A study of physico-geographical factors for formation of hyperconcentrated flows in the Loess Plateau of China

Semi-arid climate, poor vegetation cover and highly erodible loess can be regarded as the main natural factors responsible for the formation of hyperconcentrated flows on the Loess Plateau, China. The degree to which the hyperconcentrated flows develop, especially their extreme suspended concentration, shows a significant areal differentiation. This is closely related to the grainsize composition of suspended sediment. An optimal grainsize composition of suspended sediment has been identified, which leads to the highest value of extreme concentration among different river basins. This optimal composition is related to the combination of three surface material types, i.e., loess, wind-blown sand and weathered bedrock, and it occurs as a result of seasonally alternating wind and water processes operating in this area.