Peak hourly flow. The peak sustained hourly flowrate occurring during a 24 hour period based on annual operating data. Data on perk hourly flows are needed for the design of collection and inter captor sewers, wastewater-pumping station, wastewater flowmeter, Grit chambers, sedimentation tanks, chlorine-contact tanks, and conduits or channels in the treatment plant. The use of peaking factors to determine peak flowrates is discussed in Chap 5 .