Frost Protection - UTL Repository

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F R O S T P R O T E C T I O N : F U N D A M E N T A L S , P R A C T I C E A N D E C O N O M I C S
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occurs when the local topography is changed due to road or building
construction. A careful study of topographical maps can often prevent major
frost damage problems. Also, the use of smoke bombs or other smoke generating
devices to study the down slope flow of cold air at night can be informative.
These studies need to be done on nights with radiation frost characteristics, but
not necessarily when the temperature is subzero. Once the cold air drainage flow
pattern is known, then proper placement of diversion obstacles can provide a
high degree of protection.
There are examples where diversion of cold air drainage has led to effective
frost protection. One good example pertains to a high-value cut-flower
producer. The crop was located in a canyon on one side of a stream (Figure 6.6).
On the opposite side of the stream from the cropped field, the canyon wall was
steep. On the crop side of the stream, the ground was relatively flat, but the
canyon wall again sloped steeply upward on the opposite side of the field from
the stream. Upslope from the field, the canyon narrowed to where only the
stream cut through the canyon. Upslope from there, the canyon widened out to
a broad relatively flat area. During frost nights, dense cold air accumulates over
the flat area upslope from the canyon narrows. As long as the prevailing wind
was gently blowing upslope, the cold air was kept on the upslope side of the
canyon. However, if the wind stopped, cold air would drain through the narrows
into the cropped field (Figure 6.6).
FIGURE 6.6
Cold Air Drainage
COLD AIR
COLD
COLD
Cold air drains down-slope along a river valley and into a crop.
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