• Title/Summary/Keyword: Bed sediment

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An Experiment on Flow Simulation Depending on Opening Configuration of Weir Using a Numerical Model (수치모형을 이용한 보의 개방구성에 따른 흐름모의 실험)

  • Kang, Tae Un;Jang, Chang-Lae
    • Ecology and Resilient Infrastructure
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    • v.7 no.3
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    • pp.218-226
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    • 2020
  • This study investigated that the numerical experiment for analysis on free overtopping flow by a weir of levee type, as the first stage of the development of a numerical technique for prediction methodology based on a numerical model. Using 2-dimensional flow models, Nays2DH, we conducted numerical simulations based on existing experimental data to compare and verify the models. We firstly discussed the numerical reproducibility for the discontinued flow by weir shape, and calibrated the computational flow through preprocessing of channel bed. Further, we carried out and compared the simulations for prediction on the overtopping flow by the number of weir gates. As a result of simulations, we found that the maximum flow velocity of downstream of weir increases when the number of weir gates increases under the same cross sectional area of flow. Through such results, this study could present basic data for hydraulic research to consider the water flow and sediment transport depending on weir operation in the future work.

Estimation of Ecological Instream Flow Considering the River Characteristics and Fish Habitat in the Downstream of Yongdam Reservoir (용담댐 하류의 어류서식처를 고려한 생태학적 유지유량 산정)

  • Jang, Chang-Lae;Shin, Jae-Ki
    • Korean Journal of Ecology and Environment
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    • v.42 no.3
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    • pp.374-381
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    • 2009
  • Ecological instream flow was quantitatively calculated based on the river characteristics and fish habitat in the downstream of Yongdam Reservoir. The river bed and width did not change from 1988 before the am construction to 2004 after the dam construction, but the bed sediment size was attenuated a little in 2004. According to result that investigate fishes, 4 family 11 species including Acheilognathus koreensis were collected. Among them, Zacceo koreanus of cyprinidae was dominant, and Coreoleuciscus splendidus did sub-dominant. The habitat suitability indexes were estimated for two fish species Zacco koreanus and Coreoleuciscus splendidus using Physical Habitat Simulation System (PHABSIM) considering the river characteristics. In Gamdong and Daeti sites, the optimal ecological flow for Z. koreanus and C. splendidus were $13.90\sim12.60\;m^3\;s^{-1}$ and $15.50\sim11.60\;m^3\;s^{-1}$, respectively. In contrast, the optimal flow for the two species in Bunam site were $7.00\;m^3\;s^{-1}$. The ecological instream flow in the downstream of Yongdam Reservoir was between normal and high flow rate.

Assessment of Channel Stability with Groynes (수제 설치에 의한 하도 안정성 평가)

  • Kim, Gi Jung;Jang, Chang-Lae;Lee, Kyung Su
    • Ecology and Resilient Infrastructure
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    • v.6 no.4
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    • pp.314-327
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    • 2019
  • This study investigates channel stabilities with groynes by developing the assessment of it and applying a 2-dimensional numerical model, which simulates flow and sediment transport with various flows in the channel. Evaluation inventories are composed of five items, which are width to depth ratio, sinuosity, bed slopes, velocities in the flow flied, Shields number with discharges and geomorphic characteristics in the study reach. The channel stability is evaluated by applying the evaluation indicators to the channel with and without groynes in the study reach between Dalseong-weir and Gangjeonggoryeong-weir in the Nakdong river. Width to depth ratio, sinuosity, and bed slopes, which are index of river characteristics, little affect the channel stability. However, velocities in the flow flied, and Shields number, which is dimensionless tractive, near the banks of the channel strongly affect the stability. The evaluation values of the stability in the channel on the left and right banks decrease as the number of groynes increase in both the left and right banks, which means that the bank stability increases with the groynes.

Flume Experiments on Channel Morphology at a Tributary Junction (하천 합류점의 하도형상에 관한 수로실험)

  • Taeho Kim
    • Journal of the Korean Geographical Society
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    • v.33 no.3
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    • pp.355-364
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    • 1998
  • Flume experiments are conducted to describe the channel morphology at a tributary junction and to examine the influence of channel arrangements and hydrologic conditions on the channel morphology. When flow momenta of two tributaries are equal, a receiving stream tends to align with an axis bisecting junction angle. It causes lateral migration of a receiving stream according to an initial channel arrangement. As a result, the post-fonfluent channel morphology varies with plan geometry of a confluence such as symmetry, transition and asymmetry. Bed scour is the most notable morphology within a junction site. Its shape is characterized by steep walls which are primarily influenced by junction angle. Key control of scour dimension is also junction angle. Although the principle of accordant junction has been undoubtedly accepted, discordance is commonly developed at model and natural stream confluences. Unit discharge ratio of confluent streams is the most crucial factor because both discharge and sediment concentration ratios have an effect on discordance at a junction.

