What Swimming Pools, Basements and Septic Tanks Have in Common
The idea of leaving your home flooded after the storm has passed may seem out of place in light of the damages that water causes when left in a home. After floodwaters drop below ground level people generally want to begin the cleanup of their homes as quickly as possible. This is of course to prevent additional deterioration and salvage as many things as possible. Generally, this is the correct response. There are some situations where recovery should be delayed. If you have a below ground pool, spa, septic tank or basement then pumping the water out too soon or all at once may result in more damage than pumping it out gradually.
Overall, when the subsurface landscape around a home is still flooded, removing water from the buried or underground structure creates a buoyancy that can be powerful enough to lift it right out of the ground. If your basement begins to float like a boat the structural damage to your home is profound.
Pools and Spas
While pools and spas natural state is to be filled with water, flood waters are filled with debris and dirt. Cleaning out the pool can involve removing the water.
While the ground remains saturated, below ground swimming pools and spas can literally pop out of the ground or collapse inward if they are emptied. Most people don’t realize concrete can float, but it can be buoyant when the shape is right. As the water is pumped out, the water in the ground pushes the pool or spa upward. This potentially results in collapse or permanent damage. Although it is not pleasant to leave contaminated floodwater in a pool or spa, it is probably better to wait to pump these out until you are sure ground water has receded enough. As long as the pool or spa remains full of water, the weight of the water inside will counter the hydro-static pressure pushing inward from the water in the soil.
Septic Tanks
Sometimes homes in more rural areas have septic and other types of underground storage tanks that may have filled with floodwater. The septic tank may have filled up with silt and other debris and will need to be pumped so that it can start being used again so as not to experience immediate overflow.
Pumping the septic tank while ground water levels are still elevated may cause the septic tank to float upward and pop out of the ground, thus destroying any chance for an easy inexpensive fix. If the septic tank has filled to overflowing with floodwater, it is probably best to have it pumped down only one or two feet to provide for immediate use.
The tank can also be monitored to see if it rapidly fills back up with more water. In this case, ground water has not yet receded enough to pump it further. Just wait a few weeks for the ground water to fully receded to a depth below the septic tank.
Basements
Not many buildings in the Houston area have basements, but those that do can be severely damaged by pumping them out too quickly after they flood. There have been numerous cases where a well-meaning fire department has gone around pumping basements dry before the ground water has receded. The force of the ground water has then caused the basement to cave inward resulting in the collapse of the home or other severe damages.
Just because surface water has receded doesn't mean that ground water levels have dropped. If you do have a basement that is significantly flooded with water - it needs to be pumped down in stages to match the levels of ground water that remains. Emptying it too quickly can cause the foundation walls to collapse causing significant additional structural damage. As long as the basement is flooded the presence of the water in the basement will keep the foundation intact by applying an equal force on both sides of the basement wall.
Tips for removing water safely
When pumping out a basement, do it in stages. The water should be lowered about two feet and the water level marked on the wall.
Wait a few hours to see if the water level begins to rise. If the water level goes up, it indicates the ground remains saturated at the foundation and no more water should be removed until the ground water level drops.
If after waiting a few hours the water level hasn’t risen, then it’s generally okay to pump out a couple more feet of water. Repeat this process until the basement is dry.