Changes

On highly permeable soils (e.g., infiltration rate of 45 mm/hr or greater), a maximum stone reservoir depth of 2 metres is recommended to prevent soil compaction and loss of permeability from the mass of overlying stone and stored water.

On highly permeable soils (e.g., infiltration rate of 45 mm/hr or greater), a maximum stone reservoir depth of 2 metres is recommended to prevent soil compaction and loss of permeability from the mass of overlying stone and stored water.

===To calculate the invert of the underdrain from the base of the reservoir===

===For partial infiltration design, to calculate the depth of the storage reservoir needed below the invert of the underdrain pipe===

For designs that include an underdrain, the depth of the storage reservoir below the invert of the underdrain pipe (''d<sub>r'') can be calculated as follows:  

For designs that include an underdrain, the depth of the storage reservoir below the invert of the underdrain pipe (''d<sub>r'') can be calculated as follows: