The correct answer is: C. Both (A) and (B).
A minimum velocity of 0.45 m/sec is required to prevent solids from settling in the sewer, while a maximum velocity of 0.90 m/sec is required to prevent scouring of the sewer pipe.
If the velocity is too low, solids will settle in the sewer and create a blockage. This can lead to flooding and sewage backups. If the velocity is too high, it can scour the sewer pipe and create holes. This can lead to leaks and sewage spills.
Therefore, it is important to maintain a minimum velocity of 0.45 m/sec and a maximum velocity of 0.90 m/sec for efficient working of a sewer.
Here are some additional details about each option:
- Option A: Minimum velocity of 0.45 m/sec, is maintained at its minimum flow.
A minimum velocity of 0.45 m/sec is required to prevent solids from settling in the sewer. If the velocity is too low, solids will settle in the sewer and create a blockage. This can lead to flooding and sewage backups.
- Option B: A maximum velocity of 0.90 m/sec, is maintained at its maximum flow.
A maximum velocity of 0.90 m/sec is required to prevent scouring of the sewer pipe. If the velocity is too high, it can scour the sewer pipe and create holes. This can lead to leaks and sewage spills.
- Option C: Both (A) and (B).
Both a minimum velocity of 0.45 m/sec and a maximum velocity of 0.90 m/sec are required for efficient working of a sewer. If either velocity is too low or too high, it can lead to problems such as blockages, scouring, leaks, and spills.