• Title/Summary/Keyword: gravel-bed river

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Calculation of Roughness Coefficient in Gravel-bed River with Observed Water Levels (실측 수위에 의한 자갈하천의 조도계수 산정)

  • Kim, Ji-Sung;Lee, Chan-Joo;Kim, Won
    • Journal of Korea Water Resources Association
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    • v.40 no.10
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    • pp.755-768
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    • 2007
  • The purpose of this study is to analyse the characteristics of Manning's roughness coefficient according to change of discharge by using observed data obtained from a stable gravel-bed river and to investigate the applicability of the relevant existing empirical methods to it. Observed water level and discharge data are used as input data for the USGS computer program NCALC model for calculation of the roughness coefficient. Calculated values are compared with roughness values which are estimated with four widely used methods. The results show that though the empirical methods are able to give similar roughness values only for flood flow, they seem to have rather high uncertainty because of necessity of subjective judgement and differences of resultant values. Roughness coefficients for normal-low flow cannot be estimated from the existing empirical formulae. Especially, using the Manning equation for calculating them should be careful as this provides a wide range of estimated values in normal-low flow. The relations between the roughness coefficient and characteristic size of bed materials are different from them in flood flow even though they have a close relations.

Sedimentary Environments, Geochemical Characteristics of Sediments and River waters, Hwasun-cheon (화순천의 퇴적환경 및 퇴적물과 하천수의 지구화학적 특성)

  • 오강호;고영구;김주용;김해경
    • Journal of Environmental Science International
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    • v.11 no.9
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    • pp.881-895
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    • 2002
  • Sediments and river waters form the channel of Hwasun-cheon were studied in sedimentological size and geochemical analyses of metallic elements for the purposes of identification of depositional environments and geochemical characteristics. The sizes of sediments are assigned to pebble to coarse sand in mean size and polymodal in distribution. And the sediments are poorly to very poorly sorted and positively skewed. According to the grain size distributions of the sediments, the Hwasun-cheon belongs to gravel-bed river on the basis of the grain size distribution of the sediments. The behaviors of metallic elements in the sediments mainly depend on not grain size distribution but the geology connected with geomorphological reliefs near the stream. Contamination indices(CI) of Zn, Cu and Pb are 2.83 to 6.96 with average 4.31 in the sediments. Hwasun-cheon is assigned to general stream type in accordance with water quality of physical factors and chemical characteristics by Piper's diagram. Though meaningful values of BOD, T-N, T-P were locally depicted near Masan-ri, Hwasun-eup and Jiseok-cheon areas, artificial metal concentration do not represent in the most area of the stream. Sediments and river water are considered that the relatively more or less high metallic contents in the stream are originated from coal mine and urban area.

Stable Channel Design for the Gravel-bed River Considering Design Constraints (설계구속인자를 고려한 자갈하상 하천의 안정하도 설계)

  • Ji, Un;Jang, Eun-Kyung
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.16 no.4
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    • pp.2860-2867
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    • 2015
  • Stable channel design is to determine the width, depth and slope for satisfying the condition that the upstream incoming sediment rate is equal to the sediment transport rate at the design channel. Therefore, the most sensitive variable when designing a stable channel is the selection of a sediment transport equation applied for the channel design. Especially if in the case of gravel beds the designer uses the equation developed by using the data of sand rivers, the calculation result of the stable channel section has large errors. In this study, the stable channel design has been applied to the gravel bed river using the previous stable channel design program with newly added the sediment transport equation for gravel beds; and the stable channel section considering design constraints has been produced by using the analytical method. As results, in the case of the application with the fixed width, the depth predicted by Ackers and White's equation was the shallowest and Meyer-Peter and $M\ddot{u}ller's$ equation was 0.8 m deeper than the current section of 2.4 m. In the case of the application with the fixed depth, the width predicted by Engelund and Hansen's equation was twice wider than the current section and by Meyer-Peter and $M\ddot{u}ller's$ equation was 20 m wider than the current section of 44 m.

