Model seepage profiles with flexible inputs for estimates. Generate gradients, discharge, and elevations from your parameters. Download CSV and PDF outputs for site records.
This calculator offers two estimation approaches. The recommended option is the unconfined seepage approximation based on the Dupuit assumption, which produces a curved phreatic line profile.
For steady seepage between two constant heads over an impervious base with horizontal length L:
y(x)2 = H12 − (H12 − H22) · x / L
Discharge per unit width: q = k · (H1² − H2²) / (2L)
A straight-line interpolation used for rough screening:
y(x) = H1 + (H2 − H1) · x / L
Use this only for quick comparisons; it does not model curvature.
Sample inputs and a few computed points for illustration.
| H1 (m) | H2 (m) | L (m) | Method | x (m) | y (m) |
|---|---|---|---|---|---|
| 8 | 1 | 30 | Dupuit | 0 | 8.000 |
| 8 | 1 | 30 | Dupuit | 10 | 6.555 |
| 8 | 1 | 30 | Dupuit | 20 | 4.690 |
| 8 | 1 | 30 | Dupuit | 30 | 1.000 |
Use site data to refine assumptions and boundary heads.
The phreatic line represents the seepage surface inside an embankment or foundation zone. A quick estimate supports slope stability checks, filter and toe‑drain layout, and construction‑stage monitoring. It also supports rapid sensitivity checks during design reviews and change control. Use it to compare scenarios, not as a substitute for instrument data or detailed seepage modeling.
Enter upstream head H1, downstream head H2, and seepage length L measured above the same base reference. Heads can come from reservoir levels, tailwater, standpipes, or piezometers. Choose L from the cross‑section stationing that matches your base line and boundaries.
If you have laboratory or field results, enter permeability k to estimate discharge per unit width. As a screening reference, compacted clays may fall around 1×10−9 to 1×10−7 m/s, silts often around 1×10−7 to 1×10−5 m/s, and clean sands can be 1×10−5 to 1×10−3 m/s or higher. Porosity n is used to convert discharge into an average seepage velocity for screening.
The point table provides y(x) (head above base) and, with base elevation, absolute phreatic elevation. Average gradient indicates overall driving slope, while exit gradient highlights downstream intensity where piping risk is most critical. For the curved option, discharge increases with larger head difference, higher k, and shorter L.
Compare computed elevations to instrumentation at matching chainage, then adjust heads for staged loading. Record assumptions: section location, base reference, boundary conditions, and chosen method. Export the CSV for tabulation and plotting, and attach the PDF as a compact calculation note in your site file.
The phreatic line is the seepage surface where pore pressure equals atmospheric pressure. It bounds saturated seepage below and unsaturated conditions above in a section.
Use the curved option for steady unconfined seepage estimates. The linear option is a quick screening line for comparisons when you do not need curvature.
They are boundary heads above the same impervious base reference at upstream and downstream. Use measured water levels, tailwater elevation, or controlled boundary conditions.
Select the horizontal distance between boundaries along the base line used in your cross‑section. If a drain, cutoff, or geometry changes the path, revise L.
For the curved option, q is a discharge per unit width estimate based on permeability and boundary heads. It helps compare design alternatives and anticipate seepage handling needs.
Exit gradient is an approximate downstream hydraulic intensity near the seepage outlet. High values can indicate piping susceptibility and are often reviewed with filters and drains.
Use it as a baseline screen only. Layers, anisotropy, internal drains, and rapid level changes can shift the seepage surface, so validate with monitoring or detailed seepage analysis.
Accurate seepage estimates need soil data and engineering judgment.
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.