• The design of line canals is always done by Kennedy‚Äôs Theory..
  • Following equations given by Kennedy are used in the design.

\[V0= 0.54mD^{0.64}\]

\[V= \frac{R^{2/3}S^{1/2}}{N}\]

Values of Rugosity Coefficients N
Values of Rugosity Coefficients N
  • 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.
Mehboob section lined canal
Mehboob section lined canal
  • 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.

Design steps.

  • 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.

\[Q= AV\]

\[V= \frac{R^{2/3}S^{1/2}}{N}\]

Steps. (i)

  • 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.