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Prevailing
wind
50-100cm
sand
accumulates
20-30cm
Fig. 2.18
The installing techniques of high standing sand barrier
1. Setting up in the furrow
The materials used in this method are hard, such as the branches of
Nitraria
tangutorum
,
Artemisia ordosica
and
Alhagi sparsifolia
. First, a furrow, width
15 cm, depth 20 cm should be dug. Second the materials are put into the furrow
with the roots up and the tips down and the sheaves or branches are overlapped
(see Fig.
2.17
). It is better to keep the degree of density of the sand barriers at
20-30 %. The height of the low standing sand barriers is usually around 30 cm.
Finally, the furrow is filled with sand and then tamped firm. Sometimes, in order
to avoid the base of the sand barriers being destroyed by the wind, some broken
straws are firstly filled into the furrow on the windward side of the sand barriers
and then covered with sand.
2. Setting up by pushing down the straws
For some soft straws, such as wheat straws, it is not necessary to dig a furrow
when the sand barriers are set up. The steps for installation of such sand barriers
are as follows (see Fig.
2.19
):
(1) lay the straws along the designated lines evenly and make the run of the
straws vertical to the lines; (2) press the middle of the straws into the sand to a
depth of around 10-15 cm with a blunt spade. Thus the two ends of the straws
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