Submerged dams better than swales?

Cut a slice of ground out of a slight sloped area, fill it with clay. You have a dam below grade. This will slow down the seepage,  raise the water table, and force the water around the edges of the "dam" which will cover a broader area for a longer time.

This should avoid blowouts also.

2 things led to this idea.

1. I believe my swales are more of a depth guage than a water retainer. I can get 1" of rain and it fills up, but is empty the next day. If i get 12" of rain (it has happened twice), the swale stays full for weeks. The first week it is full, like water sheeting out the down hill side of the berm. As weeks pass,  the level drops "slowly". The only water the swale retained was the first filling. After that, it's was showing how far below the surface the water was still seeping. Had the swale not been there, the water would still be flowing underground. So the swale is actually doing a lousy job, collecting 100's of gallons instead of thousands of potential gallons. This is my opinion and would like opinions if this is correct.

2.  Best video for anyone contemplating a pond. Watch Zach Weiss presentation on Paul Wheatons 2017 PDC course. Its on Paul's youtube page and is free! When he builds a pond, he looks for the clay layer that the seepage is flowing on. His dam is dug down to this layer. and has a clay core. NO OTHER PART OF THE POND IS SEALED ! brilliant. He is catching the seepage,  everything up hill is greener. You can see it in the pictures. Without the dam into this clay layer,  you have a hole in the ground. I think he called it a basin. I have a basin. The seepage is going under my pond. My pond is filled by runoff only and needs to be sealed to be effective. If it caught the seepage, the thousands of gallons instead of the hundreds.........

Combine both thoughts and it seems viable.

I think it depends on what you're using them for, and what you seek to accomplish.

If water infiltration into the aquifer is the ultimate goal, then the swales are doing their job just allowing water to spread laterally across the slopes before sheeting down, then letting it sink in to the ground.

I think slowing the water infiltration so that you can use it on your property is a valid consideration, but I don't think a dam structure is a good way to describe what you're thinking, and I will tell you why I think so.

Dams stop water. You don't want to cause a build-up of subsurface water, or unless you know the geology and hydrology of your land in excruciating detail, you're running the risk of encouraging mudslides.

I could definitely see the utility in adding some clay to overly fast-draining swales, such that perhaps the percolation into the subsoil is not only slowed, but also carries some clay particulates down with it, to carry the water-retention lower in the soil strata.

But honestly, my approach in amending swales that just suck water down so fast there's no distribution across the land, and no opportunity to use it, would probably include not only powdered bentonite clay (or local clay that I would dry and sift, if it's a possibility), but also probably gypsum grit and dust, and some wood chips and duff.

Your submerged clay dam approach might avoid blowouts, but in a heavy rain event, it would probably saturate the soil layers behind it, gathering weight that would easily push the less-saturated soil downhill right out of the way.

That would be my concern, anyways. The observation, though, that infiltration sometimes happens too fast in these water harvesting features to be locally useful is a good one. I like the clay basin idea for the pond.

-CK

Thanks for the reply Chris. I hope others will join in. It's gonna take "this won't work cause....." to get to the pros and cons.

As far as mudslides, this technique is already used by Weiss and Sepp. I am just proposing to make the dam less tall, invisible.

The pros of this is:
No loss of farming or ranching land.
The ability to dig a shallow well thats subsurface clean,  where pond water is not, in an area where that would not be possible.
The ability to  provide clean gravity fed water down stream via a monk pipe (submerged) or a spring casing (submerged). Either option can be added when slice is cut for dam. The equipment is there to add it. Both of these are covered in Zachs presentation. Brilliant man! Its worh noting that my clay dam is burried, thus stronger than a pond dam or berm, both of which can blow out.

On the water dropping and adding clay in  a swale. I'm not saying its a problem. Its actually good. Sinking in 3 days eliminates mosquitos so eliminates other methods to remedy the mosquitos . My point was that it is a depth gauge of the seepage level. The only water "collected" happened immediately, all subsequent water is the result of underground seepage, which would occur whether there was a swale or not.

