• 한국지구과학회:학술대회논문집
• /
• 2010.04a
• /
• pp.128-132
• /
• 2010

울릉분지 북동쪽 독도 주변 해역은 해수면 위의 작은 섬들과 해저에 큰 화산체로 구성된 독도와 해수면 아래 큰 규모의 해산 두 개(심흥택해산, 이사부해산)가 위치하고 있으며 그 중 해수면위로는 독도만 솟아 있다. 정밀해저면영상기(MS-1000)를 이용하여 큰 규모의 조사선으로 접근이 어려웠던 동도-서도 주변 연안에 대한 정밀해저면영상 조사를 2010년 1월에 소형조사선을 이용하여 수행하였다. 부두 동쪽 해안은 동도와 근접하고 있어 큰 규모의 돌출 암반이 많이 분포하고 있으며 부두 북쪽으로는 모래층의 연흔구조가 많이 나타나며 소규모의 암반 및 자갈들이 많이 분포하는 것으로 판단된다. 동도와 서도사이의 해저면영상을 분석해보면 동도 선착장부근으로는 모래퇴적물의 연흔구조가 많이 나타나고 동도와 서도 중앙부로 가면서 모래보다는 작은 자갈들이 많이 분포하며 서도쪽으로 가면서는 모래 및 자갈퇴적물이 암반구조로 이루어져있는 것으로 판단된다. 정밀해저면영상기(MS-1000)는 고정밀한 해저면영상을 획득할 수 있으며 불규칙한 지형으로 기존 장비가 접근하없어지며기 어려운 해저지형에도 사용하기 적합한 것으로 판단된다. 향후 항구 및 해안구조물 등과 같은 고정밀해저면영상이 필요한 분야에 활용성이 높을 것으로 생각되고 또한 유지/보수가 필요한 수중 군시설 및 부두시설에 대한 정밀조사를 통하여 효율적 관리 정보제공할 수 있을 것으로 판단된다.

• Korean Journal of Remote Sensing
• /
• v.26 no.2
• /
• pp.115-122
• /
• 2010

In this study, we analyzed ridge-runnel structure and ripple marks by using Envisat ASAR, JERS-1 SAR images and in-situ data in Mongsanpo intertidal flat located in Taean-Gun, Korea. A group of light-and-dark lines parallel to the shoreline, alternating 3-5 times, were observed in the intertidal flat in Envisat ASAR images. The patterns are related to ridge-runnel structure in the intertidal flat exposed to air. Well-drained runnels, typically with ripple marks, showed strong backscattering while runnels submerged by surface water or ridges, typically smooth with no ripple, have weak backscattering coefficients in Envisat ASAR images. In JERS-1 SAR images, however, the backscattering was very low on the entire intertidal flat and no ridge-runnel structure could be observed. The wavelengths of ripple marks measured from in-situ observations have ranges from 4 to 10 cm that satisfies the Bragg scattering condition of the 1st-order in Envisat ASAR images operating in C-band, but not in JERS-1 SAR that used L-band. Through this study using SAR images, we could successfully analyze the sedimentary conditions of intertidal flats with ridge-runnel and ripple marks which are not easily observed by optical sensors. It is expected that the results of this study with SAR images will contribute to the sedimentary research over intertidal flats.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.31 no.4
• /
• pp.209-220
• /
• 2019

Even though the scale of hard structures for beach stabilization should carefully be determined such that these structures do not interrupt the great yearly circulation process of beach sediment in which the self-healing ability of natural beach takes places, massive hard structures such as the submerged breakwater of wide-width are frequently deployed as the beach stabilization measures. On this rationale, asymmetric ripple mat by Irie et al. (1994) can be the alternatives for beach stabilization due to its small scale to replace the preferred submerged breaker of wide-width. The effectiveness of asymmetric ripple mat is determined by how effectively the vortices enforced at the contraction part of flow area over the mat traps the sediment moving toward the offshore by the run-down. In order to verify this hypothesis, we carry out the numerical simulations based on the Navier-Stokes equation and the physically-based morphology model. Numerical results show that the asymmetric ripple mat effectively capture the sediment by forced vortex enforced at the apex of asymmetric ripple mat, and bring these trapped sediments back to the beach, which has been regarded to be the driving mechanism of beach stabilization effect of asymmetric ripple mat.

