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.

Kim, K.H. and Shim, K.T., 2014. A field investigation of waves and wave-induced currents at the Youngrang Coast of the Republic of Korea.

An accurate identification of the root cause of beach erosion should be taken in the precedence over designing reliable countermeasures. This study reviews the characteristics of the wave-induced currents by using the observation results on wave and current. The observed patterns were taken from comprehensive observation results which studied characteristics of wave and wave induced current as well as suspended load and bed load. The observations were conducted at the Youngrang Coast in the east coast of Korea. Based on the field observation results, Youngrang Coast has intermittently shown the occurrence of high waves due to winter monsoons. Affected by the high waves, the wave-induced currents have shown to exist inside the wave-breaking zone with a current velocity of 0.5–1 m/s. Such strong wave-induced currents are considered to be acting the main source of winter longshore sediment transport and beach erosion.

Shin, C.H.; Noh, H.K.; Yoon, S.B., and Choi, J., 2014. Understanding of rip current generation mechanism at Haeundae Beach of Korea: Honeycomb waves.

Many studies have proposed the generation mechanism of rip currents observed at Haeundae beach. Most of them suspect the rip channels as a rip current generating mechanism at this beach. This study focuses on the understanding of rip current generation mechanism in a different point of view based on the CCTV images and the numerical simulations. The CCTV images captured when the rip currents occurred show that the rip currents are accompanied by the waves of honeycomb pattern. The rip currents are developed along the nodal lines of honeycomb waves. To confirm the new mechanism of rip current generation at Haeundae Beach a series of numerical experiments are conducted using a phase resolving numerical model based on the nonlinear Boussinesq equations. The numerical results with the simplified beach topography and the incident honeycomb waves similar to real ones show that the rip currents can be generated without the rip channels. The rip currents generated by the honeycomb waves can grow much faster and the intensity of the rip currents is much stronger than those generated by the unidirectional waves over the rip channels. The magnitude of rip currents agrees reasonably well with that observed using CCTV image analyses. The role of rip channels developed by the rip currents is also discussed.

Yoon, S.B.; Park, W.K., and Choi, J., 2014. Observation of rip current velocity at an accidental event by using video image analysis.

In order to investigate the magnitude of rip currents of an accident event, in which dozens of people were rescued by coast guards at Haeundae beach, the floating velocities of swimming tubes of people caught by the rip current were estimated by using an analysis of video camera images. The analysis was conducted by tracking the locations of the floating tubes in the video images, converting the image coordinate system into the conventional map coordinate system, and evaluating their Lagrangian velocities. The rip current was strongly developed southwardly from the shore at the center of the beach and its maximum velocity was about 1.12 m/s when observing waves with Hs =0.9 m, Ts=8.2 sec, and θp =S4°E. The observation results was used for a verification of the numerical simulation performed using the nonlinear Boussinesq model FUNWAVE which can resolve wave-phase interactions and simulate rapid wave-induced currents with generation, evolution, and dissipation of vortex pairs. The observation and the computation reasonably agreed with each other.

Cho, W.C.; Kim, J.H.; Hur, D.S., and Kim, I.H., 2014. Rip currents generation by geomorphological change in Gyeongpo Beach, South Korea.

Most beaches in Gangwon-do, South Korea have topographic characteristics that are mainly influenced by waves and seabed conditions. Gyeongpo Beach is one of the most famous beaches as a tourist attraction in the east coast of South Korea, and many people have visited and enjoyed sea-bathing in this area during the summer holiday season. However, rip currents are often source of danger for the swimmers because rip currents drag the swimmers away from the beach and put them to death by drowning. As Gyeongpo Beach has a straight shoreline, it is directly exposed to high waves that induce a significant change of bottom topography. Sandbars are usually formed in the processes of topographical changes from the swash zone to the surf zone and increase the possibility of rip current occurrence. Therefore, the monitoring of the topographic changes in this region is important to understand the mechanism of rip current generation. In this study, field observations were performed to measure foreshore slopes, water depths, and cross-sectional changes of bottom topography from the swash zone to the surf zone from December, 2013 through February, 2014. In order to trace nearshore currents, a GPS mounted on buoy-type equipment was designed, considering the minimization of wind effect. A single beam echo sounder equipped with RTK GPS (Real Time Kinematic GPS) was also used to observe the formation and movement of sandbar. The field observation results were used to understand the correlation between the sandbar movement and the rip current generation. According to the analysis results of two different field observation events in Gyeongpo Beach, a kind of salient beach is formed between O-ri Rock and the beach. Also, the results show that both arc sandbars and straight sandbars are mixed in the entire area. Finally, the field investigation results in this study show that the mechanism of rip current generation is closely related to the shape and location of sandbars.

