As a deep-water wave enters shallow water, the part of the wave in the shallowest water slows down. the deeper-water portion of the wave crest keeps moving at a relatively rapid speed. this wave refraction causes the entire wave crest to progressively rotate toward being with the shoreline.

Parallel with the shore line.

Explanation:

As the waves are generated on the sea or the open water they create a swell zone and this zone occurs in the deep waters, as the waves move further there peak velocity occurs with the winds.  

When they reach near the shorelines and thus they become transnational and these waves are carried forward to the breaker waves and these then merge with the shallow waves which are then flattened out on reaching the shores.

Thus as they gradually slow down these waves form s a parallel or surf zones with the beach. As the shallower the waves the shallower is the flow of the water.