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Okay. So you'd use selective sealing to both keep water in the soil upswale, and allow for enough drainage out of that soil so it doesn't go travelling or cause anaerobic issues.

It kind of reminds me of the subsurface pond idea, where a reservoir is stacked with boulders, and topped with discrete layers of ever-finer grades of pebble, until soil and sod can be laid atop it.

As long as the well site is well-chosen, the proposed method has the advantage of using the soil strata as a very conventional sand filtration setup, and depending on the location of the swale on the grade, you could have a storage capacity far exceeding the volume of almost any constructed pond.

I think this might be a very useful tool for manipulating hydrology, and one I think I will probably keep in my permaculture toolshed, should the need arise.

-CK

wayne fajkus wrote:

1. I believe my swales are more of a depth guage than a water retainer. I can get 1" of rain and it fills up, but is empty the next day. If i get 12" of rain (it has happened twice), the swale stays full for weeks. The first week it is full, like water sheeting out the down hill side of the berm. As weeks pass,  the level drops "slowly". The only water the swale retained was the first filling.

I guess I'm a little confused about the cause of your unhappiness with your swales.  Swales aren't meant to retain water - they are meant to slow it and allow it to soak in.  So by your description, your swales are working correctly.  After 1" of rain the soil is still dry so the swale soaks quickly.  After 12" of rain the soil is saturated so the swale soaks slowly.  

Tyler Ludens wrote:

wayne fajkus wrote:

1. I believe my swales are more of a depth guage than a water retainer. I can get 1" of rain and it fills up, but is empty the next day. If i get 12" of rain (it has happened twice), the swale stays full for weeks. The first week it is full, like water sheeting out the down hill side of the berm. As weeks pass,  the level drops "slowly". The only water the swale retained was the first filling.

I guess I'm a little confused about the cause of your unhappiness with your swales.  Swales aren't meant to retain water - they are meant to slow it and allow it to soak in.  So by your description, your swales are working correctly.  After 1" of rain the soil is still dry so the swale soaks quickly.  After 12" of rain the soil is saturated so the swale soaks slowly.  

It does its job but is it? The swale is a 100 gallon solution to a million gallon problem(,or a million gallon potential). We are capturing and slow releasing such a small part of the whole. The surface runoff is small compared to whats happening underground. The underground is happening for days(or weeks), the surface runoff happens for hours(or days). Its obvious when you see Zachs presentation.  Green and lushness upstream of his pond. Thats from damming the seepage.  

This seepage dam is holding and releasing like a swale, just much bigger. Where a swale provides water down stream, the dam provides it upstream and downstream and around the side.  

The earthworks no longer have to be on the highest part of the property. It can now be in the middle, or down low

Ok, I'm still confused!  If you have that much run-off not being captured by the swales, you need more swales or big infiltration basins, like the one we have on our place.  Not saying your idea is incorrect, just I'm not really seeing the need for a different kind of construction.

I hear you, but that doesn't make this the solution for all problems otherwise fixed by earthworks, like it might be taken the way you just phrased it.

I could totally see modifying my construction of swales this way. I mean, if you were to construct a swale and make an addition of clay into it in otherwise too-well-draining soil, would that not still accomplish the submerged dam effect you describe?

But I have to say, I am with you in principle. It really appeals to me to be able to use that water first, and longer, than would otherwise be possible. And as it's a slow seep idea, not a dam-it-up-and-hoard-it scheme, the water eventually gets downhill, and if it spends time on well-stewarded land, it won't leave any worse for wear.

-CK

The runoff is being collected, its seepage thats not being collected. No matter how big your swales are, there's probably a thousand times more water seeping under the swale. Im proposing that seepage be collected underground. Dammed, slowed down.  We are collecting 100 gallons when we could be collecting millions.

