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=                          Bivouac_shelter                           =
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                            Introduction
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A bivouac shelter or bivvy (alternately 'bivy', 'bivi', 'bivvi') is
any of a variety of improvised camp site or shelter that is usually of
a temporary nature, used especially by soldiers or people engaged in
backpacking, bikepacking, scouting or mountain climbing. It may often
refer to sleeping in the open with a bivouac sack, but it may also
refer to a shelter constructed of natural materials like a structure
of branches to form a frame, which is then covered with leaves, ferns
and similar material for waterproofing and duff (leaf litter) for
insulation. Modern bivouacs often involve the use of one- or
two-person tents but may also be without tents or full cover. In
modern mountaineering the nature of the bivouac shelter will depend on
the level of preparedness, in particular whether existing camping and
outdoor gear may be incorporated into the shelter.


                             Etymology
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The word 'bivouac' is French and ultimately derives from an
18th-century Swiss German usage of 'Beiwacht' ('bei' by, 'Wacht' watch
or patrol). It referred to an additional watch that would be
maintained by a military or civilian force to increase vigilance at an
encampment. Following use by the troops of the British Empire the term
became also known as 'bivvy' for short.


                            Construction
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Artificial bivouacs can be constructed using a variety of available
materials from corrugated iron sheeting or plywood, to groundsheets or
a purpose-made basha. Although these have the advantage of being
speedy to erect and resource-efficient, they have relatively poor
insulation properties.

There are many different ways to put up a bivouac shelter. The most
common method is to use one bivouac sheet as the roof of the shelter
and a second as the groundsheet. The 'roof' flysheet is suspended
along its ridge line by a cord tied between two trees which are a
suitable distance apart. The four corners of the flysheet are then
either pegged out or tied down to other trees. Care must be taken to
leave a gap between the ground and the sheet to ensure that there is
enough air flow to stop condensation.

A basha is a simple tent, made from one or two sheets of waterproof
fabric and some strong cord. Generally a basha is made of reinforced
nylon with eyelets and loops or tabs located along all four sides of
the sheet and sometimes across the two central lines of symmetry. The
basha is an extremely versatile shelter that can be erected in many
different ways to suit the particular conditions of the location. (The
word also sometimes refers to a special type of bivouac sack described
below).

==Bivouac sack==
A bivouac sack is a smaller type of bivouac shelter. Generally it is a
portable, lightweight, waterproof shelter, and an alternative to
larger bivouac shelters. The main benefit of a bivouac sack shelter is
speed of setup and ability to use in a tiny space as compared to
tent-like shelters. A bivouac sack is therefore a common choice for
hikers, cyclists or climbers who have to camp in tight areas, or in
unknown areas. A bivouac sack will usually have a thin waterproof
fabric shell that is designed to slip over a sleeping bag, providing
an additional 5 to 10 °C of insulation and forming an effective
barrier against wind chill and rain.

A drawback of a simple bivouac sack is the humidity that condenses on
the inner side, leaving the occupant or the sleeping bag moist.
Moisture severely decreases the insulating effect of sleeping bags.
This problem has been alleviated somewhat in recent years with the
advent of more waterproof, but breathable fabrics, such as Gore-Tex,
which allow some humidity to pass through the fabric while blocking
most external water. A traditional bivouac bag typically cinches all
the way down to the user's face, leaving only a small hole to breathe
or look through. Other bivouac sack have a mesh screen at the face
area to allow for outside visibility and airflow, while still
protecting from insects. Fully zipping up a bivouac sack is poor
practice, both from the obvious risk of hypoxia and the dramatically
increased levels of condensation that will form inside the bag.


                             ''Boofen''
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In the German region of Saxon Switzerland in the Elbe Sandstone
Mountains, climbers refer to overnighting in the open air as 'Boofen'
(pronounced "bo-fen"). The spot selected for overnight stays usually
comprises an overhang in the sandstone rock or a cave, the so-called
'Boofe' ("bo-fe"). This has often been adapted with a sleeping area
and fireplace. In the national park itself, 'Boofen' is only permitted
at designated sites and only in connection with climbing, although in
this case lighting fires is absolutely forbidden. The colloquial Saxon
word 'boofen' was derived from 'pofen' (= sleep soundly and for a long
time).


                              Examples
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Count Henry Russell-Killough, the "hermit of the Pyrenees", is broadly
accredited with the invention of the bivouac in extreme, inhospitable
places. He would bivouac in the open, creating a blanket of rocks and
earth or using a simple bag.

An example of a bivouac being made in a time of urgency was shown when
the climber Hermann Buhl made his ascent of Nanga Parbat in 1953 and
was forced to bivouac alone on a rock ledge at 8000 m altitude, in
order to survive until the following morning.

Modern bivouacs have evolved to offer heightened levels of comfort for
climbers and explorers. Modern portaledges (the vertical camping
version of a tent) are a more comfortable, safer, and sturdier option
to hanging hammocks.


                              See also
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* Bothy
* Shelter half
* Swag (bedroll)
* Mountain hut
* Wilderness hut
* Portaledge
* Ultralight backpacking


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