The coastline can be affected by various sea conditions mainly generated by the wind. It generates swell by blowing across the surface of the sea and you can see this as the rolling motion of the ocean.
Swell is usually associated with movement of only the upper level of ocean. As the swell gets closer to the coastline and the ocean floor becomes shallower, it forms the waves that you see crashing on the shoreline.
The size of the waves depends on:
Waves can take on three forms depending on the shape of the ocean floor at the coastline. Look at the images below.
Plunging waves break with tremendous force, usually in shallow water. They are dangerous to swimmers and surfers.
Spilling happens when the top of the wave tumbles down the face of the wave. It is the safest type of wave and the best for body surfing.
Surging waves never actually break as they approach the water's edge. They can be dangerous to small children as they are hard to notice.
Waves usually travel in groups of between two and four called a set. The break between sets is called a lull. Waves in a set also differ in size with:
This image shows a set of waves.
Waves push water towards the beach and as the beach slopes upwards, the water returns to its original level. The water then moves out to sea forming currents in areas along the coastline. The most common current is a rip which is responsible for more than 89% of rescues and drownings that occur around Australia. A rip is typically associated with water moving out to sea constantly.
Click on the arrow to show the water movement in a rip.
A rip has the following characteristics:
If you are caught in a rip remember to:
The larger the waves, the more intense the rip will be. Why? The more water that is being pushed towards the beach, the more water that has to return out to sea.
Ocean conditions are constantly changing. This includes the depth of water you may be in when waves travel past you, sometimes lifting you from the ocean floor. Many rescues occur because of this normal action of the ocean. When a wave comes through, even if it isn't breaking, it can lift you off the sand. This, combined with water moving back out to sea, results in people struggling with the depth of water and needing to be rescued.