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Swales on heavy clay soil?

 
gardener
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Location: Olympia, WA - Zone 8a/b
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Hello all,

I'm getting ready to start putting in water features on my property. Currently, I'm thinking about a series of ponds along a seasonal stream that flows through the middle of my property with swales on the hills along the stream and also swales from the ponds that would drain into a lower swale that would bring the water back "up" the property in order to greatly increase the distance the water would flow. Overall, I like the idea but I'm concerned with the possibility of the hillside sliding due to the water being captured by the swales. Since most of my soil is heavy clay it tends to be mostly saturated already through the fall, winter and spring months. I dug a test hole on the top of one of the hills and it had standing water for the whole winter until I filled it back in. When I dug it I could watch water flowing out of the edges into the hole. Recently, I dug a hole to plant a tree on the southeast side of the property and when I got about a foot down I hit standing water - this is in an area that is a fair bit (8 to 10ft) above the wetland area of my property and on a slight slope.

In regards to the soils on my property - there is about 10-15 feet of mostly clay with some sand/gravel towards the bottom. Below that layer is a naturally compacted impermeable layer (15 to 25ft thick based on well logs) of sand and gravel (used to be the base of a large glacial lake). My thoughts is that for most of the fall/spring and all of the winter my soils are fully saturated because of the clay sitting on top of the impermeable layer. Since the soil is already saturated for a big chunk of the year any swales are likely to just have standing water in them for a fair bit of time.

So is my burning question for you all. If the soil remains saturated for the winter and a fair bit of the spring and fall are swales still a good idea?

I see swales as being a great fit for capturing any late spring and early summer rains that might come and that could help keep the land hydrated but if the soils are saturated for most of the fall/winter/spring seasons already I'm not sure if I would get much of a benefit from installing swales. I don't want to do work that would not provide any real benefit and I also don't want to do work that might cause problems (landslides).

Now I could just treat the swales as ponds for most of the wet part of the year. This could have the nice benefit of helping to warm my land in the winter and providing habitat for amphibians and other wildlife. We have a large amount of slugs so if I can increase the amphibian and garter snake population that could really help me with the slug problem. Standing water would also help bring in wild ducks which would also help with the slugs. So on that note I think the swales acting as ponds would not be a big issue. But I'm still concerned about causing landslides if I have water sitting on the hillside while the soil is completely saturated.

So what I see as my options are this:
- Install a series of swales on the uplands and ponds along the seasonal stream. The swales would act as seasonal ponds. This would create a very dynamic environment and would result in a lot of wildlife habitat but may have landslide issues. This would also help capture the late or early rains in late spring / early summer and late summer / early fall.

- Install the ponds along the seasonal stream and use terraces, and/or berms to enhance the uplands. I think this would involve more work and has the potential to be more expensive depending on how I went about creating the berms. Should minimize landslide issues while still creating wildlife habitat. But this does not give me the option to bring water from the seasonal stream to the uplands. Less overall water retention but potentially minimizes the negative impacts of the first option.

- Install just the ponds along the seasonal stream. Would still hold water and create wildlife habitat but it would have limited benefits to the uplands of my property.

- Do a hybrid of the first two options. Use some swales on the lower parts of the uplands and have these connected to the ponds and the seasonal stream and then also install terraces and/or berms on the higher/steeper uplands to provide benefits to these areas while minimizing the potential negative impacts.

So what do you all think? I'm leaning towards the hybrid option but I'm still a little nervous using swales because of the reasons I mentioned early. I would love to hear what you all think!

Thanks all!

PS: See the attached pic of my property outlined in red. The yellow dots show my test hole (west side of my property) and where I dug the hole for a tree (southeast side) that had standing water after about a foot. Other picture is an old Google street view from 2011 looking at the path of the seasonal stream that I marked in blue.
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Overview of the property
wildridefarm_streetview.PNG
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2011 Google street view
 
Posts: 59
Location: Canada
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Hard for me to tell what is going on there from just pictures. It almost looks like the property is basically 2 sides of a ravine and you may have large amounts of water moving under the surface through that area because of the size of the catchment area?

We have heavy clay on our property and a fair bit of slope but I highly doubt we have that type of water under the soil.  Also figuring out our earth works probably to install them next year. I will be digging some test holes in different locations  probably 6+ feet deep just so see what's down there other then clay.
 
Daron Williams
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Matthew Lewis wrote:Hard for me to tell what is going on there from just pictures. It almost looks like the property is basically 2 sides of a ravine and you may have large amounts of water moving under the surface through that area because of the size of the catchment area?

We have heavy clay on our property and a fair bit of slope but I highly doubt we have that type of water under the soil.  Also figuring out our earth works probably to install them next year. I will be digging some test holes in different locations  probably 6+ feet deep just so see what's down there other then clay.



