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White Water River
Rafting is an unobtrusive way to enjoy nature's
waterways.Rafting difficulty ranges from Class
I (easiest) to Class VI (hardest).
is formed in a rapid, when a river's gradient
drops enough to 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.
Three factors, separately or in combination,
can create rapids: gradient, constriction,
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
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 to
riverbed events (rocks, drops, etc.)
Lastly, there is 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 "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 past the obstruction is less violent,
often an eddy is formed; eddies may be swirling
and whirlpool-like, or simply sheltered areas
where boaters can stop to rest, scout or leave
the main current. These days the term has a
broader meaning, applying to any river or creek
that has a significant number of rapids and
the term is also used as an adjective describing
boating on such rivers. Ex. One of his hobbies
is whitewater kayaking.
of White Water Rapids
The most widely used grading system is the International
Grading System, where whitewater (either individual
rapids, 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,
which is difficult enough to tax the most experienced
crew of rafters to the limit).
The ability of a paddler, thrown from his raft,
to swim through a rapid in safety is also a
consideration when rapid grades are fixed.
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 often wrongly downgraded
to grade-V or V+ if they have been run successfully
many times. Harder rapids (for example a grade-V
rapid on a mainly grade-III river) are often
portaged. The term is French for carrying i.e.
the boater lands and carries the boat around
the rapid. A rapid's grade is not fixed, since
it may vary greatly depending on the water depth
and speed of flow.
Some rapids may be easier at high flows because
rapids are covered or "washed-out and others
may be easier at low flows when the currents
are slower. The grade of difficulty of any given
section of whitewater will depend upon the degree
of skill required to negotiate it, or indirectly,
upon the nature of the obstruction that the
raft crew needs to overcome. Grades do vary
when water levels vary. As a generalisation
grades tend to go higher as water levels increases
because of the steep nature of river gradients
in this country. These grades are referred to
as the NORMAL grade. Below are the general characteristics
of the six grades of whitewater.
RAPID GRADE  Rapids are small regular
waves. The passage is clear an easy to recognise
and negotiate. Care may be needed with obstacles
like fallen trees and bridge piers.
RAPID GRADE  Rapids with regular medium
sized waves (less than 1 m); low ledges or drops;
easy eddies and gradual bends. The passage is
easy to recognise and is generally unobstructed
although there may be rocks in the main current,
overhanging branches or log jams.
RAPID GRADE  Rapids with fairly high
waves (1-2 m); broken water, stoppers and strong
eddies; exposed rocks; small falls. The passage
may be difficult to recognise from on the river
and inspection from the bank may be required.
Maneuvering to negotiate the rapids is required.
RAPID GRADE  Difficult rapids with
high, powerful, irregular waves; broken and
confused water; often boiling eddies; strong
stoppers; ledges; drops and dangerous exposed
rocks. The passage is often difficult to recognise
and inspection from the bank is preferable.
Precise and sequential maneuvering is required.
RAPID GRADE  Very difficult rapids
with confused and broken water; large drops;
violent and fast currents; abrupt turns; difficult
powerful stoppers and fast boiling eddies; numerous
obstacles in the main current. Detailed inspection
from the bank is normally required and is strongly
recommended for rapids not recently transited
at the prevailing water level. Complex, precise
and powerful sequential maneuvering is required.
A buoyancy vest equipped swimmer risks injury
and this is the extreme for commercial operations.
RAPID GRADE  All previous difficulties
increased to the limit of practicability. Nearly
impossible, very dangerous and cannot be attempted
without a definite risk of life. The rapids
under this grade is also known as suicidal rapids.