When it rains, the water on your landscape can become a destructive force. Within hours, stormwater can wash away gardens and undermine structural foundations. Without proper design, you are at the forces of Mother Nature every time it rains.
Permaculture is a design science that can help us develop effective erosion control strategies for any landscape. Permaculture designers have a few tools in their toolbox to help with erosion control.
- Biological Stabilization
- Swales and Terracing
- Rock Retaining Walls
- Logs, rock & brush on Contour
Controlling erosion requires more than just picking any one of those tools mentioned above and placing them anywhere. It takes observation, experience and exploration.
Let’s dive into them a little deeper so that you may be able to have a bit more experience using Permaculture design for erosion control.
Observation, Experience and Exploration
Before we dive into the methods of erosion control that we can use, it is very important to address the foundation of effective Permaculture Design, which is observation.
Twelve years ago I was tasked with developing a property in Malibu, CA into a Permaculture Food Forest complete with water harvesting techniques, erosion control and fire suppression.
At first I looked at each of those issues separately, but eventually I came to see how they could all work together. As I watched the rain fall, I learned where I could slow it down, spread it out and sink it into the landscape. Effectively harvesting water and controlling erosion at the same time.
It also helped benefit fire suppression in the fire resistant plants that grew because of the additional water. When clearing brush, we cleared it on contour so that what remained could harvest water and control erosion where needed.
All of this came from observation. Observing how water flowed through the landscape. With those observations, I used the experience and knowledge gained through years of studying Permaculture and land management to implement swales, terraces, gabions and brushy check dams to create positive solutions for the landscape.
As I implemented the systems on the landscape, I continued to observe and explore with little changes here and there to optimize the system. Eventually, the landscape all came together and an oasis was born.
Utilize Observation, Experience and Exploration in your designs. Keep learning and keep testing out new things and eventually, it will all come together for you too.
Before we go digging up the earth, destroying soil life and making big changes to the environment, we should consider the simplest solutions first. Biological Stabilization for erosion control is so simple yet often overlooked.
Here in the tropics, cliff sides and steep inclines are stabilized with a deep-rooted grass called Vetiver. Bamboo helps hold up river banks and giant deep-rooted trees hold in soil when the 100-year storm arrives.
Placing these plants on contour to the landscape can also help harvest water that falls in the landscape, trap soil that is eroding from elsewhere and create the conditions for new life to thrive.
Using the roots of plants to help with erosion control also helps aid the purification of that water, so when the water flows off site, the contaminants do not come with it.
Where NOT To Use Biological Stabilization
Nowhere. Everywhere could use more plants. But in some areas, that’s just not possible.
You may need to set the conditions for biological stabilization to take place. Rock walls or brushy check dams may have to be implemented first to trap enough soil and moisture for biological life to occur.
Our end goal is to increase biological life, so what do we need to do to make the conditions right for this to occur?
Swales and Terracing
Swales are one of the most popular techniques people use when it comes to harvesting water on the landscape, but it is also an effective erosion control technique as well.
Swales are ditches dug on contour with a berm on the downhill side of the slope that harvest water falling on the landscape.
They also help to slow the velocity of water down, creating a very effective water control strategy. If used high enough on the landscape and continued down the lower parts, once rushing rivers during a storm can be mitigated into slowly spreading water across the entire landscape.
Terracing is another very effective form of water control that is used throughout agricultural regions of tropical southeast Asia and could find more of a place in the tropical US such as Hawaii.
Terraces act similar to swales in that they slow the velocity of water dramatically. They are employed in the wet tropics to help retain soil and as a way to manage the abundance of water that falls from the sky.
More landscapes can benefit from applying such designs into their watersheds.
When NOT To Use Swales or Terraces
Sometimes your landscape is just not equipped to have swales or terraces. Either your as flat as a pancake or you have super rocky soil or no soil. I live on the side of a volcano, shovels are no good here. One inch down and it’s all lava rock.
What would be better for me is to utilize rocks since I have an over abundance of them. I can stack them on contour, making rock walls, check dams or “swales” instead of digging or terraforming land into terraces.
Rock Retaining Walls
Rock Retaining walls act similarly to terraces, in fact they are terraces. By building a dry stacked rock wall, you can level off the landscape while still allowing water to flow through. This allows the water to slow down and soil to remain in place.
If your site has an abundance of rocks this technique can work for you. Importing rocks is costly and harmful for the environment they’re imported from.
Just because you have rocks though doesn’t mean this job would be easy to accomplish. Building a rock retaining wall takes a lot of back breaking work and skill to lay the rocks just right so the whole thing does not fall over.
Rock Retaining walls are a great solution for areas where water is already running quickly. When well constructed, they are able to handle large flows and effectively slow down the water.
When NOT To Use Rock Retaining Walls
Not every solution is going to work everywhere. Rock retaining walls are no exception. As I already mentioned, if you don’t have any rocks, it doesn’t make much sense building a rock wall.
If the area has a high water flow and you are inexperienced as a rock wall builder, then you may want to consider another option as well.
Logs, Rock & Brush On Contour
There are times when resources are tight, land is rocky and hard to dig and all you have on site are some rocks, some downed trees and some brush. Simply placing these resources on contour to the landscape, in berms or check dams, can have a dramatic effect on erosion control.
These methods of control absorb water, retain nutrients and rehydrate the landscape as well as slowing runoff which lessens erosion.
Using this method of erosion control is accessible to almost anyone in the world, regardless of income level. All it takes is a little work and something to measure the contours of the landscape like a water level or bunyip.
When NOT To Use Logs, Rocks and Brush On Contour
While this method can be universally utilized, there are still times when it would be inappropriate.
If using these materials to slow water in fast moving washes, all you may be doing is adding material to be washed away in the next storm. What would be better is to use the next technique in these situations.
Gabions are an effective form of erosion control used by engineers across the country, as well as permaculture designers. Gabions can be made with either tons of rock encased in wire fencing or with logs and brush pegged in with stakes.
Gabions are very effective in slowing down and spreading water out in a fast moving gulley. As the water approaches the gabion dam, it slows down, dropping sediment before slowly trickling down stream.
I have installed a few gabion check dams in washes that caused severe erosion only to see them mitigate the damage almost over night.
When NOT To Use Gabions
While a very effective tool to be employed in erosion control, Gabions are not suited for every situation.
They require a lot of natural material to construct. If you do not have access to a lot of stones or brush, they may be difficult to construct.
Gabions are also not designed to slow down erosion on a broader landscape. Gabions are strictly for fast moving, narrow washes where erosion is already occurring. They must be engineered to withstand the flow of at least a 50 year storm.
If you are not ready to build them correctly, don’t even try. It will just leave a mess of wire in the wash and rocks scattered downstream.
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