• Journal of Ecology and Environment
• /
• v.29 no.6
• /
• pp.573-580
• /
• 2006

A sediment core from the Cheollipo arboretum ($36^{\circ}$ 47' 57'N, $126^{\circ}$ 09' 04') was studied for pollen analysis in order to reconstruct postglacial vegetational change and environmental changes around the central western region of the Korean Peninsula. The record shows four pollen assemblage zones: Zone CHL-I, Quercus stage (ca. 9,300$\sim$6,200 yr BP): zone CHL-II, Quercus-Pinus stage (ca. 6,200$\sim$4,600 yr BP); zone CHL- III, Pinus-Quercus stage (ca. 4,600$\sim$1,160 yr BP): zone CHL-IV and Pinus stage (ca. 1,160 yr BP-present). During the 9,300$\sim$8,500 yr BP, the early Holocene, researchers have guessed a piece of cool-temperate norihern/altimontane mixed coniferous and deciduous broad-leaved forest. Between 8,500$\sim$4,600 yr BP the Quercus dominated the landscape of study area and the established dates of this typical cool-temperate central/montane deciduous broad-leaved forest vegetation might be ca. 6500 yr BP, and then the Pinus developed around the site at ca. 5,700 yr BP. The abrupt increase of Pinus and NAP (non-arboreal pollen) after ca. 1,100 yr BP indicates the vegetation changes due to human activities. From the dynamics of the Chenopodiaceae pollen indicating salt marsh and freshwater pollen flora such as Typha, Trapa, Nymphoides and so forth, we suggest that the tidal flat was altered into freshwater lake around 6,500 yr BP.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.32 no.1
• /
• pp.55-68
• /
• 2020

In order to investigate the hydraulic characteristics of a boundary layer streaming over the beach cusps appeared in swells prevailing mild seas, we numerically simulated the shoaling process of Edge waves over the beach cusp. Synchronous Edge waves known to sustain the beach cusps could successfully be duplicated by generating two obliquely colliding Edge waves in front of beach cusps. The amplitude A_B and length L_B of Beach Cusp were elected to be 1.25 m and 18 m, respectively based on the measured data along the Mang-Bang beach. Numerical results show that boundary layer streaming was formed at every phase of shoaling process without exception, and the maximum boundary layer streaming was observed to occur at the crest of sand bar. In RUN 1 where the shortest waves were deployed, the maximum boundary layer streaming was observed to be around 0.32 m/s, which far exceeds the amplitude of free stream by two times. It is also noted that the maximum boundary layer streaming mentioned above greatly differs from the analytical solution by Longuet-Higgins (1957) based on wave Reynolds stress. In doing so, we also identify the recovery procedure of natural beaches in swells prevailing mild seas, which can be summarized such as: as the infra-gravity waves formed in swells by the resonance wave-wave interaction arrives near the breaking line, the sediments ascending near the free surface by the Phase II waves orbital motion were carried toward the pinnacle of foreshore by the shoreward flow commenced at the steep front of breaking waves, and were deposited near the pinnacle of foreshore due to the infiltration.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.32 no.1
• /
• pp.69-84
• /
• 2020

Natural shoreline repeats its re-treatment and advance in response to the endlessly varying sea-conditions, and once severely eroded under stormy weather conditions, natural beaches are gradually recovered via a boundary layer streaming when swells are prevailing after storms cease. Our understanding of the boundary layer streaming over surf-zone often falls short despite its great engineering value, and here it should be noted that the most sediments available along the shore are supplied over the surf-zone. In this rationale, numerical simulation was implemented to investigate the hydraulic characteristics of boundary layer streaming over the surf zone in this study. In doing so, comprehensive numerical models made of Spatially filtered Navier-Stokes Eq., LES (Large Eddy Simulation), Dynamic Smagorinsky turbulence closure were used, and the effects of turbulence closure such as Dynamic Smagorinsky in LES and k-ε on the numerically simulated flow field were also investigated. Numerical results show that due to the intrinsic limits of k-ε turbulence model, numerically simulated flow velocity near the bottom based on k-ε model and wall function are over-predicted than the one using Dynamic Smagorinsky in LES. It is also shown that flow velocities near the bottom are faster than the one above the bottom which are relatively free from the presence of the bottom, complying the typical boundary layer streaming by Longuet-Higgins (1957), the spatial scope where boundary layer streaming are occurring is extended well into the surf zone as incoming waves are getting longer. These tendencies are plausible considering that it is the bottom friction that triggers a boundary layer streaming, and longer waves start to feel the bottom much faster than shorter waves.