Ya, the ravine goes through most of the property. There is a decent catchment area that all feeds into the property. Even the top of the sides of the ravines stay wet on the surface during the winter months and are still wet - though we are having a record wet spring.

My understanding of swales is that they are supposed to slow water down moving through the land and collect it on contour so that it can then settle out through the landscape. In my case I think the swales would act as ponds for all of the winter and a decent amount of the fall and spring. This would mean that the water would not be settling out since the water would have no where to go due to the surrounding soil already being saturated. But during dry times of the year the swales could help make sure that any rain event is captured and held on the land.

I'm leaning towards using swales as side channels to the stream. Essentially, a swale would leave an upper pond on contour. This way the water would spread out across the slope and then spill over at the end of the swale. This spillway would then connect to a lower swale that would have its spillway back as close to the original pond as possible. This would add a lot of travel time to the water in the seasonal stream and could help keep the property hydrated. This stream is seasonal but it is fed by a large catchment area that has been developed enough that a fair bit of water is channeled into this stream. The issue of course is that this system of swales would also just act like a pond for a large portion of the year.

Really I'm just stuck on the issue that on my property the swales would stay full for about 5 months or so (Nov, Dec, Jan, Feb, Mar) depending on how much rain we get. Assume that I'm correct in this analysis - would you all still install swales in this situation? I can see arguments for swales and against the swales. I'm also thinking about climate change and long term water issues - but in my area that is predicted to mean wetter winters and drier summers so I'm not sure if swales are the best option for my place even when taking climate change into account.
 
master pollinator
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I am thinking you will not benefit much from swales.

Swales are an excellent way of retaining and slowing water that is lost, especially in sheeting action across the land. I have this issue because I live on a big hill and water moves off this hill, through gravely loam and thus quickly, so I install swales, but Paul Wheaton does not...because...well it is not an issue he has.

I don't think you do either. You have dug test holes and confirmed this.

Like everything it has its challenges, but to me it does not sound like swales is part of the overall plan for your farm...and that is perfectly okay. Just because it is a permicultural practice does not mean it has to be done on every farm. You can save the time and effort you would have spent installing swales and put it into a lofty effort that does overcome a challenge your land has.
 
Matthew Lewis
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With the amount for water that moves through your property maybe you can make a series of ponds instead of swales. Ponds higher up could be used as Gravity feed irrigation if you ever need it. They are also great for biodiversity and increase the value of the land.
 
pollinator
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I am definitely not a swale expert... But looking to your contour map makes me think those hillsides are too steep for swales.  Putting swales on steep hills can cause some pretty horrific damage... Ask me how I know!  Terracing is a more stable alternative.  And if your property is already saturated, there isn't much advantage to holding more water there.
 
Daron Williams
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Thanks all for the feedback - ya, I have been leaning away from swales and I appreciate you all confirming that not using swales seems like the best option in this particular situation. There is one area on my property that is not steep and is adjacent to a dirt road with a fair bit of runoff that I think I will put in at least one swale but it is very different than the rest of my property. One or two swales in this area will help me control the runoff from the road and should improve the area a fair bit. Though the soils are still saturated in this area for a fair bit of the year so it will be more an exercise in controlling the runoff and ponding that already happens in this area. The contour lines in the first picture are a bit off in this area of the property - fill material from the construction of the dirt road was pushed in this area and it was also flattened a bit but it still has a slight slope running north towards the wetland area.

At this point I think I'm going to start with ponds along the seasonal stream to help retain water and create more diverse habitat. I really want to increase the population of garter snakes and frogs on my property to help minimize the number of slugs. I have a lot of slugs currently! Overtime, I may do some terraces on the hills but I think these might just be small circular ones that will be focused around specific core fruit trees. I might place rocks on the backside of these terraces to also act as heat traps - this would be on a south/southwest slope.

I also have some deer issues and I'm thinking about trying to address this issue and some potential water issues at the same time by constructing parallel hedgerows about 3 or 4ft apart and about 5ft high and 5ft wide each with the occasional small tree thrown in. I want to keep them fairly low so they don't shade out the land behind them. Based on some discussions with local experts and some online research it seems like deer will not want to jump into such a small space despite the fairly low plant height. I also figured that placing hedgerows on contour when possible would also help control any surface water runoff but in a way that would not cause the issues that swales could. The outer hedgerow where the deer could reach it would be mostly native plants that can resist or at least deal with deer browse. The inner hedgerow would be mostly edible berries and such that would not be very deer resistant. These hedgerows would provide a great crop and would be designed to funnel deer away from my more intensive production areas towards my zone 4/5 areas and some open fields that my neighbors have. Hopefully, this would also help with my water issues and provide a fair amount of chop and drop material to help with water retention in addition to a good harvest. Anyways, not exactly an earthworks topic so I will resist talking about it more in here!

