Author(s): Tetsuya Sumi; Makiko Iguchi
Linked Author(s): Tetsuya Sumi
Keywords: Reservoir sediment management; Reservoir bottom sediment; Critical shear stress; Erosion rate; Liquid limit; Water content; Ignition loss; Humic substances
Abstract: In order to maintain dam storage capacity, sediment management is important for dams suffering from sediment accumulation. As a fine cohesive sediment removal method, resuspending and releasing fresh deposits from low-level outlet can be devised. Examining reservoir bottom sediment physical properties and relationship with its erosion process is one of the subjects to find out the possibility of this removal method. In this study, cohesive bottom sediment samples had been gathered from five reservoirs and physical properties, such as water content, particle diameter, ignition loss and liquid limit, were examined. Flume experiments were conducted to measure the critical shear stresses and erosion rates of these bottom sediments. The physical properties of bottom sediment varied among reservoirs and it was found that organic matter content mainly dominates their shear strengths. The presence of humic substances in the organic matter was considered to increase greatly their viscosity. The relationship between their critical shear stresses and water contents were linear on log-log paper, as having been recognized by the experimental results using lake or estuarine bottom sediments. It was shown that the coefficient of this relationship could be represented as liquid limit. According to the plot of erosion rates versus friction velocity, erosion rate coefficient, at least within this experimental result, depended on the type of sediments but seemed merely depend on water content which have a great influence on critical shear stress.