French Drains

[turningtim]

Hi All

does anyone have any experience with French Drains or field drains?
Our house is in the middle of a half acre sloping site with one 3" high retaining wall about 8" from the rear, that 8" to the house is more marsh than lawn! Im thinking of digging as close to the low side of the wall as possible, missing any founds it might have, If i dig a trench for a drain should I

a: line it with landscape fabric and fill with gravel then roll the top of the fabric over to make a gravel sausage in effect
b: use plastic peforated "land drain" in the base then gravel fill
c: both a: and b:

Rather than dig out a sump I can run this into the rainwater gully if I dont go to deep -how deep should I go, obviously a gradient ending at gully depth would be ideal but I don't know how deep that is might only be 18 inches

Can I add an inch or two of top soil and re-seed the lawn on top.

 

[TRyan]

I used the plastic piping last year (4 inch) to drain a very wet part of the garden. Simple enough - just dug a trench with a slight gradient to the outlet put drainage stone in first then pipe then covered pipe with stone.
To finish it used good top soil (only a couple of inches) and reseeded.
The former wet area is the driest part of the garden now.

 

[Thermo]

weve done quite afew of these. just think of the trench as a pipe. in effect your keeping a route through it open for the water to flow down. If you can get it to go to the surface water then fine. If it needs to go to a soakaway, think carefully about it. if your land is not draining then all a soakaway will do is hold the water and possibly cause flooding in that area.

we normally do them with the 4 inch perforated pipe, and backfill over with 20mm shingle. if your turfing above it then you need a good 4 inches of decent soil to stop the turf drying out too quick. I dont use a fabric around the pipe as i think they clog too easily over time.