• 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.

• 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.32 no.6
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• pp.446-457
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• 2020

Crescentic sand bar in the coastal zone of eastern Korea is a common morphological feature and the rhythmic patterns exist constantly except for high wave energy events. However, four consecutive typhoons that directly and indirectly affected the East Sea of Korea from September to October in 2019 impacted the formation of longshore uniform sand bar and overall shoreline retreats (approx. 2 m) although repetitive erosion and accretion patterns exist near the shoreline. Widely used XBeach to predict storm erosions in the beach is utilized to investigate the morphological response to a series of storms and each storm impact (NE-E wave incidence). Several calibration processes for improved XBeach modeling are conducted by recently reported calibration methods and the optimal calibration set obtained is applied to the numerical simulation. Using observed wave, tide, and pre & post-storm bathymetries data with optimal calibration set for XBeach input, XBeach successfully reproduces erosion and accretion patterns near MSL (BSS = 0.77 (Erosion profile), 0.87 (Accretion profile)) and observed the formation of the longshore uniform sandbar. As a result of analysis of simulated total sediment transport vectors and bed level changes at each storm peak Hs, the incident wave direction contributes considerable impact to the behavior of crescentic sandbar. Moreover, not only the wave height but also storm duration affects the magnitude of the sediment transport. However, model results suggest that additional calibration processes are needed to predict the exact crest position of bar and bed level changes across the inner surfzone.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3B
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• pp.311-319
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• 2006

A bed level change model(SED-FLUX) is introduced based on the realistic sediment transport process including bed load and suspended load behaviours at the bottom boundary layer. The model SED-FLUX includes wave module, hydrodynamic module and sediment transport and diffusion module that calculate suspended sediment concentration, net sediment erosion flux($Q_s$) and bed load flux. Bed load transport rate is evaluated by the van Rijn's TRANSPOR program which has been verified in wave-current fields. The net sediment erosion flux($Q_s$) at the bottom is evaluated as a source/sink term in the numerical sediment diffusion model where the suspended sediment concentration becomes a verification parameter of the $Q_s$. Bed level change module calculates a bed level change amount(${\Delta}h_{i,j}$) and updates a bed level. For the model verification the limit depth of the bed load transport is compared with the field experiment data and some formula on the threshold depth for the bed load movement by waves and currents. This model is applied to the beach profile changes by waves, then the model shows a clear erosion and accumulation profile according to the incident wave characteristics. Finally the beach evolution by waves and wave-induced currents behind the offshore breakwater is calculated, where the model shows a tombolo formation in the landward area of the breakwater.

• Journal of The Geomorphological Association of Korea
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• v.19 no.1
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• pp.17-27
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• 2012

Coastal dunes help stabilize the coastal landscape and protect the hinterland through dynamic interaction with sand beaches. Sometimes dune erosion occurs during the tropical cyclones, while dune recovery may naturally follow after the event. As the typhoon Kompasu passed through the Korean Peninsula early-September in 2010, it caused a rise in water in association with the storm, wave run-ups, and heavy rains in coastal areas. As the result, coastal dunes along the west coast of Korea were severely damaged during the storm. However, the degree and extent of erosion and recovery of dunes were found to be related with the condition of beach-dune systems including gradients of foreshore and front slope of the dune, sediment supply, vegetation, wind activity, and human interferences. Some dunes retreated landward more and more after the erosional event, while others recovered its original profile by aeolian transport processes mainly during the winter season. Vegetated dunes with pine trees were less recovered after the erosion than grass-covered dunes. In addition, dunes with artificial defense were more eroded and less recovered than those without hard constructions. According to the observation after the severe storm, it is likely that the sand transport process is critical to the dune recovery. Therefore, the interactions between beach and dune must be properly evaluated from a geomorphological perspective for the effective management of coastal dunes, including natural recovery after the erosion by storm events.

• Spatial Information Research
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• v.10 no.2
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• pp.317-329
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• 2002

Coastal landforms such as sand beach and coastal sand dune are changing dynamically, and the research about them is being conducted. Conventionally the leveling method has been applied to measuring heights of dynamic morphological surface in coastal landforms. We applied the photograrmmetric method which was not considered to measure the heights on coastal sand dune’s profile to calculating the heights of coastal sand dune; that is, the heights of unknown points on coastal sand dune’s profile was reckoned from the digital photographs’stereo pairs through bundle adjustment and backward transform of collinearity condition equation. we used six GCPs to perform bundle adjustment. After backward transform the error of heights between surveyed value and computed value was estimated around 10cm. In general, the pole is not adamantly fixed on the surface of coastal sand dune because of its softness, and then the disturbance of coastal sand dune adjoining surveyed area can be made in small area. Digital photogrammetry can solve the problem which conventional leveling method has, and be replaced it.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.15 no.1
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• pp.35-42
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• 1979

