French drain

A French drain is a trench, lined with fabric, filled with gravel, with a perforated pipe along the bottom. Water in the surrounding soil seeps into the gravel, drops into the pipe, and travels to a lower outlet — a dry well, a drainage ditch, or daylight at the edge of the property.

It is the standard fix for a chronically soggy lawn, water sitting against a foundation, or a slope that dumps onto a patio. Grading moves surface water by shaping the ground; a French drain handles the water already in the soil, so the two solve different halves of the same problem.

The detail that makes or breaks it is the outlet. A drain with nowhere to go is just a buried bathtub. It needs continuous fall along its length and a real low point to empty into, or it quietly fills and stops working.