Which way is the best formula to design open chanel to transfer wast water or agriculture water?

I agree with Sir Alex Al Yazouri

Many natural and man-made channels are approximately trapezoidal.

 trapezoidal channel design

 trapezoidal is more efficiency and economic

thank you for invitation

I accept with eng. Rami Batikh

agree with previous answers

precast parabolic segments are the best channels for water flow due to most economical and efficient system