Controlling Sand Movement Through Mechanical Measures: China’s Experience - Combating Desertification in Asia, Africa and the Middle East - page 38

barriers, clay sand barriers with a height of around 20 cm and a width at the bottom
of about 60 cm are often adopted. With the row spacing being shortened, the size of
the clay sand barriers should also be narrowed and cut down, but if the size of the
clay sand barrier is too small, the barrier is liable to be destroyed by wind, livestock
or people. Under normal conditions, the row spacing and the height of clay sand
barriers is 2-4 m and 15-25 cm, respectively. For different row spacing and sizes of
clay sand barriers, the amount of earthwork and manpower are also different.

4.4 Installation of Straw Sand Barriers

The best seasons for setting up straw sand barriers are the end of autumn and early
winter. Because the sand is moist in these periods, a lot of labor can be saved and
the base of the sand barrier firmly established. If sand barriers are set up in the
summer or spring, the base of the sand barrier is easily destroyed by the wind
because the sand is dry in these seasons, and it is difficult to set up sand barriers
on dry sandy land.

4.4.1 Installation of High Standing Sand Barriers

The heights of standing sand barriers that are made of tall and supple stalks (such
as reeds and the stalks of Achnatherum splendens ) should be more than 70-80 cm.
The installing techniques of standing sand barriers are as follows: (1) dig the furrows
along the designated lines. (2) put the materials-stalks-into the furrow with the tip
of the stalks up and the base down. More should be in the furrow than out of the
furrow. The barrier must be very dense and leave no spaces in it or it will be liable
to be destroyed by wind. (3) fill the furrow with the broken stalks first and then with
sand above the broken stalks on both sides of the sand barrier.
In order to make the sand barriers very firm, the filled sand on both sides of the
sand barrier should be more than 10 cm above the ground level (see Fig. 2.18 ).
The density of the materials should be about 0.2-0.4 kg/m but if the material
sources are not locally abundant, the cost of establishing the barrier is much higher.
Standing stalk sand barriers can break the sand-driving wind no matter whether the
wind is strong or weak.

4.4.2 Installation of Low Standing Sand Barriers

The materials for low standing sand barriers are usually as follows: grasses, shrubs,
sub shrubs, branches of trees, wheat straw and other crop stalks or straw. The
installing techniques can be divided into two kinds according to the different
materials used: