Blocked french drain

[MarkAT]

Last year I added some french drain to my rear garden to supplement existing drainage. The latter supported drainage from an active spring(!) and two open covers to allow excess surface water to flow. Our field backs onto open fields which run off into our garden. This flows through 100mm pipe into a ditch 60yds away. There is also a 12' land drain at the rear of the fields. The ground is clay.

I added some additional french drain in the garden to stop it getting totally sodden in winter/spring. This was piped into the existing land drain in the garden. One drained from a flat area of garden which was sodden due to the aforementioned spring. It works perfectly and works very well. The other ran from from the top of the garden (being joined part-way by another) and fed into the original pipe from the spring: i.e. the one that should carry the bulk of the water. This latter pipe has become clogged. Although it joins the 1st pipe later on.

Even in this weather the spring flows well! The blockage has caused the water to backup and then seeps out of the drainage pipe and through the ground.

I dug an exploratory hole to see what was going on and the pipe is full of water but without any sediment in the area where I inspected. I wanted to rod it through but was concerned that any blockage may block further down the pipe resulting in a far bigger problem!

During the winter the run off from the fields was bad and resulted in the garden being flooded (2" rise in 3 mins). To ease the problem I opened up part of the drain to allow run-off to flow into it. This is into the area that is now causing problems.

I don't understand why this problem should have shown itself now, given the current heat. Any ideas?

Is rodding/flushing likely to cause bigger problems?

Is it likely that gravel has clogged one of the junctions and then caused an increase of silt build up?

Any ideas /thoughts would be very gratefully received as a boggy lawn is not welcome - even in this heat!

Mark

[danensis]

If you rod from the downhill end (which is the right way to rod anyway) you shouldn't cause any problems, though you may get wet.

[84-1093879891]

I agree - rodding is the first strategy to try. It may be summat dead simple like a collapsed joint, or (and don't laugh!) a dead rat that has not decomposed fully.

Use rods to determine just where the blockage opccurs, and, if the rods don't shift it, dig down there to find out why.

[MarkAT]

I had to dig to do the rodding (the builder never left a rodding point!).

The drain was blocked with roots and silt (we have clay soil). Should vegetation like this really be there to cause problem?

[84-1093879891]

No, but, if the eejit builder wasn't bright enough to include a rodding eye or other access point, it's unlikely that the drain was enveloped in a root/silt membrane, as is shown on the Land Drainage pages of this website. That's more'n likely the root cause of the problem (ha ha!)