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An Experimental Study on Depositional Properties of Cohesive Sediments in Masan Port (마산항 점착성 퇴적물의 퇴적특성에 대한 실험적 연구)

  • Yang, Su-Hyun;Kim, Nam Hun;Hwang, Kyu-Nam
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.27 no.6
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    • pp.434-442
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    • 2015
  • In this study, a series of deposition tests have been performed using an annular flume in order to estimate depositional parameter of natural sediments. The sediment of Masan Port has been collected for deposition tests, and total 18 deposition tests have been carried out on different bed shear stress respectively but with the same initial concentration. As the results, the minimum bed shear stress ${\tau}_{bmin}$, standard deviation ${\sigma}1$ and time scale parameter $({\tau}_b^*-1)_{50}$ are found to be $0.10N/m^2$, 0.54 and 0.87 respectively. Through comparing with results from previous studies for other sediments, the results of this study are shown to be good enough to verify.

Origin of Carbonate Flat Pebble Conglomerate of the Upper Cambrian Hwajǒl Formation, Chosǒn Supergroup, Korea (조선루층군(朝鮮累層群) 상부 캠브리아계(系) 화절층(花折層)에 협재(挾在)된 Carbonate Flat Pebble Conglomerate의 성인(成因))

  • Park, Byong-Kwon;Han, Sang-Joon
    • Economic and Environmental Geology
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    • v.18 no.2
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    • pp.177-184
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    • 1985
  • The carbonate flat pebble conglomerates (CFPC) are interbedded as lenticular bed in the greenish rhythmite of the upper part of $Hwaj{\check{o}}l$ Formation, $Jos{\check{o}}n$ Supergroup. Pebbles are composed mainly of lime-mudstone with small amounts of bioclasts and silt-sized subangular quartz grains. The matrix among pebbles is composed mainly of sparry calcite with relatively much amounts of bioclasts, silt-sized subangular quartz grains and authigenic pyrite crystals or grains. The sparry calcite of the matrix seems to be the results of neomorphism of skeletal sands and bioclasts. The pebbles are well rounded and no plastic deformations are found. Some pebbles show the outer rim of glauconite. CFPC are not associated with any other intertidal features such as stromatolites, flaser bedding and channel structures. Also any features indicative of subaerial exposure such as dessication cracks, fenestrae and so on are not found in the bed. The sedimentological features of CFPC suggest that the following conditions appear to have been necessary for the formation of CFPC : 1) episodic deposition of thin, permeable calcareous beds separated argillaceous beds; 2) preservation of these beds near the sediment-water interface where they could become rapidly cemented; 3) erosion and redeposition of the partially lithified beds by storms or other exceptional erosional events. Eventually storm erosion and redeposition together represent only one of several critical conditions in the genesis of CFPC. The CFPC are very common in Cambrian and lower Ordovician formations, and become very rare in the younger carbonate formations. The expansion of infauna after Ordovician Period eliminated the widespread potential for rapid submarine cementation which is one of the critical factors to form CFPC.

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Analysis of Hydraulic Characteristics Using SMS RMA2 and SED2D Model in the Downstream of Gyeongan-Cheon (SMS를 이용한 경안천 하류구간의 하천흐름 분석)

  • Hong, Seong-Min;Jung, In-Kyun;Lee, Joon-Woo;Kim, Seong-Joon
    • Journal of the Korean Association of Geographic Information Studies
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    • v.7 no.1
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    • pp.94-104
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    • 2004
  • The purpose of this study is to analyze various hydraulic characteristics using SMS (Surface Water Modeling System) RMA2 model. It is based on 2-D finite element method. River reaches (13.8km) from Gyeongan gauge station to the inlet of Paldang lake was selected. Finite element was made by RIMGIS Data, and the analysis of river-changes was operated by unsteady flow. The sediment concentration and bed change was simulated using SED2D model. This River's velocity was distributed that 0.05~3.85m/s and bed change was changed about 0.0003~0.0135m.

