is about whitewater.
Whitewater
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"Wild water" redirects here. For the Norwegian rock band, see
Wild Water band.
Vivid water of the
Torne River between Sweden and Finland.
Whitewater,
[1] usually spelled
white water in both American and British English,
[2][3][4] is formed in a
rapid, when a
river's
gradient increases enough to disturb its
laminar flow and create
turbulence,
i.e. form a bubbly, or aerated and unstable current; the frothy water
appears white. The term is also used loosely to refer to less turbulent
but still agitated flows.
[citation needed]
The term "whitewater" also has a broader meaning, applying to any
river or creek itself that has a significant number of rapids. The term
is also used as an adjective describing boating on such rivers, such as
whitewater canoeing or
whitewater kayaking.
[citation needed]
Rapids
Four factors, separately or in combination, can create rapids:
gradient, constriction, obstruction and flow rate. Gradient,
constriction and obstruction are streambed topography factors and are
relatively consistent. Flow rate is dependent upon both seasonal
variation in precipitation and snowmelt and upon release rates of
upstream dams.
[citation needed]
Streambed topography
Streambed topography is the primary factor in creating rapids, and is
generally consistent over time. Increased flow, as during a flood or
high rainfall season can make permanent changes to the streambed by
displacing rocks and boulders, by deposition of
alluvium or by creating new channels for flowing water.
[citation needed]
Gradient
The
gradient of a river is the rate at which it loses
elevation
along its course. This loss determines the river's slope, and to a
large extent its rate of flow. Shallow gradients produce gentle, slow
rivers while steep gradients are associated with raging torrents.
[citation needed]
Constriction
Constrictions
can form a rapid when a river's flow is forced into a narrower channel.
This pressure causes the water to flow more rapidly (hence the name)
and to react differently
[dubious – discuss] to riverbed events (rocks, drops, etc.).
[citation needed]
Obstruction
A boulder or ledge in the middle of a river or near the side can
obstruct the flow of the river, and can also create a "cushion"; a
"drop" (over the boulder); and "hydraulics" or "holes" where the river
flows back on itself—perhaps back under the drop—often with fearful
results for those caught in its grasp. (Holes, or hydraulics, are
so-called because their foamy, aerated water provides less buoyancy and
can feel like an actual hole in the river surface.) If the flow passes
next to the obstruction, an
eddy
may form behind the obstruction; although eddies are typically
sheltered areas where boaters can stop to rest, scout or leave the main
current, they may be swirling and whirlpool-like. As with hydraulics
(which pull
downward rather than to the side and are essentially
eddies turned at a 90-degree angle), the power of eddies increases with
the flow rate.
[citation needed]
In large rivers with high flow rates next to an obstruction, "eddy
walls" can occur. An eddy wall is formed when the height of the river is
substantially higher than the level of the water in the eddy behind the
obstruction. This can make it difficult for a boater, who has stopped
in that particular eddy, to reenter the river due to a wall of water
that can be several feet high at the point at which the eddy meets the
river flow.
Stream flow rate
A marked increase or decrease in flow can create a rapid (where
previously wasn't one), "wash out" a rapid (decreasing the hazard) or
make safe passage through previously-navigable rapids more difficult or
impossible. Flow rate is typically measured in cubic metres per second
(cumecs), or in cubic feet per second (cfs), depending on the country.
[citation needed]
Classification of whitewater
The most widely used grading system is the
International Scale of River Difficulty,
where whitewater (either an individual rapid, or the entire river) is
classed in six categories from class I (the easiest and safest) to class
VI (the most difficult and most dangerous). The grade reflects both the
technical difficulty and the danger associated with a rapid, with grade
I referring to flat or slow moving water with few hazards, and grade VI
referring to the hardest rapids which are very dangerous even for
expert paddlers, and are rarely run. Grade-VI rapids are sometimes
downgraded to grade-V or V+ if they have been run successfully. Harder
rapids (for example a grade-V rapid on a mainly grade-III river) are
often
portaged, a French term for carrying. A portaged rapid is where the boater lands and carries the boat around the hazard.
