[amp_mcq option1=”Equal to HMD when flowing full” option2=”Less than HMD when flowing full” option3=”Greater than HMD when flowing full” option4=”None of the above” correct=”option2″]
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. This is incorrect because the HMD for an egg-shaped sewer flowing two-thirds full is less than the HMD when flowing full.
- Option B: Less than HMD when flowing full. This is the correct answer because the wetted perimeter of the flow is greater when the sewer is flowing two-thirds full.
- Option C: Greater than HMD when flowing full. This is incorrect because the HMD for an egg-shaped sewer flowing two-thirds full is less than the HMD when flowing full.
- Option D: None of the above. This is incorrect because option B is the correct answer.