Before beginning the sizing calculations most of the following parameters must be known or estimated.
Before beginning the sizing calculations most of the following parameters must be known or estimated.
The exceptions are the depth (''d'') and Permeable area (''P''), as only one of these is required to find the other.
The exceptions are the depth (''d<sub>T</sub>'') and practice permeable (footprint) area (''A<sub>p</sub>''), as only one of these is required to find the other.
Note that some of these parameters are limited:
Note that some of these parameters are limited:
#The ''maximum'' total depth will be limited by construction practices i.e. not usually > 2 m.
#The ''maximum'' total depth will be limited by construction practices i.e. not usually > 2 m.