Suspended sediment transport in a small Mediterranean agricultural catchment

The aim of this study is to analyze suspended sediment transport in a Mediterranean agricultural catchment under traditional soil and water conservation practices. Field measurements were conducted in Can Revull, a small ephemeral catchment (1.03 km(2)) on the island of Mallorca. This study uses continuous turbidity records to analyse suspended sediment transport regimes, construct and interpret multiple regression models of total suspended sediment concentration (SSC) and of SSC related to stormflow discharge, and assess the sediment loads and yields of three hydrological years (2004-2005 to 2006-2007). An annual average SSC of 17.3 mg l(-1), with a maximum of 2270 mg l(-1), was recorded in the middle of the winter period when rainfall intensities are high and headwater slopes are ploughed and thus bare. Strong seasonal contrasts of baseflow dynamics associated with different degrees of dilution provide a large scatter in SSC and in the derived rating curves, reflecting that other factors control the supply of suspended sediment. Multiple regression models identify rainfall intensity as the most significant variable in sediment supply. However, under baseflow conditions, physical and biological processes generate sediment in the channel that is subsequently removed during high flow. In contrast, when baseflow is not present, rainfall intensity is the only process that supplies sediment to the channel, mostly from hillslopes. Considering the study period as average in terms of total annual rainfall and intensities, suspended sediment yields were an order of magnitude lower than those obtained in other Mediterranean catchments, a factor that can be related to the historical use of soil conservation practices. Copyright (C) 2009 John Wiley & Sons, Ltd.