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swale: significance of "on contour"?  RSS feed

 
Michael Vormwald
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I watched a lot of geoff lawton's stuff on permaculture and he keeps referring to swales on contour. I get the purpose of slowing water movement downhill and redirecting as necessary but not sure I see the significance of the contour?

Thoughts?
 
Cj Sloane
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If it's on contour, it's perpendicular to how the water wants to flow. If it's not on contour, then it's not level and the water will flow down the slope.

My first swale was not exactly on contour but it mostly worked anyway.

Now, I use an A-frame because I might as well do it right.

It is worth noting the proponents of key-line think slightly off contour is better.
 
Jennifer Wadsworth
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A few things about swales: they are dug to the same depth, this way all areas along the swale get equal amounts of water (you don't get dry spots or waterlogged spots), swales are great pacifiers of water flow, slowing it and sinking it. "On contour" simply ensures that the swales fill up evenly and allows you to choose the optimal site(s) for level sill overflows. In other words, the water doesn't get to choose where it overflows - you do.

If you were to randomly put in swales across your property without taking into consideration contour, some parts might form deep ponds (where the land is lower) while other parts might overflow immediately because they are on slightly higher land. This could cause the berm to give way and create downslope problems and increasing water velocity and sediment load and the likelihood of severe damage.

Don't know if that helps - let me know.

BTW - there is some confusion over the term "swale". The way it's used in permaculture is as described above, level ditches on contour with a downhill berm. In engineering and hydrology a "swale" is a diversion earthwork (off contour) that is used to move or divert water away from an area.
 
Michael Vormwald
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Ah...so the contour is only if the slope changes. For example, if I was on top of a hill that had a north facing slope, but also sloped around to the east, the swale would contour around to stay perpendicular to the changing slope. On the other hand, if I simply had a north facing slope (and I do btw), I might have a swale that simply trenched east-west.

Hmm here's an interesting one...I just made the raised bed/mounds for my vegetable garden. This is a very slight north facing slope with the beds running east to west. So my walk ways are sortof all mini swales...
Prolly what I should do is create a 'real swale' on the south (uphill) end of the garden to better hydrate the garden
2014-05-17-18.25.07-w.jpg
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Jennifer Wadsworth
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Michael Vormwald wrote:Ah...so the contour is only if the slope changes. For example, if I was on top of a hill that had a north facing slope, but also sloped around to the east, the swale would contour around to stay perpendicular to the changing slope. On the other hand, if I simply had a north facing slope (and I do btw), I might have a swale that simply trenched east-west.


Contour is simply land of equal height. Even flatlands have some kind of contour but the contour lines will be much more spread out than on a slope. The steeper the slope, the closer together the contour lines will be.



While your swales will most likely run east and west on a north facing slope, you still have to find the land that is all at the same height - contour lines are not equally spaced or concentric but depend on the lay of your land. You'll need some kind of tool to measure this - an A-frame, a bunyip, a transit level or a laser level. Simply putting them in east and west without taking into consideration contour (land of equal height) could cause significant problems (as mentioned in my post above).

Michael Vormwald wrote:Hmm here's an interesting one...I just made the raised bed/mounds for my vegetable garden. This is a very slight north facing slope with the beds running east to west. So my walk ways are sortof all mini swales...
Prolly what I should do is create a 'real swale' on the south (uphill) end of the garden to better hydrate the garden


That would probably work to help slow water coming down the slope and stop the uppermost bed(s) from eroding over time.
 
Burra Maluca
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"On contour" means "perfectly level."

If the swale is perfectly level, the water will sit in the swale and be gradually absorbed into the land.

If the swale is 'off contour', which means 'not level', it's basically a drain. The water will flow to the low end instead of being absorbed.

This video only takes a few seconds to watch, but explains contours very well for people who difficulty imagining how they work.

 
Cj Sloane
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Michael Vormwald wrote:So my walk ways are sortof all mini swales...


The walkways should be mini-swales, catching the water so it doesn't flow away from the garden.
 
Michael Vormwald
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I get it. My challenge was that most of my land (a mere 3 acres) up on a hill is primarily a straight north facing slope without a round hill like curvature. As such any swale would be east/west with no curvature.
Now it would seem that a swale is principally effective at catching and holding surface run off. So it would seem that a well draining soil would see little benefit or less benefit than a poor draining soil.


 
Michael Vormwald
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Cj Verde wrote:
Michael Vormwald wrote:So my walk ways are sortof all mini swales...


The walkways should be mini-swales, catching the water so it doesn't flow away from the garden.


Actually, my garden is pretty much at the top of the hill here and I think the slope is not really great enough to merit a swale...just as I think a swale has no value on flat land.
 
