3.3.18. Measuring Slope

Modern surveyors use very expensive and sophisticated equipment to measure slope and find contours. We dont’ need that level of sophistication and can make our own tools to measure slope, using ancient techniques that have been used to build massive ancient structures. We’re sharing three ways to measure slope that cost almost nothing (or maybe nothing if you have the equipment).

Water or Bunyip Level

Brad Lancaster has created a nice video on how to make a water level, or Bunyip level as it is also called. This works on the principle that water will always find its level - a lake, for instance, is perfectly horizontal.

How to make a Bunyip level (water level): https://www.youtube.com/watch?v=pRjNA0DZZb4

How to measure a berm with a Bunyip level: https://www.youtube.com/watch?v=xNnFknvSaMc

Short version: https://www.youtube.com/watch?v=bawJTYSG-as

We have used this tool to level the lip of ponds, to level the garden bed path, and to build swales. We made it using bamboo from our garden, tied it with palmetto, and all we needed was a yardstick, a marker to mark the inches on it, and a clear plastic hose. They are best used on smaller jobs.

A-Frame

See the Hands On Activity for how to build and use this. There are also numerous YouTube videos if you prefer a video. I have personally not found any that were clear, accurate and to the point enough to include here.

We made a bamboo A-frame with hemp string, a rock, and a marker. We made this more permanent by screwing the A-frame together. I have used an A-frame tied together that I can fold up to get into the car. I have to recenter/recalibrate it every time I use it, so I prefer using a water level.

I can also cover more ground more quickly with a water level or string. A-frames are best for small, close work in my opinion. A sturdy A-frame with a level on it is the most reliable. There is one you can purchase that is collapsible as well.

String level

https://www.youtube.com/watch?v=Zc660JkRuLg

This is useful for covering more ground, like the example in the video.

Laser level

We use a laser level which is much less expensive than a surveyor’s transit but can be rented or borrowed for one’s personal property rather than buying, if you need it at all. The main advantage is that I can rapidly mark contour on a large piece of land with a laser level. (As is normal with technology this model is now discontinued but of course still works well. The advantage is that a factory refurbished one can be had for under $400.) CST/Berger Rotary Laser Level.

A Homemade Device for Laying out Contour Lines

Nearly all rainfall erosion control methods, including strip cropping, the ditch and bank system, and terracing, are done on the contour (i.e. across the slope). Laying out contour lines that mark the path for plowing, crop rows, and barriers is an important skill to master. You can show farmers how to do this easily and accurately using a device called an A-frame.

Figure 1: Plumb-line A-frame (left) and carpenter's level A-frame (right) used for laying out contour lines.

Making and Calibrating an A-frame

Items Needed: Two wood or bamboo poles about 6' long, one wood or bamboo pole about 3-4' long, a hammer, nails and string. A small carpenter's level or a homemade plumb-bob and 3' of string.

STEP 1: Build the A-frame as in the drawing above. Poles cut from brush or bamboo will do fine. Twine or nails can be used to secure the 3 pieces together. The crossarm is placed about 1/2-2/3 of the way up and should be mounted reasonably level. Make the feet somewhat pointed at the bottom.

STEP 2: You can use either a plumb-line or a carpenter's level on the A-frame for determining contour lines. A plumb-line will be accurate enough when the wind is still but isn't reliable in any type of breeze.

A. Mounting the plumb-line: It should be hung from a nail (centered in the juncture) where the 2 legs meet. Hang a small weight like a fishing sinker or piece of metal scrap at the end as a plumb-bob.

B. Mounting a carpenter's level: In this case, be sure to use a very straight and smooth piece of wood for the crossarm. Tie the carpenter's level firmly to the crossarm with twine as shown above. NOTE: You can try using a small string level instead.

STEP 3: Now you can calibrate the A-frame to make it accurate as follows:

A. Calibrating a plumb-line A-frame

• To find the level mark on the crossarm, choose a fairly level spot of ground. Now pound 2 pointed stakes about halfway into the ground at a distance equal to the spread of the A-frame's legs. (You can also make marks on concrete or use sticks or flags - just mark where the legs go)

• Stand the A-frame on the stakes and make a pencil mark where the plumb-line comes to rest. Now reverse the legs and make a second mark. The true level mark will be located exactly halfway between. Use a ruler to find that spot and Mark it with a pencil.

• To double-check your calibration, adjust the A-frame's position by gradually pounding one of the stakes further into the ground until the plumb-line comes to rest. on the true level mark. Now reverse the A-frame's legs again; if the plumb-line returns to rest on the level mark, the A- frame is properly calibrated.

B. Calibrating a carpenter's level A-frame

• In this case, you want the carpenter's level to read level (i.e. bubble centered between the 2 lines) when the A-frame's legs are sitting on 2 points that are perfectly horizontal to each other. The easiest approach is to make sure that the following measurements in Figure. 1 are equal to each other: AB = AC, DB = EC; also make sure that the piece of wood used for the crossarm is perfectly straight.

• To test the A-frame, set its legs on 2 stakes that have been hammered into the ground (as in a. above). If the bubble rests to the right of center, gradually pound the right stake into the ground until the bubble is centered between the lines. If the bubble rests to the left, do the same with the left stake.

• As a final check, rotate the A-frame 180 degrees so that the position of the legs is exactly reversed. The bubble should indicate level again. If not, either the distances DB and EC aren't equal or perhaps the carpenter's level is defective. (When placed on a perfectly horizontal surface, an accurate level will produce no change in the bubble's centered position when rotated 180 degrees.)

Laying Out Contour Lines with an A-frame

Contour lines run at right angles to the slope (across the slope). All points on the line are at the same elevation. Here's how to lay out a contour line with an A-frame:

Items needed: A-frame, stakes, hammer (or stone).

STEP 1: Pound a stake into the ground at the starting point for a contour line (i e. the start of a proposed contour ditch or a strip of a closely-sown crop that will run across the field).

STEP 2: Stand the A-frame in the soil with one leg directly at the base (not on top) of the first stake and the other leg pointing in the approximate direction the contour line will run.

STEP 3: Now keep the leg at the base of the first stake in place and use it as a pivot point to move the other leg up and down the slope until you get a level reading with the plumbline (or carpenter's level). Pound in a second stake where this leg comes to rest.

STEP 4: Now shift the A-frame one stake over so that the leg that rested at the base of the first stake now rests at the second stake. As in Step 3, move the other leg uphill or downhill until you get a level reading, and pound in another stake.

STEP 5: Keep repeating Step 4 until you reach the end of the field.

STEP 6: Even out irregularities: Even on uniform slopes, small rises and depressions in the terrain may cause some stakes to be out of line. You can take out any abrupt deviations by slightly altering some of the stakes' positions as shown in Figure 3. This is done by continuing past the abrupt deviations and place a stake past the irregularity on an even line. Then come back and make any adjustments as needed.