Search

ABSTRACT 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 since 2013. As part of the project, we have measured over three years of AWAC measurements at a water depth of 22 m and 1.8 km from the beach. Intensive measurements of wave, current, sediment transport near the surf-zone in summer and winter have been made using AWAC, VECTOR, and ADV with OBS. Analyses of nearshore currents induced by seasonal waves in the surf-zone have shown that cross-shore currents in summer are mainly induced by strong waves from the SSW or S that propagate to the beach due to wave breaking and shoaling effects on the reef near the beach. However, longshore currents in winter are induced by high waves from the E or ESE that propagate to the shoreline by diffraction at the east coastline. Eroded sand in summer returns along the beach by cross-shore and weak longshore currents induced by waves from the SSW or S. However, suspended sand in winter is moved to the west by strong longshore currents induced by waves from the E or ESE. Due to its pocket beach shape, beach erosion and sediment transport are caused by variations of nearshore currents induced by seasonal waves. [ABSTRACT FROM AUTHOR]

ABSTRACT Shim, W.J. and Kim, C.W., 2018. The necessity of coastal management in Busan Considering human and natural conditions: The case of barrier islands in Nakdong-estuary. 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.1501–1505. Coconut Creek (Florida), ISSN 0749-0208. The Busan coasts have complex natural and human conditions including dynamic coastal, river processes and human activities. These complex natural and human factors have had direct and indirect impacts on the coastal areas of Busan, so a spatially integrated approach for management is required. Especially, the barrier islands located in the Nakdong River estuary are proper examples that show the effect of the sediment budget as natural and human conditions. This research aims to identify the effects of natural and human conditions on the barrier islands. The area of the barrier islands, sediment budget from the watershed, the amount of dredging at Nakdong-Estuarine-Dam and land use coverage were compared using correlation analysis. The more sediment eroded from watershed and the less sediment was dredged at Nakdong-Estuarine-Dam, the larger area of the barrier islands. This indicates that boundary conditions such as the supply of sediment from the rivers are related to the barrier islands; thus river and watershed management are important. Regarding land use, used and barren areas are positively correlated with the barrier islands, but water, forests and agricultural lands are negatively correlated. Internal factors within Busan, such as coastal modifications and urban growth, are affecting coastal dynamics, which change the sediment budget. These results show that the barrier islands sensitively respond to boundary conditions from the river and watershed and to internal conditions such as shoreline management and development. Therefore, for the effective management of Busan's coasts, it is necessary to consider how natural and human conditions interact spatially. [ABSTRACT FROM AUTHOR]

ABSTRACT Woo, S.-B. and Yoon, B.I., 2018. Numerical simulation of fortnightly modulations of the convergence zone by residual volume transport in a macrotidal estuary. 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. 606–610. Coconut Creek (Florida), ISSN 0749-0208. This study examines the fortnightly modulation of convergence zone by residual volume transport of main channel using a numerical model in the tidally dominated Han River estuary (HRE), South Korea. The numerical model, EFDC (Environmental Fluid Dynamics Code), was simulated for 124 days, from May to August 2009, and used observed freshwater discharge for major rivers of HRE. The residual volume transport discharged into the HRE from the Yeomha channel and Seokmo channel had a ratio of 44:56 over thirty days under normal freshwater conditions. The model results show that a temporal variation of the residual volume transport (Lagrangian transport = Eulerian transport+Stokes transport) is formed near the Yeongjong Bridge with spring-neap variability, and net transport is outflowed to the west through the channel between Ganghwa and Yeongjong. Due to magnitude change of the residual volume transport by fortnightly (spring-neap) modulation, convergence zone (junction location of residual volume transport) show upward and downward spatial variation. We found that the convergence zone moves downstream during the spring period because of; 1) strong net downward barotropic flow by increased sea level difference between upstream and downstream during the spring tide; 2) decreased baroclinic flow towards the upstream of the main channel, caused by intensified tidal mixing during the spring period; and 3) increased outflow through the tidal flat channel between Ganghwa and Yeongjong during the spring period. [ABSTRACT FROM AUTHOR]

