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〒278-8510 千葉県野田市山崎2641) 2 正会員 (株)日水コン 名古屋下水道部 技術第一課 (〒456-0002 愛知県名古屋市熱田区金山町1-7-5) 3 正会員 博(工) 東京理科大学准教授 理工学部土木工学科 (〒278-8510 千葉県野田市山崎2641) 4 非会員 東京理科大学 理工学部土木工学科(同上)Recent extreme flood affected huge flood disaster with a large number of levee breaches which were mainly caused by overflow erosion. For increasing the resistance of levee to overflow erosion with attention to fine fraction of levee materials, we examine the resistance of armored and GRS (Geosynthetic-Reinforced Soil) levees. Various laboratory tests were conducted to evaluate the resistance of this method to overflow erosion. The results indicated that 1) the resistance of armored and GRS levees have high resistance against overflow erosion with the increase of fine fraction of levee materials mainly due to low permeability and high cohesion of fine sediment and 2) the GRS levee with fine sediment maintained the height of the levee during a longer duration than that with sand.

Yusuke YOSHIMORI, Kazuaki OHTSUKI and Yasuo NIHEIA measure to reduce the environmental impacts of dams is a dam removal which has been conducted in Arase dam, Kuma River. However we have poorly understood influences of dam removal or construction on riverbed evolution in lower reach of dam. In this study, we attempted to clarify the response of riverbed evolution after dam removal or construction by data analysis for long-term monitored riverbed and 1D analysis for riverbed evolution under various sediment supply conditions. The numerical results indicated that the propagation process of riverbed evolution to the downstream direction seemed to be a kind of diffusion process. Using this results, we can simply evaluate the riverbed evolution in lower reach after completing removal of Arase dam.