Flow Dynamics in Open Channels and Rivers

Instructional Objectives
On completion of this lesson, t
he student shall be able to learn:
1. The physical dynamics of water mo
vement in open channels and rivers
2. The mathematical description of
flow processes in the above cases
3. Different types of free surfac
e flows: uniform, non uniform, etc.
4. Different channel shapes and cross sections and their representations
5. Computation steps
for gradually varied water surface profiles
2.8.0 Introduction
It is common for water resources engineer
s to design a water system involving
flow of water from one place to another, usually passing a variety of structures on
the way some of them meant for controllin
g the flow quantity.
Rivers and artificial
channels, like canals, convey water with a
free surface, that is, the surface of
water being exposed to air as opposed to fl
ow of water in pipes. It is easy to
visualize that for any such open channel flow, as they are called; the presence or
absence of a hydraulic structure controls t
he position of the free
surface of water.
Knowing the mathematical description of fl
owing water, it is possible to compute
the water surface profile, which is import
ant for example in designing the height
of the channel walls of t
he water conveying system.
Another example, the case of river flow
obstruction by the pr
esence dam may be
mentioned. The water level of the river
increases on construction of the dam and
it is essential to know the maximum
possible rise, perhaps during the maximum
flood, in order to know the degree of
submergence of the la
nd behind the dam.
Barrages are low height structures, and
hence, the rise of water will not be
occurring uniformly across the river,
again due to the difference of gate
operation.
In this lesson, the behavior and corres
ponding mathematical description of flow
in open channels are reviewed in order
to utilize them in designing water
resources systems.
Version 2 CE IIT, Kharagpur
2.8.1 Flow in natural rivers
Figure1 shows a river carrying a low discharge.