Shin, B.S. and Kim, K.H., 2014. Rip current monitoring using video analysis.

The coast of South Korea is increasingly exposed to serious coastal erosion problems. It is vital to develop scientific and systematic approaches for a quantitative review of the problem so that appropriate countermeasures can be established. Recently, a research method employing video images has become significant in field investigation and real-time monitoring. The proposed approach of this study is to measure the sea surface rather than to measure specific sea spots. Using the collected video images, each images are extracted an hourly basis in a specific time zone. Also, the extracted images are calibrated using geometrics and then the mechanism of wave-induced current occurrence and its moving path are investigated. Using dyes, the flow conditions of wave-induced current were filmed on a regular basis. As a result, the paths of longshore current and strong rip current were found. It is expected that the Video Metric System employed in this study will be effectively utilized in field tests in near future to further study the mechanism of wave induced current occurrence and its paths.

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.

Fletemeyer, J., 2014. The reliability of turbidity and debris moving seaward to spot rip currents on Florida Beaches and the need for better warning and education programs. In: Lee, J.L.; Leatherman, Stephen P., and Lee, J. (eds.), Proceedings 3^rd International Rip Current Symposium (Busan, Republic of Korea). Journal of Coastal Research, Special Issue, No. 72, pp. 39–43. Coconut Creek (Florida), ISSN 0749-0208.

In response to the estimated 100 bathers that fatally drown in rip currents on America's beaches every year, several warning and public education programs have been developed and implemented. Results from a 20-year study conducted by Fletemeyer on Panama City Beach, Florida reports that these programs, although well intended, are marginally effective with little gains in what bathers accurately know about rip currents. Education programs are often predicated on the belief that the public can learn how to spot rip currents while standing on the beach and studying the water. Two indicators believed key in spotting rip currents are turbidity and debris entrapped in the rip current and floating seaward at approximately the same velocity as the current. The results of this investigation determined that rip currents cannot be reliably identified on SE Florida beaches using these two indicators. Consequently, rip current education programs relying on the belief that the public can learn how to identify rip currents must be re-evaluated. In some cases, although well intended, rip current education programs may be contributing to drowning.

Ishikawa, T.; Komine, T.; Aoki, S.I., and Okabe, T., 2014. Characteristics of rip current drowning on the shores of Japan.

The characteristics of rip current drowning on the shores of Japan was investigated using the analysis of the lifesaver's rescue reports of 2013 and field observations of some beaches. Although the necessary rescue equipment and the water safety information such as signboards were mostly prepared, a large amount of rip current drowning occurred. On most re-occurring rip current drowning beaches, there are permanent rips and fixed rips associated with the characteristic of topography and the coastal structures at most beaches under the relatively high wave condition. Especially, in the case lifesavers cannot determine the swimming areas, swimming areas are generally determined by the local regulations from local governments and shop owners on most beaches. The most important outbreak factor regarding the rip current drowning is the human factor such as the management problems and coastal structures, which was concluded.

Paxton, C.H. and Collins, J.M., 2014. Weather, ocean, and social aspects associated with rip current deaths in the United States.

The purpose of this research is to provide a better understanding of the physical and social aspects of rip currents in ocean areas that will lead to better forecasts, better governmental policies in beach areas, and ultimately to save lives. The primary factors associated with rip current formation on beaches are variations in the local beach bathymetry, wind-generated waves of significant wave height typically 1 m or higher, and lower tidal stages. The methodology followed for this study included a review of demographics from over 500 rip current drowning reports along the Atlantic Ocean, Pacific Ocean and Gulf of Mexico coasts of the United States. This research indicated that tourists are often the victims and rescuers often become the victims. For each state or sub-state area where rip current drownings are prevalent, an analysis of social aspects and associated ocean and weather patterns was conducted using buoy and tide data and composite weather patterns. It is important to understand the evolution of these fatal events with respect to the trends of wave height, period, and pressure patterns and resulting surface wind fields that produce the waves.