Determination of Equivalent Roughness for Estimating Flow Resistance in Stabled Gravel-Bed River: I. Theory and Development of the Model

  • Park, Sang-Woo;Lee, Sin-Jae;Jang, Suk-Hwan
    • Journal of Environmental Science International
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    • v.17 no.11
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    • pp.1203-1210
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    • 2008
  • Flow resistance in a natural stream is caused by complex factors, such as the grains on the bed, vegetation, and bed-form, reach profile. Flow resistance in a generally stable gravel bed stream is due to protrudent grains from bed. Therefore, the flow resistance can be calculated by equivalent roughness in gravel bed stream, but estimation of equivalent roughness is difficult because nonuniform size and irregular arrangement of distributed grain on natural stream bed. In previous study, equivalent roughness is empirically estimated using characteristic grain size. However, application of empirical equation have uncertainty in stream that stream bed characteristic differs. In this study, we developed a model using an analytical method considering grain diameter distribution characteristics of grains on the bed and also taking into account flow resistance acting on each grain. Also, the model consider the protrusion height of grain.

Determination of Equivalent Roughness for Estimating Flow Resistance in Stabled Gravel-Bed River: II. Review of Model Applicability

  • Park, Sang-Woo;Lee, Sin-Jae;Jang, Suk-Hwan
    • Journal of Environmental Science International
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    • v.17 no.11
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    • pp.1211-1220
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    • 2008
  • In this study, we estimated, the equivalent roughness using an estimation model, which considered grain distribution on the bed and the protrusion height of the grains. We also reviewed the appropriateness of the estimated equivalent roughness at the Goksung and Gurey station in the Seomjin River. To review the appropriateness of this model, we presented the water level-discharge relation curve applying the equivalent roughness to the flow model and compared and reviewed it to observed data. Also, we compared and reviewed the observed data by estimating the Manning coefficient n, the Chezy coefficient C, and the Darcy-Weisbach friction coefficient f by the equivalent roughness. The calculation results of the RMSE showed within 5% error range in comparison with observed value. Therefore the estimated equivalent roughness values by the model could be proved appropriate.

Experimental Study on the Shearing and Crushing Characteristics of Subaqueous Gravels in Gravel Bed River (수중 자갈의 전단 및 파쇄 특성에 관한 실험적 연구)

  • Kim, So-Ra;Jeong, Sueng-Won;Lee, Gwang-Soo;Yoo, Dong-Geun
    • Journal of the Korean earth science society
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    • v.42 no.2
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    • pp.164-174
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    • 2021
  • The study examines the shearing and crushing characteristics of land-derived subaqueous granular materials in a gravel-bed river. A series of large-sized ring shear tests were performed to examine the effect of shear time and shear velocity on the shear stress characteristics of aquarium gravels with a 6-mm mean grain size. Three different shear velocities (i.e., 0.01, 0.1, and 1 mm/sec) were applied to measure the shear stress under the drained (long-term shearing) and undrained (short-term shearing) conditions. Different initial shear velocities, i.e., 0.01→0.1→1 mm/sec and 0.1→0.01→1 mm/sec, were considered in this study. The test results show that the grain crushing effect is significant regardless of drainage conditions. The shear stress of coarse-grained materials is influenced by initial shear velocities, regardless of the drainage conditions. In particular, particle breakage increases as grain size increases. The shearing time and initial shear velocity are the primary influencing factors determining the shear stress of gravels. The granular materials may be broken easily into particles through frictional resistance, such as abrasion, interlocking and fracture due to the particle-particle interaction, resulting in the high mobility of granular materials in a subaqueous environment.

