What is the Difference Between Infiltration Rate and Percolation Rate?

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The key difference between infiltration rate and percolation rate lies in the processes they describe:

  • Infiltration Rate: This refers to the volume of water that flows into a unit area of soil. In other words, it is the velocity or speed at which water enters per unit surface area of soil. When water is supplied to the soil, the infiltration rate tends to decrease from its initial high rate due to the formation of a thin layer of water on the soil surface.
  • Percolation Rate: This refers to the flow of water through soil and porous or fractured rock. It is the rate at which water moves into the soil after it has infiltrated the surface.

In summary:

  • Infiltration rate is the volume of water that flows into a unit area of soil.
  • Percolation rate is the rate at which water moves within the soil after it has infiltrated the surface.

These terms should not be used synonymously with permeability, which is the property or capacity of a porous rock, sediment, or soil for transmitting a fluid. Essentially, permeability is how well water can flow through a material, while infiltration and percolation are the rates at which water can travel through materials.

Comparative Table: Infiltration Rate vs Percolation Rate

The main difference between infiltration rate and percolation rate lies in the process they describe:

Infiltration Rate Percolation Rate
Refers to the volume of water that flows into a unit area of soil. Refers to the rate at which water moves into the soil as determined by the percolation test.
Measures the velocity or speed at which water enters per unit surface area of soil. Measures the downward movement of water through the soil after it has infiltrated the surface.
Usually decreases from its initial high rate due to the formation of a thin layer of water at the soil surface, called a "seal". Tends to overestimate infiltration rates and can be off by a factor of ten or more.
Can be measured using devices like infiltrometers, permeameters, and rainfall simulators. Can be estimated using the percolation test, which is related to the infiltration rate.

In summary, infiltration rate is the volume of water that flows into a unit area of soil, while percolation rate refers to the movement of water within the soil after it has infiltrated the surface.