Choi, J.; Lim, C.H., and Yoon, S.B., 2014. A rip current warning system based on real-time observations for Haeundae Beach, Korea.

A real-time rip current warning system was studied to help mitigate against rip current accidents at Haeundae Beach. The system produces a real time sequence of index representing the risk and the likelihood of rip current based on the real time observations such as waves, currents, and tide. The index is estimated by using the rip current likelihoods derived from the results of various numerical simulations with various sea conditions, the parameters of which correspond to the observation quantities. The rip current warning system is operated by taking into account the effect of wave height, wave period, wave direction, wave spectrum (i.e., frequency-directional spreading), longshore currents, and tidal elevation on the rip current likelihood. The real-time wave and tidal observations at the Haeundae coast in 2012 were applied to the rip current warning system, and its performances at several real events observed from the video cameras were presented and analyzed.

Eom, H.; Yun, J.H.; Jeong, C.K.; Seo, J.W., and You, S.H., 2014. Introduction to KMA operational forecasting system for rip current.

A rip current, commonly referred to simply as a rip, is a strong channel of sea water flowing seaward from the near the shore, typically through the surf line. Rip currents can be found on the Haeundae Beach every year and make a very large number of rescues each year (106 in 2009, 144 in 2010 and 220 in 2012). The main reasons that it is present on the Haeundae Beach are the geographical factor, wide surf zone and mild slope, and meteorological factor, seasonal southern wind and normal waves. When waves travel normal from deep to shallow water, there is a greater than normal transport of wave energy into a surf zone which may result in an elevated rip current risk. Korea Meteorological Administration (KMA) developed a rip current forecast system that considers bathymetric and meteorological effect through Research and Development program. The system is based on high resolution topography and uses wave direction, height and period of incident wave, tidal elevation and wind condition for operating. And boundary conditions are obtained by the Regional Data Assimilation and Prediction System (RDAPS) and Coastal Wave Prediction System (CWW3), a weather forecasting system of the KMA. The rip current forecast system predicts a daily 72-hour current field. Additionally forecasters analyze hourly conditions which are wave height, wave period, wave direction and wind direction and then support cooperation organizations with a rip current information (safe, advisory, warning and danger). Recently rip currents also occur on Yangyang (Naksan Beach), Jeju island (Jungmun Saekdal Beach). Therefore we plan to extend the prediction areas by applying the forecast system to Naksan and Jungmun.

Lee, W.D.; Shin, S.W.; Jeong, Y.M., and Hur, D.S., 2014. Numerical studies on rip current control using scene-friendly structures at Haeundae Beach, Korea.

The sporadically occurring rip currents put swimmers in risk during the season of every summer vacation. It is known that the rip current generation is affected by the characteristics of incident waves and bottom topography but the mechanism of the rip current occurrence is still not clear. In order to understand the mechanism of the rip current and to establish countermeasures, 3D numerical simulation was performed based on the realistic bathymetry of Haeundae Beach by using LES-WASS-3D. The numerical simulation results showed that the wave heights vary parallel to the shore line by inequality of bottom bathymetry (submerged shoal and rocks) and this wave height variation induces the water level difference. The model results also showed that the rip currents were generated through the region of relatively deep water and low water level that is caused by the water level difference. The present study suggested scene-friendly structures such as submerged breakwaters, drainage layers, and gabions as the countermeasures of rip current control. These structures successfully reduced rip current by controlling the energy unbalance in the region of rip current occurrence.

Hur, D.S.; Cho W.C.; Yoon, J.S.; Kim, I.H., and Lee, W.D., 2014. Control technologies in reducing rip currents around the open inlet between two submerged breakwaters.

In the present study, we investigated the flow generated around the open inlet between two submerged breakwaters installed at Songdo Beach, Busan, Korea. We also performed the numerical analysis on the characteristics of the rip current generated around the open inlet with various sizes and arrangements of the submerged breakwaters. Furthermore, based on the numerical results of this study, we suggested three technologies to control the rip current and applied these technologies around the submerged breakwaters to find out the effectiveness of the control technologies. From the numerical analysis, we found out that RCCT-3 (Rip Current Control Technology-3), which installs a drainage channel inside the submerged breakwater to reduce water surface elevation at the rear side of the submerged breakwater, is most effective in reducing the rip current around the open inlet.

