Controlling Sand Movement Through Mechanical Measures: China’s Experience - Combating Desertification in Asia, Africa and the Middle East - page 36

Fig. 2.15 The relationship
between the height and the
row spacing of the sand
barrier

High Standing sand Barrier

Low standing
sand Barrier

Sand barrier

The steep slope

The gentle slope

The horizon

Fig. 2.16 The relationship between the slope of sand and the row spacing of sand barrier

Tabl e 2. 1 The ranges of row spacing of straw and branch sand barriers
The general height of the barriers The row spacing for various slopes (m)

5 ı 5 ı -10 ı 10 ı -15 ı Types Height (cm)

Low standing sand barriers 20-40 3-5 2-3 1-2

High standing sand barriers 60-80 7-10 5-7 3-4

The row spacing of clay sand barriers (or other low standing sand barriers with
dense structure established for afforestation on the sand dunes) is mainly determined
on the basis of the special needs of planting.
The intention of sand barriers that are set up for afforestation is that a depression
among the sand barriers will form after several episodes of strong sand-driving wind
and the sand will heap up around the barriers simultaneously. If the run of the sand
barrier is correct, the depression will quickly become stable.
The depth of the steady depression among the sand barriers is about 1/12 of the
row spacing of the sand barriers. And the deepest part is not more than 1/10 of the
row spacing. The wider the row spacing, the deeper the depression.
If the height of the sand barriers is less than 1/10 of the row spacing, the sections
between the sand barriers will be eroded. On the contrary, if the height of the sand
barriers is more than 1/10 of the row spacing of the sand barrier, the sand will heap
up in those sections. Therefore the phenomenon of sand-dropping or erosion on the
surface of sand dunes which are protected by sand barriers can be determined not
only by the row spacing of sand barriers, but also by the height of the sand barriers
(Fig. 2.17 ).