Plan sanitary sewer capacity with fast peakflow estimates. Compare average flow, infiltration, and design margins. Use clear outputs, tables, exports, and graphs for reviews.
| Scenario | Population | Per Capita Flow | Industrial Flow | I/I | Peak Factor | Design Peak Flow |
|---|---|---|---|---|---|---|
| Residential Catchment | 4,000 | 180 L/person/day | 40 m³/day | 2.5 L/s | 3.333 | 35.02 L/s |
| Mixed Use Area | 8,500 | 160 L/person/day | 75 m³/day | 3.2 L/s | 3.025 | 58.78 L/s |
| Expansion Zone | 15,000 | 150 L/person/day | 120 m³/day | 4.0 L/s | 2.779 | 88.26 L/s |
The table shows how increasing population, industrial contribution, and infiltration changes design peak flow. Adjust safety factor to reflect project standards and local risk tolerance.
Domestic average flow = Population × Per Capita Flow ÷ 1000
Total average flow = Domestic average flow + Industrial flow
Average flow in L/s = Total average flow × 1000 ÷ 86400
Harmon peaking factor = 1 + 14 ÷ (4 + √P), where P is population in thousands
Peak sanitary flow = Average flow × Peaking factor
Design peak flow = (Peak sanitary flow + Infiltration and inflow) × Safety factor
This approach separates dry weather generation from wet weather allowance. It helps planners test reasonable design flow envelopes before detailed hydraulic modeling.
Enter the projected service population first. Add the selected per capita wastewater generation rate based on local criteria or historic metered records.
Next, enter any industrial or institutional daily flow that should be added to domestic wastewater generation. Then enter infiltration and inflow as an allowance in L/s.
Select Harmon Formula for a standard peaking estimate or choose Custom Factor if your utility uses a different design standard. Add a safety factor for conservatism.
Press the calculate button. The result block appears below the header and above the form. Review average flow, peak sanitary flow, and final design peak flow.
Use the CSV and PDF buttons to export the computed values. The graph helps compare the average, peak sanitary, infiltration, and final design flow components.
Sanitary sewer design should reflect both expected dry weather discharge and short duration peaks. Underestimating peakflow can overload gravity mains, lift stations, and treatment plant influent structures. Overestimating it can inflate project cost. A structured calculator supports quicker early-stage screening, option comparison, and design review.
This page focuses on common planning inputs: served population, per capita wastewater generation, industrial base flow, infiltration allowance, and a selected peaking factor. The calculator converts daily flow to L/s, applies the peak multiplier, then adds wet weather allowance and a safety factor. The result is a practical design peak value for preliminary sizing checks.
Because standards vary, the calculator includes both the Harmon method and a custom factor option. That makes it useful for municipal concept design, rehabilitation studies, phased developments, and utility capacity conversations. The example table and graph provide a fast way to compare scenarios before moving into pipe hydraulics, slope checks, or full network modeling.
It estimates sanitary sewer design peak flow from domestic loading, industrial contribution, infiltration allowance, and a selected peaking approach.
Use Harmon when you need a common planning-level peaking factor tied to contributing population and no local custom standard overrides it.
It is the added wet weather allowance entered in L/s for groundwater leakage and direct storm-related entry into the sewer system.
Industrial discharge often does not scale directly with population. Separate input improves mixed-use and employment-area flow estimates.
No. It provides a design peak flow. Pipe sizing still needs slope, roughness, depth ratio, velocity, and hydraulic capacity checks.
Choose the value required by your utility or project standard. Many teams use modest allowances for uncertainty during early design.
Yes. Select Custom Factor and enter the multiplier used by your local guideline, master plan, or engineering judgment.
The main output is Design Peak Flow in L/s. It combines peak sanitary discharge, infiltration allowance, and the safety factor.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.