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.

Bradstreet, A.J.; Brander, R.W.; McCarroll, J.R.; Brighton, B.; Dominey, H.D.; Drozdzewski, D.; Sherker, S.; Turner, I.; Roberts, A., and MacMahan, J., 2014. Rip current survival principles: Towards consistency.

Advances in applied rip current research over the past 10 years have dramatically increased our collective understanding of the hazard posed to communities by rip currents. Repeated drifter, dye, swimmer, in situ instrumentation, and model experimentation has demonstrated the highly variable nature of rip currents, which has significant implications for long standing survival strategies. Analysis of prevalent rip current survival advice revealed that under variable rip current conditions, the advice may not prove effective in-situ, resulting in individual adopting alternative behaviours, which may or may not have been endorsed or promoted by safety authorities. This paper discusses evidence supporting key principles prominent in the discourse between public safety practitioners and rip current researchers, and presents how these principles relate to each other in practice. The principles are set into two categories: avoidance and survival. They have been developed to support consistent engagement, education and communication strategies for community resilience and further reduce the burden of rip current related drowning globally.

Leatherman, S. P., 2014. Rip current: Science and threat communication.

There have been major advances in defining the nature of rip currents and how to communicate this threat to the public. The 3^rd International Rip Current Symposium built upon previous professional gatherings and further advanced our understanding of these dangerous currents. It is an exciting time to be working in a coastal science that is rapidly developing and evolving with such importance to public safety at the world's foremost recreational areas—surf beaches.

Park, S.S.; Rhim, Y.T.; Kim, M.J.; Kim, S.K., and Yoo, J.I., 2014. The influence of perceived risk on participation motivation and re-participation intention in marine sports.

The purpose of this study was to identify the influence of perceived risk on participation motivation and intention for re-participation amongst marine sports participants. To achieve this purpose, the established path among measurement items and analyzed self-administrated surveys collected from 300 marine sports club members were analyzed using SPSS and AMOS as follows. First, both exploratory and confirmatory factor analysis were conducted to examine the reliability and validity of scale and to descriptive statistics. Second, multi group analysis was conducted to examine if there was a significant difference in the established path model between sexes. Third, both correlation and multiple regression analysis were conducted to examine the inter relation among measurement items of the established path. Forth, path analysis was conducted to examine the path of established study model. The results were as follows. First, the structure of each measurement item was confirmed. Second, there was significant difference in established path model between sexes. There were significant differences in participation motivation and intention to re-participate between sexes, higher in men, but no significant difference in perceived risk. Third, there is a significant positive or negative correlation among each measurement item. Forth, perceived risk has a direct influence on participation motivation (direct effect= −.33), and participation motivation has a direct influence on re-participation intentions (direct effect= .56). As a result, this research shows that the lower the perceived risk, the higher the participation motivation and the re-participation intention in marine sports.

Kim, J. and Cho, D., 2014. Policy suggestion and implications for the use and management of bathing beaches.

In the Republic of Korea, beaches are the most popular holiday destination; approximately 70 million people visit beaches every year. The maintenance and management of beaches are deemed important because more than 50% of marine activities take place on at beaches. This paper reviews the status of Korean bathing beaches and addresses safety management, environmental pollution, and legal and institutional issues. In addition, policies for sustainable use and the maintenance of bathing beaches as well as the use of marine tourism attractions are proposed. The relevant laws and regulations urgently need to be modified for the effective use and management of bathing beaches. In addition, close cooperation with non-government organizations is needed for the safety management of bathing beaches. Safety measures and education to protect users from hazards such as rip currents and jellyfish, etc. need to be strongly implemented.

Kim, M.J.; Chun, S.B.; Kim, W.K., and Lee, C.W., 2014. Analysis of beach safety perception and satisfaction among Haeundae Beach visitors through CIT method.

