Extension of shoreline under erosion (period between 1958 and 2010)

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Graph: 
Source: 
APA, 2016

The existing data, corresponding to 2010, show that the length of low-lying sandy coast and low rocky coast supported by dunes under critical erosion is about 180 km, with retreat rates with variable magnitude.

The average narrowing rates in the period 1958-2010 range from 0.5 m/year to 9.0 m/year  (Litoral Working Group Report, 2014; Lira et al, 2016).

The magnitude of the erosive process reaches its largest expression in the coastal cells 1b, 1c and 4, according to the division made by the Littoral Working Group, in 2014, based on the different characteristics of the Mainland Portugal shoreline with regard to geomorphology and sediment dynamics. These cells include the following coastal stretches: Espinho - Torreira, Praia da Barra - Mira, Figueira da Foz - Leirosa and Costa da Caparica, which show an average coastline retreat ranging from 200m to 300m over the last 60 years (Sediment Working Group Report, 2015).

Sediment deficit (i.e. decrease in the supply of sediments to the shoreline) in the respective coastal cells, combined with a high-energy wave regime and intense longshore drift (i.e. the sediment transported parallel to the shoreline during a given time interval) contribute to the installed erosive trend.

The magnitude of coastal erosion, and the respective associated risk, determined that most of the investment made in the coastline over the last decade, amounting to approximately 244M€, was allocated to coastal protection and defence interventions.

In order to decrease risk to people and assets, some coastal urban areas (e.g. Espinho, Esmoriz-Cortegaça, Furadouro, Costa Nova, Vagueira, Cova Gala, Costa da Caparica) were protected by means of “hard” measures (i.e. rock armour revetment, seawalls and groins) and beach nourishment operations.

The systematic and continuous monitoring of Mainland Portugal's shoreline (COSMO Programme) is expected to start early in 2017 (over a period of 3 years), specifically focused on the evolution of the coastline and nearshore seabed, always based on the extent of Mainland Portugal's coastline, according to the official cartography - the coastline orthophotomaps provided by the Directorate-General for Spatial Planning -, which will allow to periodically identify the length of coastline under critical erosion, according to the applicable criteria.

Ordem de aparecimento: 
5
Indicator: 
Coastline under erosion