Peaking factors for sewer design: For sewer mains of 0.5 m to 1.0 m diameter, what ratio is commonly assumed for maximum daily sewage flow to average daily sewage flow?

Introduction / Context:
Sewer hydraulics must accommodate diurnal and seasonal peaks. A simple way to reflect daily peaking is to multiply the average daily flow by a peaking factor that depends on catchment size and network characteristics.

Given Data / Assumptions:

• Medium-sized mains (0.5–1.0 m diameter) serving urban populations.
• Average daily flow known from per capita contributions.
• Daily peaking factor chosen per local guidelines.

Concept / Approach:

For the stated mains, a commonly adopted planning value is 2.0 for max daily/average daily. Larger systems with population averaging may have lower ratios; smaller systems may experience higher peaks. Final design should also consider hourly peaking and infiltration/inflow allowances.

Step-by-Step Solution:

Verification / Alternative check:

Compare with local standards (e.g., Harmon/Metcalf recommendations) and adjust based on observed flow monitoring where available.

Why Other Options Are Wrong:

1.5 may understate peaks; 2.5 or 3.0 are more typical for smaller basins or for hourly peaking rather than daily.

Common Pitfalls:

Applying hourly factors to daily sizing; ignoring I/I contributions; neglecting future growth.

Final Answer:

2.0