A sand boil occurs when the weight from the high river water pushes down (pressure) on the soil layers under the levee. If the water can find a weak spot in the soil, it will seep up to the surface on the land side of the levee. Sometimes it can look like it is bubbling or "boiling" and that is where it gets its name.
Sand boils can develop anytime the river level is very high, not just during heavy rain events. You typically can spot them a few feet from the base of the levee, but they can also be found hundreds of yards away too.
How do we respond to sand boils during a flood fight?
Flood officials, like RD1000, address sand boils by putting sandbags around them making a ring shape. The water from the boil will slowly fill up the ring around it, and this will cause some back pressure on it.