Experimental study of sediment fluxes on Barcelona's nearshore

The presence of suspended sediment in marine waters has several impacts, such as a degradation of the coastal ecosystem, pollution or a damaging effect on the tourism-oriented economies. FIELD_AC is a European project that aims to provide an improved operational service for coastal areas and generate added value for GMES predictions. This is achieved by the analysis of field cases. In this context, this minor thesis is based on the study of the information obtained in a field campaign carried out on Barcelona’s near shore between November of 2010 and January of 2011. The data studied in this minor thesis was acquired in two different deployments: A1 and A2, located at 24 m depth in front of the combined sewer overflow of Bogallet and in front of the Besós river mouth respectively. These deployments consisted of a concrete structure provided with an AWAC current profiler, able to measure current velocities and wave parameters, and two different SSC sensors: a turbidimeter and an optical backscatter. In the first place, a quality control of the measurements provided by the instruments is done in order to verify its validity in relation to each instrument measuring range and in relation to the expected behaviour for each parameter. The only instruments that show problems with the validity of the measurements are the turbidimeters and the optical devices. Data acquired until the 8th of December shows optimal reliability. From that date until the 5th of January, turbidity data suffers a decrease of reliability and from the 5th of January onward, turbidity measurements are not valid, as the behaviours observed cannot be explained by natural processes. In the second place, the validated data is studied. Including meteorological conditions (wind, atmospheric pressure and rainfall), sea level, wave climate (significant wave height, maximum wave height, period and direction), currents and continental inputs (combined sewer overflow spills and river discharges). These parameters are the driving forces that control sediment transport processes. In the third place, sediment fluxes, current shear stress, wave shear stress and critical conditions for resuspension are calculated and significant SSC increase events are identified. Finally, each turbidity increase event is studied thoroughly in order to establish the agents responsible for the presence of sediment in the water column. Three agents are observed to have the capability of incorporating sediment to the water column in Barcelona’s near shore: waves, currents and offshore fluxes of continental inputs