Water Table Considerations

When you are choosing a location for a pond, another factor to consider is the property’s water table. The water table is the depth at which you can dig into the ground before you hit water. In some places this could be 1 foot down, while in others it could be hundreds of feet. It’s definitely easiest to build a pond if you don’t go below the water table on the property. If you’re not sure of the water table, then it’s usually best to figure it out before you start digging your pond. It’s fairly easy to determine the water table by digging a test hole where you plan to install the pond. If you hit water, then you might have a high water table; if you don’t, then you’re probably fine. Keep in mind that in many locations, the water table can fluctuate seasonally.

If you do need to build a pond in a location where the lowest part of the pond is below the water table, don’t worry. It’s still possible. A common way to deal with this situation is by digging a dewatering well next to the pond excavation. Inside the dewatering well you would install a sump pump that pumps the ground water out of the well. This will lower the water table in the surrounding area as long as the pump is running.

To dig a dewatering well, choose a location next to your pond that’s out of the way and not needed as part of the pond excavation. At least 3 or 4 feet away from your pond, dig a hole in the ground until you get below the water table. It doesn’t need to be very wide—just big enough to let you keep digging down. Once you hit water, you can then rent a sump pump from a local hardware company and pump the water away from the pond excavation. It’s best to pump as far away as you can to prevent the water from just running straight back into your pond or pumping well. Also, be careful about pumping water directly into your city’s sewer system, since many areas require special permits to do this. Once your pond is filled with water, you can turn off the sump pump and the weight of the water in your pond will keep the ground water out.

Keep in mind that if you have a high water table and you empty the pond completely, water might start creeping in beneath the liner. It’s best, therefore, to limit this to short periods if possible, or rent a sump pump when needed to keep the water table at bay.