Scale Independence and Spatial Uniformity of Specific Sediment Yield in Loess Areas of the Wuding River Basin, Northwest China

Most of the sediment loads of the Chinese Yellow River originate from the 113,000km(2) Hekou-Longmen Section. This study investigated the spatial pattern of specific sediment yield in the Wuding River basin, a tributary of the section. Data collected in 36 instrumented watersheds were used. Stratifying the watersheds in terms of surface regolith reveals a scale uncorrelated and a roughly constant SSY (mean annual specific sediment yield) of 18,720Mgkm(-2)yr(-1) in the loess areas of the basin, with basin areas varying between 0.107 and 9,355km(2). A zero-variable model (i.e. SSY=18,720) thus performs well with a mean error of approximately 15%. The spatial uniformity even holds at the annual time scale; a spatially invariable SSYa (specific sediment yield for a single year) remains applicable with a mean error of the order of 40%. The spatial uniformity in SSY and SSYa allows a direct scale extrapolation. Moreover, the established zero-variable models and the scale extrapolation are even applicable to the Hekou-Longmen Section. The spatially uniform SSY accords with the spatial invariability of many sediment-yield related factors, such as basin slope and rainfall in the loess areas of the Wuding basin. Given the fact that sediment delivery ratio is close to 1 in the Loess Plateau, a spatially uniform SSY is equivalent to a uniform erosion rate among watersheds. This finding, contrasting with current consensus that erosion and sediment yield vary greatly in space, is greatly helpful in predicting erosion and sediment yield in the Loess Plateau. Copyright (c) 2016 John Wiley & Sons, Ltd.