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Swales in wet climates

Marshy swales

One of my early projects in the forest garden was to build mounds and swales in an attempt to deal with waterlogged soil.  The mounds did their job well --- they raised plants up high enough out of the water that they survived.  The swales were more problematic.

Dry climate swaleThe permaculture literature discusses swales as used in dry climates.  There, swales capture runoff so the precious liquid doesn't disappear onto the neighbor's property.  A dry climate swale is basically a linear, wet-weather pond that runs along a contour line, filling up during rains, then releasing the water into the surrounding area over the days and weeks that follow.  Bill Mollison and other permaculture practitioners plant moisture-loving trees and shrubs on the downhill side of these swales for free irrigation.

Check damsIn wet climates, a different kind of swale is used to channel runoff across flood-tolerant vegetation, cleaning the water and preventing erosion.  In this case, swales are built perpendicular to a slope to keep water moving, then check-dams are added at intervals to slow the water down and help silt drop out.  Wet climate swales are often located next to roads or parking lots, as is shown in this photo, and they allow runoff to sink into non-waterlogged soil.

You'll notice that both types of swales capture water and let it sink into the ground.  The big difference in function is that dry climate swales can be built in ground that doesn't "perk" since the goal is to make the water stick around as long as possible.  Wet climate swales are built on well-drained soil with the goal of getting that runoff into the groundwater as quickly as possible.

I wish I'd realized the difference between dry climate and wet climate water management when I installed my swales, because I learned the hard way that creating a dry climate swale in our neck of the woods can turn wet ground into a marsh.  Marshes have their place, but a marshy ditch in the middle of a "lawn" becomes a mowing hazard quickly.  Rather than ruin the lawn mower, Mark skipped mowing these spots, with predictable results.

Putting logs in swalesAs part of my campaign to streamline maintenance of the forest garden, I'm starting to build the swales back up to ground level.  I figure rotten logs in the holes will capture and hold water, releasing it to the nearby plants during dry spells.  Once I hunt down enough logs to fill the swales up, I'll mulch over top so that that area won't need to be mowed at all this year.

Of course, even my improved swales hold onto water rather than draining it out of the waterlogged area.  I might eventually turn to ditching to deal with that issue, but for now, I think I can take advantage of the extra water.  I'll just keep building up so that roots don't drown.

Our chicken waterer keeps chicks healthy from day 1 with clean water and dry bedding.


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I'm still learning and picking up bits of info, so you might have already heard of this, but you are right about the rotten logs soaking up water. It's part of the main idea of hugelkultur (http://www.richsoil.com/hugelkultur/). I just tried my hand at two small hugel beds. I'm hoping it will help with our small, raised bed veggie garden. We have fairly thick clay. :-/
Comment by Kelly Fri Feb 24 09:03:00 2012

Hi Anna,

Can you recommend any resources on how to build swales in wet climates? My residential neighborhood is on a hillside, but my house sits in a little dip in the hill. Whenever it rains, the water flows down the hill and stops in my yard for a bit before continuing on. For about three weeks out of the year, I have a pond for a yard. Unfortunately, this tends to occur right around when I should be planting a veggie garden, so I haven't been able to really grow any food, and I'd like to remedy that situation.

Thank you!

Comment by Leslie Fri Feb 24 09:08:10 2012
I've been using a modified version of hugelkultur in that area for a few years with (mostly) good results. Since my soil is so waterlogged, I start at the soil surface instead of digging down, which is why I say modified. That's actually my goal for the whole space --- raise it up with hugelkultur as I find the materials!
Comment by anna Fri Feb 24 09:08:58 2012

Leslie --- There's a lot of technical information out there from agencies that build swales to treat greywater coming off huge parking lots. I suspect you'd need to tweak it a bit to match a backyard environment, but here are a couple of sources to get you started:

http://pubs.ext.vt.edu/BSE/BSE-4/BSE-4.html --- This is for wet swales, where the bottom of the swale can sit below the water level all the time. (You might not be wet enough for that.)

http://pubs.ext.vt.edu/BSE/BSE-20/BSE-20.html --- Grass channels might be more appropriate for your area.

If you find better sources, or make your own swale, I hope you'll come back and share your experiences!

Comment by anna Fri Feb 24 09:36:32 2012
Can you grow cranberries in VA? I know that you could grow cattails. About the only thing I really liked from "Stalking the Wild Asparagus" was the cattail flowers lightly steamed with butter. They were so delicious. And a few cranberries with your Thanksgiving turkey (or chicken)...
Comment by Eric in Japan Fri Feb 24 11:00:52 2012

We live on a mountain with hard clay soil. There are areas that have a natural water way for rain to continue on its journey. But, because our summers are so dry, I need to stop this rain from leaving the top so that I can ulilize the water with my plants.

This is the first year I have incorporated hulgeculture into my garden. I think I have gone kind of crazy. I am runnig a hulgle bed all along the edge of the hill and using large tree limbs cut from the trees that shade that area. Then I have a friend that will give me wood shavings from his saw mill and leaves that I rake up in the forest. If I have to I will fill it in with straw. Then dirt and plant in it. So far I have about 60' of hugle pile started and another 40' more that I can put in.

I am excited about this project.

Comment by Mona Fri Feb 24 11:24:38 2012

Eric --- I think I remember reading on your blog when you ate the cattail flowers. I want to try them out this year, if I can remember! We actually have a bunch of wild cattails just up the holler, so no need to plant them here.

A friend of mine grew cranberries a few years ago and got such low yields that she ripped them out. I may still experiment with them sometime, though, because I really like cranberries. But I think we're a bit too warm (or something?) for them to do well.

Mona --- It sounds like you may be a good candidate for dry climate swales! Combined with your awesome hugelkultur experiment, you may soon have created an oasis.

Comment by anna Fri Feb 24 11:59:07 2012

One very unique homestead, $1,500 per acre, the opportunity of a lifetime