Author(s)

C Sá-Pires, Ó Ferreira & J A Dias

Abstract

During the last decades, the Ria Formosa barrier island system (Algarve, South Portugal) has been undergoing a global infilling process in its lagoon area. To improve water circulation throughout the entire lagoon area, a major intervention program was performed between April 1999 and July 2000. This program included, the dredging of a substantial part of the Ria Formosa channels to a depth of 4 m below mean sea level. The dredged material was used for beach nourishment when of adequate grain size or dumped in the nearshore when too fine. The main purpose of this study is to compare the behaviour of nourished and non-nourished areas, on the same barrier island or peninsula, using beach profiles monitoring. The selected studied sites were: Ancao Peninsula, Tavira Island and Cabanas Island. For each profile obtained the volume (m3/m) above mean sea level was computed and for each studied site (island or peninsula), volume changes at natural and replenished profiles were respectively grouped. The cumulative volume changes through time for natural and replenished profiles was computed and the correlation between cumulative volume changes after interventions, at natural and nourished profiles, was determined for each island or peninsula. The replenished profiles had a very similar behaviour to the natural ones, including erosion associated with a storm event, and net gains of material immediately afterwards and also during summer. These results show a rapid naturalisation process of the fills, reflecting correct placement of the fill. The observation of a beach volume at the end of the monitored period similar to

Keywords