FACTORS AFFECTING FORESTATION IN THE DOWNSTREAM REACHES BELOW A DAM

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Rivers and streams are among the most world’s valuable and diversified ecosystems that have been seriously altered/ affected by means of human activities, particularly civil engineering works including barrage construction near river mouths, dam construction across rivers, gravel mining, channelization, and other regulation measures. Vegetation in rivers channel and flood plain creates a valuable natural environment and maintains a dynamic ecosystem. The spatial distribution of flood plain vegetation is strongly dependent on the flood system, particularly flooding, river bank erosion and sediment deposition, and the regeneration of riparian vegetation. Construction of dams, their decommissioning, and sediment flushing from the reservoir have been associated with vegetation dynamics in many studies. The increase of the amount of vegetation as well as forestation immediately downstream in the interval topical dam could potentially illustrate the changes in the amount of vegetation at longer distances from these dams. There is not much available information on the longitudinal impacts of dams on vegetation, such as how far downstream and the degree of regulation to which a dam on a river can influence riparian woodlands. However, factors governing the spatial changes of forestation in the floodplain after dams have not been explored extensively. It was hypothesized that, magnitude of forest coverage (FCR) of downstream varies due to dam type, the hydrological and climatic factors. It was assumed that effect of dam on downstream forests diluted with distance and the spatial pattern of forestation affected by the land use of the river channel and catchments. In this study, we examined the interacting effects of dam and land use on the vegetation/ forestation changes in dams’ downstream along with land coverage systems in the river channel floodplain.In this study, we used freely accessible Google Earth® (GE) satellite images in high spatial resolution as direct data resources to explore potential uses of land use/cover area. Different land use areas were determined within the study area from an appropriate aerial (above ground) viewing height (or zoom) for making visual vegetation cover fractions using Google Earth® is 50-100 m. Spatial land coverage data was obtained from April to December 2013 using available images from Google Earth® (version 7.1.2.2041) (http://earth.google.com). We used the Google Earth® polygon creation tool to estimate land use as well as vegetation coverage area in the flood plain channel zone because it allows a more accurate interpretation of images by controlling distance and work scale alignment. The data was calculated by making segments from the dam to the first tributary, from first tributary to second tributary, from second tributary to third tributary, and so on. The tributaries entering the main river channel were considered by the number of inflows. The data was calculated on the parameters were classified as follows: forest covered area, grass or herbaceous covered area, agricultural area, sports area, wasteland area, sandy or gravel area, total area and water area in the river channel, sandbars and floodplain. Downstream data was calculated for about 25km following the dam, which varied in some cases based on the distance to the ocean. Dyke distance was measured in the river channel crosswise by the Google distance calculator in each segment, taking an average of more than 10 times/points. Data on maximum and minimum river stream flow rate (m3/sec) was collected from the Global River Discharge Database. In case of Japan, the hydrologic data were collected from the latest statistical year database provided by Ministry of Lands, Infrastructure, Transportation and Tourism, Japan.The downstream forest coverage ratio (FCR) of flood control dam is not significantly different from that of hydropower and multipurpose dams but it is significantly different between hydropower and multipurpose dams (p<0.01). Because there is no significant difference between flood control with multipurpose dams while hydropower are significantly different from flood control and multipurpose dams in relation to discharges flows (p<0.01) from dam. The rivers which have lower difference in maximum and minimum flows ensure sufficient water is available for environmental needs and forest development. The systematic approach is to restore more naturalized in stream flow patterns to allow natural recruitment and growth processes. Differences in flood frequency, duration, and intensity are the most important factors controlled by physical attributes of the river and its floodplain such as water volume, channel shape, and slope of the river bed that determine differences in floodplain forest vegetation. Dam is disrupted the natural process of rivers flows which affects the morphology of the riverbed, downstream floodplains. That’s why, downstream forest as well as vegetation coverage ratio is not significantly ...