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 since 2013. As part of the project, we have measured over three years of AWAC measurements at a water depth of 22 m and 1.8 km from the beach. Intensive measurements of wave, current, sediment transport near the surf-zone in summer and winter have been made using AWAC, VECTOR, and ADV with OBS. Analyses of nearshore currents induced by seasonal waves in the surf-zone have shown that cross-shore currents in summer are mainly induced by strong waves from the SSW or S that propagate to the beach due to wave breaking and shoaling effects on the reef near the beach. However, longshore currents in winter are induced by high waves from the E or ESE that propagate to the shoreline by diffraction at the east coastline. Eroded sand in summer returns along the beach by cross-shore and weak longshore currents induced by waves from the SSW or S. However, suspended sand in winter is moved to the west by strong longshore currents induced by waves from the E or ESE. Due to its pocket beach shape, beach erosion and sediment transport are caused by variations of nearshore currents induced by seasonal waves. [ABSTRACT FROM AUTHOR]

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 OBS, intensive observations were made of waves, currents, and sediment transport in the surf zone. Wave and current variations were simultaneously analyzed at a water depth of approximately 18 m (W1) using long-term deployed AWAC data. Wave statistical analysis at station W1 shows that high waves from the NNE and NE are dominant in winter due to strong northeasterly winds from the NE. However, in summer, high waves coming from the NE and ENE are prevalent due to seasonal winds from the E and SE. By analyzing currents observed in the surf zone with waves, we found that a cross-shore current is generated by high waves, predominantly in winter, with incoming waves normal to the shoreline. Following the direction of incoming waves, longshore currents are separated into SE or NW directions depending on high waves come from the NNE or ENE, respectively. The variations of wave-induced currents caused by incoming wave height and direction accounts for the observed beach erosion and sediment transport, which in turn leads to beach cusp formation and crescentic sand bar migration during high wave periods. [ABSTRACT FROM AUTHOR]

The South Yellow Sea (SYS) is strongly influenced by large amounts of sediment input from surrounding rivers, but the dispersal patterns of these sediments, especially how they accumulate in the central Yellow Sea mud (CYSM) region, have not been well illustrated. Here, we present a detailed temporal variation record of the clay mineral compositions from core YSC-10 of the northern SYS near the western margin of the CYSM, trying to investigate sediment provenance and to discuss transport processes occurring during the Holocene. The clay mineral assemblages of core YSC-10 mainly consist predominantly of illite (68 ± 3%), followed by chlorite (15 ± 2%) and kaolinite (10 ± 2%), with scarce amounts of smectite (6 ± 3%). Combined with published data, our results suggest that the fine sediments of core YSC-10 are most likely a mixing product of the Huanghe (Yellow River), Changjiang (Yangtze River) and Korean Peninsula small river sediments, with notable temporal changes. During 8.4–6.4 ka, the Huanghe sediments from the Bohai Sea flowed directly into the SYS and played major roles in the sedimentation therein. In addition, as the modern ocean circulation pattern was formed ∼6 ka, the ocean front developed along the Shandong Peninsula coastal area of the SYS, which would have prevented the dispersal of the Huanghe sediments to the CYSM. The Changjiang sediments delivered by the diluted water replaced those from the Huanghe as the main source of the CYSM during the period of 6.4–4.2 ka. After 4.2 ka, the coastal shear front weakened and moved seawards due to the weakening and eastward shift of the Yellow Sea Warm Current (YSWC) in winter and the weakening and shrinking of the Yellow Sea Cold Water Mass (YSCWM) in summer. The Huanghe sediments seem to have increased and fluctuated frequently to core YSC-10 since then. Our study thus highlights that the coastal shear front may have played an important role in the source-to-sink processes of the SYS. • Clay mineral assemblages of core YSC-10 which near the western margin of the CYSM since the Holocene. • The source and transport mechanism of clay minerals of core YSC-10 in different time periods since Holocene. • The oceanic front played critical role in the source to sink processes of the SYS. [ABSTRACT FROM AUTHOR]

