Roberta Ivaldi

Late Quaternary deposits from the Ligurian continental shelf (NW Mediterranean): A response to problems of coastal erosion

The Ligurian continental shelf is a terrigenous platform characterized by variable extension and subsidence of the continental margin and thick accumulation of sediments originated by repeated sea-level oscillations. Its genesis and evolution occurred during the Plio-Quaternary, even if early erosive modelling in some sectors has been dated to the Late Miocene. The present morphology of the shelf is the result of transgressive–regressive Quaternary cycles. Using a high-resolution seismic grid of more than 1000 km, we have been able to define the seismostratigraphic characteristics of the Ligurian Sea shelf. On the basis of our studies, it has been possible to describe in detail the seismostratigraphy of the Late Quaternary and Holocene sediments that cover the shelf to various depths, in terms of sedimentary sources, for the purpose of distinguishing ‘relic’ deposits suitable for nourishing beaches undergoing erosion. From this detailed study of the evolution of the most superficial deposits, it is possible to distinguish between different sedimentary bodies deposited during a transgressive phase and located at a water depth ranging between 20 and 70 m; they are represented by relic sands cropping out at the sea bottom due to a relatively thin Holocene drape and could be explored for beach nourishment programmes.

Discovery of Versilian deposits suitable for beach nourishment on the continental shelf of Western Liguria

In this paper we present the results of a study conducted in collaboration with the Ligurian Region, in the framework of the E.U. Beachmed-e Interreg IIIc Project, to distinguish relic coastal deposits on the continental shelf, suitable for beach nourishment. These deposits are related to transgressive-regressive sedimentary cycles, and they are due to Quaternary glacio-eustatic sea level variations. In fact, during the sea level low stand associated with the last glacial maximum (c.18–20,000 yBP) the sea level was 110–120 m lower than its present level and the continental shelf was exposed. During the Versilian Transgression the coastline migrated from the shelf break to its present position. This migration was not continuous and conspicuous sediment bodies, associated with deltaic or littoral systems, were deposited during static periods. The results of a marine geology campaign with seismostratigraphic and sedimentological analyses enabled us to distinguish gravelly and sandy littoral deposits at depths of 20–40 m near the coast and 60–80 m on the outer shelf, in areas with only a thin Holocene mud cover (high stand deposits).

Artificial nourishment of the Vesima beach (Genoa): Sedimentological and morphological results

In Italy artificial nourishment has been considered as a suitable tool for dealing with the problem of coastal erosion for some years, following successful experimental programmes. In this article, we present some of the results of a case study of a nourishment programme on the beach of Vesima (Genoa). This programme was undertaken to limit the coastal erosion and increase the use of the beach and the littoral near very urbanized areas where there are extensive recreational activities such as sun bathing, swimming, fishing and vacationing. In particular, we studied the evolution of the morphological profiles of the surficial beach and the variations in the sedimentological and morphometric characteristics before and after the nourishment. These profiles represent two different seasonal settings of the beach, during calm (summer) and stormy (winter) weather. The grain size and morphometry of the sediments and the morphological profile of the beach were studied in four seasonal surveys. The elaboration of the data allowed us to correlate the nourishment and the seasonal accumulation of sediments. These studies have been extremely important for our understanding of the movement of sediments and changes in the morphology of the beach due to dynamic nearshore processes and variations to the budget of the littoral sediments. After the nourishment work in March 2000, the width of the dry beach was stable; the estimate of nourishment material (20,000u200am3) and of the material left on the dry beach after 2 years (4800u200am3) indicates that a remarkable quantity of sediment was taken from the shoreface to form the nearshore zone.