What is a rip?
A rip current (often called a rip) is a narrow body of water moving out to sea. These pose a risk to swimmers as they can sweep people out to sea quickly.
How are rips formed?
As waves travel from deep to shallow water, they eventually break near the shoreline. As waves break, they generate currents that flow both offshore (away from the coast) and alongshore (along the coast). The larger the surf, the stronger the rip current.
How to identify a rip current
Look for these features to help you identify a rip:
- Calm patches in surf with waves breaking each side
- Rippled or criss-crossed water
- Discoloured water
- Foamy water
- Sand bars with the above features between them
If you get caught in a rip
- Don’t panic!
- Let the rip sweep you along until the current weakens
- When the current has subsided, swim parallel to the shore for 30-40 metres before returning to shore, swimming slowly
- If you are in trouble, float on your back to preserve energy and wait until the rip has stopped taking you out before swimming away from it. If you are at a patrolled beach, raise your hand to alert the surf lifeguards that you need assistance.
Types of rip currents
Permanent rips are stationary year round. As the intensity of the surf increases, so too does the intensity of the rip. Permanent rips often occur where there is a barrier to water movement along the beach such as headlands and rocks, or man-made barriers, such as wharves and drainage pipes. In many areas, permanent rips are given names relating to nearby landmarks or streets. Such identification can be invaluable when surf lifeguard teams answer emergency calls.
A permanent rip at Karekare beach.
Fixed rips are accompanied by a hole or gully on the ocean floor, with sand as its base. Once established, the fixed rip may last from several hours to many months. The length of time depends on the movement of sand. These rips are usually created when water from incoming surf increases (such as on a high tide) between the shore and offshore sandbars. The water then returns to sea through the path of least resistance, the lowest point in the sandbar system.
A fixed rip at North Piha.
Flash rips are temporary rips generated by increased volumes of water brought on to the shore. These rips can occur without warning, and subside rapidly. The nature of these rips means swimmers can be pulled out to sea quickly from areas of water that were safe only moments earlier.
Travelling rips move out to sea and along the beach. They are pushed by the prevailing direction of the waves and usually occur when the swell is moving strongly in one direction. Travelling rips moving along the beach can cause big problems for swimmers, often pulling large numbers offshore.
Unlike rip currents that are formed by wave energy, rip tides are caused by tidal action. Rip tides typically occur as water rushes through estuary and inlet entrances during tidal changes.