why river stones needed close to foundation
Rock instead of plants or mulch keeps the foundation dry (or better so than plants or mulch than soak up the water and retain it)
Prevents grass and weeds from growing by a wall, if used with a barrier underneath, to make it easier for trimming without hitting the wall.
Prevents splashing up of dirt or mulch onto walls. I have a garden out by a shed that would splash up mud onto the wall of the shed during a storm, so I added a row of rock like this which stops it.
Similar to the first item, it overall allows better drainage so that water does not build up by the wall.


I'm not sure what this practice would be called, but it does have useful purposes and can look really nice when done right with nice rock.