Swale Question: How to increase drainage with clay soil?

Hi All - long time observer, first time poster.

I'm hoping to create a series of swales on my property (West Sonoma County, California) that tie into a large drainage ditch. The goal is to divert a portion of the water from the drainage ditch into a first swale, that will then overflow into a second, and then overflow into a third, before routing back into the drainage ditch and off our property.

With these swales, we plan on planting a series of fruit trees and native plants.

When I dug the first swale, they immediately started to fill with water from various gopher holes. It's now been dry for days and the water isn't draining. Any advice on how to encourage faster drainage in our clay soil? Add organic matter to the bottom of the swale? Any particular kind of organic matter?

I've added two photos to show the swale which was dug on contour with the help of an A-frame level ; and the second photo shows the drainage ditch that the swale will tie to.

Thanks in advance for any feedback/advice!

Two steps.  First immediate.  Tractor with a subsoiler.  Rip down open the soil at the bottom of the trench.  Second over time.  All the organic matter you can find.  Wood chips, moldy hay bales, cardboard, leaf litter, grass clippings.  Get the soil the carbon it needs to help the microbes live and start breaking down the clay into plant food.  

Hello Jr!

Welcome to permies!

Looks like you have some nice clay there.  I would add a mulch layer to cover the ground.   This will help with drainage by giving cover to worms and other decomposers.   They will poke holes in your clay and incorporate the porous organic material with the clay.  It could be leaves, straw, sticks and forest debris, whatever is easy for you to get that you know is organic (no chance of pesticides).

There is a lot of useful info for this in the World Domination Gardening movie.

https://permies.com/wiki/earthworks-gardening

If you have access to a tractor for subsoiling, I would also widen the bottom of the swale. Generally gradual sloped sides and a flatter bottom will work better for absorption. If a tractor is not an option, I would use a broad fork or a sturdy digging fork to loosen but not invert the soil layers. If the soil is high in Magnesium relative to calcium like many coastal CA soils, oyster shell in addition to organic matter can be a good addition, and I would add it to the loosened soil. Looks like you have a great plan overall to me.

Lots of good advice here.

I am a fan of ditches rather than swales.

To me swales are good for trees.

Ditches get water moving faster.

And berms can work for stopping water.

Hello!
I think I see a few things going on.  Yes, it appears you have a high clay component with a degree of compaction, but that isn't the only thing that I see. I'm not sure when the pictures were taken, but it appears there is a lot of tree canopy. That in itself isn't necessarily a bad thing, but to grow most things under that, my guess they will need more light than what they will get there.

Have you done a soil test? In looking at the current vegetation, I'd also guess the plants that are there aren't getting the nutrition they need. This could be the pH of the soil. Maybe the nutrients the plants need aren't there. Maybe both? You need to be able to get something into the soil somehow in order to add lime? or nutrients. Subsoiler as suggested?

I don't care for equipment myself as it's expensive and tends to have a short term effect. To break up your compaction - long term - organic matter would be what I'd add. The best way to add OM is through roots of grasses. Of course, the grasses have to be able to grow which means nutrients, and the roots also have to be able to overcome the compaction. The earthworms would be nice to incorporate surface added OM, but the soil is too compacted.

You have a bit of a vicious cycle or circle here. Roots to address the compaction, om to address the compaction, nutrients to feed the plants but can't get in the soil because of the compaction, etc.

I'd look at planting some deep rooted plants that CAN break up the compaction. Forage radish, possibly alfalfa, turnips. The radishes will also collect nutrients and make them available to other plants when they die and decompose.

The long term increase in OM will help with compaction as well as help with water retention.  I bet the area dries out completely and turns into a 'brick' during the summer. Getting the soil to absorb some of that water will assist with the ponding, but it will also decrease the long term dryness I'm sure you have encountered, or will encounter.

Lovely spot!
Let me clarify your intent. Sounds  like your goal is to infiltrate water into the soil, clay, on your property versus draining it away into the ditch?
If so, for infiltration, slowing the flow is needed. Faster moving water will carry away your soil.
There are great suggestions already: Widening the trough, making shallower sides. Adding organic materials to both slow flow, hold moisture and allow biology to begin to change your soil structure. Broad forking to open the soil, and perhaps using compost tea or extract afterward to introduce biology deeper into the soil. Planting in the trough as mentioned, and plantings on your mounds.

