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Seagrass is an essential component of coastal ecosystems because of its capability to absorb blue carbon, and its involvement in sustaining marine biodiversity. In this study, support vector machine (SVM) technologies with corrected satellite imagery data, were applied to identify the distribution of seagrasses. Observations of seagrasses from satellite imagery were obtained using GeoEye-1, Sentinel-2 MSI level 1C, and Landsat-8 OLI satellite imagery. The satellite imagery from Google Earth has been obtained at a very high resolution, and was to be used within both the training and testing of a classification method. The optical satellite imagery must be processed for image classification, throughout which radiometric correction, sunglint, and water column adjustments were applied. We restricted the scope of the study area to a maximum depth of 10 m due to the fact that light does not penetrate beyond this level. When classifying the distribution of seagrasses present in the research region, the recently developed SVM technique achieved overall accuracy values of up to 92% (GeoEye-1), 88% (Sentinel-2 MSI level 1C), and 83% (Landsat-8 OLI), respectively. The results of the overall accuracy values are also used to evaluate classification models.

Severe shoreline erosions are commonly observed due to the side effects of breakwaters constructed to protect the habitat. These breakwaters can cause wave energy differences behind the structure due to diffraction, inducing longshore sediment transport and resulting in shoreline changes. Therefore, it is essential to correctly simulate the effect of wave transformation in the lee side of structures, but such studies reporting performance of models in the field have been relatively rare. In this study, two wave models of the TELEMAC system were used to investigate the accuracy of modeling the wave transformation effect in a lee area of a breakwater built to secure the harbor’s tranquility, near Jukbyeon Port in Korea, through comparisons with field observations. Two cases of wave conditions with different wave heights and directions were tested. In both cases, the TEL EMAC–ARTEMIS model had lower errors than TELEMAC–TOMAWAC at the onshore wave location, confirming that the phase-resolving ARTEMIS showed better performance in simulating the wave transformation than the phase-averaged TOMAWAC, as expected. However, ARTEMIS had slightly higher errors than TOMAWAC at the offshore location, probably due to the interference by reflected waves from the complex coastlines formed by the different coastal structures. The results also provide various implications learned from the numerical experiments, which can be usefully applied to engineering aspects, such as for the estimation of harbor tranquility.

Beach erosion is a serious problem that can be aggravated by human-made structures, and the modeling of breaking waves near the coast and around coastal structures can be used to determine their impact. In this study, OpenFoam was employed to simulate turbulent flows around a submerged breakwater (SBW) to compare the performance of two turbulence modeling schemes—RANS and LES. We coupled a Lagrangian sediment particle module with OpenFoam to examine the turbulence caused by breaking waves. The numerical setup for the simulations was based on bathymetry measurements made at Hujeong Beach in South Korea. The results show that the wave heights simulated by LES were higher than those simulated by RANS in the front and lee areas of the SBW, and they were lower at the top of the SBW. This indicates that a larger amount of wave energy was conserved after passing over the SBW according to LES. These results were also confirmed via the obtained turbulent kinetic energy (TKE). When using LES, TKE increased in the lee area, where the waves broke after passing over the SBW. In case of RANS, however, TKE was not successfully conserved; it significantly decreased in the lee area. Lagrangian sediment motions show that, when using LES, a strong eddy formed, which entrained and dispersed the sediments into the water column. In the case of RANS, however, no evidence of such turbulent eddy formation was found, which confirms the better performance of LES for resolving turbulence.

Since Gangneung Harbor breakwaters were built in the east coast of Korea from 1992 to 2002, the shoreline inside the harbor had severely changed as it was accreted in the area inside the harbor but eroded further south during the observation period (1979–2005). We investigated this process using Telemac-2DH model to calculate flows, waves, sediments and morphological changes in unstructured grids. The performance of the model was validated using the experiment data by Graven and Wang (2007). The model was run in two cases by turning on/off the diffraction mode using the formula by Holthujisen et al. (2003). For this, we tuned the model by setting a shadow zone behind the breakwaters and by applying the diffraction formula only inside the shadow zone. The model results showed that wave heights significantly increased inside the shadow zone when the diffraction mode was on, compared to the case when the diffraction mode was off. This effect of diffraction was confirmed by the observations as the wave heights measured inside the shadow zone became 10–20% lower than those measured outside, which were nicely simulated by the model. In addition to the wave height, the wave-induced currents became stronger in the innermost area of the shadow zone with the diffraction mode. The model also successfully predicted the observed morphological change pattern because it simulated the shoreline erosion at the southern end of the shadow zone where the currents were bifurcated. Inside the shadow zone, sediment deposition occurred, corresponding to the observation, when the diffraction mode was on, whereas this deposition process was not simulated when the mode was off. The results support that the observed shoreline accretion in the harbor was mainly due to the reduced wave and current energy, which emphasizes the importance of accurate modelling of diffraction effect in the prediction of shoreline evolution.

