• Journal of Environmental Science International
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• v.22 no.5
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• pp.599-608
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• 2013

Jeju island, which is located along the moving path of typhoon, suffers from flooding and overflow by torrential rain. So abrupt runoff occurring, damages of downstream farm field and shore culturing farms are increasing. In this study, Oaedo stream, one of the mountainous streams on Jeju island, was selected as the basin of study subject and was classified into 3 sub-basins, and after the characteristics of subject basin, the soil erosion amount and the sediment delivery of the stream by land usage distribution were estimated with the use of SATEEC ArcView GIS, the sediment yield amount of 2000 and 2005 was analyzed comparatively. As a result of estimating the sediment yield amount of 2000, the three sub-basins were respectively 12,572.7, 14,080 and 157,761 tons/year. and sediment yield amounts were estimated as 35,172.9, 5,266 and 258,535 tons/year respectively in 2005. The soil erosion and sediment yield amount of 2005 using single storm rainfall were estimated high compared with 2000, but for sub-basin 2, the values rather decreased due to changes in land use, and the land coverage of 2005, since there are many classifications of land usage compared with 2000, enabling to reflect more accurate land usage condition, could deduce appropriate results. It is anticipated that such study results can be utilized as basic data to propose a direction to predict the amount of sediment yield that causes secondary flooding damage and deteriorates water quality within detention pond and grit chamber, and take action against damages in the downstream farm field and shore culturing farms.

• Journal of The Geomorphological Association of Korea
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• v.25 no.4
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• pp.21-35
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• 2018

The distribution and size of sandy beaches along eastern Korea has a close relationship with the presence of granite rocks. In general, elongated and wide beaches with abundant sands are likely to develop along the coasts where granitic basic rocks comprise the dominant geology or where a large amount of sands are supplied by streams from inland granitic rocks. Small sandy beaches, in contrast, appear in non-granitic rocks (i.e., under sedimentary and/or metamorphic geology). Hence, large beaches are observed continuously along the shore of Gangwon-do, of which coasts consist predominantly of granitic geology. Such continuity declines from Samcheok city to Pohang city. The rock of Gyeonbuk-do is commonly known as sedimentary, deposited between the late Triassic and the early Tertiary Periods. Because few sands are supplied from the upstream areas, sandy beaches unlikely develop along the coasts of the province, only showing a sporadic, discontinuous distribution under Bulguksa granite, granitic gneiss, and some volcanic rocks. Erosion was rarely observed in the beaches where granitic rocks are distributed, whereas merely five beaches seemed to have undergone some level of erosion in non-granitic regions. This is presumably because a larger amount of sands than that which had been eroded away was replenished in areas under granitic geology, while under non-granitic geology having a deficit in sands, no large sandy beaches had formed at first.

• Journal of The Geomorphological Association of Korea
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• v.23 no.1
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• pp.129-140
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• 2016

Camera monitoring data for 5 years from January 2009 to January 2014 are analyzed to investigate changes in beach erosion on Sangju, Gujora and Haeundae beaches on the South sea and Jungmun beach on the south shore of Jeju Island. The data show the time series of beach area changes obtained from digital orthoimages rectified from oblique images taken near the beaches by cameras. Each beach has different sediment sizes and shapes, but faces the South and is eroded mainly during Typhoons. However, each beach often responds differently to the same Typhoon, and some beaches outside the influence of the Typhoon are also eroded. This study shows that high frequency data of beach area changes obtained from cameras can effectively analyze the seasonal changes in beach area.

• Journal of Digital Convergence
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• v.15 no.3
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• pp.211-219
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• 2017

Among government projects for reduction of coastal disaster, coastal maintenance project stage 1(2000~2009) and stage 2(2010~2019) to reduce coastal erosion and sedimentation are currently under process. In performing the coastal maintenance projects, it is necessary to install artificial concrete armor units for coastal protection. Presently in Korea, products manufactured in Japan are applied to the site, or blocks self-developed by the construction firms are installed. However, there is a lack of technical reviews such as verification of hydraulic characteristics, securing the stability and design techniques. This study is intended to develop waterfront shore protection blocks with good accessibility of people and excellent coastal disaster reduction and protection capability. Through this study, hydraulic characteristics and stability coefficients of shore protection blocks could be drawn.

