I've been lurking here a while & this is my first post!
I'm designing a food forest on a slope and would like to put some smallish swales in. I see a ton of info about how to find contour, but little about choosing the contour itself. In a blank canvas landscape, it seems you could choose any random line of contour for a swale. Is there a way to determine where the best placement would be? Or is it just common sense based on how water might flow down the landscape? So, for example, swales should be on the downhill side of the steepest bits, like at the foot of what are kind of natural terraces in the land. (And maybe up above these spots too.)
Good question. On contour is rather a vague instruction, isn't it?
Things to consider - you don't want to put swales on too steep a slope, I'm thinking the recommended limit is about 15%, above that go with a net and pan approach rather than swales. Someone correct me if I have the grade wrong
You want to hold water as high as possible on your landscape, so the first swale wants to be high on the slope. Not clear up at the top, where it might not collect run off, but only a few feet below. Depending on the scale of your particular installation and your overall plans, you determine the distance you want between your swales.
If I had a slope with a natural terrace, I would be inclined to put my swale on the inside of the terrace, cutting into the slope above a bit and berming on the terrace. The terrace is sort of a swale analogue already, placing a swale immediately below seems redundant to me.
Four videos? The link referenced takes you to what appears to be an introduction to Yeomans keyline model. Am not seeing the connection the OPs question.
Location: Fennville MI
posted 4 years ago
The key line concept is definitely informative when you are considering where to place swales.
Key line design involves the same principles that are in play with swales, slowing and manipulating water in your landscape by moving it along contour, spreading it out and soaking it in.
Location: Cache Valley, zone 4b, Irrigated, 9" rain in badlands.
posted 4 years ago
I have had the most success by placing swales just above breaklines or just below keylines as shown in the following drawing... At my place the keyline-swale is best placed far enough below the keyline that the swales don't fill completely with gravel during the first storm: I prefer to let the gravel settle out on the gentler slope just above the swale. Swales on steep slopes in my climate in the desert require a lot of maintenance that I am not able to provide. Build the highest elevation swales first in order to keep as much water as high in the landscape as possible for as long as possible. It seems to me like the higher elevation swales give the best return on investment.
Place the first swale as high up the landscape as practical. Slow the water coming onto your property.
If you own the top off the hill, then build it as soon as you can collect enough water to fill it, which is closer to the top than you think.
Keep in mind human and animal access. Moving a swale slightly up or down slope can make access roads and animal laneways much simpler to build.
If the goal is machine access in between the swales for alley cropping, size them for the machines to make even rounds between them.
If you want silvopasture for grazing, the swales should be about as far apart as the height of the canopy.
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An interesting post with such varying answers. My land is mostly flat with the only slope going OFF my property. So when I was placing swales I was placing them before the slope as pretty much everything that gets on the slope is going off my land, small pond I'm planning excluded.
So I guess the answer is it really depends on what you are looking to do and what your land is like. Just have to observe the water movement and decide from there. My current swales aren't even on contour as I needed them to move water from our driveway. They've done a great job with that. All of my future swales I will mark on contour though.
In one of Geoff Lawton's videos (I forget which one, but one of them on Geofflawton.com) he says a good place to start looking at water and earthworks is at the lowest point on the highest property line. Of course every property and set of objectives will change how the earthworks could be done, but I think his suggestion is a good one. It allows a contour line to extend across the entire (or most) of the property while still being as high as possible. If you're lost on where to begin that may be a good place to start.
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