• Proceedings of the Korea Water Resources Association Conference
• /
• 2012.05a
• /
• pp.558-558
• /
• 2012

다수의 자연 하천은 유사 이동과 하안의 침식으로 인하여 사행 하천이 발생한다. 사행 하천에서의 이차류는 원심력, 편수위로 발생하는 중력에 의한 압력차, 그리고 난류로 인하여 발생하는 응력으로 인하여 형성되며 나선형 구조 형태로 표면 유속은 외부로 향하고 하천 바닥의 유속은 안으로 향하게 된다. 이러한 2차류의 형성은 주 흐름의 특성을 변형시킨다. 자연하천에서 2차류는 주 흐름의 15-25%의 크기를 가지고 있으나, 하상의 변화, 유사의 이동 등과 연관되므로 2차류의 영향을 정확히 해석하는 것은 수리학적으로 매우 중요하다. 본 연구에서는 사행수로에서 발생하는 2차류 거동을 수치모의를 통하여 수행하였다. 우선 2차류의 분석을 위하여 실험을 통한 결과물을 비교하였다. 자연 하천의 특성을 반영할 수 있도록 서일원(2006)이 수행한 S-자 형태의 실험 수로의 실험 결과를 분석하였다. 수치 모의를 위하여 3차원 전산유체역학 프로그램을 사용하여 사행수로의 2차원 유속 구조를 모의할 수 있도록 하였다. FLOW-3D 프로그램을 이용하여 실험 결과와 모의 결과를 비교할 수 있도록 하였으며 비교 후 보정을 실시하였다. 모의는 주로 LES (Large Eddy Simulation) 모형을 통해 이루어졌으며, 이를 통하여 실험에서 획득한 결과와 비슷한 유속구조 분포를 확인할 수 있었다. 보정 및 검증 후 수치 모의를 통한 유속 데이터를 이용하여 민감도 분석을 실행하였다. 이후로는 수로의 만곡부, 조도, 수심 등 인공수로의 조건을 변경하여 수치 모의를 수행하였다. 보정된 결과를 이용하여 추가적인 모의를 통한 유속 분포 구조의 비교가 이루어졌다. 이를 통하여 각 조건이 이차류의 크기에 미치는 영향을 확인할 수 있었으며, 모의를 통한 유속분포 결과는 대체적으로 실험을 통한 이차류의 연직분포 구조와 일치하였다.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2022.05a
• /
• pp.230-230
• /
• 2022

최근 기후변화로 인해 예측이 어려운 국지성 호우가 빈번하게 발생하고 있다. 국지성 호우는 대량의 홍수를 일으켜 유송잡물을 동반한 흐름을 야기할 수 있다. 대량의 유송잡물이 하상에 퇴적되면 통수능을 저하시키기도 하며 식생효과와 마찬가지로 유목주변으로 유속이 증가하면서 세굴현상이 발생하게 되는데, 이는 하상저하를 일으키며 수공구조물의 안정성에 지속적으로 피해를 줄 수 있다. 기후변화는 또한 강우패턴을 변화시켜 식생의 성장과 활착에도 영향을 미치게 된다. 본 연구지역인 내성천 회룡포의 경우, 2015년 대가뭄 발생 이후 식생활착으로 인해 식생대 면적이 증가하고 잇는 상황이다. 이는 연구지역의 흐름과 사주교란 및 하상변동에도 큰 영향을 미칠 것으로 판단되며, 특히 식생의 증가는 유송잡물의 증가를 야기 할 수 있기 때문에 식생과 유송잡물의 영향이 하천에 미치는 영향을 예측하는 연구가 필요할 것으로 판단된다. 따라서 본 연구에서는 2차원 흐름모형인 Nays2D와 입자법기반의 유목동역학 모형을 활용하여 식생과 유송잡물이 하상변동에 미치는영향에 대한 수치실험을 수행하고 결과를 분석하였다. 여기서, 식생의 경우, 식생성장모형을 적용하여 시간에 따라 식생이 성장하여 항력이 증가하는 것으로 가정하였으며 유송잡물의 경우, 하상에 퇴적되는 유송잡물의 개수와 면적만큼 항력이 증가하는 것으로 가정하였다. 흐름의 경계 조건은 일반화된 부정류 수문곡선을 입력하였으며 초기 하도의 형상은 일정한 경사를 가지는 평지로 가정하여 부정류에 따라 하상변동이 발생하는 것으로 모의하였다. 시뮬레이션 결과, 유송잡물보다 식생대 번성이 하상변동에 상대적으로 큰 영향을 주는 것으로 나타났으며, 유송잡물의 경우 국부적으로 퇴적 분포되어 그 주변으로 침식을 일으키는 것으로 나타났다. 또한 유송잡물은 하안의 얕은수역에서 주로 퇴적되었다. 본 연구는 만곡부 하상변동에 대해 식생과 유송잡물을 고려하여 예측모의를 수행한 사례로서, 식생과 유송잡물이 흐름과 하상변동에 미치는 영향을 이해하는데 도움이 될 것으로 판단된다. 또한 이는 추후에 식생을 고려하는 하천관리방안을 수립 시, 식생과 유송잡물의 영향을 물리적으로 설명할 수 있는 근거자료로 제시할 수 있을 것으로 보인다.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.26 no.2B
• /
• pp.209-216
• /
• 2006

