Then the water runs back down the beach - this is called the backwash. With a constructive wave, the swash is stronger than the backwash. With a destructive wave, the backwash is stronger than the ...

"Both the swash and backwash from waves can be powerful and catch most people unawares," the Mid and North Wales Coastguard said. "What may appear like solid footing can disappear within a second." ...