A new method for numerically predicting the total sediment load in a river is proposed. The method can be used to predict the total sediment load with information on channel geometry and slope, flow, and bed materials. The conventional method uses a 1D approach that assumes the channel has a wide rectangular shape. However, the proposed method computes depth-averaged velocity over the width and predicts the total sediment load based on the flow computations. The new method, therefore, is expected to predict better if the flow changes significantly in the lateral direction. The proposed method was applied to three large sand-bed rivers in Korea, where information is available regarding suspended sediment. Five formulas were tested of use in making total sediment load computations, namely Engelund-Hansen's, Ackers-White's, Yang's, Brownlie's, and Karim's formulas. The predicted total sediment loads are compared not only with measured data but also with results calculated using the 1D approach. Discrepancy ratios between the predicted and measured total sediment loads are given and the results are discussed. [ABSTRACT FROM AUTHOR]

Min, J. E., Choi, J. K., Yang, H., Lee, S., Ryu, J. H. 2014. Monitoring changes in suspended sediment concentration on the southwestern coast of Korea. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 133-138, ISSN 0749-0208. Concentrations and distribution patterns of suspended sediment (SS) are key indicators of marine environmental change, particularly in coastal areas, which gives good information on the deposition and migration of sediments from land. In this study we analyzed 632 scenes (79 days × 8 scenes) of Geostationary Ocean Color Imager (GOCI) data in order to investigate SS variations relating to tides, tidal currents, bottom morphology, river discharge, and so on. We also compared them to the numerical model of tidal currents for the Yellow Sea. The study area, the coastline of Mokpo, is characterized by shallow water depths (<50 m), a relatively large tidal range (8 m) and by strong tidal currents (1 to 2 m/s). The coastal area of Mokpo shows extremely high SS concentrations (SSC) caused by a resuspension of bottom sediments. GOCI, the world's first geostationary ocean color observation satellite, can obtain data hourly during daylight. Therefore, GOCI is well equipped for the detailed analysis of time-series variations in SSC with regard to tides and tidal currents along Mokpo. The concentrations and distribution patterns of SS in the study area were mainly affected by tidal currents. During flood tide, SSC showed higher values than during ebb tide, and the SS distribution pattern flowed in a northerly direction. On the other hand, during ebb tide, the SS distribution pattern flowed towards the south. Bottom morphology also displayed a similar pattern to the SS distribution. [ABSTRACT FROM AUTHOR]

This study aims to investigate possible source and long-term distributional patterns of coastal sands in the high slope-gradient, wave-dominated coast with no large rivers, eastern Korea. Chirp (2-7 kHz) seismic profiles show that the coastal sand deposits, the uppermost transparent layer, are up to 7.1 m thick off small, mountainous stream mouths, and thins laterally, showing a radial distribution from the stream mouths with a slightly SE-skewed elongated (i.e., alongshore) geometry. These features suggest that the terrigenous coarse sediments emptied by the streams during the summer flash flooding season have been a major source to the adjacent coastal sands. Hydrodynamic measurements with benthic tripod systems indicate that alongshore currents occurring during episodic storms play a significant role in the displacement of the coastal sands toward the southeast, resulting in the slightly SE-skewed elongated (i.e., alongshore) distributional geometry of the sands. [ABSTRACT FROM AUTHOR]

The Yellow Sea is fringed with deltas and estuaries on the Chinese and Korean coasts, respectively. The Korean estuaries, rock bound on the Ha coast, are represented by the Han estuary, the largest in the eastern Yellow Sea. To reveal the relationship between extensive tidal flats and major channels in the Han estuary, suspended sediment transport was observed from the water column down to the bottom boundary layer. Transecting channels and deploying benthic tripods were accomplished at a number of critical sites during different spring tides, mostly under the fair-weather conditions of dry seasons in 2006-08. The hydrodynamic measurements unraveled the role of macrotidal currents in estuarine suspended transport. According to lateral momentum analyses, cross-channel flows were governed by two forces: rotation and surface slope. The estimations of suspended flux and lateral momentum balance elucidated that, of the two candidate channels, the Yeomha Channel dominantly supplied riverine muds to the adjacent vast Ganghwa tidal flats. The other larger channel, Sukmo, was found to displace muds up the channel to the Han River mouth. Another offshore major channel, Jangbong, revealed small suspended flux, reflecting no substantial mud input of offshore origin into the Han estuary. This study maybe timely in that most Korean estuaries have artificially developed and are facing various environmental problems. [ABSTRACT FROM AUTHOR]

