Calculate the speed at which water enters the soil (Basic Infiltration Rate).
The drop in water level measured in the ring/tube.
Duration of the measurement.
Infiltration Rate (Hourly)
0 mm/hr
Infiltration Rate (Daily equivalent)
0 mm/day
Soil Classification Estimate
Pending
function calculateInfiltration() {
// 1. Get input values
var depthInput = document.getElementById('waterDepth').value;
var timeInput = document.getElementById('timeDuration').value;
// 2. Validate inputs
if (depthInput === "" || timeInput === "") {
alert("Please enter both the water depth infiltrated and the time elapsed.");
return;
}
var depth = parseFloat(depthInput);
var time = parseFloat(timeInput);
if (time <= 0) {
alert("Time elapsed must be greater than zero.");
return;
}
if (depth < 0) {
alert("Water depth cannot be negative.");
return;
}
// 3. Calculate Rate
// Formula: Rate (mm/hr) = (Depth (mm) / Time (min)) * 60
var ratePerHour = (depth / time) * 60;
var ratePerDay = ratePerHour * 24;
// 4. Determine Classification (FAO Standards Approximation)
var classification = "";
var classStyle = "";
if (ratePerHour = 5 && ratePerHour = 15 && ratePerHour = 30 && ratePerHour = 65 && ratePerHour < 125) {
classification = "Rapid (Sand)";
classStyle = "class-fast";
} else {
classification = "Very Rapid (Coarse Sand/Gravel)";
classStyle = "class-fast";
}
// 5. Display Results
document.getElementById('resHourly').innerHTML = ratePerHour.toFixed(2) + " mm/hr";
document.getElementById('resDaily').innerHTML = ratePerDay.toFixed(1) + " mm/day";
var classDiv = document.getElementById('resClass');
classDiv.innerHTML = classification;
classDiv.className = "inf-classification " + classStyle;
// Show result section
document.getElementById('resultSection').style.display = "block";
}
How to Calculate Rate of Infiltration
The rate of infiltration is a critical metric in hydrology, agriculture, and soil mechanics. It measures how fast water enters the soil surface. Understanding this rate is essential for designing efficient irrigation systems, preventing soil erosion, and managing stormwater runoff. If water is applied faster than the soil's infiltration rate, it results in ponding and surface runoff, which can waste water and carry away topsoil.
The Basic Formula
To calculate the infiltration rate manually, you essentially measure the depth of water that absorbs into the soil over a specific period. The formula is:
Infiltration Rate (I) = Depth of Water Infiltrated (mm) / Time Elapsed (hours)
Since measurements are often taken in minutes, the calculator above converts the time automatically:
I = (Depth in mm / Time in minutes) × 60
Factors Affecting Infiltration
Soil Texture: Sandy soils have large pores and high infiltration rates. Clay soils have small pores and slow rates.
Soil Structure: Well-aggregated soil (crumbly) allows water to move faster than compacted soil.
Initial Moisture Content: Dry soil absorbs water rapidly at first (sorption), but the rate slows as the soil becomes saturated.
Surface Crusting: Raindrop impact can seal the soil surface, drastically reducing infiltration.
Typical Infiltration Rates by Soil Type
According to the Food and Agriculture Organization (FAO), basic infiltration rates generally fall into these ranges:
Soil Type
Infiltration Rate (mm/hr)
Classification
Sand
> 30
Rapid
Sandy Loam
20 – 30
Moderately Rapid
Loam
10 – 20
Moderate
Clay Loam
5 – 10
Slow
Clay
< 5
Very Slow
How to Measure Field Infiltration
The most common method for measuring this in the field is using a Double Ring Infiltrometer.
Setup: Drive two concentric metal rings into the ground.
Filling: Fill both rings with water. The outer ring acts as a buffer to force water in the inner ring to flow vertically downward rather than spreading horizontally.
Measurement: Measure the drop in water level in the inner ring over a set time interval (e.g., 15 or 30 minutes).
Calculation: Enter the drop distance (mm) and the time (minutes) into the calculator above to get the rate.
Why This Matters
For Irrigation: If your sprinkler system delivers 15 mm/hr, but your soil is clay with an infiltration rate of 5 mm/hr, you will have significant runoff. You must lower the application rate to match the soil.
For Drainage: Knowing the infiltration rate helps civil engineers determine how much rainfall will soak into the ground versus how much will flow into storm drains during heavy storms.