Jeong, Y.M.; Kim, S.G.; Lee, J.H.; Yoon, J.S., and Lee, W.D., 2017. Understanding characteristics of upward and downward flows in coral reef region for safety of recreational diving. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 35–39. Coconut Creek (Florida), ISSN 0749-0208.

The goal of this study is to gain an understanding of the flow characteristics in reef regions through numerical simulations for safe recreational diving in the region. The applied numerical model was first validated to verify its feasibility and validity for carrying out the numerical simulations. Subsequently, an underwater survey was conducted in the Visayan Islands in the Philippines to model the reef region. Based on the underwater survey results, simulations were conducted in a three dimensional numerical wave tank with a model coral island. According to the numerical analysis results, stronger currents were generated if either currents or both currents and waves entered the low water level lagoon area of the coral island. In addition, an overall trend of stronger flow velocities was observed when both waves and currents were present than when only currents were present. Particularly strong upward and downward flows and strong vortices were generated near the reef crest. Thus, open water divers who are inexperienced in underwater swimming need to pay particular attention when swimming in these areas. Lastly, six tips for safe diving in reef regions were obtained from analysis of the numerical results.