While I keep hearing from authorities and forum dwellers alike that swales, roads, and other structures can be placed optimally on contour, I have seen little material on actually accurately following the contour. I have a few methods in mind, but I'm hoping that someone here will have a method that's easier than either.
1. Eyeball it. I anticipate that swales and roads don't need to be perfectly on contour, but just mostly on contour. This I can probably do with my own senses. The biggest downfall I see to this is that, because I'm working with limited rainfall, I won't be able to see immediately where the real mess-ups of contour are. While I don't mind a little extra work due to trial-and-error, I'd prefer to avoid it if possible.
2. Laser level. The other concept that I have in my mind is using a poor man's laser level, a carpenter's level with a laser pointer. This would be a two man job, with one person pointing the laser and the other marking the contour. I have a hard time justifying dropping $1k on a laser level that I'm only going to use a couple of times. Perhaps you've had success with a cheaper laser level? The video I've seen is this one:
Whether it's with the expensive of cheap version, I see this as being the most accurate of the bunch.
3. A-frame level. In my search for answers, I came across this method:
While this seems cheap and practical, I worry about incremental error. Is this a justifiable concern?
While it's tempting to eyeball it, I have found that eyeballs LIE! And failed earthworks can be pretty spectacular depending on slope and volume of water...
I've used a laser level (FUN!) but they are costly. The cheap and accurate alternatives are the A-frame (which you've already found) and the bunyip (or "bunny-yip" as a friend of mine likes to call it). Personally I'm very fond of the bunyip and find it very accurate. Plus, it easily goes around corners.
Here's how to make/use one with water harvesting guru, Brad Lancaster:
Subtropical desert (Köppen: BWh)
Elevation: 1090 ft Annual rainfall: 7"
Bunyip is probably the best method as well as having a cool factor of 100. It is important to know the exact contour and follow it as closely as possible so you won't have any "OMG the Dam just Broke" moments later on.
It also makes for a much more predictable water plume downhill from the swale. If you need a laser level just once or twice, some of the Rental places have them so that you don't have to make such a huge purchase for a once and done project.
I forgot to mention a tip for making it easier to get the air bubbles out: if you mix a few drops of dish washing detergent into the water you fill the tube with, the air bubbles will pop easier, of course any wetting agent will work but I like to keep things biodegradable as much as possible.
I admit I haven't done anything on contour yet. My main focus has been taking water from the road/drive and to do that it has to be off contour so it can be bled onto the property. I've been eye balling it and so far it's worked a dream for what I want. Being short on time, resources and help I may just continue as for the rest of the property. I would love to get a keyline plow though. Oh dreams! If I got that I'd do it on contour.
Have to give it up to the bunyip water level. Amazing tool.
I know the A-frame is the baseline tool most permie teachers train their students with, but I prefer the bunyip. We used one to find contour lines for three swales on our land and I also use it for any landscaping projects such as building retaining walls, laying pavers, etc. We have also learned that when we want to know how long a contour line is we simply ensure the clear tube is a specific length between stakes so we always know how far apart our contour pegs are. Count pegs and multiply by the distance you know is between your bunyip stakes and, voila! you have your linear distance.
The A-frame is certainly something we should all have the ability to build and use because you can make it from primitive objects around the landscape. But, if we have clear tubing available and the ability to graduate two stakes, then I like a bunyip level. Just my preference. You can cover more ground if you don't need a landscaping peg every five feet. We have our bunyip set for 20 feet and that has worked just fine for larger swales. I would want to shorten the distance for smaller swales or on land that was highly convoluted. They also make an easy tool to verify your earthworks as you're working along. Not everyone is an expert with an excavator or back hoe or front-end loader. With someone helping you do level checks, things can go better without much going back and correcting. A bunyip is perfect for this.
Regarding the eyeball method ... I know gross changes in elevation can be seen, but we're not talking about perceiving gross changes in elevation, but rather subtle changes. There's no way I'd be able to find contour or plow a keyline without some kind of tool defining the contour line or an off-contour line that changed only an inch every 50 feet. Maybe I'm blind, but there's no way I could do that.
When I made a water level, I added strong brewed tea to the water to improve the visibility of the readings.
I found that an easier method, requiring only one person, was to use my 4-foot carpenter's level. Three pieces of 2x2 lumber were cut (one 48" piece and two 8" pieces). An 8-inch "leg" piece was attached at right angles to each end of the 4' piece. The level was tied to the top of the 4' piece, so that it was raised above the ground while the legs at the ends of the level made contact with the ground. The leg ends could be pointed somewhat for more accuracy.
With a bag of pegs at my waist, I could quickly mark a contour line with that modified carpenter's level. It would take no more than 10 seconds to extend the line by 4' (at which rate I could cover about 25 feet per minute, working quickly by myself). The resulting contour line was marked every four feet.
Before using this setup, I checked that it would give the same reading when I switched the leg positions on the same two points on a hard surface (in other words turn the level 180 degrees and see if you get the same reading). Corrections could be made, if necessary, by lengthening one of the legs a little bit (easy to do if it's screwed together: just unscrew the leg a little until it's correct, then immobilize the joint with some tape or a wedge).
Different length carpenter's levels could be used, and combined with longer pieces of lumber, if desired (with longer lengths probably requiring two people).
I built my water-level with a 5 gallon bucket on one end, clear tubing on the other, and garden hose in the middle. That allows me to use it without a helper and to use as short or as long of lengths of garden hose as I want.