Calculator Inputs
Use the responsive form below. Large screens show three columns, smaller screens show two, and mobile shows one.
Example Data Table
Use this sample dataset to test the calculator quickly and confirm that the response table, chart, and exports behave correctly.
| Scenario | f₀ | fc | k | Duration | Eval Time | Rainfall | Area | Rate Unit | Time Unit | Area Unit |
|---|---|---|---|---|---|---|---|---|---|---|
| Test Plot A | 75 | 12 | 2.1 | 3 | 1.5 | 40 | 120 | mm/h | hours | m² |
| Compacted Lawn | 42 | 8 | 1.3 | 2 | 1 | 20 | 85 | mm/h | hours | m² |
| Coarse Sandy Strip | 2.5 | 0.7 | 0.95 | 180 | 75 | 1.4 | 1800 | in/h | minutes | ft² |
Formula Used
The Horton model describes how infiltration rate decreases from an initial rate toward a lower steady value as the soil wets up.
Where f(t) is infiltration rate at time t, f₀ is the initial infiltration rate, fc is the final or equilibrium rate, and k is the decay constant.
F(t) gives the cumulative infiltrated depth over the analysis period. The tool also computes a rainfall-limited rate when you provide rainfall intensity.
Here i is rainfall intensity. When rainfall is less than the Horton capacity, actual infiltration cannot exceed rainfall supply.
Depth is converted to meters internally for cubic meters. Liters are derived directly because one millimeter spread over one square meter equals one liter.
How to Use This Calculator
- Enter the initial and final infiltration rates for your soil condition.
- Provide the Horton decay constant using the same reciprocal time basis as your selected time unit.
- Choose duration, evaluation time, and plotting step size.
- Optionally add rainfall intensity to cap infiltration by available water supply.
- Enter infiltration area to estimate stored volume.
- Press Calculate Infiltration to show results above the form.
- Use the CSV button for spreadsheets and the PDF button for printable reports.
Frequently Asked Questions
1) What does Horton infiltration represent?
It models how soil intake capacity declines during wetting. The equation starts with a high initial rate and approaches a lower steady infiltration rate as the surface becomes saturated.
2) Why does the calculator ask for both f₀ and fc?
Those two rates define the upper and lower bounds of the decay curve. Their difference controls how much infiltration capacity drops during the storm or ponding period.
3) What units should I use for the decay constant?
Use the reciprocal of the selected time unit. If time is in hours, k is per hour. If time is in minutes, k is per minute.
4) Why is there an optional rainfall intensity field?
Horton gives infiltration capacity, not always actual infiltration. When rainfall is lower than the soil capacity, the actual infiltrated rate is limited by rainfall supply.
5) What is cumulative infiltration depth?
It is the total depth of water that has entered the soil over the selected period. The calculator reports it in millimeters and inches.
6) How is infiltrated volume calculated?
The tool multiplies cumulative infiltration depth by the selected area. It then reports the absorbed amount in liters, cubic meters, cubic feet, and gallons.
7) Does a smaller time step improve results?
Yes. A smaller step produces a smoother table and chart and improves the numerical estimate when rainfall limits actual infiltration during the event.
8) When should I use this calculator?
Use it for hydrology studies, drainage checks, irrigation design, stormwater screening, field infiltration interpretation, and quick scenario comparisons across different soil conditions.