Journal of the Japan Society of Erosion Control Engineering, Vol.58,No.1,2005
Wind tunnel study on the effect of a wind break fence constructed on an
embankment
Tomoki SAKAMOTO Yoji ISHIDA Hiroaki HAGINO
Abstract
A planted Japanese black pine (Pinus Thunbergii) shelterbelt, which had grown
upward satisfactorily in the back of an artificial embankment, ceased growing
after reaching a certain height. The apparent reason for this was that the tree
tops of the shelterbelt had come out above the area where the wind speed had been
mitigated by the embankment and were exposed directly to strong sea winds. A wind
break fence was thus constructed on the embankment in order to protect the trees
from the wind, and the trees have begun growing again. The embankment is 2.66m
in height, 2.0m in width at the top and the slope is 1:1.5. The fence is 2.35
m in height. The position where tree height had stagnated in the past was 1.1]1.9m
above the ground. The present tree height range is 4.2]7.5m, and the trees have
grown 1.6]1.9m during the last five years (in the five years since the fence was
constructed). The wind tunnel experiment was conducted in order to consider how
effectively the combination of the embankment and the fence has mitigated the
wind speed, both in absolute terms and in comparison with a large embankment which
has the same height as the embankment plus the fence. Three models were made,
i.e., of the embankment, of the combination of embankment and fence, and of the
large embankment. The model scale was 1/25. Wind speed in the wind tunnel was
4.8 m/s and 6.8 m/s, assuming local wind speed of 14 m/s and 20 m/s. The addition
of the fence on the embankment remarkably expanded the area where the wind decreased,
and there was even an area where the wind speed ratio was under 0.2, which had
not been seen before the fence was constructed. The combination of the smaller
embankment and the fence was much more effective than the large embankment and
it appears to have enabled the trees to begin growing upward again.
Key words:wind tunnel, artificial embankment, wind break fence, seacoast shelterbelt
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