Sewer network terminology: The conduit that receives and conveys combined flows from two or more main sewers toward the outfall is called a…

Introduction / Context:
Consistent terminology helps in planning and communicating sewer layouts. Networks generally progress from laterals to mains, then to trunks, and finally to the outfall that discharges to treatment or disposal.

Given Data / Assumptions:

• Two or more main sewers discharge into a larger downstream conduit.
• The downstream conduit is not yet the final outfall to the treatment works.
• Gravity system with hierarchical branching.

Concept / Approach:

A trunk sewer is the large collector receiving flows from several main sewers and conveying them toward the system’s outfall. The outfall sewer is the terminal conduit that carries sewage to the treatment plant. An intercepting sewer diverts combined sewer overflows or intercepts existing outfalls to a centralized treatment facility.

Step-by-Step Solution:

Verification / Alternative check:

Check system maps and design notes; the outfall is typically singular and directly connected to the plant headworks.

Why Other Options Are Wrong:

(b) Outfall is the final conduit to treatment; (c) a main is smaller and upstream; (d) interceptor serves diversion/control functions.

Common Pitfalls:

Using “outfall” generically for any large sewer; confusing interceptor with trunk in separate sewer systems.

Final Answer:

Trunk sewer