TABLE OF CONTENTS ............................................................................................................ iLIST OF FIGURES .................................................................................................................. ivLIST OF TABLES ................................................................................................................... xiiACKNOWLEDGEMENTS ................................................................................................... xiiiABSTRACT ............................................................................................................................ xivChapter 1. GENERAL INTRODUCTION ................................................................................ 1Research background ...................................................................................................... 1Hypotheses ...................................................................................................................... 7General objectives ........................................................................................................... 7Chapter 2. METHODS............................................................................................................... 8General methods ............................................................................................................. 8Statistical analyses ........................................................................................................ 18Chapter 3. RESULTS............................................................................................................... 30 Forest coverage ratio of river channel .......................................................................... 303.1.1. Dam type ................................................................................................................ 303.1.2. River flow .............................................................................................................. 313.1.3. River slope ............................................................................................................. 313.1.4. Climatic zone ......................................................................................................... 32 Spatial changes of forestation (FCR) along the river channel after dam ...................... 363.2.1. Forestation changes after dam with distance ......................................................... 363.2.2. Herbs changes after dam with distance .................................................................. 433.2.3. Relation between forest and herb coverage ratio at downstream .......................... 483.2.4. Relationship of forest coverage ratio and dyke distance ....................................... 543.2.5. Relationship between forest coverage ratio and number of inflows ...................... 60 Forest coverage ratio and land use pattern in the river channel .................................... 683.3.1. Forest coverage ratio and land use pattern in the river channel in Japan .............. 683.3.2. Forest coverage ratio and land use pattern in the river channel in South and North Korea ................................................................................................................................ 743.3.3. Forest coverage ratio and land use pattern in the river channel in Europe ............ 793.3.4. Forest coverage ratio and land use pattern in the river channel in Southern Africa.......................................................................................................................................... 823.3.5. Forest coverage ratio and land use pattern in the river channel in South America 843.3.6. Forest coverage ratio and land use pattern in the river channel Worldwide .......... 873.3.7. Forest coverage ratio and land use pattern in the non-dam river channel Worldwide........................................................................................................................ 903.3.8. Effects of catchment land use on river channel forestation ................................... 933.3.8.1. Effects of catchment land use on river channel forestation in Japan .............. 933.3.8.2. Effects of catchment land use on river channel forestation in North and South Korea ............................................................................................................................ 943.3.8.3. Effects of catchment land use on river channel forestation in Europe ........... 953.3.8.4. Effects of catchment land use on river channel forestation in Africa ............. 973.3.8.5. Effects of catchment land use on river channel forestation in Africa ............. 993.3.8.6. Effects of catchment land use on river channel forestation in worldwide .... 100Chapter 4. DISCUSSION ...................................................................................................... 104 Forest ...

指導教員 : 淺枝隆

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博士の専攻分野の名称 : 博士(学術)学位授与年月日 : 平成27年3月24日

