Backwash

I go surfing quite often. Whenever I surf at a break that is close to the beach backwash becomes a part of the session. The backwash is created by water flowing down the slope of the beach back into the water. A wave is created that moves out into the ocean. When it collides with another wave a large peak is created then the backwash and wave continue on in their original paths. It is clear that they do not bounce off each other because the wave going back out is the same size as the backwash and the wave approaching shore is the same size as the original wave. Therefore waves can go through eachother.