Infiltration Rate Calculation

Infiltration Rate Calculation

A typical method of Infiltration Rate Calculation is given below. Typical values for the Infiltration Rate of soils area given here, though these are indicative only. It is important that Infiltration Rates are tested before a Soakaway design is completed.

First a trial pit should be dug to the same depth as the proposed soakaway, and around 1m wide and 2-3m long. It must have vertical sides and can be filled with granular material if required for stability. If granular fill is required, an observation tube will be required to take accurate measurements of water depth to enable the Infiltration Rate Calculation to be completed. The pit must be measured carefully before the trials start so that the dimensions can be used in the subsequent calculations.

Next the pit needs to be filled with water to its effective depth. This needs to be done quickly to accurately measure the Infiltration Rate, though care needs to be taken that the sides of the excavation do not collapse. The pit needs to be filled three times and each time the time taken to empty the pit is measured.

The soil Infiltration Rate is calculated from the time it takes for the water to fall from 75% full to 25% full. This can be calculated using the below formula;