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 are made based on different criteria as follows.
- Classification Type 1
- Natural Channels
- Artificial Channels
Natural open channels include all channels that exist naturally on the earth. They are generally very irregular in shape.
Example: Rivers, tidal estuaries etc.
Artificial open channels are the channels develops by men. They are usually designed with regular geometric shapes.
Example: Irrigation canals, laboratory flumes, spillway chutes, drops, culverts, roadside gutters etc.
- Prismatic Channels
- Non-prismatic Channels
A channel with unvarying cross-section and constant bottom slope is called prismatic channel. All the artificial channels are usually prismatic. The rectangular, trapezoid, parabola and circle are the most commonly used shapes of prismatic channels.
A channel with varying cross-section and constant bottom slope is called non-prismatic channel. The natural channels are usually prismatic.
- Rigid Boundary Channels
- Mobile Boundary Channels
A channel with immovable bed and sides is known as a rigid boundary channel.
Example: Lined canals, sewers and non-erodible unlined canals.
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 that comprising the channel perimeter.
- Small Slope Channels
- Large Slope Channels
An open channel having a bottom slope less than 1 in 10 is called a channel of small slope (Chow, 1959). The slopes of ordinary channels, natural or artificial, are far less than 1 in 10.
An open channel having a bottom slope greater than 1 in 10 is called a channel of small slope (Chow, 1959). Some artificial channels like drops and chutes have far more than 1 in 10.