IntermediateTopic 76 of 112Civil & Structural
Open channel design
Channels are sized with Manning's equation for uniform flow.
In depth
Lined and unlined channels designed with Manning's equation for uniform flow; most efficient section is semicircle or half hexagon; trapezoidal common. Check velocity limits (scour vs silting), freeboard and Froude number. Gradually varied flow profiles computed by standard-step method.
Key points
- Hydraulic radius
- Best hydraulic section
- Permissible velocity
ExampleA trapezoidal drain with 1:1.5 side slopes carries stormwater from a car park.
What is Open channel design?
Channels are sized with Manning's equation for uniform flow.
Why is it important to understand open channel design?
Open channel design sizes canals, drains and rivers so they carry the design flow without overflow or erosion.
What is uniform flow?
Flow in which the depth and velocity do not change along the channel, and it is the usual basis for channel design.
What is the danger of high velocity?
Fast water erodes channel beds and banks, so velocity limits or linings are used to protect the channel.
How is Open channel design used in practice?
Typical applications include sizing a trapezoidal drainage channel for a design storm, checking the capacity of an existing river channel for flood flow and designing a lined canal with a slope that gives a safe velocity.
What should I learn before Open channel design?
Study "Rainfall-runoff analysis" first (topic 75 of 112 in Civil & Structural). It covers the groundwork this topic builds on.
What are the key points of Open channel design?
Hydraulic radius. Best hydraulic section. Permissible velocity.
Can you give an example of Open channel design?
A trapezoidal drain with 1:1.5 side slopes carries stormwater from a car park.
What comes after Open channel design?
The next topic is "Culverts and drainage", which builds directly on this one.
How difficult is Open channel design?
It is classed as Intermediate in Civil & Structural (topic 76 of 112). It is an intermediate topic. Work through the beginner topics in Civil & Structural first.