If flow through the swale maze is still too heavy at times, you might add loose leaky rock dams  intermittently to slow flow and catch soil. Though I suspect the other measures should suffice. The ditch might be a place to consider this, depending on your needs. Slowing water is usually a good thing.
Best of luck.  Looking forward to updates.

Toxtli

geologically speaking, clayey soil has low hydraulic conductivity. The conductivity is measured as flow per unit of area. So like others have said, if you can change the soil conductivity by making it more porous and less compacted then more flow can go through. But if the clay is extensive in area and depth, the water may eventually saturate the more-conductive region you have made and be stopped by the low conductivity material at depth. Increasing the area is also helpful; and making a porous zone around the swale has that effect to some degree, but making the swale bigger is also going to help (the ditch in the photo is pretty small). Another option may be to dig through surface clay and find more conductive soil below. You might be able to find some "lithology" at a local agricultural extension office or public library (possibly easier than digging, possibly not!).

Swales are often built with a fairly gentle slope of 1:3 between the bottom and surrounding surface. Because the swale can be better-watered than other areas, it can grow more luxuriant vegetation and a gentle slope can be mowed. Also, a gentle slope is less prone to erode.

Ahhoi. Like the topic starter, I am in exactly the same "category" with regard to Permies, i.e. a long-term observer-learner but a first-time participant in the topic. I have experience with land improvement works, including excess moisture and drainage systems. If you look at the top picture, 1) it is clearly visible in the left part that the soil has started to collapse into the ditch, therefore this part cannot be soil with a majority of clay. Considering that the soil in the entire excavation visible in the picture has the same texture and color and the color does not vary, it can be concluded that the entire upper layer is soil with a similar and rather low clay content; 2) the vegetation in the adjacent area is bright green, which indicates a sufficiently rich soil; 3) it is evident from the side wall of the excavation that there are no differences in the soil layers; 4) there are also no different colors and possible layers noticeable in the soil lifted from the excavation; 5) in the upper left part of the picture, where there is an unmowed area, a taller growing mass is also noticeable. These five characteristics lead to the conclusion that in the trench visible in the upper image, the upper part of the soil, i.e. the part of the soil above the water line, is rather a rather valuable soil and the water is probably standing on the clay that came up exactly from the bottom of the trench. According to the lower image, one could assume that the water has actually decreased by about half or even more, at the bottom of the image, colorful stripes can be seen along the edges of the trench, they can only be caused by the water level or, more precisely, by a change in the level. In essence, this does not change the matter very much. In summary, we can say that 1) the clay in the lower layers is possible that it is not too heavy clay, because otherwise the water would not have decreased at all, or 2) the clay in the lower layer is strong but the water seeped into the lateral layers. I suggest that the following options could be considered: A) dig a deeper hole, or so-called control hole, in a couple of places (then it will be more certain whether the soil layers are the same or different in several places), to make sure what the soil layers are deeper. Speed ​​is very important with this option, because it is likely that when digging, it can immediately overflow. It could help here if there is another hole next to the inspection hole, which is deeper than the inspection hole, and water that would otherwise overflow into the inspection hole can be directed there. This is easier said than done, of course. However, if an excavator is available, it is possible to deliver more efficiently. Or pump the water out. The idea of ​​this option is to understand whether the clay layer on which the water remains is thin or thick, and whether it is expensive to make a deeper trench than this. Option B) do not make the trenches deeper. Fill the existing trenches with the filling necessary for the formation of good soil, which has been well described in previous posts, and use the existing and additional similar trenches as they currently function - this water is the wealth to use in raised beds. At the same time, build valves to the drainage ditch running perpendicularly down, which can be easily removed, like sluices or mini-dams, in case there seems to be too much water, then you let some of the water drain through the drainage ditch. Over time, i.e. after 1-2-3 years, as the organic matter added to the bottom of the ditch decomposes, more water will be absorbed and the need to divert excess water may decrease. This option assumes that the ditches have a sufficient but minimal slope towards the drainage ditch so that when you open your mini-dam, the excess water can also seep or flow away. Option C) combine option B with new lateral trenches running from top to bottom. You also fill these with organic material. When viewed from above, it looks like an S or multiple S depending on how many long trenches you plan to make, when you mentioned "series of swales". The idea of ​​this option is that the water meanders through your desired areas and then the excess exits through a drainage ditch. The assumption of this option is that each ditch is sloped in the opposite direction so that the S can work.

