There are many experimental approaches,field investigations and numerical calculations for movements of woods in a clear water and debris flow.However,kinematic conditions for accumulated logs and the interactions bet...There are many experimental approaches,field investigations and numerical calculations for movements of woods in a clear water and debris flow.However,kinematic conditions for accumulated logs and the interactions between a main flow and logs have not been fully evaluated.Mitigations for woods need taking into account the characteristics of tree species such as conifer and broad-leaf trees and of shapes such as root swells and crown.In the present study,we focus on the differences in specific weight of conifer and broad-leaf trees with some moisture in a sediment-water mixture flow with narrow flow width,and consider that conifer and broad-leaf tree are floating and submerged solid phase,respectively.Flume tests are conducted in steady flow of clear and debris flow over a rigid bed in order to evaluate conifer and broad-leaf tree movement in clear water and debris flow.Experimental data indicates that dimensionless transverse diffusion coefficient can be 0.1 to 0.4 and 0.3 to 0.9 in flow direction.Those diffusive characteristics seem to be independent of Reynolds number and Froude number,but dependent of bed slope,i.e.,gravity,though detailed considerations are needed to discuss about flow characteristics such as spatial eddy structures,momentum transfer induced by interactions of logs and so on.展开更多
Bedload governs riverbed channel variations and morphology, it is necessary to determine bedload discharge through an arbitrary cross section in a mountain fiver. A new system with submerged load cells has been develo...Bedload governs riverbed channel variations and morphology, it is necessary to determine bedload discharge through an arbitrary cross section in a mountain fiver. A new system with submerged load cells has been developed to directly measure bedload discharge. The system consists of： （1） an iron box which is 1 m long, 0.5 m wide and 0.1 m in depth, （2） two submerged load cells 0.7 m apart, （3） a pressure sensor and, （4） an electromagnetic velocity meter. This system has been designed to exclude the effect of the hydraulic pressure of water on direct measurements of bedload particle weight. Initial tests in a laboratory were conducted to examine the accuracy of measurements with the system under aerial conditions. The system has been installed in the supercritical flume in Ashi-arai-dani River of the Hodaka Sedimentation Observatory of the Disaster Prevention Research Institute （DPRI） of Kyoto University to obtain bedload discharge under natural conditions. Flume tests were conducted in this channel by artificial supply of uniform sediment particles of several grain sizes. The average velocity of the sediment particles near the bed was estimated using cross-correlation functions for weight waves obtained by the two load cells, Bedload discharge calculations were based on time integration of the product of sediment velocity and sediment weight obtained by the two load cells. This study clarifies the reasons why bedload measurements are difficult, and provides some solutions using the monitoring systems with submerged load cells through the field measurements. Additionally, the applicability of bedload measurement with the submerged load cells is explained based on experimental artificial sediment supply data.展开更多
The importance of irrigation development is considered a key factor for food security and poverty reduction because it improves crop productivity,and ensures stable expansion of agricultural production.However,irrigat...The importance of irrigation development is considered a key factor for food security and poverty reduction because it improves crop productivity,and ensures stable expansion of agricultural production.However,irrigation development requires understanding of the avail-able resources including the suitability of the land for agriculture.In this study,the land suitability for paddy fields was evaluated within the United Republic of Tanzania mainland by integrating the geographic information system(GIS)and analytical hierarchy process(AHP).In this study,11 criteria based on various sources(soil type,soil drainage,soil organic carbon,soil pH,soil depth,elevation,slope,land use,topographic wetness index,temperature,and precipitation)were used.These criteria were used within the GIS-based AHP to identify the most suitable land for sustainable paddy field cultivation considering the preservation of the natural environment of forests and protected areas by examining two scenarios:rainfed condition and irrigation priority.The former ten criteria were assumed to be constant in both scenarios and were assigned the same scores,while the latter criterion(precipitation)was assigned different scores for varying amounts to plan new irrigation projects.Unsuitable land represents 72.8%of the study area,reducing the potential agriculture land(PAL)appropriate for cultivation to 27.2%.In the rainfed condition scenario,the very high and high suitability classes represent 17.6%of the total land of the study area and 64.7%of the PAL.In the irrigation priority scenario,the same classes represent 21.4%of the total land of the study area and 78.6%of the PAL.Finally,the distribution of the land suitability for both scenarios was analyzed within eight administrative irrigation zones to determine the irrigation zone with the greatest potential for paddy field cultivation.展开更多
