For many homeowners, the sound of a running pump in the basement is nothing unusual after a heavy rainfall. If asked, most could probably tell you it is their sump pump at work; but if pressed, many homeowners may well have to admit they don't entirely know how it works or how exactly it helps to prevent flooding after a heavy rainfall.
A sump pump is a pump that has a floating switch activation system located in a sump pit, which is essentially a hole in your basement floor. The switch is normally off, in a lowered position, but when rising water levels push the flotation device on the switch upward, it sends a signal for the pump to activate. The pump then drains the water, which in turn lowers the flotation device on the switch until it reaches its initial position, thereby turning off the pump.
Pumps can come in two types: submersible types, which will be found at the bottom of the sump pit, and pedestal types, in which the motor is located above the floor near the sump pit.
A heavy rainfall means that a large amount of water has been poured onto the ground. Depending on the type of soil and on the geography of the area, differing things will happen to that water. If a soil is very permeable and had a low moisture content to begin with, the water from the rain will drain through it quickly. However, if the soil is not very permeable, or it was already very wet, the water cannot drain quickly. And as the water builds up around the foundation of a house, hydrostatic pressure will push it through the floors and walls.
If the house is located on a slope, there is less water build-up as a result of gravity pulling excess water down the hill. In flat areas, water build-up is much greater, as there is nowhere for the water to drain but through the ground.
After a heavy rainfall, hydrostatic pressure is pushing water through the floors and walls of your home. Without a sump pump, the amount of water would keep increasing, resulting in flooding.
However, when there is a sump pit, the water will flow and accumulate into the pit. This in turn activates the sump pump, which will begin the process of removing the water. Until the time where the rainwater has finally managed to drain through the soil to a depth lower then where your house is located, water will keep being pushed into your basement, and the pump will keep working to remove that water.
There are two things that are important to remember regarding sump pumps. The first is that if the pump's capacity is not great enough for your home, flooding can still occur. The second is that a sump pump is still a mechanical device, and as such should be periodically tested, to make certain it still works.
Sebastien Rocheleau is completing his Bachelor of Science in biology and English literature at the University of Waterloo. He has helped author operating procedures and technical reports for organizations such as Agriculture Canada and Atomic Energy of Canada.