The ground thaws while snow melts and spring rains come. At the same time, the thaw is happening all the plant life is dormant and not drinking water. The water accumulates under and around your home. This is called a high water table or perched water.
The thing to understand here is that the high water table is part of the earth and cannot be graded away. Think of the water being flat like a table top. Because it rains over a wide area water table typically covers a wide area.
When the water table rises, it does not just rise at your house, because it did not rain on your house only. The rain usually falls over a wide area of many square miles so all this water goes into the earth at the same time. Water tables can become elevated when they receive more water than they drain off. This can be from unusually high amounts of rain or excess water from higher elevations.
High water tables are often above the level of basement floors or crawlspaces. This almost always causes flooding in these areas.
The level of the water table varies greatly due to the amount of rainfall, time of the year and type of soil that surface water drains through. The water table is generally higher in areas with high-density soil related to clay content. The denser the soil is, the slower the movement of the water (percolation) of the water through the soil occurs. The rate at which the high water table descends is related to the percolation rate, which is related to soil density.
What is a French Drain?
The earliest forms of French drains were simple ditches, pitched from a high area to a lower one and filled with gravel. These were described and popularized by Henry French (1813-1885) a lawyer and Assistant US Treasury Secretary from Concord, Massachusetts in his book Farm Drainage.
A French drain has perforated hollow pipes along the bottom to quickly vent water that comes from a rising water table. French drains are common drainage systems, primarily used to prevent ground and surface water from penetrating or damaging building foundations.
The system is designed to prevent water from flooding your basement. It is installed in the basement, below the floor, around the perimeter. This French Drain controls the water, delivers it to the sump pump(s), and discharges it out of the house. This system comes with a life-of–house transferable guarantee that your basement floor will not have any water on it.
How a French Drain can lower the water table under the basement floor.
- The drainage pipe of the French Drain is placed alongside the footings at approximately 6-8” below the basement floor level. The water under the basement floor gets pumped away at that level before it comes up to the floor level.
- A French drain is much unlikely to clog than an exterior perimeter drain partially due to the fact that it is not sitting underneath several feet of soil.