Thanks again all and I appreciate the advice!
 
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I don't mean to throw a wrench in the gears, but I put swales in heavy clay, and they do fine. They are slightly off contour, so they drain. They do turn into ponds sometimes, but it hasn't seemed to be an issue yet. Definitely oversize them if you do install any.
IMG_20160718_161532.jpg
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chad Christopher
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This a very early picture. Since this has been taken, they have smoothed themselves out, and have become incredibly lush. I was also surprised how quickly the soil structure grew. I will post a current picture, if I ever get the time
 
pollinator
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In the middle ages up to the 19th century this kind of situation was used to build series of ponds. Those were used to grow fish (karp and such) and/or acted as a kind of water 'battery' for water mills. The water was used to drive the weel when waterlevels were low.

Swales have secondary purposes such as stopping erosion and sediment movement over your terrain.
 
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Study Keyline contour concepts. Its an aussie practise that may help you.

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I do swales in clay slopes up to about 12% grade and haven't had any issues.

That said, the more I play with swales the less I am sold on them. They are kinda large disturbances and they create access issues. They certainly have benefits but are not appropriate for every place.

I might recommend looking into Keyline for water distribution and soil building though planting (esp grasses) for water retention.
 
gardener
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This is an old thread --- it's nice to see it brought back to life.

Something that no one is mentioning is that a swale does more than just water catchment.  They also are a soil-building strategy.  Because a swale stays wet longer and provide an indentation in the land where biomass can accumulate, the bottom of a swale often has much richer soil than the land around it.  Humus builds up much quicker there, which increases not only the permeability of the soil but the sponge-like retention of water.  It sounds counter-intuititive, but swales (over the long haul) increase water infiltration.

Clay is wonderful stuff.  It's highly fertile and the negatively charged particles "grab onto" N, K, and P, as it washes through the soil profile.  But you've got to have carbon to make it fertile and to make it permeable for water infiltration.  A swale helps tremendously with that process.

You may wish to just try something small --- just 8" deep or so --- just the depth and width of a shovel.  Dig that on contour and see what happens over the next two years.  Is the soil at the bottom of the swale getting richer?  I dig little "micro swales" like this and notice that they quickly fill up with leaves and other bio-mass, particularly at this time of year.  It doesn't have to be a massive earthwork in order to capture some of the benefits.

 
John C Daley
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I have very hard clay in places, denuded by overgrazing or horses in the past.
I have found If I simply run a ripper through, with one or two passes sometimes and leave that disturbed soil, it starts a process of improvement. Slowly.
But if I did nothing, there is no improvement.
The ripping fractures the harder and compacted sold, and allows some air and water to penetrate, which is the 1st step on the improvement path.
 
pollinator
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Hi Daron,

Hope things are going well with you.

I just wanted to address a few points.

An approach you might want to consider is to lay woody debris on contour as you would swales. If things roll, maybe stake them in place with a bit of branch or whatever, or make a disturbance for them to sit in, on contour, where you'd otherwise perhaps consider swales. These will act as sediment traps. You can seed them with whatever pioneer species you want, or just let things happen. Eventually, sediment and duff will catch uphill of your traps, creating lines of soil on contour across your slopes. Sufficient root networks will actually serve to stabilise the slopes you're worrying about, and as Marco mentioned, the workings of root systems down in the soil will eventually increase water infiltration, driving down through that impermeable compacted layer you mentioned.

The strategy mentioned above can easily be done as you walk your property without as much effort as digging swales, even tiny ones. You'd effectively be rearranging the soil surface to help your hydrology terrace the sloped areas you're working with, and then the root zones spreading down and out from the sediment traps will help your excess water infiltrate down through your clay and into the aquifer. And any organic matter that you drop or that ends up on the soil because of your actions will simply help fuel the soil-building process.

-CK
 
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Great to be here with you all. This is lovely
 
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Daron,

How big are your swales?
 
Daron Williams
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At this point I decided to hold off on the swales in part due to the concerns I had and others mentioned. As of today I can walk around the area where I thought about installing swales and see standing water and hear a squish sound as I walk on it. It stays that way all winter for the most part.

I'm going to eventually go with the suggestion made earlier by Chris and just place woody debris on contour. I will also be building some garden beds on contour in a relatively flat area on the top of the slope.

But this project got put on hold due to some other priorities that came up but I will move forward with the garden beds hopefully next fall. The woody debri swales will need to wait longer until I get some other stuff done.
 
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