Concept reference

Peaking Factors

C.1Plain-language definition

A peaking factor is a ratio between a chosen high flow and a stated average. It compresses demand diversity, diurnal timing, population and sometimes infiltration into one number. The time scale matters: an instantaneous, hourly and daily peak do not size the same component.

C.2Governing relation or decision logic

Qpeak = PF · Qaverage, with both flows in the same units and PF dimensionless. The factor may come from local records, an adopted formula or a regulatory table. Its population basis, averaging period and inclusion of wet-weather/infiltration allowances must travel with the value.

C.3The failure to name

Multiplying an already peaked or wet-weather-inclusive flow by another factor double counts conservatism. A formula calibrated for a regional population range is not automatically transferable to a small station, industrial duty or potable fire-flow condition.

C.4Field review checklist

• Define numerator, denominator, duration and return/occurrence basis.
• Separate sanitary/demand variation from infiltration, inflow, fire flow or other independent additions.
• Prefer representative monitored data and reconcile it with governing criteria.
• Match each design flow to the component and failure consequence it actually sizes.

C.5Where it fits in the course

§1.4 turns averages into design flows and distinguishes installed from reliable capacity.