Lessons from inlet relocation: examples from Southern Portugal

Inlet relocation is a coastal management tool that, when applied to a migrating inlet, involves the artificial opening of a new tidal inlet along the historic migration path of the inlet. The old inlet is then artificially closed, or it is left open and will eventually close if the new inlet captures the entire tidal prism. Two inlets were relocated in such a manner in Southern Portugal and then were the subject of a monitoring program that included the acquisition of quantitative (topo-bathymetric surveys) data. Data was acquired for 4 years after the relocation at one of the inlets (Ancão Inlet) and for 2 years at the other (Fuzeta Inlet). The data obtained from the monitoring program were analysed together with the wave climate and then compared with historical information on the natural inlets, in order to assess the degree of success of the relocation actions. One of the relocations studied, Ancão Inlet, was considered to be successful even though an initial unexpected behaviour produced some material damage to property. On the contrary, the relocation of Fuzeta Inlet did not have the expected results, and the new inlet was affected by the same problems as the old one.It was found that the most important factor for a relocation action to succeed is the correct choice of the opening location. A theoretical procedure to enhance the possibilities of relocation success is suggested. (1) Hydrodynamic studies are needed in order to determine if the present conditions are similar to the historical ones. (2) The position for the inlet opening is chosen according to the hydrodynamic conditions, but there are other factors to be taken into account, i.e., the historical migration paths and typical inlet width of the natural inlet; the hydrodynamics of the backbarrier; the morphology of the backbarrier and, for multi-inlet barrier island systems, the proximity to adjacent inlets. (3) Once the position is chosen, environmental impact studies should be made in order to assess the risk of the relocation for the ecosystems of the area. Only if the environmental impact studies are favourable should a relocation action be performed.