The west coast of South Korea is characterized by a wide macrotidal area with a maximum tidal range of ∼10 m. The sea surface elevation varies with the tidal phase, which leads to significant changes in the vertical structure of the physical, chemical, and biological properties of the water column, especially when the interaction by waves and/or the freshwater and sediment input from the river increases. Under such conditions, it is difficult to carry out continuous and consistent measurements of the vertical structures of the water qualities using a conventional observation system that is fixed to the seabed or sea surface because the thickness of the water column constantly changes. Based on the demand for long-term observations of the vertical structures of the water properties in macrotidal environments, the Intelligent Buoy System (INBUS) was developed by the Korea Institute of Ocean Science and Technology (KIOST). INBUS is a buoy equipped with an instrument frame, which is similar to other buoys that are fixed to the sea surface. During every measurement, INBUS detects the water depth and sends the frame down to the seabed to measure the water quality at every vertical level set up in the system. For example, if N levels are set in INBUS, the water depth of each measurement is divided by N layers and the instruments in the lifting frame measure the water properties of each of the N layers while they are descending to the bottom. Based on this procedure, the vertical structure of the water column is consistently measured in N layers regardless of changes of the water depth due to tides and waves. The lifting and measuring process is automatically controlled by INBUS once it is set up in the system. In addition, because INBUS allows bidirectional communication through code division multiple access (CDMA), the system can be controlled by stations on land. If the CDMA communication becomes inoperable owing to extreme wave conditions or the buoy is lost because of incidents such as a collision with a ship, the location of INBUS can be tracked by low-earth-orbit satellites.

Crescentic bars with wavelengths of 250–450 m were observed on a micro-tidal, open coast (Anmok Beach, Korea) to unravel the flow patterns over them under various wave conditions. The horn and bay environments of the crescents were distinguished to measure respective near-bottom flow conditions in the nearshore 3–8 m deep. Offshore waves were measured at a station about 18 m deep. The measurement duration spanned approximately one winter month and two stormy spells of several days each in summer and another winter comprising three different field campaigns. In addition, bar morphologies were measured with single- and multi-beam echo-sounders before and after each hydrodynamic measurement. Winter-storm waves yielded discernable bar movements offshore accompanied by a merging of small bays into a larger one. During the field campaigns, the bars moved alongshore by far less than a half of their wavelength. Hydrodynamic measurements show a suite of the flow patterns including onshore and offshore uniform flows and rip cell circulations. The flow patterns depend exclusively on the offshore significant wave height (Hs), or a non-dimensional parameter $$ {\mathrm{H}}_{\mathrm{p}}={H}_s\sqrt{\tan \theta }/{h}_c $$, where hc is the water depth of the bar crest and tanθ the slope gradient. Therefore, the specific ranges of Hp could be given to individual flow patterns measured. These results are used to illustrate a coupled behavior of the bars and flows in a beach-state cycle forced by varying wave energies.

Kim, C.H.; Kim, H.W.; Park, C.H.; Kim, W.H.; Lee, M.H.; Choi, S.Y., and Do, J.D., 2018. Coastline change measurement using shipborne mobile LiDAR in Anmok Beach, Gangneung, Korea. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 601–605. Coconut Creek (Florida), ISSN 0749-0208. Coastal areas, used as human utilization areas like leisure space, medical care, ports, and power plants, etc., are regions that are continuously changing and interconnected with ocean and land. Regular monitoring of coastline changes is essential at key locations with such volatility. For effective monitoring coastal changes, KIOST (Korea Institute of Ocean Science & Technology) has constructed a shipborne mobile LiDAR system. The shipborne mobile LiDAR system, installed in a research vessel, comprised a terrestrial LiDAR (RIEGL LMS-420i), an IMU (MAGUS Inertial+), a RTKGNSS (L...

