How to calculate infiltration rate

Written by cinda roth
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How to calculate infiltration rate
Digging with a fork helps prevent compaction. (garden image by memorialphoto from

Occurring only if open space is present in the soil, infiltration is the process by which gravity and capillary action pull water into the soil. Typical units for infiltration rates are inches per hour or millimetres per hour. Ease of entry, storage capacity, transmission rate and current moisture levels affect the infiltration rate. By calculating infiltration rates, you can design drainage systems to minimise flooding and stagnant water, thereby reducing the risk that mosquitoes will breed in stagnant pools or rotting plant roots.

Skill level:

Things you need

  • Rule
  • Timer
  • Fork (optional)

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  1. 1

    Dig a hole that is at least 30 centimetres deep with your hands or a fork. Take care not to compact the sides while digging.

  2. 2

    Fill the hole with water and wait for it to drain completely.

  3. 3

    Fill the hole with water and use a ruler to measure the depth of water in the hole immediately after filling in millimetres, centimetres or inches.

  4. 4

    Measure the depth of the water remaining in the hole after 15 minutes in millimetres, centimetres or inches.

  5. 5

    Multiple by the number 2 the difference in the initial depth of water in the hole and the depth after 30 minutes to obtain the infiltration rate in millimetres, centimetres or inches per hour.

Tips and warnings

  • In most cases, millimetres are the best unit to measure because infiltration rates typically range from 1 millimetre per hour to 210 millimetres per hour based on soil type, according to Toronto Homeowners' Guide to Rainfall.

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