The hydraulic mean depth (HMD) for an egg-shaped sewer flowing two-third full is A. Equal to HMD when flowing full B. Less than HMD when flowing full C. Greater than HMD when flowing full D. None of the above

The correct answer is: B. Less than HMD when flowing full.

The hydraulic mean depth (HMD) is a dimensionless number that is used to characterize the flow of a fluid in a pipe or channel. It is defined as the ratio of the cross-sectional area of the flow to the wetted perimeter of the flow.

The HMD for an egg-shaped sewer flowing two-thirds full is less than the HMD when flowing full because the wetted perimeter of the flow is greater when the sewer is flowing two-thirds full. This is because the water in the sewer is not in contact with the entire surface of the sewer when it is flowing two-thirds full.

The following is a brief explanation of each option:

• Option A: Equal to HMD when flowing full.
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