• 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.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.

• Journal of Korea Water Resources Association
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• v.43 no.3
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• pp.265-273
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• 2010

This study proposed the method that can calculate discharge using hydraulic characteristics that can acquire easily-comparatively such as hydraulic radius, bed slope, depth to improve the stage-discharge curve equation considering only stage. Roughness coefficient n value and C value that hydraulic characteristics of rivers is reflected from Manning's equation and Chezy's equation using the measured data of the natural open channel in the report of Albert University estimated and calculated discharge on the basis of this. The method proposed in this study was calculated stunningly to measured discharge. And that compared with discharge by existent stage-discharge curve.

• Journal of Korea Water Resources Association
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• v.33 no.1
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• pp.39-50
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• 2000

Generally speaking, a hydrodynamic model needs a friction coefficient (Manning coefficient or Chezy coefficient) and eddy viscosity. For numerical solution the coefficients are usually determined by recursive calculations. The eddy viscosity in numerical model plays physical diffusion in flow and also acts as numerical viscosity. Hence its value has influence on the stability of numerical solution and for these reasons a consistent evaluation procedure is needed. By using records of stage and discharge in the downstream reach of the Han river, I-D models (HEC-2 and NETWORK) and 2-D model (SMS), estimated values of Manning coefficient and an empirical equation for eddy viscosity are presented. The computed results are verified through the recorded flow elevation data.n data.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.2B
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• pp.165-173
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• 2011

In this study, FESWMS FST2DH model was used to analyze the change of flow characteristics after making the riparian forest. The additional flow resistance is calculated based on the drag-force concept acting on each tree and the lateral momentum transfer between planted and non-planted zone could be satisfactorily reproduced by parabolic turbulence model in this depth-averaged 2-D numerical model. For model validation, the simulated velocities were compared with the measured data, showing good agreement in both tree density cases of experiments. The previous method using a proper Manning's n coefficient gives reasonable solutions only to evaluate the conveyance, but the calculated approach velocity at each tree was different from realistic value. The proposed procedure could be widely used to evaluate hydraulic effects of riparian trees in practical engineering.

• Ecology and Resilient Infrastructure
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• v.8 no.4
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• pp.212-222
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• 2021

In this study, the flow resistance coefficient was calculated considering the physical properties and distribution characteristics of floodplain vegetation, and the effect of floodplain vegetation distribution on flow characteristics was analyzed by reflecting it in a two-dimensional numerical simulation. The three-dimensional point clouds of vegetation acquired using ground lidar were analyzed to apply floodplain vegetation's physical properties to the existing formula for vegetation flow resistance calculation. The floodplain vegetation distribution in the modeling was divided into locally distributed and fully distributed conditions in the floodplain. As a result of the simulation of the study site, the flow resistance coefficient of floodplain vegetation was found to have a value of about five times or more compared to the flow resistance coefficient of the main channel bed when the design flood occurs based on Manning's n coefficient. Also, it affected the hydraulic characteristics in the main channel and floodplain.