Soil Infiltration Rate Calculator
Calculate the speed at which water enters soil based on field test data.
Millimeters (mm)
Centimeters (cm)
Inches (in)
Minutes
Hours
0 mm/hr
Calculated Basic Infiltration Rate
Imperial Rate
0 in/hr
24-Hour Intake
0 mm
Soil Classification Estimate: –
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How to Calculate Soil Infiltration Rate
The soil infiltration rate is a measure of how fast water enters the soil surface. This metric is crucial for agricultural irrigation planning, designing drainage systems, and assessing flood risks. It is typically calculated using data from a field test, such as a double-ring infiltrometer test or a simple percolation test.
The Formula
The basic formula for infiltration rate ($I$) is the change in the depth of the water ($H$) divided by the time interval ($T$) during which the drop occurred:
Infiltration Rate = Water Level Drop / Time Elapsed
For example, if the water level in a test ring drops 30 mm in 60 minutes (1 hour), the infiltration rate is 30 mm/hr.
Interpreting the Results
Infiltration rates vary widely based on soil texture, compaction, and organic matter content. Below is a general guide to interpreting your results:
- Rapid (> 30 mm/hr): Typically sands or gravels. Water drains very quickly, often requiring frequent irrigation with smaller amounts.
- Moderate (15 – 30 mm/hr): Sandy loams and loams. These soils generally have good structure and are ideal for most crops.
- Slow (5 – 15 mm/hr): Silt loams and clay loams. These soils hold water well but may be prone to runoff during heavy rain.
- Very Slow (< 5 mm/hr): Heavy clay or compacted soils. These have high runoff potential and poor drainage.
Factors Affecting Infiltration
Several physical factors influence the rate calculated above:
- Soil Texture: Coarse soils (sand) have large pores and high infiltration; fine soils (clay) have small pores and low infiltration.
- Soil Structure: Aggregated soil particles create macropores that facilitate water movement.
- Compaction: Heavy machinery or foot traffic compresses soil pores, drastically reducing infiltration.
- Moisture Content: Dry soil absorbs water faster initially (sorptivity) than saturated soil (steady-state infiltration).