Bar Development in Gravel-bed River (자갈하상하천의 bar지형 발달에 관한 연구 -골지천을 사례로-)

  • Yang, Hee-Kyung
    • Journal of the Korean Geographical Society
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    • v.32 no.4
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    • pp.435-444
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    • 1997
  • Bars in a river bed show the flow of the river, the shape of a river bar can be easily measured in any river. The purpose of this study is to research the morphological characteristics of river bars. The case study area is the lower Golgi River, six bars were examined. All six bars are gravel bars with a grain size in excess of 2 millimeters. Four of the bars are longitudinal bars, in which the direction of the bar follows the river current. After analyzing the gravel in the bars, it was determined that as the gravel flows down the river, gravel grain size decreases while grain roundness increases. The shape of bar varies locally according to flow regime, channel slope, and w/d ratio.

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Analysis of Roughness Coefficient in Gravel-bed Rivers (자갈하천의 조도계수 특성 분석)

  • Lee, Chan Joo;Kim, Yong Jeon;Kim, Ji Sung;Kim, Won
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.30 no.2B
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    • pp.149-157
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    • 2010
  • The purpose of this study is to analyse characteristics of roughness coefficient based on bed-material size of the gravel-bed rivers using field data obtained from nine domestic rivers. Roughness coefficient is calculated using Manning's equation. Roughness coefficient decreases with increasing discharge, but above a certain discharge, it tends to be constant. Similarly, roughness coefficient shows reverse relationship with relative smoothness (R/D). The regression equation adopting theoretically derived value of 2.03 as log coefficient indicates close similarity with the previous equation proposed by Limerinos (1970). Roughness coefficient values converged above certain discharges lie in the range from 0.024 to 0.045. From them, empirical equations based only on bed-material size are derived and compared with those suggested by the previous studies.

Estimation methods of maximum scour depth in steep gravel-bed bend channel (급경사 자갈하상 만곡수로의 최대세굴심 산정공식 평가)

  • Cho, Jaewoong;Nam, A-Reum;Woo, Tae Young;Park, Sang Deog
    • Journal of Korea Water Resources Association
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    • v.49 no.6
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    • pp.529-536
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    • 2016
  • The existing methods to estimate the maximum scour depth in the bend of steep gravel bed channel have been evaluated by the hydraulic movable-bed experiments. In the $90^{\circ}$ bend steep-slope channel paved with the fluvial gravels which are uniform in size and have a mean diameter of 43mm, the maximum scour depths due to the flow discharge and the gradient of bed slope have been investigated and compared with the scour depth computed from the equations. The local scour has occurred in conditions that the bed slope is steeper than 0.02 and the $F_r$ is greater than 0.95. Except Lacey's equation and Zeller's equation, the existing methods computing the maximum scour depth overestimate the maximum scour depth in the steep channel with the very coarse gravel bed. However, Lacey's equation with the bed material size and Zeller's equation considering the approach channel gradient and the bend angle may be relatively used to estimate the scour depth in bend of the steep gravel-bed river.

Estimation of Bed Resistance in Gravel-bed Rivers Using the Equivalent Roughness Height (등가조고를 이용한 자갈하천의 하상저항 산정)

  • Kim, Ji-Sung;Kim, Yong-Jeon;Lee, Chan-Joo;Kim, Won
    • Journal of Korea Water Resources Association
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    • v.42 no.8
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    • pp.619-629
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    • 2009
  • The objective of this study is to estimate bed-resistance in gravel-bed rivers using the equivalent roughness height($k_s$). We calculated the friction factor(f) with the measured data from 8 domestic gravel-bed rivers and investigated the size distributions of the bed materials. The averaged $k_s$ in each cross-section, which is determined under the hypothesis that the vertical velocity distribution follows the logarithmic law, is compared with the reach $k_s$ which is calculated with the cumulative grain diameter distribution curve of bed materials. Moreover, the applicability of existing formulae, such as Strickler type equations, is examined by comparing with Manning's n value converted from the $k_s$. According to the results, the reach $k_s$ proves to be a good indicator of representative characteristic of bed materials in a reach, and the Manning's n based on the reach $k_s$ is appropriate for practical estimation of the bed-resistance, for RMS errors between calculated and measured Manning's n is less than 0.003. The correlation between the $k_s$ and specified bed-material size($D_i$) is very low, so it is difficult to select a proper one among the existing empirical equations.