A French drain is a trench filled with gravel or stones, covered by an impermeable material like plastic, and surrounded by soil. The purpose of this technique is to redirect surface water flow away from structures like buildings to prevent erosion.

The French drain was invented in the 1860s by French civil engineer, Georges-Eugene Haussmann. His drain design consisted of several trenches that allowed for both clean water runoff near farms and contaminants to stream toward rivers away from city drains. At this point, there were no sewers so all liquid waste simply flowed through these types of drainage systems. Additionally, French drains are also known as “subsurface” or “subsoil” drainage systems – they only handle the stormwater that flows through the soil right above them.

The French drain is good at preventing erosion because of its downward slope of 1% to 2%. This can be explained by looking at Fnet, the net force acting on the soil. This net force must be zero for equilibrium, so that there is no acceleration in any direction. The only way for this to happen is if there is an equal amount of acceleration in opposite directions – in other words, a downward slope due to gravity and an upward slope from frictional forces.

Since it is a drainage technique used around buildings or large areas with high water table levels , it should not be confused with an “underdrain” which would remove groundwater from being absorbed into the soil within a construction site.

In contrast, for a typical thoroughfare, a French drain would be ineffective since the slope of a road is usually 0.1% to 0.5%. Even if the water drains through the trench, it will have no effect on lowering the surrounding area’s ground saturation levels. This is because while water flowing over an impermeable surface will increase the flow rate, any level change in that flow due to gravity is negligible compared to the infiltration rate of the soil itself. In summary, this means that while some amount of rainfall can be drained from non-impervious surfaces like sidewalks or driveways with enough gravel and perforated piping, this technique cannot remove groundwater at construction sites.

French drains are still used today by farmers and homeowners in agricultural areas, or when building homes or buildings in flood-prone areas such as the Midwest.

Part of the reason for this is that it allows water to drain through horizontally, rather than vertically like a pipe would. This means that it only takes half the length of French drain to remove an equivalent amount of water compared to a drainage pipe. Furthermore, since the bottom and sides of the trench become saturated with groundwater, they will act as natural filters removing any contaminants in the water before it reaches nearby bodies of water.

 

For more information, contact Vinny’s Jersey Plumbing, located in Wayne, New Jersey.  We also service other towns in New Jersey, such as Paramus, West Orange and Teaneck.