An excerpt from Handbook For Boys, by the Boy
Scouts of America, June 1953, page 157.
This
article can be used by experimental archaeologists, re-enactors
or historical trekkers of the late 18th and early 19th
centuries, or by anyone who is interested in wilderness survival or camping. Updated November 2, 2021 –
Author’s note.
The
lyric, “seeking shelter against the wind”, is from Bob Seger’s song “Against
The Wind”1, and while Mr. Seger was talking metaphorically about
life and it’s struggles and challenges, it is also an excellent piece of
survival advice, as well. So how do you
go about seeking shelter against the wind?
With a windbreak of course! But
is there a science to windbreaks? Why
yes, there is!
Much
of what has been written about the science of windbreaks has come from the
viewpoint of agricultural scientists, writing about providing shelter for
wildlife and livestock, but hey if it works for moose and cows, it will work
for you too!
The
purpose of a windbreak is, obviously, to break the wind, this reduces the
effects of wind chill and at the same time protects you from wind-blown rain,
sleet, and snow. You can either find
windbreaks, like large rocks, fallen trees, or thickets and groves of trees, or
you can build them yourself from the materials at hand in the wilderness. There are two types of windbreaks, solid ones
like rocks, walls and logs, and permeable ones like groves of trees and
thickets, which are also called shelterbelts.
As
the wind blows against a solid, straight windbreak, it
is either forced around or over it. When
air is forced over a windbreak the air pressure increases on the upwind or
windward side and its velocity increases.
On the downwind or leeward side, a slight vacuum is created as the wind crests
the top of the obstacle. This vacuum
causes turbulence, which acts to dissipate the wind’s energy and velocity. The area of wind protection downwind from a
solid windbreak is about fifteen times the height of the windbreak.
Solid windbreaks, Figure 1, from “Wind And Snow
Control Around The Farm”, by Don D. Jones, William H. Friday, and Sherwood S. DeForest.
From “Engineering Practice Planning Guide: Livestock
Shelter Structure”, page 6.
During
the winter, the wind will drop its snow load in two places. On the upwind side of a solid windbreak, snow
will drift at a 45o degree angle in front of it. On the downwind side, the wind no longer has enough
energy and velocity to carry the snow, which then drops out and creates a snow drift. With a solid windbreak, like a fallen log or
a large rock, the distance of this drifting is about five times the height of
the windbreak and a solid windbreak will also protect you from the wind for about
twenty times the height of the windbreak.
The authors of the “Engineering Practice Planning Guide: Livestock
Shelter Structure”, note that there should be a mostly snow drift free area, in
the lee of the windbreak, out to two times the windbreaks height, with the snow
drifting occurring after that out to five times the height of the windbreak2.
Figure 5.1, from “Functioning of a windbreak”, by the Food
and Agriculture Organization of the United Nations.
A
grove or stand of trees acts as a permeable windbreak and as the wind blows
through a grove of trees, with a vegetation density of 50 to 60%3,
the wind is both forced over and through the trees. Just as with a solid windbreak, when the wind
is forced over a grove of trees, the air pressure increases on the upwind or
windward side and its velocity increases.
On the downwind or leeward side, a slight vacuum is created as the wind
crests the grove and this vacuum causes turbulence, which acts to slow the
wind. The area of wind protection,
downwind from a grove of trees, is between fifteen to twenty times the height
of the trees. The wind reduction provided
by a 32-foot, 10 meter, tall grove of trees can be as much as 70% within the
first 100 feet, or approximately 30 meters, dropping to 50% out to 200 feet, or
approximately 60 meters, from the lee edge of the grove of trees.
 |
Figure 5, from “Wind And Snow Control Around The Farm”,
by Don D. Jones, William H. Friday, and Sherwood S. DeForest.
During
the winter, the wind as it blows over a thicket or a grove of trees will drop
its snow load in two places. On the
upwind side of the trees, the snow will drift into the trees and create drifts on
the windward side of the stand of trees.
On the downwind, or lee side, the wind is slowed and no longer has the
energy and velocity to carry snow and the snow then settles out to create a snow
drift. In the lee of a grove of trees,
the distance of this drifting is about five to ten times the height of the grove
and this type of windbreak will also protect you from the wind for about fifteen
to twenty times the height of the grove.
From “Shelterbelt agriculture uses trees to protect
soil and water resources”, by Henry Kock.
During
the spring, summer or fall, the best type of windbreak is a thicket or grove of
trees, and the best spot for protection from the wind, would be somewhere
within five to ten times the trees height, away from the edge of the grove. You will also find that during the summer
that within this area it will be the cooler than anywhere else. According to the “Wind And Snow Control
Around The Farm”, by Don D. Jones, William H. Friday, and Sherwood S. DeForest,
“a dense tree area has a substantial cooling effect. On a hot summer day,
there is up to a 10-degree difference in temperature between an open field and
a grove of trees. This is more than shade effect. The leaves of one mature tree
can evaporate over 200 gallons of water per day, producing evaporative cooling
equivalent to an 8-10 room air conditioner!”
During
the winter, the best spot to be would be about ten times the trees height away
from the edge of the grove. This spot
will give you the best protection from the wind and it will also put you beyond
the snow drift zone4.
However,
in open country, you won’t be able to find a handy thicket or a conveniently
placed stand of spruce trees, and you will have to build a windbreak to protect
your lean-to or your tent. When you
build a windbreak, its final shape will depend on the materials that you have available
build it with. If you are in a forested
area and are using logs, your walls will, of course, be straight, and your
windbreak will be “V” shaped. If you are
using snow blocks, are digging through the snow to the ground and piling the dug-up
snow to the windward side, or are using piled up rocks, the best shape will be
semicircular. In the Arctic, or during
the winter, Alan Innes-Taylor, who wrote the Arctic Survival Guide, suggested
the following about windbreaks.
