French Drain with Trees in Existing Clay Ditch

[mechanicalchad]

I have a large clay drainage near an industrial gravel pad that runs several hundred feet that I was considering installing a large French drain with trees (I'll describe below). It can be deep at certain points to maintain grade and has steep side slope which has caused concern about general safety and the ditch sluffing in. The best of both worlds would be to have it filled in and greenery added, at a cost effective price, and still have a good drain. This led me to an idea.

I have lots of top soil from stripping the pad, but screened rock is expensive. The clay ditch is about 6 feet deep with steep side slopes. The source of water is from both a 16" culvert upstream and from the runoff off the pad. The ditch runs for a couple hundred feet then hits an approach with another culvert, and so on.

It is an important drainage; however, I was thinking of extending 16" perforated pipe from the upstream culvert to the downstream culvert in the bottom of the ditch, then covering the perforated pipe with screened rock to a height of just a few inches above the top of the perforated pipe saving on screened rock. Then I was going to lay a geotextile down to separate the screened rock from the layer above, which I was thinking would be about 4" of sand for filtering. Finally on top of the sand, I was thinking of placing the top soil for the final 4 feet, actually 3 feet so there is still a natural draw into that area, and then I would plant some trees so it looks easy on the eyes.

Would this work? Would the water still flow down through the soil into the weeping tile, and how fast would it flow? Would there be enough moisture in the top soil for trees to grow? Would each horizon stay in their proper place over time (especially the sand top soil layer)? Last, how much (if any) filtering would this provide?

It's just an idea, and so I would love to hear some feedback from someone with expertise or experience in this area. Any ideas are appreciated!

Thanks,
Chad

 

[GeoPaveTraffic]

Could be made to work, but probably easier to install solid pipe and one or two area inlets in the draw to take the surface water. You would need to look at drainage areas and local conditions to determine how many inlets you would need.

As for how the trees would fair, will depend on the type of tree and local conditions.

Good luck.

Mike Lambert

 

[cvg]

if your soil is clay than you will be limited in the amount of water that will percolate into the ground. the tree roots will search out the moisture source and will end up choking your perf pipe. trees are generally not a good idea around pipes and subdrains. GPT's idea is better or use an open ditch.

 

[mechanicalchad]

Thanks for the feedback guys! I like the idea of a solid pipe, but was initially questioning how easily it would get plugged over time (if debris were to go through the area inlets), but given the mainline is a 16" line it would probably take quite a bit to plug, and unfortunately this is along a roadway and so the open ditch creates a safety hazard.

Are there good off-the-shelf and cost effective suppliers of this type of piping with tees and area inlets? I could easily create something custom with steel or HDPE, but don't want to re-invent the wheel if I don't have to, and steel could be cost prohibitive.

Thanks again,
Chad

 

[oldestguy]

Don't forget that if you place screened rock against native soil, that will cause the rock to be plugged from that source. If you must use screened rock, surround it COMPLETELY with non-woven geotech fabric. Non woven is a better filter than woven stuff. A less labor intensive method is use pipe with 1/8" slots and backfill with ASTM -33 concrete sand. No other fabric or graded filter needed in the ditch. Alternative to 1/8" slots is a few rows of holes on the bottom side, 3/16" diam. Water tuns out of the pipe as well as in and that may cause problems.