This study was designed to look into the safety status of Haeundae Beach in Busan city from its visitors' perspective. Rather than researching based on the perspective of experts, as is typical in research, the authors of this study analyzed the experiences regarding beach safety of the actual users of the beach, who expressed both positive and negative emotional perceptions. The Critical Incident Technique was used for the analysis, with the selection of 104 research subjects. The research subjects were asked to answer a questionnaire which included open questions about positive and negative experiences during their visits to Haeundae Beach. The results showed that the research subjects were satisfied the most with the dedicated and hard work of the lifeguards and the Coast Guard, according to an analysis of their reported positive experiences. On the other hand, the research subjects were mostly concerned about the relatively small number of lifeguards, dangerous trash on the sand, and misbehaving drunken people at night, in that order. From the result of the study, the researchers concluded that specialization and increasing the number of lifeguards are the key points if seeking to develop a higher standard of safety at Haeundae Beach and at other beach sites in Korea. To achieve this, it is strongly recommended that Haeundae officials and local governments take beach safety into account and promote more mature citizenship.

Jo, E.; Yun, H.S.; Suh, Y.C.; Lee, J., and Lee, J.L., 2014. Economic analysis of beach safety level on the contingent valuation in Haeundae Beach.

The beach is the most popular tourism place during the summer vacation, which contributes to local economic improvement and plays the key role in beach tourism resources. However, environmental resources, like beaches, have characteristics of public properties and it is difficult to evaluate them as a market value. This study employs Contingent Valuation Method (CVM) to investigate how much of the tourist's decision is affected by beach safety, according to emergency accidents caused by rip current or bad weather, which often occurs in Haeundae Beach. Referring to the Australian study for the relevant between economy and lifesaving, we applied the methodology to Korean beach lifesaving. In other words, the present contingent study is carried out mainly through the survey data in regard to how much beachgoers are willing to pay for going to a safe beach. Through this survey, it is possible to estimate the economic value of a safe beach as well as the value of lifesaving, which has been previously recognized as unimportant factors. The economic evaluation of nonmarket value of safe beaches or lifesaving can draw the necessity of beach safety management and guideline establishment as to contributing to the mitigation of drowning accidents.

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.

McCoy, G.K. and de Mestre, N.J., 2014. Surf hazard rating: a decision-making system for application to competition through the surf zone.

This paper introduces and details a new and universal Surf Hazard Rating system for rating the prevailing surf conditions at any beach in real time. The system uses primarily seven easily observable and measurable surf zone characteristics. These basic characteristics are defined and rated separately in terms of their potential risk to the safety of competitors within the surf zone. They aggregate to form an overall rating of the hazardous nature of the prevailing surf conditions. The Surf Hazard Rating is the first of two components that, when compared, will form the Competitor Surf Safety Index. This will be a single-value index to assist decision makers and competitors assess the appropriateness of continuing in the prevailing surf conditions at the time. The system has applications for surf sport participants and the beach-going public all over the world, but is being applied at present to Australian surf carnival events.

Wu, G.; Wang, J.; Liang, B., and Lee, D.Y., 2014. Simulation of detailed wave motions and coastal hazards.

A laboratory experiment combined with numerical experiment had been carried out to test the applicability of a phase resolving model with non-hydrostatic pressure, SWASH, in simulating the time evolution of the detailed wave motion and hence in predicting the wave induced coastal hazards. Such model can also be used to investigate how fast wind waves adjust to new water depth when propagating over the rapidly varying water depth. A series of laboratory experiments were conducted at the 2-D wave flume. The surface wave elevation, underwater orbital motion and bottom pressure were measured at different locations of the flume when waves propagate over varying water depth. When the observed time series surface elevation together with orbital wave motion estimated from the observed waves are used as boundary condition, the SWASH model simulated the time series of surface elevation as well as wave spectra close to the observation data at 10 different locations of the wave channel, which justifies the applicability of the model in simulating various wave induced coastal hazards. The analysis of numerical simulation using SWASH model showed that waves propagating to the different water depth adjust quickly to the new water depth and wave dynamics can be estimated from the local water depth. The further applications of the model in simulating various coastal hazards are discussed.

Min, B.; Park, K.; Youm, M., and Suh, K., 2014. Improvement of the wet and dry algorithm for an inundation problem using a parallel numerical model.

