2.5
Energy of the River
A
river gets its energy from
two sources – its velocity
and discharge. The greater
the river energy, the
greater will be the ability
to erode. The
characteristics of a river
channel influence the
velocity of a river while
the characteristics of a
drainage basin influence the
discharge of water in a
river.
2.5.1
Velocity
Channel
gradient – Due to
gravity all rivers flow
downhill. A river flowing
down a steep slope or
gradient has higher velocity
than one which flows down a
gentler gradient. For
example, the speed of flow
in a river that plunges down
a steep slope in the form of
a waterfall is much higher
than the speed of flow in a
river that winds down a
gentler slope.
Channel
roughness – Flowing
water in a river channel
encounters various forms of
resistance, which reduces
its energy. In [fig 2.5(a)],
the channel is smooth while
that in [fig 2.5(b)] is
rough or uneven with
boulders on the river bed as
well as rocks that protrude
out from the bank. A river
that flows through such a
river has to overcome such
obstacles and therefore
there will be more friction
and the velocity of the
river is reduced
 fig2.5(a) fig2.5(b)
Channel
shape - The
shape of the channel or its
cross section affects the
wetted perimeter. The wetted
perimeter refers to the
extent to which water is in
contact with its channel.
The greater the wetted
perimeter, the greater the
friction between the water
and the banks and the bed of
the channel, and the slower
the flow of river.
Wetted
perimeter is calculating
by adding the length and the
breadth of the channel in
contact with water.
2.5.2
Volume
The
volume of the river depends
on:
- Size
of Drainage Basin
- Vegetation
Cover
- Amount
of Rainfall
- Temperatures
- Permeability
of rocks and other
ground surface
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