Author(s): Trung Vinh La; Junji Yagisawa; Norio Tanaka
Linked Author(s): Norio Tanaka
Keywords: Boat-generated wave; Bank erosion; Shear stress; Simulation; Vegetation
Abstract: Bank erosion by boat-generated waves is an increasingly severe issue on navigable channels and rivers causing serious damage. A field investigation designed to elucidate the relationship between boat-generated wave and bank erosion rate, was conducted in Ca Mau Province, Vietnamese Mekong Delta. Both soil of riverbanks and wave characteristics were measured in-situ at a number of sites over a range of flow conditions for analysis. The results indicated that under boat wave attacks, the stability of riverbanks in this region was highly being threatened since the boat-induced shear stress acting on the riverbank were excessive the critical shear stress of soil and bank failures therefore have been occurring. In addition, vegetation was considered as a countermeasure to protect the riverbanks from erosion. Two parameters of vegetation including the vegetation density N and vegetation width l were taken into consideration. Various designs of vegetation belt based on these two parameters were evaluated in terms of effectiveness of reducing shear stress acting on the bed by numerical simulation. In the case of sparse vegetation, i.e. N=0.77 tree/m 2, the vegetation width is 10 m whereas such a 8 m vegetation width is needed in the case of dense vegetation, i.e. N=1.32 tree/m2 to protect the riverbank from erosion.