• Korean Journal of Remote Sensing
• /
• v.40 no.3
• /
• pp.295-305
• /
• 2024

This study aims to analyze the micro-sedimentary structures of the Hwangdo tidal flats using ultra-high resolution unmanned aerial vehicle (UAV) data. Tidal flats, located in the transitional area between land and sea, constantly change due to tidal activities and provide a unique environment important for understanding sedimentary processes and environmental conditions. Traditional field observation methods are limited in spatial and temporal coverage, and existing satellite imagery does not provide sufficient resolution to study micro-sedimentary structures. To overcome these limitations, high-resolution images of the Hwangdo tidal flats in Chungcheongnam-do were acquired using UAVs. This area has experienced significant changes in its sedimentary environment due to coastal development projects such as sea wall construction. From May 17 to 18, 2022, sediment samples were collected from 91 points during field surveys and 25 in-situ points were intensively analyzed. UAV data with a spatial resolution of approximately 0.9 mm allowed identifying and extracting parameters related to micro-sedimentary structures. For mud cracks, the length of the major axis of the polygons was extracted, and the wavelength and ripple symmetry index were extracted for ripple marks. The results of the study showed that in areas with mud content above 80%, mud cracks formed at an average major axis length of 37.3 cm. In regions with sand content above 60%, ripples with an average wavelength of 8 cm and a ripple symmetry index of 2.0 were formed. This study demonstrated that micro-sedimentary structures of tidal flats can be effectively analyzed using ultra-high resolution UAV data without field surveys. This highlights the potential of UAV technology as an important tool in environmental monitoring and coastal management and shows its usefulness in the study of sedimentary structures. In addition, the results of this study are expected to serve as baseline data for more accurate sedimentary facies classification.

• 한국해양학회지
• /
• v.29 no.3
• /
• pp.239-247
• /
• 1994

Bedform morphology of the giant ripples have been studied on the continental shelf of the Yellow Sea, East China sea and Korea-Tsushima Strait on the basis of side-scan sonar image, sub-bottom profile, sedimentary facies, geomorphology evidence and hydrology. There are well developed giant ripples ranging from 100 to 500 m in wavelengths and from 2 to 10 m in wave height at nine sites in the study area, which are covered by medium to fine sand. Most of them have been formed under the present hydrologic regime where the tidal currents and local currents or turbulence flows are superimposed. In the study area, giant ripples are produced on two different environments. One is at the geomorphic narrow zone such as the Korea Strait where currents are accelerated by the topographic effects, while the other is the sandy flat plain where tidal currents and local currents are harmonized.

• The Korean Journal of Petroleum Geology
• /
• v.4 no.1_2 s.5
• /
• pp.12-19
• /
• 1996

Directional sedimentary structures (channel structure, cross stratification, and current ripple) were observed in fine to gravelly ye.y coarse sandstones of the Cretaceous Mayans Group (lljig, Hupyeongdong, and Jeomgok formations) in the northeastern part of Euiseong subbasin of Kyongsang basin, Southeast Korea. Large and small scale channel structures are common in all formations. Trough cross-stratification and channel structure frequently occur in the lljig formation (proximal fluvial deposit), whereas planar cross- stratification, cross lamination, and current ripple occur abundantly in the Hupyeongdong and Jeomgok formations (distal braided fluvial to marginal lacustrine deposits). The paleocurrent directions inferred from a statistical analysis of total 43 directional sedimentary structures show a mean azimuth of $290^{\circ}C$ with a standard deviation of $\pm68$. It suggests that the main flow of the paleocurrents moved toward the WNW direction and the source area of the sediments would be located somewhere in the ESE direction beyond the study area.

• Journal of the Korean earth science society
• /
• v.37 no.4
• /
• pp.218-229
• /
• 2016

The bedform stability diagram indicates the shape and size of bedforms that will occur to a given grain size and flow velocity. The diagram has been constructed from experimental data which have been mostly acquired by flume experiments. Generally, the flume experiments have been performed on well sorted sediments with unimodal grain size distribution, in order to understand relationship between grain size and flow velocity. According to the diagram, a ripple structure initiates to be formed from lower flow regime flat bed, as the flow velocity increases on the surface of fine-sand or medium-sand sediments. This study aims to verify that the experimental result of bedform stability diagram will be reproduced in our flume experimental systems, and also to confirm that the result is consistent not only on well-sorted sand sediments but also on poorly-sorted sand sediments with bimodal grain size distribution. The experimental results in this study show that initiation of 2D or 3D ripple structure on poorly-sorted sand sediments requires higher flow velocity and shear stress than those for initiation of the structure on well-sorted sand sediments. In general, carbonate sediments are characterized by poor sorting due to inactive hydraulic sorting and bimodal grain size distribution with allochems and matrices. The results suggest that the carbonate depositional system possibly need a higher flow velocity for initial formation of 2D or 3D bedform structures. The reason might be the fact that pulling off and lifting of a grain in poorly sorted sediments require more energy due to sorting, friction, stabilization, armour effects, and their complex interaction. This preliminary study warrants additional experiments under various conditions and more accurate analysis on the relationship between formation of bedforms and grain size distribution.