With all the emphasis we see on pigs for sealing a pond, it turns out Sepp doesn't seal a pond. He dams up the seepage.  This is assuming Zach got this method from Sepp. The vid was so eye opening. We in the permies world focus on the pig. The pig is not needed. Damming the seepage is THE key. Its huge. Its not talked about here.  You can interchange between ponds and swales easily, so use whichever context makes sense to you. If you can envision this with a pond, use a pond as your thought provoker. Its not a different type of construction if this is the method for Zach and Sepp. Its the preferred method. And we have missed it in favor of pigs.

If I am understanding correctly you are having two problems.

1.  1inch rain events overwhelms your swale/tiny dam and you something get 6x even 12x that.
2.  You would like to see your swale/tiny dam/ditch hold unto the water better.

So you are kinda on the right track in that your swale/tiny shallow dam is not doing enough.
You could make the swales deeper so3ft deep vs just 1ft deep, you can also make them 9ft wide.
A 3ft by 9ft swale can hold alot more water than a 1ft by 1ft swale.

Now you can also put in more swales on your property. If your acreage only have 10 swales double it by putting in another set of swales between the existing ones.


And now for your last problem. You want to see the soil storing more water during rain even, you can plant daikon radishes to increase soil aeration, increase the amount on worms and other soil life so that water soaks in more.

But maybe what you are really saying is that I have a desire to build some ponds. I think that you should go for it.  

wayne fajkus wrote: Im proposing that seepage be collected underground.

Swales and infiltration basins store the water underground.  That is their purpose.  The idea is that eventually the water will end up in the aquifer, at least in shallow aquifers like some we have here in Central Texas.  Probably not in "fossil aquifers" which are too deep to be affected much.

I think your idea would work if you want to make a bog or swamp.  If you seal the soil with clay, the water can't infiltrate and will remain "perched" shallowly under the surface. In wet weather that underground pond will fill up and the surface of the soil will remain soggy until dry conditions return.  That soggy condition may result in anaerobic soil.

Unless I am completely misunderstanding what you want to construct!

S Bengi wrote:

Now you can also put in more swales on your property. If your acreage only have 10 swales double it by putting in another set of swales between the existing ones.

Yesterday I participated in a water management webinar featuring Ben Falk, who said he has a mile of swales and ponds on his 10 acres!


http://www.wholesystemsdesign.com/where-we-are

Here is how zach builds a water retention pond. A pond that fills and stays full based on underground seepage, not just surface runoff like a pig sealed or clay/plastic lined pond would have.

He starts by digging a trench directly below the dam site.  He digs til he finds the right clay. 40%. This clay layer is the seepage river underground. All water infiltrates until it hits this layer, then travels down the slope on this layer.

He fills this trench with 40% clay and continues upward to build the dam. He then covers the clay with soil on both sides to keep the clay acclimated.

Does this better describe how he is damming up the seepage?

If that makes sense then lets look at my example. The infiltration from a swale (i" think") is directly related to the initial runoff that fills it. Thats what you captured and infiltrated.

For the next week, 6 weeks, 12 weeks (depending on amount of rain) the seepage happens. You may not see it cause eventually the swale is dry. You can only see the depth of this seepage until your swale is dry, cause its a depth gauge the day after it rains. Call it a temporary high water table if you want.

So what you collected is a mere puny total of what nature is doing. If you could capture or slow that,  you have more water. Way more water. This is why Zachs ponds are full with no seal in the pond except for the dam, and everyone else is getting ducks and pigs to poop in their pond, hoping for a miracle cure.

So the swale does nothing except extend the infiltration at the end of the cycle. Think of a cake pan set down in the rain.  It holds a quart. If 1 gallon of rain fills it, only 1 quart is stored. Same with a swale. The rest overflows away.

