The Use of Relict Sand Lying on the Continental Shelf for Unprotected Beach Nourishment

Abstract

The best possible policy in relation to contrast beach erosion and coastal retreat in coasts heavily exploited by tourists is artificial beach nourishment. The success of such a policy strongly depends on the availability of large quantity of sand (in the order of millions of cubic metres). The exploitation of marine sand deposits buried in the continental shelf may meet such a large need. The prospection of sand is mainly realised with reflection seismic profiles, first shot at a regional scale then concentrated in the most promising areas. Seafloor sampling is then used to verify the geophysical data and characterise the sand. The identification of sand-prone deposit is based on a detailed geological interpretation of the seismic data that allows definition of the evolution of the shelf during the last glacial cycle (20 000 years). In fact, the sea level rose from -120 m to 0 in less than 20 000 years and caused the coastline to migrate across the shelf, possibly leaving relict sand prone deposits at various depths. Unfortunately, such deposits are rare, relatively difficult to image and usually buried below the present-day shelf mud. A typical stratigraphic situation, taken from the Regione Lazio, is described as reference.