Scale effects on specific sediment yield in the Yellow River basin and geomorphological explanations

Abstract

Based on data from 199 stations in the Yellow River drainage basin for which more than 5 years of data are available, the relationship between specific sediment yield ( Y s) and drainage area ( A) has been studied. This relationship for the Yellow River basin is different from those for many other rivers of the world, both at the scale of whole basin and at local scales. With increasing basin area, the specific sediment yield increases, reaches a maximum, and then declines. The non-linear variation in the Y s– A relationship can be explained by, first, surface material distribution; second, adjustment of the basin at macro time- and space-scales; and the third, the variation of energy expenditure with drainage-basin scale. As the loess deposits in the high-relief headwater areas is thin, it can be exhausted much more rapidly by flowing water erosion than in other areas, so the underlying erosion-resistant bedrock may be exposed much earlier. In many rivers in the study area, bedrock is exposed in the upper part of the drainage basin, and loess appears in the middle part, with a thickness that increases downstream to a peak, followed by a decline. Due to the influence of these spatial patterns of surface material distribution, a spatial pattern of specific sediment yield appears. The non-linear Y s– A relationship may be interpreted as an indication that the fluvial system of the Yellow River is still at the stage of strong adjustment to the environmental change of Pleistocene–Holocene transition, especially to the change of dominant geomorphic agency from wind to flowing water. This non-linear relationship can also be explained by the variation of stream power with the drainage basin scale. The stream power increases with drainage area to a peak value, and subsequently decreases, a trend that is similar to the trend of the Y s– A relationship.