Constructive waves
A wave with a strong SWASH and a weak BACKWASH which contributes deposition to a beach.
Destructive waves
A wave with a strong BACKWASH and a weak SWASH which erodes a coast.
Constructive wave size
Low and long
Destructive wave size
High and steep
Swash
The process where water moves up a beach
Backwash
The process where water moves back out to sea