STABILIZATION OF RIVERBANKS AT THE DOWNSTREAM OF ISHIKARI RIVER -PREVENTION OF BANK EROSION CAUSED BY WIND WAVES AND RECOVERING DIVERSE BANK LINES-

Abstract

Since the flood in 1981, dredging works have been conducted to expand the channel width at the downstream Ishikari River in Hokkaido, Japan. As a result, bank erosion was generated and the shape of river bank was simplified at the most part of the right side bank. However, such phenomena are not generated at the left side bank. It was revealed that wind waves were the primary cause of erosion by the field observation in 2004. Erosion control measures were examined in 2005, leading to the invention of a wind wave mitigation net aimed at restoring the diversity of bank lines at a lower cost. For field test, three types of wave-dissipating works were devised and their effectiveness has been confirmed on site since late March 2006. Another objective of the works was the sediment deposition that would serve as the foundation of emergent plants. With the passage of time, the deposition progressed between the slopes and breakwaters, and a foundation for creating bank line diversity is currently being established.