Open Channel Flow

An open channel is a natural or man-made structure in which liquid flows with a free surface at atmospheric pressure.

The prime motivating force in open channel flows is gravity flow. For example, flow in rivers, streams, flow in sanitary and storm sewers flowing partially full.

TYPES OF CHANNELS

Prismatic and Non-Prismatic Channels

• A channel in which the cross-sectional shape, size, and bed slope are constant is termed a Prismatic channel.

• All-natural channels generally have varying cross-sections and consequently are known as Non-prismatic channels.

• Most man-made channels are prismatic channels over long stretches. Rectangle, trapezoid, triangle, and circle are commonly used shapes in man-made channels.

Rigid and Mobile Boundary Channels

• Rigid channels are those in which the boundary is not deformable. The shape and roughness factor is not a function of the flow parameter.

• In other words, in Rigid channels, the flow velocity and shear stress distribution will be such that no major scouring, erosion, or deposition will take place in the channel and the channel geometry and roughness are essentially constant with respect to time.

• For example, lined canals and non-erodible unlined canals.

• In Rigid channels, only the depth of flow may vary with space and time depending on the nature of the flow. Hence these channels have one (1) degree of freedom.

• Mobile channels are those in which the boundaries undergo deformation due to the continuous process of erosion and deposition due to flow.

• In mobile channels, the resistance to flow, the quantity of sediment transported, and channel geometry all depend on the interaction of flow with channel boundaries.