What is the difference between constructive and destructive waves?

Constructive waves have a strong swash and a weak backwash which means that they deposit more material than they take away. These have a low energy and are infrequent, with around 6 waves per minute. However, destructive waves have a strong backwash and a weak swash, which means they erode at material. These have high energy with a large wave height and are more frequent with 10-14 waves per minute.