Rain has hit us hard this past week with over 5 inches at my house in 5 days. Yesterday the water was at the bottom of my thick brick pool coping and today it is at the top. 2.25 inches of rain overnight. Also last night a good client of mine who had me build her a pool two years ago called to let me know her pool was nearly full and ask if there was anything she should do about it. Here is the cold, wet truth about pool water levels.
At my work we get calls every rainy season from several clients who are panicked because their pool is nearly full and it is still raining. Their fear is that once the pool overflows their whole backyard will flood. This is usually not the case. As long as your backyard could handle the rain if the pool WAS NOT EVEN THERE, then an overflowing pool will cause no additional flooding hazard. Water will not start pouring out of the pool once it reaches the top; the only water coming out will be exactly the amount which will fall on the pool as rain. If instead the pool is a runoff basin (which it should not be) then an overflowing pool could lead to enhanced flooding. If the pool is actually taking a load off of the drainage system, then once it can no longer help, the drainage system could be overwhelmed.
In most cases a properly built pool will be unable to cause property damage due to flooding. As a pool builder I CHOOSE the finished elevation of the pool with the potential for flooding in mind. Normally, if the pool is to be roughly at the same level as the home, we set the final elevation of the pool coping about 2 inches below the level of the home. That means that water would have to be 2 inches over the top of the pool coping before the house and its contents are in danger of flooding. We also make sure that decks are pitched away from the pool (not to prevent flooding but to keep pollen and algae spores out of the pool during rains) and away from the house. This creates a "valley" effect which should further keep both the pool and house safe. As long as there are no "dams" keeping the water in the backyard any floodwaters should be able to flow along the surface around the house long before getting inside. As a landscape designer I pay close attention to allowing unimpeded flow around the home, even if there is an underground drainage system.
In general there is no real danger to the pool itself if it is full to the brim. There can however be danger to any surrounding structures (including pool decks), especially if the pool is built on expansive clay soils. On any pool, and especially an older pool, there is no guarantee that water will not find its way underneath the coping through small cracks or other passages through the bedding mortar which holds the coping in place. This joint is designed to be strong, but not necessarily waterproof as is the pool tile and pool interior. As such a completely full pool may be leaking water from below the coping and in the surrounding soils. If you have a concrete pool deck or any other structure adjacent to your pool you should take action if the pool is filled to the top. If the pool is allowed to sit full of water for an extended period of time water may get underneath the surrounding deck, and in areas of expansive soils this can lead to decks lifting, heaving, or cracking. These things happen when normally dry soils expand as they wet and exert extreme forces in the only direct that they can; upward. Once a deck has lifted, even by a small amount, it will usually not sink back to the original level. Cracks in concrete are of course undesirable and do not heal by themselves.
So now that we know about pools and flooding, how do we get excess water out of the pool? We can force it out or just let it evaporate by itself. If there is no danger to the house and no danger to the pool or deck (for example if you have no deck around your pool, just lawn) then there is no reason to do anything but let nature take its course. Evaporation will do all the work for you. If you do need to lower the water level in a hurry you can siphon it out with a garden hose, pump it out with a submersible pump, or pump it out using the pool pump. Regardless of the method you use it should be done fairly quickly to get the water level down at least an inch or two below the bottom of the pool coping.
You can easily set up a siphon made from a garden hose or two connected together as long as you have sufficient "fall" to get the siphon started. If you have a submersible pump it can be connected to a garden hose, which is run out to the street (or anywhere else that won't cause additional flooding). Another method is to use the pool pump to lower the water level. Some pool equipment sets will have a hose-bib plumbed into the piping at the equipment. Simply connect a garden hose to this hose bib and turn the pump on. Open the hose bib and pool water should be flowing out of the hose. It is also possible to "backwash" the filter (if your filter is the type that allows for "backwashing" and direct the wastewater into the street or other area that will not cause further flooding. remember to recharge the filter if you use this method. As a last resort, or if you are not comfortable doing any of the aforementioned methods, is to call your pool professional. We have several submersible pumps available for rent, or if you'd prefer for a small charge we can send a serviceman out to set the pump and collect it once the pool is down a bit.
