Enter lengths, diameters, and condition to model I/I. Adjust groundwater depth and manhole leakage factors. Download CSV or PDF for review, bidding, and tracking.
| Scenario | Length (m) | Diameter (mm) | Head (m) | Condition | Average total (L/s) | Peak total (L/s) |
|---|---|---|---|---|---|---|
| New subdivision reach | 900 | 200 | 0.6 | Excellent | ~0.22 | ~0.29 |
| Typical urban main | 1200 | 300 | 1.2 | Good | ~0.94 | ~1.22 |
| Aged trunk segment | 1800 | 450 | 2.0 | Poor | ~7.10 | ~9.23 |
This calculator uses an empirical scaling model that starts with a baseline infiltration rate and adjusts it for pipe size, groundwater head, joint density, and condition.
Infiltration and inflow (I/I) can quietly consume wet-weather capacity, distort peaking assumptions, and trigger surcharge or overflow risk. A practical estimate helps you size storage, select pump duty points, and justify rehabilitation budgets. Use this calculator to compare scenarios consistently using the same reference basis.
The strongest predictors are groundwater head, pipe defects, and joint density. Populate inputs using CCTV scores, manhole inspections, and local groundwater observations. Where monitoring exists, set the base rate so the model reproduces measured average infiltration during stable groundwater periods.
Exponents a, b, and c represent sensitivity rather than physics. Larger values increase how aggressively diameter, head, and joints affect results. For preliminary design, keep b near 1.0 and use a conservative condition multiplier for unknown assets.
| Input set | L (m) | D (mm) | Head (m) | Joints/100m | Manholes | Condition | Estimated average (L/s) |
|---|---|---|---|---|---|---|---|
| Baseline | 1200 | 300 | 1.2 | 15 | 8 | Good | ~0.94 |
| Rehab target | 1200 | 300 | 1.2 | 15 | 8 | Fair | ~1.47 |
| High groundwater | 1200 | 300 | 2.4 | 15 | 8 | Good | ~1.76 |
Use the allowance to reflect uncertainty in manhole sealing, service laterals, and unmapped defects. Apply the peak factor for design checks such as pump station wet-well turnover, force main capacity, and wet-weather surcharge screening.
Export CSV for spreadsheets and PDF for submittals. Keep one “current condition” run and one “post-rehabilitation” run to quantify expected reduction. Record the base rate source, monitoring period, and assumptions so future teams can update the estimate as assets age or groundwater conditions change.
Infiltration is groundwater entering through defects and joints. Inflow is direct stormwater entry through openings like covers, roof drains, or cross connections. This calculator focuses on infiltration-style scaling inputs.
Start with a local guideline if available, then calibrate using flow monitoring during dry-weather periods with stable groundwater. Adjust the base rate until the model matches observed average infiltration for a representative reach.
Use an average head above the pipe line based on nearby piezometers, bore logs, or seasonal groundwater maps. If only depth-to-water is known, convert it to head relative to pipe elevation using surveyed levels.
Condition is a broad multiplier, while joint density captures how many potential leak locations exist. Two “good” pipes can behave differently if one has more joints, service connections, or segmented construction.
Manholes often contribute disproportionately in high groundwater. Use inspection results to pick a per-manhole rate. After sealing, rerun with a reduced rate to quantify benefits and update wet-weather capacity checks.
Increase allowance when data is limited, assets are older, laterals are unassessed, or there is evidence of leakage paths not represented by the inputs. Keep it lower when calibrated monitoring and inspections exist.
Not exactly. Here it scales average infiltration to a peak estimate for design screening. Use hydraulic modeling to confirm surcharge risk and storage needs, especially where inflow or surface connections dominate wet-weather flow.
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.