Changes

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

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

For designs that include an underdrain, the maximum depth of the stone reservoir below the invert of the underdrain pipe (''d_{s, max}'') can be calculated as follows:  

For designs that include an underdrain, the maximum depth of the stone reservoir below the invert of the underdrain pipe (''d_{s, max}'') can be calculated as follows:  

<math>d_{s, max}=\frac{f'\times '}{0.4}</math>

<math>d_{s, max}=\frac{f'\times t}{0.4}</math>

{{Plainlist|1=Where:

{{Plainlist|1=Where:

*''f''' = Design infiltration rate (mm/hr), and

*''f''' = Design infiltration rate (mm/hr), and