• Ocean and Polar Research
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• v.25 no.1
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• pp.89-106
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• 2003

Analyses of tidal observations and a numerical model of the $M_2$ and $M_4$ tides in the Uldolmok waterway located at the southwestern tip of the Korean Peninsula are described. This waterway is well known fer its strong tidal flows of up to more than 10 knots at the narrowest part of the channel. Harmonic analysis of the observed water level at five tidal stations reveals dramatic changes in the amplitude and phase of the shallow water constituents at the station near the narrowest part, while survey results show a decreasing trend in local mean sea levels toward the narrow section. It was also observed that the amplitudes of semi-diurnal constituents, $M_2$ and $S_2$ are diminishing toward the narrowest part of the waterway. Two-dimensional numerical modeling shows that the $M_2$ energy flux is dominated by the component coming from the eastern boundary. The $M_2$ energy is inward from both open boundaries and is transported toward the narrow region of the channel, where it is frictionally dissipated or transferred to other constituents due to a strong non-linear advection effect. It is also shown that the $M_4$ generation is strong around the narrow region, and the abrupt decrease in the M4 amplitude in the region is due to a cancellation of the locally generated M4 with the component propagated from open boundaries. The superposition of both propagated and generated M4 contributions also explains the discontinuity of the M4 phase lag in the region. The tide-induced residual sea level change and the regeneration effect of the $M_2$ tide through interaction with $M_4$ are also examined.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.28 no.1
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• pp.19-40
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• 2023

To investigate the role of water masses in the Jeju Strait in summer on the shallow coastal region and the characteristics of water properties in the strait, temperature and salinity were observed across the Jeju Strait in June, July, and August 2019. The cold water pool, whose temperature is lower than 15℃, was observed in the mid-depths of the central Jeju Strait and on the northern bottom slope of the strait. The cold water pools have the lowest temperature in the strait. To identify water masses comprising the cold water pool in the Jeju Strait, mixing ratios of water masses were calculated. The mid-depth cold water pool of the Jeju Strait consists of 54% of the Kuroshio Subsurface Water (KSSW) and 33% of the Yellow Sea Bottom Cold Water (YSBCW). Although the cold water pool is dominantly affected by the KSSW, the YSBCW plays a major role to make the cold water pool maintain the lowest temperature in the Jeju Strait. To find origin of the cold water pool, temperature and salinity data from the Yellow Sea, East China Sea, and Korea Strait in the summer of 2019 were analyzed. The cold water pool was generated along the thermohaline frontal zone between the KSSW and YSBCW in the East China Sea where intrusion and mixing of water masses are active below the seasonal thermocline. The cold water in the thermohaline frontal zone had similar mixing ratio to the cold water pool in the Jeju Strait and it advected toward the Korea Strait and shallow coastal region off the south coast of Korea. Intrusion of the mid-depth cold water pool made temperature inversion in the Jeju Strait and affected sea surface temperature variations at the coastal region off the south coast of Korea.

• Geomechanics and Engineering
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• v.28 no.3
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• pp.283-298
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• 2022

Landslides triggered by the combination of heavy precipitation and anthropological disturbance in hilly areas cause severe damage to human lives, properties, and infrastructure constructions. A comprehensive investigation of the influencing factors and failure mechanisms of landslides are significant for disaster mitigation and prevention. This paper utilized the combination of detailed geological investigation, physical experimental testing as well as numerical modelling to determine the failure mechanism, and proposed a countermeasures of the Lantian landslide occurred on 2, July 2017. The results reveal that the Lantian landslide is a catastrophic reactivated slide which occurred in an active tectonic region in Southwest China. Because of the unique geological settings, the fully to highly weathered basalts in the study area with well-developed fractures favored the rainwater infiltration, which is the beneficial to slide reactivation. Engineering excavation and heavy precipitation are the main triggering factors to activate the slide motion. Two failure stages have been identified in the landslide. The first phase involves a shallow mass collapse originated at the upper slopes, which extends from the road to platform at rear part, which is triggered by excavation in the landslide region. Subjected to the following prolonged rainfall from 19 June to 2 July, 2017, the pore water pressure of the slope continually increased, and the groundwater table successively rise, resulting in a significant decrease of soil strength which leads to successive large-scale deep slide. Thereinto, the shallow collapse played a significant role in the formation of the deep slide. Based on the formation mechanisms of the landslide, detailed engineering mitigation measures, involving slope cutting, anchor cable frame, shotcrete and anchorage, retaining wall and intercepting ditch were suggested to reduce the future failure risk of the landslide.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.8 no.2
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• pp.137-145
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• 1996

Effects of nonlinear terms on the generation of M$_2$ tide residual elevation and M$_4$ tide in the Yellow Sea and the East China Sea are investigated using a depth-integrated two-dimensional nonlinear M$_2$tidal model. The model domain (117$^{\circ}$E-130$^{\circ}$E, 24$^{\circ}$N-41$^{\circ}$N) covers the whole region of the Yellow Sea and the East China Sea with grid resolution of 1/6$^{\circ}$ in longitude and 1/8$^{\circ}$in latitude. A radiational boundary condition is used along the open boundaries. Calculations show that advection terms yield negative residual elevation, while shallow-water terms in continuity equation yield positive residual elevation. The contribution of both advection terms and shallow-water terms to tile generation of the M$_4$ constituent is more than 90 percents, but that of quadratic bottom friction terms to the M$_4$ constituent is comparatively small.

