Variations in sediment yield from an agricultural drainage basin in central Belgium

At the outlet of a 250 ha agricultural drainage basin in the Belgian loess belt, discharge and suspended sediment samples were sampled to study variations in sediment: yield. Sediment yield during the observation period of 14 months equalled 9.8 t ha(-1) year(-1). In winter suspended sediment concentrations are relatively high because of the absence of significant vegetation cover on the fields. In summer, fields with high vegetation cover produce runoff but very little sediment. Furthermore, these fields trap sediment eroded further upslope, resulting in lower sediment concentrations for similar discharges. However, early spring events contribute the most to total sediment yield as they have very high discharges. Within most events a clockwise hysteresis was observed. Grain-size distribution of the suspended sediment is discharge-dependent: up to a discharge of 0.25 m(3) s(-1) the sediments were enriched in fine partticles.