Natural open channels include all channels that exist naturally on the earth. They are generally very irregular in shape.
Example: Rivers, tidal estuaries, etc.
2. Artificial Channels
Types of Open Channel
An open channel is a conduit in which water flows with a free surface. The free surface is subjected to atmospheric pressure. The classification of open channels is made based on different criteria as follows.
Classification Type 1
1. Natural Channels
Artificial open channels are the channels developed by men. They are usually designed with regular geometric shapes.
Examples: Irrigation canals, laboratory flumes, spillway chutes, drops, culverts, roadside gutters, etc.
Classification Type 2
1. Prismatic Channels
A channel with an unvarying cross-section and a constant bottom slope is called a prismatic channel. All artificial channels are usually prismatic. The rectangular, trapezoid, parabola, and circle are the most commonly used shapes of prismatic channels.
2. Non-prismatic Channels
A channel with either a varying cross-section or a varying bottom slope is called a non-prismatic channel. The natural channels are usually prismatic.
Classification Type 3
1. Rigid Boundary Channels
A channel with an immovable bed and sides is known as a rigid boundary channel.
Example: Lined canals, sewers, and non-erodible unlined canals.
2. Mobile Boundary Channels
If a channel boundary is composed of loose sedimentary particles moving under the action of flowing water, the channel is called a mobile boundary channel.
Example: An alluvial channel is a mobile boundary channel transporting the same type of material comprising the channel perimeter.
Classification Type 4
1. Small Slope Channels
An open channel having a bottom slope of less than 1 in 10 is called a channel of a small slope (Chow, 1959). The slopes of ordinary channels, natural or artificial, are far less than 1 in 10.
2. Large Slope Channels
An open channel having a bottom slope greater than 1 in 10 is called a channel of a small slope (Cow, 1959). Some artificial channels like drops and chutes have far more than 1 in 10.
