
One of the simplest and significant actions you can take to mitigate the problem of an eroding slope is to break up the rate of water decent by constructing terraces. It’s also what allows someone to have a garden on an otherwise challenging if not impossible location. Terraces give you the opportunity to create a series of mini-gardens. Erosion is prevented by shortening a potentially long slope into a series of more level steps. This allows heavy rains to soak in rather than run off, taking soil with it.
Think of terraces like steps in an embankment. Soil is cut out of the hill to create the level tread or landing area. As with garden steps, the level area is not exactly level. Sloped terraces should be graded by about 2% perpendicular to the incline in order to gently direct drainage towards one side or the other.
Proper spacing between slopes depends on the slope itself. But in all cases, the shorter the slope length, the less chance there is for runoff. Terracing is most effective when the slope is divided into discrete segments.
For extra water management, you can capture and redirect excessive runoff by installing perforated drainage pipe just below the surface. Run the pipe across the direction of the slope. Position the drainage pipe in a gravel bed, with the perforated side down. Again, position the drain pipe at a 2% slope in the gravel bed.
When constructing terraces, it is important to retain the exposed side. A number of building materials can be used. Some of the most common include: landscape timbers, railroad ties, interlocking landscaping blocks, stones, bricks and treated and weather resistant wood. Whatever you use, be sure the material is firmly anchored against the soil. If you are stacking material, angle it back slightly towards the terraced level with each course. The force of water is powerful. It is always flowing downhill and the pressure can easily push out against the wall; especially in freezing and thawing conditions.
The height of a terraced wall depends on the steepness of the slope. However, because of the force of a wall under pressure, it is advisable that to seek the help of a professional for heights greater than 24 inches (61cm). Also check local building codes for constructing walls and terraces.
Retaining walls are another way to slow runoff and erosion but their primary function is to support and retain an embankment. Unlike a terrace that is designed to have a level surface area, hence the name, the area behind a retaining wall can be level or sloped.
Materials used for constructing retaining walls are generally more decorative. In addition to the materials listed above, native stone or stack stone is often used. However, whatever the weight, it must be strong enough to hold back the pressure of a great amount of soil weight, yet porous enough to allow for adequate drainage. Pipes for drainage are often installed every 24 inches (61cm.) and six inches (15cm.) from the ground.
Retaining walls can be stacked without the use of mortar or with a bonding agent such as cement, concrete or mortar. Dry walls should be sloped back against the soil to give it greater strength. The general rule is to slope the wall back 4-6 inches per foot of rise. Another rule is the width of its base should be about one third of its height.
So, now that you know why it’s so important to retain that sloped area of your yard for runoff and erosion control, I suppose I can go ahead and tell you how to plant that garden on the slope. It’s easy. Simply make sure the soil behind the terraced support or retaining wall is well amended and plant away. The hardest part was getting the soil level!
References:
Natural Resource Conservation Service;
Backyard Conservation Tip Sheet.
Alabama Cooperative Extension Systems;
Soil Management to Protect Water Quality;
Structural Measures for Soil Management
About Joe Lamp'l
Joe Lamp'l is the Host and Executive Producer of the award winning PBS television series Growing A Greener World. Off camera, Joe dedicates his time to promoting sustainability through his popular books, blog, podcast series, and nationally syndicated newspaper columns. Follow Joe on Twitter
Thanks for talking about different ways you can control erosion in your yard. I had no idea that using a retaining wall and using erosion control could actually save you so much water. My sister has been wanting to plant a garden in her backyard but she needs to get some erosion control back there first. I will be sure to share this with her.
My wife and I have a bit of a slope in our yard, and I think that retaining walls would be good option for us. I’m glad that you talked about retaining walls and terraces in your article, and how they can help prevent erosion by shortening the slope. I think that being able to talk to a contractor who builds retaining walls would be good for us, and maybe a landscaper to see how we could design around our need for them! Thanks for the help!
PS Our orchard trees are all fruit trees. 2 single fruit trees & 6 grafted multiple-fruit trees.
Not only with our long, rectangular acre (with jutting out at very back corners of the property …. have we had a lot of soil erosion over the 19 years we have lived here (and will have to backfill with soil eventually …. the issue with our fruit tree orchard, and other parts of our back property areas … is water flowing like a river, moving anything in its way ….. from our country road well above our property, down the entire property to the creek made in the very back before we even moved in …. to carry this deluge of water then OFF our property.
Our organic garden is on long, higher than normal, raised beds in the shape of a LONG ‘W’ shape in our fenced off area behind our above-the ground pool deck and our polyurethane clear greenhouse. We also have two heavy duty plastic storage buildings to store our gardens (large flowerbeds as well as organic garden), now orchard and our pool items in the winter. So our garden is well off the ground and needs no ‘flood control’.
Our orchard fruit trees, however, will not be on raised ground … and definitely be exposed to both soil erosion and flooded, standing water that will enhance ‘root rot’ …. so they have to be terraced within gradually sloping wooden box terraces of some style.
Cannot believe I am having such a hard time finding the right videos or pictures I need to show my husband who has to build them! Any suggestions, or other websites, or YouTube videos I might have missed?? Thanks!!
Hi Pat. Looks like this is a topic we need to revisit. it was a long time ago when we published that post. I will add this to the to-do list. But at the moment, I do not know of a good place I can refer you for videos. Hard to believe Youtube doesn’t have something to help you. I hear they have everything! Maybe this is the exception. 🙁
I was looking for pictures of different ways, & of different materials, to build individual terraces around our 6 new organic orchard trees, which are in the last 1/4 of our almost 1 acre rectangular lot …. ALL of the acre on a gradual slope from the road above our house and long drive …. back to a man-made creek (already here when we moved in 19 years ago.
Though I appreciate your article’s very good advice on Terracing, the only picture is of a retainer wall, and NO pictures of gradual terraces.
My husband, bless his heart, is not a ‘natural build-it-from-scratch’ kind of guy, so he needs either sketches penciled out by me …. or pictures I can find on the Internet that gives the idea of how to go about building something he has never built before. His ADHD kind of gets ‘in the way’ also, so he needs pictures or videos to give him the initial visual, as well as to keep referring back to them.
Might want to consider multiple choice pictures of different ways to do whatever, terracing in this case, and videos would be even better!
Thank youu!
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