Swale over a keyline = Why would you?

Hello

A buddy asked me why not put a swale over a keyline to help the water get deeper, faster into the ground.

My reply was its redundant. The whole point of a swale is to slow the water to allow it soak into the soil and begin its seepage down hill underground. Also a keyline is more suited to force the water off contour instead of strictly on contour as a swale does. Another point is you don't cover your keyline with trees.

As far as I know this is correct. Am I amiss?

It also depends on what you want to grow. Swales are great for trees and perenials while keyline works well for annual crops and pastures and large holdings managed with machinery.

I think you could clarify what you are saying a little more.

A swale is a ditch, most commonly a ditch on contour.

Just as a Contour Line is no a physical thing (It's an abstraction that help us describe and understand the landscape), A keyline is not a physical thing - it's a contour line that extends out from the keypoint, at the inflection point where the valley changes from concave to convex. You can do things with that keyline, such as rip it with a keyline plow, or put a swale on it, or plow parallel to it so that water moves out to the ridges.

So when you say "a swale over a keyline" I'm taking that to mean installing a ditch on contour uphill from the keyline. That would be a valid approach depending on what you want to accomplish.

You can combine keyline plowing and swaling, with a swale installed along the keyline, and keyline plowing parallel to that swale. Thus you capture large rainfall events, and also spread water out to the ridges.

Search the forum for "keyline swales" for more info about different approaches this.

A swale is a ditch, most commonly a ditch on contour.

That is also how I think of a swale.

The soil that is dug out of the swale is usually piled on the downhill side, thus creating a berm.
Quite often, the entire structure (swale and berm) is referred to as a 'swale', which can lead to confusion.

As far as planting trees on a (ripped) keyline goes, I would think that could be a good idea for trees that grow tap roots.