Design of Alluvial Channels in Irrigation Engineering

Open Channel Flow vs Pipe Flow

• The main difference between open channel flow and pipe flow is the presence of a free surface in open channels, whereas pipe flow is under pressure.

Open Channel Equations

• The basic equations used for water flow in open channels are the equations of continuity and motion.

Channel Lining

• The purpose of lining a channel is to reduce water loss, prevent erosion, and increase the flow rate.
• A lined channel requires a smaller size to convey a specified flow rate compared to an unlined channel.

Open Channel Characteristics

• Open channels receive water from rain, melting snow, and groundwater.
• Irrigation water is conveyed in lined or unlined canals.

Channel Types

• A stable channel is defined as a channel in which the flow transports sediment having the same characteristics as that of the material in the channel bottom.

Design of Stable Alluvial Channels

• The rational approach for the design of stable alluvial channels utilizes the laws governing sediment transport and resistance to flow.
• The regime theory for the design of stable alluvial channels relies on observations of natural rivers and was developed based on empirical data.

Erodible Channels

• To prevent erosion of the channel bottom and sides in erodible channels, the velocity should be kept low.

Canal Velocity

• If the velocity becomes less than the critical velocity in a canal, sediment deposition occurs.

Canal Design

• In erodible channels, the type of soil is crucial to consider, as canals may be excavated through soil such as clay.
• In non-alluvial soil, the canal design should consider the canal's ability to resist erosion.

Sediment Load

• The regime theory is typically applicable to channels carrying sediment load with a concentration less than 500 ppm by weight.

Channel Types

• A lined channel may be more economical than an unlined channel in some cases.
• The empirical approach for the design of stable alluvial channels was developed based on observations on a number of irrigation canals.