When a Sump Pump Isn't Your Best Bet

Rising exterior floodwaters create inward pressure against the walls of the building. A rapid rise or drawdown may create enough elevation difference between the interior and exterior water surfaces to damage a building’s walls or foundation.

The lateral pressure associated with floodwaters is approximately 62 to 64 pounds per square foot for every foot of differential. So, if the outside water were to reach two feet above the floor of a building before any significant amount of water leaked into the building, the lower section of the wall would experience a maximum inward pressure of 128 pounds per square foot. However, once the water reaches the same level on the inside as the outside, this force is eliminated. So, in a “leaky” building there would be a low potential for damage in this manner.

However, a problem sometimes is encountered when the rapid drawdown of basement water occurs due to mechanical means following a flood. Well-meaning efforts to empty flooded basements with high capacity pumps can actually cause the lateral pressures of saturated soil to exceed the structural capacity of basement walls. The result? An inward collapse of the basement wall itself.

The presence of water inside the basement walls, countering against the exterior lateral pressure, may actually help protect the wall’s structural integrity.

My advice during a severe flooding situation is this: turn OFF the sump pump, move your furniture and other possessions to higher ground and wait. Wait for the soil’s saturation to subside, and the exterior pressure on those walls to decrease. Hard as it may be, patience may be your best strategy.

Call me at 627-6873 or send an email to tom@zugassociates.com to discuss plans for your building or project.