Sump Inflow Rate Calculator
Estimate groundwater inflow into a mine sump using the rising-head method: measure how fast the water level climbs when pumps are off, and convert that rise into a flow rate. It is a quick, equipment-light way to size dewatering pumps and check whether inflow is trending up.
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Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the sump plan area in square metres (length × width for a rectangular sump).
- Enter the measured water-level rise in metres over the test window, with pumps switched off.
- Enter the time period in hours over which that rise was measured, then read the inflow rate in m³/h, L/s and m³/day.
How it works
With pumps off, all inflow accumulates in the sump. Inflow rate Q = plan area × water-level rise ÷ time, giving cubic metres per hour. The tool also reports litres per second (Q × 1000 ÷ 3600) and cubic metres per day (Q × 24) so you can compare against pump duty and daily balance.
Worked example
Worked example. A 200 m² sump rises 0.5 m in 4 hours: Q = 200 × 0.5 ÷ 4 = 25 m³/h, which is 6.94 L/s or 600 m³/day.
Common mistakes
- Leaving a pump running during the test — any pumping removes water and understates the true inflow.
- Using a sump with sloping or stepped walls so the plan area changes with depth; the method assumes a constant plan area.
- Timing over too short a window, so a single splash or measurement error dominates the result.
Frequently asked questions
Do I have to stop pumping to run this test?
Yes. The rising-head method assumes all inflow is captured by the rising water level, so pumps must be off for the whole measurement window.
What if my sump walls are not vertical?
The formula assumes a constant plan area with depth. For a tapered or stepped sump, use the average plan area over the measured rise, and treat the answer as approximate.
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Cite this tool
Zerdly. (2026). Sump Inflow Rate Calculator. Retrieved from https://www.zerdly.com/tools/sump-inflow-rate-calculator/
Tip: Enter any known values to calculate the remaining results.
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