Which of the following best describes an outfall sewer in a sewerage network?
- AIt carries wastewater from a single building to the street sewer.
- BIt only carries storm runoff from roadside drains.
- CIt conveys sewage from branch and main sewers to the treatment or disposal point.Correct
- DIt is a small sewer laid inside private premises only.
Solution
Concept
Role of outfall sewer in collection networks
Formula
NONE
Step-by-step solution
1. Sewer networks follow a collection hierarchy from building drains to laterals and branch sewers. 2. Branch sewers feed into main and trunk sewers. 3. The terminal main sewer carrying all accumulated sewage to treatment or outfall disposal is the outfall sewer. 4. Hence, option C correctly describes an outfall sewer. Answer: C
Explanation
An outfall sewer is the terminal main trunk sewer of a municipal wastewater collection network. It receives accumulated flow from branch and main sewers and conveys it directly to the wastewater treatment facility or the final outfall disposal point.
Why the other options are wrong
A) A building sewer carries wastewater from an individual structure to the street lateral. B) Stormwater drains convey surface runoff. D) Internal sanitary piping handles building plumbing, not public outfall conveyance.
Shortcut
Outfall sewer = Final trunk line conveying sewage to treatment plant or disposal point.
Common mistake
Confusing outfall sewers with house drainage connections or storm drains.
Correct answer: C) It conveys sewage from branch and main sewers to the treatment or disposal point.