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the right earthwork for the right location

 
jill giegerich
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Hi desert dwellers. I'm in Joshua Tree CA working on my 5 acres of gently sloping land. The slope is about a 4.5% grade. The soil is lots of loose decomposed granite with small amounts of clay. When the monsoons hit, amazing amounts of water come sheeting down the land. I have put in one swale so far, planted honey mesquites and blue Palo Verdes on the berm and am watching the swale fill very quickly with sediment after each rain event. I'm considering putting in two more above it but the sediment issue is a big one, especially if we get the predicted major El Nino. While it is catching huge amounts of water, I foresee endless hassles with sediment fill and berm failures. I'm wondering if a smaller, less dramatic approach might make more sense. I'm thinking about simple rock lines on contour. Not sure if trees could get established just using rock lines. Any thoughts?
 
Rene Nijstad
Posts: 164
Location: La Mesa, Cundinamarca, Colombia
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dog food preservation forest garden trees
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Hi Jill,

You write: "When the monsoons hit, amazing amounts of water come sheeting down the land." Does that mean that there are no gullies where the water collects? How big is the swale that fills up so fast, is it possible to make it big enough that it won't fill up with sediment too fast?

Right now I would guess that there are no or hardly any gullies and that the amount of sediment is really too big. In that case I think walls of rock on contour properly spaced and with rocks big enough to withstand the water and sediment weight and pressure, the sediment will flatten out your terrain as terraces. That would mean that rains coming after that won't take so much sediment with them, because the water would just sink in. Because the edge still are rocks on contour excess water can slowly flow out through all the openings. It would at least help a lot with the erosion you're experiencing right now. These terraces can then of course be planted. Good luck, I hope you can figure out the best way.
 
jill giegerich
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Hi Rene,

There are some shallow gullies that empty into the swale. This swale is about 70' long, 4' wide and was about 3 foot deep. One of the problems is that I put this first swale at the bottom of my land instead of starting at the top. So it's picking up sediment that upper swales might have caught. Thanks for your input. I will consider rock terraces. I'm having some permie friends over this week to look it over with me. I took a week long watershed restoration course last month hoping to find out how to deal with the sediment problem. Amazing course! The instructor, Craig Sponholtz, isn't a fan of swales because of the maintenance issues with sediment.

 
Rene Nijstad
Posts: 164
Location: La Mesa, Cundinamarca, Colombia
20
dog food preservation forest garden trees
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Hi Jill,

The shallow gullies are good news, because they might actually bring most of the sediment to your swale. Water in gullies has a higher speed and carries more sediment with it than shallower sheet flow on land. What you could easily try is to build gabions (rock dams) in those gullies which will cause the sediment to be deposited there. If that is indeed the case less sediment will end up in your swale. For gabions check out geoff lawton who has some videos on how they look and their effects. A good book on water in drylands is Burt Lancaster's 'water harvesting in drylands vol2' which gives multiple clear options on how to deal with water as a recourse especially in dry climates. (Vol1 is more background and less practical and vol3 is about cysterns etc).

Try to look at your problem as being a solution. If you have natural forces moving earth maybe you can use those forces to put that earth where you want it. Build something small to see if it works, observe the effects, think about it, and improve. Make it a feed back cycle from what you see, to you manipulating it to help you, to watching if it works out. It's always better to try some things small scale with not too much work to scale up once you figure out the effects.

I know nothing of your instructor, but I did notice you put things right in your title: the right earthwork for the right location
 
Michael Newby
gardener
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Location: Mount Shasta, CA Zone 8a Mediterranean climate
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jill giegerich wrote:One of the problems is that I put this first swale at the bottom of my land instead of starting at the top.


I would say that you've identified one of the key problems right there. There's nothing along almost all of your property to stop any sediment that already has been picked up so you are overloading that one swale with everything coming down the hill. If you do decide to go forward with putting in the two other swales I would highly recommend putting the first one pretty close to the high point on your land and then put the third in the middle. Is the land suitable for Yeoman style keyline ripping? If it is you might consider doing that in between the swales to help increase infiltration and slow down that runoff. Get that water to infiltrate instead of sheet runoff and you will greatly diminish how much sediment gets deposited in your swales.

Depending on what the watershed looks like coming into your property you're probably going to have to deal with regular sediment buildup at the top of your property wherever you first slow down the incoming flow of water. You can design with this in mind and make a settling pond or similar area that's easily accessible for when you do have to clean out the built up sediment. Seems to me that one of the more difficult things to deal with in desert areas isn't so much the water that falls on your land but the the water (and what it brings) that comes onto your land from your neighbor's land and beyond.

