# Most Economical Section of a Channel

Which is the Most Economical Section of a Channel in Fluid Mechanics? Discussion about most economical section in rectangular channel, trapezoidal channel, triangular channel is given below. A channel is said to be most economical if
• It gives maximum discharge for a given cross -sectional area and bed shape,
• It has minimum wetted perimeter, and
• 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.
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 at 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 the circular channel.
7. The velocity through a channel of circular section is maximum when the depth of water is equal to 0.81 times the diameter of circular channel.