Lim, H.S.; Kim, M.; Do, J.-D.; Kim, S.-S.; Lee, H.J., and Kim, D.H., 2018. Variation of nearshore currents induced by seasonal waves in Haeundae. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 686–690. Coconut Creek (Florida), ISSN 0749-0208. Wave-induced currents at Anmok, located on the eastern coast of the Korean Peninsula, are one of the main causes of beach erosion related to high waves. Coastline changes induced by beach erosion and deposition are predominantly caused by sediment transport in the surf zone. This sediment transport is generated by wave-induced currents and depends on the wave height and direction. To understand beach erosion processes and the sediment transport mechanisms, field measurements of beach elevation and water depth were conducted for one month in winter 2015–2016. Using AWAC, ADP, VECTOR, and Aquadopp Profiler with OB...

Lee, H.J.; Do, J.-D.; Kim, S.S., and Lim, H.S., 2018. Sands Escaping Haeundae Beach. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 1006–1010. Coconut Creek (Florida), ISSN 0749-0208.Haeundae Beach has been hypothesized to lose sands from the nearshore of the western extremity of its pocket-beach system with a tidal range of 0.5 – 1.2 m. To test the hypothesis, a measurement station was located in this area to observe a suspended transport of sands near the seabed. The hydrodynamic measurements included water level, wave, currents and suspended sediment concentration with a benthic tripod for longer than one month of the 2013–2014 winter. In addition, a Telemac-2D tide model was run to simulate tidal currents for the same period of time as the measurements. A total of 6 events of two tidal cycles each were selected and analyzed to represent a variety of combinations of tidal phase, wave energy and wave direction. The results show that the suspended sand transport occurred continuously and was controlled predominantly by ebb-dominant tidal currents. Thus it was always directed offshore. Waves higher than 1 m sporadically took place during the measurements. However, high waves could just reorient the offshore suspended sand transport from obliquely to normal to the shoreline. This is because they created residual currents flowing roughly parallel to the shoreline. Neither offshore wave direction nor tidal phase evidently influenced the characteristics of residual currents. Therefore, the escape of the Haeundae sand from the area of interest has been proven to occur year round intrinsically by tidal currents. Waves intermittently contribute much to enhancing the suspended sand flux offshore by vigorous resuspension processes.

Kim, M.; Lim, H.S.; Do, J.-D.; Kim, S.-S.; Lee, H.J., and Shim, J.-S., 2018. Variations of nearshore currents induced by seasonal waves in Haeundae. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 1551–1555. Coconut Creek (Florida), ISSN 0749-0208. Haeundae, located on the southeastern coast of the Korean Peninsula, is a famous sand beach with a 1.6 km long, 70 m wide coastline. It suffers from wave-induced beach erosion in both summer and winter. For beach restoration, the Korean government has conducted beach nourishment (620,000 m3), and installed submerged breakwaters at both ends of the beach. Despite these efforts, the beach is still vulnerable to erosion caused by high waves. To understand beach erosion processes and sediment transport mechanisms, the government initiated an R&D project for the development of coastal erosion control technology ...

Crescentic nearshore sandbars (CNSBs) that are observed in the shallow waters ( 3 m developed in the site over a one-month period in January 2020 when the CNSB formed. The first storm wave had a sharp peak wave height that reached ~5 m and lasted ~2 days. The second storm wave had lower wave energy but several peak waves of ~4 m height and a total storm period of ~6 days. During both storm periods, the infragravity wave energy increased and strong (>0.5 m/s) offshore and longshore (northwest) currents developed for ~1 day and ~ 3 days for the first and second storm respectively. The results from video monitoring data show that a nearly developed SNSB system transformed into a weakly developed CNSB system after the first storm when alongshore variability on the nearly SNSB was intensified to become horns and bays of the weak CNSB. During the second storm, the CNSB system fully developed as the horns moved further onshore and the bays further offshore shaping the clear horn and bay pattern. This indicates that positive feedback between the flows and sediments played a key role for the formation of the CNSB and, therefore, the self-organization mechanism might be appropriate to describe the process during the two storm periods. Specifically, the high infragravity wave energy and strong quasi-steady currents were important because they could trigger the development of rip channels during the first storm whereas the channels were further strengthened by the long consistency of currents during the second storm.

