How can bulding up natural levees with stone and concrete often make flooding worse downstream?

Question

How can bulding up natural levees with stone and concrete often make flooding worse downstream?

Answer 1

A stones and concrete can not soak up some of the water initially rising along a river.  A levee built up with mainly dirt or soil based initially can soak up store some of this river water when the surface is not completely saturated.

So a levee made up with stones and concrete will allow more water to pass initially downstream.  With more water heading downstream. the flooding chances will also increase.  If flooding is already occurring downstream, than this additional water amount can only maker the flooding situation worse.

Answer 2

If the floodwater is stored behind a levee, a breach of the levee will send a wall of water downstream instead of a gradual flooding.