Dong Soo Hur

Shoreline Change due to Construction of the Artificial Headland with Submerged Breakwaters

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

Numerical Analysis on Energy Dissipation of Tsunami through Vegetation Zone

ABSTRACT Park, J.R.; Jeon, H.S.; Jeong, Y.M., and Hur, D.S., 2017. Numerical analysis on energy dissipation of tsunami through vegetation zone. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 194–198. Coconut Creek (Florida), ISSN 0749-0208. We have improved a 2-D Numerical Wave Tank (NWT) based on a Porous Body Model (PBM) for the simulation of energy dissipation during the interaction with a tsunami. In order to quantitatively evaluate the energy dissipation by vegetation drag during the process, the fluid resistance with regard to the vegetation and the vegetation drag coefficient according to the Reynolds number were applied. Moreover, to confirm the validity and effectiveness of the improved NWT, the results were compared with the existing numerical experimental results of tsunami vegetation interaction. The comparison showed that the water waveforms of the tsunami around the vegetation zone well are well simulated. As a result, the height of tsunami, the width, the density of vegetation, the reflection of the tsunami by freeboard, and the reflection and transmission characteristics of the tsunami were confirmed. In addition, the characteristics of the decrease in the energy of the tsunami as it passes through the vegetation zone were analyzed. As the vegetation width, height, and density increase, the transmission coefficient decreases, the decrease in the energy increases, and the reflection coefficient does not change significantly. In addition, since a vegetation zone with a large porosity gradually decreases the energy, the decrease in the energy becomes clear as the vegetation width increases.

Study on Rip Current Generated by Submerged Breakwaters: Field Observation and Numerical Simulation

ABSTRACT Kim, I.H.; Lee, W.D.; Shin, S.; Kim, J.H.; Hur, D.S., and Cho, W.C., 2016. The Study on Rip Current Generated by Submerged Breakwaters: Field Observation and Numerical Simulation. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1352 - 1356. Coconut Creek (Florida), ISSN 0749-0208. Jetties and submerged breakwaters have been constructed at Gangmun beach, Korea, for the past several years in order to protect the beach and to secure the estuary channel. However, drowning accidents due to rip currents have often occurred in the gap between the jetty and the submerged breakwater. In this study, field observations and numerical simulations were performed to understand the mechanism of the rip current occurrences at Gangmun beach. The field investigation included the geomorphological change as well as the rip current occurrences. Three-dimensional numerical simulations were carried out to find out the occurrence mechanism of the rip currents and the countermeasure for the rip current reduction. The results showed that the mean water level difference between the gap and the area behind the submerged breakwater induced the rip currents. The numerical model results also showed that the drainage channel in the submerged breakwater can reduce the rip current magnitude.

Numerical Model Study on the Wave and Current Control by Coastal Vegetation

ABSTRACT Lee, W.D.; Cox, D.T., and Hur, D.S., 2017. Numerical model study on the wave and current control by coastal vegetation. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 219–223. Coconut Creek (Florida), ISSN 0749-0208. In this study, three-dimensional numerical simulations were conducted to investigate the effect of the coastal vegetation on the wave and current controls. The model was modified to apply three-dimensional Navier-Stokes solver based on porous body model for the direct simulation of the wave energy dissipation through the vegetation. The new formula of a vegetation drag coefficient based on the wave-vegetation interaction was proposed through the hydraulic model tests and the formula was implemented to the model. The modified numerical model was tested and the results were compared with the experimental results to verify the numerical model capability. The model results well reproduced the wave energy dissipation inside the vegetation zone. Moreover, the numerical modeling was also conducted for the hydrodynamics on permeable submerged breakwater and the model results were compared with the results of vegetation. Inside the vegetation zone, the wave energy slowly decreased and the water level behind the vegetation was not increased seriously. Since the vegetation reduces the wave energy gradually, the width of the vegetation zone is an important factor for the effective control of the wave energy. Because the water level behind the vegetation zone did not increase too much, the return flow was small compared with that in the gap between the submerged breakwater cases. Therefore, if we deploy coastal vegetation effectively, this may be a better measure than coastal structures in terms of effectiveness and economy.

