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I am trying to build a wetland filter for a pond. Basically, you dig a big hole, fill it with rocks (large at bottom, small at the top), and pump water deep under these rocks, so the water slowly trickles upwards.

The major problem with such as system, is you have a pump that pumps the water, and but you need to distribute that output across a large area (in my case, 20 ft by 20 ft area), so it isn't blasting water in one place, but is spitting out the same volume across the area underground. There are commercial products designed to do just this, but they seem ridiculously expensive for being just pieces of plastic with holes in it (as best as I can tell from the pictures).

My solution is to simply buy some big PVC, attach it to the output pipe of the pump, and drill many holes in it so it looks like a flute and bury that underground:

  ___    water flow--->              hole
 [   ]_________                       |
 [   ]_________\                      V
 [   ]         \\______o____o____o____o____o___o____o____o___o___o___
/     \         \____________________________________________________] <--cap on end
    ^                          ^
    |                          |
   pump                      2" diameter PVC pipe

Will such a design lead to the water coming out equally in each hole? Do I need to vary the size of the holes (e.g. larger the further away)? Do I need to make each hole the same, but if 10 holes, make them 1/10th the diameter of the pipe?

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  • $\begingroup$ If the flow speed through the perforated pipe is small, pressure drop in it will also be small and you won't need to adjust hole size. You achieve this by using a large diameter pipe, as flow speed through it will be small, compared to the case of an undersized pipe. $\endgroup$
    – Gert
    Commented Nov 20, 2020 at 19:43

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