Haeundae Beach represents Korean pocket beaches that are currently erosional and dominated by summertime typhoons. The decadal wave characteristics 9 km offshore of Haeundae Beach were analyzed using the WAM model that was validated through the 2007 wave observations. The wave statistics modelled for 1979–2007 indicates that the seasonal mean significant wave height (H s ) is highest (0.6–0.7 m) in summer due to typhoons, in contrast to the lowest (around 0.5 m) autumn analog. The wave direction is also pronouncedly seasonal with the principal bearings of SSW and NE in the summer and winter seasons, respectively. The WAM results additionally show that the H s has gradually increased over the region of Haeundae Beach since 1993. Beach profiling during June–November 2014 shows the opposite processes of the typhoon and fair-weather on beach sands. During a typhoon, foreshore sands were eroded and then accumulated as sand bars on the surf zone. In the subsequent fair-weather, the sand bars moved back to the beach resulting in the surf-zone erosion and foreshore accretion. A total of 5 cycles of these beach-wide sand movements yielded a net retreat (up to 20 m) of the shoreline associated with large foreshore erosion. However, the surf zone only slightly accumulated as a result of the sand cycles. This was attributed to the sand escape offshore from the westernmost tip of the beach. The present study may provide an important clue to understanding the erosional processes in Haeundae Beach.

Shoreline processes observed by a video monitoring system were investigated under different wave conditions. A 30 m-high tower equipped with video cameras was constructed in Hujeong Beach, South Korea, where coastal erosion was suspected to occur. Two-year shoreline data since December 2016 showed that beach area, Ab, has decreased, but periods of rapid increase in Ab were also observed. Shoreline change was closely related to the wave propagation directions and bottom topography. Ab increased when waves approached the shore obliquely, whereas it decreased when they approached in a normal direction. The shoreline became undulated when Ab increased, while it became flatter when Ab decreased. The undulation process was influenced by nearshore bedforms because the shoreline protruded in the lee area where underwater rocks or nearshore sandbars actively developed, with a sheltering effect on waves. Specifically, the locations of shoreline accretion corresponded to the locations where the sandbar horns (location where a crescentic sandbar protrudes toward the shore) developed, confirming the out-of-phase coupling between sandbars and shoreline. When waves with higher energy approached normal to the shore, the sheltering effect of sandbars and underwater rocks became weaker and offshore sediment transport occurred uniformly along the coast, resulting in flatter shorelines.

Coastal structures, such as revetments, are built to protect specific areas and facilities from the attack of extreme waves. However, unexpected environmental damage could be induced from these structures when inappropriately applied. Here, we present the results of measurements carried out using a video monitoring system, indicating the rapid collapse of a coastal revetment due to the attack of storm waves. The destruction occurred in sequence, that is, it was initiated by human activities, followed by a natural disaster. First, the beach in front of the revetment was eroded, even under moderate wave conditions, because sediments transported into this area were blocked by a rip-rap jetty. After the beach width was severely reduced due to the erosion, the revetment collapsed when storm waves attacked the area. The destruction seems accidental and inevitable because it was directly caused by the storm. However, it could have been avoided by predicting and preventing the erosion due to the jetty. This study provides insights into sequential processes that lead to the failure of coastal revetments, which could be applied for prevention of similar anthropogenic disasters.

Sea water level variations are generally influenced by a variety of factors such as tides, meteorological forces, water temperature, salinity, wave, and topography, etc. Among non-tidal conditions, atmospheric pressure is one of the major factors causing water level changes. In the East Sea, due to small tidal range which is opposite to large tidal range of the Yellow Sea, it is difficult to predict water level changes using a numerical model, which consider tidal forcing only. This study focuses on the effects of atmospheric pressure variations on sea level predictions along the eastern coast of Korea. Telemac-2D model is simulated with the Inverted Barometer Effect(IBE), and then its results are analyzed. In comparison between observed data and predictions, the correlation of prediction with IBE and tide is better than that of tide-only case. Therefore, IBE is strongly suggested to be considered for the numerical simulations of sea level changes in the East Sea.

This paper reports the results of hydrodynamic measurements at two different water depths to observe wave properties in the course of wave propagation, especially during storm periods, in Hujeong Beach, Korea. In addition to hydrodynamic measurements, video monitoring data and satellite images from Sentinel-II were employed to compare the temporal changes in shoreline positions and shallow water bathymetry during the storms. Through combination of a variety of observational data sets, the accuracy of analysis could be enhanced by preventing possible misinterpretation. Two significant storms were observed from two experiments conducted at different times and locations of the beach. The hydrodynamic conditions were similar in both of the periods in terms of wave and current conditions as well as wave nonlinearity such as skewness. However, the response of shoreline during the two storms was the opposite because it was eroded during the first storm but advanced during the second storm. This suggests that other controlling factors such as storm duration need to be investigated to support the analysis of cross-shore sediment transport and consequent shoreline evolution for future studies.

