Seepage Flow Calculator

1. Pick the method: use Darcy for a known flow area; use flow-net for seepage under structures.
2. Enter permeability: choose k and units based on tests or references.
3. Define heads and geometry: input Δh and L (Darcy) or H, Nf, Nd, and b (flow-net).
4. Optional stability screening: enable the advanced check for i_crit and FS.
5. Submit: results will display above the form for quick review.
6. Export: download CSV/PDF for records, reviews, and audits.

1) Why seepage estimates matter on sites

Seepage governs dewatering loads, uplift pressure, and piping risk around excavations, cofferdams, and foundations. A small change in head or permeability can produce large changes in discharge. This calculator standardizes inputs and produces comparable outputs for daily planning and design reviews.

2) Typical permeability data for quick screening

Permeability varies by gradation and density. Coarse gravel may exceed 100 m/day, clean sands often fall near 10–50 m/day, silty sands commonly range 0.5–5 m/day, and compacted clays can drop below 0.01 m/day. Use test results when available and treat published ranges as preliminary.

3) Darcy method inputs and practical interpretation

For one-dimensional flow, Darcy uses Q = k·(Δh/L)·A. Keep A as the net cross-section normal to flow, not the excavation footprint. When seepage is through a cut-off wall or soil plug, define L along the actual seepage path, not the shortest distance.

4) Flow-net method for seepage beneath structures

When geometry is complex, flow nets convert the seepage field into counts of flow channels (Nf) and potential drops (Nd). The calculator applies Q = k·H·(Nf/Nd)·b. For “per meter width” sections, set b = 1 m to report discharge per meter.

5) Hydraulic gradient thresholds and observations

Hydraulic gradient i drives seepage force and can indicate boiling potential. For many cohesionless soils, gradients approaching 0.8–1.0 warrant careful evaluation near exit points. If the computed i is high, consider longer seepage paths, relief wells, drainage blankets, or cut-offs.

6) Piping screening using critical gradient

The optional check estimates i_crit = (Gs−1)/(1+e). For example, with Gs = 2.65 and e = 0.70, i_crit ≈ 0.97. The factor of safety is FS = i_crit/i; many projects target FS ≥ 1.5 as a conservative screening benchmark.

7) Converting discharge into pumping and logistics

The tool reports m³/s, m³/day, L/s, and gpm to align with common pump datasheets. For planning, compare m³/day with storage capacity, discharge permits, settlement tanks, and expected rainfall inflow so dewatering systems are not under-sized.

8) Documenting assumptions and quality checks

Reliable seepage outputs depend on boundary heads, layered permeability, and anisotropy. Record test sources for k, define where heads were measured, and note whether the soil is saturated. Export CSV/PDF to keep a traceable calculation package for method statements, inspections, and design audits.

1) Which method should I use: Darcy or flow net?

Use Darcy when you can define a seepage area and flow length confidently. Use flow net when seepage paths curve under structures or cofferdams and you can count Nf and Nd from a flow net.

2) What permeability unit is best for site work?

m/day is common for geotechnical reports and is convenient for daily pumping volumes. If laboratory data is in cm/s or design models use m/s, the calculator converts all inputs to m/s internally.

3) Why is my calculated flow extremely high?

High flows usually come from large k, large head loss, short flow length, or a large area/width. Re-check units, confirm that L represents the seepage path, and verify that k matches the controlling layer.

4) How should I choose the seepage area A?

A should be the net cross-sectional area normal to flow through the soil mass. Avoid using the full excavation footprint unless flow truly passes through that entire section in parallel.

5) What does the factor of safety (FS) represent here?

FS compares critical gradient to the estimated gradient. FS below 1 suggests boiling/piping is possible under the stated assumptions. Use it as screening; final stability should follow project-specific criteria and engineering review.

6) Can this handle layered soils or anisotropy?

This calculator assumes a representative k for the flow path. For layered or anisotropic conditions, consider equivalent permeability along the seepage direction or run separate scenarios to bracket expected behavior.

7) How do I include safety margin in pumping selection?

Add allowances for uncertainty in k, construction disturbance, and rainfall inflow. Many teams add 20–50% contingency to calculated discharge and validate performance with field drawdown monitoring and adjustment of well spacing or pump capacity.