Estimate the rate at which water infiltrates soil using field measurements or theoretical models — ideal for hydrology, agriculture, and drainage design.
Infiltration Rate at End:
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Cumulative Infiltration:
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Soil infiltration is the process by which water enters the soil surface and moves downward through the soil pores. This fundamental hydrologic process affects:
The tool uses three different approaches to estimate infiltration:
Concept: Uses actual measurement data from field tests like double-ring infiltrometer tests.
Calculation Flow:
Formula: f(t) = f_c + (f₀ - f_c)e^(-kt)
Where:
Physical Basis: Models infiltration based on soil physics principles including capillary suction and hydraulic conductivity.
Key Parameters:
This is the instantaneous rate at which water enters the soil at a specific time. Typical values:
This represents the total depth of water that has entered the soil over the entire duration. This is crucial for:
Infiltration Rate Curve: Should show a decreasing trend over time as soil pores fill with water. Steep decline = rapid saturation. Gentle decline = gradual saturation.
Cumulative Curve: Should show a steadily increasing curve that may flatten slightly as infiltration rate decreases. Steeper slope = faster infiltration.
Q1: Why does infiltration rate decrease over time?
Answer: Initially, dry soil has many empty pores and strong capillary forces (suction). As water fills these pores, the driving forces decrease and water must move through smaller, remaining pores, slowing the rate.
Q2: What's the difference between infiltration rate and hydraulic conductivity?
Answer: Hydraulic conductivity (K) is a soil property - how easily water moves through saturated soil. Infiltration rate is a process rate that depends on K but also on soil moisture, surface conditions, and time.
Q3: Which method should I use for my project?
Answer: Use field test data when you have actual measurements (most accurate). Use Horton's model for stormwater modeling and short-duration events. Use Green-Ampt for detailed hydrological studies and when you know soil properties.
Q4: How do soil texture and structure affect infiltration?
Answer: Texture (sand, silt, clay) affects pore sizes. Sand has large pores = fast infiltration. Clay has tiny pores = slow infiltration. Structure (aggregation, compaction) can override texture effects - compacted clay can be nearly impermeable.
Q5: What units should I use and why?
Answer: mm/hr or in/hr for rates, mm or inches for cumulative depth. These are standard in hydrology. Remember: 1 mm/hr = 0.0394 in/hr. For design, use consistent units throughout your calculations.
Classroom Exercise 1: Soil Texture Comparison
Design Problem 1: Stormwater Basin Sizing
Field Exercise: Parameter Sensitivity
Infiltration connects to several important civil engineering areas:
Content Verified: January 2026. This educational content has been reviewed for technical accuracy in representing fundamental principles of soil infiltration hydrology. The calculator implements standard engineering models (Horton, Green-Ampt) using accepted computational approaches. Always verify site-specific conditions with field testing before final design.
Learning Objective: This tool helps civil engineering students and practitioners understand how soil properties affect water movement into soils, a fundamental concept in hydrology, stormwater management, and geotechnical engineering.
Last Updated: July 5th, 2025
Made changes to fix a few issues.