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View Full Version : How deep for a French Drain ?


lself
07-18-2006, 01:54 PM
My property slopes front to back and pretty much level side to side. There is a creek which is always flowing at the back proprety line. My back yard has several real mushy areas with one large "swamp" at the lowest point.

The County Soil & Water Dept says it's water table runoff. They recommend a French Drain. I have read a good bit and understand what it is and why I need it. But I can't find anything that says how much lower than the surface where the water stands I need to dig the ditch. The Soil & Water man said 4ft deep at the level I need to run the ditch. Where he suggested I run the ditch is 18 inches higher and roughly 25 ft from the standing water. The creek is maybe 15ft from this low point and only a foot or so deep from the surface of the bank and always has water. I have dug a couple trenches to the creek but the ground still stays too mushy to mow or walk.

Do I need to go 2 1/2 feet deeper than the water? I don't see how I can grade a drain to the creek if I go that deep.

Will I need a catch basin and pump? If so, can I use this water and build a pond then run that off to the creek. That would thrill the wife.

Any suggestions will be appreciated . . .
Les Self

Signature Landscaping1
07-18-2006, 03:11 PM
2ft deep I belive.

sheshovel
07-18-2006, 04:15 PM
Can you take some pics of the areas you have in mind here?
Gotta see it.

jeffinsgf
07-18-2006, 05:59 PM
There's no set depth. The theory is to run from the boggy area down hill, exiting at ground level. So, say in your boggy area, dig down a couple of feet, and then run the trench away from there, always moving slightly downgrade until it comes out at daylight. In a perfect world from what you describe that could be just about the top of the creek bank. Now layer the bottom of the trench with filter cloth and install 4 or 5 inches of coarse gravel. Now put in a 4 inch perf pipe that is sleeved with filter cloth. Now cover the pipe with more coarse gravel. Top that with filter cloth and then grade in your topsoil. Now, the water in the boggy area will gravitate to the path of least resistance, which will be the perf pipe. It will flow downhill to the creek. Forget pumps. If the creek is below your problem, all you've got to do is help nature out a little.