Jooyong Lee

Generation Mechanism and Numerical Simulation of Rip Current at Haeundae Beach

At Haeundae Beach in Busan, people were swept away by the fast-moving rip current and rescued, on August 13th and 15th, 2009 & July 29th and 30th, 2010. In predicting the wave-induced current and consequent tube movement for public safety, the coastal flows and waves are calculated at each time step and grid point by means of systematic interfacing of hydrodynamic and wave models (Lee, 2001). To provide a user-friendly simulation tool for end-users, the forecasting system has been built in a software package called HAECUM. Outputs from the system are viewed as graphs of tube positions with combined current vectors for easy decision of emergency management officials. The tube-wave interaction is taken into account and the traces of swim tube are simulated by using a Lagrangian random walk (Chorin, 1978; Lee, 1994). In this study, we use the Lee`s approach (Lee, 1993) in estimating the surface onshore currents due to wave breaking.

Design Methodology Study on the Steel Breakwater III. Morphological Changes behind a Permeable Detached Steel Breakwater

In order to solve various problems associated with gravity-type breakwaters, the permeable breakwaters are recently taken into account as an alternative tool to control wave heights to an acceptable level. In particular, they are favored from the point of view of coastal environment, since they do not in general partition the natural sea. In this study, therefore, we present a morphodynamic model applied to scattering wave fields. The numerical solutions are compared with experimental data on wave profiles and morphological change rates under a surface-piercing breakwater system. Our numerical study involves several modules: 1) nonlinear wave dynamics analyzed by a plane-wave approximation, 2) suspended sediment transport combined with sediment erosion-deposition model, and 3) concurrent morphological changes. Scattering waves are solved by using a plane wave method without inclusion of evanescent modes.

Introduction to Automated System in HAECUM (HAEundae Current Model)

ABSTRACT Lee, J.; Yoo, C., and Lee, J.L., 2014. Introduction to automated system in HAECUM (HAEundae Current Model. Wave-induced currents must be predicted for the sake of public safety, and coastal flows and waves are produced at each time step and each grid point by means of a systematic interface of the hydrodynamic and wave models. The flow velocity is influenced by the tides, wave-induced currents, and free surface flow from the waves, and a forecasting system has been written into a software package called the Haeundae Current Model (HAECUM) in order to provide a user-friendly simulation tool for end-users. The HAECUM system has been written in a modular manner with two sub-models: a wave model that uses radiation stress and a current model. The flow velocity and the water level resulting from the tide-induced combined flow are determined by solving depth-integrated equations of mass and motion, and the forcing terms in this model include the surface pressure, surface shear stress due to wind, bottom friction, Coriolis effects, and tide potential. The radiation stresses are used as feedback for the the circulation model to calculate the wave-induced current.

Vertical Structure of Rip Current Observed at Haeundae Beach

ABSTRACT Kim, I.; Lee, J.L.; Hwang, J.S.; Lee, S., and Lee, J., 2014. Vertical structure of rip current observed at Haeundae Beach. On 4 and 7 August, 2012, more than 200–300 people were swept away by the fast moving seaward current at Haeundae Beach, which is located on the southeastern corner of the Korean Peninsula, and they then had to be rescued Beach patrons were carried away 50 to 100 meters away from the shore by rip currents, to an area where swimming is restricted due to safety reasons. Rip currents are narrow currents that begin close to the shoreline and strongly flow seaward through the surf zone and beyond. Although rip currents can cause tragic accidents and are of considerable interest to scientists and to the general public, our current understanding of the spatial and temporal behavior of rip currents is limited. As a result, the Korean Meteorological Administration installed monitoring equipment that can assess weather conditions and issue rip current warnings on Haeundae beach starting from 2010. Rip current kinematics and beach morphodynamics were measured for 50 days at Haeunadae beach using several instruments, including velocity and pressure sensors, such as an Aquadopp profiler for shallow water, and the morphology consisted of a low-tide terrace with incised quasi-periodic rip channels, which are representative of transverse bars. The spatial distribution of the sediment is reflected in the background rip current flow field with mean velocity magnitudes within the rip channel that increase offshore both with a decrease in the tidal elevations and with an increase in the sea-swell energy. The vertical velocity profile on the bar indicated that the flow was predominantly shoreward. The Aquadopp profiler is a high-resolution current profiler that operates at sub-cm scales and collects data at up to 8 Hz. The instrument is generally used in boundary layer studies at the bottom 1–2 meters of the ocean and in low energy environments. In addition, the HR profiler excels at providing flow details that are not attainable with any other instrument. In this study, the data from the Aquadopp profiles was used to investigate the detailed vertical structure of dangerous rip currents at Haeundae beach, and we were able to quantitatively understand the mechanism of a rip current.

