When do you need a French drain? If you have a wet soggy back yard? Or, perhaps a driveway that continuously washes out. Is there an area that has excessive water pooling?. You probably need a French Drain.
How A French Drain Works
French drains provide an easy channel for water to flow through. Water runs into a gravel filled trench, then into perforated pipe at the bottom of the trench.
Water always flows downhill, and by the easiest route possible. That’s the basic concept behind a French Drain, a slightly sloped trench filled with round gravel and a pipe that diverts water away from you house.