Aeolian process-induced hyper-concentrated flow in a desert watershed

Summary Ephemeral desert channels are characterized by very high rates of sediment transport during infrequent flood events. Here we show that aeolian process-induced hyper-concentrated (AHC) flows occur in the Sudalaer desert watershed in the Ordos Plateau of China, which primarily transport 0.08–0.25 mm non-cohesive aeolian sand and have a peak suspended sediment concentration of 1.1–1.4 × 10 6  mg l −3 . Aeolian sand supply and storage in the channel play a crucial role in causing hyper-concentrated flow. Our results indicate that non-cohesive aeolian sand can be entrained from the bed and suspended in the turbulent flow when the channel bed slope exceeds a critical threshold (0.0003). We also show that if the frequency ratio of wind-blown sandstorms to rainstorms T w / T p exceeds β ( γ  −  γ 0 )/ α ( P / V 3 ) ( A / L ) (where α is the wind-blown sand transport coefficient, β is the runoff coefficient, γ  −  γ 0 is the increase in suspension concentration caused by addition of aeolian sands, P is the density of rainstorms, V is the wind speed of sandstorms, A is the runoff-generating area, L is the aeolian sand-filled channel length), an AHC flow occurs during the passage of a flood in a desert channel. Since high-frequency aeolian processes provide an adequate quantity of transportable sediment and promote AHC flow, most of the infrequent rainfall-induced floods occurring in arid zones can develop as AHC flows.