Dewatering volume calculator.
Estimate the groundwater volume you'll need to pump from an excavation, zone by zone. Enter each zone's seepage area, soil type, drawdown and flow-path length, and this calculator applies Darcy's Law to estimate the daily inflow, then scales it over your stated dewatering duration for a total volume. This is a preliminary sizing estimate for planning pump capacity and duration, not a substitute for a proper groundwater assessment — real inflow depends on ground conditions a permeability estimate alone can't fully capture. See how AI extracts subsurface data from geotechnical reports on our Groundworks & Subsurface page.
Drop an Excel or CSV file or to replace the table below.
Column A: zone/face name. Column B: seepage area. Columns C-E (optional): soil type, drawdown and flow path length — rows without a recognised soil type default to silty sand.
Parsed entirely in your browser — your file is never uploaded to our servers.
| Zone / face | Seepage area (m²) | Soil type | Drawdown (m) | Flow path length (m) | Daily inflow (m³) | Row actions |
|---|---|---|---|---|---|---|
| — | ||||||
| — | ||||||
| — |
How we calculate this.
Estimate the groundwater volume you'll need to pump from an excavation, zone by zone. Enter each zone's seepage area, soil type, drawdown and flow-path length, and this calculator applies Darcy's Law to estimate the daily inflow, then scales it over your stated dewatering duration for a total volume. This is a preliminary sizing estimate for planning pump capacity and duration, not a substitute for a proper groundwater assessment — real inflow depends on ground conditions a permeability estimate alone can't fully capture. See how AI extracts subsurface data from geotechnical reports on our Groundworks & Subsurface page.
For each zone (row): hydraulic gradient i = drawdown ÷ flow path length, then Darcy's Law gives inflow rate Q = k × i × area (in m³/s), converted to a daily volume. The daily inflows across every zone are summed, then scaled by the stated dewatering duration for a total volume estimate.
| Assumption | Value | Source |
|---|---|---|
| Darcy's Law | Q = k × i × A | The fundamental groundwater-flow equation (Darcy's Law): flow rate = permeability × hydraulic gradient × flow area. Hydraulic gradient i is taken as drawdown ÷ flow path length. |
| Soil permeability (k) | Gravel 1×10⁻², sand 1×10⁻⁴, silty sand 1×10⁻⁵, silt 1×10⁻⁶, clay 1×10⁻⁹ m/s | Representative order-of-magnitude permeability values by soil type — standard ranges published in geotechnical references (e.g. Craig's Soil Mechanics & Foundations). Site-specific permeability testing should confirm the real value for any actual dewatering design. |
This is an early-appraisal planning estimate, not a quotation or a substitute for a surveyed takeoff. Last reviewed 31 Aug 2026.
This calculator uses Darcy's Law — inflow rate = soil permeability × hydraulic gradient × seepage area. Pick the closest soil type for a representative permeability, or use your own site investigation figure if you have one.
Drawdown is how far you need to lower the water table below the excavation base. Flow path length is an estimate of the distance water travels to reach the excavation — a rough radius of influence. Both are commonly estimated from a site investigation or pumping test.
Yes — select a soil type per zone, or treat the closest match as a starting point and refine with your own site investigation data.
That depends on your programme, not the ground — set the duration to match how long the excavation will stay open. The total volume scales directly with it.
Yes — click or drop an Excel (.xlsx/.xls) or CSV file onto the upload area. The first column should be an item name and the second the measurement for that row; extra columns this calculator uses are read too if present. The file is parsed entirely in your browser — it's never uploaded to our servers. Download the blank template first if you're not sure of the layout.
Yes — use the metric/imperial switch above the calculator. Values you've already entered convert automatically; nothing is lost switching back and forth.
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