Abstract
The inner continental shelf is regarded as a repository of hyperpycnal flow (HF) deposits the analysis of which may contribute to hydrogeological risk assessment in coastal areas. In line with the source to sink paradigm, we examined the dynamics of the coastal watersheds facing the Salerno Gulf (Southern Tyrrhenian Sea) in generating hyperpycnal flows and investigated the shallow marine sediment record to verify their possible occurrence in the recent past. Thus, the morphometric properties (hypsometric integral, hypsometric skewness, hypsometric kurtosis, density skewness and density kurtosis) of the watersheds together with the potential rivers’ discharge and sediment concentration, calculated by applying altitude- and extent -based experimental relations, allowed to detect the rivers that were prone to producing HFs. In the shallow marine environment record of the last 2 kyr, anomalous sedimentation, possibly linked to HF events, was identified by comparing the sand-mud ratio (S/M) down-core —at three sites off the main river mouths — to the expected S/M calculated by applying the relation governing the present-day distribution of sand at the seabed in the Salerno Gulf. A return period of major HF events ≤ 0.1 kyr can be inferred for rivers which fall into the category “dirty rivers”. In these cases, the watersheds have a hypsometric index ranging between 0.2 and 0.3, coastal plains not exceeding 30% of the entire catchment area and a maximum topographic height ≥1000 m. A return period of about 0.3 kyr has been inferred for the “moderately dirty rivers”. In these other cases, about 50% of the watersheds develop into a low gradient coastal plain and have a hypsometric index ranging between 0.09 and 0.2. The observations on land and offshore have been complemented to reach a more comprehensive vision of the coastal area dynamics. The method here proposed corroborates the effectiveness of the source to sink approach and is applicable to analogous sediment records in temperate continental shelves which encompass the last 3 kyr, a time interval in which the oscillations of relative sea level can be overlooked.
Highlights
Floods are a common occurrence in Italy
Where A is the watershed area in km2 while a = 1.1922 and b = 0.8384 are two coefficients calibrated for the rivers of Campania region [61]
In the present work we evaluated the tendency of three categories of Southern Apennines watersheds—very small (Asa e Bonea), small (Tusciano, Solofrone and Picentino) and medium (Sele) —to trigger hyperpycnal flow (HF) events, by integrating the morphometric analysis of river catchments with the quantitative analysis of marine cores in the shallow water environment, in line with the source to sink paradigm
Summary
Floods are a common occurrence in Italy. Between 1279 and 2002, about 837 flooding events out of 1019 caused fatalities [1]. These events included sudden inundations caused by failure of levees and dams, inundations of major rivers as well as flash floods along torrents and minor streams. 1400 and 2002, the high magnitude of flood events was responsible for the highest number of fatalities in Emilia Romagna, Sicilia, Lazio and Lombardia regions while the density of fatal floods was the highest in Liguria, Campania and Friuli-Venezia Giulia regions [1]. Vennari [2]PEER analyzed the Geosciences 9, xal.
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