Mark Reynolds wrote:
I'd look at planting some deep rooted plants that CAN break up the compaction. Forage radish, possibly alfalfa, turnips. The radishes will also collect nutrients and make them available to other plants when they die and decompose.

Daikon! "Daikon radish" can be up to a foot long and up to 3-4" thick. I have searched this topic to death because the spot where my kitchen garden will be has a sub layer of nearly solid clay; like, you could mold an ashtray out of it. I'll be ordering 3000 seeds for $8. The reviews complain it's more like 2000, lol, but that's still the best bargain I found. From what I hear, I'm supposed to plant the daikon all over, let it grow as long as possible, then chop & drop the greens and leave the daikon in the ground to decompose. This will add the biggest possible pockets of organic matter. I can't wait til spring to try it!

I'll just throw in that clay subsoil on a slope (which appears to be the case here) is often not totally consistent and evenly distributed like you would find in flat catchment basins, so it may be worth prospecting a ways across the slope in either direction with some deeper test holes or maybe just a rebar probe to see if you find a thinner area with different soil or bedrock below that's easier to reach for an infiltration 'drain' point.

Kim Wills wrote:

Mark Reynolds wrote:
I'd look at planting some deep rooted plants that CAN break up the compaction. Forage radish, possibly alfalfa, turnips. The radishes will also collect nutrients and make them available to other plants when they die and decompose.

Daikon! "Daikon radish" can be up to a foot long and up to 3-4" thick. I have searched this topic to death because the spot where my kitchen garden will be has a sub layer of nearly solid clay; like, you could mold an ashtray out of it. I'll be ordering 3000 seeds for $8. The reviews complain it's more like 2000, lol, but that's still the best bargain I found. From what I hear, I'm supposed to plant the daikon all over, let it grow as long as possible, then chop & drop the greens and leave the daikon in the ground to decompose. This will add the biggest possible pockets of organic matter. I can't wait til spring to try it!

Kim, as for your Daikon radish (that is the most commonly known one), go to a feed store and inquire about purchasing the radish seed. You'll buy it by the pound, not the number of seeds. 3,000 radish seeds sounds like highway robbery to me for $8.00!

I didn't find radish seed yet, but check out these numbers of seed per pound and the cost. You will quickly understand my reaction and what I mean by 'highway robbery'.

Here are my figures for this year.  K500 alfalfa, 227,000 seeds per lb., $2.58 dollars per lb., equals 87,984 seeds per dollar.  Climax timothy, 1,152,000 seeds per lb., $1.06 dollars per lb., equals 1,086,792 seeds per dollar.  Baraula orchardgrass, 416,000 seeds per lb., $2.44 dollars per lb., equals 170,492 seeds per dollar.  Seed seems less expensive now.

Another good seed source is Great Basin Seed.  They specialize in seeds for alkaline soils.  Some parts of Ca have alkaline soils.  

Another great source for seeds by the pound is Green Cover Seed.  They are out on the great plains somewhere, they have seeds for most every kind of soil.  And they can make cover crop blends.

Both have websites and are wonderful companies.

And back to clay soil.

You might want to research your clay enough to find out if you can flocculate it!  Clay particles can carry an electric charge.  Clays can be quite different from one another.  Not all clays will flocculate, but with some, it is like magic!  The slick dense slippery mass turns into something like cornmeal size pieces, cottage cheese only smaller.

Some annuals might be a good idea too, with fibrous roots.  When they die they leave their roots in the soil.  To go with the daikons.  

Saslo, consider installing a small gravel layer or drainage pipe at the base of the swale to guide excess water out more efficiently.

Welcome to our first time posters.  I'm happy you believe this online community will be able to provide suggestions of value and that you have something positive to contribute to the discussion.

If I understand your explanation correctly, I think this is a rather elegant design element.  Bravo.

As others have suggested, I think it makes sense to know what you have.  A simple jar test can confirm the clay/silt/sand proportions.  I think confirming your soil profile would also be valuable...perhaps you're not far away from a more permeable layer below in which case perforations through like a broadfork could accomplish may allow the water to seep.

