Quantitatively distinguishing the factors driving sediment flux variations in the Daling River Basin, North China

Abstract

Understanding the riverine sediment load regime is crucial to sustainably managing fluvial-deltaic ecosystem restoration. However, in studies on global river sediment transport characteristics, small mountainous rivers (SMRs), transporting 45% of the global sediment flux into the sea, have been largely ignored. Furthermore, SMRs have hydrologic characteristics of instantaneous enormous fluxes under extreme climate, but the research on their driving factors affecting sediment transport is insufficient. Partial derivation method and multiple double mass curves were applied to a small mountainous river in North China, the Daling River to study how the three most variable factors—precipitation, vegetation coverage, and reservoirs—have quantitatively controlled sediment flux in the basin and its subregions in the last 50 years. The results of the two methods showed that the 78.55% reduction in sediment flux from 1961–1979 to 1980–2015 was due primarily to restored vegetation coverage (50.42%-61.11%), followed by reservoirs (18.13–44.09%) and precipitation (5.49–22.34%) in the Daling River Basin (DRB) and its subregions. The restored vegetation in the DRB has intercepted a large amount of sediment, reducing the sediment flux transported to the reservoirs. Besides, the Daling River releases enormous amounts of sediment during heavy rainfalls. However, increasing vegetation coverage in recent years has changed the transport characteristics of sediment into temperate changes in runoff and sediment flux under extreme climatic conditions; thus this river provides a useful example of studying the characteristics of sediment transport controlled by nature and human activities against extreme climate conditions. In the DRB, topography, lithology, and vegetation density are the motivators for the differences in sediment flux and its change rates, from upstream to downstream. These findings emphasize the crucial role of vegetation in driving sediment transport from source to sink in temperate SMRs.