Many people who
drown in rivers have no intention of being in the river at
all. Approximately 54% of people who drowned in rivers either
fell in, were washed away or crashed into the river in their
vehicles.
Here is what they were doing. - Road vehicle 97 - accidental
immersions, e.g. falling in from the bank 104 - suicide 38 - swimming
36 - crossing rivers (e.g. tramping, hunting) 14 - rafting and tubing
9 - kayaking or canoeing 15 - net or
shell fishing or angling 18 - boating (including jet boating,
rowing craft and dinghies) 10 - diving/jumping 12 - commercial
(employment related) 4 - rescuing others 6 - other 9.
New Zealand has almost double the drowning rate per head
of population of Australia and over four times the drowning
rate per head of population of Great Britain.
Which fact do you find the most surprising and why?
Which facts do you think your friends and family should know
about and why?
If you are standing next to a knee deep river 10 metres wide
flowing at walking pace about seven cubic metres of water
will be flowing past you each second. A cubic metre of water
weighs about a tonne so that means seven tonnes per second.
This is the weight of about four elephants. Imagine trying
to stop that!
Maori believe that when a person drowns in a river a tapu
(a spiritually important restriction) is laid on the location
and can only be lifted by a tapu lifting ceremony performed
according to local protocol.
How Rivers Work
Water in rivers exerts a very powerful force against any
fixed object. This force once in place remains constant unlike
the ocean where the force is released with each tidal surge.
Even clam looking rivers are very powerful, do not be
deceived.
The downstream flow of water is called Laminar Flow. As
water flows down the river channel, friction along the edges
of the river bank and bed slightly slow the flow. Also, water
near the surface will be slowed slightly by contact with the
air, particularly if a strong wind is blowing upstream. The
strongest current therefore will be found midstream just below
the surface.
Water flows in a straight line, changing direction at
points of high resistance. The line of greatest depth and
strongest laminar flow will be on the outside of the corners.
The water on the inside of the bend is slower moving.
Within New Zealand there is a recognized grading system for
rivers. This classification is based upon difficulty, loss of
height, amount and speed of water, and the number of hazards.
Grade 1 is the easiest, such as slow moving lowland rivers.
Grade 6 is the hardest, with rivers that have large
waterfalls, violent water and are potentially life threatening
for swimmers and other river users.
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