Internal erosion
Internal erosion is like a sneaky robber that steals dirt and sand inside a dam or levee. It happens when water starts moving underground, like sneaky ants going through a hidden hole. As the water move, it may carry some dirt, sand or other stuff with it, making a little tunnel for itself. But if there is too much water moving too fast, it can make a bigger tunnel and take more dirt and sand with it.
If the tunnel gets bigger and bigger, it may create a dangerous hole in the dam or levee which can make it very weak, like a person with a broken leg. When this happens, the dam or levee can break and let all the water out, like a big waterfall. This can be very dangerous for the people and animals living near the dam or levee.
To make sure that internal erosion doesn't happen, people that build dams and levees use special materials and techniques to make them strong and durable, like using big rocks and stones, making special layers of soil and clay, and adding special pipes to help drain water that may be in the dam or levee.
If the tunnel gets bigger and bigger, it may create a dangerous hole in the dam or levee which can make it very weak, like a person with a broken leg. When this happens, the dam or levee can break and let all the water out, like a big waterfall. This can be very dangerous for the people and animals living near the dam or levee.
To make sure that internal erosion doesn't happen, people that build dams and levees use special materials and techniques to make them strong and durable, like using big rocks and stones, making special layers of soil and clay, and adding special pipes to help drain water that may be in the dam or levee.