Manhole spacing vs. pipe size: If manholes are spaced about 300 m apart on a straight reach, the sewer diameter is most likely

Introduction / Context:
Manhole spacing depends on sewer diameter, maintenance requirements, and equipment reach. Smaller sewers require frequent access due to cleaning needs; very large sewers permit longer spacing and sometimes human entry for inspection.

Given Data / Assumptions:

• Straight alignment with no junctions or gradient changes.
• Typical utility guidance for spacing vs. size.
• 300 m is relatively long for routine access on small pipes.

Concept / Approach:

Typical spacing: 30–100 m for small sewers, increasing with size. A spacing of ~300 m suggests a very large conduit where maintenance can occur from fewer access points without compromising service. Hence, diameters exceeding 1.5 m are consistent with such spacing on straight reaches.

Step-by-Step Solution:

Verification / Alternative check:

Large combined or trunk sewers often have manholes or access shafts at wider intervals, supplemented by CCTV or walk-through inspections.

Why Other Options Are Wrong:

0.9–1.5 m diameters commonly need closer spacing for cleaning access, especially in grit-laden systems.

Common Pitfalls:

Ignoring the need for manholes at bends/junctions regardless of straight-run spacing; confusing maximum code-allowed spacing with recommended practice.

Final Answer:

> 1.5 m