Question
I buried 20' of 3" pvc to divert rain water to create a wet spot in south facing garden.  Created a drainage bed, 3 'deep, and 3' square. Lined the bottom with 6 " layer of rock wrapped in landscaping cloth.  It has never worked effectively-backs up and overflows-slowly seeps out into its destination.  Pipe is clear. What do I need to do so water flows freely into the drainage area=short of digging up the whole line?

Answer
Hello,

The pipe should also have a proper pitch to it. Perhaps the pitch is too shallow for the water to flow with any speed.

Or perhaps the pipe outlet is not at the right height. If you have the outlet of the pipe near the top you will only get the overflow water from the trench. The pipe outlet should be as close to the bottom as possible. Also,for this size trench,a 3 inch pipe sounds a bit undersized;at least a 4 inch pipe would be better.

If you backfilled the pit with soil and that soil has poor drainage characteristics such as a clay soil would have,then perhaps the water is being held in the soil. The pit should be backfilled with rock or gravel up to the first 18 inches. Good luck. Let me know if I can be of further help.


This pit is really not very large. Sounds like it has a volume of about 60 gallons. If some of the water is seeping out into the surrounding soil then not much will get to your garden. Gravel or rock fill would further reduce the water volume.

If the pipe is backing up then perhaps the pitch is not steep enough. A slow seepage from the pipe may just mean that not enough water is getting from the pit into the pipe since the pit has such a low volume.

Depending on how much garden area you want to water,I would suggest you make the pit bigger and think about installing a plasctic drywell or a lining of some other material to prevent water loss into the surrounding soil. Perhaps you could leave the top open with a grate over it or lay topsoil over it. Plastic drywells have precut holes for installing pipes. Good luck. Let me know if I can be of further help.

Mark  Harshman
http://www.mahdrafting.com
Email: [email protected]

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