If Q is discharge is cubicmetres per sec and D is the economical diameter of the pipe. According to Lea

• A. D = 0.67 to 0.87 Q
• B. D = 0.77 to 0.97 Q
• C. D = 0.97 to 1.22 Q
• D. D = 1.22 to 1.33 Q.