Sediment budget in the lower course of a Mediterranean River (La Tordera, Catalan Coastal Ranges)

Abstract

The objective of this study is to assess the sediment budget of the Lower Tordera River (894 km2, Catalan Coastal Ranges) by means of sediment transport measurements and geodetic surveys through an 11 km river channel reach. Study period (1997-1999) was relatively dry compared to the mean annual water yield. Mean annual transfer of sediment in the upper section of the fluvial system was 30,000 tonnes, 60% of which transported as bedload and the rest in suspension. At the river outlet, mean annual sediment exportation was 21,500 tonnes, 65% of which moved as bedload and 35% in suspension. Results indicate that river is experiencing a phase of aggradation. This process is more intensive during years having a permanent fluvial regime in the upper reaches and an ephemeral regime in the lower sections. During such years most floods do not reach the lower end of the river and, therefore, sediment does not. Mean accumulation of sediment is 8,500 tonnes per year, especially around the area affected by gravel mining between 1960 and 1980.