Impacts of soil properties on flow velocity under rainfall events: Evidence from soils across the Loess Plateau

Abstract

Flow velocity is one of the most significant hydraulic parameters directly connected to sediment transport-deposition processes. Four soils were collected from north to south of the Loess Plateau, namely Sandy Loess (SL), Loessial Soil (LS), Heilu Soil (HS) and Anthrosol Soil (AS), to examine the impacts of soil property on mean flow velocity in both interrill and rill flows under different simulated rainfall experiments. The mean velocity of interrill flow (MVIF) followed the order of LS > HS ≈ AS > SL at 90 mm h−1 rainfall intensity and LS > HS > AS > SL at 120 mm h−1 rainfall intensity. The mean velocity of rill flow (MVRF) decreased as LS ≈ HS > AS at 90 mm h−1 and LS ≈ HS > AS > SL at 120 mm h−1. The order of MVIF and MVRF on four soil slopes is determined by the relations of runoff discharge, Darcy-Weisbach friction factor in interrill area (fI) and rills (fR), which are closely related to soil properties. Soil properties also changed the effects of rainfall intensity on flow velocities in different erosion stages, resulting in the increasing trend of MVIF on SL, HS and AS slopes and the decreasing trend of MVIF on LS slope with the increase of rainfall intensity. Moreover, soil properties may change the variations of MVIF and MVRF with the increase of slope gradient, by altering the relations of sealing progress and slope effect. The slope effect determined the increasing trend of MVIF with the increase of slope gradients. However, the sealing progress may offset the slope effect and cause the decrease of MVIF on the critical slopes, and the critical slope decreased from the north (20° and 25°) to the south (15°). The equal roles of rill bed roughness and slope effect caused the unchanged of MVRF on LS and HS slopes, while rill bed roughness dominated the fluctuations of MVRF on SL and AS slopes.