Question

Self-cleansing velocity is:

• A. The minimum velocity of flow required to maintain a certain amount of solids in the flow
• B. The maximum velocity of flow required to maintain a certain amount of solids in the flow
• C. Such flow velocity as would be sufficient to flush out any deposited solids in the sewer
• D. Such flow velocity as would be sufficient to ensure that sewage does not remain in the sewer

Hint:

Self-cleansing velocity in sewers is designed to prevent sedimentation, not to maximize flow speed.

Answer 1

The Correct Option is C

Step 1: Understanding self-cleansing velocity.
Self-cleansing velocity refers to the minimum velocity required in a sewer so that solid particles do not settle and any deposited matter is carried forward by the flowing sewage.
Step 2: Analyzing the purpose of self-cleansing.
The main objective is to prevent deposition of solids, which can lead to blockages, foul odour, and reduced carrying capacity of the sewer.
Step 3: Evaluating the options.
(A) Incorrect, as it does not address removal of deposited solids.
(B) Incorrect, since self-cleansing velocity is not related to maximum velocity.
(C) Correct, because it directly defines the velocity needed to flush out deposited solids.
(D) Incorrect, as this relates more to detention time rather than solid transport.
Step 4: Conclusion.
The correct definition of self-cleansing velocity is (C), which ensures removal of deposited solids in sewers.