ABSTRACT
Soil erosion on the loess hillslope has an obvious vertical zonation at different hillslope positions. Each erosion zone has its runoff and sediment characteristics, and the runoff and sediment from an upslope erosion zone affects the runoff and sediment from its downslope erosion zone. In this paper, relationships for runoff and sediment between upslope and downslope erosion zones and their controlling mechanisms at the loess hilly region are quantified. Natural runoff plots were installed at different hillslope positions, representing different forms of dominant erosion processes from sheet, rill to shallow gully in the loess hilly-gully region. Sediment samples were collected after each rainfall. Results showed that the distribution of erosion and sediment on a loess hillslope is affected by rain intensity and rainfall energy. As rainfall intensity and energy increase, the location of maximum erosion changes from the rill erosion zone to the shallow gully erosion zone. The runoff and sediment from the sheet erosion zone contributed a 13.5% to 37.7% increase in sediment production and a 19% to 36.4% increase in rill erosion from the rill erosion zone. The runoff and sediment from the sheet + rill erosion complex zone contributed a 6.5% to 82.2% increase in sediment production and an annual increase of 41% from rill erosion and 44.5% from shallow gully in the shallow gully erosion zone. The increased erosion caused by runoff from the upper erosion zones is closely related to runoff rate and sediment concentration from the upper erosion zone, rainfall intensity and energy and erosion developing stage. Regression equations for the relative downslope increase of erosion are presented. These relationships include factors such as rainfall intensity, energy, runoff rate, and sediment content from upper erosion zones. Developmental stages of erosion features also affect the upslope runoff factor.
