We always used the Abney level in Laos to conduct topographic surveys in the mountains, hills and forest, from the spring down to the village. With a relatively small team and with limited materials, you can easily collect the data to draw the topographic profile; in order to estimate the hydraulic feasibility and to design your gravity fed system (GFS).
A clinometer? For what?
To draw a topographic profile between 2 points, you need to know the distance at ground level and the vertical distance (or difference of altitudes) between these 2 points. You can easily measure the distance at ground level – called L – with a measuring tape. But the difference of altitude – called ΔH – can be calculated if you know the inclination angle – called α – between these 2 points and remembering your trigonometry lessons. Your Abney level measures this angle. Sinus α = ΔH/L
- 1 clinometer Abney level.
- 1 30m measuring tape.
- 2 wooden or bamboo stick of the same length. The extremity of the sticks is marked with red scotch tape.
- Red spray (to mark the road followed).
- Field sheet (to collect data).
- 1 person for Station 0 (measuring vertical angle and horizontal distance).
- 1 person for Station 1.
- 1 person for data collection.
- Village’s volunteers to guide the team to the springs, to clear the way, to prepare the short wooden stick (to mark the stations)…
- Preparation of equipment and tools.
- To define Station 0 (starting point of the survey).
- To define Station 1 on a low or high point of the topography and visible from Station 0.
- To measure the soil distance (L) between Station 0 and Station 1 (using the measuring tape).
- To target the extremity of Station 1 from the extremity of Station 0 using the Abney level.
- The Stations 0 and 1 are marked with short wooden sticks hammered in the soil. On these short sticks are written the number corresponding to the Station and the distance; in addition the nearest rock or tree from the Station is marked using the red spray
- Once the 2 parameters are measured (horizontal distance and vertical angle) and the 2 Stations are marked, the Station 0 stick is moved – with the clinometer – to the Station 1 and the Station 2 has to be defined.
For the topographic survey, the shortest way to the village has to be followed and showed/cleared by the villagers. However, huge slopes have to be avoided as well as river’s bed.
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