A rapid's grade is not fixed, since it may vary greatly depending on
the water depth and speed of flow. Although some rapids may be easier at
high flows because features are covered or "washed-out," high water
usually makes rapids more difficult and dangerous. At flood stage, even
rapids which are usually easy can contain lethal and unpredictable
hazards (briefly adapted from the American version
[5] of the International Scale of River Difficulty).
- Class 1: Very small rough areas, requires no maneuvering. (Skill Level: None)
- Class 2: Some rough water, maybe some rocks, small drops, might require maneuvering. (Skill Level: Basic Paddling Skill)
- Class 3: Whitewater, medium waves, maybe a 3–5 ft drop, but
not much considerable danger. May require significant maneuvering.
(Skill Level: Experienced paddling skills)
- Class 4: Whitewater, large waves, long rapids, rocks, maybe a
considerable drop, sharp maneuvers may be needed. (Skill Level:
Advanced Whitewater Experience)
- Class 5: Whitewater, large waves, continuous rapids, large
rocks and hazards, maybe a large drop, precise maneuvering. Often
characterized by "must make" moves, i.e. failure to execute a specific
maneuver at a specific point may result in serious injury or death.
Class 5 is sometimes expanded to Class 5+ that describes the most
extreme, runnable rapids (Skill Level: Expert)
- Class 6: While there is some debate over the term "Class 6",
in practice it refers to rapids that are not passable and any attempt to
do so would result in serious injury, near drowning or death (e.g. Murchison Falls). If a rapid is run that was once thought to be impassible, it is typically reclassified as Class 5.
Features found in whitewater
On any given rapid there can be a multitude of different features
which arise from the interplay between the shape of the riverbed and the
velocity of the water in the stream.
Strainers or Sifts
Strainers are formed when an object blocks the passage of larger
objects but allows the flow of water to continue - like a big food
strainer or
colander.
These objects can be very dangerous, because the force of the water
will pin an object or body against the strainer and then pile up,
pushing it down under water. For a person caught in this position, it
will be difficult or impossible to get to safety, often leading to a
fatal outcome.
Strainers are formed by many different natural or man-made objects,
like storm grates over tunnels, trees that have fallen into a river
("log jam"), bushes by the side of the river that are flooded during
high water, wire fence, rebar from broken concrete structures in the
water, or other debris. Strainers occur naturally most often on the
outside curves of rivers where the current undermines the shore exposing
the roots of trees and causing them to fall into the river forming
strainers.
In an emergency it is often best to try and climb on top of a
strainer so as not to be pinned against the object under the water. If
you are in a river, swimming aggressively away from the strainer and
into the main channel is your best bet. If you cannot avoid the
strainer, you should swim hard towards it and try to get as much of your
body up and over it as possible.
Sweepers
Sweepers are trees fallen in or heavily leaning over the river, still
rooted on the shore and not fully submerged. Its trunk and branches may
form an obstruction in the river like strainers. Since it is an
obstruction from above, it often does not contribute to whitewater
features but may create turbulence. In fast water sweepers can pose a
serious hazard to paddlers.
Holes
Holes, or "hydraulics", (also known as "stoppers" or "souse-holes". See also
Pillows),
are formed when water pours over the top of a submerged object, or
underwater ledges, causing the surface water to flow back upstream
toward the object. Holes can be particularly dangerous—a boater may
become stuck under the surface, in the recirculating water—or
entertaining play-spots, where paddlers use the holes' features to
perform various
playboating
moves. In high & low volume water flow, holes can subtly aerate the
water, enough to allow floating watercraft to fall through the aerated
water to the bottom of a deep 'hole'.
