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Help please - Bunyip / Water level and marking contour lines for swales

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posted 7 years ago

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Howdy folks,

It's my first time doing earthworks and tools available are only a u-tube / water level (Bunyip as they call it in australia).

100% understand that the bottom of the swale ditch must be level.

Spillways need to be well planned and offset to ensurethe berm is not breached

My question is :

While mapping the contour points, if we are unable to find 2 points 100% the same, do we abandon the exercise and start afresh?

Let's say we could not find a point within the radius/length of the u-tube, so the closest was say 0.5" different, will it drastically affect the way the swale performs?

e.g.

Point A - 28"

Point B - 28"

Point C - 28"

Point D - 27.5"

Point E - 28"

I understand that if there is a variation at a point then it carries over to the corresponding points and over a distance it is totally off contour....however please refer back to the Points A to E listed above.... that we are trying to stick to the same point through out with only a slight variation in between.

Thanks

Miles Flansburg

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posted 7 years ago

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Howdy A Tee welcome to permies.
When I am marking out a contour for a swale, I do not worry to much about getting within an inch or two on the first pass. I know that my shovel or machine will be digging out soil and placing it up on a berm .This is not going to end up being within a half inch, and maybe not even within a half a foot. I know that I will have to come back and redo the top of the berm to find my final level.
As the swale will be used to collect and spread water I feel that the top of the berm being level is more important than the bottom of the swale. The top will determine where the water overflows. Where it overflows naturally becomes the spillways. If I need more soil to make the berms more level I can always take more from the bottom of the swale even though this may leave small, deeper , ponds than what may be elsewhere all along the swale.

In your example, If you are getting point E from point D and then points F and G from D than everything from D onward will be lower and possibly lower still as you continue?

To compensate you may have to make two more points, C and a half, and C and 3/4 to get 28" on either side of point D ? And get point E from point C and 3/4 ?

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Dan Grubbs

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First off, I have to ask the question I should have asked myself before I started a couple of earthworks projects ... can I design a different solution and achieve nearly the same results without earthworks. If not, then I consider earthworks. If I can get close with different design, then I'll avoid the earthworks. I know it's not as fun, but doing surgery should follow other solutions, right?

That out of the way ... I agree with Miles in that your tolerances are probably less critical than you may think. I use a bunyip level for establishing contours and I prefer them to lasers. What laser can go around a corner or go through an object? What A-frame level can span 15-20 feet and miss a big tractor tire rut? The bunyip is my preferred tool.

Comment 1 - Unless you're really really good with a backhoe (track hoe, excavator), your 1/2-inch variance may not matter when you're roughing in your swale. As Miles said, you can groom things to better tolerances if you think you need that exactness. I personally found that I don't worry about a 1/2-inch variance when the measurement from the bottom of the ditch to the top of the berm is at least 24 inches. I don't see a structural issue if there is a wavering of even an inch of the top of the berm. I know for a fact the berm soil won't settle evenly over time and the contour of the top of the berm will vary more than an inch. That's my experience, at least.

Comment 2 - If I want to ensure that I don't continue a linear error and magnify it down to the end of the contour line, I do what I call back points -- a kind of back checking. My bunyips are normally made with a clear hose of 25 feet (about 8 meters). If I measure back points, I'll start with my back pole at the first steak (A), pull my front pole out about half the distance of the tube and steak there (B), then pull the front pole out the full distance and steak (C). Then set the back level pole at B and check C with the front pole and then pull out front pole to full distance and stake (D). Repeat this process as a double-check way to ensure your contour line is accurate. I have done this, but don't feel it's really necessary because of grooming the berm/ditch to refine things.

Maybe I'm all washed up and more experienced people can refute what I describe. I'm open to that.

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Andy Tee

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posted 7 years ago

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Miles Flansburg wrote:Howdy A Tee welcome to permies. When I am marking out a contour for a swale, I do not worry to much about getting within an inch or two on the first pass. I know that my shovel or machine will be digging out soil and placing it up on a berm . This is not going to end up being within a half inch, and maybe not even within a half a foot. I know that I will have to come back and redo the top of the berm to find my final level./

Welcome! Understood about the initial work and not bothering about dressing too much.

Miles Flansburg wrote:As the swale will be used to collect and spread water I feel that the top of the berm being level is more important than the bottom of the swale.

I think they are equally important as an uneven tilt or dead spots in the bottom of the swale will cause water to collect in certain area's over others. Totally agree on the berm uniformity though.

Miles Flansburg wrote:The top will determine where the water overflows. Where it overflows naturally becomes the spillways. If I need more soil to make the berms more level I can always take more from the bottom of the swale even though this may leave small, deeper , ponds than what may be elsewhere all along the swale.

Agreed... also there is a lot of mixed terminology as some people refer to the actually mound/ridge as berm... whereas others (I assume you and I) are referring to the lip between the ditch and the mound as berm?

Miles Flansburg wrote:In your example, If you are getting point E from point D and then points F and G from D than everything from D onward will be lower and possibly lower still as you continue?

To compensate you may have to make two more points, C and a half, and C and 3/4 to get 28" on either side of point D ? And get point E from point C and 3/4 ?

Yes the issue is that there will be a linear error for all forward points, so I've sort of been back tracking every now and then. Thanks so much for your suggestions and I will be trying out your tip!

Andy Tee

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posted 7 years ago

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Dan Grubbs wrote:First off, I have to ask the question I should have asked myself before I started a couple of earthworks projects ... can I design a different solution and achieve nearly the same results without earthworks. If not, then I consider earthworks. If I can get close with different design, then I'll avoid the earthworks. I know it's not as fun, but doing surgery should follow other solutions, right?

