River
features cont'd
By
Marjorie Henry, Contributor
 |
Culinary
Arts Expo for high and primary
schools at Terra Nova Hotel.
- Ian Allen Photo |
IN
THE lesson last week, I began reviewing
the work of the river, another topic
under geomorphic system. Two questions
taken from past examination papers were
given in the lesson.
Both
referred to river features, namely,
deltas and levées. I shared
with you information on river deposition,
one of the threefold actions of the
river. Both features were formed by
this action.
Today
I will focus on the question on levées.
Just in case you missed the lesson
last week, let me restate the question
I am discussing this week.
June
2000 - Question 3
(e)
(i) Explain how levées are
formed. (4 marks)
(iii)
Explain how the development of levées
may result in the development of deferred
junctions. (2 marks)
Before
answering the question, there is no
harm in reminding ourselves of what
is a levée. The Dictionary
of Geography tells us that a levée
is 'a natural embankment alongside
rivers, built up during periods of
floods.' In other words, it is formed
as a result of alluvial deposits.
Levées
can be artificial (man-made) or natural.
Since we are studying the work of
the river, it follows that we would
be concerned about levées formed
by the river.
The
formation of a levée is clearly
stated in one of your recommended
textbooks, The Caribbean Environment
(New Edition) by Mark Wilson, Page
43. It states as follows:
1.
After a period of heavy rain, the
river is swollen with flood water,
which contains sediment from higher
up the valley. The river floods the
flat ground along the valley floor.
2.
The flood waters move more slowly
than the main channel, and cannot
carry as much sediment. Most of the
sediment is deposited quite near to
the main river channel.
3.
When the flood waters recede, a thick
deposit of mud is left along the river
banks. After this process has been
repeated many times, a levée
is formed.
May
I encourage you to refer to the text
and be familiar with the diagrams
there which support what is written.
Practise to draw and label them properly.
Although this question did not ask
you for diagrams, you can use diagrams
to assist you in answering your questions.
Make sure that they are properly done
and labelled.
The
second part of the question which
asks that you explain how the development
of levées may result in the
development of deferred junctions
can be easily answered by the information
given in the Dictionary of Geography.
It states that 'a deferred tributary
is one which does not join the main
river directly on entering a flood
plain because of a barrier, such as
a levée. Instead, it flows
parallel to the main river for some
distance before joining it. The confluence
of the deferred tributary and the
main river is called a deferred junction.'
Here
are sections of questions on the work
of the river and features formed,
taken from past examination papers.
Source the information needed to answer
them as best you can.
June
1999 - Question 2
(b)
(i) Describe the processes of hydraulic
action and corrosion (abrasion) carried
out by running water (rivers). (4
marks)
(c)
(i) Explain how the following river
features are formed:
-
Levées.
-
River cliffs (under-cut slopes)
(8 marks)
Since
the formation of 'levées' was
already discussed, focus on the formation
of 'river cliffs'.
June
2001 Question 2
(b)
(i) How does a river use its energy?
(3 marks)
(ii)
Describe TWO ways by which a river
transports its load. (4 marks)
*
Marjorie Henry is Geography teacher
at Glenmuir High School in Clarendon.
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