2.9.2
Middle Course
In
the middle course,
- The
river channel is wider
and deeper.
- Its
cross-section is asymmetrical.
- A
steep river cliff
develops on the concave
bank and a gentle
slip-off slope on the
convex bank.
2.9.2.1
Meanders [fig
2.9.2(a,b)]
The
amount of water and material
in the river increases as
more tributaries join in.
The bed widens, its slope
becomes gentler, and the
water flows much more slowly
as the river flows out of
the mountains. As a
slow-moving river cannot
keep heavy material moving,
piles of gravel form along
the banks. At this stage,
the river carries its load
of sand, mud, and small
stones suspended in water.
It also begins to swing from
side to side, cutting into
some banks and drifting away
from others. As there are no
obstacles such as rapids,
the river's course becomes
smoother and more regular.
A
floodplain is a wide and
flat plain. It is built up
by alluvium laid down on the
river banks during repeated
flooding.
When
there is a flood, the river
overflows its banks. When
the flood subsides, there is
a decrease in the volume of
water and the river starts
to deposit its load. Most of
the alluvium is deposited on
the banks close to the
river. With repeated
flooding, the materials that
are deposited on the river
banks accumulate to form
floodplains.
The
path of the middle river is
always changing as it cuts
sideways into the land and
starts to deposit its load.
Loops, called meanders, and
oxbow lakes are typical
features of this part of the
river. During a storm,
meanders stop river water
flowing easily. This causes
water to build up in places,
and may lead to flooding.
Fig
2.9.1(b)
