Activities
of the river (Part 2)
By
Marjorie Henry, Contributor
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| Young
DJs show their skills on the turntables
with FAME DJ Dimitri at the radio
station's School Rules party held
at York Castle High late last
year. - Contributed Photo |
Part
(b) (i) of the second question, which
was restated last week, is based on
how the river uses its energy. The information
is as follows:
THE
RIVER USES ITS ENERGY TO:
Flow towards the sea, and overcome
the friction between the water itself
and the channel through which it runs.
Erode the material on its banks and
bed.
Transport the material it has eroded.
(Source:
The Caribbean Environment: Mark Wilson)
Part
(b)(ii) of the same question is asking
for ways by which a river transports
its load. These are:
(i)
Carrying matter in solution. Some
minerals are dissolved in the water.
(ii)
Carrying it in suspension. Fine clay
particles float along in the river
water.
(iii)
Rolling it along the bed, i.e. bottom
traction. Coarser materials such as
pebbles, stones, rocks and boulders
are rolled along the riverbed. Material
moved by traction is known as the
bed load.
(iv)
Moving it by a series of jerks and
jumps, a process known as saltation.
Sand particles are often 'bounced'
along the riverbed.
(Source:
The Caribbean Environment: Mark Wilson)
Here
is another question on running water
(the river). This comes from the question
paper of June 2005 - Question 3 (b)(i)
Draw
diagrams to show the following drainage
patterns and state where EACH may
develop:
a)
Radial
b)
Dendritic
c)
Trellis
 This
question is testing the specific objective
which states - 'describe and illustrate
trellis, radial and dendritic drainage
patterns'.
In
answering this question, I will share
with you the information from the
text Certificate Physical and Human
Geography by Goh Cheng Leong, P47.
The
initial stream that exists as a consequent
of the slope is called the consequent
stream. As the consequent stream wears
down the surface by deepening its
channel downwards, it is joined by
several tributaries either obliquely
or at right angles depending on the
alignment and the degree of resistance
of the rocks.
If
the rocks are composed of homogeneous
beds of uniform resistance to erosion,
the tributaries will join the main
valley obliquely as insequent streams.
The drainage pattern so evolved will
be tree-like in appearance, and is
therefore described as dendritic drainage,
after a Greek word dendron meaning
'tree'.
On
the other hand, if the rocks are made
up of alternate bands of hard and
soft rocks, the tributaries tend to
follow the pattern of the rock structure.
If the outcrops of the rocks occur
at right angles to the main valley,
the tributaries will join it at right
angles as subsequent streams. The
drainage pattern so developed will
be rectangular in shape and is called
trellised drainage.
Streams
flowing outwards and downhill from
a dome or volcanic cone give rise
to a radial drainage pattern just
like the spokes of a bicycle wheel.
Although
all of this information is not needed
to answer this particular question,
I shared it since sometimes you are
asked to explain the relationship
between geology and drainage pattern
and this information would be needed
for that explanation. Here are the
diagrams that you would draw to go
along with the question.
In
specific reference to the question,
your response should be, for example,
'Radial drainage pattern develops
from a dome or volcanic cone'.
In
the next lesson, I will present another
question on rivers. I hope you are
reading on the topic as well.
*
Marjorie Henry is Geography teacher
at Glenmuir High School in Clarendon.
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