Sandy replenishment of St George's Bay

Architect Fortunato Said (The Sunday Times, May 23) raised the issue of the effect on natural sea currents and wave action on the sand that has recently been placed at St George's Bay.

Sand within the bay can be lost either through wave action or as a result of significant water flow down the valley. The loss of sand would be permanent if the seagrass meadows (Posidonia oceanica) at the foot of the beach were to be compromised in any way.

These meadows are priority-protected habitats under the EU Habitats Directive, in view of their importance as nursery and breeding grounds for marine organisms.

In 2000, the Ministry of Tourism duly commissioned Environmental Impact Assessment studies to investigate the effect of the placement of a large volume of sand in the bay. The EIS included mapping of the seabed, statistical hindcast of storms impacting the bay, and a hydrodynamic model of the replenished beach. Two different sizes of sand grains were tested in the model: the 0.17 mm type, which is the size of the sand grains currently in the bay, and the 2 mm grain.

The model results indicate that a beach nourished with the 0.17 mm sand will lose sand more rapidly than an equivalent beach nourished with the 2 mm sand. Furthermore, sand lost from the 0.17 mm nourishment is lost below the -5 m contour and practically smothers the seagrass meadows in the area. On the other hand, the 2 mm sand appears to come to rest around the -3 m contour, thereby avoiding these impacts and making the recuperation of the displaced sand easier.

The above model also indicated that the specific gravity of the sand to be used in the replenishment exercise would have to be greater than 2.6 (by comparison, local limestone has a specific gravity of 2.2).

It was on the basis of these considerations that the specifications of the sand to be utilised for the replenishment project were established.