Macrotidal beaches are scattered in the west coast of Korea mostly in small embayments of the ria-type coastline and islands. In contrast to well-known tidal flats, these beaches have been little studied from the hydromorphologic viewpoint. Byunsan Beach was chosen to investigate beach processes affected by winter monsoon, which creates strong waves and wind-generated currents. The multiyear (2005-2008) profiling of the beach, together with the intensive sampling of surface sediments, provided the details of morphologic characteristics of the beach. Deep water winter wave characteristics were based on the measurements of an offshore buoy. A benthic tripod was deployed on the beach to observe waves, currents, and suspended sediments during a winter storm. The estimated morphodynamic parameters suggest that Byunsan Beach be classified as an ultradissipative state during winter. The tendency of grain size toward systematically fining seaward could be explained by the lateral displacements across the beach of swash and surf zones owing to a high tidal range. In addition, the tripod observations show that a storm readily generated offshore return flows capable of considerable beach erosion. The storm waves also significantly contributed to the erosion. This may reflect that the macrotidal, open beaches in the west coast of Korea are seasonally susceptible to pronounced erosion by winter monsoon. The results of this study may be useful for evaluating man-made environmental impacts caused largely by seawalls and dykes on the natural beach state intrinsic to the west coast of Korea. [ABSTRACT FROM AUTHOR]

Abstract: Understanding the impact of marine sand mining operations in a complex coastal environment requires a combined observational and modeling approach. Here, we use field measurements collected during mining operations in Kyunggi Bay, Korea to develop sediment parameters and source conditions for a three-dimensional (3D) sediment transport model built on the Regional Ocean Modeling System (ROMS). The model is run with realistic forcing obtained from a 9km meteorological model, tides, and river discharges. The resulting vertical and horizontal distributions of sediment show encouraging agreement with the field data, demonstrating markedly different dispersal patterns due largely to the differential settling of the various sand classes. The resulting depositional patterns suggest that only the coarser size classes (500 and 250μm) particles remain close to the mined site, while finer size classes are widely dispersed. These results suggest that this new methodology of multi-size class, 3D sediment transport modeling is quite promising, and further work is ongoing to include more realistic representation of sediment resuspension processes. [Copyright &y& Elsevier]

Hydrodynamic measurements and analysis of suspended sediments were conducted in the coastal area to reveal the source and dispersal processes of muds accumulating in Jinhae Bay, one of the largest bays in the Korea Strait. A number of hydrographic stations in the bay were occupied in order to obtain time series of suspended sediment concentrations, currents, water level, temperature, and salinity for one or two tidal cycles. The results, measured in May through October, suggest that a slight net influx of suspended sediments into the bay occurs consistently under low-wave, microtidal conditions. They also show a passageway of suspended sediments selectively through an entrance facing the open sea. The hydrodynamic measurements, together with tidal current pattern and landsat image of the suspended plume in the Korea Strait, indicate that the mud in Jinhae Bay has been fed largely by the adjacent Nakdong River, rather than by offshore sources. [ABSTRACT FROM AUTHOR]

• GSDs reveal offshore limit of lateral sediment transport in the East Sea. • Lateral sediment transport from the Korean Peninsula is within ~70 km offshore. • Eolian sediments in the SKP were transported by upper westerlies and winter monsoons. • East Asian winter monsoon intensity controlled eolian sedimentation in the East Sea. We investigated grain size records of a sediment core (05-P21) from the South Korea Plateau in the East Sea, located ca. 270 km east of the east coast of the Korean Peninsula. To verify an exclusive eolian origin for the detrital components of the sediments, we first examined how far offshore lateral-sediment-transport contributions from the eastern margin of the Korean Peninsula could reach, based on spatial changes in the grain size distribution (GSD) of surface sediments. To distinguish grain populations representing different transport processes, we performed end-member analyses (EMAs) of the GSDs of detrital fractions using the AnalySize software. EMA of the surface sediment GSDs showed that they consist of three end-member (EM) grain populations representing contributions from lateral (EM1 and EM2) and eolian transport (EM3). EM contributions by lateral transport reached only ca. 70 km seaward, confirming the exclusive eolian origin of detrital components of the 05-P21 core sediments. EMA of GSDs of the 05-P21 sediments distinguished two EM grain populations with fine (3.6 µm) and coarse (9.5 µm) median sizes, suggesting transport by upper westerlies and winter monsoon northwesterly surface winds, respectively. Variation in the proportions of fine and coarse EMs since ca. 186 ka indicated controls by both orbital and sub-orbital scale changes in intensity of the East Asian winter monsoon in association with global ice volume changes and Dansgaard–Oeschger cycles. [ABSTRACT FROM AUTHOR]

