Quantification of inlet-related hazards in barrier island systems. An example from the Ria Formosa (Portugal)

Determination of inlet hazard areas (IHAs) is important for the management of barrier island systems such as the Ria Formosa. An IHA is an area of natural importance that can be easily destroyed by inlet-related processes and covers the land adjacent to inlets [CAMA, 2004. Handbook for Development in Coastal North Carolina. Division of Coastal Management from the North Carolina State Department of Environmental and Natural Resources. http://www.nccoastalmanagement.net/Handbook/contents.htm, (accessed 07.04)]. One parameter is defined in order to quantify the extension of the inlet-associated hazards within a barrier island system. This parameter, the minimum inlet hazard area (IHAmin), represents the extent of the minimum area that should be taken into account when analysing inlet-associated hazards and is determined using the following criteria: (a) inlet maximum width; (b) inlet migration path and (c) existence of frequently overwashed areas that can be related to present or historic inlets. The calculation of the IHAmin was applied to the Ria Formosa barrier island system (southern Portugal) for a time scale of decades. For the Ria Formosa the IHAmin represents approximately 45% of the total length of the system. Most of the occupied areas within the barrier chain are located inside the IHAmin. Changes in the configuration and number of inlets of the system would modify the total IHAmin calculated for the entire area. However, assuming that the typical migration patterns identified for the system do not change, the herein proposed methodology can still be applicable to calculate the new associated IHAmin. This study showed that other studies should be considered in future work including: (i) quantifying buffer distances on both sides of the IHAmin and (ii) analyses of the inland extent of the hazardous areas. The IHAmin is an easy-to-use parameter that could be quantified for other inlets located in other parts of the world.