Site Selection, Survey and Treatment Plan - Afforestation, Reforestation and Forest Restoration in Arid and Semi-arid Tropics - page 56

Fig. 3.3 Marking contour
lines on ground with a
hydrostatic level

of much relevance in afforestation projects of the kind that this topic is concerned
with. It suffices to say that equipment like the total survey stations, or the GPS-
based survey devices integrated into geographical information systems (GIS), are
sophisticated, costly, and efficient methods of surveying which can be used where
comprehensive watershed treatment plans, including a large number of engineering
structures, are to be prepared.
These advanced methods and equipment are not discussed further in this topic.
The interested reader can consult one of the references in the list at the end of
the topic.

3.6 Setting Out Contours With Hydrostatic Level

An important surveying task in afforestation projects, apart from preparation of site
plan, is to set out and mark contour lines on ground for alignment of the soil and water
conservation (S&WC) works. A rapid, efficient, and accurate method of marking such
contours is with a hydrostatic level—a simple equipment capable of being assembled
anywhere by anyone. It consists of two 1.50 m long wooden graduated staffs, with
the two ends of a 15 m long transparent, flexible rubber tube running in a groove
along the lengths of the staffs (Fig. 3.3 ).
When water is filled in the tube and the two staffs are kept at a common point, the
reading against water level in each staff will be the same. If one of the staffs is placed
at 2 m distance from the other, the water levels will read different if the ground is
sloping. By moving the forestaff up and down the slope, it can readily be placed
at a point where the readings in the two staffs are identical. The point so located is
marked with whitewash. The operation is repeated as long as the tube length allows.
After that the rearstaff is taken ahead of the forestaff (that is, in fact it becomes the
forestaff), continuing the operation further until some stream is encountered. All the
points so marked will fall on a contour and are therefore joined with a smooth line
marked with whitewash. A visible and accurate contour is thus set out with relative
ease, and with high degree of accuracy. The operation is so simple that it requires no