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Besides the different scales within which coastal processes manifest their energy, the majority of the world's coastal regions exhibit forms of sediment heterogeneity that are physically significant. One example of a heterogeneous environment is Cassino beach, located at the southernmost part of Brazil, a fine-grain-sized sandy beach where fluid mud sporadically is transported to the nearshore and eventually onto the beach. At this site in 2005, as part of a field experiment, a video system was installed. Three years after the installation, a large mud transgression event took place in February 2008 and had 5 km of extension. In this context, the goal of the present work is to characterize the mud deposition pattern across the surf zone, describing the consequences of mud on nearshore dynamics using remote sensing techniques, beach profiles and suspended matter concentration. The surveyed beach profiles registered the deposition of fluid mud at the inner surf zone with concentrations up to 12 mg/l. The material was deposited close to the shoreline and had a cross-shore width of 100 m during the first deposition day occupying the entire water column. From surf zone time series of pixel intensity, it was possible to detect the attenuation of the surface wave spectra due to the presence of fluid mud. The combination of video techniques and field data allowed one to follow the formation of a double-layer system, where fluid mud overlays the sandy bottom. The video-based system at Cassino demonstrated that remote detection of fluid mud and quantification of its effect on the nearshore dynamics is feasible. The combination of beach profiles, measurements of suspended matter concentration and intensity timestacks allowed the analysis of the short-term evolution of the mud depositional processes. |
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