This paper concerns the receding of the eastern coastline of Korean peninsula at a macroscopic point of view, the result is as following. 1. Eastern coast is gradually developed from maturity stage to full maturity stage. 2. The coastline recession due to sea level rise is amounted to the receding distance, x=0.045 m per yr. 3. The author proposes another classification from the new view point, which is classified by comparing quantities between river supplying sediment loads, and the littoral drifting due to wave actions. According this, eastern coast is receding(Type Q-A), and we could find it's geomorphological characteristics. 4. The general piofile of eastern coast sand beach is erosional storm profile(Type I) which accompany offshore bar. 5. From the wave measuring data of eastern coast(Hoopo port), I can derive the linear regression line of the exceedance probability of wave height from the log-normal distribution. $z=O. 113+4.335 log_lo H, r=0.983.$ Above equation made it possible to estimate $\omega[=P(H>H_c)]for the effective wave height H_c=2. Om4, 4. Om and their corresponding values are considerable (7.8%, 0.3%) 6. Eastern coastline certainly have the tendency of erosive and receding, owing to the sea level rise, poor sediment source and effective wave actions. It's very desirable to survey coastline evolution for a long time systematically, in order to make more elaborate diagnosis.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.4
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• pp.151-158
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• 1990

Various factors may contribute on the mixing processes in the surf zone formed by irregular waves. The turbulence motion driven by wave breaking may be one of the major causes, the effect due to spatial variation on current velocity be a secondary one, and the additional process may result from the irregular superposition of radiation stresses or wave breaking dissipation incurred by random breaking waves in a broadened surf zone. In the present study a numerical model of spectral waves and induced currents was developed using a superposition technique with ${\kappa}-{\varepsilon}$ closure for mixing process and applied to a field situation of longshore current generated by spectral waves on a uniform beach. It was found from the application that the surf-zone mixing processes formed by irregular waves can be well described by using ${\kappa}-{\varepsilon}$ equations if the source of ${\kappa}$ is properly represented. The nonlinear energy transfer was also found to have some influence on the velocity profile of longshore current particularly in very shallow water region near coast.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.1
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• pp.81-96
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• 2007

Nonlinear shoaling characteristics over surf zone are numerically investigated based on spatially averaged NavierStokes equation. We also test the validity of gradient model for turbulent stresses due to wave breaking using the data acquainted during SUPERTANK LABORATORY DATA COLLECTION PROJECT(Krauss et al., 1992). It turns out that the characteristics length scale of breaking induced current is not negligible, which firmly stands against ever popular gradient model, ${\kappa}-{\varepsilon}$ model, but favors Large Eddy Simulation with finer grid. Based on these observations, we model the residual stress of spatially averaged NavierStokes equation after Lagrangian Dynamic Smagorinsky(Meneveau et al., 1996). We numerically integrate newly proposed wave equations using SPH with Gaussian kernel function. Severely deformed water surface profile, free falling water particle, queuing splash after landing of water particle on the free surface and wave finger due to structured vortex on rear side of wave crest(Narayanaswamy and Dalrymple, 2002) are successfully duplicated in the numerical simulation of wave propagation over uniform slope beach, which so far have been regarded very difficult features to mimic in the computational fluid mechanics.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.4 no.2
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• pp.117-126
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• 1999

Hampyong Bay is a semienclosed and macrotidal bay which opens to the eastern Yellow Sea through a narrow inlet in the southwestern coast of Korea. In order to understand the tidal-flat sedimentation in the semienclosed setting, morphology, sediments, accumulation rate and sea cliff erosion were investigated in the tidal flat of Hampyong Bay. The tidal flat of Hampyong Bay lacks intertidal drainage systems, and generally shows the concave-upward profile whose relief is designated by marked morphological features such as high-tide beaches, intertidal sand shoals and tidal creeks. Surfacial sediments of the tidal flat mainly consist of mud, sandy mud, gravelly mud, gravelly sand and muddy gravel, thus showing the textural characteristics of multimodal grain-size distribution, poorly sorting and positive skewness. The sediments generally coarsen landward due to the increase in coarse fraction content. Sedimentary structures are deeply bioturbated, but parallel lamination and lenticular bedding are locally found in the mudflat near mean low water line. Annual accumulation rates across the tidal flat (along Line SM) average -5.2 cm/yr with a range of -45.8~+4.2 cm/yr, indicating that the tidal flat is erosional. In general, erosion rates of upper and lower tidal flat are higher than those of middle tidal flat. Seasonally, the erosion rates are much higher during spring and winter when dominant wind direction corresponds to the long axis of Hampyong Bay. Sea cliffs are eroded at a rate of 1.4 m/yr. The biggest sea cliff erosion generally occurs 1~2 months later after tidal flats were extensively eroded. Such erosions of tidal Oats and sea cliffs in the semienclosed bay setting are interpreted to be due to wind waves coupled with local sea-level rise.