Some of the most dangerous types of holes are formed by low head dams (
weirs),
and similar types of obstruction. In a low head dam, the 'hole' has a
very wide, uniform structure - there's no escape point - and the sides
of the hydraulic (ends of the dam) are often blocked by a man-made wall,
making it impossible to paddle around, or slip off the side of the
hydraulic, where the bypass water flow would become normal (laminar). By
(upside-down) analogy, this would be much like a surfer slipping out
the end of the pipeline, where the wave no longer breaks. Low head dams
are insidiously dangerous because their danger cannot be easily
recognized by people who have not studied swift water. (Even 'experts'
have died in them.) Floating debris (trees, kayaks, etc.) is often
trapped in the retro-flow 'grinder' for weeks at a time.
Refs:
NFPA-1006 Standard for Technical Rescuer,
Swiftwater rescue,
Canyoning
Waves
Waves
are formed in a similar nature to hydraulics and are sometimes also
considered hydraulics as well. Waves are noted by the large smooth face
on the water rushing down. Sometimes a particularly large wave will also
be followed by a "wave train", a long series of waves. These
standing waves can be smooth or, particularly the larger ones, can be breaking waves (also called "whitecaps" or "haystacks").
Because of the rough and random pattern of a riverbed, waves are
often not perpendicular to the river's current. This makes them
challenging for boaters since a strong sideways or diagonal (also called
" a lateral") wave can throw the craft off.
In fluid mechanics, waves are classified as laminar, but the
whitewater world has also included waves with turbulence ("breaking
waves") under the general heading of waves.
Pillows
Pillows are formed when a large flow of water runs into a large
obstruction, causing water to "pile up" or "boil" against the face of
the obstruction. Pillows normally signal that a rock is not undercut.
Pillows are also known as "pressure waves".
Eddies
Eddies
are formed, like hydraulics, on the downstream face of an obstruction.
Unlike hydraulics, eddies swirl on the horizontal surface of the water.
Typically, they are calm spots where the downward movement of water is
partially or fully arrested - a nice place to rest or to make one's way
upstream. However, in very powerful water, eddies can have powerful,
swirling currents which can flip boats and from which escape can be very
difficult.
Undercut rocks
Undercut rocks are rocks that have been worn down underneath the
surface by the river, or loose boulders which cantilever out beyond
their resting spots on the riverbed. They can be extremely dangerous
features of a rapid because a person can get trapped underneath them
underwater. This is especially true of rocks that are undercut on the
upstream side. Here, a boater may become pinned against the rock
underwater. Many whitewater deaths have occurred in this fashion.
Undercuts sometimes have pillows, but other times the water just flows
smoothly under them, which can indicate that the rock is undercut.
Undercuts are most common in rivers where the riverbed cuts through
sedimentary rocks like
limestone rather than
igneous rock like
granite. In a steep canyon, the side walls of the canyon can also be undercut.
A particularly notorious undercut rock is Dimple Rock, in Dimple Rapid on the Lower
Youghiogheny River,
a very popular rafting and kayaking river in Pennsylvania. Of about
nine people that have died at or near Dimple Rock, including three in
2000, several of the deaths were the result of people becoming entrapped
after they were swept under the rock.
[6] [7]
Sieves
Another major whitewater feature is a sieve, which is a narrow empty
space that water flows through between two obstructions, usually rocks.
Similar to strainers, water is forced through the sieve, resulting in
higher flow velocity which forces water up and creates turbulence.
Whitewater craft
A solo kayak paddler performs a
high brace in foamy water. One of the hazards of whitewater paddling is that highly-aerated water decreases the effect of buoyancy.
There are many different types of whitewater craft that people use to
make their way down a rapid, preferably with finesse and control. Here
is a short list of them.
Whitewater kayaks
differ from sea kayaks and recreational kayaks in that they are better
specialized to deal with moving water. They are often shorter and more
maneuverable than sea kayaks and are specially designed to deal with
water flowing up onto their decks. Most whitewater kayaks are made of
plastics these days, although some paddlers (especially
racers
and "squirt boaters") use kayaks made of fiberglass composites.
