Design Of Non Erodible Channels

The Initial dimensions of a channel are determined by uniform flow or manning formula. But final dimensions are determined on the basis of

1. Hydraulic efficiency
2. Empirical rule of the best section.
3. Practicability And Economy

Factors Considered In The Design:

1. Kind of material to find.
2. Minimum Velocity (2-3ft/s)
3. Maximum velocity.
4. Bed slopes.
5. Side slopes
6. Free board.
7. Kind of material is important to find the roughness coefficient of channel.
8. Minimum Velocity is 2-3 ft/sec -> non silting velocity to prevent aquatic growth.
9. Maximum velocity is upto 8 ft/sec more than the above value, the lining blocks, are pulled away by moving water.
10. Bed slope is dependent upon topography and energy required for flow of water.
11. Side Slope: It Depends upon the material forming the chemical section e.g earth with lime stone h1 : 1v
    earth with concrete h1/2 : 1v
12. Free Board: Distance between top of channel to max water surface it should prevent waves it should be 5-13 % of depth.

U.s B.r ---> F = underroot cy

F = Free Board In ft C=1.5 --->20ctt

Y = Depth in ft 2.5--->3000cft

Best section ---> Max Q for min p( wetted perimeter)

Best Section Of Half Hydrogens, Trapezoid (formula) Underroot 3y power 2, 2underroot 3y , y/2 4/3 2y 3/2y 3/5

Rectangular 2y power 2 4y y/2 2y 2y 2.5

Designing Steps For Non Erodible Channel:

1. Collect All information And estimate n and s.
2. Computer section factory AR2/3 = nq/1.486 s 1/2.
3. Substitute The values of a and r from

A = (b+zy) y
p = b+2y underroot 1+z power 2
R = (b+zy)y/b+2y underroot1+z power 2