• Journal of Korea Water Resources Association
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• v.48 no.11
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• pp.879-889
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• 2015

The pattern of headward erosion at tributary and the separation zone formation in a loosed bed at confluence according to the confluence angle, discharge ratio, and dredging depth ratio have been analyzed. The separation zone is defined the inside of zero velocity boundary at downstream of confluence. The limit of separation zone occurrence is presented with dredging depth ratio. The propagation length of knickpoint increases as the confluence angle, discharge ratio, and dredging depth ratio increase in general and its regression equation has been suggested. The length and width ratios of separation zone in a loosed bed increase as discharge ratio and confluence angle increase as well as in a fixed bed. The length ratio decreases and the width ratio increases as dredging depth ratio increases results in great increase of shape factor and backwater rise by the conveyance reduction at confluence. The regression equation of shape factor with confluence angle, discharge ratio, and dredging depth ratio has been suggested.

• Journal of the Korean Geographical Society
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• v.49 no.6
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• pp.795-811
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• 2014

Stream piracy is one of the dynamic geomorphic processes in the mountainous area. If many stream piracies were concentrated in a certain region, the concentrated distribution of those might reflects the geological structure and tectonic movements of that region. In this study, the stream piracies identified in the lower areas between the Chiri and the Deokyoo mountainous areas were analyzed in relation with the tectonic line from Kwangju to Pohang and the so-called Hansan Mountains. The stream piracy at the Subunchi occurred between the lower-altitude, higher-gradient upper reach of the Seomjin-River flowing on the lower-level basin and the higher-altitude, lower-gradient upper reach of the Geum-River flowing on the higher-level basin. The geomorphic evidences concerning the stream piracy and the human responses to the headward erosion might be found in the vicinity of stream piracy site. Together with the Deunbongsaem(the source fountain of Geum-River), the Subunchi at which the geomorphic processes of stream piracy could be identified in a small area will be a good site for the geography education as well as the geo-tourism.

• Journal of the Korean association of regional geographers
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• v.11 no.4
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• pp.453-462
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• 2005

The study deals with surface erosion patterns due to the development of cropland toward hillslope and hilltop in the Oncheon-gun, pyeongbuk province and Nampo city of west coast area in the North Korea, using Quick Bird satellite images with 60cm resolution. In North Korea, for national economic difficult after 1980 year, newly developed croplands have been along the gentle hillslope, in which it is possible for individual man power different from the tideland which needs large scaled man-power and equipment. The new croplands are named Darakbat(terraced farm with embankment) and Bitalbat(titled farm developed on the original hill slope), neighboring with orchard and grouped settlement in lower valley. For supplying agricultural water, irrigation ditches and temporal crop storages have been constructed, connecting Darakbat, Bitalbat and orchard. These cropland developments have caused surface erosion composed of 3 types such as pit, linear and headward erosion, together with rill and gully. Owing to poor management of cropland and irrigation system, topsoil erosion and, collapse and sedimentation of ditch and pool, caused the decrease of agricultural productivity. These analysis using Quick Bird images can suggest original raw data about geographical facts on North Korea agriculture and help to recover their agricultural system and plan future national unified land.

• Journal of the Korean Geographical Society
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• v.39 no.6 s.105
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• pp.833-844
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• 2004

In Chugaryeong rift valley, lava plateau formation by the fissure eruption had vanished original landforms and effected on drainage derangement and revision. 4 rivers including Namdae-cheon, Bukhan-gang, Imjin-gang and Hantan-gang watersheds have shared Cheolwon-Pyeonggang lava plateau, that is, ownerless watershed. Main agency of the dividing process are central-eruption volcanic peaks such as Orisan(453m) and 680 Peak. Especially, Orisan has played the role of divide point for 4 watersheds. In the lower-relief plateau zone, complex drainage system have caused continually river capture between neighboring watersheds. In more elevated range slope, river capture have proceeded to headward erosion. Hydrogeomorphologically, lava-filled valley has initiated decrease of the original size of flood plain, maybe, causing higher capability of inundation by heavy rains, and then more active dissection of lava plateau layer.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.259-259
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• 2018

