DESIGN OF LINED CANAL
- The design of line canals is always done by Kennedy’s Theory..
- Following equations given by Kennedy are used in the design.
- The value of N for protected type of linings is taken same as for natural soil.
- The value of N of natural soil varies from 0.02 to 0.025.
- In order to obtain the most economical section, it is necessary to adopt the best discharging section.
- The flow will be greater when the friction is least.
- This happens when wetted perimeter is least for any particular given area of the channel.
- In other words, the discharge will be maximum when Hydraulic mean depth (H.M.D.) is maximum.
- A semi-circular section of channel is considered as the best theoretical section.
- But Trapezoidal channel section is mostly adopted on practical grounds.
- In order to increase the H.M.D., the angle subtended at the corners at bottom should be same as side slopes of channel make with the horizontal.
- Following data should be known before design of the canal can be carried out:
(i) Discharge of the channel (Q).
(ii) Rugosity coefficient (N).
(iii) Longitudinal slope (S).
(iv) Slope of banks.
(v) Permissible velocity of flow
(V). Use following equations.
- Knowing the limiting values of V, N, and S find out the H.M.D.
(ii) From an expression in terms of Bed width (B) and depth (D) by pudding values in R = A /P .
(iii) From another equation in terms of B and D from equation Q = AV.
(iv) By solving equations formed in step (ii) and (iii), find out the unknown values of B and D.
- For different values of side slopes, the sectional area, wetted perimeter, in terms of B and D is given as follows.
- The radius of arc for monitoring bottom corners is taken equal to depth of water.