Wind zone information in, for example, EIA-222-F provides general
broad averages that don't take full account of local terrain shape
and roughness. Under some conditions wind forces can be as much as
double the values predicted without more detailed terrain consideration.
An example of a general method to include the effects of hills, ridges
and other terrain features, as well as the effects of buildings,
forrestation and other roughness elements, is the British Standards
Institution's "Code of Basic Data for the Design of Buildings, Wind
Loads", CP3, Ch. V, which you can order from the BSI, London, W1A 2BS.
If you are interested in more about this issue, it's a big factor in the
design and siting of wind-energy systems. A complete summary of efforts
to measure and model local winds is found in Hunter & Elliot, "Wind-
Diesel Systems,", Cambridge Press, 1994, Ch. 3 (Assessing the wind
resource) and in Wegley, et al, "Siting Handbook for Small Wind Energy
Conversion Systems," WindBooks, P.O. Box 4008, St. Johnsbury, VT 05819,
telephone 802-748-3360, 1980.
There are wind scales that estimate peak and average winds by the nature
of tree and plant growth in a locality, and generally you can get a
pretty good idea of how your own winds relate to the regional or
county averages by whether you have any tall trees that aren't broken
by the highest winds they've experienced.
The bottom line is that, if you are going to live under your tower and
big Yagi, you owe it to yourself to include local terrain considerations
in your estimate of the peak winds you expect during the useful life of
the installation.
73 de Dave, W6NL (ex-QHS)
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