The Cone of Depression

how a french drain affects the water table

French drains are an effective solution for managing water in your yard or basement. They are essentially trenches filled with gravel or other permeable material that allow water to seep into the ground while preventing soil erosion. It's important to understand the impact that French drains can have on the water table and the surrounding water table.

When water enters a French drain, it naturally moves down into the soil due to gravity. As the water flows downward, it creates a void or space in the soil that is filled with air. This void is called a "cone of depression," and it is created when water is extracted from the soil, either naturally or by a drain system.

In the case of French drains, the water that is collected in the trench creates a cone of depression in the surrounding water table. The water table is the level at which the ground becomes saturated with water, and it fluctuates depending on the amount of precipitation and other factors. When the water in the French drain seeps into the surrounding soil, it lowers the water table in that area, creating a cone-shaped depression in the water table.

The size of the cone of depression depends on the size and depth of the French drain, the permeability of the surrounding soil, and the amount of water that is collected in the drain.

The cone of depression helps us determine how deep a drain needs to be and how far drains should be spaced apart when creating drain grids.