A diachronic analysis of estuarine turbidity due to a flood following an extreme rainfall event

摘要

During floods following rainfall events characterized by long return period, rivers bring to their mouths the higher concentration of sediments. This paper deals with a qualitative assessment of coastal water and turbidity load in estuarine waters as a consequence of an intense rainfall event occurred on the 16~(th) and 17~(th) September 2003 in the eastern part of Sicily. Although empirical relationships to estimate turbidity using remote sensing can be found in literature, however models parameters need to be calibrated through in situ measures acquired via intensive field campaigns. The algorithm used within this research was calibrated using field data acquired during three periods in 2008 (at the beginning of July, August and September). Plumes caused by two rivers, the Simeto and Anapo, were spatially and temporally analyzed. The rivers belong to two catchments characterized by different pedology and land cover. It was proved that the turbidity plume at the estuary has a strict correlation with distance from river mouth, however it strongly depends on catchment characteristics. A multitemporal analysis of MODIS images with 250 m spatial resolution showed that nephelometric turbidity (NT) rises as the flow discharge reaches the gulf, then it sharply decreases tending to an asymptotic base value approximately after a decade. Finally, the coarse spatial resolution of MODIS images was judged not appropriate to characterize plume dynamic close to the mouths of the rivers under investigation.