Title Page
Contents
Abstract 22
국문 요약 24
General introduction 26
Part Ⅰ. Successional Pathway and Spatial Distribution of Riparian Vegetation According to the Construction and Operation of the Weirs in the Geumgang River, South Korea 30
1. Introduction 31
2. Methods 34
2.1. Study site 34
2.2. Hydrological and geomorphological changes by the weir operation 37
2.3. Field survey 40
2.4. Remote sensing 41
2.5. Statistical analysis 44
3. Results 47
3.1. Terrain changes 47
3.2. Classfication of riparian vegetation 50
3.3. Vegetation distribution 56
3.4. Vegetation succession series 61
4. Discussion 68
Part Ⅱ. Environmental Changes with the Succession of Riparian Vegetation in the Geumgang River, South Korea 73
1. Introduction 74
2. Methods 77
2.1. Study site 77
2.2. Elapsed exposure time 78
2.3. Topography environment 78
2.4. Soil environment 79
2.5. Hydrological factors - Numerical model 79
2.6. Statistical analysis 81
3. Results 83
3.1. Environment characteristics by vegetation 83
3.2. Relationships environment and vegetation 89
3.3. Environmental changes along the succession 91
3.4. Regression of succession and its relationship to hydrological factors 95
4. Discussion 98
Part Ⅲ. Simulation of Successional Changes in Riparian Vegetation Reflecting Weir Operation Using Machine Learning Models in the Geumgang River, South Korea 101
1. Introduction 102
2. Methods 105
2.1. Study site 105
2.2. Collecting data 105
2.3. Building a model 109
2.4. Evaluating and validating the model 113
2.5. Interpreting and applying the model 114
3. Results 116
3.1. Evaluate and validate the model 116
3.2. Variable importance 119
3.3. Vegetation response 121
3.4. Vegetation distribution by scenario 123
4. Discussion 131
Conclusions 133
References 135
Supplementary materials 150
Part Ⅰ. Successional Pathway and Spatial Distribution of Riparian Vegetation According to the Construction and Operation of the Weirs in the Geumgang River, South Korea 8
Table Ⅰ-1. Area of time-lapse successional stages in the study section of the Geumgang River, South Korea. Numbers in parentheses indicate percentages 48
Table Ⅰ-2. Indicator species of riparian plant communities in the Geumgang River, South Korea. The classification of communities was identified by optimally partitioning similarity relationships and was... 54
Table Ⅰ-3. Ecological characteristics and community structure of the riparian plant communities in the Geumgang River, South Korea. Species diversity was calculated using the Shannon-Wiener diversity... 55
Table Ⅰ-4. Area of riparian plant communities with successional stages in the Geumgang River, South Korea. Numbers in parentheses indicate percentages 60
Part Ⅱ. Environmental Changes with the Succession of Riparian Vegetation in the Geumgang River, South Korea 8
Table Ⅱ-1. Environmental characteristics of topography, soil, and hydrology in the Geumgang River, South Korea. (n = 663, Min = minimum, Max = maximum, SD = standard deviation, CV = coefficient... 85
Table Ⅱ-2. Results of the linear regression between environmental variables and the elapsed exposure time. β is the slope of the environmental variable and R-squared represents the explanatory power of... 93
Part Ⅲ. Simulation of Successional Changes in Riparian Vegetation Reflecting Weir Operation Using Machine Learning Models in the Geumgang River, South Korea 9
Table Ⅲ-1. Model variables and weir operation conditions for applying these variables for the simulation of successional changes in riparian vegetation of the Geumgang River, South Korea 107
Table Ⅲ-2. Algorithm of R packages and optimal values of hyperparameters used for constructing the riparian vegetation succession model using the train data set through the 10-fold cross-validation method 112
Table Ⅲ-3. Scenarios for the final riparian vegetation succession model in the Geumgang River, South Korea. Each scenario reflects the weir operation and floods from 2020 to 2022 115
Table Ⅲ-4. Sensitivity of the machine learning algorithms for each plant community in the riparian vegetation succession model. A model was constructed using the combination of the train data set and... 117
Table Ⅲ-5. The confusion matrix comparing the vegetation map drawn from the riparian vegetation succession model with the actual vegetation map from part 1 of this thesis (OW = Open water, So0 =... 118
Table Ⅲ-6. Importance of variables in the ensemble model. The accuracy of the original ensemble model is 0.7697. Accuracy is determined by creating datasets with each variable permuted, and then... 120
Table Ⅲ-7. Occupied area (ha) of riparian plant communities predicted by the riparian vegetation succession model according to the different scenarios in the study sections of the Geumgang River,... 129
Table Ⅲ-8. Occupied area (ha) of riparian plant communities predicted by the riparian vegetation succession model according to different scenarios of the weir operations in the study sections of the... 130
Part Ⅰ. Successional Pathway and Spatial Distribution of Riparian Vegetation According to the Construction and Operation of the Weirs in the Geumgang River, South Korea 17