An excerpt from Arctic Survival Guide, by Alan
Innes-Taylor, page 59.
Also,
the SAC Land Survival Guide Book, most likely authored by Alan
Innes-Taylor, had this to say about windbreaks, “In open country you can
build a low snow-block wall not more than four feet away from the tent and
semicircular in shape. Strengthen the
windward side by throwing water on it and letting it freeze.”
From R. L. Jairell, and R. A. Schmidt, “Snow
management and Windbreaks”, page 2.
From “Engineering
Practice Planning Guide: Livestock Shelter Structure”, page 4. Note that in Figure 1a, the width of the
shelter is labeled “D” and the Drift-Free area is ¾ of the width at 1-½ times
the width from the corner of the shelter.
The
authors of the “Engineering Practice Planning Guide: Livestock Shelter
Structure”, much like the authors of the SAC Land Survival Guide Book, thought
that the semicircular windbreak was the best shape, as the semicircle protects
27% more area, for the same shelter length, than does the “V”-shape
windbreak. They also wrote that, during the winter, whether you are building a “V”-shape
or a semicircle windbreak, if you wished to avoid snow drifts, you should make
sure that the shelter width (which is marked as “D” in both illustrations)
should be no more than fifteen times the total height your walls. This way the snow drift free area behind your
windbreak, will be no less than ¾ of the shelter’s width.
If
the walls of your windbreak are 3 feet, or almost 1 meter high, then the width
of the mouth of the semicircle or “V”, should not be more than fifteen times
the height, which is equal to 45 feet or almost 14 meters. During periods of drifting snow, this will
give you a drift free area in the lee of the windbreak that is 33 feet, or 10
meters wide
So,
the next time you are seeking shelter from the wind, build or find a windbreak
and set up camp in its lee.
I
hope that you continue to enjoy The Woodsman’s Journal Online and look for me
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That
is all for now, and as always, until next time, Happy Trails!
Notes
1
The song “Against The Wind”, by Bob Seger is from the 1980 album, Against
The Wind.
2
So, for example, if you build a wall or find a fallen log or big boulder that
is three feet, or almost 1 meter, high, the wind will create a drift zone in
the lee of the windbreak, that can equal 15 feet, or almost 5 meters, which is
the height of the windbreak times five.
It should be remembered that the area behind the windbreak out to 6
feet, or almost 2 meters, should be mostly drift free. The windbreak will also block or reduce the
wind for about fifteen times the height of the windbreak, which at 3 feet, or
almost 1 meter, will be 45 feet or just over 14 meters.
3
From “Functioning of a windbreak”, Food and Agriculture Organization of the
United Nations,
4
So, for example if you are downwind of an approximately 30-foot, or almost 10
meter, tall grove of spruce trees; the wind and snow will create a drift zone
that can extend as far as 150 feet to 300 feet, 46 to 91 meters, which is the
height of the grove of trees, times a factor of five to ten. The trees will also block and slow the wind
for between fifteen to twenty times the height of the grove, which at 30 feet,
or almost 10 meters, will extend 450 to 600 feet, 137 to 183 meters, from the
edge of the grove.
Sources
3904th
Composite Wing Strategic Air Command, SAC Land Survival Guide Book, [SAC
OFFUT AFB, July 8, 1952], page 66
Boy Scouts of America, Handbook For Boys,
[Boy Scouts of America, New York, New York, June 1953], page 157
Brandle, James R., and
Finch, Sherman; “How Windbreaks Work”, University of Nebraska Extension, EC
91-1763-B, https://www.fs.usda.gov/nac/assets/documents/morepublications/ec1763.pdf, accessed December 10,
2020
Food and Agriculture
Organization of the United Nations, “Figure 5.1 Functioning of a windbreak”, http://www.fao.org/3/t0122e/t0122e0a.htm,
accessed December 10, 2020
Innes-Taylor,
Alan; Arctic Survival Guide, [Scandinavian Airlines System, Stockholm,
1957], page 54-55 and 63
Jairell,
R. L.; and Schmidt, R. A.; “Snow management and Windbreaks”,
[University of Nebraska, Lincoln, December, 1999], page 2, https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1132&context=rangebeefcowsymp, accessed December 10, 2020
Jones, Don D.; Friday,
William H.; and DeForest, Sherwood S., P.E.; “Wind And
Snow Control Around The Farm”, NCR-191, [Purdue University, Cooperative
Extension Service, West Lafayette, IN; 1983], https://www.extension.purdue.edu/extmedia/ncr/ncr-191.html, accessed December 10, 2020
Kock, Henry; “Shelterbelt
agriculture uses trees to protect soil and water resources”, Ecological Agriculture
Projects, [McGill University (Macdonald Campus), Ste-Anne-de-Bellevue, QC, Canada,
1990], https://eap.mcgill.ca/MagRack/SF/Summer%2090%20M.htm,
accessed December 10, 2020
North Dakota,
“Engineering Practice Planning Guide: Livestock Shelter Structure”, May 2016,
pages 3-7, https://www.nrcs.usda.gov/wps/PA_NRCSConsumption/download?cid=nrcseprd1088613&ext=pdf,
accessed December 11, 2020
“Trees can provide living
windbreaks”, The Houghton Lake Resorter, Houghton Lake, Michigan; January 15,
2015, [© 2018-2020 The Houghton Lake Resorter], https://www.houghtonlakeresorter.com/articles/trees-can-provide-living-windbreaks/,
accessed December 10, 2020
