Sewage Flow Calculator Formula

Understand the math behind the sewage flow calculator. Each variable explained with a worked example.

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Formulas Used

Average Sewage Flow

avg_flow = avg_sewage

Peak Sewage Flow

peak_flow = avg_sewage * peak_factor * (1 + infiltration / 100)

Peak Flow Rate

peak_lps = avg_sewage * peak_factor * (1 + infiltration / 100) / 86.4

Variables

VariableDescriptionDefault
water_demandAverage Water Demand(m^3/day)2000
return_factorSewage Return Factor0.8
peak_factorPeak Flow Factor2.5
infiltrationInfiltration Allowance(%)10
avg_sewageDerived value= water_demand * return_factorcalculated

How It Works

Sewage Flow Estimation

Wastewater flow is derived from water consumption, reduced by a return factor.

Formulas

Average sewage = Water demand x Return factor

Peak sewage = Average x Peak factor x (1 + Infiltration)

The return factor (0.7-0.9) accounts for water consumed (irrigation, evaporation) that does not reach the sewer. The peak factor accounts for diurnal variation, and infiltration accounts for groundwater entering through pipe joints.

Worked Example

2000 m^3/day water demand, 0.8 return factor, 2.5 peak factor, 10% infiltration.

water_demand = 2000return_factor = 0.8peak_factor = 2.5infiltration = 10
  1. 01Average sewage = 2000 x 0.8 = 1600 m^3/day
  2. 02Peak sewage = 1600 x 2.5 x 1.10 = 4400 m^3/day
  3. 03Peak flow rate = 4400 / 86.4 = 50.9 L/s

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