Rip Current Research Using a CCTV Image Analysis Including Swimmer Detecting Techniques at Haeundae Beach, Korea

ABSTRACT Hwang, J.S.; Yun, H.S.; Suh, Y.C.; Lee, J., and Kang, S.C., 2014. Rip current research using a CCTV image analysis including swimmer detecting techniques at Haeundae Beach, Korea. In this study, a rip current analysis method using images from a CCTV installed on a beach was investigated. A method that automatically calculates the absolute coordinates of a swimmer captured via CCTV by combining image recognition technology and single photo-based photogrammetry was developed, and a method by which the analysis of many calculated absolute coordinates could be used for the monitoring of rip current occurrence, studies on rip current occurrence trend, and the measurement of stream velocity at the surface of a rip current was suggested. The image captured during the occurrence of a rip current at Haeundae Beach was analyzed as an example. Based on this analysis, it was found that the method suggested in this study was appropriate for the research and monitoring of a rip current.

Quantitative Risk Assessment for Beach Drowning Management

ABSTRACT Yang, B.; Lee, J.; Hwang, J.S.; Kweon, H.M., and Lee, J.L., 2014. Quantitative risk assessment for beach drowning management. The beach is recognized as the most important resource because it provides the best recreational amenity to tourists. However, the beach safety aspect is getting more relevant, because the drowning risks all over the world are much too high and do not decrease enough. Especially, drowning is a major public health problem with substantial personal, societal, and economic costs, each year many people drown at the beach and many more are seriously injured. In Korea, most of the beach safety services belong to personnel rescue services. In contrast, Australia and the United Kingdom have developed several practical integrated beach risk management programs and safety systems. In this study, we have carried out field survey for beach safety on 4 popular beaches along the Korean coast, and conducted a beach risk audit and prepared a report. In addition, we developed a quantitative risk assessing method with reference to the Australian method. In this method, three parameters that were related to emergency rescue factor, risk avoidance factor and safety preparedness factor, are included in the risk assessment for management purpose. The purpose of coastal drowning risk assessment is to make decisions, based on the outcomes of risk analysis, about which risks need treatment priorities. From these results, we will implement preferred treatment options or an action plan for managing the beach safety in order to minimize the risk of injury by drowning.

Analysis and International Comparison of Drowning in South Korea

ABSTRACT Shin, E.H.; Kang, D.Y., and Lee, J., 2017. Analysis and international comparison of drowning in South Korea. 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. 21–25. Coconut Creek (Florida), ISSN 0749-0208. From WHO (World Health Organization), drowning is the third leading cause of accidental death in the world. The number of drowning around the world is collected from the lifesaving organizations through ILS (International Lifesaving Federation) based on the statistics office in the nations. The cause of death is categorized by international and/or national code of disease and most of nations comply with the codes however some of LMICs (Low Middle Income Country) manually count the drowning by accidents reported in the newspapers. After Sewolho ferry wreck in 2014, which brought about 300 drowning in South Korea, more attention has been drawn to water safety but there has been no statistical data in accordance with international guideline in South Korea. Korean Coast Guard and National Emergency Management Agency make annual report of drowning accidents, which states that the annual drowning is about 30 but it is far away from the actual number around 700 drownings from National Statistics Office in South Korea. This study is designed to provide realistic numbers of drwonings to establish national water safety and drowning prevention strategy. Numbers of drowning from 2008 to 2012 is collected from National Statics Office based on KCD (Korea Classification of Disease) and it is analysed by gender, age, place and etc. Also the characteristics of drowning accidents is compared to the international ones.

