Abstract
The results of this study have allowed verification that longshore sediment transport along the coast of Napoli Gulf (southern Italy) takes place from Northwest to Southeast. The current analysis describes the results of an integrated sedimentological and geomorphological study of the Neapolitan coastal area. A sedimentological and morphosedimentary study was carried out by bathymetric survey and sampling of bottom sediments. The analysis of modal isodensity curves shows that all the sediments are moved from NW to SE by longshore currents parallel to the coastline. The morphological evolution of the Castellammare di Stabia Gulf coastal area, based on historical coastline changes, starts from 1865, when the sandy littoral was wide and in its natural state. Since the construction of the Torre Annunziata harbor in 1871, sediments transported by a NW-SE longshore drift have become trapped, inducing the genesis of a new wide triangular-shaped beach on the updrift side (NW) of the harbor breakwall. This process induced a significant shoreline retreat of the south-east sector of the littoral. Widespread beach erosion of the coastal physiographic unit of Castellammare di Stabia Gulf (delimited by two ports) is more developed in the southern portion. This study highlights a slight rotation of the shoreline toward the East and a general trend of regression, with typical overall accentuation of shoreline concavity, and significant widening of the triangular-shaped beaches at the end of the falcate. This reduced sediment input removed from the sedimentary budget a large amount of deposits, which are hardly restorable due to the scarce supply of sediment load by the Sarno river and its tributaries. In addition to this new and important derived morphologic feature, other recent human interventions have contributed to further modifications of morphologic characteristics of emerged and submerged beach. The intense use of the territory caused modifications on both the fluvial course and river mouth with direct and indirect effects on the shoreline and the drainage network of the Sarno River.
Highlights
Longshore sediment transport is important on most of the coastline; the direction of the net longshore sediment transport of the coastline may be manifested from natural features and by the accumulation of sediment behind obstacles such as harbors, breakwalls and groynes
The Torre Annunziata harbor caused a radical modification in the natural morphological sediment transport processes, with direction from NW to SE; it traps the sediments carried by structure of the coastal zone located to the South, in the Gulf of Castellammare di Stabia, resulting into the longshore currents, allowing them to be accumulated in a new wide beach (Figure 3 and 5C), a general coastal erosion on the downdrift side (Figure 6)
The continuous subtraction of drifting sediments trapped by Torre Annunziata harbor has led to a marked coastal erosion in the Gulf of Castellammare di Stabia, located on the downdrift side (Figure 6)
Summary
Longshore sediment transport is important on most of the coastline; the direction of the net longshore sediment transport of the coastline may be manifested from natural features and by the accumulation of sediment behind obstacles such as harbors, breakwalls and groynes. A detailed geomorphological and sedimentary study of a coastal area affected largely by human-induced alteration of the coastline and longshore sediment budget. Sketch of southern Italy (the study area is shown in the circle) It consists of a narrow sandy beach, surrounded by the artificial harbors of Torre Annunziata to. The presence of artificial harbors located at the extremes of the units impliesby a the Sarno transport. The presence of artificial harbors located at the extremes of the units implies different by wave-generated longshore currents, which causes a weak rotation of the a differenttowards transport wave-generated longshore currents, causesside a weak of the shoreline theby.
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