I am not personally disagreeing with your mapping style. It is a long standing OSM convention  that the coastline tag is not used on small water bodies not connected to the ocean.

As far as I am aware the only exception to this is the Caspian sea, which  due to its size would be impractical to use a mulitipolygon tagged as natural = water.

Could you please explain what you mean by a "permeable embankment"
 