Controlling Sand Movement Through Mechanical Measures: China’s Experience - Combating Desertification in Asia, Africa and the Middle East - page 30

Fig. 2.7 The indication of the prevailing wind ( a ) is the initial condition after stabilizing the dune
with standing sand barriers ( b ) is the location of plantings of trees and shrubs between the dunes
and ( c ) the reduced size of the dune at some future time

however, the base of this type of barrier is not liable to be destroyed, and a steady
surface of sand between two sand barriers will soon be formed. This phenomenon
can protect the seedlings of plants seeded on the sand dunes where the sand barrier
is set up. In order to avoid the seedlings of sand plant being buried by the shifting
sand on the leeward side of the barrier, the plantation site between two sand barriers
should be kept at a distance from the sand barrier. The low windproof or dense
structural sand barriers should be installed before the planting of vegetation between
sand barriers is started.

4.3 Installation of Standing Sand Barrier

Standing sand barrier are the most widely used in sand-control, especially the straw
sand barriers that have often been adopted by local people to protect farmlands
and irrigation canals. To protect railway lines and major infrastructure located in
the sand areas, hedges of wood chips are usually used, and along the fringes of
the villages or farmland, sand-protecting walls of earth are often adopted by local
people. In recent years, clay sand barrier, which belong to the low windproof sand
barrier type, have been widely used in desert areas. Techniques for installing various
standing sand barriers are described in the following section:

4.3.1 Run of Standing Sand Barriers

The run as well as the disposing patterns of a standing sand barrier should be
determined in the light of the direction of the prevailing wind, the patterns (shapes)
of sand dunes and the purpose of the sand barriers. The run of a sand barrier should
meet the direction of the prevailing wind at right angles. Therefore, the direction
of the prevailing wind in the area that is to be protected must first be found out.
According to the practical experience, there are three indicators: (A) the length of
the windward slope and the leeward slope of existing sand dunes; (B) the patterns
of sand ripples; (C) the run of sand plaits (Fig. 2.7 ).
On the work site, the run of the sand barrier can be determined in the light of the
above-mentioned indicators. The windward slope of sand dunes is longer and gentle,