Definition

A rip current can be defined as a seaward-directed flow of water driven by breaking waves that originates close to the shoreline and extend seaward across the surf zone, and beyond.

Within the lifeguard community rip currents have traditionally been referred to as ‘a body of water flowing out to sea’ following ‘a path of least resistance’.

Waves that break on beaches create currents in the surf zone. The surf zone is defined as the region between the shoreline and the point where the waves are breaking.

Why are they important?

Beaches provide a natural playground for millions of people who visit the coast each year. Unfortunately, thousands of people drown on beaches worldwide annually and hundreds of thousands more are rescued, mostly because of rip currents.

In the UK, RNLI lifeguards, who patrol many of the nation’s beaches, report that rip currents are responsible for two-thirds of all water-based incidents that they respond to. A similar percentage is reported from the USA and Australia. Annual rip current related fatalities exceed 100 in the USA and 20 in Australia.

Where do they form?

Rip currents typically develop on beaches when there is a variation in the amount of wave breaking along the length of the beach.

Sandbars that create variations in water depth (and therefore wave breaking) along the beach are by far the most common cause of rip currents. Other, generally less important, but sometimes locally more important, causes of variations in wave breaking along the beach include: refraction effects of reefs/shoals/canyons offshore of the beach; sheltering effects of headlands, rocks or coastal structures; and waves travelling from different wave directions.

Rip currents are most commonly found on sandy surf beaches that have sandbars (large shallow regions) with deeper channels between them (rip channels). Collectively, such topography is referred to as bar/rip morphology.

How fast are they?

Average rip current flow speeds are typically 1-2 mph, but they fluctuate over time, and can exceed 4 mph during pulses. 

This doesn’t sound very fast, but even an elite swimmer would have difficulty out-swimming a pulsing rip current. To put it into context, the 400 m freestyle world record (as of 2013) was swum at an average speed of 4.1 mph. The average human swims at about 1 mph and therefore cannot out-swim a rip current.

This helps to explain why rip currents are the main hazard to bathers on surf beaches.