Sediment control and logs capturing in sand pocket with combination of sabo dam with large conduit and iron bars

In the Otoishi River, a tributary on right side of the Akatani River in the Chikugo River basin, a large amount of sediment and woody debris were deposited on riverbed due to the sediment disaster caused by the heavy rainfall in northern part of Kyushu Region on 5th to 6th July in 2017. As one of countermeasures to control the outflow of sediment and woody debris to the Akatani River, a sand pocket is planned with the sabo dam with large conduit parts and the log broom works. In this study, hydraulic model test and flume test were carried out to obtain knowledges for design of the sand pocket. Iron bars are installed vertically at the upstream front of the large conduit parts for capturing sediment and logs, and those intervals are desirable to be set in consideration of sediment diameter and sediment movement without the dam. Besides, it is necessary to consider capturing function and flow characteristics such as shockwave when the log broom works is planned in setting of layout and dimensions

Hydraulic model test on channel shifting and yielding woody debris on the fan after sediment disaster in the past

The re-movement of sediment and woody debris in torrents after huge sediment transport in the past could cause new flood and sediment disasters due to heavy rainfall events. However, it is not clear how re-movement of logs effects on bed variations such as bars and river channel divergence. In present study, hydraulic model tests were carried out referring to the magnitude of floods, that was over the plan size, in Tottabetsu River basin in August in 2016. These tests include different magnitudes of flood, suppling logs from bed/side bank erosion, and existence of sabo facilities. The key results were as follows: The presence of logs by bed/side bank erosions influences on the patterns of flows and sediment transport, because deposition of logs affects formation of bars. Difference of the magnitudes of the floods affects the activeness of the interaction between logs and sediment transport. In additions, the locations and slits of the sabo dam need to consider hydraulic conditions and characteristics of woody debris for appropriate control of sediment and woody debris

Sediment control and logs capturing in sand pocket with combination of sabo dam with large conduit and iron bars

In the Otoishi River, a tributary on right side of the Akatani River in the Chikugo River basin, a large amount of sediment and woody debris were deposited on riverbed due to the sediment disaster caused by the heavy rainfall in northern part of Kyushu Region on 5th to 6th July in 2017. As one of countermeasures to control the outflow of sediment and woody debris to the Akatani River, a sand pocket is planned with the sabo dam with large conduit parts and the log broom works. In this study, hydraulic model test and flume test were carried out to obtain knowledges for design of the sand pocket. Iron bars are installed vertically at the upstream front of the large conduit parts for capturing sediment and logs, and those intervals are desirable to be set in consideration of sediment diameter and sediment movement without the dam. Besides, it is necessary to consider capturing function and flow characteristics such as shockwave when the log broom works is planned in setting of layout and dimensions

Hydraulic model test on channel shifting and yielding woody debris on the fan after sediment disaster in the past

The re-movement of sediment and woody debris in torrents after huge sediment transport in the past could cause new flood and sediment disasters due to heavy rainfall events. However, it is not clear how re-movement of logs effects on bed variations such as bars and river channel divergence. In present study, hydraulic model tests were carried out referring to the magnitude of floods, that was over the plan size, in Tottabetsu River basin in August in 2016. These tests include different magnitudes of flood, suppling logs from bed/side bank erosion, and existence of sabo facilities. The key results were as follows: The presence of logs by bed/side bank erosions influences on the patterns of flows and sediment transport, because deposition of logs affects formation of bars. Difference of the magnitudes of the floods affects the activeness of the interaction between logs and sediment transport. In additions, the locations and slits of the sabo dam need to consider hydraulic conditions and characteristics of woody debris for appropriate control of sediment and woody debris