This study is to analyse the characteristics of bar migration, which is important roles to bank erosion and meandering development, for the meandering channels with erodible bed by using a 2-D numerical model in the generalized coordinate systems. The results of the numerical experiments showed that the features of bar migration were affected by the meandering wavelength to the width ratio, and had a relatively good agreement with the criterion for bar migration through a bend suggested by Kinoshita and Miwa (1974). The bar migrated with speed in the channel with long wavelength and broad width, and the criterion for bar migration was increased. The bar celerity was decreased abruptly near the criterion.

• Journal of the Korean association of regional geographers
• /
• v.3 no.1
• /
• pp.51-62
• /
• 1997

In various places of drainage basins of major rivers in South Korea are distributed intermontane basins. Basin floor covered with fluvial deposits carried from the surrounding mountane area becomes alluvial plain. Its productivity is comparatively higher than anywhere else. Thus basin is a local administrative, economic, and cultural core area. Intermontane basin consists of backward mountane area, gentle hills, and alluvial lowland. The purpose of this paper is to elucidate the morpogenetic processes and development age of Angae Basin located in the sedimentary rock region. Hills with the height of a.s.l. $80{\sim}100m$ distributed in Angae Basin are residual landforms, which are the remnants of dissection of the etchplain that results from the denudation of bedrock deeply weathered along tectolineaments under the warm and moist climate, and reflect lithological differentiation of bedrock. Those hills have been comparatively higher ridges since the initial stage of the original etchplain, and they have been immune from fluvial processes. The etchplain appeared as $80{\sim}100m$ hills. the high terrace distributed in upstream reach of Nakdong River drainage basin and the old meander-cut at Seoburi in Wicheon drainage basin, are formed at the same stage when riverbed of Wicheon Stream functioned as a local base level according as the fluvial system of Wichoen arrived at dynamic equilibrium.

• Journal of Korea Water Resources Association
• /
• v.51 no.1
• /
• pp.35-48
• /
• 2018

Groynes are installed generally to protect the riverside or the river bank from the erosion caused by water flows by controlling the flow direction and velocity in rivers. In the past, groynes were used to secure enough depth of water in canals. As there has been a growing interest in river restoration and the natural river maintenance since 2000, groynes are proposed as a major environmental hydraulic structure because the flow control and various river bed conditions around the groyne can contribute to habitat functions. Groynes are typically installed in a series. In designing groyne series, groyne spacing is an important factor because the flow changes in the main canal and the flow inside the groyne area occurs variably depending on the groyne spacing. This study provide information to determine the groyne spacing suitable for the purpose of the groyne by examining the flows that variably changes according to the groyne spacing and angle in the recirculation zone of the groyne field. In particular, the formation of vortex, the location of vortex core and the water flow near the river bank, all of which occur in the recirculation zone inside the groyne area, were mainly analyzed to examine the flow characteristics near the river bank that influences the safety of the river bank area. The results of the experiment will serve as important basic data to examine changes in the river bed inside the groyne area as well as the safety of river banks following the installation of groyne series.

• Ecology and Resilient Infrastructure
• /
• v.10 no.4
• /
• pp.97-106
• /
• 2023

This study analyzed morphological changes in the Singwangcheon and Naengcheon streams in Pohang caused by flooding due to Typhoon Hinnamnor. Analysis of the changes in river channel area from the past to recent times using aerial photos and drone-taken images showed that the river width had gradually decreased since the 1960s. However, after the flood, the river width increased again. Changes in the river cross-section before and after the flood show that a large amount of coarse sediment was deposited inside the river bend while the outer bank was eroded. The water levels calculated using HEC-RAS for the pre-flood cross-section based on the flood frequency discharges and estimated discharge from Oer Reservoir were significantly lower than the observed water level, which means that the cross-sectional change was not considered. The results of this study suggest that it is necessary to consider cross-sectional changes due to sediment transport when estimating the flood level of small and medium-sized mountain streams, and it is needed to investigate the geomorphic changes after floods.