Luckily the release happens as the seepage or saturation from the rain event dwindles. This means the swale EXTENDED the infiltration by ruffly 1 day(even if its 6 weeks later when it happens). It couldnt release it cause the water table was as high as the swale level. As the table dropped, the water was released. Or it continually released and got refilled from above on a 1:1 ratio. The original amount stored stayed the same.

So a swale extends the length of time water infiltrates.  It does it towards the end, and only an amount equal to its volume.

But i could be talking bullshit. This is all theory.

This is the result of Zachs dam method. You get a green area uphill of the pond, where normally the greening is  downhill. Its evident in real life in his video.

In addition to uphill, you get greening around the sides of the dam. This is important cause you now split the seepage into two rivers, working their way around both sides of the dam. You have severely increased the width of area getting the benefit.

In response to just build more swales, one "pro" i mentioned is more available grazing or farming land.

I guess one "con" would be not permie artistic viduals like you get with swales and berms. If you had this seepage dam with no swale or  pond, the aerial would just show green. No standing water, no swamps, just green in a patch of brown.

Here is the video i keep referring to. I consider it the best video i have seen in regards to water retention.

Watch "Zach Weiss presentation: elemental ecology" on YouTube
https://youtu.be/05vqJaH5uS4

Hi Wayne,

Can you tell us specifically what is growing on the slope above and below the swales and what you want to do with that land as part of your overall design? I ask this because what your goals are for this ground in your overall design can impact your earthworks mainframe. Without knowing your specific context, I try to help people think a bit more holistically when dealing with slope in their designs and not so quickly jump to swales as an immediate solution to something they're facing -- in this case, runoff.

When dealing with runoff, here's something to add to the total holistic equation. It's astounding how much rain you can percolate by keeping living plants in the soil. I have completely stopped haying pasture. This allows the grasses and forbs grow fully and seasonally die out or get trampled under hoof in a rotational mob grazing approach. Dense grasses and forbs provide a lot of protection by reducing the kinetic energy of falling and moving water while increasing the organic material in the soil. As silly as it sounds, if you can stop or break apart the drops that fall from the sky and not directly hit the surface, you create a mist within the above-soil plant zone. An omni-directional mist caused from splashing rain drops now broken into many smaller droplets with reduced velocity means reduced downslope flow. If many plants are growing out of the ground, they cause obstruction of flow of the water that does make it to the surface. The more live plants, dying plants, ground litter you have at the surface, the more water will be arrested and allowed to penetrate the surface. Then, as we all know, increased organic matter within the soil allows for increased percolation capabilities. Keeping tall grasses also helps reduce soil temperature because it shades the ground and provides thatch when it dies off. Soil temps that rise above 80F can really hinder soil biota. Cooler soil temperatures usually mean more robust root structure due to more plant-available nutrients due to increase soil biota population.

For people feeding animals and their pasture is not providing enough forage ... with hay prices where they are at now, it's likely to be a net gain to bring bales onto the property than it is to have your pastures hayed or grazed fully down which causes a host of bad things to happen, not the least of which is increased run off.

Just something to think about.

Dan, thanks for joining in. I don't have a specific problem, just a question thats been lingering a couple of years. I originally posted it here with little response.
https://permies.com/t/62490/swale

After watching Zach, i ,think i got my answer and so happy about it i started a thread.

The questions:
Is the swale as limited as i expressed,  that it ruffly extends the rain by one day and only by the amount of the swales volume. Not a multiple of it.

Would a zach style dam, set underground and invisible, increase the total amount of water by tens if not hundreds times more. It sends water uphill! Not really but the effect is such.

If so, is it worth discussing or implementing. More grazing and farmimg land. The ability to tap into a homemade spring. No blowouts of swales. The surface runoff seems so small compared to whats going on under ground. This clay river bed is taking this water off the property unless you have the bottom land also.

What am i missing?

Some grass roots will go down 10ft+ so grasses that are higher uphill will still have root access to the pond water.
Capillary action can also extend the even more.
Also if the pond is active it will have a higher nutrient load (harvested bugs that turned into fish manure)
and that will make the grasses above to the side and below it greener.