Rip current flow is dependent on wave-induced set up and thus on wave conditions and wave dissipation. Waves will break over the bar if the ratio of wave height to water depth exceeds a certain value. This implies that rip currents are not only dependent on wave height but also on water level that might be modified by the tide. Many studies noticed rip-current in tidal environments is that tide acts mainly as a change in water level. In coastal regions, the flooding and ebbing of the tide and waves play important roles in the local ecosystem and coastal physical processes. The complex physical process of a flood and ebbing wave presents a nontrivial modeling challenge. For a closed water body, where evaporation, precipitation and ground absorption are not considered, the total water mass should be conserved during inundation or draining. In this study, the ADCIRC (Advanced CIRCulation Model) was configured for a 120 by 120 km, square-shaped model domain. A bowl-shaped water system, with a surface diameter of 60 km and a maximum depth of 9 m, was embedded in the center of the model domain. A mass conserving wetting and drying scheme, which is very simple and practical. The water mass removed from any wet cell is uniformly redistributed into the system to maintain the water mass balance. Since there is a uniform change in the system, the hydrodynamic balance between the pressure gradient and the flow fields in the system is maintained. The redistribution of the water mass and readjustment of the sea surface elevation in the system are performed by the model in subsequent steps. The advanced wetting and drying scheme shows a good performance. This study was conducted as part of the wave-tide-surge coupling model (ADCIRC-SWAN) development which system can be used for predict the rip-current system combined with tidal environment.

Shin, S.; Cox, D., and Yoon, H.D., 2014. Numerical modeling of surf zone hydrodynamics over movable bed.

Understanding of hydrodynamics over moveable bed is crucial for predicting rip current generation. The capability of a numerical model based on Reynolds-averaged Navier–Stokes equations, COBRAS (COrnell BReaking waves And Structures), to simulate hydrodynamics over a movable barred beach was verified. The numerical simulation results were validated with the data collected from a large-scale two-dimensional experiment, which was conducted at the Hinsdale Wave Research Laboratory at Oregon State University. In this study, numerical model results were compared with the experimental results in terms of significant wave heights, wave setup, time-averaged horizontal velocities, and turbulent kinetic energy in different cross-shore locations. The COBRAS model successfully predicted the significant wave heights and setup from the offshore boundary to the vicinity of the bar location, but it slightly overestimated the significant wave heights when broken waves propagated to the shoreline. The numerical simulation was able to predict time-averaged horizontal velocities and turbulent kinetic energy well for all measurement locations. Overestimation of the turbulent kinetic energy at bar trough is because of the limitation of the turbulence closure scheme. Overall, based on the results of this study, the COBRAS model can be used to predict hydrodynamics in barred beaches, but improvement of the turbulence closure scheme is still required.

Kim, I.H.; Lee, H.S.; Kim, J.H.; Yoon, J.S., and Hur, D.S., 2014. Shoreline change due to construction of the artificial headland with submerged breakwaters.

The littoral drift cell of Bongpyeong Beach in Gyeongsangbuk-do ranges from Jukbyeon harbor to Goljang harbor. The beach erosion has largely occurred due to the expansion construction of Jukbyeon harbor. Headlands were installed as a countermeasure, however, the effectiveness of headland was not good as expected because of complicated coastal hydraulic phenomena. Furthermore, the headlands spoil the coastal landscape. Therefore, in this study, the field investigation of the shoreline and beach profile was conducted to analyze the characteristics around Bongpyeong Beach from 2013 through 2014. The causes of the beach erosion were identified by physical oceanographic investigation and numerical analysis. As a result, the complicated flow characteristics due to the construction of headlands and submerged breakwaters appear. The results also show that the sand has moved toward both sides of the headlands, and the beach erosion has accelerated in the beach located between the headlands.

Yoo, J.; Shin, S.; Do, K.D.; Shim, J.S.; Ha, T., and Jun, K.C., 2014. Laboratory investigations on effects of water level change on surf-zone processes.

Tidal level and current often influence the rip current and the morphological changes in the macro-tidal beaches. Effects of water level change on surf zone processes were investigated through laboratory experiments conducted in a two dimensional wave flume. A movable beach was installed using a find sand in the flume starting with 1/50 slope from the offshore and ending with 1/20 slope near the shore. Irregular waves were generated by a piston type wave maker with active absorption. In the meantime, water level was changed gradually by using a pump and drain system to consider waves and tide simultaneously. Herein, three different tidal phases (i.e. flood tide, full tide and ebb tide) were conditioned with a gradual depth change of about 10 ~ 15 cm in the offshore during a period of about 30 minutes per phase except the full tide, while only one wave condition was kept targeting a significant wave height of 12 cm and significant wave period of 1.7 s. Measurements of wave attenuations in the wave breaking zone influenced by the tidal change were made using in-situ sensors and an image-based analysis method. The rates of wave attenuation (i.e. the ratio of wave height to water depth) measured during the both of flood and ebb tides were found to be larger, ranging from about 0.8 to 1.4, compared to those recorded during the full tide with little depth change. In addition, the attenuation coefficient of the flood tide tends to be larger than that of the ebb tide.

