In the surf zone the short waves lose height and energy and can no longer balance
the bound long waves which are therefore released as free long waves. The free long
waves are substantially reflected from the beach and either progress back out to sea
(for normally incident short waves), termed the leaky mode or refract and turn back
to the shore to be re-reflected, termed the trapped mode. The trapped free long waves
then form three-dimensional edge waves with a wave height which decreases with
distance from the shore.