• Journal of Korea Water Resources Association
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• v.35 no.1
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• pp.13-24
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• 2002

In a physically realistic but simplified manner, an attempt is made in this study to develop a predictive model for swash hydrodynamics across the shore due to the storm waves on an arbitrary beach profile. Date from the SUPERTANK laboratory Data Collection Project are used for the model development, in which experiments were designed to simulate dune erosion under storm conditions at a prototype scale. The model predicts variations of swash height, velocity and period across the beach face in a swash zone. In general, the model proves to be capable of predicting variations of swash height, velocity and period across the shore. Quantitatively better predictions for the swash parameters could be achieved by improving the prediction of the beach face elevation, ymax, where the significant swash height becomes zero.

• Ocean Systems Engineering
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• v.5 no.4
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• pp.319-329
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• 2015

Submerged breakwaters are used to prevent shore line erosion and sediment transportation. One of their advantages is low visual impact. In this paper, the effects of discontinuous submerged breakwaters over water surface elevation was numerically studied considering the extended Boussinesq equations as governing equations using MIKE21 software. The result of discontinuous breakwater was compared with a beach without breakwater. The results showed that the gap dramatically effects on surface elevation from shore line to offshore. It is also evident from results that with approaching the center of the gap, fluctuation of surface elevation is generated. It is because of passing longshore currents towards offshore through the gap which leads to an increase in sediment transportation rate. Nevertheless, transferring water mass from breakwater gap results in powerful rip currents leading to high changes on longshore wave profile.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.1
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• pp.28-39
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• 2019

In the design process of counter measures against the beach erosion, information like the main sediment transport mode and yearly net amount of longshore and cross shore transport is of great engineering value. In this rationale, we numerically analyzed the yearly sediment budget of the Mang-Bang beach which is suffering from erosion problem. For the case of cross sediment transport, Bailard's model (1981) having its roots on the Bagnold's energy model (1963) is utilized. In doing so, longshore sediment transport rate is estimated based on the assumption that longshore transport rate is determined by the available wave energy influx toward the beach. Velocity moments required for the application of Bailard's model (1981) is deduced from numerical simulation of the nonlinear shoaling process over the Mang-Bang beach of the 71 wave conditions carefully chosen from the wave records. As a wave driver, we used the consistent frequency Boussinesq Eq. by Frelich and Guza (1984). Numerical results show that contrary to the Bailard's study (1981), Irribaren NO. has non negligible influence on the velocity moments. We also proceeds to numerically simulate the yearly sediment budget of Mang-Bang beach. Numerical results show that for ${\beta}=41.6^{\circ}$, the mean orientation of Mang-Bang beach, north-westwardly moving longshore sediment is prevailing over the south-eastwardly moving sediment, the yearly amount of which is simulated to reach its maxima at $125,000m^3/m$. And the null pint where north-westwardly moving longshore sediment is balanced by the south-eastwardly moving longshore sediment is located at ${\beta}=47^{\circ}$. For the case of cross shore sediment, the sediment is gradually moving toward the shore from the April to mid October, whereas these trends are reversed by sporadically occurring energetic wind waves at the end of October and March. We also complete the littoral drift rose of the Mang-Bang beach, which shows that even though the shore line is temporarily retreated, and as a result, the orientation of Mang-Bang beach is larger than the orientation of null pont, south-eastwardly moving longshore sediment is prevailing. In a case that the orientation of Mang-Bang beach is smaller than the orientation of null pont, north-westwardly moving longshore sediment is prevailing. And these trend imply that the Mang-Bang beach is stable one, which has the self restoring capability once exposed to erosion.