To reconstruct the variations in sea surface temperature (SST) during the Holocene, the alkenone unsaturation index of marine sediments from two deep-drilled cores and 81 different core-top surface sediments recovered from the Heuksan Mud Belt, located off the southwestern coast of the Korean Peninsula, was measured. First, comparison of the alkenone temperature estimates of 81 core-top sediments with in situ temperatures indicated that the alkenone temperatures corresponded to the average SST in April to October. The spatial distribution pattern of the core-top alkenone SST showed a north–south temperature gradient, which represented the in situ temperatures well. This indicated that the effects of the resuspension and lateral transport of sediments on the past temperature estimation might be insignificant. Based on the two deep-drilled cores, variations in the alkenone SST during the Holocene were reconstructed. In general, the alkenone SST decreased by less than 1 °C from the early to late Holocene. An interesting feature was the presence of two long and pronounced cold (approximately 2 °C) periods, which occurred at 3–5 kyr and 6.6–8.4 kyr B.P. These cold periods were also observed in other mid-latitude regions in East Asia, indicating that the cooling pattern was regional. The cold periods appeared to be associated with the southward migration of the westerly jet at that time. Investigations into the effects of local sea level changes and resultant changes in the tidal regime on changes in the SST during the Holocene period suggested that they were insignificant in the study area. • Alkenone temperatures of 81 coastal core-tops represent mean SST in April to October. • Two long and pronounced cold periods occurred at 3–5 and 6.6–8.4 kyr B.P. in East Asia. • Holocene cooling was associated with the southward migration of the westerly jet. [ABSTRACT FROM AUTHOR]

We identify and describe five giant seafloor depressions from the southeastern continental shelf of the Korean Peninsula using multibeam bathymetry, sub-bottom profiler, and multi-channel seismic reflection data, supplemented by piston cores. Multibeam bathymetry data from the shelf show four crescent-shaped depressions (SD1 to SD4) and one near-circular depression (SD5) within a group of NW-SE trending depressions, the largest covering an area of about 7 km2 on the seafloor. The depressions reach up to ~4.5 km in width and ~2 km in length and have asymmetric cross-sections. Some have depths as large as 40 m below the surrounding seafloor with walls as steep as 45°. The depressions are confined to water depths between 130 and 170 m and bounded on the north by a large submarine channel that was plausibly formed by fluvial or tidal processes during the Last Glacial Maximum (LGM) sea-level lowstand. Multi-channel seismic and sub-bottom profiler data reveal truncated depression walls and the presence of sediment drift deposits within the depressions, indicating that both erosion and deposition are active processes. Flaser and lenticular bedding in the cored drift deposits along with variable grain size (ranging between ~2.6 phi and ~4.3 phi) are diagnostic features of the bottom currents influenced by tidal forces. Depressions SD1 to SD4 lack evidence of fluid or gas escape. In contrast, many features of depression SD5 are characteristic of gas escapes and blowouts, including acoustic anomalies, a 20-m-high carbonate mound or carbonate-encrusted mound, and mud dikes and mud patches in cores. Based on the SD5 example, we think it is likely that the other crescent-shaped seafloor depressions formed originally as pockmarks by gas/fluid venting, and have since become inactive. The pockmarks represent zones of weakened sediment that were eroded, expanded, and merged by bottom currents to form larger seafloor depressions. Modern currents are strong enough to transport shelf sediments, and these currents were probably much stronger at lower sea levels when the Korea Strait was a more restricted passage between the East China Sea and East Sea. • Four crescent-shaped seafloor depressions (SD1 to SD4) from the SE shelf of Korea • These depressions have 25 to 40 m of depths below the adjacent shelf • Evidence of drift deposits inside the depressions and erosion at the depression walls • SD1 to SD4 probably began as pockmarks and then were modified by submarine currents • We also document a smaller circular depression (SD5) that we consider as pockmark [ABSTRACT FROM AUTHOR]