Something that crops up occasionally in aquaponics or hydroponics is what happens with an outdoor or greenhouse sump tank that is sunk into the ground.
See if the water level in a barrel or other light weight tank that is sunk into the ground gets really low while there is a high water event in the vicinity, there is a chance that the sump tank will float up out of the ground. Some times it can do this with quite a bit of force. I haven’t personally had this happen but I’ve seen plenty of pictures of aquaponic or hydroponic sump tanks that have come up out of the ground. It is often kind of a disaster to the system if the situation isn’t noticed immediately. It can also break plumbing lines or the tank.
As you can see from the picture, where I live can get really heavy downpours. It is important that if you build a pond or in ground tank for an aquaponics system, that you make sure the top rim of the tank or pond is set such that a heavy rain event won’t be washing dirty ground water into your system. Leaves, wood chips, dirt all that would be fairly disruptive to smooth system operation and if chemical laden water were to wash into a system it could result in a bacteria crash or even a major fish kill. So keep this in mind when designing an aquaponics system. In ground tanks should have the grading done so that water will drain away from them rather than into the hole to float them. If the water level is to fluctuate in the tank, make sure the fluctuations happen above the ground water level and make sure the top rim of the tank is above the surrounding ground so a heavy rain event won’t flood into the tank.