Scale effect on sediment yield from sloping surfaces to basins in hilly loess region on the Loess Plateau in China

Based on data from two runoff plots and ten stations in hilly loess region Dalihe drainage basin ranging in area from 0.0006 to 3983 km² on the Loess Plateau, the relationship between mean annual specific sediment yield (Y _s) and drainage area (A) is studied, which is different from those for many other drainage areas of the world, neither at the scale of whole basin nor at local scale on the Loess Plateau. With increasing drainage area, the mean annual specific sediment yield experiences two peak values: the first peak value appears at 0.00408 km² in area corresponding to the whole slope surface, and the second peak value appears at 96.1 km² in area. The non-linear variation in the Y _s–A can be explained as follows: the first peak value can be explained by the abrupt increase in slope gradient and flow shear stress resulting in highly increased sediment concentration and specific sediment yield. And the second peak value can be explained by the combined influence of flow shear stress and drainage density, represented by dimensionless variable Ω.