Sedimentary Characteristics of Ephemeral and Intermittent Channels: A case study of the Baiyanghe fan, Xinjiang, China

Abstract

A topographical investigation of modern deposits of the Baiyanghe fan in Xinjiang show that two types of fluvial channels are developed on the surface of the fan:intermittent channels and ephemeral channels. The latter, which have flow occupancy between < 50% and zero, are mainly formed by occasional flooding during summer rains. The occupancy rate of intermittent channel flow is about 50%, and their flow output is between that of ephemeral and perennial channels. The main Baiyanghe channel is intermittent, occupying 2.1% of the fan surface area. Its deposits are mainly coarse-grained gravels, highly rounded, well sorted, and with low mud content and higher imbricated characteristics. The course of the channels change, with sediments fining downstream. Ephemeral channels, which are distributed over about 97.9% of the fan surface area, contain finer sediment with low roundness, poor sorting and higher mud content. The scale of ephemeral channels decreases downstream and bifurcation increases. Intermittent channels are dominated by seasonal runoff, and the source of the sediment load is mainly remote from the fan. The sediment carried by ephemeral channels is dominated by sheet flow and debris flow from colluvium and debris-flow deposits near the apex of the fan, together with some sediment from earlier deposits within the fan itself. The fan lobe are mainly constructed by intermittent channels, whereas ephemeral channels play a role in re-shaping the fan. This study has increased the understanding of the sedimentary process and characteristics of alluvial fans in arid areas and enriched the sedimentary model of fan research.