We also have to realize that the pond(deep swale) is not just catching the runoff that is directly above it.
The rest of the swale is also acting like a "gutter" and "funneling" all the water from catchment area to the pond.
And the water that the swale is funneling is not just water just for say 3hrs during a  "3hr" rain event.
But all the seepage/infiltration from above that is  happening days later after the rain even.
And if you have another rain event during that week, then the swale is pretty much constantly funneling water to the pond.

Ok, I think I see what you're talking about now, wayne.  The deep cut with the clay soil is the "key" of the dam - a key is necessary for most dams to hold water.  So what you're talking about (I think) is just making the key without the above-ground part of the dam (the dam wall), which will hold water in the soil uphill of the key.

I think it might be an interesting experiment to see what might happen if you make a dam key without a dam wall.  I think you will likely get that damp area with lusher grass.  In a wet climate it might get soggy.  The ground below the key (underground dam) may be somewhat drier than the surrounding soil, because it will not be getting seepage from uphill.

If i knew what "key" was, that would have saved some time.  Lol. Sorry for the struggles to describe this.

Benji, are you agreeing that the swale just contributes by one volume fill per rain event,  but there's other things it does? Like redirecting water. I'm not understanding.

As a side note,  I'm not trying to bash swales. I'm trying to get an understanding. But i think its not helping as much as we think. I did walk down hill from my swale. 15 paces from the swale down is green. After that its brown. Based on this, maybe a second swale would green up the next 15 paces.

Here's the swale that can drain in a day, or drain in 6 weeks depending on rainfall event. Tyler probably remembers the 12"+ rainfall event in Texas.

This event made me a permaculture genius. My dry creek bed flowed for several weeks. Thought that i did something  that had long lasting impact on my geography. But in reality, i did nothing that could support that much change. Then i start thinking how much the swale helped. What did it do? My conclusion is it held one full volume during the first hour of rain.  After that it did nothing. And the actual infiltration happened weeks later. The impact may have been that the creek flowed for 6 weeks and 1 day vs 6 weeks if i didnt have the swales.  If i had a mile of swales, maybe it added 2 additional days.

wayne, where does the overflow from your swale go?   Could it be the swale needs to be larger to infiltrate more water?  If the swale overflows right away, it isn't going to be able to infiltrate much water.  Rain harvesting earthworks are generally sized for the large events - so if you get a lot of rain all at once (like we sometimes do here) swales and basins need to be large or more numerous.  Otherwise the water just runs off the land.


Apparently it can take years for the water table to be recharged by these structures, so we aren't likely to see dramatic changes any time soon, like springs appearing downhill or a constantly running creek (what I dream about!)

Tyler, you are missing a point on my theory. The fact that the swale is full means water is seeping below it. Which means the water table is temporarily raised. So the swale is a gauge. Like a gas gauge in your car. Its showing the height of the water table. If thats true. How is the water infiltrating? Its going at a 1:1 ratio. 1 gallon is leaving but another gallon is coming in. Thats why it stays full. The swale is a gauge.

If this is true, then can you imagine the sheer volume of water flowing in and out? If you put math to it, it could be hundreds or thousands times more water than the swale holds. Which makes the swale trivial compared to whats happening under it.

If there's hundreds time more water flowing,  and a key can slow that down, hold some,  spread some out, now you are doing something.

I dont agree wirh the swampy issues.  I could agree that you can create a natural wicking bed with the key. Maybe not 12 months at a time. Think about that in Texas for annuals. Youve tested the gabe brown thing with little success(throw out seeds do nothing else). You can appreciate the impact this can have.

Tyler Ludens wrote:


Apparently it can take years for the water table to be recharged by these structures, so we aren't likely to see dramatic changes any time soon, like springs appearing downhill or a constantly running creek (what I dream about!)

.

