Design Earthworks & Earth Resources General Land Surveying Swales

Rapidly-Cut Swales with Tractor Blade

Bill Wilson August 7, 2015

1 2 minutes read

We are making early progress on our 320-acre Missouri permaculture-farm project (Jordan Rubin’s Heal the Planet Farm). Last fall, a local dozer operator was brought in to dig the first swales. It was a small dozer but it did a respectable job and did the work in a relatively short period of time compared to an excavator. See the blog post with video here.

Before we brought the dozer back in this spring, Kevin, a long-time farmer in the area who is also Jordan’s lead farmer on this project, suggested that we simply try the 135hp farm tractor with it’s 8-foot tilting scraper blade to see what kind of swales it would cut. It certainly seemed worth trying though I’d never seen it done before.

Adam and I headed out early one morning with the laser level and marked off about a mile of swales with white-wire flags. When Kevin arrived later in the morning with the tractor all he had to do was adjust the angle of the blade, drop it down, and start running. He ran three passes on every swale we had marked and did it all in about 60 minutes!

We repeated this process over the next two days and in the end Kevin had cut about 3 miles of swales in about 5 hours including the time it took to put in the spillways.

This is huge… for with just a basic farm tractor and a simple blade the farm is now capable to holding an additional 100,000 gallons of water every time there is a good rain and the swales fill. And with all of the rain they have had this spring it probably comes to 1/2 million gallons of water that has now soaked into the landscape rather than running off into the ravines and creeks.

Is this really helpful? Because of the poor quality of the farm’s soils (low organic matter, compaction, clay) it’s ability to absorb water is very limited. The recent soil percolation tests we did showed that the soil can only absorb 1/3 – 1/2 inch of rainfall per hour. When 2 inches of rain pours down within a one-hour period (not uncommon here) that means that most of it runs off the property adding to flooding conditions down stream and leaving plants thirsty just a few days later. What if the farm had absorb all 2 inches! No flooding downstream. More water for plants. Better plant growth. Greater yields. It’s all very simple math really.

With a second and third pass the wheel of the tractor dropped into the swale cut which dropped the blade down further as well, allowed the blade to take another 3-4 inches from the bottom of the swale with each additional pass.

By pulling away the berm soon after being cut, the sod below is not damaged and now becomes an excellent spillway capable of handling a lot of water without eroding.

Here is what the swales look like 4 months later.

Field view of 4 of the freshly cut swales. An existing livestock pond on the right.

Hear is a top-down view of the locations of the same 4 swales. All 7 of these swales cover about a 40-acre area that is 1/3 of a mile long. The white marks along the swale are where we placed the spillways.

Here is a view of the entire 320 acres with the location of the swales and existing and proposed pond locations. This is just the beginning. The plan is to put in many more swales, ponds and also keyline the entire farm.

How do we know that the soil only absorbs 1/3 – 1/2 of an inch of rainwater per hour? We did multiple ‘perc’ (percolation) tests throughout the farm.

How to perform a Perc Test? Dig a 1-foot wide/deep hole. Fill with water and let hole saturate for several hours. Return and drive in marker stake. Fill with water again to any of the lines. Come back in an hour and note how much the water level dropped. In this hole the water started at the 9″ mark. Looks like a little less than 1/2 an inch soaked in.

Me (Bill Wilson) with laser level — With two stadias (long measuring rods) and laser readers, Adam and I were able to mark out the swales quickly. One of us would take the first readings, putting in wire flags, and the other would come through and double check the first’s readings. Just like in carpentry “measure twice – cut once”.

Adam Haugeberg, the farms full-time permaculture designer and worker, measures the depth of the deepest swales. The swales varied in depth of between 14-20 inches. Where the soil was softer, the blade dug in deeper. With this kind of blade there is not a way to pre-set the depth so the operator’s skill and ability is important.

I know this is not a common way to cut swales and the water sits towards the back of the cut instead of soaking into the berm, but for the amount of time it takes to put them in and for the amount of water the swales hold, it certainly seems like it might be a perfect option for many other permaculture design projects. It’s perfect for us because the swales also create the contour template from which our keyline plowing plan will work from. More on that later.

Rapidly-Cut Swales with Tractor Blade, Youtube Video

Give us a shout if you have questions.

If you have already experimented with a tractor blade or you end up trying what we’ve done, please share with us what sort of results you get. The more we learn from each other…the better.

Toward a greener world… Bill

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