Disc Permeameter Infiltration Calculator
Step 1 – Sorptive number (a*)
a* describes how strongly your soil absorbs water. You can enter a known value or estimate it from measurements at multiple tensions.
Step 2 – Enter reservoir readings
Enter time and reservoir level readings for a single tension. The calculator will detect steady-state and compute K(h).
| Time (min) | Reservoir Level (cm) | Cumulative Infilt. (cm) | Rate (mm/hr) | |
|---|---|---|---|---|
| – | – | |||
| – | – | |||
| – | – |
Upload field data
Upload a CSV with your multi-site, multi-tension field readings. The calculator will compute K(h) for every site and produce summary reports with pore-class analysis.
Quick Start
What you're measuring: Unsaturated hydraulic conductivity K(h) — reveals near-saturated pore-size structure.
Quick Calculator — enter reservoir readings from a single tension run. The calculator detects steady-state and computes K(h). If you don't know a* (the sorptive number), use Step 1 to estimate it from multi-tension data first.
Batch Analysis — upload a CSV of all your field data (multiple sites, tensions, depths). The tool computes K(h) for everything and generates summary tables, pore-class charts, and downloadable reports.
Field Protocol
Standard three tensions: −15 → −6 → −3 cm (most negative first).
- Prepare site: gently level; apply 2–3 mm fine sand contact layer; carefully level disc.
- Run heads in order: −15 → −6 → −3 cm.
- Readings: 0–10 min each minute; 10–30 min every 2–3 min; 30+ min every 5 min. Stop when 3 consecutive readings vary by < 5%.
Approximate pore mapping: −15 cm ≈ 0.20 mm; −6 cm ≈ 0.50 mm; −3 cm ≈ 1.00 mm.
Interpreting Results
Comparing K across tensions isolates conductance from different pore-size bands:
- < 0.2 mm ≈ K(−15)
- 0.2–0.5 mm ≈ K(−6) − K(−15)
- 0.5–1.0 mm ≈ K(−3) − K(−6)
Larger contributions at less negative heads indicate stronger structural macroporosity and potential preferential flow.
Quality Indicators
Tail CV% measures how stable the last N readings are:
- < 20% — Excellent
- 20–30% — Good
- 30–50% — Fair
- > 50% — Poor (steady-state not reached)
Limitations
- Disc permeameters do not measure micropores (< 0.03 mm).
- Practical lower limit ~ −15 to −20 cm (membrane air entry).
- The Wooding equation assumes homogeneous, isotropic soil.
CSV Format for Batch Analysis
Your CSV must contain these columns (header names must match exactly):
| Column | Description | Example |
|---|---|---|
| Date | Date of measurement | 2025-03-15 |
| Treatment | Treatment or land-use name | Pasture |
| Plot | Plot number | 1 |
| Subsample | Subsample/replicate ID | A |
| Soil depth (cm) | Depth of measurement | 0 |
| Head (cm) | Applied tension | -6 |
| Constant rate (cm/min) | Steady-state reservoir drop rate | 0.0123 |
This calculator analyses measurements made using disc permeameters at different tensions. It is a beta product, primarily made to assist us in assessing soil infiltration, porosity etc. We are keen for any feedback!
See a User Guide here>
See Report Measuring Soil Water Infiltration using Disc Permeameters here>