Soil and Water Conservation Works - Afforestation, Reforestation and Forest Restoration in Arid and Semi-arid Tropics - page 92

The section of a V-ditch should be checked by carefully measuring it with the
help of a frame, a bar, or a tape. A bar will always be more convenient, as tapes
are inconvenient in measuring excavated sections. Particular care should be taken
to ensure that the sloping part of the section is flat and not bulging, especially if
a frame is not being used for verifying the section. In case a frame is used, this is
automatically detected when a frame runs through the section.
The ends of a V-ditch can be curved up in case the soil is light and friable. This
will prevent the ends of the section from collapsing in, and the stored water from
escaping the ditch. In heavier soils, the section is more likely to stay in shape and
prevent such overflow of water. Alternatively, each continuous stretch of the ditch
can be provided with a surplussing arrangement in the form of a weir-on-the-bund
made of dry stone masonry.

5.4 Digging of Pits

Pits can be round or square, though the latter are preferred. In the correct technique
of pit digging the soil should be dumped in a heap downside of the pit. This will
facilitate construction of water-harvesting saucers later. If the depth of fertile soil
is limited, the topsoil should be heaped separately initially and later used for filling
in the immediate vicinity of the root zone of the plants during planting operation.
If the excavated soil contains excessive boulders, stones, or other undesirable or
toxic materials, the soil should be picked clean of these. Use of appropriate tools—
depending upon the size and shape of the pit and hardness of the soil—will result
in improved output of work and better work quality. Digging should be carried out
with care so as to ensure appropriate depth and size. Pits should not be dug in areas
where these will be short of the specified size for lack of adequate soil depth.
Size of the pits must be verified using a frame of the designated size. Using tapes
is neither efficient nor appropriate. Even a small error in a dimension of the pit will
result in an error up to three times as large in volumetric terms.

5.5 Contour Dike-Cum-Terraces

Contour dikes are made of dry stone masonry with mud mortar or lime mortar coping.
Construction of dry stone wall has already been discussed in Chap. 4, and the same
precautions that apply to fencing wall apply here also. Dikes should be constructed
in continuous fashion, and no breaks need be given, except where the contour line
ends or suddenly turns. Coping made of mortar or concrete should invariably be
provided, or else the wall will scatter away during the first downpour. The ends of a
stretch of contour dike can be turned up to avoid spillage of soil and water (Fig. 5.3 ).
Terracing is done by transporting soil from nearby. Soil for this purpose should be
loamy or clayey and not sandy or friable. Soil filled in a wedge-shaped section will
give a flat and horizontal terrace, the width of which will depend upon the slope of the
terrain and the height of the dike. Sometimes it is useful to give reverse slope to the