Changes

The sizing calculations require that most of the following parameters be known or estimated.  

The sizing calculations require that most of the following parameters 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'') and Permeable area (A<sub>p), 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. usually ≤ 2 m.

#The ''maximum'' total depth will be limited by construction practices i.e. usually ≤ 2 m.