Effects of stability, transport distance and two hydraulic parameters on aggregate abrasion of Ultisols in overland flow

During runoff on soil surface, aggregates travel, abrade, and produce finer and more transportable particles, resulting in a significant effect on sediment transport, water infiltration and soil erosion. This study was to assess the effects of stability, transport distance and two hydraulic parameters on aggregate abrasion using Ultisols in subtropical China. Aggregate stability was investigated for soils from two parent materials (Shale and Quaternary red clay) with different land uses using LB methods. They were studied with a series of aggregate abrasion experiments in a 3.8 m long flume with a fixed bed. Results indicated that slaking and mechanical breakdown were probably the main mechanisms of aggregate breakdown in these study soils. Two stages of aggregate abrasion process could be distinguished via the coefficient α in different transport distances. Aggregates were first rapidly abraded, became round, and was predominantly broken apart into smaller fragments, followed by weakly abrasion of smaller fragments and round aggregates, making them even light and less angular. A good multiple regression equation was obtained for estimating aggregate abrasion in overland flow with consideration of mechanical breakdown index RMI and transport distance x. From two selected Ultisols (SX3 and QX1) and under the combination of five slopes and five discharges, exponential relationships were found between aggregate abrasion and flow depth or friction factor. This research makes a good attempt at analyzing the aggregate abrasion in overland flow from simple laboratory experiments settings, and the results of the analysis could be valuable for the development of adequate soil erosion models.