Unfortunately, you're experiencing the same thing that many contractors and engineers find out the hard way when using stone to line stormwater impoundments, settling basins, and what are called 'forebays'. Stone of a correctly engineered size can be very useful in changing the velocity of stormwater flows. But the downside is that when that same stone installation becomes clogged with sediment and debris, there's really no good way to clean it other than removing and replacing it. Therein lies the problem with the use of stone for dealing with surface drainage where the introduction of sediment in the runoff is likely. And you've experienced it first hand.

Probably the tedious method you're using is the best way, tiring and frustrating as it might be.

In the long run, to avoid future problems of the same sort, you'll have to change the direction of the surface flow, or cover the stone with a filter fabric with a sufficiently fine mesh to trap the sediment before it gets mixed into the stone.

Admittedly, neither are appealing at first glance, but until the adjacent surfaces are vegetated or treated in such a fashion that runoff heading towards the stone is 'clean' the problem will persist.

Thanks for your advice. I very much appreciate it.

Perhaps you can suggest my next step of action. I have access to some rock about 3" in diameter - this is the same stuff railroads use to ensure good drainage of their roadbed. Should I use my old rock and put some mesh on top of it, or would I be better off to completely replace the rock I already have with the 3" railroad ballast rock?

For the mesh, you want to use landscape fabric, not hardware cloth or screen. What we've seen recommended, is to wrap the landscape fabric around the pipe, rather than on top of the rock. Of course, it's usually done at installation time, so after the fact will be a lot more work.

I'm not sure on the rock, but if you call your local planning dept I'm sure they could tell you exactly what's best.

Actually, if you have a perforated pipe wrapped in fabric and then surrounded by stone, landscape fabric will do nothing to prevent the stone itself from becoming clogged with sediment. Once the stone is clogged, water can't find it's way to the pipe, and the installation pretty much becomes uselss.

If there's no way to change the direction of the surface flow (which I'm guessing is the case) then you'll want an installation which provides for relatively easy removal of sediments that will accumulate. Ultimately, it may be best to completely remove the stone and pipe, line the trench with a good filter fabric (bottom, sides, and enough hanging out of the top to wrap the completed stone installation), place 2-3 inches of stone in the trench, replace the pipe on that stone (perforations down), then fill the trench to within a couple of inches of the adjacent grade. Fold the loose fabric at the top over the stone to create an envelope around the stone. Having left the top ofthe stone a couple of inches down from grade, you should be able to fill that with a more decorative or slightly larger stone. That last couple of inches should end up being the only place you'll have to clean the sediment out of before the adjacent areas become sufficiently vegetated to prevent further siltation.

Railroad ballast may be suitable for the top couple of inches, but around the pipe I'd stick with something more in the range of 3/4" stone.