About Lesson
Define hydraulically best section of a channel.
- It will be known as the cross-section of the channel which carry maximum discharge (Q) when hydraulic radius will be maximum and wetting perimeter is less.
Channel Cross-section
- The cross section of a channel which carry large flows should be such that it will give the largest possible hydraulic radius under the natural surface conditions.
- The most efficient cross-section for an open channel is semi-circular as the wetted perimeter would then be minimum, its hydraulic radius maximum.
- In case, of the rectangular cross-section, half a square is the best discharging rectangular channel i.e. when depth = ½ , breadth i.e. d = b/2 .
- The best hydraulic cross section of a trapezoidal channel under favourable structural conditions is ,
b = 2d. tan θ/2
where,
b = bed width
θ = the angle between the side and horizontal
d = depth of flow of water.