Designing a Sustainable Beach Replenishment Scheme for a Site in Malta

Abstract

FIRMAN, K., KEMP, L, FINCH, D., MALLIA, A and SCIORTINO, J., 2011. Designing a Sustainable Beach Replenishment Scheme for a Site in Malta. In: Micallef, A. (ed.), MCRR3–2010 Conference Proceedings, Journal of Coastal Research, Special Issue, No. 61, pp. 36–43. Grosseto, Tuscany, Italy, ISSN 0749–0208.The Malta Tourism Authority is planning to undertake environmentally sound beach replenishment along a rocky stretch of coastline immediately south of Qawra Point, Salina Bay. Refinement and confirmation of an initial beach layout through numerical modelling was undertaken to support Environmental Impact Studies required for the development permit for the creation of a recreational beach. There is no offshore sand available for replenishment in Malta. Instead, sand must be crushed from rock originating from an overseas quarry; local limestone is too friable. This reduces the risk of biological contamination and enables the granulometric characteristics of the sediment to be designed to suit the wave conditions and meet the design specifications. The proposed design life for the artificial replenishment, before major replenishment becomes necessary (i.e. when the cumulative dry beach area loss reaches 30%), was set at 10 years. It was recognised that hard modifications to the existing coastline, i.e. control structures, may be required to stabilise the replenishment and prevent migration of the sand however, such modifications were to be kept to a minimum and not compromise the marine environment. Important features of the site included a tidal rock pool (overtopped under certain conditions) along the spit linking Qawra Point to the mainland and the location of nearshore Posidonia oceanica meadows (an Annex I priority habitat under the European Union Habitats Directive) restricting the extent of the beach. Wave modelling was undertaken to establish extreme and morphologically representative wave conditions. The results were used to assess the typical beach plan shape which was found to be quite stable and not subject to large variations. The stable beach profile was assessed to provide an indication of the overall footprint of the beach within the bay and cross-shore sediment transport modelling was used to determine beach draw-down during storm events. Modelling studies showed that it may be possible to create a beach at the site. However, there are several factors for consideration such as the offshore extent of the beach toe, thought to place some risk on the nearshore seagrass, and overtopping from the tidal pool. Mitigation methods suggested included the adoption of coarser, narrowly graded material as well as the use of beach retaining structures. A 3D mobile bed physical model was recommended to further refine the scheme.