geomorphology of rivers

Instructional Objectives
On completion of this lesson, the student
shall be able to learn the following:
1. The components of a fluvial system
2. Mechanics of sediment erosion,
transportation and deposition by rivers
3. Causes of riverbed
aggradation and degradation
4. Bar formation in rivers
5. Causes of meandering, lateral mi
gration and river width adjustment of
rivers
6. Relationships between velocity, perimet
er, slope, velocity, etc. of alluvial
rivers
2.9.0 Introduction
In the previous lesson, we discussed t
he mechanics flowing wa
ter. In the earth
system, this water may be thought of as t
he water flowing downhill after a splash
of rain, which carries with it some amount of soil that
has been eroded by the
action of flowing water. The flowing wate
r of river moving down to the ocean also
carries huge amounts of sediment whic
h have been accumulated from other
smaller streams joining the river.
In general, the water moving over the land surface is the dominant agent of land
space alteration. Near surface weatheri
ng provide sediment load for the flowing
streams. Some of the load
gets deposited along
the path of the river and only a
fraction of the total material waste from
the lands is carried by the rivers to the
sea. In fact, the land space evolves essent
ially due to the water flowing over it in
small rills and gullies, joining to form small streams, which combine to form
rivers. The process of these watercour
ses eroding and conveying water is a
continuous process and has been going on
since the formation of this planet and
the elements surrounding it. Hence rive
rs are ever changing but in a man’s
lifetime it may not be much dependi
ng on the land space through which it
passes. The general adjective
fluvial (from Latin fluvial meaning river) is applied
for the work done by river and fluvial syst
em applies to all the area draining a
particular river extending fr
om the drainage divides in
the source areas of water
and sediment, through the channels and valleys of the drainage basin, to
depositional area such as the coasts.
In this lesson, it is intended to under
stand the flow and sediment transport
behaviour of natural
channels and rivers. More app
lied theories of sediment
dynamics and their application
to natural rivers and arti
ficial channels have been
discussed in Lesson 2.10.
Version 2 CE IIT, Kharagpur