How can I easily carry out a topographic survey in rugged forest terrain?
This is a question that I've been asked in the field so I wanted to share it with everyone on KnowledgePoint
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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