A concrete wall

This is a concrete wall covering a levee. This kind of materials which became old are apt to become really dirty.　This is different from the stone wall that the antique look is deepened as It becomes old.

Even if only the surface of the levee is covered, there is not much significance. There is a case that it collapse by losing soil of the inside.
If the bank of the river is covered by reeds and water plants without artificial materials, ability for purification of water rises.