Controlling Sand Movement Through Mechanical Measures: China’s Experience - Combating Desertification in Asia, Africa and the Middle East - page 41

Fig. 2.20 Installation of materials in furrows

Fig. 2.21 The section of clay
sand barrier. Major barriers
are placed 2-4 m apart with a
base of 15-25 cm in the lower
slopes and 45-75 cm in the
upper parts

on the moving dunes. The effectiveness of the clay sand barrier for sand-control
near farmlands and irrigation canals is also very satisfactory. Clay sand barriers are
widely accepted by the local people living in the sandy areas. In general, the clay
sand barrier is set up at the lower part (approximate 2/3 of the slope) of the windward
slope of sand dunes. Before setting up, the lines should be drawn on the basis of the
direction of the prevailing wind, the shapes of the sand dunes, section of the dunes,
size and row spacing of the sand barriers and so on. The narrow mounds, along the
lines, are piled with clay that is taken from lowland between the sand dunes. A row
spacing of 3 m and a mound of 20 cm in height are usually used (Fig. 2.21 ).
For the sand barriers that are established on the upper part of the slope and
on the steep slopes of sand dunes, the row spacing should be shortened and the
height should be raised. For areas where the ground is gentle and the sand dunes
are steady, a sand barrier of smaller size can be used. The width of the mound
should be kept even, or it will be destroyed by wind at the narrowed part. In order
to maintain an uneven surface, lumps of the clay should be used, but very big lumps
of clay should not be used because they will probably cause wind-erosion around
them. Clay barriers should be examined after several exposures to strong winds. The
following aspects should be examined: (1) whether the run of the barrier is correct
or not; (2) whether the depressions among the sand barriers are eroded or not; (3)
the angles between the run of sand ripples and the run of the sand barriers; (4) the
angles between the sand plaits and the run of the clay sand barriers; (5) whether any
part of the sand barrier has been destroyed.