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Ria Formosa

Case study sites

Site description

Keywords: Coastal lagoon with barrier islands

The Ria Formosa coastal lagoon Case Study site is located on the southern coast of Portugal. It consists of a lagoon protected by five barrier islands and two peninsulas, spatially distributed to produce a cuspate shoreline that extends over 55km. The barrier islands are highly dynamic systems in a constant process of recycling, mostly driven by inlet breaching and migration. At present, two out of the six tidal inlets are artificially constructed, three have been relocated and only one preserves its natural origin. The back-barrier area consists mainly of tidal flats, salt marshes, small sandy islands, and tidal channels.

Tides are semi-diurnal, with mean spring tidal range of 2.8 m and mean neap tidal range of 1.3 m. The input of freshwater to the system is very low as a result of the low fluvial and rain input. This explains the semi-arid character of this region with low precipitation and surface runoff. Consequently, water levels and tidal prism within Ria Formosa are modulated by the tidal range, storm surge and the actual lagoon topography. The wind-field is dominated by westerly and easterly winds. The regional wave climate is also dominated by two main wave directions, W-SW and E-SE. The geographical, geomorphological and climatic conditions of Ria Formosa made the lagoon a breeding and transit area for fishes and birds. The area is internationally recognized and protected within the Wetlands of International Importance Convention (Ramsar) and the Birds and Habitats Directive (Natura 2000 Network). At a national level, Ria Formosa was integrated within the Natural Park network of Portugal since 1987.

Why was this area selected?

The combined factors of a low lying barrier island system with high ecological value and the existence of multiple anthropogenic activities, classify Ria Formosa as a very complex system with potential for the occurrence of significant impacts due to climate change and low-frequency, extreme storm events.

Land, coastal and marine uses

Keywords: Nature, Tourism, Aquaculture, Salt extraction, Residential use

The number of residents inhabiting the Ria Formosa drainage basin increased remarkably from approximately 99,950 to 159,530 between 1970 and 2001, with the subsequent increase of the anthropogenic pressure. The main land uses within the site's surroundings concern tourism, nature conservation, aquaculture and salt extraction. Urban development in Ria Formosa is relatively low and occupies a very small area of the system, concentrated mainly in 5 villages. Most of them are located at the back-barrier shores. However, Praia de Faro and Farol expanded seaward of the frontal dune facing the direct effect of the storms. A large part of Ria Formosa has maintained its natural state, with the important economic activities being developed only in a small portion of the lagoon area. The beach and dune systems occupy 13% of the total system among which more than 6% are grey dunes, a high priority habitat type. The rest of the system is low-lying lagoon area, such as marsh and intertidal flats, with a significant percentage of important habitats like the Zoostera marina and Zoosteranolti meadows.

Hazards

Keywords: Coastal flood, Erosion, Sea level rise

The main hazards at the area are related with the impact of storm events and surges inducing overwashes, coastal erosion, barrier breaching, inlet opening and coastal flooding. Storms with wave heights above 4m occur almost every year impacting and causing damages at occupied areas, due to barrier overwash and shoreline retreat. Inlet opening is also responsible for house and shellfish farming destruction. Ria Formosa is often subject to strong storms (e.g. cyclones of 1941 and 1961) with significant morphological changes, including barrier breaching and inlet opening. Recently (February/March 2010) coastal erosion and inlet opening, induced by a group of storms associated with high water levels (storm surge & spring high tide), lead to the destruction of more than 40 houses and restaurants within the entire Ria Formosa.

Socio-Economic losses & Environmental Impacts

Keywords: Loss of habitat, Aqua/shellfish culture damages, Coastal towns’ inundation

The receptors of the above hazards are both persons and habitats. Due to the relevant human occupation (fishermen and tourism settlements at the barriers, coastal villages at the inner area, clam farming and aquaculture), the impacts and consequences of extreme events over people and the local economy are high. Furthermore, the barrier island system accommodates extensive dune fields classified as priority protected habitats of vital importance for the conversation of the entire system as they have a key role on protecting the lagoon from the wave action.

Partner in charge

University of Algarve

Members of the project’s end-users and stakeholders board

The Institute for the Sea and Atmosphere

Photo Gallery

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Praia de Faro

Fig.1: Evolution of the shoreline in Praia de Faro (Ria Formosa) between 1990 and 2014. The top picture shows the impacts of extreme phenomena in the coast (storm of March 1990), whereas the bottom picture demonstrates the reconstruction of beach and occupation through various rehabilitation measures.

 

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