최근 우리나라는 기후변화에 따른 태풍발생빈도 증가 및 이상강우, 유역내 토지이용의 고도화로 인한 유역특성 변화로 유역내 홍수량은 증가하고 홍수 도달시간이 짧아지는 양상을 보이고 있다. 이로 인해 홍수에 따른 치수방어 대책으로 하천의 제방축조 및 보강방법이 주로 채택되었으나, 최근에는 홍수시 직접적인 하천내 수위 저감을 위한 방안으로 하도내 저류효과를 확대하기 위한 보 설치 및 하도정비를 통한 하도준설을 시행하고 있다. 그러나 본류 하상저하에 따른 지류하천의 하상변동(두부침식)으로 하도내 세굴 침식에 의한 하천시설물 피해 사례가 늘게 되면서 과거 홍수에 의한 제방월류 피해에서 하상변동에 의한 하천시설물 붕괴로 하천피해 양상이 바뀌게 되었다. 이와 같은 피해를 방지하기 위해 지류하천 합류부에 하상변동 방지책으로 하상유지공을 설치하고 있지만 국내에는 이와 관련된 구체적 설계기준 및 연구가 미비하여 일선에서는 아직도 하천구조물의 용도가 다른 보나 낙차공의 설계기준을 준용하는 등 하상유지공 용도에 특성화된 설계기준(최적 위치선정 및 형식 등)이 없는 실정이다. 본 연구에서는 감천(낙동강 지류하천)유역내 하도준설 및 홍수로 인한 하상유지공의 유실에 따른 지류하천의 피해사례를 통해 수치해석결과 및 실측자료를 바탕으로 하상유지공 계획의 중요성을 검증하고자 하였다. 또한 하도준설로 생성된 지류합류부의 단차구간에 안정성을 확보한 최적의 하상유지공 위치 및 형식 등을 선정 검토하고 설치 유 무에 따른 유수흐름 및 하상변화양상을 비교 분석하였다. 본 연구의 결과를 토대로 향후 하도굴착 및 하상유지공 계획시 고려해야할 사항(지형현황 및 수리특성 등)을 인지하고 극한상황에서도 안전한 하상유지공의 위치 및 형식 등을 선정하는데 활용 가능할 것으로 판단된다.

• Journal of the Korean Society of Safety
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• v.32 no.4
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• pp.46-52
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• 2017

Sediment exchange in river has been affected by artificial changes such as dredging and abnormal climate changes like intense rainfall. Over last decades in Korea, there were many constructions, restoration or rehabilitation in rivers. Therefore, deposition and erosion become more actively occurred than before, which may threaten the river safety such as flood defense. For safety's sake, the dredging of river bed, which is considered as the most typical measure, has been increased to extend hydraulic conveyance compared with previous conditions. However, since it might change the sediment mechanism, there would be another risk at which unexpected side effects such as headward erosion could be occurred. Particularly, sedimentation at abrupt expansion region is able to lead to hydraulic characteristics like water elevation in the upstream region in the beginning of dredging, which, however, has been barely studied in this field. Therefore in this study, the relationship between sediment mechanism at dredging section and hydraulic characteristics in upstream region were presented through numerical simulations in the idealized abruptly widen channel using Delft3D. The ideal channel of 2,000 m length with each side angle of 45 degrees at abruptly widen expansion region was employed to consider the sediment angle of repose. The sensitivity analysis was performed on the dimensionless factors consisted of upstream and downstream depths($h_u$, $h_d$), width($w_u$, $w_d$), water level(H), flow rate(Q) and discharge of sediment($Q_s$). And the sedimentation amount at dredging and the upstream hydraulic characteristics were investigated through that analysis. It showed that $h_d/h_u$, $H/h_u$ and $w_d/w_u$ were more influential in sequence of effect on sedimentation amount, while $h_d/h_u$, $w_d/w_u$ and $H/h_u$ on upstream region. It means that $h_d/h_u$ was revealed as the most significant factors on sedimentation, also it would most highly affect the rising of water level upstream.

• Journal of the Korean association of regional geographers
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• v.7 no.2
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• pp.71-81
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• 2001

According to the change of stream power/resisting power relationship due to the crustal movement or the climatic change, most channel landforms which reflect the equilibrium state of fluvial system are eroded and a part of them is remained as a river terrace. In many rivers in Korea are extensively distributed the relatively younger low river terraces. But their accurate formation mechanism is not known. In this paper, the formation processes and the dating of low river terraces distributed in Nakdong River basin will be investigated. Stream power of the downward erosion was revived because the sea level fell down. So stream power was superior to the resisting power under the cool-wet climatic condition during the last glacial period. Thus the river bed was excavated deeply, so that low river terraces were built up. And many incised meander loops were cut during this period. But, when fluvial system did not have equilibrium over all reaches, the last glacial period ended and the sea level initiated to rise rapidly. The headward erosion from the fall of sea level during the last glacial period had kept up to Hagye Fall because of the cutting of incised meander loops. Deeply excavated valleys and abandoned channel of cut-meander in lower reaches of a stream were filled with sediments. Thus the longitudinal profile of the uppermost reaches reflect the last interglacial, the upper reaches the last glacial, and the middle/1ower reaches recent fluvial system. Therefore low river terraces have been formed since the last glacial period.