A flow net is a graphical representation of two-dimensional steady seepage through soil. It consists of flow lines (streamlines) and equipotential lines that are orthogonal to each other, forming a curvilinear square mesh.

What formula does this calculator use?

The calculator uses Darcy's law adapted for flow nets: q = k × h × (Nf / Nd), where q is seepage flow per unit width, k is hydraulic conductivity, h is the head difference, Nf is the number of flow channels, and Nd is the number of equipotential drops.

What units does the result use?

If you input k in m/s and h in meters, the output q is in m²/s (flow per unit width). Multiply by the structure width (in meters) to get total flow in m³/s.

How do I count Nf and Nd?

Nf is the number of flow tubes (spaces between adjacent flow lines). Nd is the number of equipotential drops (spaces between adjacent equipotential lines). Count both directly from your flow net sketch.

What is a typical Nf/Nd ratio?

For a simple earth dam the ratio is commonly between 0.3 and 0.5. More complex geometries or anisotropic soils can yield different values.

Does the tool handle anisotropic soils?

For anisotropic soils (kx ≠ kz) use the equivalent isotropic conductivity k_eq = √(kx × kz) as your input k. The flow net must be drawn in a transformed coordinate system.

Seepage Flow Net Calculator

Name: Seepage Flow Net Calculator
Availability: InStock
Author: Nham Vu

Enter flow net parameters to compute seepage flow rate per unit width using Darcy's law.

Flow Net Parameters

Number of Flow Channels (N_f)

Count the flow tubes between adjacent streamlines.

Number of Equipotential Drops (N_d)

Count the potential drops between adjacent equipotential lines.

Hydraulic Conductivity, k (m/s)

Saturated hydraulic conductivity of the soil.

Total Head Difference, h (m)

Upstream head minus downstream head driving seepage.

Results

Seepage Flow Rate per Unit Width

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m²/s

N_f / N_d Ratio

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Hydraulic Gradient, i

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(h / average L)

Flow Net Sketch Reference

Summary