Table Ⅰ-S1. List of multispectral satellite images used to distinguish successional stages and mapping of riparian vegetation in Geumgang River, South Korea. Threshold values for binarization were... 151
Table Ⅰ-S2. Floristic composition and landscape photograph of the riparian plant communities in the Geumgang River in South Korea 152
Part Ⅱ. Environmental Changes with the Succession of Riparian Vegetation in the Geumgang River, South Korea 18
Table Ⅱ-S1. Location of water level observation stations from downstream to upstream of the study reach in the Geumgang River, South Korea 160
Table Ⅱ-S2. Water level and discharge data in the four study sections used for numerical hydraulic modeling of the Geumgang River, South Korea 161
Table Ⅱ-S3. Water level and discharge data for the four study sections used for numerical hydrualic modeling of the Geumgang River, South Korea 162
Part Ⅲ. Simulation of Successional Changes in Riparian Vegetation Reflecting Weir Operation Using Machine Learning Models in the Geumgang River, South Korea 21
Table Ⅲ-S1. Classification performance of the machine learning algorithm for the riparian vegetation succession model. A model was created by combining the train data set, and evaluated with the test... 184
Part Ⅰ. Successional Pathway and Spatial Distribution of Riparian Vegetation According to the Construction and Operation of the Weirs in the Geumgang River, South Korea 11
Figure Ⅰ-1. Map showing the study site in the Geumgang River, South Korea. Red lines indicate the boundaries of each study section, and gray arrows indicate the location of water level observation stations. 36
Figure Ⅰ-2. Water level changes from 2017 to 2022 at the water level observation stations of the Geumgang River, South Korea. The locations of the water level observation stations refer to the gray... 39
Figure Ⅰ-3. Flowchart for distinguishing successional stages using multispectral satellite images. The periods marked on the successional stages based on the first survey time (NDWI = normalized... 43
Figure Ⅰ-4. Map showing the distribution of time-lapse successional stages in the study sections of the Geumgang River, South Korea as of the year 2020. 49
Figure Ⅰ-5. Heatmap showing the Bray-Curtis dissimilarity between riparian plant communities in the Geumgang River, South Korea. Communities were identified by optimally partitioning similarity... 53
Figure Ⅰ-6. Vegetation map of the study sections in 2020 in the Geumgang River, South Korea, in 2020. 58
Figure Ⅰ-7. Percentages of plant community area according to the lotic, lentic and terrestrial habitats in the Geumgang River, South Korea. Refer to Table Ⅰ-2 for abbreviations. 59
Figure Ⅰ-8. Network graph illustrating chages of successional stages from 2020 to 2022 in the riparian plant communities of the Geumgang River, South Korea. Node positions are determined based on... 64
Figure Ⅰ-9. Box plot showing the elapsed exposure time for the riparian plant community in the Geumgang River, South Korea. Different letters above bars indicate significant difference between... 65
Figure Ⅰ-10. Response curves of the successional stages with respect to elapsed exposure time in the riparian plant communities of the Geumgang River, South Korea. These curves were derived from the... 66
Figure Ⅰ-11. Biplots using two axes each for the three dimensions of detrended correspondence analysis of vegetation coverages in the Geumgang River, South Korea. All ellipses were drawn at the 95%... 67
Figure Ⅰ-12. Schematic diagram of successional pathways in riparian plant communities of the Geumgang River, South Korea (green arrow = progressive pathway, red arrow = retrogressive... 72
Part Ⅱ. Environmental Changes with the Succession of Riparian Vegetation in the Geumgang River, South Korea 13
Figure Ⅱ-1. Box plot of topographical variables of riparian plant communities related to riparian successional stages in the Geumgang River, South Korea. Different letters above bars indicate... 86
Figure Ⅱ-2. Box plot of soil variables of plant communities related to riparian successional stages in the Geumgang River, South Korea. Different letters above bars indicate significant difference between... 87
Figure Ⅱ-3. Box plot of hydraulic variables of riparian plant communities related to successional stages in the Geumgang River, South Korea. Different letters above bars indicate significant difference... 88
Figure Ⅱ-4. Biplots of principal components analysis of environmental variables in the plant communities of the Geumgang River, South Korea. All ellipses were drawn at the 95% confidence... 90
Figure Ⅱ-5. Biplots of non-metric multidimensional scaling of vegetation coverage in the Geumgang River, South Korea. All ellipses were drawn at the 95% confidence intervals. (a) site (The color of the... 94
Figure Ⅱ-6. Comparison of maximum water depth and maximum shear stress of the destroyed and non-destroyed plant communities of Persicaria lapathifolia. Different letters above bars indicate... 96
