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When NOT to use a swale

 
Posts: 18
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Is there any guidance on when NOT to use swales?

My situation:
1) I live on 6-acres of forest, on an 8% slope hillside.
2) My soil is 3in of tree-droppings (loam), + 3in of black soil, + all the glacial till you could ever want (sand, rock, & clay)

My problem:
I have water running down the hill, through the loam and soil layer (not over-surface), ending-up on my driveway. In the winter, that water freezes and turns my driveway into an ice-rink. Also, this water is running towards my house, and my foundation drainage system is having to work to keep my foundation dry. I would like to divert the under-surface water flow.


Question:
1) Do swales divert under-surface water flow? Or do they only divert over-surface flows?
2) When making a swale, do I need to dig & displace the loam & soil to make a trench, or can I just build-up more soil (drop a tree, and add soil or strawbales) to do the same job?

I looked, but I didn’t see my question in any other forum.

Thank you all!

-Scott
 
master pollinator
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I'm not an expert, having no experience with large-scale swales, only small hand-dug ones, so the following is opinions based on that limited experience.

1)  Swales divert both surface water and underground water, depending on the depth of the swale.
2)  I have built structures like you are talking about and I like them if the grade is swallow enough that they are stable.  If you drop a tree along the contour, you can leave some downhill branches sticking out to help hold the tree, but at some point, those branches are going to rot and you don't want to lose the tree down your slope.  Straw bales make great soil, but again, I wouldn't put them anywhere that is steep enough to have a blow out.  If you aren't trying to catch all the water, and just want to divert it, blowouts aren't as big a concern because no real pressure builds up against the berm.  With only 6 inches of soil to dig, I would do both, making your structure and then piling the soil on it.  

Is it possible to post some pictures so the scale you are working with is evident?
 
master pollinator
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A swale would help because it is essentially a ditch at high water times. In your case you would not put it on contour, but just run it to daylight as it is called, or in other words, pitched downhill.

I think you might be getting a lot more surface water than you think though. It depends on where you live, but if it ends up on your driveway and freezes, then I would think your soil is freezing too, and so it is running under the melting snow, but over the frozen soil. In the summer of course, you would not see this; it would migrate through the soil (I have the same type of soil as you).

But I could be wrong.

But water does not run up hill, so if you build a swale/diversion ditch to capture the water as it emerges at the edge of the driveway, or before our house, it does not matter how the water arrives, it will take the path of least resistance and travel down the swale/drainage ditch.

What you do with it then, is up to you; divert it to a small pond, or just let it keep going if you do not have drought problems. If the ditch ends up with gobs of water, then we can talk about some rock check dams and stuff then.
 
Scott Billups
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Hello All,

Thanks for your feedback.

Definition clarification:
I believe a berm is when I add mound of material (drop a tree, add strawbales, and pile-on some soil. No digging of a ditch/trench.
A swale is when I dig a channel/ditch/trench, and make a pile of soil on the downhill-side, to collect surface-running water, stop it, and let it sink in to the soil.

Do berms (adding material only) diver sub-surface water movement in the soil?




Here is a sketch of my situation:
Water is flowing down a gentle slope.
All water is sub-surface (water movement is in the soil).
The water pools on my driveway, freezes in the Winter, and makes the driveway hazardous.
The water also flows right at my house (basement), and I'd like to divert that.


What I want to do is drop a few trees, pile-up some straw bales, and add some covering dirt (make a mound, potential Huglemound)
Let the mound divert the water away from my driveway, and away from my house (basement).

Do berms (adding material only) diver sub-surface water movement in the soil?



The photos show how the water has flowed on to my driveway (in the rocks), and frozen. The flow is sufficient to cover the rocks and make it slippery.
Filename: Driveway-Water-Berm-or-Swale.pdf
File size: 38 Kbytes
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Posts: 31
Location: Port Angeles, WA, United States
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Hello! My reply is based upon years of observing water move through the forest as a member of crews building and maintaining trails through the forest. Water management is the biggest factor in maintaining trails so they last a long time and also don't damage the environment. A single truth comes to mind:

1) Water flows away from wherever it is, and there is no stopping it. You can slow it down, you can divert it to a different path, you can make it run uphill for a bit,  you can hold it and make it stop for a while, but it WILL flow, and overall, it flows down the gradient. If the soil can hold more water than the system is currently giving it, then by slowing it down and holding it, the water will leave the surface for a while, and then (unless taken up by plants), it will continue subsurface on its merry way downhill until it comes to a break -such as the one your road provides- where it pours out to the surface. If the subsoil is already saturated, the water remains on the surface, and will travel downhill.

(Strategies for delaying water's journey through a landscape (keylining, swales, ponds) are, in my mind, strategies for attempting to heal a desertified area, produce crops and/or store water for other uses during times when less water is entering the system. From the original post, I don't think that is what is being asked here-correct me if I am wrong).

