Te water cycle in karst regions is quite different than in non-karst regions, so I wanted to start a thread on swales as well as working with the water cycle of karst regions in general, as none of the permaculture literature that I've found has taken karst into account when describing earthworks and rainwater collection.
Karst regions are more droughty than you would expect given the climate, because so much of the water ends up escaping downwards into the underground watercourses and our of reach of any plants. Catching water is a more complex issue here because of the many interfaces between the surface water and the groundwater. I know people who've had success with swales in the ozarks, but mine that I've dug over the last few years haven't yet made a noticeable difference. They catch water during heavy rainstorms, but drain quickly. I'm worried that most of the water the swales catch just works its way downward through the karst rather than being available to the plants nearby, especially in the one swale that I dug over two feet deep. The others are more shallow, and I think any more that I dig will be shallower, but I'll only dig more if I start to notice a difference from the ones I already have.
I'm still hopeful that the swales will prove helpful once the young trees around them have larger root systems that work their way into the swale itself. I had put in some organic matter after building them, but this past winter, I added much more to two of my swales, including woodchips, rotting logs, a bit of compost, weeds, and nearly filled them up. I'm thinking that a ton of organic matter is the only way to make the swale useful here, as then the moisture caught has a chance to actually be held in a place useful to the plants rather than drain away through the karst.
Anyone else living on karst have hay experiences with earthworks and rainwater harvesting on such a landscape? I imagine it varies quite a bit, as even in my local area, it ranges from very little soil above the karst to a few bottomland and bench lands that have a deep soil with few rocks for many feet down, but the majority of the area has a pretty thin, rocky soil which doesn't hold water well. Still, I think having a thread focused on what does and doesn't work in karst regions would prove quite helpful.
Keep in mind, however, that not all karst areas are the same. Much of Iowa is shown as karst on the map, but most of that area has so much glacial till above the karst that they don't have the issues that the ozarks do. Much of the gulf coastal karst areas have a high water table, giving them very different issues to deal with than me. So, not all karst areas have the droughtiness that I described.
Very interesting! I think the only real solution is to build up organic matter. The old rule of thumb is the 3 inches of humus can hold 1 inch of water.
As for swales, I think you are on the right track with shallow and wide with lots of organic matter in it. You might take it a step further and create a gley on the bottom of the swale to keep the water there longer.
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i think neal may have something worth trying out, if drainage is generally fast, then stopping drainage may be a good idea
also lots of trees and what not to build organic matter i suppose
and maybe hugelkulturs?
i normally recommend adding texture to the lanscape, im not sure if this would help or hinder your situation however
and if nothing else, if your area looks anything like the wikipedia page, at least you got a really pretty place to live:D
We're karst here. On top of that, my property is eroded Baxter cherty silt loam -- quite rocky -- and well sloped at the bottom of a hill. The height of summer can be really tough on plants, but the surface water does at least drain my way. I have one large swale upslope which helps prevent further erosion. It seems to be collecting a lot of silt from upslope and it stays pretty wet after a hard rain -- certainly the grass stays greener and thicker there. Farther downslope, I have an area that stays wet for an extended time after rain as the hillside drains, but once it's dry it's DRY. I really can't get anything to grow in that combination of water logged / bone dry.
Other than those two spots, my land stays pretty dry when it hasn't actually been raining. The trees along the wooded area actually make it worse because they suck the soil dry and little can survive near/under them.
Based on these fairly limited observations, I am starting to think a rain-garden style approach will work better than a swale, much like you are doing by filling up your swales. I am considering excavating my low spot even further and filling it with organic matter so I can then plant things over it which can handle the wet feet but don't have to be so drought tolerant.
I've also pondered excavating a pond and lining it with clay, and then planting around it. The clay, I am thinking, might slow down the seepage enough to let the nearby plants get a good drink of water from time to time.
Location: Missouri Ozarks
posted 6 years ago
Thanks for the tips. I'll look into the gley if I dig any more swales this fall/winter.
And yes, the Ozarks are a beautiful place. There are plenty of challenges to working with this land, but the rougher terrain is also what largely keeps the industrial monoculture that dominates the midwest out of this area.
For what it's worth, when I saw Goeff Lawton give a talk, I remember him saying that a landscape with swales on contour as the main water harvesting system may take up to 7 years to become fully saturated with water after swales are installed.
I also remember him saying that any landscape can become fully saturated within 7 years from the time swales are put in place.
That is what I remember him saying.
He was talking a lot about his work in Jordan during this talk where the soil looks to be super low in organic matter and very, very porous.
So, maybe this will take more time on your property if you stay with swales.
From reading Sepp's latest book, it appears his techniques might work more quickly than swales on contour for restoring water balance on the landscape.
A lot of things come out of nowhere, so look everywhere.
What is the latest on your swales? I also live in the Missouri Ozarks and am facing a karst challenge. We have a spring that we really want to improve the recharge of and would like for it to release water slower and over a more spread out period (it floods in the spring and can go dry by July).
I agree Richard. Any updates? I'm in Kentucky trying to design a farm that has karst issues. I'm also working on my design project for the online PDC with Geoff Lawton and not sure if swales and ponds are the right way to go or not. Anyone have any extended time working with this type of landscape?
I'd also be interested in an update. This is my first productive year in the Ozarks (the summer of 2012 was too dry). I installed 3 swales and have learned a great deal since all 3 vary a bit.