• Journal of the Korean Geographical Society
• /
• v.42 no.3 s.120
• /
• pp.368-387
• /
• 2007

In order to explain geomorphological characteristics of the Korean Peninsula, it is necessary to understand the spatial distribution of tectonic movements and its causes. Even though geomorphological elements which might have been formed by tectonic movements(e.g. tilted overall landform, erosion surface, river terrace, marine terraces, etc.) have long been considered as main geomorphological research topics in Korea, the knowledge on the spatial distribution of tectonic movement is still limited. This research aims to identify the spatial distributions of tectonic movement via sequential analyses of Digital Elevation Model(DEM). This paper first developed a set of terrain analysis techniques derived from theoretical interrelationships between tectonic uplifts and landsurface denudation processes. The terrain analyses used in this research assume that elevations along major drainage basin divides might preserve original landsurfaces(psuedo-landsuface) that were formed by tectonic movement with relatively little influence by denudation processes. Psuedo-landsurfaces derived from a DEM show clear spatial distribution patterns with distinct directional alignments. Lines connecting psuedo-landsufaces in a certain direction are defined as psuedo-landsurface axes, which are again categorized into two groups: the first is uplift psuedo-landsurface axes that indicate the axis of landmass uplift; and the second is denudational psuedo-landsurface axes that cross step-shaped pusedo-landsurfaces formed via surface denudation. In total, 13 axes of pusedo-landsurface are identified in the Korean Peninsula, which show distinct direction, length, and relative uplift rate. Judging from the distribution of psudo-landsurfaces and their axes, it is concluded that the Korean Peninsula ran be divided into four tectonic regions, which are named as the Northern Tectonic Region, Center Tectonic Region, Southern Tectonic Region, and East Sea Tectonic Region, respectively. The Northern Tectonic Region had experienced a regional uplift centered at the Kaema plateau, and the rate of uplift gradually decreased toward southern, western and eastern directions. The Center Tectonic Region shows an arch-shaped uplift. Its uplift rate is the highest along the East Sea and the rate decreases towards the Yellow sea. The Southern Tectonic Region shows an asymmetric uplift centered a line connecting Dukyu and Jiri Mountains in the middle of the region. The eastern side of the Southern Regions shows higher uplift rate than that of the western side. The East Sea Tectonic Region includes south-eastern coastal area of the peninsula and Gilju-Myeongchun Jigudae, which shows relatively recent tectonic movements in Korea. Since this research visualizes the spatial heterogeneity of long-term tenonic movement in the Korean peninsula, this would provide valuable basic information on long-term and regional differences of geomorphological evolutionary processes and regional geomorphological differences of the Korean Peninsula.

• Journal of Korea Water Resources Association
• /
• v.47 no.5
• /
• pp.459-468
• /
• 2014

Groyne to control the direction and velocity of flow in rivers is generally installed for the purpose of protecting riverbanks or embankments from erosion caused by running water. In particular, as interest in river restoration and natural river improvement increases, groynes are proposed as a key hydraulic structure for local flow control and riparian habitat establishment. Groynes are installed mainly in groups rather than as individual structures. In case of groynes installed as a group, flow around the groynes change according to spacing in between the groynes. Therefore, groyne spacing is regarded as the most important factor in groyne design. This study aimed at examining changes of flows around and within the area of groynes that take place according to the spacing of groynes installed in order to propose the optimal spacing for upward groynes. To examine flow characteristics around groynes, this study looked at flows in main flow area and recirculation flow area separately. In main flow area, it examined the impact of flow velocity increasing as a result of conveyance reduction that is exerted on river bed stability in relation to changes in the maximum flow velocity according to installation spacing. As a factor causing impacts on scouring and sedimentation within the area of groynes, recirculation flow in the groyne area can lead problems concerning flow within the area and stability of embankment. As for recirculation area, an analysis was conducted on the scale of rotational flow and the flow around embankment that exerts impacts on stability of the embankment. In addition, a comparative analysis was carried with reference to changes of the central point of rotational flow that occur within the area of groynes. As a result of compositely examining the results, the appropriate installation spacing is proposed as min. four times-max. six times considering a decrease in flow velocity according to the installation of upward groynes, river bed stability and stability of embankments against counterflow within the area of groynes.