The correct answer is C. 0.70 m/sec.
The self-cleaning velocity of a sewer is the minimum velocity required to prevent the settling of solids on the bottom and sides of the sewer. This velocity is important to maintain in order to prevent blockages and backups.
The self-cleaning velocity is affected by a number of factors, including the diameter of the sewer, the slope of the sewer, and the type of sewage being transported. In general, the larger the diameter of the sewer, the lower the slope of the sewer, and the less dense the sewage, the lower the self-cleaning velocity required.
For Indian conditions, the self-cleaning velocity recommended for large sewers is 0.70 m/sec. This velocity is based on the average diameter of sewers in India, the average slope of sewers in India, and the average type of sewage being transported in India.
If the self-cleaning velocity is not maintained, solids can settle on the bottom and sides of the sewer. This can lead to blockages and backups, which can cause flooding and other problems. It is important to regularly inspect sewers to ensure that the self-cleaning velocity is being maintained.
The other options are incorrect because they are not the recommended self-cleaning velocity for Indian conditions.