Cj Sloane
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Michael Vormwald wrote:
Actually, my garden is pretty much at the top of the hill here and I think the slope is not really great enough to merit a swale...just as I think a swale has no value on flat land.


Except that the top of a hill would be the driest spot around. According to Geoff, swales do have value on flat land, he tends to show pics of the Netherlands with deepish swales bordering fields. If your up for an experiment, do one of the paths between your beds extra deep and observe it after a downpour.
 
Jennifer Wadsworth
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Michael Vormwald wrote:Actually, my garden is pretty much at the top of the hill here and I think the slope is not really great enough to merit a swale...just as I think a swale has no value on flat land.


I think it's challenging to get one's head around all the different types of earthworks that are out there. And all the different ways to slow and harvest water.

Swales on flat land take the form of infiltration basins - without them, hot, dry areas around the world (like Phoenix, where I am) would not be revegetated. In fact, earthworks on flat lands have the potential to hold more water than swales down a slope. I belong to a group that builds dozens of these every year.





 
Jennifer Wadsworth
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This blog does a nice job of describing and illustrating swales: http://www.tenthacrefarm.com/2014/02/using-swales-in-the-landscape-part-2/
 
Michael Vormwald
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Jennifer Wadsworth wrote:This blog does a nice job of describing and illustrating swales: http://www.tenthacrefarm.com/2014/02/using-swales-in-the-landscape-part-2/


Exactly as I have stated... a swale is used on slopes to slow water that would otherwise run off and be lost and allow it to perk into the soil.
 
Jennifer Wadsworth
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Yep - I think we're all agreed on what swales do (permaculture definition).

I think your original question was about why swales should be "on contour".

I guess what myself and other folks are trying to say is that being "on contour" is critical for swales to function properly and it takes some form of measuring device to find out where "land of exactly the same height" (the definition of contour) falls on your property. Going around your site with an a-frame level, bunyip or any other kind of level is called "pegging" - you stick pegs in all the areas of equal height and then you know where to dig your swale - usually to a depth of at least 8-12" and often more.

Here's a video of a guy measuring and marking out where his contour lines are:



Jen - Certified Water Harvester, Watershed Management Group, Phoenix
 
Dan Grubbs
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Though your property may appear to be a nice even north-facing slope, do not trust your eyes as to its "even-ness". I used a bunyip water level to survey out five swales on a long slope on my property and I was amazed at how far off our vision is when it comes to the lay of the land. I won't trust my eyes when it comes to topography without confirmation by some other means. I wouldn't do any earthworks based on visual information alone. What looked like a nice even slope for me had curved and "wiggly" contour lines that I simply could not have detected by looking at the land from any perspective. My bunyip level cost me all of $6 to make, and I use a 20-foot clear tube so I can get about 15 feet between my pegs (survey stakes). Surveying a contour line was fun for my wife and me to do and it doesn't take long.

I also wouldn't underestimate how much water does flow downhill through the topsoil even in "well-drained soil". I am amazed at how much water our swales catch that now doesn't run off the property through the topsoil and into a neighbor's creek. And we have topsoil that does drain pretty well.

 
Kelly Smith
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Michael Vormwald wrote:
Exactly as I have stated... a swale is used on slopes to slow water that would otherwise run off and be lost and allow it to perk into the soil.


because water ALWAYS finds its own level, and a swale on contour IS level, the swale IS what holds water that would otherwise be lost and allows it to soak in.

 
Jen Shrock
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On "flat" land (all land has some drop), swale contours can be made with a little artistic license since the variance in depth to get it level might only be an inch or two. In sloped areas, swales should follow contour.

I, personally, am employing the slightly mounded mulch technique instead of an actual swale until my soil builds a better texture. I have a lot of clay in my soil and I get a significant amount of precipitation so I feel that is best to wait until the soil gets into better condition for holding water before installing swales. Right now I don't have problems with water laying on my land (my lot is relatively "flat"). Due to the amount of rain that I receive and the general flatness of my land, I might never build a swale and simply rely on the slight elevation of growing areas that I have installed on my property. The couple of inches of difference in height is more than enough for me to slow water on my "flat" property.

Each permaculture technique needs evaluated for each site because not all techniques will be applicable to all sites. Often techniques can be tweaked for multiple purposes and not just the original one intended. For example, with swales, they could technically also be ever so slightly sloped so that their water collection mechanism is actually used to help fill ponds and then serve as overflow areas for the pond before releasing their water into the landscape. Depending on what the land is to be used for, too, swales might not be appropriate or, at least, in significant quantities. I know that I am stating what is "permie standard knowledge", but the swale berms are tree growing sytems and not crop farming systems.
 
