A French drain is an easy-to-install method of keeping moisture out of an area of soil that's frequently flooded. If your drain is overflowing, you could find the reason by checking any of the following:
1. Clogged with Debris
The most frequent reason for a French drain overflowing is that the drain is clogged with debris. Leaves, grass clippings, mud, rocks and more may get caught in the drain. You can use a plumber's snake to try and unclog some of the debris yourself or you may need to use a power rooter. If you can't use a power rooter yourself, call a plumbing professional.
2. The Drain Uses Gravity
An incorrect installation may also be to blame for a French drain overflowing. If you don't use a sump pump, you'll have to design the drains so that they use the power of gravity to drain the excess rainwater away. If your drains are not adequately pointed down a hill, you may need to install a sump pump.
3. The Drain Doesn't Disturb Natural Water Flow
You may also experience overflowing with your French drain if you installed it in such a way that natural water flow is disturbed. If the drain blocks a downward slope of soil that once allowed rainwater to trickle away, it may be collected in a pool and make it seem as if the drain is overflowing.