Does anyone have some insight into the difference it makes in having a swale mound that's been raked down smooth compared to one that's been left rough on a larger swale? I'm currently grading the overflow smooth and consistent.
I've been contemplating if I should even bother smoothing out the non-overflow mound of the swale though. The mound is fairly large, probably between 4-5' tall. I'm not able to come to any conclusion as to why it would be better than leaving it rough, other than it looking cleaner. If I leave it rough there are more, "pockets", and such along the top of the mound that will allow seed, and organic matter to settle into, which I can only see as a benefit to helping get trees started, especially starting them by seed in place. The mound is a little steeper on the downhill side which may make it a little more difficult for plants to get established on that part? But I don't know if that's going to make a big enough difference long term.
Smoothing out the mound would also make it wider by around maybe 10'. I would prefer to keep the mound narrower over making it wider. And I would have to adjust the overflow a little bit. The overflow is currently set at 2' lower than the mound and I would prefer to keep it around that.
I've kept a few smaller swales rough as well as a large mound in a catchment pond/swale for collecting silt, and I haven't seen a big difference compared to the ones I've smoothed out. I haven't had a lot of monsoon events which I was concerned about causing issues on the steeper downhill sides of those mounds, though there have been a few monsoon rains fall on them last year and I don't see anything at this point to show it being a cause for concern. But they're all fairly new within the last year so I don't have any long term perspective on it.
Anyone have experience or knowledge on this? I haven't come across anything throughout the years saying one way or another being better. I'm trying to determine if I should put in a little more effort and smooth out the mound or just leave it rough.
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When making swales and mounds (berms) you need to get that berm growing something immediately so you don't experience erosion of the berm.
That means leaving them "rough" should be out of the question since rough means easier to erode and you can seed then smooth so there is good soil contact with the seeds for better germination.
You do not plant trees on the top of any berm, trees go on the opposite side of the berm from the swale.
The best plant for berms is some type of grass, (grains are grasses).
Over flow usually refers to the water that will sheet over the berm once the swale is full.
You want the overflow water to sheet because that reduces erosion everywhere.
Mark Shepard's book "Restoration Agriculture" goes over these details, how to set them up correctly and where to place collection ponds.
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I believe the best practice is cleaning up the swale berm in one way or another. Try to break up large clumps on the surface and make at least an area that can act as a seed bed. In our area of Missouri, we have lots of clay. When you dig, or have one done, try to place at least some of the top soil along the top of the berm to help you grow things quickly.
Not all clumps need to be broken up. Your berm does not have to look like a garden bed!!! The clumps will eventually break down with some rain and the area will evolve sediment will wash into the ditch and provide good growing conditions for other grasses and plants.