Sedimentary Environments after the Construction of Iwon seawall

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Transport Paths of Nearshore Surface Sediment on Coast of East Sea, Korea

모멘트 입도분석을 통해 구해진 퇴적물 입도조직변수(평균입도, 분급도 및 왜도)를 이용하여 동해 연안 사질 퇴적물 이동경향을 밝힐 수 있는 Gao and Collins (1992) 방법을 소개하였다. 그 결과로써 파랑에 기인한 연안류가 연안 퇴적물 이동에 관여하는 것으로 밝혀졌다. 동해 연안 표층퇴적물의 이동 경로를 제시할 수 있는 퇴적물 이동벡터가 제시되었으며, 실제 이를 반영하는 지형적인 형태로서 남대천 입구에 사취가 존재하는데 연안류에 의한 퇴적물 이동의 결과로 사취가 남쪽으로 길게 발달해 남대천과 바다와의 순환을 차단하는 결과를 가져왔다. 차후 이를 검증할만한 계절적인 조사와 수역학적인 관측이 보완되어야 할 것으로 생각된다.22Nothe

Sediment Characteristics in Gwangyang Bay and Adjacent Sea Area

남해 특별관리해역으로 지정되어 관리되고 있는 광양만 및 주변해역의 퇴적학적 특성을 밝히기 위해 표층퇴적물 시료를 채취하여 입도분석과 저서성유공충 분석을 하였다.2

Field applications of low-crested facilities for the control of sedimentary process

Although the dimension and layout of coastal artificial structures are optimized in many- sided viewpoints, the subsequent changes in the hydrodynamics and sedimentary processes may cause environmentally undesirable problems. In fact, for the past 30 years, due to the various development of large dimension, Korean coastal area has suffered from many environmental problems such as the destruction and reduction of tidal flat, retreat of coastline, siltation of navigation channels, etc. Thus effective policy and methods for sustainable and eco-friendly coastal management have been demanded since early 1990s. Relatively small-scaled low-crest facilities of eco-friendly materials may meet the demands. Three kinds of low-crested facilities, artificial seaweeds, timber fence and gabion groin, were constructed and their effects have being monitored. Artificial seaweeds were installed on Iwon tidal flat of Taean-gun in 2001 and Ganghwa tidal flat in 2004. A timber fence and gabion groin were constructed on Iwon tidal flat and Baeksajang beach of Anmyeondo, respectively.Tidal flats around the artificial seaweeds and timber fence at Iwon have shown seasonal characteristics. During winter season, erosion and coarsening occur due to high waves and wind-driven current, while deposition and fining during mild seasons. It indicates that enhancement of turbulent intensity due to the facilities plays a deposition-promoting role in mild season, while a erosion-promoting role. The low-crested gabion groin to trap the bed load have shown good performance. Judging from the data from various instruments, wind-driven currents cause relatively large transport of sediments.These field applications have shown that low-crested eco-friendly facilities can be effectively and economically used for coastal management. For their good performance, however, the dimension and layout should be properly decided based on the intensive field measurements of hydrodynamics, wind field as well2

On the Limitation of Turbidity Generation Unit

The method of the turbidity generation unit (TGU) of Naki (1978) is simple and useful in estimating the rate of release of sediment into the ambient waters caused by coastal development works. However, it oversimplifies the related phenomena, which results in the inconsistency of the TGUs even in the sites of similar conditions. An alternatively simple empirical relationship between the rate and current speed is provided based on the field measurements in a macotidal waterway with a vessel-mounted acoustic Doppler sensor system. Its power relationship seems to be more reasonable because bed erosion rate generally has been formulated as a function of the bed shear stress.2

Mass physical properties of surface sediments in the KODOS(KR5) area, northeast equatorial Pacific

Sea floor sediment have been extensively studied to understand the correlation of mass physical properties and sedimentological process in the Clarion-Clipperton fracture zone of northeast equatorial Pacific. Within the past twenty years sediment characters such as sediment types and ages, bioturbation, porewater nutrients, mineralogical and chemical compositions, and mass physical properties were broadly analyzed in the Korea deep ocean study (KODOS) area. However the geological and geophysical survey was recently concentrated on the KR5 block, formerly B2. The objective of this study is to show the textural parameters and mass physical properties of surface sediments intensively in the KR5 area.2

Seasonal Sedimentary Characteristics and Depositional Environments after the Construction of seawall onthe Iwon Macrotidal Flat