It looks as though you have a native forest, or at least, a functioning forest. Forests provide an essential service to the world by stewarding water as it moves through the landscape. On the one hand, the presence of trees raises the water table by virtue of their roots actively siphoning up water through their roots (this siphon is powered by moisture transpiring through the needles and leaves). Much simplified, but this is how trees and plants release water and oxygen back into the atmosphere, and also pull water up through the soil profile. You might think, hey, if I cut down some trees, then the water table will drop, and my subsurface problem will go away.

But of course, nothing ever 'goes away,' although the consequences of our actions may move far enough away from us that we don't notice them... Remove enough trees quickly enough and the water table will drop to a level where plants cannot reach it, and you can create a desert. But more to the situation in this post, remove enough trees and you can cause more surface water, higher water speeds, and more erosion. Because trees, and the associated small soil organisms and larger plants that live among them, also take up some surface water, and slow the flow downhill.  After removing trees, the water will still move downhill through your landscape, perhaps at a higher speed and in greater volume than before.

I think in your situation, I would consider a more direct approach. If damage is being done to the house foundation, consider a curtain trench drain on the uphill side to protect the house. To find out how deep to dig it in order to divert the subsurface water, many techniques suggest that you dig a hole during a period when it hasn't rained for a few days so you know that no surface water is flowing. As you dig, you will come to a depth where the water starts to seep from the sides of the hole: this is where the subsurface water is running, and you will have to dig your trench below that level in order to catch the water and divert it from your home. (If you dig this hole in the dry season, this weeping will be lower in the soil profile, and you won't get a good picture of what is happening during the wet time of year.) You may need to install drain tile, or pumps, or piping. The downhill end of this trench or pipe or pump will send water...wherever you design it to go. Maybe you have a suitable area for a series of swales for gardening or growing fruit trees, or for a pond? Or a cistern to hold water for your needs during the dry season? Or maybe you just need to move it downslope? Whatever you decide, keep in mind that you always want to slow down the movement of water, never make it run more quickly.

As for the road, I don't know at what angle it runs along the slope, but if you are able, then dig a curtain trench on the uphill side of the road, and bring it to a crossing on the road where you have constructed a broad, gentle dip. After you have guided the water to cross the road gently in a single location of your choosing, you may then resume the water's path on the other side of your road by directing it to a swale, a creek, a pond...whatever your designed pupose may be.

As for other appoaches, it may be that your property has places farther uphill well-suited for swales or ponds where you can temporarily hold water while it soaks deeper into the soil. If you are wanting to create places for planting, then piling debris into mounds could get you the dry space your plants may need. But if all you want is to keep your driveway from flooding and your home from being water-damaged, you will be better served to research methods of moving the water away from those structures and getting it to move downhill via a different pathway.

Finally, it may be that the builders of your house and road did not place them in the most favorable location in regards to water movement. If this is the case, you will need to spend more time, money and effort to mitigate the water damage caused by not designing the property to work with the inexorable movement of water through your land. An unfortunate, inherited situation, and one faced by many.

In my experience, simply dropping trees on the ground and piling debris on them will not stop the water from moving. It could have the opposite effect of causing the water to pool and spread and then flood your road and home even more. I have deep reservations about clearing away trees unless there is a plan to build a food forest, or a home, or some other planned tool to help the land serve us better....my opinion, of course...

There are many threads on permies and elsewhere on building drains to protect structures and roads...hope this was helpful, and good luck!
 
pollinator
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Location: La Mesa, Cundinamarca, Colombia
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That clarifies things a bit, especially the drawing in the PDF.

No, what you add on top of the soil doesn't generally influence subsurface water flows.

Your driveway seems to be below grade, with no ditch on both sides, and no grading of the driveway itself. That causes water to collect on the surface of your driveway. For a solution I would fix these things first, dig a ditch on both sides of the driveway, grade the driveway itself so water flows into these ditches, and then continue these ditches downslope, to a point where the water can drain away passively, by itself.

If that is not enough, then you can dig diversion swales, or diversion ditches, which are gently sloped downward in a direction where you want water to flow to, to get rid of (some of the) subsoil water, and all of the above soil runoff if there is any. You can dig these where you indicate that you could put berms of material. However, I don't think you'll need these if you make the improvements to your driveway. Plus, if your subsurface water level is that high, you most certainly don't need more water infiltrating into the soil.

Good luck!
 
carla beemer
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Location: Port Angeles, WA, United States
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And I neglected to add: if your land is wet enough, you might be able to plant some water-loving species along the road (willows, native dogwoods, nine-bark, others...). When these plants are actively growing, they can remove an enormous amount of water from the soil. In my experience, this is really helpful during the spring and fall seasons. But during the winter, the wettest and fully dormant season (in my home the pacific northwest), they won't, and so you still would have to manage runoff via more mechanical means...
 
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As a road builder, I can say you have been given good advise.
If cash flow is an issue, I would suggest the following steps
- create a drain on the uphill side of the driveway, as suggested by Rene, and take that water right away from where it can move towards your house.
- If possible allow it to go across the road in a controlled manner as described by Carla.
- Create a contour drain or small swale above the house to catch any water in that area and divert it as far away as you can.
Both those actions could be done with a ditcher tool on a tractor.
Its a spinning blade that throws soil to one side and creates a semi circular drain in the ground.
 
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