• The Journal of Engineering Geology
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• v.23 no.1
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• pp.1-17
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• 2013

It is sometimes necessary to change the location of the collection conduit, which is constructed in shallow sediments in a stream, if the concentrations of $Fe^{2+}$ and $Mn^{2+}$ become too high for water treatment. A total of nine wells, including four shallow wells with a depth of 3 m and five deeper wells with a depth of 6 m, were installed in the study area at Naeseong-cheon in Yecheon-gun. The change in hydrogeochemical features of groundwater and the concentrations of $Fe^{2+}$ and $Mn^{2+}$ were examined at the wells during 5 hours of pumping. As pumping was performed, the velocity of groundwater flow was increased around the pumping well and aeration conditions were developed to precipitate iron and manganese oxides in an oxidizing environment. In addition, the concentrations of $Ca^{2+}$ and $Cl^-$ at the pumping well were increased following the mixing of surface water and groundwater. It is suggested that the center region of the stream would be more suitable for a new collection conduit, considering the concentrations of $Fe^{2+}$ and $Mn^{2+}$ in groundwater and their reducing effect during pumping. The installation of a collection conduit based on field tests performed to ensure water quality enables a reduction in the construction and management costs at water treatment facilities.

• Journal of Soil and Groundwater Environment
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• v.15 no.6
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• pp.9-16
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• 2010

Groundwater sampling was performed at 38 wells where they are located in the areas with high uranium and radon (marked as A and B, respectively) concentrations, which were based on the previous research results. In-situ parameters (temperature, pH, EC, Eh, DO) and natural radionuclides (uranium and radon) were analyzed to figure out the characteristics of groundwater environments. In-situ data did not show any relations to natural radionuclide data, which could be caused by groundwater mixing, depths of wells, and geological settings, etc. But the highest radon well presented relatively low temperature value and the highest uranium well presented relatively low pH values The highest uranium concentration ranging $1.14{\sim}188.19{\mu}g/L$ showed in the area of A region consisted of Jurassic two-mica granite. The areas of Jurassic biotite granite and Cretaceous granite in the A region have the uranium concentrations ranging $0.10{\sim}49.78{\mu}g/L$ and $0.36{\sim}3.01{\mu}g/L$, respectively. The uranium values from between wells of community water systems (CWSs) penetrating fractured bed-rock aquifers and personal boreholes settled in shallow aquifers near the wells of CWSs show big differences. It implies that the groundwaters of the two areas have evolved from different water-rock interaction paths that may caused by various types of wells having different aquifers. High radon activities in the area of B region composed of Precambrian gneiss showed ranging from 6,770 to 64,688 pCi/L. Even though the wells are located in the same geological settings, their rodon concentration presented different according to depth and distance.

• Korean Journal of Ecology and Environment
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• v.38 no.2 s.112
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• pp.249-260
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• 2005

Dynamics of phytoplankton community were monthly examined at two sites in Lake Juam from January to December 2003. One site is located near the Dam, an intake tower, where obtain a drinking water resource, the other site is located in the shallow region, Mundeok-bridge, the upstream or effluent part of lake. During the study, there made little the differences in physicochemical factors between two sites, but numbers of species and standing crops of phytoplankton differ remarkably. Totally, 41% of green algae and 35.8% of diatoms were comprised of total phytoplankton species, while 46.3% of dinoflagellates and 27.6% of cyanobacteria contributed in total standing crops of Phytoplankton community. Cyanobacterium Microcystis aeruginora and diatom Fragilaria crotonensis dominated the Dam site during a warm season, while dinoflagellates Peridinium bipes and Asterionella formosa were at the shallow region during a cold season, respectively. According to the CCA analysis, dissolved oxygen, chemical oxygen demand and total phosphate strongly affected the growth of P. bipes with low water temperature. In addition, the increment of total nitrogen and water temperature affected biomass of a cyanobacterium M. aeruginosa. Collectively, it may suggest that the majority of annual primary production of Lake Juam is covered by two dominant species Peridinium bipes in cold season and Microcystis aeruginosa in warm season.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2006.11a
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• pp.285-289
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• 2006

Recently the target area for the installation of structures have been changed from shallow water into deep one by reservation and use of the wider coastal region, and development of deep water. Additionally, great emphasis in the improved human life quality has been placed on the necessities for the preservation of the agreeable natural and coastal environments and development waterfront, recreation, and resort in the sea. However, the existing gravity-type breakwater did not appropriately cope with the recent changes of circumstances, but required the enormous construction coat for coping with them. Until now, floating breakwuater, which was adequate for the environment and construction cost, has been actively studied in the other countries including Japan. This floating breakwater has been already constructed in many places and satisfactory in poor subsoil and deep water in Japan. Also it showed the same function as a gravity-type breakwater. But floating breakwater was not control long period waves by reason of constructive characteristic. The aim of this study is to discuss field application of Floating Breakwater with Compound Plate Type(FBCPT) in coastal region by using numerical analyses and hydraulic model test.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.1
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• pp.61-71
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• 1994

A modified method obtained by expanding Longuet-Higgins and Stewart's method (1964) is proposed. which can easily derive the group-bountied long wave due to the irregular were group as well as the regular wave group. The result of the proposed method agree well with those of both second order nonlinear theory and radiation stress theory. Particularly in the shallow water region, three equations from the proposed method, the second order nonlinear theory and the radiation stress theory become identical.

• Korean Journal of Environmental Biology
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• v.31 no.2
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• pp.154-157
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• 2013

Length-weight relationships were estimated for 11 fish species caught in Baekya Island, Korea. Samples were caught in depths of <15 m by fish pots between November 2008 and July 2009. The sampling gear, fish pots, is a widely used as commercial fishing gear in shallow waters of the region. The most abundant families were Hexagrammidae (20.7%), Cottidae (18.5%), Tetraodontidae (14.8%) and Scorpaenidae (13.3%). Estimates for parameter b of the length-weight relationship ($W=aL^b$) ranged between 2.454 and 3.361.