A French drain allows proper drainage of excess surface water collecting on the ground to somewhere that it can properly drain into. Here is an overview of how the process works.
1. The ditch collects water. A French drain always involves a sloped ditch that excess surface water can run into.
2. The gravel prevents erosion. The ditch for your French drain is lined with a layer of landscape fabric and gravel, which prevents the runoff from eroding your soil.
3. The drain channel reroutes the water away from your building foundation. A solid or perforated pipe protected by landscape fabric and gravel will run the length of your trench. If you have a perforated pipe, the water can seep inside as it travels down your trench. If you have a solid pipe, it will drain through the mouth of the pipe at the bottom of the trench. Your water can be routed to a municipal storm drain.