Under lawn drainage

[MrC]

Moved into a new house, the lawn has under grass drainage pipes which start about 3 inches deep at one end and run to about 12 inches deep at the other. The low end used to run into a natural drainage ditch with a hedgrow growing within.

I assume this used to work great but we found out that just before selling the house they put up a fence at the low end and backfilled to level the lawn. The problem was that rather than poking the drainage pipe out under the fence (and into the ditch) then simply covered it with top soil leaving the end blocked.

To add to this there is a lot of clay around. I believe there are several feeder pipes into this main pipe, not been hunting yet though.

My questions are; how deep should this pipe be at it's shallowest and deepest? Should it be surrounded by gravel, if so to what diameter? How may branches should it have or is it a case of the wetter the ground the more pipes you put in?

Many thanks.

[Newt]

Hi MrC,
Congratulations on your new home! I'm going to try and answer your last questions first.

how deep should this pipe be at it's shallowest and deepest?

At it's shallowist, it can be as shallow as an inch below the soil line. At it's deepest, it should go down an inch for every 12" of run to keep it flowing.

Should it be surrounded by gravel, if so to what diameter?

If the pipe has holes in it, it should be surrounded by gravel and landscape fabric. The diameter of the pipe would depend on how much water you are trying to move, but a 2 1/2" to 3" pipe should be sufficient. The gravel should be about 3" to 4" deep.

How may branches should it have or is it a case of the wetter the ground the more pipes you put in?

Not sure what you mean here. I have pipes that run under the lawn and are attached to my downspouts. The pipe runs 50' across the back of the house, makes a turn and runs another 60' to the street. The pipes that come off it are from other downspouts that run into the main pipe. Generally the water is moved from one area to a well, ditch or drain and there would be as many leads as needed to move the water from wet areas or just one wet area.

The low end used to run into a natural drainage ditch with a hedgrow growing within. ...they put up a fence at the low end and backfilled to level the lawn. The problem was that rather than poking the drainage pipe out under the fence (and into the ditch) then simply covered it with top soil leaving the end blocked.

I'm thinking that what is happening is that your pipes have drainage holes all along them (mine is solid and just carries the water to a drain) and the entire area is now wet all the time. If that is so, you will need to dig down where the pipe ends and extend it to the ditch, keeping the pitch so the water will continue to flow.

Take a look at these sites to see if they are helpful.

http://www.askthebuilder.com/175_Dry...ch_Drain.shtml
http://www.michaelholigan.com/depart...GNT9PBV4N9512#
http://www.gardenadvice.co.uk/howto/...d/frenchdrain/

Hope this helps,
Newt