Whitewater kayaks are fairly stable in turbulent water, once the paddler
is skillful with them; if flipped upside-down, the skilled paddler can
easily roll them back upright. This essential skill of whitewater
kayaking is called the "
Eskimo Roll", or simply "Roll." Kayaks are paddled in a low sitting position (legs extended forward), with a two-bladed paddle. See
Whitewater kayaking.
Rafts
are also often used as a whitewater craft; more stable than typical
kayaks, they are less maneuverable. Rafts can carry large loads, so they
are often used for expeditions. Typical whitewater rafts are inflatable
craft, made from high strength fabric coated with PVC, Urethane,
Neoprene or Hypalon; see
rafting. While most rafts are large multi-passenger craft, the smallest rafts are single-person whitewater craft, see
packraft.
Catarafts
are constructed from the same materials as rafts. They can either be
paddled or rowed with oars. Typical catarafts are constructed from two
inflatable pontoons on either side of the craft that are bridged by a
frame. Oar-propelled catarafts have the occupants sitting on seats
mounted on the frame. Virtually all oar-powered catarafts are operated
by a boatsman with passengers having no direct responsibilities.
Catarafts can be of all sizes; many are smaller and more maneuverable
than a typical raft.
Canoes are often made of fiberglass, kevlar, plastic or a combination of the three for strength and durability. They may have a
spraycover,
resembling a kayak, or be "open," resembling the typical canoe. This
type of canoe is usually referred to simply as an "open boat."
Whitewater canoes are paddled in a low kneeling position, with a
one-bladed paddle. Open whitewater canoes often have large airbags and
in some cases foam, usually 2 lb density ethyl foam, firmly attached to
the sides, to displace water in the boat when swamped by big waves and
holes and to allow water to be spilled from the boat while still in the
river by floating it up on its side using the foam and bags. Like
kayaks, whitewater canoes can be righted after capsizing with an Eskimo
Roll; however this requires more skill in a canoe.
C1s are similar in construction to whitewater kayaks. However,
they are paddled in a low, kneeling position. They employ the use of a
one-blade paddle, usually a little shorter than used in a more
traditional canoe. They will have a spraycover, essentially the same
type used in kayaking. Like kayaks, C1s can be righted after capsizing
with an Eskimo Roll.
McKenzie River dory
or "Drift Boat" by some. A more traditional "hard sided" boat. The
design is characterized by a wide, flat bottom, flared sides, a narrow,
flat bow, a pointed stern, and extreme rocker in the bow and stern to
allow the boat to spin about its center for ease in maneuvering in
rapids.
River bugs are small single person inflatable craft where a person's feet stick out of one end.
River Bugging is done feet first with no paddle.
Safety
Running whitewater rivers is a popular recreational sport but is not
without danger. In fast moving water there is always the potential for
injury or death by drowning or hitting objects. Fatalities do occur;
some 50 people die in whitewater accidents in the United States each
year.
[8]
Strainers and sieves can pose a particular hazard. If the sieve is
visible above water, a boater can be pinned against it and may
eventually be forced underwater as the current passes through. If the
sieve is completely submerged, it is especially insidious because it may
not be discernible at all. In shallow water, bows of boats can get
caught in submerged sieves, as the current pulls the nose down below the
rocks where it can lodge. If this happens, it is likely that the whole
boat will get pulled under water. Sieves pose a particular hazard to
swimmers because even the smallest sieves can trap a person's foot if
they stand up in the current. The force of the current then pushes the
whole body underwater, becoming a deadly situation in a matter of
seconds. It is for this reason that one of the first things whitewater
boaters learn is never to stand up in more than ankle deep water where
there is a current.
The dangers can be mitigated (but not eliminated) by training, experience, scouting, the use of safety equipment (such as
personal flotation device, helmet, throw ropes), and using other persons as "
spotters".
Scouting or examining the rapids before running them is crucial to
familiarize oneself with the stream and anticipate the challenges. This
is especially important during flood conditions when the highly
increased flow have altered the normal conditions drastically.
