Soil and Water Conservation Works - Afforestation, Reforestation and Forest Restoration in Arid and Semi-arid Tropics - page 87

Chapter 5
Soil and Water Conservation Works

Abstract Soil and water conservation (S&WC) works consist of a comprehensive
package of practices including digging of pits for planting, linear contour-based soil
and water conservation structures, and check dams and stop dams for harvesting
water in situ. As water is the most crucial resource in arid and semiarid areas, these
works are central in determining the success of a plantation. It is therefore necessary
to exercise great care both in designing and in executing these works correctly and
effectively. Like all other works involving human effort—rather than machines—the
quality and effectiveness of these works will depend upon the skill and workmanship
of the workers, and high standards of close supervision.

5.1 Alignment of Structures

All linear soil and water conservation structures should be aligned on contour lines.
If not aligned properly, not only will these be ineffective and constitute a wasteful
expenditure but also will accelerate soil erosion and cause loss of moisture. The
point structures, however, will be aligned individually, depending upon the purpose
of each. In any case, accuracy in aligning all kinds of S&WC structures should be
maintained.
Contour lines can be marked on ground using a variety of techniques and methods.
If skilled personnel are available, any of the engineering methods using instruments
such as the dumpy level, the tilting level, or the theodolite, may be employed. A
simple, fast, accurate, and reliable method of marking contours is to use hydrostatic
level (see Sect. 3.6). The method enables a team of four persons to mark contour
lines up to 1,000 m a day. Contour lines should always be marked on ground with
whitewash and should be prominently visible on inspection. Contour lines should
be marked continuously and completely. In a hilly terrain, a contour line starts near
a stream and ends near another. If certain portions in between are untreatable, these
should be excluded from soilwork but not from marking of the line. Portions that are
unapproachable due to thick shrubs or any other obstruction may, however, be left
out of marking.
A thorough walk-through inspection and occasional testing with the help of a
tilting or dumpy level is a necessary follow-up before taking the contour lines to be
finally correct. The instrument should be set up at a point from where a number of
contour lines will be visible. By keeping a staff at different points on the lines drawn,