Hi friends. I'm making a duck wonderland edible foraging forest. I had a permaculture friend come help with ideas, and she encouraged me to do swales/berms. So I've dug them out, but it is quite impossible to get things level. There are old buried redwood stumps that I've been axing for days, lots of pipes to work around and under. It's not a large space, just a back yard, so I can't avoid this stuff. Also I rent. Also this project got way bigger than I wanted, and I love it, but I'm ready to be done, yesterday.
Aside from uneven water percolation into the soil, is there anything disastrous that's going to happen from unlevel swales? The most important thing to me is getting the water away from the house, so it goes downhill from the downspouts. Otherwise, unless I rent a grinder and a level, it's just not going to happen. Plant nice water loving plants near the low spots?
I have silty soil. Drains really well as long as it's moist. Light and powdery to dig in.
Location: Central Texas zone 8a, 800 chill hours 28 blessed inches of rain
posted 3 months ago
The purpose of leveling the bottom of the trench is so the water 'pacifies' and does not flow, creating more erosion problems. If you goal is simply create trenches to catch water and get it away from the house, then no issue with an uneven bottom. Just make sure you don't have trenches that become creeks flowing out the other end and creating erosion or arroyos in your yard. You will have to monitor your 'pocket ponds' as they fill to ensure they don't flow. Creating moving channels of water on your property can create nightmares that are expensive to rehabilitate.
If I understand correctly, there are swales, which are on contour and intended to catch and soak the water, and there are ditches, intended to move water from one location to the other.
It sounds like you are trying to move water away from the house, in which case you want a ditch. I think it should have a very slight gradient (1% or so) to avoid erosion as mentioned previously. And the ditch moving water away from the house could of course feed a swale further out in the yard if desired.
As far as level goes, if it is on contour in general, with some deeper areas and some shallower areas, I think the deeper pockets will fill first and then the Shallower areas will fill next - not ideal, but shouldn’t be a huge problem if no slope to the swale. Eventually I would think the deeper sections will fill in with silt and level out.
All that said, observe what happens when it rains, and fix any issues as they arise. It’s all a grand experiment, and you get to play mad scientist!
“All good things are wild, and free.” Henry David Thoreau
I suggest revising your approach ;) Rather than thinking "swales on contour", think "duck paradise rain garden" :). And then design accordingly, with the caveat that your design moves water away from the house. I'm thinking that with the terrain and infrastructure issues you're describing, small ponds linked by overflow swales would be more appropriate