Michael Vormwald
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I understand contour - thank-you. My follow-up was that a trench on relatively flat land is no more a swale than a handful of twigs covered with soil is a hugelkulture.
I guess the confusion comes when there's rain and there's water in the trench, but like a mud puddle, that's simply water that would have been saturated in the soil that was removed. The value is capturing water that would otherwise run off and be lost down hill...

The swale dug into a slope prevents the rapid run off that would occur during a heavy rain by slowing the water down, giving it time to seep into the ground where it has been confined. Unless your thinking miniature sky pond, this of course is unnecessary on relatively flat land as it happens naturally without earthworks.
I watched a 2 part video of a fellow that dug swale after swale 25 yards apart on land with very little slope. A good concept gone bad and severely scaring his land with potential hazards to people, equipment and livestock.

Don't get me wrong, I appreciate the swale concept but feel it belongs on slopes and any good thing done to excess may be bad.

Footnote: I saw another video where on a north facing slope a fellow put a swale in front of an east-west hugelkulture bed - what a great idea - one I just might try.
Hugelkulture Swale

JUST MY OPINION...YOURS MAY VARY
 
Jamie Wallace
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Great information Jennifer...thanks for posting.
 
Richard Gorny
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As Geoff Lawton repeats a number of times in his online PDC course and videos, swales are tree growing systems and mostly they should serve that purpose. I have asked him about on contour tolerance and the answer was that they should be perfectly leveled to maximize water soaking, but also nutrient gathering and density, as well as diversty of plants growing on berms. The more off contour swale is, the less water is being harvested, the less fertility is being captured and the less diversity of life along the swale develops. Saying that Geoff also admitted, that a swale which is a bit off contour is certainly better than nothing and that it is up to you what you choose and what exact purpose your swales are suppose to serve.
 
Michael Vormwald
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There's little point in flogging a dead (horse) thread, but just to clarify, my initial question was because contour typically means CURVE and although a rounded hillside would tend to require a contoured swale to maintain a level bottom, this is not always the case. I have a section of land with a north facing slope that would require a swale with very little (if any) actual contour (curve) in order to maintain a level bottom.
 
Jamie Wallace
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Michael it is my understanding that 'contour' is a representation of a given elevation. So your quite right a contour on a slope could run dead straight. It is all about elevation, the curves are generally a bonus.
contour.jpg
[Thumbnail for contour.jpg]
contour map example
 
Cj Sloane
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Michael Vormwald wrote: I have a section of land with a north facing slope that would require a swale with very little (if any) actual contour (curve) in order to maintain a level bottom.


Michael, can you post a satellite pic showing the contour? Also, how big or how many swales were you thinking?
 
Matt Reed
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I couldn't find a definition of contour that meant curve, so maybe that's the misunderstanding.
 
Jamie Wallace
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Contours represent the same elevation on a map or on the ground:
From Wikipedia

Contour may refer to:

an outline or silhouette
a contour line on a contour map, or the corresponding line on the ground or sea bed
Contour (linguistics), a phonetic sound
Pitch contour (music), a melody shape
Contour (camera system), a 3D digital camera system
Equal-loudness contour, a measure of sound pressure
Service contour, a coverage area in US broadcasting
Jama Contour is a software package, produced by Jama Software
Contour provided by Cox Communications, which displays custom, recommended programming based on the users viewing history, as well as the capability to record 6 shows at once, and store 1,000 standard definition shows. [1]
 
Richard Gorny
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Michael, perhaps reading this will provide a clear answer to your question:

http://permaculture-and-sanity.com/pcarticles/permaculture-earthworks-and-swales.php
 
Michael Vormwald
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WEBSTER:
con·tour noun \ˈkän-ˌtu̇r\
: the outline or outer edge of something

Full Definition of CONTOUR

1
: an outline especially of a curving or irregular figure : shape; also : the line representing this outline

Nowhere do I find contour defined as level.

But as I already wrote - I GET IT or what is intended.
 
Cj Sloane
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The sound quality isn't great, but here's Geoff talking about how Level Passifies Water. And, at least in terms of Permaculture, level and contour are exactly the same thing.



And a big takeaway is that water always flows at right angle to contour (unless something is in the way)
 
Jamie Wallace
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Micheal...I deal with contour maps in my work all the time.
It is great that you get it....contours on a map are lines/elevations which share a common value.
The attached image shows a 4' wide bio intensive planting on contour, in this case it is straight.
IMG_5286.JPG
[Thumbnail for IMG_5286.JPG]
bio intensive bed on contour
 
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