10. The most economical section of a rectangular channel is one which has hydraulic mean depth or hydraulic radius equal to
A. twice the depth
B. half the depth
C. twice the breadth
D. half the breadth
10. The most economical section of a rectangular channel is one which has hydraulic mean depth or hydraulic radius equal to
A. twice the depth
B. half the depth
C. twice the breadth
D. half the breadth