Aggradation‐Degradation Process in Alluvial Channels

Abstract

The effects of sediment size gradation σi and sediment loading ratio m on the aggradation‐degradation process and related flow characteristics in an alluvial channel were investigated experimentally. Three different size gradations of sediment were used. For each gradation, experiments were carried out for four different sediment loading conditions, namely, initial equilibrium, overloading, underloading, and clear water. Hydraulic characteristics, sediment transport rates, and gradations were measured during experiments. A linear model of sediment transport under overloading and underloading conditions was developed. Experimental results show that with nonuniform sediment, the aggradation‐degradation cycle is found to be irreversible. Under a given loading ratio, speeds of the aggradation wave and degradation wave increase with increasing σi and with decreasing m. The recovery ratios of bed elevation and bed slope decrease as σi increases. Regression relations have also been derived from the experimental data obtained.