• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.324-328
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• 2005

This study is to figure out uncertainty relationship between input data and calibrated parameter on unsteady hydraulic routing model. The uncertainty would be present to model results as a variant water surface profile along the channel. Firstly, Manning's n is calibrated through the model with assumed uncertainty on input hydrograph. Then, spatially distributed n-values sets based on the calibrated n values are used to get water profile of each n-values set. The results show that ${\pm}0.002$ of error in Manning's n cause ${\pm}30cm$ of maximum water surface differences at the Sumjin river.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.6
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• pp.1560-1565
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• 2007

In this study, Chiu's velocity distribution equation recently developed from the probability and entropy concepts is used to establish a linkage between the mean velocity obtained from the Manning's equation and the corresponding velocity distribution in a channel cross section. The linkage to be established enables computing the velocity distribution along with the mean velocity, from simple hydraulic data such as Manning's n, hydraulic radius and channel slope irrespective of including sediment or not.

• 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.

• Proceedings of the KAIS Fall Conference
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• 2007.11a
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• pp.113-115
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• 2007

본 연구에서는 Norman Herrick Brooks의 박사논문(1954)에서 심층적으로 시행한 실험실 실측자료를 사용하여 Manning과 Chiu의 연결고리로 제시한 F(M)과 Manning의 n, R(동수반경), I(수로경사)와 같은 아주 간단한 입력자료 만을 가지고도, 수로수직단면의 전체유속분포를 잘 표현할 수 있으며, 동시에 그동안 취득하기 어려운 최대유속($U_{max}$)도 실측하지 않고 손쉽게 산정할 수 있음을 증명하였다.

• Journal of the Korean association of regional geographers
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• v.16 no.2
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• pp.100-109
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• 2010

The study examines two different sites to analyze the difference of stream channel profile between two different landuse areas on Neponset River, Boston, MA. Landuse represents the current status of land in terms of human, agricultural or forest, industry and environmental activity types. According to the previous research, forest and urban area are significantly distinguished in chemical characteristic, shape and bed load of the stream. On the chosen sites, I look at the cross-section profile, the slope, velocity, and roughness of the channels. With the data collected at the site I determined the value for the channel bed material using Manning's equation, and compared with the result of HEC-RAS model with the cross-section profile data I measured. In the forest area, water surface elevation and bed material obtained through Manning's equation are very close to HEC-RAS model result. However, in the resident area the Manning's 'n' value calculated much higher than assumption which was considered as cobble whose 'n' value is 0.03-0.06. The difference could be caused by unusual steep elevation on the site and the dam present down further. With the steep elevation upside of dam, there is critical-depth condition occurs. The difference of Manning's 'n' value reflects the difference of depth. HEC-RAS model was run to analyze the difference and the result shows that depth is 0.36 much less than 0.688 what I computed when the Manning's n value is 0.03(cobble) instead of the result of the study (0.13292). Beside, dam is a major source of fragmentation and degradation of stream, and it's possibly inferred upstream water levels are increased and stream velocity is decreased. This study is meaningful for introduction of HEC-RAS in geography field to analyze different sites with channel bed material, and it is going to be used more actively to manage river and river side.

• Journal of Korea Water Resources Association
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• v.45 no.2
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• pp.137-149
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• 2012

Field measurements of resistance to flow are analyzed for 739 rivers vegetated with grass (281 channels), shrubs (150 channels) and trees (308 channels). The measured distribution of Manning roughness coefficients ranges from 0.015~0.250 for grass, 0.016~0.250 for shrubs, 0.018~0.310 for trees. Significant trends are obtained between Darcy-Weisbach (or Manning roughness coefficients) and flow discharge, friction slope, and relative submergence. The regression equations for Darcy-Weisbach and Manning roughness coefficients in vegetated rivers are: $f_{veg}=0.436Q^{-0.363}$, $f_{veg}=3.305S_f^{0.508}$, and $n_{veg}=0.061Q^{-0.124}$, $n_{veg}=0.144S_f^{0.199}$, $V=5.3(h/d_{50})^{1/8.3}{\sqrt{ghS_f}}$, $\sqrt{8/f}(=V/u*)=5.75log(5h/d_{50})$, respectively. These semi-empirical relationships should be useful for hydraulic engineering practice.

