Flow through perforated pipe

In practices such as bioretention, bioswales or stormwater planters, the flow limiting component is usually the filter media. See Flow through media page for guidance in estimating the maximum flow rate through bioretention filter media. In underground practices such as infiltration trenches, infiltration chambers, and exfiltration trenches, the perforated pipe that delivers water to the practice will be the primary flow limiting component. 
Manufacturers of perforated pipe are often able to provide the open area per meter length. Where this information is not directly available, the open area can be calculated by measuring the perforations and summing the open area per meter. The maximum flow rate through a perforated pipe (Qmax, pipe, m3/s) is calculated similarly to flow through an orifice: 
Q_{max, pipe}=L\times B\times C_{d}\times A_{o}\sqrt{2\cdot g\cdot h_{max}}
===Example calculation===
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:
\frac{0.008\ m \times 0.0015\ m\times6}{0.03\ m }= 0.0024\ m^{2}/m
Then the maximum flow rate per planter is calculated:
Q_{max, pipe}=8\ m\times 0.5\times 0.61\times 0.0024\ m^{2}/m\sqrt{2\cdot 9.81\ m/s^{2}\cdot 1.1\ m}=0.027\ m^{3}/s
===Note===
While it is recognised that many smaller perforations present a greater resistance to flow than fewer, larger perforationsPabst, M., & France, J. (n.d.). GETTING WATER INTO PIPES -NOT AS EASY AS IT SEEMS. Retrieved from http://dnrc.mt.gov/divisions/water/operations/docs/dam-safety/technical-references/getting_water_into_pipes.pdf, calibrating for this is quite complex Hazenberg, G., and U. S. Panu (1991), Theoretical analysis of flow rate into perforated drain tubes, Water Resour. Res., 27(7), 1411–1418, doi:10.1029/91WR00779.Murphy, P. (n.d.). THE HYDRAULIC PERFORMANCE OF PERFORATED PIPE UNDER-DRAINS SURROUNDED BY LOOSE AGGREGATE. Retrieved from http://tigerprints.clemson.edu/all_theses. The practice of approximating, using the open area of the pipe per unit length, is commonplace, and we are unaware of ill effects arisingDepartment of Planning and Local Government South Australia. (2010). Water Sensitive Urban Design Technical Manual Greater Adelaide Region Bioretention Systems for Streetscapes. Adelaide. Retrieved from https://www.sa.gov.au/__data/assets/pdf_file/0010/19837/WSUD_chapter_10.pdfADS pipe. (2004). Outflow from Perforated Pipe. Retrieved March 12, 2018, from http://discountdrainage.com/dev/wp-content/uploads/Technical_Note_2.105_Outflow_From_Perforated_Pipe.pdfTitan Industries Inc. (n.d.). To Calculate the Amount of Water Flow (GPM) Through Slotted PVC Well Screen. Retrieved from http://www.titanpipe.com/Engineering_Titan_Industries_In/Water Flow PVC Well Screen.pdfWaveRail. (n.d.). WATER WELL SCREEN & CASING SYSTEMS. Retrieved March 12, 2018, from http://www.waverail.nl/images/Template_content/PDF/documentatie/Filter-buizen.pdf.
==See also== 
*flow control
*underdrains. 
----
category:Calculations