As swales were explained to me, the goal is to slow water flow across the landscape, allowing it to infiltrate which creates a lens of water downstream of the soil.  That's why it's valuable to plant trees below or on the berm of a swale.

What's the water table like in your location?  Is it possible that it's high enough to prevent infiltration?  I wouldn't expect that as you show us images of a slope (wish I had some of those) so I wouldn't expect an intersection with the water table until lower down the landscape.

Depending on the timing of what you want to do, perhaps native grasses and forbs have a deep enough root system to have an impact - the berm could be planted to that (which could also have benefits for pollinators and create a swath of beauty and you could plant the desired trees later.  Here on the prairies, the native grasses can have very deep root systems getting down several meters (well beyond 10').

As noted, organic matter can be the solution for a large percentage of soil issues...it's just that it takes time to decompose for dead matter or to reach lower if we're talking about live roots in the soil.

Good luck and keep us posted as to how things go.

I, too, would try to widen the swale, and gentle the sloped edges to increase the square footage for infiltrating.

It looks like you've got a lot of shrubbery and trees around. Have you considered making biochar? (https://permies.com/f/190/biochar) I use biochar to help lighten my clay soil.

Planting a polyculture of whatever seeds you can get is good also. Yes, some plants may be more helpful than others, but I wouldn't fret if you can't get the best. Dandelions have a good tap-root, grow easily, and are great for your pollinators, as an example! (although I admit that I am partial to daikon radish!)

Here's what I did in a very clayey, poorly drained back yard recently....I made swales and berms or raised beds right next to each other, the yard was relatively flat so I oriented them north-south for light distribution. I started by digging out the swales and turning the sods upside down over the adjacent strip of undug ground, thus doubling the thickness of the topsoil layer...these became a set of raised beds.  I then filled the trenches with every imaginable free organic matter source...branches and sticks, leaves, paper and cardboard, wood chips, etc. Any weeds that were pulled or garden debris that was generated was simply thrown in all summer and fall.  Thereafter, every year I would shift the soil from one or more of the beds on top of the stuff in the adjacent swale, thus creating a sort of hugel-bed.  At the same time I would bury any half-finished compost, humanure compost, and anything else both useful and also needing sequestration for a few years.  The end result after several years is that the entire area consists of a set of raised beds with coarse organic matter under them, with the beds above background grade, but with ready access to moisture accumulating in the swales. Given the quick breakdown of organic matter in this climate this process could probably continue indefinitely.  In a climate like California, a policy like this also gets along very well with fire suppression, since one is continuously burying organic matter under the soil, rather than leaving it on top where it can burn.

I like all the above recommendations, but I would also add biochar to the mix along with all the organic material you can get.

Thank you all so much for the feedback and moral support

I've heeded some initial advice and made the swale wider and the slopes more gentle.

However, the next morning, one problem I'm already seeing is that the swale is naturally filling with water, either from gopher holes or is maybe percolating up? I don't know how deep our water table is, but our well goes down 300 ft so I don't think that's the problem. Also, the water that is pooling in the swale looks almost rusted.

I've attached a few more images of the project
1) Shows a better perspective of the drainage ditch and length of land I'll need to dig out to connect it to the swale (to start diverting some of the water)
2) A wider swale with slopier slides
3) A rusted spot on the side where I think water is coming out of? It all came overnight, and you can't easily visualize where the water is coming from.


A few other notes based on other comments:
1) Despite the trees, this is west facing and it will get ample sun in the summer/fall months.
2) I have a broad fork and use this to make the bottom of the swale more porous  and look for a different soil structure below this clay.

My next steps:
1) Need to ensure the berm is level and that the bottom of the swale is mostly level if not slightly angled so that the water carries to the furthest end.
2) Make the berm a bit more rounded so that it's easier to plant into .
3) Add a ton of organic matter into the base of the swale to start encouraging a transition away from the clay - perhaps Daikons!

Thanks again for all of your time and feedback!

Jr Saslo wrote:However, the next morning, one problem I'm already seeing is that the swale is naturally filling with water, either from gopher holes or is maybe percolating up? I don't know how deep our water table is, but our well goes down 300 ft so I don't think that's the problem. Also, the water that is pooling in the swale looks almost rusted.