Kweon, H.M.; Choi, Y.H.; Kang, J.W.; Lee, W.D.; Hong, S., and Park, S.K., 2014. Reduction of the expected wave overtopping probability and its rate upon seawall utilizing STB(Steel Type Breakwater).

Wave overtopping damages at seawalls, which separate lands from coastlines, are increasing as residences and commercial facilities are recently becoming concentrated near coastlines. The wave overtopping volume or probability can be decreased by increasing the crest elevation or width of the existing structure. Crest elevation or width increase of structures like seawalls, however, violates the citizens' view rights, and public water reclamation leads to an increase in the construction cost. The STB (Steel Type Breakwater) is a submerged-type non-reclamation structure, can be quickly constructed at a very low cost, and incurs almost no additional responding costs for the sea level rise. The feasibility of the new economical areal protection combination construction method that can reduce the EWOP (Expected Wave Overtopping Probability) without violating the citizens' view rights was validated in this study.

Lim, H.S.; Kim, C.S.; Lee, H.J.; Shim, J.S.; Kim, S.J; Park, K.S., and Chun, I., 2014. Variability of residual currents and waves in Haeundae using long-term observed AWAC data.

The Haeundae in the southeastern Korean Peninsula is a famous beach which is one of the most popular tourist attractions of Korea in summer. It is about 1.6 km long and 40 m wide facing the southeastern sea of Korea and Korea Strait. During strong winds in winter and severe typhoons in summer, the beach is significantly eroded by waves and nearshore currents in the surf zone. The intensive coastal developments during last 30 years have caused substantial beach erosion and bathymetric changes in the nearshore area, despite various beach restoration projects, including beach nourishments. Recently, the government decided to construct two submerged breakwaters near both ends of the beach to enhance the preservation potential of the beach replenishments. We estimated the seasonal variations in residual currents from one-year flow measurements using the Acoustic Wave and Current (AWAC) meter, at two locations of Haeundae at approximately 15 m and 22 m in depths. Short-term flows were measured in the surf zone during summer and winter. The moving average method was applied fortnightly to estimate the residual currents. In addition, waves measured with the AWAC were analyzed to characterize seasonal variations in the beach environment of Haeundae. The observed residual currents were well matched with the simulated counterpart from a wave and current coupled model. These simulated nearshore currents appear well correlated with seasonal variations in beach erosion and accumulation. The wave and current data were also used to validate an operational coastal modeling system for the prediction of hydrodynamics. These observations will be incorporated in simulations of sediment transport in Haeundae coastal waters for developing coastal erosion control system.

Kim, H.; Jin, J.Y.; Jang, C.; Yoo, H.J., and Hwang, D.H., 2014. Simulation of seasonal bathymetric change at Haeundae Beach with two representative wave settings.

Long-term shoreline position of Haeundae Beach has been quite stable notwithstanding seasonal oscillatory movement. Bathymetry around Haeundae Beach was surveyed on 7 August 2007 and 12 November 2007 by using an echo-sounder, while wave, tide, and tidal current were measured between the two survey days, so that bathymetric change at Haeundae Beach was obtained from the two surveys. According to the surveys the east part of the beach was eroded, and the west part of the beach was accreted. Measured waves from SSE, SE, ESE, E during the period were stronger than measured waves from S, SSW, SW, WSW. A numerical model system CST3D was adopted to reproduce the bathymetric change at Haeundae Beach during the period. Two representative wave settings are chosen for the period as a minimum number to represent the time-series of wave record, based on equivalent sediment flux concept contained in the CERC formula. Wave field, wave-induced force field, wave-induced current field, sediment transport field, and bathymetric change are computed from individual modules, SWAN, WIF, FLOW, SED in CST3D, respectively. Computed bathymetric change agrees reasonably well with measured one. It is believed that selection of two representative wave settings is useful for simulation of seasonal bathymetric change for fairly straight morphology like Haeundae. CST3D is thought to effectively describe overall seasonal sediment transport pattern and consequent bathymetric change at Haeundae Beach.

