Rip current related swimmer safety
Summary
Rip currents form a significant challenge for beach safety. These nearshore seaward currents are often hard to spot and even harder to predict. Although several studies have been done on this topic, by far the most were conducted in countries with swell dominated coasts instead of wind-sea dominated coasts like in the Netherlands. Along the Dutch coast, every summer bathers get into trouble because of rip currents. Here, conditions (e.g. number of bathers and environmental parameters) differ along the coast and it is yet unknown under which conditions rip currents have the largest impact on swimmer safety. Therefore, the following research question is formulated: Under what circumstances do rip currents pose the greatest threat for bathers along the Dutch coast? The aim of this research is to find the link between rip current related rescues and environmental weather and water parameters along the Dutch coast. To answer this question, rescue data was obtained from three different sites (Egmond, The Hague and Monster) for the summer periods (May – September) of 2020 till 2023, in cooperation with the NIVZ, the Dutch institute for safe swimming waters. The data was then subdivided in three categories: rescues are either (1) certainly, (2) probably or (3) possibly related to rip currents. Subsequently, this research focussed on the category 1 rescues and linked these to the local parameters. The coupling included water data such as: wave height, wave angle, wave period and water height, but also weather data: wind angle, wind speed, temperature, rainfall, and sunshine. Extraordinary days with three or more rescues were compared with similar days in the dataset on basis of outstanding environmental parameters, to figure out what made these days so dangerous for bathers. The results revealed that determining the causal relationship between rip currents and rescues is challenging but a few parameters consistently stood out. Notably, waves always arrived at an oblique incident angle with water levels generally below mean sea level. The wind rarely blowed directly offshore and was on the high incident days always directed in the same direction as the waves. Between sites, Egmond predominantly showed rip current related rescues with waves from the south while The Hague and Monster showed more rescues with waves from the north. The differences in wind angle between sites were less clear. The study also underlines the role of weather parameters in rip current danger, highlighting the increased danger on dry, warm, and fully sunny days when beach attendance is the highest. For future research, a consistent registration system for rescues is recommended, making it easier to investigate specific causes of beach/sea related danger and harm. On a longer term, the application of artificial intelligence for an automated detection of rip currents from satellite or video footage is recommended. Moreover, to prevent people from getting into problems it is also proposed to further invest in creating awareness, such as through school programs, an app/site, commercials, citizen science and better information on location.