Analysis of Roughness Characteristics in Open Channel Flow due to Vegetation
식생에 의한 개수로 흐름에서의 조도 특성 분석

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dc.description학위논문 (박사)-- 서울대학교 대학원 : 건설환경공학부, 2015. 2. 서일원.-
dc.description.abstractRoughness coefficients of the river are very important to accurately predict the flood level of the river. As river restoration projects are activated in Korea, if training an existing river to a close-to-nature river, it is very necessary to accurately predict vegetative roughness when determining roughness for the entire river channel.
In this study, the quantitative variation of roughness coefficients depending on the characteristic factors by each vegetation is examined by performing hydraulic experiments for grass and woody vegetation. Based on this, the applicability of n-VR relationship typically presented for vegetative roughness in previous studies was reviewed and the effect of each new applied dimensionless parameter was analyzed based on the experimental data measured to replace VR and new evaluation equation for vegetative roughness coefficient n4 is presented.
The results for vegetative roughness element n4 based on n-VR relation equation were reviewed by performing experiments based on various hydraulic conditions for grass vegetation such as Zoysia matrella, Pennisetum alopecuroides (L.) Spreng., Phragmites communis Trin., Phragmites japonica Steud., Miscanthus sacchariflorus (Maxim.) Benth. typically found in domestic rivers. According to the results of the review, the effect of relative depth and in vegetation rigidity depending could not be considered properly with a single n-VR relation equation. Therefore, in order to propose a new relation equation that can take the place of existing n-VR relationship in this study. Several dimensionless parameters are selected through the dimensional analysis. Those are MEI that can take into account the rigidity of vegetation simultaneously and considering height of vegetation as main characteristic factors, and stem Reynolds number which can consider the effect of diameter of vegetation for flow conditions.
In this study, evaluation equations of vegetative roughness as a single relation equation are proposed in consideration of all of changes in the rigidity of vegetation due to seasonal distinction, relative inundation depth of vegetation, and influence of flow conditions by vegetation and coefficient of determination. of the presented relation equations are more than 0.76 and convenience, accuracy and applicability for evaluating vegetative roughness are improved compared to existing relation equation. Therefore, when comprehensively reviewing the equation presented for each vegetation in this study, relationship that has been traditionally used is considered to be replaced based on the results of this study.
Stems with the canopy form were extracted from Salix gracilistyla Miq., Salix subfragilis Andersson, Salix koreensis Andersson found a lot in the Central Region of Korean peninsular in trees growing in river channels. The variation of biomass depending on inundation depth was identified by performing an experiment for various hydraulic conditions. The relationship between vegetative roughness element and dimensionless parameters , , selected through the dimensional analysis was examined as in grasses. According to the results of the review, when considering , for roughness coefficients, is more than 0.97, indicating that the influence of both parameters is very large but the increase of explanatory power depending on the addition of a dimensionless parameter is very small (0.00 or 0.01) so in the case of shrubs, the effect of for vegetative roughness was found to be insignificant in this study. Therefore, in the case of shrubs, the usability of the equations presented based on dimensionless parameters , is considered to be very high compared to the existing roughness selection method using references widely used now. However, the applicability of the presented evaluation equation of woody vegetative roughness was examined and as a result, it was found that although the fully submerged condition is implemented, the magnitude of total roughness keeps increasing so when considering the experimental conditions, the application range of the evaluation equations presented for woody vegetative roughness is , that is, it should be applied restrictively for the emergent condition and just submerged condition.
dc.description.tableofcontentsTABLE OF CONTENTS

1. Introduction 1
1.1 Research Background 1
1.2 Research Needs 5
1.3 Research Objectives and Scope 7
1.3.1 Grasses 7
1.3.2 Trees (Shrubs) 8

2. Theoretical Background 9
2.1 Flow Resistance 9
2.1.1 Hydraulic Flow Resistance 9
2.1.2 Vegetation Roughness 11
2.1.3 Equations of Roughness Coefficients 11
2.1.4 Manning Roughness Coefficients 12
2.2 Vegetative Roughness 17
2.2.1 Introduction 17
2.2.2 관계 18
2.2.3 USSCS (US Soil Conservation Service) Evaluation Method 22
2.2.4 Reflection of Vegetation Characteristics 28
2.3 Drag Coefficient 33
2.3.1 Acting Force 33
2.3.2 Drag Coefficient 36
2.4 Roughness Coefficient Evaluation using Drag Coefficient 38
2.4.1 Introduction 38
2.4.2 Simple Vegetation Elements 39
2.4.3 Vegetation with Branches 41
2.4.4 Momentum Balanced Model 43
2.4.5 Researches on Experiments by Drag Force Measurement 46
2.4.6 Evaluation of Roughness Coefficient by Drag Measurement 60

3. Experimental Study 63
3.1 Vegetation Selection 63
3.1.1 Grasses 63
3.1.2 Trees (Shrubs) 68
3.2 Dimensionless Parameters 71
3.3 Experiments with Grasses 73
3.3.1 Experimental Channel 73
3.3.2 Measuring Equipments and Method 77
3.3.3 Experimental Conditions and Roughness Calculation Method 79
3.4 Experiments with Trees 82
3.4.1 Artificial Elements 82
3.4.2 Experiments with Single Trees 92
3.4.3 Semi-real Scale Vegetation Experiments 103

4. Analysis of Experimental Results for Grasses 117
4.1 Korean Velvet Grass (Zoysia matrella) 117
4.2 Korean Pennisetum (Pennisetum alopecuroides (L.) Spreng.) 121
4.3 Reed (Phragmites communis Trin.) 127
4.4 Dal (Phragmites japonica Steud.) 140
4.5 Amur Silver Grass (Miscanthus sacchariflorus (Maxim.) Benth.) 145
4.6 Summary 150

5. Analysis of Experimental Results for Trees 161
5.1 Artificial Vegetation 161
5.2 Experiment with a Single Tree 163
5.2.1 Bigcatkin Willow (Salix gracilistyla Miq.) 163
5.2.2 Seonbeodeul (Salix subfragilis Andersson) 165
5.2.3 Korean Willow (Salix koreensis Andersson) 167
5.2.4 Summary 170
5.3 Semi-real Scale Experiment 177
5.3.1 Single Group 177
5.3.1 Staggered Group 181

6. Conclusion 185
6.1 Summary and Conclusions 185
6.2 Recommendations for Future Research 189

References 191
dc.format.extent21245569 bytes-
dc.publisher서울대학교 대학원-
dc.subjectflow resistance-
dc.subjectvegetation roughness-
dc.subjectn-VR relationship-
dc.subjectrelative depth-
dc.subjectseasonal change-
dc.subjectdimensionless parameters-
dc.subjectmultiple regression analysis-
dc.titleAnalysis of Roughness Characteristics in Open Channel Flow due to Vegetation-
dc.title.alternative식생에 의한 개수로 흐름에서의 조도 특성 분석-
dc.citation.pagesxvi, 203-
dc.contributor.affiliation공과대학 건설환경공학부-
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College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Civil & Environmental Engineering (건설환경공학부)Theses (Ph.D. / Sc.D._건설환경공학부)
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