Absolutely right. Contour row/hedge planting without advanced earthworks also yields good results in some places. I think "We are Swales" is not the look we should be going for. To put this in context, this is dryland with about 600mm rain that is sometimes erratic and can be one day yielding 10-15% of that and then nothing for months. The soil is red, ferrous soil, rich in minerals but 0 organic matter and does not retain moisture. These swales will become treelines but also produce an abundance of weeds which is free organic matter to then build soil. There's probably like a dozen trees on 3 hectares... so not a lot!

Dan Grubbs wrote:That out of the way ... I agree with Miles in that your tolerances are probably less critical than you may think. I use a bunyip level for establishing contours and I prefer them to lasers. What laser can go around a corner or go through an object? What A-frame level can span 15-20 feet and miss a big tractor tire rut? The bunyip is my preferred tool.

Yep, bunyip trumps because it can go through bushes and tree's! Though on this property a laser would have been easy as it's pretty much barren. The other reason to use the bunyip is that we want to show the local villages that it is something within their reach. Everyones used a water level before. Positive results are usually attributed to illogical things (e.g. technology of laser, money power etc). With the simple approach there's not a lot to turn around and point it... we hope it will spark interest in a few years when there's visible progress in the landscape due to regeneration efforts.

Dan Grubbs wrote:
Comment 1 - Unless you're really really good with a backhoe (track hoe, excavator), your 1/2-inch variance may not matter when you're roughing in your swale. As Miles said, you can groom things to better tolerances if you think you need that exactness. I personally found that I don't worry about a 1/2-inch variance when the measurement from the bottom of the ditch to the top of the berm is at least 24 inches. I don't see a structural issue if there is a wavering of even an inch of the top of the berm. I know for a fact the berm soil won't settle evenly over time and the contour of the top of the berm will vary more than an inch. That's my experience, at least.

The bottom of the ditch to the top of the mound is definitely over 24".

Dan Grubbs wrote:Comment 2 - If I want to ensure that I don't continue a linear error and magnify it down to the end of the contour line, I do what I call back points -- a kind of back checking. My bunyips are normally made with a clear hose of 25 feet (about 8 meters). If I measure back points, I'll start with my back pole at the first steak (A), pull my front pole out about half the distance of the tube and steak there (B), then pull the front pole out the full distance and steak (C). Then set the back level pole at B and check C with the front pole and then pull out front pole to full distance and stake (D). Repeat this process as a double-check way to ensure your contour line is accurate. I have done this, but don't feel it's really necessary because of grooming the berm/ditch to refine things.

I've got a 10 metre clear tube and I started using the back points approach after 2-3 swales were done because a) The initial partner I had was goofing off and resulted in some obvious errors when I walked the land b) backtracking always helped to get a longer more consistent contour line across the landscape than something where a point was off and having a swale 1/2/ the length of what would be possible.

Thanks for your responses. I did a trial run of a couple of swales on 1 acre and definitely learned. Your responses are reassuring. One thing is that we are working with excavator operators that are only used to cutting straight trenches in a landscape. First operator flat out refused as the machines here are all on tyres and no tilt buckets... managed to get another operator that understood the concept and with me watching like a hawk making sure he sticks to points we cut some nice curvy lines. There were a few moments when I wasn't watching and we ended up with some semi straight lines but no biggie, they are still going to sink the water coming off the side of the road just above and outside the boundary of the property.

Ben Zumeta

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posted 7 years ago

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Welcome to permits Andy, sounds like a good project. I also made the mistake about confusing the importance of level in the bottom and top of swales. Then I saw a video where Bill Mollison explicitly says

“the top of your berm must be perfectly level, the bottom of the swale can have dips and crests, what matters is that it’s permeable.”

This echoes the advice you’ve gotten about the berm ridge/primary spillway. I have built small French drain “swales” with 4” weeping tile, and in that case saw it as worthwhile to level the bottom of my ditch/swale so the pipe laid flat and help spread the water as it entered the ditch, which I then covered with woody debris and chips to use as a path between hugel beds.

This is all just my opinion based on a flawed memory

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Andy Tee

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Ben Zumeta wrote:Welcome to permits Andy, sounds like a good project.

Thanks mate. Def exciting as it will be experimental and also a demonstration of what can be achieved with simple planning and low investment.

Ben Zumeta wrote:I also made the mistake about confusing the importance of level in the bottom and top of swales. Then I saw a video where Bill Mollison explicitly says

“the top of your berm must be perfectly level, the bottom of the swale can have dips and crests, what matters is that it’s permeable.”

Got to love Bill! It is indeed very permeable. This soil will not hold any moisture and is free draining. Which is why these swales are important to kickstart biomass production and get organic matter onto the soil to create that sponge effect.

Ben Zumeta wrote:This echoes the advice you’ve gotten about the berm ridge/primary spillway.

The spillway provisions have been done quite thoughtfully. We have to finish the swale off by hand due to the rocky nature of the site. Primary and secondary differ slightly and below berm to give that insurance. These initial swales have also been oversized to see how much they fill and how quickly the water infiltrates.

Ben Zumeta wrote:I have built small French drain “swales” with 4” weeping tile, and in that case saw it as worthwhile to level the bottom of my ditch/swale so the pipe laid flat and help spread the water as it entered the ditch, which I then covered with woody debris and chips to use as a path between hugel beds.

I learned about french drains, at the university of youtube... very clever. What you described seems like a landscaping beauty and stacked functions with the paths and hugel bed. Classic work, hope to do stuff like this !

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