• 한국해양학회지
• /
• v.23 no.2
• /
• pp.76-88
• /
• 1988

Size distribution of suspended particulate materials (SPM) in the coastal waters of eastern Korea was studied using a laser particle size analyzer. Mean particle size (MPS) ranges from 3.69 to 8.40 ${\mu}m$ in surface waters, from 3.38 to 6.43 ${\mu}m$ in mid-depth waters, and from 3.88 to 8.30 ${\mu}m$ in near-bottom waters. For smaller MPS, the size distribution is unimodal, whereas it becomes polymodal as the MPS increases. Particle concentrations increased with the increases in MPS, suggesting that processes of adding larger particles in the waters such as resuspension of bottom sediments are more important in controlling MPS in the area than processes of removing smaller particles such as flocculation of fine particles. Observations of higher MPS near the coast in mid-depth waters, and at the continental slope in near-bottom waters appear to support the above idea. For surface waters with high MPS, mean particle density was noticably low, indicating the importance of biological activities in the formation of suspended particles.

• Korean Journal of Heritage: History & Science
• /
• v.46 no.3
• /
• pp.68-77
• /
• 2013

This report is based on the investigation of potholes which are formed by fluvial erosion. A pothole is called so because it is a hole that looks like a coffeepot. The results of previous studies are applied to the 'Jakgwaecheon Porthole' of this study. The study is focused on the dimension and morphology of the Pothole and investigates the effects of stream sediments, river flow, geological structural lines, etc. on the formation of potholes. As a result of measuring 61 potholes in this area, we recognized that the elliptical dish-shaped cross sections are dominant and inferred that their longitudinal direction on the plain is affected by the direction of the stream flow. Also, 'Jakgwaecheon Pothole' is very characterized in terms of scale and morphology. Furthermore, it is harmonious with the beautiful landscape, humanity, and historical values and it can be suggested that it is qualified to be registered as a geoheritage structure.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.26 no.2
• /
• pp.63-81
• /
• 2021

In this study, we investigated the tide-induced flow patterns near the ocean outfall of the Jeju and Bomok Wastewater Treatment Plants (WTP) in Jeju Island by using measurements of Acoustic Doppler Current Meter (ADCP) and a numerical experiment with inserting passive tracer into a regional ocean model. In late spring of 2018, the ADCP measurements showed that tidal currents dominate the flow patterns as compared to the non-tidal components in the outfall regions. According to harmonic analysis, the dominant type of tides is mixed of diurnal and semi-diurnal but predominantly semidiurnal, showing stronger oscillations in the Jeju WTP than those in the Bomok WTP. The tidal currents oscillate parallel to the isobath in both regions, but the rotating direction is different each other: an anti-clockwise direction in the Jeju WTP and a clockwise in the Bomok WTP. Of particular interest is the finding that the residual current mainly flows toward the coastline across the isobath, especially at the outfall of the Bomok WTP. Our model successfully captures the features of tidal currents observed near the outfall in both regions and indicates possibly high persistent pollutant accumulation along the coasts of Bomok.

• Journal of the Mineralogical Society of Korea
• /
• v.15 no.4
• /
• pp.259-272
• /
• 2002

This study was tried to interpret the important major factors controlling some physicochemical properties by comparing mineralogical and physicochemical characteristics such as pH, cation exchange capacity, Methylene Blue adsorption amount, swelling, viscosity, strength (compressional and tensile), and surface area etc. Investigated bentonite samples are five Korean samples from Dusan, Naa, Oksan, Dongyang, and Yeonil deposits and two Japanese bentonites from Tsukinuno and Tomioka deposits which were formed under a similar geological environment of the Tertiary basin. Tsukinuno bentonite is only natural Na-type bentonite and the others are all Ca-type bentonites. Most of the properties are not explained by the montmorillonite content only though the most important factor controlling the physicochemical properties is the montmorillonite content. The layer charge of montmorillonite will strongly control cation exchange capacity and Methylene Blue adsorption. Zeolite bearing bentonites show the strong alkaline character and causes the increase of cation exchange capacity, however decrease swelling, viscosity and strengths. Pyrite bearing bentonites decrease green compressional strength and wet tensile strength. The exchangeable interlayer cations control some physicochemical properties. Na-type bentonite than Ca-type shows more strong alkaline character and much more advanced swelling and viscosity. Also the size and thickness of montmorillonite flakes seem to control some physicochemical properties. Bentonite mainly composed of montmorillonite of very thin and large flakes is characterized by the very high surface area, cation exchange capacity, viscosity, swelling, Methylene Blue adsorption, green compressional strength and wet tensile strength. Domestic Dusan bentonite shows the most excellent physicochemical properties, which is due to the high content(84%) and very well crystallinity of montmorillonite.