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A Study on the Behavior of Surface Settlement due to the Excavation of Twin TBM Tunnels in the Clay Grounds (점토지반에서 TBM 병렬터널 굴진 시 지표침하거동에 대한 연구)

  • You, Kwangho;Jung, Suntae
    • Journal of the Korean GEO-environmental Society
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    • v.20 no.2
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    • pp.29-40
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    • 2019
  • Mechanized constructions have been frequently increased in soft ground below sea bed or river bed, for urban tunnel construction, and for underpinning the lower part of major structures in order to construct a safer tunnel considering various risk factors during the tunnel construction. However, it is difficult to estimate the subsidence behavior of the ground surface due to excavation and needs to be easily predicted. Thus, in this study, when a twin tunnel is constructed in the soft ground, it is proposed a simpler equation relating to the settlement behavior and a corrected formula applicable to soft ground and large diameter shield tunnels based on the previously proposed theory by Peck (1969). For this purpose, it was analyzed to long-term measurement values such as the amount of maximum settlement, the subsidence range by ground conditions, and interference volume loss due to the parallel construction, etc. As a result, a equation was suggested to predict the amount of maximum settlement in the soft sediment clay ground where is located at the upper part of the excavation site. It is turned out that the proposed equation is more suitable for measurement data in Korea than Peck (1969)'s.

An Ecological Study on the Sand Dollar, Astriclypeus manni (VERRIL 1867), in Hamdock, Cheju Korea (제주도 함덕 연안에 서식하는 구멍연잎성게, Astriclypeus manni (VERRIL 1867)의 생태학적 특성에 관한 연구)

  • KANG DO-Hyung;CHOI Kwang-Sik;CHUNG Sang-Chul
    • Korean Journal of Fisheries and Aquatic Sciences
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    • v.32 no.3
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    • pp.345-352
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    • 1999
  • The sand dollar, Astriclypeus manni is commonly encountered on a subtidal sand bottom along the coast of Cheju Island. limited information has been reported on their ecology despite their natural abundance. This study reports ecology and an annual reproductive cycle of the sand dollars present at Hamdock, northern coast of Cheju Island. A. manni collected from Hamdock revealed that they are 80 to 200 mm in test diameter. Sediment Brain size analysis indicated that A. manni mostly occurs on medium (particle diameter of 500 $\mu$m) to very find sand (particle diameter of 125 $\mu$m), particularly on fine sand (particle diameter of 250 $\mu$m). Internal morphology and in situ observations on their feeding habit indicated that A. manni is a deposit feeder, feeding on organic debris contained in the sediment around its habitat. A. manni were more frequently observed near Zostrea marina bed where content of organic matter in the sediment is considered to be higher. Gonadal tissues of the male were yellow in color while female gonads appeared to be purple. Fully mature eggs, with a mean diameter of 381 $\mu$m, and sperm were observed from the histological slides of the sand dollars collected in late July to August, suggesting that A. manni spawn during July to August when water temperature reaches 20 to $25^{\circ}C$.

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Channel-forming discharge calculation and stable channel section evaluation for downstream reach of Yeongju dam in Naesung stream (내성천의 영주댐 하류 구간의 하도형성유량 산정 및 안정하도 단면 평가)

  • Jang, Eun-Kyung;Ahn, Myeonghui;Ji, Un
    • Journal of Korea Water Resources Association
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    • v.51 no.3
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    • pp.183-193
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    • 2018
  • Channel-forming discharge for downstream section of Yeongju dam in Naesung stream was calculated to analyze stable channel geometry. Determined channel-forming discharge was applied to design stable channel slope, depth, and base width at Yonghyeol station. Used data for channel-forming discharge and stable channel analysis were collected in downstream section of Yeongju dam in Naesung stream before the dam construction. Specified recurrence interval discharge, effective discharge, and bankfull discharge were analyzed and compared to decide final channel-forming discharge which was $260m^3/s$ of bankfull discharge. Stable channel analysis and design program was applied to predict stable channel section of width, depth, and slope with various sediment transport equations of Ackers and White, Brownlie, Engelund and Hansen, and Yang's equations. As a result, all equations of sediment transport produced milder slopes compared to current bed slope of 0.00177 and Ackers and White equation presented the most similar flow depth of current section with the design constraint of current channel width.