• Journal of the Korean earth science society
• /
• v.22 no.2
• /
• pp.120-129
• /
• 2001

A sand shoal (1300 m long and 400 m wide) with an orientation of north-south is formed on the lower tidal flat of Gomso Bay, southwestern coast of Korea. Surface bedforms, sedimentary structures, sedimentation rate, grain size distribution and can-corer sediments have been measured and analysed along the sand shoal proper zone B and its offshore zone A and onshore zone C during the period of 14 months. These three zones can be differentiated based on sedimentological characteristics: A zone - fine sand (3${\varphi}$ mean), linguoid-type ripples, 70 mm/month in sedimentation rate and no bioturbation, B zone - medium sand (2.5${\varphi}$ mean), dunes (4${\sim}$5 m in wavelength), 30 mm/month in sedimentation rate and no bioturbation, and C zone - coarse silt (5${\varphi}$ mean), sinuous-type ripples, 10 mm/month in sedimentation rate and well-developed bioturbation. These characteristics indicate that the zone C represents a relatively low-energy regime environment whereas the zone A corresponds to a relatively high-energy environment. The zone B would play an important role for a barrier to dissipate the approaching wave energy, resulting in maintaining of low-energy conditions in the inner part of Gomso-Bay intertidal flat behind.

• The Korean Journal of Quaternary Research
• /
• v.7 no.1
• /
• pp.93-101
• /
• 1993

A sedimentation study of the Cheonripo intertidal beach sands and its related coastal dune sands, Cheonripo, Seosan Gun, Choongcheong Namdo, Korea has been carried out based on a series of several summer time field surveys. Each subenvironment in the Cheonripo coastal zone, that is, intertidal sand beach and coastal sand dune, could be differenciated in terms of textural parameters. The coastal dune sands are finer than the intertidal beach sands in mean grain size, and the sorting of dune sands is relatively poorer than that of intertidal beach sands. However, the skewness of intertidal beach and dune sands is commonly positive. Such textural parameters are characteristically differentiated on scatter diagrams. A series of megaripple bedform observations for 6 tidal cycle periods(August 13, 14 and 15, 1990) are interpreted to find out migration pattern of bedforms and its related sand migration. Such migration natures are shown on the tables and figures.

• Korean Journal of Heritage: History & Science
• /
• v.47 no.2
• /
• pp.46-67
• /
• 2014

The Dinosaur track-bearing deposits recently found at Bangudae Petroglyph site in Ulju (National Treasure No. 285) have been studied in the aspects of sedimentology, paleoenvironments, and significance in natural history. The dinosaur tracks occur in the Daegu Formation (late Early Cretaceous), and over 80 footprints including 43 ornithopod footprints, 36 sauropod footprints, and 2 theropod footprints are preserved in this tracksite. The track-bearing deposits consist of irregularly interlaminated siltstone and mudstone, calcareous sandy to silty mudstone, thin-bedded tuffaceous sandstone, planar- to cross-laminated sandstone, and thin- to medium-bedded graded sandstone, and they are interpreted to be sheetflood deposits on an alluvial plain. Diverse types of ripples and mudcracks, rainprints, and invertebrate trace fossils are observed in these deposits, and the crest-lines of wave ripples do not show preferred orientation. Dinosaur footprints occur as true prints, underprints, overtracks, and casts on the bedding surfaces, and the orientation of trackways are scattered. It is interpreted that paleoclimatic condition of the track-bearing deposits were semiarid with alternation of wetting and drying periods, and that dinosaurs frequented small and shallow ponds during wetting periods and recorded their tracks on an alluvial plain. The frequent occurrence of dinosaur tracks in study area indicates that the Cretaceous deposits around Daegokcheon Stream are very useful sedimentological and paleontological records to understand the paleoecology and paleoenvironments during the dinosaur age in Korean Peninsula. Consequently the dinosaur track-bearing deposits around Daegokcheon Stream should be further studied in sedimentary geology and paleontology in order to enhance cultural heritage value of the Petroglyphs of Bangudae Terrace as the World Heritage.