Manhole spacing standards: According to common Indian practice, what is the maximum spacing of manholes for sewers up to 0.3 m diameter?

Introduction / Context:
Manholes provide access for inspection, cleaning, and maintenance of sewer lines. Their spacing is a key design parameter balancing operational needs with construction cost and street congestion.

Given Data / Assumptions:

• Sewer diameter ≤ 0.3 m (300 mm).
• Reference to Indian practice (common guidelines and standards).
• Urban conditions requiring periodic access points.

Concept / Approach:
Smaller sewers are harder to maintain with long reaches because cleaning tools and rodding lengths are limited. Therefore, tighter spacing (around 30 m) is typically adopted for small diameters, with larger spacing permitted as diameter increases.

Step-by-Step Solution:
1) Identify the diameter class: ≤ 300 mm.2) Recall typical guidance: spacing about 30 m for small sewers.3) Choose the value that matches established practice: 30 m.

Verification / Alternative check:
Many municipal specifications and IS-based schedules use approximately 30 m spacing for small diameter sewers, increasing to 60–90 m as diameters grow and mechanical cleaning becomes easier.

Why Other Options Are Wrong:
20 m: Very conservative; increases cost without proportional benefit.45 m or 75 m: Too large for small sewers; hinders maintenance.15 m: Unnecessarily close for standard urban stretches.

Common Pitfalls:

• Using the same spacing irrespective of diameter and alignment features.
• Ignoring bends, junctions, and gradient changes that also require manholes.

Final Answer:
30 m