Design peaking factor — ratio of maximum sewage flow to average flow for mains up to 1 m diameter

Introduction / Context:
Sewer design uses a peaking factor to relate maximum (peak) flow to average daily flow, accounting for diurnal variation and simultaneity of use. Smaller mains typically experience higher variability, hence larger peaking factors, than very large interceptors that average many sources.

Given Data / Assumptions:

• Mains up to 1 m diameter.
• Typical municipal domestic wastewater without extreme industrial shock loads.
• Use of standard empirical guidance (e.g., 2.5–3.0 range for small mains).

Concept / Approach:

Conventional design manuals adopt a factor near 3 for small to medium sewers to ensure capacity during peak hours and to sustain self-cleansing velocities. Larger trunks may use smaller factors due to flow attenuation and storage in the network.

Step-by-Step Solution:

Verification / Alternative check (if short method exists):

Harmon or Babbit–Babbit formulae yield similar peaks for typical populations; attenuation in larger systems lowers the factor.

Why Other Options Are Wrong:

1.5–2.5 underestimate peak conditions for small mains; 4.0 is overly conservative for typical municipal conditions.

Common Pitfalls (misconceptions, mistakes):

Applying a single factor across an entire network regardless of size; ignoring infiltration/inflow effects that can also peak during storms.

Final Answer:

3.0