D is the diameter of a circular sewer and α is the side of a square section sewer. If both are hydraulically equivalent, the relationship which holds good, is

• πD8/3 = 4 b8/3
• πD3/8 = 4 b3/8
• πD2/3 = 4 b2/3
• πD3/2 = 4 b3/2
• none of these.