Do, J.D.; Jin, J.-Y.; Kim, C.H.; Kim, W-.H.; Lee, B-.G.; Wie, G.J., and Chang, Y.S., 2020. Measurement of nearshore seabed bathymetry using airborne/mobile LiDAR and multibeam sonar at Hujeong Beach, Korea. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1067-1071. Coconut Creek (Florida), ISSN 0749-0208.Accurate bathymetric measurements are important, especially in nearshore areas, because coastal sediment transport and the resulting beach erosion/accretion processes are significantly affected by seabed topography. At Hujeong Beach in Korea, for example, local shorelines show severe spatiotemporal variations as a result of seabed topography including underwater rocks. The accuracy of bathymetry measurements are not guaranteed, however, because high-accuracy acoustic sensors—such as multi-beam echo sounders—have a limited measurement capability. In this study, we investigated the accuracy of the nearshore bathymetry at Hujeong Beach using airborne LiDAR (a-LiDAR) data from May, 2017. One of the benefits of a-LiDAR is its ability to conduct both onshore and offshore mapping by detecting laser pulses reflected from land, the sea surface, and seabeds. The a-LiDAR measurements were validated onshore in a sloped roadside area using data measured via ship-mounted mobile LiDAR (m-LiDAR). A high agreement was found between the two datasets, with R-squared values of 0.9999 and mean square errors less than 0.05 m2. In measurements of seabed bathymetry, a-LiDAR agreed well with measurements from a multi-beam echo sounder over a sandy seabed and showed an accuracy similar to the m-LiDAR validation results. However, the accuracy of a-LiDAR measurements decreased significantly over rocky seabed; the mean square error compared to the multi-beam data increased to 0.6–0.8 m2. The high a-LiDAR errors over this rocky area may be a consequence of the irregular shape of its surface. Return signals from underwater rocks of varying shapes may be spread over wider angles, causing signal interference and reducing the measurement resolution in the area.

Kum, B.-C.; Shin, D.-H.; Jang, S.; Lee, S.Y.; Lee, J.H.; Moh, T.J.; Lim, D.G.; Do, J.-D., and Cho, J.H., 2020. Application of unmanned surface vehicles in coastal environments: Bathymetric survey using a multibeam echosounder. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1152-1156. Coconut Creek (Florida), ISSN 0749-0208.This paper presents the practical application and results of a bathymetric survey carried out in a shallow marine coastal zone (Hujeong beach, located in the East Sea, South Korea) using a multi-functional unmanned surface vehicle (USV) equipped with a multibeam echosounder. Operation of the USV was conducted along the coast in very shallow water [depth ≤ 1.5 m (0.3 m below the transducer)], which is inaccessible to manned research vessels. High-resolution bathymetric data is expected to help with assessment and prediction of rapid changes in the shallow coastal zone. This work supports the applicability of USVs to scientific research and environmental monitoring in very shallow coastal areas. The USV will be the most extensively used technique for observing marine coastal environment.

Three-dimensional modeling was performed in Tongyeong, South Korea to identify a space suitable for Yesso scallop farming that may not be successful if seawater temperature remains above 22 °C. In the research area, an underwater basin was found at a depth of 70 m; the depth outside the basin was not deeper than 30 m. It was expected that the water temperature in the interior of the basin might be low enough for farming during summer. The present study was then designed to investigate the temperature distribution in this basin area to verify if a water layer with consistently low temperature existed below the surface layer, using a MOHID (MOdelo HIDrodinamico) three-dimensional numerical model. The model applied mixed vertical coordinates so that the difficulties in modeling near the basin, where water depth sharply changes, could be overcome. In addition, a multi-level nesting system was developed based on the 72 -h forecasting system of the sea status around South Korea, which increased the modeling accuracy using updated boundary conditions. The model was validated by the measured tide and temperature data. The results showed that a strong thermocline was formed at depth of 15 m and a sub-surface space existed at depths deeper than 30 m, where seawater temperature was lower than 22 °C even in summer, which indicates the possibility of successful farming in the research area. The measurements also supported this result because dissolved oxygen and chlorophyll-a were not scarce in the sub-surface space probably due to the strong tidal mixing that could bring the surface seawater properties down below the thermocline. It was also found that the model was effective in resolving the thin thermocline and the sub-surface space below it due to the mixed vertical coordinate system.