identifier:学位記号番号 : 博理工乙第224号

収集根拠 : 博士論文（自動収集）
資料形態 : テキストデータ
コレクション : 国立国会図書館デジタルコレクション > デジタル化資料 > 博士論文
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Rivers and streams are among the most world’s valuable and diversified ecosystems that have been seriously altered/ affected by means of human activities, particularly civil engineering works including barrage construction near river mouths, dam construction across rivers, gravel mining, channelization, and other regulation measures. Vegetation in rivers channel and flood plain creates a valuable natural environment and maintains a dynamic ecosystem. The spatial distribution of flood plain vegetation is strongly dependent on the flood system, particularly flooding, river bank erosion and sediment deposition, and the regeneration of riparian vegetation. Construction of dams, their decommissioning, and sediment flushing from the reservoir have been associated with vegetation dynamics in many studies. The increase of the amount of vegetation as well as forestation immediately downstream in the interval topical dam could potentially illustrate the changes in the amount of vegetation at longer distances from these dams. There is not much available information on the longitudinal impacts of dams on vegetation, such as how far downstream and the degree of regulation to which a dam on a river can influence riparian woodlands. However, factors governing the spatial changes of forestation in the floodplain after dams have not been explored extensively. It was hypothesized that, magnitude of forest coverage (FCR) of downstream varies due to dam type, the hydrological and climatic factors. It was assumed that effect of dam on downstream forests diluted with distance and the spatial pattern of forestation affected by the land use of the river channel and catchments. In this study, we examined the interacting effects of dam and land use on the vegetation/ forestation changes in dams’ downstream along with land coverage systems in the river channel floodplain.In this study, we used freely accessible Google Earth® (GE) satellite images in high spatial resolution as direct data resources to explore potential uses of land use/cover area. Different land use areas were determined within the study area from an appropriate aerial (above ground) viewing height (or zoom) for making visual vegetation cover fractions using Google Earth® is 50-100 m. Spatial land coverage data was obtained from April to December 2013 using available images from Google Earth® (version 7.1.2.2041) (http://earth.google.com). We used the Google Earth® polygon creation tool to estimate land use as well as vegetation coverage area in the flood plain channel zone because it allows a more accurate interpretation of images by controlling distance and work scale alignment. The data was calculated by making segments from the dam to the first tributary, from first tributary to second tributary, from second tributary to third tributary, and so on. The tributaries entering the main river channel were considered by the number of inflows. The data was calculated on the parameters were classified as follows: forest covered area, grass or herbaceous covered area, agricultural area, sports area, wasteland area, sandy or gravel area, total area and water area in the river channel, sandbars and floodplain. Downstream data was calculated for about 25km following the dam, which varied in some cases based on the distance to the ocean. Dyke distance was measured in the river channel crosswise by the Google distance calculator in each segment, taking an average of more than 10 times/points. Data on maximum and minimum river stream flow rate (m3/sec) was collected from the Global River Discharge Database. In case of Japan, the hydrologic data were collected from the latest statistical year database provided by Ministry of Lands, Infrastructure, Transportation and Tourism, Japan.The downstream forest coverage ratio (FCR) of flood control dam is not significantly different from that of hydropower and multipurpose dams but it is significantly different between hydropower and multipurpose dams (p<0.01). Because there is no significant difference between flood control with multipurpose dams while hydropower are significantly different from flood control and multipurpose dams in relation to discharges flows (p<0.01) from dam. The rivers which have lower difference in maximum and minimum flows ensure sufficient water is available for environmental needs and forest development. The systematic approach is to restore more naturalized in stream flow patterns to allow natural recruitment and growth processes. Differences in flood frequency, duration, and intensity are the most important factors controlled by physical attributes of the river and its floodplain such as water volume, channel shape, and slope of the river bed that determine differences in floodplain forest vegetation. Dam is disrupted the natural process of rivers flows which affects the morphology of the riverbed, downstream floodplains. That’s why, downstream forest as well as vegetation coverage ratio is not significantly ...
TABLE OF CONTENTS ............................................................................................................ iLIST OF FIGURES .................................................................................................................. ivLIST OF TABLES ................................................................................................................... xiiACKNOWLEDGEMENTS ................................................................................................... xiiiABSTRACT ............................................................................................................................ xivChapter 1. GENERAL INTRODUCTION ................................................................................ 1Research background ...................................................................................................... 1Hypotheses ...................................................................................................................... 7General objectives ........................................................................................................... 7Chapter 2. METHODS............................................................................................................... 8General methods ............................................................................................................. 8Statistical analyses ........................................................................................................ 18Chapter 3. RESULTS............................................................................................................... 30 Forest coverage ratio of river channel .......................................................................... 303.1.1. Dam type ................................................................................................................ 303.1.2. River flow .............................................................................................................. 313.1.3. River slope ............................................................................................................. 313.1.4. Climatic zone ......................................................................................................... 32 Spatial changes of forestation (FCR) along the river channel after dam ...................... 363.2.1. Forestation changes after dam with distance ......................................................... 363.2.2. Herbs changes after dam with distance .................................................................. 433.2.3. Relation between forest and herb coverage ratio at downstream .......................... 483.2.4. Relationship of forest coverage ratio and dyke distance ....................................... 543.2.5. Relationship between forest coverage ratio and number of inflows ...................... 60 Forest coverage ratio and land use pattern in the river channel .................................... 683.3.1. Forest coverage ratio and land use pattern in the river channel in Japan .............. 683.3.2. Forest coverage ratio and land use pattern in the river channel in South and North Korea ................................................................................................................................ 743.3.3. Forest coverage ratio and land use pattern in the river channel in Europe ............ 793.3.4. Forest coverage ratio and land use pattern in the river channel in Southern Africa.......................................................................................................................................... 823.3.5. Forest coverage ratio and land use pattern in the river channel in South America 843.3.6. Forest coverage ratio and land use pattern in the river channel Worldwide .......... 873.3.7. Forest coverage ratio and land use pattern in the non-dam river channel Worldwide........................................................................................................................ 903.3.8. Effects of catchment land use on river channel forestation ................................... 933.3.8.1. Effects of catchment land use on river channel forestation in Japan .............. 933.3.8.2. Effects of catchment land use on river channel forestation in North and South Korea ............................................................................................................................ 943.3.8.3. Effects of catchment land use on river channel forestation in Europe ........... 953.3.8.4. Effects of catchment land use on river channel forestation in Africa ............. 973.3.8.5. Effects of catchment land use on river channel forestation in Africa ............. 993.3.8.6. Effects of catchment land use on river channel forestation in worldwide .... 100Chapter 4. DISCUSSION ...................................................................................................... 104 Forest ...
指導教員 : 淺枝隆