Field Observation and Numerical Modelling on the Hydrodynamics Behind a Submerged Breakwater

ABSTRACT Kim, I.H.; Kim, J.; Jeong, Y.-M.; Hur, D.S., and Shin, S., 2017. Field observation and numerical modelling on the hydrodynamics behind a submerged breakwater. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 304–308. Coconut Creek (Florida), ISSN 0749-0208. In 2014, a submerged breakwater installed near the erosion hot spot and the beach is being formed to salient beach behind the structure at Anmok beach, which is located on the east coast of Korea. The field monitoring has been carried out for past three years in order to investigate the change of beach morphology and shoreline before and after the breakwater construction. Wave gages were installed in the offshore location, in front of the breakwater and in the behind of the breakwater to investigate the wave height variation. A three-dimensional numerical model based on the Navier-Stokes equation with a Large Eddy Simulation (LES) turbulence closure scheme (LES-WASS-3D) was employed to predict the hydrodynamics near the submerged breakwater. The model used the beach topography and the bottom bathymetry before the breakwater construction to predict the wave transformation, refraction and diffraction due to the installation of the breakwater. The model simulated the wave and nearshore current fields especially behind the submerged breakwater and successfully predicted the wave heights near the submerged breakwater in high correlation (r2 = 0.98) with the filed observation results. The numerical results also showed that the predicted wave and current fields could induce the sediment deposition behind the structure.

Applicability of Multiple Submerged Narrow-Crested Breakwaters for Reduction of Mean Water Level in Rear Side and Flow Control

ABSTRACT Hur, D.S.; Cho, W.C.; Yoon, J.S.; Kang, C., and Lee, W.D., 2017. Applicability of multiple submerged narrow-crested breakwaters for reduction of mean water level in rear side and flow control. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 179–183. Coconut Creek (Florida), ISSN 0749-0208. In this study, to confirm the applicability of multiple submerged narrow-crested breakwaters (SNCBs), a 3-D numerical simulation was conducted. The numerical simulation used the numerical model developed for analyzing the 3-D flow structure around the submerged breakwaters. In addition, to verify the validity and effectiveness of the numerical model, the wave height distribution and mean water level distribution around impermeable submerged breakwater (ISB) and permeable submerged breakwater (PSB) were compared with the results of the numerical model experiment. As a result, the simulated results accurately realized the experimental values. The numerical simulation was conducted by applying the multiple SNCBs and common PSB for comparative analysis of the effectiveness on flow control and increased mean water level in the rear side, respectively. When the SNCBs are installed by more than two rows, the flow control was better than that achieved by installing PBS. However, the wave reflection was high, and the water level difference between onshore and offshore increased, owing to increased water level in the rear side. Based on this, an opening was installed on the multiple SNCBs, for the reduction of water level in the rear side. As a result, an outgoing flow toward the open sea was generated, which reduced the mean water level in the rear side. When W/Lr ≥ 0.2, the mean water level difference between onshore and offshore decreased, compared to the case of the PSB. Therefore, when appropriately installing the multiple SNCBs, whose applicability has been confirmed in this study, this can become one of the methods that can replace existing PBSs, which are bulky in size and expensive to construct.

Analysis of Beach Deformation according to Nourishing Sand in Haeundae Beach, Korea

ABSTRACT Lee, W.D., Kim, I.H., Yoon, J.S., Cho, W.C. and Hur, D.S., 2016. Analysis of beach deformation according to nourishing sand in haeundae beach, Korea. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1372 - 1376. Coconut Creek (Florida), ISSN 0749-0208. This study has analyzed the beach deformation characteristics of Haeundae Beach, which is one of the most representative beaches of S.Korea, after beach nourishment through monitoring and performing a numerical simulation. This study was able to analyze the beach deformation characteristics after beach nourishment in depth (e.g. variations in coastline, beach profile and the area and volume of beach, and beach stabilization process) in line with the results of marine geophysical survey (Do et al., 2015). This study surveyed the marine morphological changes around Haeundae Beach caused by Typhoon Neoguri, but morphological changes did not show in the water level of over 3m. In addition, this study was not only able to identify the short-term advance and retreat of coastline in the beach profile due to Typhoon Neoguri, but also understand this phenomenon on the basis of the results of wave field analysis using Numerical Wave Tank (NWT). Furthermore, this study was able to find that NWT and the coupling calculation of Contour-line model simulated the changes of coastline due to Typhoon Neoguri almost similarly. NWT and the coupling calculation of Contour-line based on long-term monitoring are expected to greatly contribute to understanding the beach deformation characteristics due to beach nourishment in future.