My well is more than 300ft deep. I understand. Zach wasnt talking about the water table. He talked about a clay layer that seepage rides over. If this has a key you will make your own water table higher up. This higher table would be available for a shallow well, gravity fed clean water for drinking or irrigation. Where my swale flowed for 6 weeks after 12" of rain, can we conclude that for another 6 weeks it flowed 3 ft lower, then anothet 6 weeks at 6 ft lower. That water can be stored with the key. Who knows, 1 rain may feed it for months.

Im reading between the lines, but when you look at zachs pond. The fact that the pond stays full and is only sealed at the dam. He might say this seepage provides 12 months out of the year. Surface runoff is not doing it. Its minor compared to seepage. Im pretty sure he stated that. This is not something i made up. He tutored under Sepp. Hard to discredit this phenomena.

Water is supposed to seep below the swale.  That's why the swale mound is not compacted.  The water is moving downhill and yes, eventually it will move off your property completely.  That's why water harvesting earthworks are started at the top of the property, because water (usually) moves downhill.  I think keyline design  moves water uphill but I'm still a little foggy on the whole keyline design idea.   Moving water uphill is what I think you are trying to accomplish with the dam-key-without-a-dam-wall idea?  I think it might work if your soil has enough organic matter to absorb a lot of water.  Otherwise I think you will get a soggy spot right uphill of the key, because water always tries to be level. You need an absorbent soil to wick the water uphill of the key.

I'd sure like to see it in action!  I hope you will be able to do an experiment on your place.

I want to clarify that I am not trying to discredit the idea - I'm trying to understand it.  I think it is a really interesting idea and I'd like to see it!

I have a place in port lavaca. Its 20ft from the canal edge. I can dig holes anywhere on the property and theres water 1 to 2 ft below the surface. I think it varies based on the tide. A four ft deep hole will have 3 ft of water. Yet i can walk over it, drive over it, etc. Thats why im not concerned about soggy.  The water can flow over and around the key. If the key was 12" below grade water can seep over. Temporary soggy is common anyway.  I dont think this would cause permanence.

Ok, I see what you're saying now.  I missed the part about the key being below grade.  Convinced!

Thanks for being patient with me.

Does a swale slow the movement of groundwater by creating an area that is more saturated than the surrounding area? I think it does and here is my reasoning.

The water holding capacity of soil is determined by the amount of space between all the individual particles. This space also determines the rate of flow through the soil.

A swale is essentially a void space which would hold more water than soil taking up the same volume. It would also take less energy for the groundwater to fill the void space of the swale than to fill the space between the soil particles.

My thought is that this would slow the flow of groundwater and essentially create a "traffic jam" backing up groundwater behind the swale and slowing the overall flow uphill of the swale.

Downhill of the swale the rate of flow should return to essentially normal which would be why a series of swales would be more effective than just one. Even if the amount of surface water is fairly minimal after the first.

My main point is that I think this reduction of the flow rate of the groundwater is a benefit of a swale in addition to its ability to intercept surface flow.

In not trying to argue against the underground dam idea - I think it is a great tool to add to the toolbox. I just think swales are doing more than was described above.

I appreciate the response.  Its kind of two different issues. What happens with swales, and is the underground dam viable.

One thing i can do. Next time the swale is full i can drill a post hole 6 ft below the swale. Since it wasn't filled by the flow, it would show if there is a temporary water table. And see if it falls at the same rate as the swale. Not sure if i can drill one on the side for the same reason. If the side doesnt have water and the lower hole does,  the swale could be the reason the water is in the lower hole. If they both hold water but the side dries first, we should be getting the amount of time the swale actually extended the water infiltration.

Any speculations on what will happen?

I think it depends on the soil on the particular site.  My soil doesn't have that clay layer - it is underlain with perforated limestone, so it drains evenly and wouldn't have that temporary water table.  For the same reason, the underground dam might not work here on my place.  It would get temporarily soggy uphill of the dam, but then drain quickly just like our big basin does.