Short answer: a French drain or yard drain has failed when water sits in the ground for days after the rain stops, when the outlet is dry or backed up, or when the grate fills with silt. Most failures are a clog, a buried outlet or a short section that has settled, and those are repaired where they sit rather than by replacing the whole drain.
A drain rarely fails with a bang. It simply stops moving water, and the first sign is a patch of yard that stays wet longer than it should. Here is how to tell whether yours is still working, what usually breaks, and what to check before you dig.
What a working drain should do
Water enters the drain through the gravel trench or a grate, moves along the pipe, and leaves at an outlet at the low end. After a storm, the ground nearby should firm up in a reasonable time instead of holding water for days. If the drain is doing its job, you will see water moving at the outlet during and right after rain, and nothing standing at the grate.
The signs it has stopped working
- A strip of lawn or gravel that stays soft and wet long after the rain has stopped.
- Water standing in a grate or catch basin, or overflowing it during a storm.
- An outlet that stays dry even when it is raining hard, which means water is not reaching it.
- An outlet that is buried under mulch, sod, leaves or the neighbor's grading.
- Silt, sand or small stones collecting at the grate, which is soil that has gotten past a failed filter.
- A basement or crawl space that was dry before and is damp again after storms.
Why they fail
Most failures come from a handful of causes. Fine soil gets into the gravel when the filter fabric was left out or has torn, and over the years it fills the stone and the openings in the pipe. Roots find the pipe through those openings and grow into it. A section settles or crushes under a driveway, a heavy vehicle or a shifting slope, so water pools in the low spot and never reaches the outlet. And the outlet gets buried. It is easy to miss, because nobody thinks of the outlet as part of the drain.
How to tell which part is failing
Walk the drain the day after a good rain, before you dig anything. Start at the outlet. If it is blocked, that is the whole problem, and clearing it costs nothing. If the outlet runs but the ground upstream stays wet, the trench or the pipe is clogged, or it no longer slopes toward the outlet. If the grate is full of standing water while the outlet is dry, the run is clogged or collapsed somewhere between them. A simple test is to run a hose into the grate and watch whether the water comes out the far end. Water that comes out slowly or not at all points to a blockage, and the spot where it stops tells you roughly where the problem sits.
What fixes it
Clear the outlet and the grate first, because that is often the entire repair. If the water still does not move, the run needs a closer look. A clog can sometimes be flushed out. A collapsed or heavily silted section usually means digging out that section and replacing it, not the whole drain. A drain that was too small for the water it receives, or that was built in the wrong place, may need to be redesigned, and that is when a proper look at the grade is worth paying for. Our grading and drainage work covers that, and our driveway drainage page covers water that runs across a drive.
Before any dig, call 811. Whether a new or altered drain needs a permit depends on where it sits and where its pipe ends up, and the rules vary by town, so read the permit question first and check with your town.
Common questions
Can I clear a French drain myself? Often, yes. Clearing a blocked outlet and lifting the grate to remove leaves and mud costs nothing and is worth doing first. Flushing the pipe with a hose is a fair test. If the water still will not move, stop before pushing a cable or jetter into the line, because that can drive silt further along the pipe and damage it.
Does a failing French drain mean I need a new one? Usually not. Most failures are a clog, a buried outlet or a short section that has settled, and those are repaired in place. A whole new drain is more likely when the old one is in the wrong place, is too small for the water it gets, or was never given a proper outlet.
Will a French drain fix a wet basement? Only if it intercepts the water that is actually reaching the house. A drain in the wrong spot, or one with no outlet, does nothing for a basement. Our post on wet basements and soggy yards explains how to tell surface water from groundwater, and that decides where the drain has to go.
Still not sure how this applies to your property? That is what a free on-site estimate is for. Call 862-268-2510 or tell us what is going on, and we will give you a straight answer, including when the answer is that you do not need us.
