Cost-benefit analysis of coastal defenses on the Vagueira and Labrego beaches in North West Portugal

• Autor(a) principal: Maia,A.
• Data de Publicação: 2015
• Outros Autores: Bernardes,C., Alves,M.
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://scielo.pt/scielo.php?script=sci_arttext&pid=S1646-88722015000100007
• topic: Ria de Aveiro; barrier; coastal defenses; coastal erosion; shoreline

The Portuguese northwest coast has been suffering for decades from severe erosion and important geomorphological changes, particularly in sandy stretches. This process is related to a number changes which include: a reduction of the supply of sediments, an increase in the mean sea level, an increase of storm frequency and anthropogenic transformations. The Aveiro coastal stretch is morphologically characterized by a sandy barrier-lagoon system often referred to as Ria de Aveiro; the barrier has been submitted to a continuous narrowing and topographic reduction that together potentiate a significant retreat of the coastline, an erosion of the beaches, and over washing. This paper analyses a coastal sector of approximately 3km in length, between the Vagueira and Labrego beaches, located at the south of the jetties that protect the access to the Aveiro lagoon. The study includes the behaviour of the erosion in the last 52 years, the projection of the coastline for the year 2020 and a cost-benefit analysis (ACB) for two scenarios: the present, with the existent coastal defenses, and another one with the absence of defenses. We examined aerial photographs taken in different years in order to determine the different shoreline positions, historical trends and mean shoreline retreat. The analysis of the economic viability of the scenarios was carried out based on the calculation of present value (NPV). The historical (1958-2010) coastline retreat shows a value of about -3.5m/year, and if the hydrodynamic conditions remain identical to the present, by 2020 a loss of approximately 7ha of territory is expected in semi-natural areas, assuming that the urban areas will continue to be protected. The cost-benefit analysis point out that investment in coastal defenses is not economically viable, particularly in hard defenses. This situation also occurs if nothing is to be done to preserve the natural and built areas. However, in the latter case the economic losses are smaller. Nonetheless, all scenarios and the impact of changes should be based not only on economic factors but also by taking into account the ecological and social importance of the coastal zones. Bearing in mind the present trend, and in order to continue to protect the urban front of Vagueira, the existing defenses will have to be maintained and reinforced, which will mean more investment in the near future.