Suppose you have a wave heading towards the beach, and under the water the surface rises suddenly then drops again back to the typical average slope of the coastline, does this have a muting affect on the water even if the rise in terrain under the wave is completely submerged?
A crude drawing of what I mean:
Would this obstacle cause the wave to increase in height or have a dampening affect on the wave? Would it have to penetrate the surface in order to have any affect on the wave's energy and momentum in this case?