A particle-size sediment budget for a Mediterranean river (the lower Tordera, northeastern Spain)

The sediment budget for the Lower Tordera has been evaluated for the dry period 1997-1999 by measuring the bed load transport in two crosssections. The mobilization of most of the river bed fractions in both crosssections is produced during floods of moderate magnitude and frequency. However, results show that coarser fractions (> 16 mm) mobilized in the upper parts of the study channel do not reach the lower ones. This can be associated with some combination of changes in channel geometry (e.g. slope reduction) and the effects of gravel extractions. In contrast, finer particles (< 4 mm) moved during low discharges and small floods in the upper cross-section are evacuated during floods in outlet basin. Overall, the sediment budget between the cross-sections exhibits a tendency to accumulate sediment along the channel during dry periods when a hydrological bimodality in the fluvial channel is observed.