Why Is It Almost Impossible to Keep Water from Seeping

Why is it almost impossible to keep water from seeping under a levee and out onto a floodplain?

A) Bigger rocks are typically placed at the bottom of levees, and they are most permeable.
B) Levees are built on floodplains marked everywhere by old permeable stream channels.
C) People building levees often forget to line the stream channel with plastic.
D) Piping (large tubes) are built near the top of the levee to prevent overtopping.
E) Metallic walls that are placed into the ground rust and fail after two or three years.