基金supported by Research Budget from Research and Development Center,NIPPON KOEI Co.,Ltd (Research theme:Modeling for debris flow with woods and their applicability)
文摘There are many experimental approaches,field investigations and numerical calculations for movements of woods in a clear water and debris flow.However,kinematic conditions for accumulated logs and the interactions between a main flow and logs have not been fully evaluated.Mitigations for woods need taking into account the characteristics of tree species such as conifer and broad-leaf trees and of shapes such as root swells and crown.In the present study,we focus on the differences in specific weight of conifer and broad-leaf trees with some moisture in a sediment-water mixture flow with narrow flow width,and consider that conifer and broad-leaf tree are floating and submerged solid phase,respectively.Flume tests are conducted in steady flow of clear and debris flow over a rigid bed in order to evaluate conifer and broad-leaf tree movement in clear water and debris flow.Experimental data indicates that dimensionless transverse diffusion coefficient can be 0.1 to 0.4 and 0.3 to 0.9 in flow direction.Those diffusive characteristics seem to be independent of Reynolds number and Froude number,but dependent of bed slope,i.e.,gravity,though detailed considerations are needed to discuss about flow characteristics such as spatial eddy structures,momentum transfer induced by interactions of logs and so on.
基金supported in part by the Research Budget from the Research and Development Center,Nippon Koei Co.,Ltd
文摘Bedload governs riverbed channel variations and morphology, it is necessary to determine bedload discharge through an arbitrary cross section in a mountain fiver. A new system with submerged load cells has been developed to directly measure bedload discharge. The system consists of： （1） an iron box which is 1 m long, 0.5 m wide and 0.1 m in depth, （2） two submerged load cells 0.7 m apart, （3） a pressure sensor and, （4） an electromagnetic velocity meter. This system has been designed to exclude the effect of the hydraulic pressure of water on direct measurements of bedload particle weight. Initial tests in a laboratory were conducted to examine the accuracy of measurements with the system under aerial conditions. The system has been installed in the supercritical flume in Ashi-arai-dani River of the Hodaka Sedimentation Observatory of the Disaster Prevention Research Institute （DPRI） of Kyoto University to obtain bedload discharge under natural conditions. Flume tests were conducted in this channel by artificial supply of uniform sediment particles of several grain sizes. The average velocity of the sediment particles near the bed was estimated using cross-correlation functions for weight waves obtained by the two load cells, Bedload discharge calculations were based on time integration of the product of sediment velocity and sediment weight obtained by the two load cells. This study clarifies the reasons why bedload measurements are difficult, and provides some solutions using the monitoring systems with submerged load cells through the field measurements. Additionally, the applicability of bedload measurement with the submerged load cells is explained based on experimental artificial sediment supply data.
文摘The importance of irrigation development is considered a key factor for food security and poverty reduction because it improves crop productivity,and ensures stable expansion of agricultural production.However,irrigation development requires understanding of the avail-able resources including the suitability of the land for agriculture.In this study,the land suitability for paddy fields was evaluated within the United Republic of Tanzania mainland by integrating the geographic information system(GIS)and analytical hierarchy process(AHP).In this study,11 criteria based on various sources(soil type,soil drainage,soil organic carbon,soil pH,soil depth,elevation,slope,land use,topographic wetness index,temperature,and precipitation)were used.These criteria were used within the GIS-based AHP to identify the most suitable land for sustainable paddy field cultivation considering the preservation of the natural environment of forests and protected areas by examining two scenarios:rainfed condition and irrigation priority.The former ten criteria were assumed to be constant in both scenarios and were assigned the same scores,while the latter criterion(precipitation)was assigned different scores for varying amounts to plan new irrigation projects.Unsuitable land represents 72.8%of the study area,reducing the potential agriculture land(PAL)appropriate for cultivation to 27.2%.In the rainfed condition scenario,the very high and high suitability classes represent 17.6%of the total land of the study area and 64.7%of the PAL.In the irrigation priority scenario,the same classes represent 21.4%of the total land of the study area and 78.6%of the PAL.Finally,the distribution of the land suitability for both scenarios was analyzed within eight administrative irrigation zones to determine the irrigation zone with the greatest potential for paddy field cultivation.