Monitoring and Analysis of Bacterial Communities during a Summer Season on Gyeongpo Beach

ABSTRACT Lee, J.L.; Kim, I.H.; Yeon, Y.J., and Lee, J., 2017. Monitoring and analysis of bacterial communities during a summer season on Gyeongpo Beach. 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. 249–253. Coconut Creek (Florida), ISSN 0749-0208. A number of tourists visit beaches in the summer to enjoy sea bathing. However, numerous accidents occur on the eastern coast because of the topographical characteristics of the beach, and most accidents are caused by rip currents. Additionally, in the summer, as many tourists prefer beaches near swash zones, exposure to non-point pollutant sources can occur, significantly harming the health of visitors. Enterococci have shown the strongest correlation to gastrointestinal symptoms in a study examining the relationship between swimming-associated gastrointestinal illness and microorganisms. The U.S. Environmental Protection Agency found a direct relationship between the density of E. coli and enterococci in surface waters and increased swimmer-associated gastroenteritis. These reports suggest that E. coli and enterococci can be used as bacterial indicators compared to total coliform. Therefore, in this study, the safety of beach seawater was evaluated using E. coli and enterococci as bacterial indicators. Enterococcus and E. coli were isolated during the summer holiday season from the Gyeongpo Beach located on the eastern coast of Korea. The results indicated that the source of pollution near a swash zone, where people are crowded, was larger than that at the dry beach and near swimming zone.

Numerical Simulations of Local Scour at Samsan Bridge Piers in Korea

ABSTRACT Lee, J.; Park, S.-K., and Hong, S., 2017. Numerical simulations of local scour at Samsan Bridge piers in Korea. 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. 154–158. Coconut Creek (Florida), ISSN 0749-0208. The Samsan Bridge connects Ganghwa Island and Incheon in the mid-western region of South Korea. The country is making an effort to improve access to the island from its major cities, and the construction of the bridge is part of that process. External factors such as wind waves, tide currents, currents, and scour depths around piers should be considered in the construction of a bridge. In order to obtain scour depth values around bridge piers, this study conducted numerical simulations on morphological changes using the SADEM (SAnd Deposit and Erosion Model). The morphological changes were calculated by solving the conservation of sediment transport equation. A field measurement was performed at the Seokmo channel in the Han River estuary (South Korea) to verify the numerical results. A 153×210 grid system with a coarse grid size of 22.8 × 30 km was used in the SADEM. The maximum stream velocities of 10, 50, and 100-year flood return periods during the ebb tide contributes to sediment mobilization in the Seokmo channel. The maximum scour depth was calculated to be 9 m around the central bridges pier during the flood ebb for the 100-year return period. This was due to the upstream discharge during river flooding. The results of the numerical simulations are expected to be objective indicators of optimal design, construction, and future maintenance of the Samsan Bridge.

Calculation of Rip Current Warning Index by a Vector Rose Diagram

ABSTRACT Kim, D.H.; Park, K.C.; Kim, I.; Lee, J.L., and Lee, J., 2017. Calculation of rip current warning index by a vector rose diagram. 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. 109–113. Coconut Creek (Florida), ISSN 0749-0208. Rip currents, which are sea tides that can carry swimmers into deep water beyond the breaking points, pose an immense security risk to beachgoers around the world. In Korea, rip current forecasting is divided into four warning levels: notice, watch, warning, and danger. However, the numerical results are represented by current vectors, and an additional process is necessary for converting these vectors into a predictive model. The primary goal of this study is to present a method that illustrates how to convert numerically simulated vectors into a rose diagram and how to divide this diagram into four warning levels for rip currents. The proposed method was validated by analyzing the correlation between warning indexes calculated from the present approach and those obtained from the NERiPs. The study was conducted at Haeundae Beach located in Busan, Korea. Different from the NERiPs, which is simply used to forecast the warning levels by the incident-wave conditions, this wave-induced currents model considers morphological effects.