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. My main problem is finding a way to make sure the water from the pond is pumped underneath the wetland filter, in an equally distributed amount. I can't have the water pouring underneath in one or two spots, it should be equally distributed.

                                                                 x |  X <-- flowers                                                                  
|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| |................(wetland filter).........|
|                   (pond)                | |ooooooooooooooooooooooooooooooooooooooooo|
|                                         | |                                         |
|     <-|-|-|-<                           | |                                         |
|_________________________________________| |_________________________________________|

A big pump is dropped in the pond, and a pipe leads it underground under the wetland filter. Its basically a space with big rocks, with water in between.

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

I need to get the water dispersed evenly underneath the wetland filter area. Some other people recommended using PVC pipe, and simply drilling holes in it. The water should go out through the holes. But those suggesting had a 5 ft wide wetland filter, mine is 150 ft long, so I don't know if that solution scales.

My concern, because I have a larger-than-typical design, with the pipe being almost 150 feet long to reach all of the bog, how do I insure the water is evenly distributed to each of the holes?

Will the water pressure equalize and cause the same amount of water to go out of each hole? Does that require carefully making sure the total accumulated size of all of the holes equals the flow rate?

Do I need to make the holes incrementally get bigger towards the end of the pipe? If so, how do I scale the holes along the distance?

  • 3
    $\begingroup$ +1 for the ASCII art. That must have taken a looong time. $\endgroup$
    – NMech
    Commented Feb 4, 2021 at 18:41
  • $\begingroup$ Do you need to have equal pressure or equal flow? Do you have any idea about the diameter of the pipe and the pump characteristics (flow, head pressure)? $\endgroup$
    – NMech
    Commented Feb 4, 2021 at 18:45
  • $\begingroup$ I don't understand the difference between equal pressure and equal flow. I want the water to come out at the end of the pipe the same as it comes out the start of the pipe. $\endgroup$
    – Village
    Commented Feb 4, 2021 at 18:54
  • $\begingroup$ The pump manufacturer recommends 2" pipe or larger. I can scale up to 4" for instance if that helps. Specs: 4,000 GPH, Max Head Height: 21". Note sure if there are other specs that are useful. $\endgroup$
    – Village
    Commented Feb 4, 2021 at 18:55
  • 1
    $\begingroup$ The difference in equal pressure or equal flow is the following, if you have the equal pressure you can have different flow rate if the diameter of the hole is different. And in general (e.g .for a level, straight pipe) you shouldn't get much pressure difference between the first and the last hole, especially given that you have more that 1Gallon per sec, going through a 2'' pipe, provided the exit holes are small enough. $\endgroup$
    – NMech
    Commented Feb 4, 2021 at 19:31

1 Answer 1


There is a better way sometimes used for ponds. It avoids the large maintenance job you will have cleaning the inlet to your pump.

  1. Dig out an area for pond and wetland. Lay a good size (like 4") plastic pipe from far end of wetland to far end of pond.
  2. Put in liner or what you are using to prevent water from soaking into the ground.
  3. Build a porous wall between the pond and wet land; I used a wall of cinder block and a second wall of face brick with holes. All openings and holes horizontal.
  4. Put a plastic tub or barrel at the far end of the wetland to hold your pump. Put many holes in the plastic ; size like 1/2 " to let water enter to the pump. I used a 5 gal bucket for my small system.
  5. Fill your wetland with the gravel you want . I used "lava" landscape stone.
  6. Fill with water, turn on the pump ..... Water will be drawn by the pump ,through the porous wall , through the gravel ,and be filtered. So the inlet water to the pump will be filtered.

Mine has run with excellent results for 20 years. I have never cleaned the gravel as bacteria and larger stuff like earth worms keep it clear (surprisingly earthworms will go under the flowing water). Also, because my pond is small ,I pump the water (in 2" plastic pipe) about 25 feet away and have a plastic lined shallow (2") stream that flows back to the pond.


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