The following are the necessary conditions that are satisfied by most economical channels.

1. Hydraulic mean depth is half of the depth of flow.

2. The depth of flow of the channel is twice the base width.

3. Half of the top width is equal to one of the sloping sides.

4. A semicircle drawn from midpoint of top width radius, equal to depth of flow will touch three sides of the channel.

Select the conditions for trapezoidal channel.