Difference between revisions of "Flow through perforated pipe"

From LID SWM Planning and Design Guide
Jump to navigation Jump to search
m
Line 8: Line 8:
*''A<sub>o</sub>'' is the total open area per unit length of pipe (m<sup>2</sup>/m),  
*''A<sub>o</sub>'' is the total open area per unit length of pipe (m<sup>2</sup>/m),  
*''g'' is acceleration due to gravity (m/s<sup>2</sup>)  
*''g'' is acceleration due to gravity (m/s<sup>2</sup>)  
*''Σ d'' is the total depth of bioretention components over the perforated pipe (mm) (e.g. ponding/[[mulch]]/[[filter media]]/[[choker layer]]),  
*''Σ d'' is the total depth of bioretention components over the perforated pipe (m) (e.g. ponding/[[mulch]]/[[filter media]]/[[choker layer]]),  
}}
}}



Revision as of 16:06, 25 February 2018

Manufacturers of perforated pipe are often able to provide the open area per meter length.

Where:d is the coefficient of discharge (0.61 for a sharp edged orifice),

  • L is the length of perforated pipe (m)
  • B is the clogging factor (between 0.5 to calculate a for matured installation and 1 to calculate a new perfectly performing BMP),
  • Cd is the coefficient of discharge (usually 0.61 for the sharp edge created by relatively thin pipe walls),
  • Ao is the total open area per unit length of pipe (m2/m),
  • g is acceleration due to gravity (m/s2)
  • Σ d is the total depth of bioretention components over the perforated pipe (m) (e.g. ponding/mulch/filter media/choker layer),


Example calculation[edit]

A part used roll of 100 mm diameter perforated pipe will be used for a stormwater planter project, where each planter will be 8 meters long. The initial design for the planters includes 750 mm depth of filter medium, 50 mm rock mulch, and a further ponding of 300 mm. Upon inspection the pipe is found to have perforations of 8 mm x 1.5 mm on six sides, repeated every 3 cm along the pipe. To calculate the maximum flow rate from each planter, first the open area of the pipe must be calculated in m2/m: Then the maximum flow rate per planter is calculated: