# Most economical Channel section

a) It gives maximum discharge for a given cross sectional area and bed shape.

b) It has minimum wetted perimeter

c) It involves lesser excavation for the designed amount of discharge

The following points are worth noting:

1) The most economical section of a rectangular channel is one which has hydraulic radius equal to half the depth of flow.

i.e R= y/2

2) The most economical section of a trapezoidal channel is one which has hydraulic mean depth equal to half the depth of flow.

3) The most economical section of a triangular channel is one which has its sloping sides an angle of 45 degree with the vertical.

4) The discharge through a channel of rectangular section is maximum when its breadth is twice the depth.

5) The discharge through a channel of trapezoidal section is maximum when the sloping side is equal to half the width at the top.

6) The discharge through a channel of circular section is maximum when the depth of water is equal to 0.95 times the diameter of circular channel.

7) The velocity through a channel of circular section is maximum when the depth of water is equal to 0.81 time the diameter of circular channel.

8) The depth of water in a channel is corresponding to the minimum specific energy is known as critical depth.

9) If the depth of water in ans open channel is less than the critical depth, then the flow is known as torrential flow.

10) If the depth of water in an open channel is greater than the critical depth then the flow is called tranquil flow.