We also have a very deep well. We have a drought much of the summer, but the winter is very wet and we have a "winter creek" that crosses our field. Areas of our lower field will have standing water on if for days following heavy rain, with a "winter water table" if that's what it would be called, within inches of the soil surface. One could think of our lower field as a flood plain for the winter creek in a sense.

We have been working hard in a number of ways to improve the quality of the soil, and the water seems to infiltrate better than it used to, judging by fewer large puddles which disappear faster than 10 years ago.

However, I'm not sure what would happen if I were to dig a trench nearer to the top of the slope. That soil is rockier and thinner for sure, and we don't tend to have standing water in "chicken holes" unless it's actively raining. What we don't know is how deeply that water is infiltrating, rather than running down the slope slightly underground.

So, reading what you've written, as a total amateur, I think the water in your swale is water that's travelling under the surface from up-slope of your swale. Trying reading up about Sepp Holzer's Spring Terrace: https://permies.com/t/32725/Sepp-Spring-Terrace and possibly: https://permies.com/t/32815/Mini-spring-swales

I think the idea of breaking up the clay to speed infiltration may be the right path, but hopefully someone with more experience in this field will speak up.

Jr,
I can’t see where the rusted spot is, but is there any chance it is an old pipe?

In SLO county we had a place with a water source … a developed spring on the other side of the road, the water was piped to a tank on top of the hill behind our house.  The house was built in about 1906.  The tank was so much higher than the road or the creek that the spring must have been up the canyon a ways.  There had to have been a pipe somewhere.  It is possible that at the time it was constructed it was all one property owner.  By the time we were there in the 70s the pipe probably crossed (under) several properties.  I have encountered similar situations through the years.

Have you dug back in to the rusty hole?

One of the gardening techniques I tend to use is making hills. Sometimes this is a "hilling up" like with potatoes, sometimes I flip the soil over in a round shape, at other times I bury food scraps, often all three. At the same time I dig a trench, which collects water to soak deep into the soil, and then deposit the soil uphill of that trench, as a means of gradual terracing. This leads toward a diverse, varied topography that resembles that of an old growth forest; water is soaked into the hillside, making the water more available to plants, and at the same time forming well drained beds for growing vegetables and trees (which may wick up water from lower levels of soil).

Maybe this would be useful? Especially if your plans are more food forest oriented, which sounds to be the case.

If you're looking to determine the source of the water, I'd consider creating some dams within your new gully and ideally drain each section, then see if you can isolate where water gets in or if it fills in all sections, it would imply it's coming from below generally from within the landscape.

Good luck.

It looks like you're making great progress!

Firstly, I would caution you against using mechanical methods on your soil when it's wet. Doing so will only further compact the soil and make your drainage issues worse. Clay and silt are especially susceptible to compaction.

Where I live, we have similar weather patterns to yours as far as winter rain and summer dry are concerned, except that it's wetter longer here. We also have mostly clay soils and lots of slopes, so I feel like I have some experience with what you are dealing with.

I am curious why you feel you need to drain the sloped area you are working on? What are you going to use it for? Are you planning on irrigating it in the summer?

And what is the history of that area? Has it been grassy for some time, exposed to the sun and rain with little to no organic material added to it?

The water in the swale must be coming from uphill. Water will naturally go downhil over time. It may seem like it's not draining, but it just might be. It could be that it's just not draining faster that it's getting filled up from the water coming from uphill.

Adding organic matter, and lots of it, always helps. The soil in the areas of our yard that have been lawn for some time has become compacted by the rain, turning it into hardpan. Sometimes it's so extensive that it's impossible to dig a hole in it. We've found that putting a thick layer of ground-up plant material on it, like arborist chips, season after season, has significantly improved the soil. When we have to plant where we haven't done that, we build a mound of soil (native is best) over the area and plant. Then we add a couple inches of compost and then mulch over that (being careful not to mulch near the trunk). All of the trees and shrubs we've planted like this have done really well.  When planting on a slope, another good trick we've found is to do the same thing but to add some logs or firewood to the downside of the slope to hold in the soil. All of these methods help both with drainage and with improving soil moisture in dryer periods.