Lee, Y.K.; Eom, J.; Do, J.D.; Kim, B.J., and Ryu, J.H., 2019. Shoreline movement monitoring and geomorphologic changes of beaches using lidar UAVs images on the coast of the East Sea, Korea. In: Jung, H.S.; Lee, S.; Ryu, J.H., and Cui, T. (eds.), Advances in Remote Sensing and Geoscience Information Systems of Coastal Environments. Journal of Coastal Research, Special Issue No. 90, pp. 409-414. Coconut Creek (Florida), ISSN 0749-0208.Sandy beaches are important habitats for coastal organisms and act as buffer zones during coastal disasters. Most of the coastal zone along the eastern coast of Korea consists of sandy beaches. However, beach erosion has been accelerating in recent years. In this study, shoreline movement and topographical changes were analyzed in Uljin-gun on the East Sea coast of Korea using remotely sensed data from airborne Lidar and unmanned aerial vehicles (UAVs). The shoreline changes extracted were statistically quantified using net shoreline movement (NSM) and linear regression rate (LRR) in the digital shoreline analysis system (DSAS). Morphological changes were quantified based on a comparison of the digital surface maps (DSM) generated by Lidar and UAVs. Shoreline movement and morphological changes were analyzed over the short-term (February 2016 to February 2019) and long-term (June 2008 to June 2018). Seaward migration was dominant for 7.02 m, 1.64 m, and 9.22 m along three defined subareas over the long-term. Over the short-term, LRR results showed landward migration as 0.7 m and 1.10 m in two of the subareas. Morphological change showed erosion and accretion occurring at approximately 0.08 m3 and 0.42 m3, respectively. This reverse trend indicates that a detailed DSM can detect volumetric change due to relocation of the sediment around artificial construction.

Kim, M.J.; Lee, S.H.; Baek, Y.S.; Do, J.D.; Lim, H.S., and Lee, H.J., 2019. In situ observations of ripples on the surf zone of a beach. In: Lee, J.L.; Yoon, J.-S.; Cho, W.C.; Muin, M., and Lee, J. (eds.), The 3rd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 91, pp. 36-40. Coconut Creek (Florida), ISSN 0749-0208.Ripple migration was observed on the surf zone of a beach in the eastern coast of Korea. A 3D sonar sensor and a current meter were placed together on a sand bar in water depth of 3.4 m for about 10 days in the spring of 2017. Bedloads were calculated from the records of ripple geometry and migration and were compared with estimates from a sediment transport model (SEDTRANS96). The ripples observed ranged in height (Hr) and length (Lr) from 0.5 to 8.9 cm and from 11.4 to 125.3 cm, respectively. They were highly dependent on the wave height (Hs) and thus wave-induced current speed (Uc). The largest ripples (Hr = 3.64 cm, Lr = 51.43 cm) occurred during the arrival of waves of 1 m height, the highest waves in the measurement period. At this time, the current and ripple migration speeds (Uc and Ur) were 4.08 cm/s and 17.13 cm/h, respectively. Therefore, the bedload was estimated as 5.785 kg/h/m. However, as Hs decreased to 0.5 m, the size and Ur of the ripples and Uc decreased simultaneously. At the wave height of 0.5 m, the values of Hr, Lr, Uc, and Ur were 1.97 cm, 18.82 cm, 2.72 cm/s, and 0.26 cm/h, respectively. The resulting bedload was estimated as 0.047 kg/h/m. A comparison of the measured and modeled bedloads indicated a model overestimation by a factor of 6–8. The model used the default values of 1 cm and 10 cm for ripple height and length, respectively. The rather large discrepancy may have been derived mainly from inaccuracy in estimating bed shear stress as well as ripple geometry. Therefore, this study emphasizes the importance of in situ ripple observations to place reasonable constraints on modeled bedloads.

In this study, we present the results of numerical model study to simulate the hydrodynamic conditions observed in Hujeong Beach in the east coast of the Republic of Kore from December, 2016 to January, 2017 during which several extratropical cyclones hit the area causing extreme wave conditions. Three acoustic instrumentation systems were moored from the coast to a location outside the surf zone where the water depth was ~8m to measure waves, currents and suspended sediment concentrations. For the numerical model, we employed the CADMAS-SURF Raynolds-Averaged Navier-Stokes (RANS) model to generate the wave conditions over the region of the field experiment.