Another difficult thing that I've found is dealing with that beginning time when I don't have very many systems in place so there's not even that many elements working together yet, everything seems a lot harder than how they show them working in the books and videos. The thing I try to keep in mind when all that starts getting me down is the fact that books and videos are showing functioning systems and I'm dealing with beginning systems, a lot of them without the network of support systems around them that are present in the functioning designs that I'm patterning my designs after. So I guess what I'm trying to get at in my long-winded way is: Yeah, it kind of sucks that your getting sediment buildup and that's making more work for you but don't give up hope yet, you still have a lot of room for building up those support systems that will start to give you more and more chances to stack functions and reduce effort.

Oh, and by the way, where's the pictures? We looove pictures of swales around here!

 
jill giegerich
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I agree. The beginning stages of these systems are anxious times. Did I do it right? Was it the right system? Does it integrate well with the land? It's a high level of experimentation and feedback loops. I observed my land for over 3 years before I took the plunge of putting in some major earthworks, including the swale. I've been mulling it over for about 2 weeks now since that last major storm cell event and have finally decided that given the attributes of my land, swales are the way to go in that particular section. And yes, the sediment problem probably will be mitigated by putting in two more swales above it with the top swale positioned at the top of the property and designed as the sediment catcher. So my tractor friend is coming tomorrow to put those in for me. I may then also run some on contour rock lines between them to further catch sediment. I don't think yeoman style ripping would work as the soil is very loose and sandy and would probably fill in very quickly. I will post a picture today of before and after storm pics of the current swale.
 
Stephen Layne
Posts: 26
Location: NE Ga, Zone 7b/8a
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Erosion control designs on areas of disturbed land specify stone checkdams for areas that drain an acre or more. I think this carries over into what you are trying to do. Building small dams in the gullies out of fist sized stone or larger lined with smaller stones or gravel on the inside to trap sediment will allow you to trap a lot of sediment and eventually create a terrace of soil ready to plant perennials to stabilize it. A series of terraces filling a shallow gully with vegetation could make a huge difference in how quickly water runs off.
Save the earth berms for smaller areas with less water flow where they won't fill up as fast, and, more importantly, are less like to fail due to being overwhelmed with a large flow of water.
 
Rob Browne
Posts: 65
Location: Blue Mountains, NSW, Australia
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A good example of why they say to start at the top and work down. Take the energy out of the water and get it to dump the sediment as high as possible. Its then easier to spread it downhill where you want it. Gabbions in your creek lines are great and low rock walls between the swales further reduce the energy.

 
jill giegerich
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Yes, absolutely best to start at the top. There was an erosion reason why I started at the bottom. I was planning on having the tractor guy back quickly to put in the others. He got busy and a super cell opened up over the land! Note to self.

When I say there are gullies that's a bit misleading. They are more like rills. Mostly it's sheet flow. I'm going to go take a picture right now so you can all see what I'm writing about. Back soon.
 
Rob Browne
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Location: Blue Mountains, NSW, Australia
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If your soil is sandy then its really important to get as much energy out of the water as soon as possible. This has a two fold effect of mitigating the erosive force and giving the water time to infiltrate into the soil. You want to keep as much as possible in your soil as its no good to your plants after it has run off.
 
jill giegerich
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Thanks Rob. Yes, that's the plan. I'm working on it. Here are some pics:

swale before.jpg
[Thumbnail for swale before.jpg]
swale before I cut open and laid out the straw bales
swale2.jpg
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swale3.jpg
[Thumbnail for swale3.jpg]
 
jill giegerich
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3 more pics
swale4.jpg
[Thumbnail for swale4.jpg]
swale5.jpg
[Thumbnail for swale5.jpg]
swale6.jpg
[Thumbnail for swale6.jpg]
 
jill giegerich
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Even though I should have started at the top, even though this one is catching way too much sediment. Even though....I've had 2 big rain events since it was built and it's captured and stored thousands of gallons of water that use to shoot off my land!
 
Rene Nijstad
Posts: 164
Location: La Mesa, Cundinamarca, Colombia
20
dog food preservation forest garden trees
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Hi Jill, looks really nice tot me. As you already concluded, best to put in the other two swales too. Just keep an eye on it afterwards and adjust things if needed. Don't worry too much on the sediment issue, it soaks the water into the ground so it does what it should do. I think you're doing a great job with them!
 
jill giegerich
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Thanks Rene. Yes, I think onward with swales and tweak them as I go.
 
I agree. Here's the link: https://richsoil.com/wood-heat.jsp
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