Volume issue with swale system

The water catchment I have set up works like a thing of beauty up to a certain point. It could gently rain all day and the Swales would fill up and overflow exactly as designed, slowing a lot of water long enough for it to soak in. But lately in oklahoma it seems like gentle rain is a thing of the past. We have been getting some heavy bursts that put down so much rain in so little time that my Swales overflow at the rate of a flowing creek.

Once the highest swale fills with water, the rain is coming with such force that it is moving gravel into the second swale and filling it on one side. It isn't until the third swale that the water is less like a creek and more like a functional swale.

I know I could expand the system and create bigger and deeper Swales, but I am in a tight location on the property and can't really expand much. I know I need to slow the water more, but I am having trouble doing so in the small space I have. Once the water from higher up grade is rushing down it naturally carries sediment, how can I get the sediment dropped and not have to shovel it out later?

For more background on the Swales check out the drawing on my project thread.


In this video I start at the top of the property where water enters and follow its flow through the garden and yard all the way out to the exit point.



Any ideas or advice is welcomed.

Zach, I wonder if you could use plants to slow it down and drop the sediment where you want it?

Miles Flansburg wrote:Zach, I wonder if you could use plants to slow it down and drop the sediment where you want it?

Exactly what I was thinking. We use grasses for this a lot. Or "one rock dams" (basically a line of rocks).

Good idea miles, I have been planning to plant arundo donax somewhere in the upper area with the idea that it would filter out some of the petroleum nasties. Now I am thinking I will place them all along the fence line and have a big clump right where the garbage bins are in the video. For a few feet after that spot the ground is really dense red clay and gravel, so having some sediment dropped there will be good.

Another plant option is the pile of prickly pear cactus I have laying around. I could plant that in a staggered pattern so they are like paddles facing perpendicular to the water flow. This would supply flowers, fruits, and biomass, and build up soil around a young mulberry in the area.

Jennifer, I could see a big clump of pampas grass or something similar working really well for breaking the energy in the flow, I will have to see what I can find for free/cheap.

I think for now I am going to pop those prickly pears in just because I have them on site and also make a few rock dams. In the next week or so I will go get some arundo donax. Supposed to be some more rain coming soon so I feel a little urgency to get something in place.

Thanks guys, I'll keep you posted.

Zach - definitely keep us posted. It's one thing to have a theory and another to have a working solution! I know what works here in the drylands, but with all that water you guys have been getting out there, I'd love to see some working examples in wetter areas. (or you could send us some of that rain!)

Best of luck!
Jen

For a quick solution, what about stacking some straw bales in front of the overflows about three feet or so down slope. This could act to slow down the water, drop out the silt, and allow the water to flow through. I'm thinking something like one bale deep by the width of the sill plus a bale or two on either side, pinned into the ground with a piece of rebar or long stake or something. You would save a lot of that fertility that is washing down to the next swale, and build some nice humus rich soil right there to plant into along with keeping your swale from being silted full. You could plant the straw bales using a little compost around a started plant stuffed right into the top and side of the bale. You would have a pretty fast and easy silt trap for those really heavy rain events that could turn into a permanent solution to your problem. Just what popped into my head when I read about your problem.

Hey Dave thanks a lot the idea. I have installed some cactus and will have to wait for a rain event to see how they do at slowing the flow. If it needs more I might use a few straw bales while I get more plants growing in that area. I like the idea of planting into the bales once they are in place and having small raised areas for things that wouldn't do well in the clay and gravel.

I'll keep at it, more rain expected soon.

You may need to peg the bales in place so they don't float away (sharpened sticks from pruning), but then you have what was called a "biodegradable silt fence." Which is kind of what you are after. Growing in them is a genius way to camouflage them and stabilize them as they decay into a mini-hugel.

Just a quick update on this, I could not track down any straw close by that was not sprayed so I used small rock dams, a tangle of trimmings from a nearby ailanthus tree, the prickly pear cactus and other living plants to slow the water and catch sediment. Everything seemed to be working on a few quick rains we had but then We had a string of steady rain and I was able to get some videos of it in action. So far everything is working pretty well and I have not had to shovel any sediment build up. Here's the vid, first shot is of my first flush catching plant mess and then it goes downhill attempting to show the various measures, i have a carpet over the ailanthus trimmings. Under all the plants in the first flush area is a small swale about 12 inches across and 12 inches deep.