• Journal of Coastal Disaster Prevention
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• v.4 no.1
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• pp.7-19
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• 2017

In this study, waves and currents observed by acoustic AWAC, VECTOR and Aquadopp Profiler in Anmok coastal waters were analysed to account for the variability of wave and current and to understand the mechanism of sediment transport generated by wave-induced current in the surf-zone. The monthly variation of wave and residual currents were analysed and processed with long-term observed AWAC data at station W1, located at the water depth of about 18m measured during from February 2015 to September 2016. Wave-induced currents were also analysed with intensive field measurements such as wave, current, suspended sediment, and bathymetry data observed at the surf-zone during in winter and summer. The statistical result of wave data shows that high waves coming from NNE and NE in winter (DEC-FEB) are dominant due to strong winds from NE. But in the other season waves coming from NE and ENE are prevalent due to the seasonal winds from E and SE. The residual currents with southeastern direction parallel to the shoreline are dominant throughout a year except in winter showing in opposite direction. The speed of ebb-dominant southeastern residual currents decreasing from surface to the bottom is strong in summer and fall but weak in winter and spring. By analysing wave-induced current, we found that cross-shore current were generated by swell waves mainly in winter with incoming wave direction about $45^{\circ}$ normal to the shoreline. Depending on the direction of incoming waves, longshore currents in the surf-zone were separated to southeastern and northwestern flows in winter and summer respectively. The variation of observed currents near crescentic bars in the surf-zone shows different direction of longshore and cross-shore currents depending on incoming waves implying to the reason of beach erosion generating the beach cusp and sandbar migration during high waves at Anmok.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.6
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• pp.434-449
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• 2019

In this study, we develop a new cross-shore sediment module which takes the effect of infra-gravity waves of bound mode, and boundary layer streaming on the sediment transport into account besides the well-known asymmetry and under-tow. In doing so, the effect of individual random waves occurring during the unit observation period of 1 hr on sediment transport is also fully taken into account. To demonstrate how the individual random waves would affect the sediment transport, we numerically simulate the non-linear shoaling process of random wavers over the beach of uniform slope. Numerical results show that with the consistent frequency Boussinesq Eq. the application of which is lately extended to surf zone, we could simulate the saw-tooth profile observed without exception over the surf zone, infra-gravity waves of bound mode, and boundary-layer streaming accurately enough. It is also shown that when yearly highest random waves are modeled by the equivalent nonlinear uniform waves, the maximum cross-shore transport rate well exceeds the one where the randomness is fully taken into account as much as three times. Besides, in order to optimize the free parameter K involved in the long-shore sediment module, we carry out the numerical simulation to trace the yearly shoreline change of Mang-Bang beach from 2017.4.26 to 2018.4.20 as well, and proceeds to optimize the K by comparing the traced shoreline change with the measured one. Numerical results show that the optimized K for Mang-Bang beach would be 0.17. With K = 0.17, via yearly grand circulation process comprising severe erosion by consecutively occurring yearly highest waves at the end of October, and gradual recovery over the winter and spring by swell, the advance of shore-line at the northern and southern ends of Mang-Bang beach by 18 m, and the retreat of shore-line by 2.4 m at the middle of Mang-Bang beach can be successfully duplicated in the numerical simulation.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.12 no.2
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• pp.96-106
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• 2000

Though the recent years, large scale structures have been built on offshore for utilization of coastal ocean space as offshore airport and marine terminals. Sometimes, those big scale structures, however, happened to act as significant barriers against waves and severe beach erosion would take place on the coast. The present study deals nearshore topography changes affected by construction of an offshore structure with different distance from the shore. The series of three dimensional movable bed experiments have been examined in detail. Moreover, in order to make clear the relation of nearshore currents and local erosions behind offshore structure, the nearshore currents are calculated by Boussinesq equation model and compared with the same scale condition of the physical model experiments.