대조차 조간대에서 방조제 건설 후 발생하는 퇴적물의 분포특성과 퇴적환경의 계절적 변화를 파악하기 위해서 4계절을 대표하는 표층퇴적물을 채취, 분석하였으며, 4개의 측선에서 2년 동안 퇴적물과 퇴적률에 대한 조사가 병행되었다. 그 결과, 방조제를 축조함으로써 반폐쇄성 연안에서 개방형 연안으로 바뀐 이원조간대의 동측 조간대 지역은 개방형 연안에서 나타나는 일반적인 계절 변화, 즉 몬순 계절풍의 영향으로 여름에는 세립질 퇴적물이 퇴적되고 겨울에는 강한 북서계절풍에 의해서 세립질 퇴적물이 제거되는 계절 변화를 보인다. 또한 측선 경사도와 퇴적물 분포양상 등을 고려할 때, 북부지역은 조석보다는 파랑작용에 크게 영향을 받고, 남부지역은 파랑보다는 조석작용이 크게 영향을 미치고 있지만 강한 조류, 파랑 그리고 태풍 등에 의해서 시간이 지남에 따라서 조립화 현상을 보이고 있다. 반면 방조제 건설에 의해 새로운 형태로 변화된 서측 끝 지역은 조간대의 발달방향이 남동방향으로 향하고 있어 북서계절풍의 영향에서 보호되는 지역으로 동측 조간대에서 보여지는 계절변화 양상과는 약간 다르게 봄에 세립하고 불량한 분급을 그리고 여름에는 상대적으로 조립하고 양호한 분급을 나타낸다. 이는 방조제 건설에 따른 지형적 원인에 의한 것으로 판단되어진다. 따라서 연구지역의 세립질 퇴적물 이동은 방조제에 의해서 겨울철에 동측 조간대에서 방조제 서측 끝 지역으로 이동하고 다시 여름철에는 동측 조간대로 이동되어지는 시계방향의 순환현상이 진행되는 것으로 보인다. 방조제 건설 후 이원조간대 지역은 2년 동안 많은 변화를 보이고 있지만 이것은 변화과정 중인 것으로 보이고 계속적인 모니터링이 필요할 것으로 보인다. In order to elucidate seasonal sedimentary characteristics and depositional environment after construction of seawall on macrotidal flat, a seasonal observations of surface sediments (total 450) and sedimentation rates on 4 transects have been investigated for 2 years. The eastern area of Iwon tidal flat, has been changed from semi-closed coast to open coast by construction of seawall, shows general seasonal changes similar to characteristics of open coast type, which represented both fining and bad sorted distribution due to deposition of fine sediments under low energy condition in the summer, and relatively coarser and better sorted distribution because of erosion of fine sediments in the winter. In considering angles of transects, distribution patterns of surface sediments, the northern and southern parts of eastern tidal flat are dominantly influenced by wave and tidal effects, respectively. As time goes by, the eastern tidal flat shows coarsening-trend of surface sediments caused by direct effect of tidal current, were and typhoon. Meanwhile the western area of seawall, which has been re-formed by construction seawall, is sheltered from northwesterly seasonal wind. The seasonal change pattern of western area of seawall is slightly different from that of eastern tidal flat. Mean grain size and sorting of surface sediments during spring is finer and worse than those during summer. This seasonal change pattern maybe influenced by topographic effects caused from the construction of seawall. In consideration of all result, the transport of fine sediments in the study area, which is supplied to limited sediments, shows clockwise circulation pattern that fine sediments are transported from the eastern tidal flat to the western area of seawall because of blocking of seawall in the winter and are transported reversed direction the summer. As a result, many changes have been observed in the study area after construction of seawall; however, this change is still in progress and is expected to need continuous monitoring.22Nkc

A Study of Mass Physical Properties in Deep-sea Sediment From the Clarion-Clipperton Fracture Zone, Notheast Equatorial Pacific

Deep-sea surface sediments acquired by multiple corer from 59 stations in the Clarion-Clipperton fracture zone of the northeast equatorial Pacific, were examined to understand the correlation of mass physical properties and sedimentological processes. The seabed of the middle parts (8-12°N) in study area is mainly covered with biogenic siliceous sediment but also with pelagic red clays, especially in the northern parts (16-17°N). In the southern part (5-6°N) of which water depth is shallower than the carbonate compensation depth calcareous sediment prevail. It was found that mass physical properties such as grain size distribution, mean grain size, water content, specific grain density, wet bulk density, void ratio, and porosity of sediments were distinctly different according to their sediment types. These variations in mass physical properties of sediments are the combined results of the following factors: biogenic primary productivity of surface water, water depth, especially with respect to the carbonate compensation depth(CCD), sedimentation rate, input of wind-blown (eolian, lithogeneous) component, and the geochemical characteristics of the bottom water (for example, formation of authigenic clay minerals and dissolution of biogenic grains).2

An analytical solution of the time dependent profile of suspended sediment concentration

The time-dependent one-dimensional vertical (1DV) conservation equation of sediment has been solved analytically in a tidal sea region. The basic advection-diffusion equation assumes constant eddy diffusivity and settling velocity of sediment particles. No net flux condition is set at the sea surface, while one of two kinds of bottom boundary conditions can be prescribed according to the bed condition including the sediment type. Flux-type bottom boundary condition with erosion rate and depositional velocity has been applied to mud beds, while the condition of reference concentration to sand beds. The governing advection-diffusion equation has been first transformed to a simple diffusion equation and then solved using the Galerkin-eigenfunction method.2