I was curious if you could expound upon what you mean by the swales "drain quickly?" I've noticed different swales I have drain at different times; there's even drainage differences within a swale (mostly due to soil type I believe).
Also what size are your swales?
Location: Missouri Ozarks
posted 5 years ago
I see some of you are interested in an update on my ozark swales. I have continued to add organic matter, and they are mostly filled with rich black dirt. My largest swale was close to three feet deep when it was dug, but is now mostly filled in. All the other swales are significantly shallower, 18" or less deep. The trees nearby are just starting to get big enough that a few roots may be reaching into it, and some of the small apple and jujube trees near the deepest one are fruiting for the first time this year, and did seem to take the dryness earlier in the summer better than some trees farther away. I really think building organic matter is the way to go in karst (in swales as well as in general), and swales are useful with organic matter to act as a sponge to absorb that runoff, as there's no water table that's close to within reach of the plants on this site. Even within the ozarks, however, there are a lot of variations in the rock types, some places are more karsty than others.
What I mean by "drain quickly" is that a few months after I dug my largest swale but before I put much organic matter in it, we were deluged (in late April/early May 2011). All the swales filled completey (and eroded the berm from overflow in one spot where I had constructed it poorly, make sure to make a stable overflow spillway for your swales. My nearly three-foot deep swale actually was something like four feet deep in water one afternoon (since the downhill berm is about a foot higher at its peak than the top of the ditch). The next morning, all the water was gone except for some tiny scattered pools, most of it presumably drained beyond the reach of plants. The same was true of my smaller swales. I have never seen them with standing water in them again (they're mostly filled with organic matter now, and we've had no deluges as insane as in spring 2011).
Richard that was ultra-helpful! Thank you so much for updating. I feel like I can make some intelligent additions to my design project now, and the farmer I'm designing for will be interested to know this as well.
I'm not actually in a Karst area, but very close to (near El Torcal in Andalusia). We've just been up on our new property to look at the landscape and in some areas it has the same features as Karst. We have large portions of bedrock sticking out of the soil. There is generally soil above the rock and I think the water will go over it in the soil. On site we realized something. We where trying to look at design options for our initial zone 1 and quickly realized, that we can't dig deep into the soil! So any water harvesting earthworks must be made "above ground". Actually, I'm not even sure, I can dig a hole deep enough to plant a tree! Our conclusion was, that we need to build up, not dig down.
So we had a look at Lancasters books again and at some of the techniques from Quivira Coalition. There are a lot of things we can user to build upwards rather than down.
Location: Kentucky knob region
posted 5 years ago
Marcus, thank you for adding your experience. What is the author, Lancaster's, first name? Are his books readily available? I haven't heard of him.
I feel silly now. I have heard of those books. I just didn't know the author's name. I didn't realize they were applicable to other locations besides dryland/desert type situations. I'll have to move them up sooner in my reading list! Thanks for the info.
We are also in a Karst area in Puglia (Southern Italy). Our five acre property was planted with olives, some over a hundred years old, walnuts, almonds, figs and a virety of other fruit trees as well as native oaks. Wild asparigus, chickories and many other edible plants grow. Our property has a natural cistern at the top of the property that had water all last summer.Durring the summer, water trucks can be seen driving all around the countryside filling peoples cisterns. We are at about 400 meters and the wells here are about that deep. Stone walls were built over the centuries to terrace the land, and look to me like they are serving a similar purpose to swales. We also have a thin layer of a redish brown clayish top soil varying in depth from about 30cm to 1 meter. The local tradition is to remove all organic matter from the soil. I am fighting this trend and also feel having a lot of mulched organic matter is the best solution for moisture retension. There is a four hundred year old drystacked limestone structure called a trullo with a cone shaped roof. I am slowly renovating this structure, but want to keep it original and off the grid.
Thanks to all for the great information on this site.
Location: Missouri Ozarks
posted 7 months ago
A few more thoughts after a few more years of working with these swales,
I have noticed wildly varying rates of water infiltration on various spots on our land, as the layers of bedrock vary from very porous to pretty solid. The soil above the bedrock matters too. Some swales that I put in a while back drained very rapidly, out of reach of the plants. I've mostly filled those in with organic matter, creating a sponge for moisture which has proved useful, but some of them aren't really doing that much for all the time and energy I put into them. Others are very helpful, it all depends on the placement. On the particular area I'm working with, there just isn't much runoff from ground that's in good vegetative cover unless the soil is really saturated, even then I think much of the water getting into the swales is coming through the soil, a temporary water table that drains down pretty quickly once the deluge ends. So, the swales in areas with good vegetative cover uphill aren't really doing much.
The swales that I do consider very helpful are the ones that are collecting runoff from impervious or compacted areas such as gravel roads. I have a couple of swales that collect water, nutrients and organic matter coming off of a low-traffic gravel road, and that keeps the area near them noticeably lusher during dry summers as long as we get a few of the types of occasional showers and thunderstorms that are common here, Even if they don't bring enough rain to make much of a difference in most places, the runoff that concentrates in the swales will moisten the area around them significantly.
Water retention is tricky in karst. If there's evidence of runoff or erosion swales may help. I could suggest digging some test holes and filling them with water to see how fast they drain, but the thing is a hole may not drain too excessively, but then when expanded into a swale may hit a spot where the water can get through cracks in the bedrock and drain fast.
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