부산대학교 도서관

The relation between discharge and suspended sediment transport in Mediterranean mountain catchments is typically non-linear. This is related to spatio-temporal variability in sediment sources and the intensity and distribution of precipitation which together control sediment supply and the downstream transport of suspended material. This study analyses suspended sediment dynamics in a meso-scale forested Mediterranean mountainous catchment (Ribera Salada, 224 km2; NE Iberian Peninsula) during three consecutive years (2005–2008). Dynamics were analysed based on: (i) rainfall, runoff and suspended sediment data at annual, seasonal and monthly scales, and (ii) the hysteresis patterns observed in discharge-suspended sediment relations (Q-SSC) at monthly and flood scales. Hysteresis was characterised by means of a hysteresis index and the time delay between peaks in Q and SSC. Additionally, variables related to rainfall, runoff, sediment transport and periodicity were used to infer the main causes of hysteresis patterns observed at each temporal scale. The spatial distribution of precipitation was obtained from images of daily rainfall fields obtained from radar information. Sediment dynamics were controlled by antecedent conditions (precipitation), flood magnitude and sediment availability, which, in turn, depend on the inactivity period between floods and the annual cycles of sediment production-deposition-depletion in the catchment. Three main situations were observed: (a) in winter, sediment availability and hydro-sedimentary were both low; (b) in spring, sediments mainly came from channels and banks, and from well-connected slopes, and the hydro-sedimentary activity was high; finally (c) in summer and early autumn, the main source of sediment was agricultural fields, with hydrological and sedimentary activity moderate. Counter-clockwise hysteresis loops were most frequent Q-SSC. This pattern happens when sediment sources are located far from where sediment transport is measured. However, the clockwise hysteresis loop is the most efficient pattern in terms of sediment load, being controlled by the release of subsurface material caused by the break-up of the surface armour layer of the riverbed during larger flood events. Despite the high efficiency of clockwise events, the Ribera Salada catchment is characterised by a low level geomorphic activity related to the limited sediment availability in the channel and the banks, and overall, in the upstream slopes, placing it in the lower bound of sedimentary activity reported for catchments of the Mediterranean region.