Soil Infiltration Rate Calculation

Calculate hydraulic conductivity and determine soil classification based on water drop tests.

Millimeters (mm) Centimeters (cm) Inches (in)

Minutes Hours

function calculateInfiltration() { // Get inputs var rawDrop = document.getElementById('waterLevelDrop').value; var dropUnit = document.getElementById('dropUnit').value; var rawTime = document.getElementById('timeElapsed').value; var timeUnit = document.getElementById('timeUnit').value; // Validate inputs if (rawDrop === "" || rawTime === "" || isNaN(rawDrop) || isNaN(rawTime)) { alert("Please enter valid numerical values for water drop and time."); return; } var dropVal = parseFloat(rawDrop); var timeVal = parseFloat(rawTime); if (timeVal = 30) { soilClass = "Sand / Sandy Loam"; desc = "(Rapid Absorption)"; } else if (rateMMPerHr >= 15 && rateMMPerHr = 5 && rateMMPerHr < 15) { soilClass = "Clay Loam"; desc = "(Slow Absorption)"; } else { soilClass = "Clay"; desc = "(Very Slow Absorption – Potential Drainage Issues)"; } // Display Results document.getElementById('resRateMM').innerText = rateMMPerHr.toFixed(2) + " mm/hr"; document.getElementById('resRateIN').innerText = rateInPerHr.toFixed(2) + " in/hr"; document.getElementById('resClass').innerText = soilClass + " " + desc; document.getElementById('resultContainer').style.display = "block"; }

Understanding Soil Infiltration Rate

Soil infiltration rate is a critical measure in hydrology, agriculture, and civil engineering. It defines the speed at which water on the ground surface enters the soil. Knowing this rate is essential for designing efficient irrigation systems, managing stormwater runoff, and assessing the suitability of land for septic systems or construction.

Why Calculate Infiltration Rate?

The infiltration rate determines how much water the soil can absorb over a specific period. If you apply water faster than the infiltration rate (whether through rainfall or irrigation), the excess water will pool on the surface or flow away as runoff, potentially causing erosion or flooding.

• Agriculture: Helps in scheduling irrigation to prevent waterlogging and root rot.
• Construction: Critical for designing drainage systems and foundations.
• Environmental Science: Used to model pollutant transport and groundwater recharge.

How the Calculation Works

The most common field method for measuring this rate is the "Double Ring Infiltrometer" or a simple percolation test. The basic formula used in this calculator focuses on the drop in water head (level) over a specific time interval:

Formula: Rate = Change in Water Level / Time Elapsed

For example, if the water level in a test hole drops 25mm in 30 minutes, the infiltration rate is calculated as:

25mm / 0.5 hours = 50 mm/hr

Interpreting Soil Texture based on Infiltration

Different soil textures allow water to pass through at drastically different speeds. Sandy soils have large pores and high infiltration rates, while clay soils have microscopic pores that restrict water flow.

Soil Texture	Typical Infiltration Rate (mm/hr)	Typical Infiltration Rate (in/hr)	Drainage Character
Sand	> 30 mm/hr	> 1.2 in/hr	Rapid
Sandy Loam	20 – 30 mm/hr	0.8 – 1.2 in/hr	Moderately Rapid
Loam	10 – 20 mm/hr	0.4 – 0.8 in/hr	Moderate
Clay Loam	5 – 10 mm/hr	0.2 – 0.4 in/hr	Slow
Clay	< 5 mm/hr	< 0.2 in/hr	Very Slow

Factors Influencing Infiltration

While soil texture is the primary driver, other factors significantly affect the rate:

1. Soil Compaction: Heavy machinery or foot traffic compresses soil pores, significantly reducing infiltration.
2. Organic Matter: High organic content improves soil structure and increases porosity, boosting infiltration.
3. Moisture Content: Dry soil typically absorbs water faster initially, but the rate decreases as the soil becomes saturated.
4. Vegetative Cover: Plant roots create channels (macropores) that facilitate water movement and prevent surface sealing.