Ha, T.; Jun, K.; Yoo, J., and Park, K.S., 2014. Numerical study of rip current generation mechanism at Haeundae Beach, Korea.

Haeundae Beach is one of the most famous tourist attractions in Busan, Korea. Every year, millions of people visit the beach. Recently, however, numerous rip current accidents have occurred along the middle of the beach. For example, in 2013, more than 500 people were swept away by a strong channel of water flowing seaward from the shore and were rescued after being dragged into deeper water. Fortunately, no casualties were reported, but the authorities said that, given the right weather conditions, rip currents could occur again at any time, not only at Haeundae Beach but also at other beaches. Some studies have been conducted to determine the rip current generation mechanism at Haeundae Beach. Previous research suggests that a known mechanism of rip current generation associated with the nodal line area of honeycomb-patterned wave crests was one of the significant factors in rip current occurrences at Haeundae Beach. In this study, we performed numerical experiments to identify the rip current generation mechanism based on the hypothesis proposed in the study mentioned. A well-known Boussinesq equation solver, FUNWAVE-TVD, was employed to simulate nearshore circulation at Haeundae Beach. The model was verified by generating a rip current for a simple beach for honeycomb-patterned incident wave conditions. The model was then used in numerical simulations of wave transformation to identify the rip current generation mechanism for Haeundae Beach, and wave transformation characteristics were examined in detail to identify the possible origins of rip currents. The original bathymetry was modified and applied to simulation of nearshore circulation to understand how reefs located off the shore of Haeundae Beach contribute to rip current generation. The numerical results corresponded to a slightly different rip current generation mechanism. It is thought that honeycomb-patterned incident waves may induce rip current event at Haeundae Beach but the other factors may contribute as well.

Yoon, J. J., 2014. Non-hydrostatic modeling of wave transformation and rip current circulation: a case study for Haeundae Beach, Korea.

Haeundae Beach in Busan, South Korea, is one of the most popular destinations in South Korea, but poses the danger of irregular, fast moving rip currents. To investigate the dominant mechanism of rip currents in this region, a numerical simulation was carried out using the non-hydrostatic model Surface WAves till SHore (SWASH), with observed wave and topographical data. In this paper, the applicability of SWASH for modeling the wave transformation and rip current circulation near the shallow foreshore is investigated. Assuming that rip current dynamics are controlled by combination of variations in wave dissipation and morphological flow constriction, we tested the effects of wave parameters, such as wave heights, wave periods, wave directions, and changes in tidal conditions, on rip current generation. The model results showed good agreement with previous studies, as well as observations in this region. A numerical study showed that wave refraction by spatial topographical characteristics (several submerged reefs near the coasts) of Haeundae Beach cause wave energy propagation in different directions towards the beach. Rip currents were simulated when longshore currents flowed out through a channel with very small wave energy in the seaward direction. The occurrence of rip currents was increased under conditions of higher waves and longer wave periods. In the case of wave direction, we tested cases from SSW to SSE, and present the spatial characteristics of the simulation results. The locations of rip channels that generate rip current are significantly affected by incident wave conditions, such as wave direction, height, and period.

Choung, Y., and Yun, H.S., 2014. Development of a coastal surface monitoring system using high-resolution images taken in Haeundae, South Korea.

Coastal erosion causes loss of properties in coastal areas, and rip currents are the main factor causing coastal erosion.The use of remote sensing data is efficient for conducting coastal erosion research due to its advantages for acquiring the geometric and spectral information of coastal surfaces without human accessibility. This research aims to develop the coastal surface monitoring system (CSMS) using the high-resolution images taken in Haeundae, South Korea. Multiple mapping and image processing techniques are included in the methodology for developing CSMS. First, the coastlines are extracted from the images using the clustering algorithm and the data conversion technique. Buffering is applied along the generated coastlines to create the coast zone, and then the multiple materials in the coast zone are identified using the clustering algorithm. Next, constant intervals are set on the generated coastlines to create coast segments. Then the major material in each segment is determined by comparing the numbers of pixels in the clusters. Finally, different-colored coastlines are generated to show the major material in each segment. The developed CSMS can be used for monitoring coastal erosion caused by rip currents.