ABSTRACT
A principal sediment yield zone is the Beiyu mountain area, from which the Wuding River, the Yanhe River, the North Luohe River, and the Jinhe River originate. The common tendency is that the modulus of sediment yield is large in the north part of the region and decreases gradually toward the south. In accordance with the variation of the size distribution of loess, the sediment concentration of rivers originating in different regions is different. In general, rivers originating in the northwest, such as Huangpuchuan, Kuye, Wuding, North Luohe, Jinhe, etc. usually are at higher concentrations, and those from the southeast, such as Weihe River, are at lower concentrations. The formation of hyperconcentrated flow and the distinguishing features of the flow in the process of confluence were analysed. Because of the extremely low erosion-resistance capacity of loess, hyperconcentrated flow can easily be formed by the combined action of splash, rill and gravitational erosion.