• Journal of Korea Water Resources Association
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• v.46 no.12
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• pp.1209-1220
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• 2013

Roughness coefficients calibrated by flow modeling using the 1-dimensional numerical model were analyzed for the downstream section of Naesung Stream in this study. Also, the bedform configuration at the Hyangseok Station was predicted for measured and simulated hydraulic conditions of flows and total flow roughness was estimated with the coefficient of grain roughness. The Manning's n coefficients calibrated by numerical modeling and estimated by considering of grain and bedform roughness were compared and examined. As a result, the Manning's n by numerical modeling was greater than the coefficient range estimated by grain and bedform roughness at the low flow regime due to the other factors such as vegetation, sinuosity, and sand bar. However, the Manning's n by numerical modeling was included in the coefficient range by grain and bedform roughness at the transition and high flow regime over $500m^3/s$ of flow discharge.

• 한국방재학회:학술대회논문집
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• 2010.02a
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• pp.96.1-96.1
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• 2010

하천의 설계홍수위를 결정할 때 가장 중요한 변수중의 하나는 우리가 흔히 부르는 Manning의 조도계수 n으로 과거 수십 년 동안 국내 외에서 많은 연구가 진행되어 왔고 현재에도 끊임없이 여러 연구자들의 관심의 대상이 되고 있다. 이러한 조도계수는 보통 부등류 모형에 의한 방법, NCALC 모형에 의한 방법, 하상재료 또는 사진 index를 통한 방법을 사용하고 있지만 일관성이 떨어질 뿐만 아니라 산정된 조도계수가 유량 또는 수위에 관계없이 일정한 조도계수 만을 제시하고 있다는 문제점을 가지고 있다. 이러한 문제점 등을 해결하고자 부정류 수치모형을 이용하여 하천 구간에서의 조도계수를 유량의 함수로 산정하는 연구가 활발히 진행되어 왔다. 본 연구에서는 이러한 조도계수의 여러 특성을 파악하고자 국내 주요 하천인 한강, 낙동강, 금강의 본류 및 지류에 대해서 수위관측소를 기준으로 구간을 구분하고 과거 주요 홍수 수문곡선을 선정하고 부정류 해석을 통하여 다양한 유량에 대한 하천 구간별 조도계수를 산정하였다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.6
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• pp.532-539
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• 2008

Kwon et al.(2008) carried out a hydraulic experiment in order to evaluate Manning coefficient, which implicates flow resistance due to bottom friction as well as drag caused by the squared piers higher than water depth and arranged with equal intervals, under the flow condition with a constant drag coefficient, $Re>10^4$. And, based on the equation of equilibrium, they proposed a formula for the equivalent resistant coefficient including empirical drag interaction coefficient obtained by using the experimental results. In this study, the hydraulic experiment was simulated using FLOW-3D, a 3-dimensional computational fluid dynamic code. The computations were compared with the experiment results as well as the semi-theoretical formula, and the comparisons show a good agreement. From the agreement, it was confirmed that when flow resistance bodies were higher than water depth, Manning n value increases with 2/3 power of water depth as shown in the theoretical formula and that drag interaction coefficient was dominated by their intervals.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.1775-1780
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• 2009

개수로 마찰흐름 특성에 관한 연구로서 유량조사사업단(2006)의 우리나라 3대강 유역 하천 관측자료와 Jarrett(1984)의 미국 Colorado지역 하천의 관측자료로 부터 흐름특성을 구분하여 개수로 흐름의 마찰특성 또는 조도계수의 변이특성을 분석하였다. 기존 지수형 완난류 마찰계수 산정식(유동훈과 이민호,1997)의 비례상수 $\alpha$에 조도계수 n을 도입하여 실무에서 보다 편하게 적용할 수 있는 새로운 산정식을 개발하였다. 유량조사사업단의 관측자료 분석에 있어서 유량 관측시 관측지점의 수면경사 및 하상경사의 미관측으로 하천정비기본계획상에 제시된 지형으로부터 관측지점의 하상경사를 추정하였으며 1차적으로 에너지경사는 하상경사와 동일하다고 가정하였다. 이러한 가정하에 하천정비기본계획상에 제시된 Manning의 조도계수를 인용하여 관측유속과 계산유속을 비교8 분석하였다. 또한 전통적 산정식인 Ganguillet & Kutter(1869)식과 Manning(1889)식으로 부터 산정된 유속과의 비교를 통하여 조도계수 n을 추정하였고 추정된n을 도입하여 새로 개발된 지수형 마찰계수 산정식의 적용성을 입증하였을 뿐만 아니라 기존 조도계수 산정의 문제점을 제시하였다.