Hydraulic and Environmental Stability Analysis in the Estuary of Gahwa River and Sacheon Bay by the Change of Discharge of Namgang Dam in South Korea

ABSTRACT Kim, T.W., Lee, W.D., Hur, D.S., Lee, J.L and Yoon, J.S., 2016. Hydraulic and Environmental Stability Analysis in the Estuary of Gahwa River and Sacheon Bay by the Change of Discharge of Namgang Dam in South Korea. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 213–217. Coconut Creek (Florida), ISSN 0749-0208. Namgang dam is located in the southern part of South Korea. Flow discharged from Namgang dam for a flood control runs Kahwa river and finally reaches Sacheon bay. In a rainy or typhoon period, the discharged flow can inundate and affect the hydraulic stability and safety of estuarine areas of Kahwa river, Sacheon river, Jungseonpo river, and Jukcheon river. In this study, we performed a 3-dimensional hydraulic experiment and numerical analysis to analyze the level of water rise in the estuarine areas and environmental effect to Sacheon bay by the change of discharge of Namgang dam. A hydraulic model, based on bathymetric and aerial LIDAR survey data, was made in the scale of 1/50. The experimental and numerical results were compared with the observational results. From the experimental and numerical results, it reveals that as the amount of discharge from Namgang dam increases, water levels in the estuarine areas of Jungseonpo river and Sacheon river and the industrial area around Sacheon bay significantly increases by the effect of backwater. In addition, analyzing the measured salinity concentration, we also find out that the range of diffusion of discharged water into Sacheon bay and it takes about 20 days to recover the original salinity concentration.

Numerical Studies on Rip Current Control Using Scene-friendly Structures at Haeundae Beach, Korea

ABSTRACT Lee, W.D.; Shin, S.W.; Jeong, Y.M., and Hur, D.S., 2014. Numerical studies on rip current control using scene-friendly structures at Haeundae Beach, Korea. The sporadically occurring rip currents put swimmers in risk during the season of every summer vacation. It is known that the rip current generation is affected by the characteristics of incident waves and bottom topography but the mechanism of the rip current occurrence is still not clear. In order to understand the mechanism of the rip current and to establish countermeasures, 3D numerical simulation was performed based on the realistic bathymetry of Haeundae Beach by using LES-WASS-3D. The numerical simulation results showed that the wave heights vary parallel to the shore line by inequality of bottom bathymetry (submerged shoal and rocks) and this wave height variation induces the water level difference. The model results also showed that the rip currents were generated through the region of relatively deep water and low water level that is caused by the water level difference. The present study suggested scene-friendly structures such as submerged breakwaters, drainage layers, and gabions as the countermeasures of rip current control. These structures successfully reduced rip current by controlling the energy unbalance in the region of rip current occurrence.

Control Technologies in Reducing Rip Currents around the Open Inlet between Two Submerged Breakwaters

ABSTRACT Hur, D.S.; Cho W.C.; Yoon, J.S.; Kim, I.H., and Lee, W.D., 2014. Control technologies in reducing rip currents around the open inlet between two submerged breakwaters. In the present study, we investigated the flow generated around the open inlet between two submerged breakwaters installed at Songdo Beach, Busan, Korea. We also performed the numerical analysis on the characteristics of the rip current generated around the open inlet with various sizes and arrangements of the submerged breakwaters. Furthermore, based on the numerical results of this study, we suggested three technologies to control the rip current and applied these technologies around the submerged breakwaters to find out the effectiveness of the control technologies. From the numerical analysis, we found out that RCCT-3 (Rip Current Control Technology-3), which installs a drainage channel inside the submerged breakwater to reduce water surface elevation at the rear side of the submerged breakwater, is most effective in reducing the rip current around the open inlet.