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Permaculture Swale Spillways – How, Where, and Why

It’s not unusual to be confused about permaculture swale spillways. It can take a bit to get your head around this concept, especially if you’re doing an online PDC (Permaculture Design Course).

Unless you’ve seen spillways in action in real life, it can be tricky to visualize exactly what is happening. I have included a great video below that shows Geoff Lawton building a swale with spillway in miniature. It shows the principles of permaculture swale spillways really well.

The first thing to mention is that spillways aren’t necessarily at the end of the swale. They can be anywhere along the swale because your swale is on contour. “On contour” means it is level, right along the whole swale.

The Importance of Swales

Your swale will hold water until you make a spillway. If you don’t make a spillway, the water will do one of three things.

  1. The water will go around the end, mainly if we forget to build it up around the end. We don’t want it to go around the end. If you have water flowing out of the end, it can cause an erosion issue because it’s not a level spillway.
  2. The water will sit in the swale. This only happens if your swale doesn’t receive a lot of water. On our property, falls of 12” in a couple of hours aren’t unusual. No swale will hold this amount of water.
  3. The water will go over the mound. It doesn’t have anywhere else to go.

Where Do You Want Your Water to Go?

As you start building your swale, you survey your contour line. While you’re doing that, think about where you want the water to go.

  • You might want it to drop into another swale, on a lower point of your property.
  • You can direct the water to a ridge. Ridges are often dehydrated, and a spillway helps you direct water to that ridge, to rehydrate it.
  • You can direct water to dams on your property.

We don’t usually build a swale with that exact purpose in mind, but it’s something to think about while you’re building it. Mark out your swale on contour and decide where your spillway will be. As your digging, pile up the dug-up earth to create the mound.

When you reach your spillway point, stop piling the dirt up into a mound. Your spillway should be on the original soil, at original surface height.

Carry on digging and mounding after your spillway, as you did before. Continue on until your next spillway, or the end of your swale.

Now, if you decide down the track that you need to put it another spillway or move your existing spillway, all you need to is take away the mound.

Just keep in mind: Don’t disturb the original soil of your spillway. Carefully move the mound, taking care not to touch the natural earth.

2 Things You Can Do With the Permaculture Swale

The swale is a super helpful tool in your permaculture design toolbox. It looks great, provides a whole new area for permaculture and garden design, rehydrates your landscape, and revives your soil. The swale is the perfect irrigation setup and no-dig garden in one.

Firstly though…

A Permaculture Swale Is No Ordinary Swale

Permaculture swales are different from what other people may refer to as a “swale”.

We need to be particular about the wording on this one. It’s not just a swale, it’s a permaculture swale. When others talk about swales, they generally refer to a diversion drain, a swale with fall to drain water away.

A permaculture swale is dead level. It has no fall at all. If you have water in your permaculture swale, it doesn’t run one way or the other, it is of similar depth at either end of the swale. This is why permaculture swales are referred to as being “on contour”, which I’ll explain later.

1. You Can Manage Hydration

Because your swale is on contour, you can position your spillway anywhere along the swale.

What is “on contour”?

On contour means that the swale is positioned along contour lines. Contour lines are lines in the landscape of a similar elevation. As this website mentions: “If you walk along a contour line, you neither gain nor lose elevation.”

They use the beach as an example. If you walk along the line where the ocean meets the land, you are at sea level. If you continue walking along this line, you are on contour, a level line. If you walk into the ocean, you are at a different elevation, a different contour line.

Positioning your swales on contour means they are level. The water level is the same at either end of the swale. There is no rise or fall of the water.

The beauty of this?

You can position your spillway anywhere along the swale. If you find the water spilling into an area that is getting too wet, you can move the spillway so it hydrates another area. You can move your spillway at any time.

2. You Can Manage Fertility Movement

Besides managing water movement, you can also manage the movement of fertility across your landscape with a swale.

Water is a major mover of nutrients. As you’re moving water across your landscape with swales and spillways, you are also moving nutrients, fertility, across your landscape.

There is some debate over whether or not to have swales. Mainly because it is a significant mechanical action on your land, and it takes a lot of energy to build.

Swales are definitely intensive to build, but if you have poor soil, they are invaluable. Mainly because of the movement of fertility. They help you speed up the process of rebuilding your soil and helping it recover.

How to Build a Swale

I love swales because they help us work on contour. They also create areas you can work with. When you put a swale in, all of a sudden you have a redesigned area with edges – swales often spark a whole new design in my mind!


  • Elle

    Jack of all trades, master of some. Wild garden grower. Loves creating stuff. From food forests and survival gardens to soap and yoghurt. A girl on a farm with two kids and one husband (yep, just one - although another one would be handy). Weirdly enjoys fixing fences and digging holes. Qualified permaculture teacher and garden go-to.

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