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Monitoring swimmer safety


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In the Netherlands, on average five people per year drown in the surf zone and in most cases rip currents play a role in these accidents. Rip currents can form spontaneously and suddenly in the surf zone, but they usually occur when waves break over a sand bar, water “piles up” between the bar and the beach, and flows out through gaps (rip channels) in the sand bar. Offshore directed velocities of over 1 m/s can be reached, which makes a rip current difficult to counter, even for adult swimmers. The website provides daily predictions of swimming conditions for the beach of Egmond. The predictions are based on model computations of nearshore tidal, wind- and wave-driven currents. The prediction system provides lifeguards and beach visitors with information about the swimming conditions, with special attention to the occurrence of rip currents.

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How to Use


The website Swimmer Safety Egmond is accessible through The only requirements for using the website are an internet connection and installation of the Google Earth plug-in (will automatically be indicated when needed). The website is known to encounter problems when accessed with Internet Explorer. For best visualization, the use of Google Chrome is advised.

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Practical Applications

Egmond Beach

In a pilot study, a forecast system for Egmond Beach was set up. The lifeguards of Egmond aan Zee have identified a strong rip current as the biggest risk for swimmers on this beach. This rip current is located in a channel that interrupts the sand bar just north of the lifeguard station. In the summer of 2010, the lifeguards attributed the rescue of 16 people to this single rip current. Therefore, they feel the need to reduce the risk arising from this rip current.


The forecasts for Egmond Beach are produced with the fully automated Coastal Storm Modelling System (CoSMoS) developed by Deltares. CoSMoS is a Matlab-based shell, which schedules jobs to download real-time data from online databases, pre-process model input, start model simulations, post-process the output and send the results to a website. The workflow of CoSMoS consists of the main loop governing the job scheduling and facilitating data downloading and storage, whereas the model loop controls the different, possibly nested, model simulations. The interval of the main loop depends on the availability of forecast data and duration of model simulations and is 24 hours for the Egmond application. The forecast window depends on the available model boundary data (i.e. meteorological input) and is 2 days for this case.


To achieve sufficient model resolution in the nearshore zone, a nested model train is used. The different models incorporate the effect of tides, waves and meteorological forcing. After running the model loop, the results of the detailed computation are presented as map fields, time series and dedicated rip current warnings. To generate the warnings, the offshore directed current velocities are translated into rip current strength and location and presented as time-stack images. The post-processed model results and warnings are automatically published on the website, where they are visualized in a Google Earth viewer. The compressed model results will in future also be stored on the OpenDAP server for public access.




Swimmer safety

The muienradar website is in first instance intended for use by lifeguards and other authorities involved with swimmer safety on beaches. The predictions of the nearshore hydrodynamics are yet to be fully validated and more experience with the forecast system needs now to be gained. Besides the pilot for Egmond, an operational application for the Sand Engine was tested by the lifeguards of Den Haag during summer 2012. The experiences of the lifeguards are presently being evaluated and the pilots will possibly continue in 2013.

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