Figure Ⅱ-7. Logistic regression of the probability of vegetation damage along a shear stress gradient at the Persicaria lapathifolia community of the Geumgang River, South Korea. AUC is the area under... 97
Figure Ⅱ-8. Changes in vegetation and environment according to the succession in the Geumgang River, South Korea. 100
Part Ⅲ. Simulation of Successional Changes in Riparian Vegetation Reflecting Weir Operation Using Machine Learning Models in the Geumgang River, South Korea 15
Figure Ⅲ-1. Flowchart for configuration of the riparian vegetation succession model. The 'Natural flow regime' dataset is consistently used in all simulations. But this dataset is deactivated to simulate... 108
Figure Ⅲ-2. Flowchart for constructing the riparian vegetation succession model. 111
Figure Ⅲ-3. Response of plant communities to environmental variables in the Geumgang River, South Korea. Response curves were drawn using kernel density estimation. The density is the kernel density... 122
Figure Ⅲ-4. Predicted vegetation map of the study sections by the riparian vegetation succession model for September 2020 in the Geumgang River, South Korea. 125
Figure Ⅲ-5. Predicted vegetation map of the study sections by the riparian vegetation succession model for June 2021 in the Geumgang River, South Korea. 126
Figure Ⅲ-6. Predicted vegetation map of the study sections by the riparian vegetation succession model for October 2021 in the Geumgang River, South Korea. 127
Figure Ⅲ-7. Predicted vegetation map of the study sections by the riparian vegetation succession model for September 2022 in the Geumgang River, South Korea. 128
Figure Ⅰ-S1. Satellite images of the Sentinel-2 of the Baekjebo section and the Gyeondongri section of the Geumgang River, South Korea. These images were taken on March 8, 2020 before the opening... 154
Figure Ⅰ-S2. Satellite images of the Sentinel-2 of the Gongjubo section and the Geumamri section of the Geumgang River, South Korea. These images were taken on January 3, 2018 before the opening,... 155
Figure Ⅰ-S3. Satellite images of the Sentinel-2 of the Sejongbo section and the Buyongri section of the Geumgang River, South Korea. These images were taken on October 30, 2017 before the opening, on... 156
Figure Ⅰ-S4. Aerial photographs of the surveyed sections using the drone (Phantom 4 pro, DJI, China) in the Geumgang River, South Korea in September 2020. The red line indicates transect of the field survey. 157
Figure Ⅰ-S5. Average silhouette width based on the number of clusters to determine the appropriate number of clusters. The 10 clusters with the widest width were selected. 158
Figure Ⅰ-S6. Heatmap displaying the main ecological characteristics of the riparian plant communities in the Geumgang River in South Korea. Values are quantified as community-level weighted means... 159
Figure Ⅱ-S1. Relationship between water level observed at the water level observatory station and the water level calculated from the numerical hydraulic simulation in the study reach of the Geumgang... 165
Figure Ⅱ-S2. Elevation above water surface simulated by the hydraulic model at the minimum discharge in the study sections of the Geumgang River, South Korea. During the fourth survey... 166
Figure Ⅱ-S3. Distance from waterfront simulated by the hydraulic model at the minimum discharge in the study sections of the Geumgang River, South Korea. During the fourth survey (September 15,... 168
Figure Ⅱ-S4. Wetness index simulated by the hydraulic model at the minimum discharge in the study sections of the Geumgang River, South Korea. During the fourth survey (September 15, 2022), the... 170
Figure Ⅱ-S5. Water depth simulated by the hydraulic model at the minimum discharge in the study sections of the Geumgang River, South Korea. During the fourth survey (September 15, 2022), the... 172
Figure Ⅱ-S6. Water depth at the maximum discharge (flood in 2020) in the Geumgang River, South Korea. During this flood event, all water gates of the weirs were water gates fully opened at this flood... 174
Figure Ⅱ-S7. Shear stress simulated by the hydraulic model at the minimum discharge in the study sections of the Geumgang River, South Korea. During the fourth survey (September 15, 2022), the... 175
Figure Ⅱ-S8. Shear stress at the maximum discharge (flood in 2020) in the Geumgang River, South Korea. During this flood event, all water gates of the weirs were water gates fully opened at this flood... 177
Figure Ⅱ-S9. Changes in topographic variables along elapsed exposure time according to the succession pathways. The regression line and equation were derived from a linear regression analysis.... 178
Figure Ⅱ-S10. Changes in soil variables along elapsed exposure time according to the succession pathways. The regression line and equation were derived from a linear regression analysis. The gray... 179
Figure Ⅱ-S11. Changes in hydraulic variables along elapsed exposure time according to the succession pathways. The regression line and equation were derived from a linear regression analysis. The gray... 181