• Journal of the Korean association of regional geographers
• /
• v.19 no.2
• /
• pp.234-245
• /
• 2013

In order to examine the amount and rate of soil erosion on Ridge Traversing Trail in Jirisan National Park, a cross-sectional area of hiking trail were monitored at 16 sites in Nogodan - Samdobong section from November 2011 to April 2012. Although all sites demonstrates an enlarged cross-section of trail, the amount of soil erosion varies from site to site: 54.9 to $908.8cm^2$. It suggests that the erosional rate ranges from $0.1cm^2/day$ to $1.72cm^2/day$. The erosional amount is also varied with a trail type: $109.3cm^2$ for a shallow gully-like trail to $573.2cm^2$ for a unilateral trail. However, the cross-sectional change is larger on a sidewall than a tread irrespective of a trail type. The erosional amounts of November to April are smaller than that of May to October. In particular, the erosional amount of November 2011 to April 2012 is smaller than the depositional amount, implying a reduced cross-section of trail. Pipkrake action puts loose soil particles on a sidewall on March and April, and then rainwash due to a heavy rainfall takes them away after May. It seems to be the most predominant erosional process in Ridge Traversing Trail. A sidewall facing north shows a larger amount of erosion than a sidewall facing south. It also implies a difference in the development of a pipkrake according to an aspect. The small amount of erosion and cross-sectional decrease, which is usually observed on April, results from the combined effect of frost heaving, pipkrake action, a small rainfall and a temporary suspension of trampling. It is necessary to establish the monitoring system of trail erosion in terms of the management of hiking trail in a mountain national park.

• Economic and Environmental Geology
• /
• v.54 no.1
• /
• pp.49-60
• /
• 2021

The Geumhwa Au-Ag deposit is located within the Cretaceous Gyeongsang basin. Mineral paragenesis can be divided into two stages (stage I and II) by major tectonic fracturing. Stage II is economically barren. Stage I, at which the precipitation of major ore minerals occurred, is further divided into three substages(early, middle and late) with paragenetic time based on minor fractures and discernible mineral assemblages: early substage, marked by deposition of pyrite with minor wolframite; middle substage, characterized by introduction of electrum and base-metal sulfides with Cu-As and/or Cu-Sb sulfosalts; late substage, marked by hematite and Bi-sulfosalts with secondary minerals. Changes in vein mineralogy reflect decreases in temperature and sulfur fugacity with a concomitant increase in oxygen fugacity. Fluid inclusion data indicate progressive decreases in temperature and salinity within each substage with increasing paragenetic time. During the early portion of stage I, high-temperature (≥410℃), high-salinity fluids (up to ≈44 equiv. wt. % NaCl) formed by condensation during decompression of a magmatic vapor phase. During waning of early substage, high-temperature, high-salinity fluids gave way to progressively cooler, more dilute fluids associated with main Au-Ag mineralization (middle) and finally to ≈180℃ and ≥0.7 equiv. wt. % NaCl fluids associated with hematite and sulfosalts (± secondary) mineralization (late substage). These trends are interpreted to indicate progressive mixing of high- and medium to low-salinity hydrothermal fluids with cooler, more dilute, oxidizing meteoric waters. The Geumhwa Au-Ag deposit may represent a vein-type system transitional between porphyry-type and epithermal-type.

• The Journal of Engineering Geology
• /
• v.30 no.4
• /
• pp.469-483
• /
• 2020

The results of long-term groundwater level and quality monitoring can be used not only as the basic data for evaluating the impact of various disasters including climate change and establishing responses, but also as key data for predicting and managing geological disasters such as earthquakes. Some countries use groundwater level and quality monitoring for researches to predict earthquakes and to assess the impacts of the earthquake disaster. However, a few cases in Korea report on individual groundwater quality factors (i.e., dissolved ions) observed before and after the earthquakes, being different from other countries. To establish the abnormality criteria for groundwater quality in Pohang, groundwater samples were collected and analyzed five times from 14 agricultural or private wells existing in Shingwang-myeon and Heunghae-eup. As a result of the analysis, it was found that Ca2+ was the dominant cation in Shingwang-myeon, while Na+ was the dominant cation in Heunghae-eup. The elevated NO3- concentration in Shingwang-myeon is contributed to the agricultural activity in the area. A high concentration of Fe was detected in a well on Heunghae-eup; the concentration exceeded the drinking water standard by nearly 100 times. Relatively higher dissolved ions were observed in the groundwater of Heunghae-eup, and it is considered as the result of the flow velocity difference and water-rock reaction accompanying the difference in bedrock and sediment characteristics. The groundwater of Shingwang-myeon appeared to be most affected by the weathering of granite and silicates, while that of Heunghae-eup was mainly affected by the weathering of silicates and carbonate. The background concentrations (baselines) of groundwater Shingwang-myeon and Heunghae-eup was identified through the survey; however, the continuous monitoring is required to monitor the possible changes and the repeatability of seasonal variation.