• Water Engineering Research
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• v.6 no.3
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• pp.123-130
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• 2005

A good understanding of the interaction between flow, vegetation, and sediment is required for successful river restoration and sustainable flood management. The purpose of this paper is to provide a summary of available methods to determine flow resistance of natural rivers with vegetation, and discuss the influence of vegetation on erosion and sedimentation processes. Recently, significant advances have been made, but the effects of vegetation on flow and sediment dynamics are still not fully understood. Possible solutions to close the gaps in the current knowledge are suggested, with special focus directed to the determination of the interactive width between main channel and vegetated floodplains, the flow resistance of flexible vegetation with and without leaves, and the flow over submerged vegetation with low water depth.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.09a
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• pp.426-427
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• 2005

• 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.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.7 no.6
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• pp.61-74
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• 2004

Hydraulic engineers and scientists working on river restoration recognize the need for a deeper understanding of natural streams as a complex and dynamic system, which involves not only abiotic elements(flow, sediments) but also biotic components. From this point of view, the role played by riverine vegetation dynamics and flow conditions becomes essential. Hydro-mechanic interaction between flow and flexible plants covering a river bed is studied in this paper and some previous works are discussed. Measurements of turbulence and flow resistance in vegetated open channel were performed using rigid and flexible tube. Measuring detailed turbulent velocity profiles within and above submerged and flexible stems allowed to distinguish different turbulent regimes. Some interesting relationships were obtained between the velocity field and the deflected height of the plants, such as a reduced drag coefficient in the flexible stems. Turbulent intensities and Reynolds stresses were measured showing two different regions : above and inside the vegetation domain. In flexible vegetated open channel, the maximum values of turbulent intensities and Reynolds stresses appear above the top of canopy. Method to predict a flow resistance in flexible vegetated open channel is developed by modifying an analytical model proposed by Klopstra et al. (1997). Calculated velocity profiles and roughness values correspond well with flume experiments. These confirm the applicability of the presented model for open channel with flexible vegetation. The new method will be verified in the real vegetated conditions in the near future. After these verifications, the new method should be applied for nature rehabilitation projects such as river restorations.

• 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.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.472-477
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• 2006

This study aims at investigating the failure cases of the pre-cast block system in river environments which widely used nowadays and reviewing the effect and flow resistance for grass concrete structure through the physical experiments by hydraulic model test and developing application method in river slope or levee which has rigid flood resistance. Grass concrete structure has been independently tested under high velocity flow under the super critical condition, it survived the 8 m/sec maximum flow velocity. This results shows grass concrete system is also suited to use in aggressive river environments such as repairing a flood damaged embankment that had placed at risk the adjacent drainage channel with vegetation.

• Proceedings of the Korea Water Resources Association Conference
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• 2004.05b
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• pp.957-960
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• 2004

From a water-environmental point of view, with a change of understanding and concern about vegetation, it changes that vegetation acts as stability of channel and bed, providing habitats and feed for fauna, and means improving those with appreciation of the beautiful but resistant factor to the flow So, it becomes important concern and study subjects that turbulent structure by vegetation, shear stress and transport as well as roughness and average velocity by vegetation. But from a hydraulic point of view, vegetation causes resistance to the flow and can increase the risk of flooding, Therefore, this thesis concern the flow characteristics in vegetated open channels. According to the experimental results, $z_0$ was on an average $0.4h_p$ in a vegetated open channel. So, the elevation corresponding to zero velocity in a vegetated channel was the middle of roughness element. The limit for logarithmically distributed profile over the roughness element was from $z_0$ to $0.80h_{over}$ for a vegetated channel. Among the existing theory, the method of Kouwen et al.(1969), Haber(1982), and El-Hakim and Salama(1992) except Stephan(2001) gave a very good value compared to the measured velocity profile.

• Journal of Ocean Engineering and Technology
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• v.31 no.2
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• pp.121-129
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• 2017

The present study numerically investigated the influence of the waveform distribution on the tsunami-vegetation interaction using a non-reflected wave generation system for various tsunami waveforms in a two-dimensional numerical wave tank. First, it was possible to determine the wave attenuation mechanism due to the tsunami-vegetation interaction from the spatial waveform, flow field, vorticity field, and wave height distribution. The combination of fluid resistance in the vegetation and a large gap and creates a vortex according to the flow velocity difference in and out of the vegetation zone. Thus, the energy of a tsunami was increasingly reduced, resulting in a gradual reduction in wave height. Compared to existing approximation theories, the double volumetric ratio of the waveform increased the reflection coefficient of the tsunami-vegetation interaction by 34%, while decreasing the transfer coefficient and energy attenuation coefficient by 25% and 13%, respectively. Therefore, the hydraulic characteristics of a tsunami is highly likely to be underestimated if the solitary wave of the approximation theory is applied for the tsunami.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.2
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• pp.307-316
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• 2019

Development of vegetation in stream channel increases resistance to flow, resulting in increase in river stage upon flood and affecting change in stage-discharge relationship. Vegetation revealed in stream by water level reaching a peak and then declined upon flood is mostly found as prone. Taking an account of flow distribution with the number of vegetation, prone vegetation layer might be at height where discharge rate is zero (0) (Stephan and Guthnecht, 2002). However, there is a tendency that flow rate is overestimated when applying the height of river bed to flow area with no consideration of the height of vegetation layer in flow rate by float measurement. In this study, reliable flow measurement in stream with vegetation was calculated by measuring the height of vegetation layer after flood and excluding the vegetation layer-projected area from the flow area. The result showed the minimum 4.34 % to maximum 10.82 % of flow deviation depending on the scale of discharge. Accordingly, reliable velocity-area methods would be determined if vegetation layer-projected area in stream is considered in flow rate estimation using the flow area during the flood.

• Journal of the Korean Geosynthetics Society
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• v.14 no.2
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• pp.71-79
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• 2015

This paper describes vegetation based soil-media hydroseeding measures that have been previously applied as slope revegetation methods show problems such as insufficient binding force, drying, and insufficient organic matter. In particular, in the case of slope faces in regions where scattering is severe, a vicious circle exists in which remarkably low vegetation cover rates and increases in withering rates over time lead to further decreases in vegetation cover rates, which lead to further increases in erosion and scattering. Therefore, in the present study, environment friendly soil stabilizers were applied for resistance against erosion or scattering and engineering evaluations such as long-term immersion tests and flow resistance tests were conducted to determine appropriate mixing ratios. According to the results of long-term immersion tests utilizing environment friendly soil stabilizers and existing greening soil based materials, 100% collapse occurred at 30 hours and 40 days in the case of soil stabilizer mixing ratios of 0% and 2%, respectively. While the original form of the samples remained intact until the experiment was completed in the case of mixing ratios exceeding 4% indicating that 2% or higher soil stabilizer mixing ratios could affect the maintenance of forms even under extreme conditions. In addition, artificial rainfall tests were conducted on 40, 45, and 55 degree slope faces to evaluate the structural stability of vegetation based materials. Flow resistance tests were conducted on soil stabilizer mixing ratios of 0, 4, 8% to evaluate erosion resistance capability. Based on the results of the tests, environment friendly soil stabilizers applied for prevention of scattering or resistance against erosion by rainwater are considered to provide large effects to reduce losses and loss rates showed a tendency of decreasing rapidly when soil stabilizers were mixed.