CLASSIFICATION OF OPEN CHANNEL
CLASSIFICATION OF OPEN CHANNEL : An open channel is a passage which conveys water at atmospheric pressure, under the influence of a gravitational force. In other words it is a conduit in which water flows with its surface in contact with the atmosphere. Flows in irrigation channels, streams and rivers, navigation channel, drainage channels and sewers are some examples of open channel flow. As the liquid flows in a channel, it will always be subjected to some frictional resistance. In order to overcome the resistance and to cause the flow in a channel, it is constructed with its bottom sloping towards the direction of flow. The flow of liquid through a pipe at atmospheric pressure or when the level of liquid in the pipe is below the top of the pipe, is also classified as open channel flow.
CLASSIFICATION OF OPEN CHANNELS
The Open Channels are Classified as:
According to the Cross Sectional form of the Channel:
(a) Natural channel
(b) Artificial channel
A natural channel is the one which has irregular sections of varying shapes, which is developed in a natural way Ex: Rivers, Streams etc.
An artificial channel is the one which is built artificially for some specific purpose, such as irrigation, water supply, water power development. Ex: Regular sections of rectangle, trapezoidal etc. canals, drainage gutters and aqueducts.
2. According to the Shape of Various Sections:
(a) Prismatic channel
(b) Non-prismatic channel
A channel is said to be prismatic if the cross-section is uniform and the bed slope is constant through out is length In a non-prismatic, either the cross-section or the slope or both changes.
The prismatic channels may be further classified according to the shape of cross-section as,
(a) Rectangular channel
(b) Trapezoidal channel
(c) Triangular channel
(d) Parabolic channel and
(e) Circular channel.
CLASSIFICATION OF FLOW IN CHANNELS
The open channel classifies the flow into the following categories
(a) Steady flow and Unsteady flow,
(b) Uniform flow and Non-uniform flow,
(c) Laminar flow and Turbulent flow,
(d) Sub-critical, Critical and Super critical flow
(a) Steady and Unsteady Flow: If the flow characteristics such as depth of flow, velocity of flow, rate of flow at any point in open channel flow do not change with time the flow is said to be steady flow otherwise it is said to be unsteady flow.
(b) Uniform and Non-Uniform Flows: If the depth, slope, cross- section and velocity remain constant for a given length of channel, the flow is said to uniform, otherwise it is said to be non-uniform flow.
(c)Laminar Flow and Turbulent Flow: .Just as in pipes, the flow in channels may also be characterized as laminar. Turbulent (or) in a Transitional state, depending open the relative effect of viscous and inertia forces. Reynolds number is a measure of this effect in channel flow also.The flow in open channel is said to be laminar the Reynold number is less than 500 to 600 laminar flow. If Reynold number is greater than 2000 the flow in channel turbulent flow
(d) Subcritical, Critical and Supercritical Flow : If Froude number is less than 1.0, the flow is subcritical. If Froude number is equal to 1.0. The flow is critical. If Froude number is greater than 1.0, the flow is supercritical.