Araújo, M.A.V.C., Di Bona, S., Trigo-Teixeira, A., 2014. Impact of detached breakwaters on shoreline evolution: a case study on the Portuguese west coast. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 041–046, ISSN 0749-0208.
The Portuguese West Coast is facing severe erosion problems that threaten both the population andthe immediate seaside properties. Some locations, such as the Vagueira region, are especially vulnerable. In an attempt to reverse the present erosional trend, a coastal defense scheme involving two detached breakwaters was introduced in a phased manner. In this work, the impact of those two detached breakwaters on the down-drift coast is investigated. The study area extends from south of the Costa Nova village southwards to Mira. The shoreline evolution is predicted, for various decades, using the GENESIS model. The present time shoreline position, from which future situations are predicted, was obtained using LIDAR data acquired in 2011. Two different future scenarios are investigated: the ‘do-nothing’ scenario, which assumes that no further engineering interventions will be performed on the coast; and the ‘detached breakwaters protected’ scenario, with the first breakwater introduced in 2011 and the second in 2026. Depending on sediment supply, two types of simulations are carried out: calibrated simulations, which assume that the amount of sediments in the future will be equal to those in the present situation; and extreme simulations, which assume an acute shortage in sediment supply. Results show that if no further interventions are executed at the Vagueira region, the entire coastal stretch will continue to erode, which could lead to extreme consequences in some locations, depending on sediment supply. If two detached breakwaters are introduced at different intervals, a new accreting trend is predicted at the Vagueira region, reversing the present erosional phase. However, the erosional trend will continue southwards, unless a 3rd detached breakwater is introduced in Mira.