Browsing by Author "Freire, P."
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- Flood hazard assessment and management of fetch-limited coastal environmentsPublication . Carrasco, Ana Rita; Ferreira, Óscar; Matias, Ana; Freire, P.Flooding is a significant environmental threat that can cause loss of human life, damage to infrastructure, disruption to economic activity, and decline in ecological resources in coastal areas. This paper presents a framework for assessing the potential implications of floods in fetch-limited coastal environments (with no significant wave setup), focused on hazard mapping and risk analysis. Hazard maps are based on defined return periods and risk estimates are determined by computing the extent of affected occupied and ecological areas lying below water levels associated with the return periods. For management purposes, this study chooses the adaptive management approach as the most feasible to improve local economies and mitigate the loss of natural areas, and identifies/recommends specific types of occupation and activity for each flood hazard zone. The proposed framework was applied to a low-energy fetch-limited beach, Ancão Peninsula backbarrier, located in the Ria Formosa barrier system (southern Portugal). Inundation levels predicted for 1-, 10-, and 100-year return periods were 2.02 m, 2.39 m, and 2.84 m above MSL (mean sea level), respectively. On this basis, flood impacts were found to be important in occupied areas, generating physical damage to residences and infrastructure. Ecological impacts of floods affected sub-aerial species inhabiting dunes. Several management options deriving from the framework’s application were recommended for the Ancão Peninsula.
- Sediment transport measurements with tracers in very low-energy beachesPublication . Carrasco, Ana Rita; Ferreira, Óscar; Matias, Ana; Freire, P.; Bertin, X.; Dias, J. A.This study investigates sediment transport at a very low-energy backbarrier beach in southern Portugal, from a spring-to-neap tide period, during fair-weather conditions. Rates and directions of transport were determined based on the application of fluorescent tracer techniques. Wind and currents were collected locally, whereas the dominant small and short-period wind waves were characterized using a morphodynamic modelling system coupling a circulation model, a spectral wave model, and a bottom evolution model, well validated over the study area. For the recorded conditions sediment transport was small and ebb oriented, with daily transport rates below 0.02 m3 day-1. Tidal currents (mainly ebb velocities) were found to be the main causative forcing controlling sediment displacements. Transport rates were higher during spring tides, tending towards very small values at neap tides. Results herein reported points towards the distinction between tracer advection and tracer dispersion in this type of environment. Transport by advection was low as a consequence of the prevailing hydrodynamic conditions (Hs < 0.1 m, and max. current velocity of 0.5 m s-1) and the tracer adjustment to the transport layer, whereas dispersion was relatively high (few metres per day). Tracer techniques allowed distinguishing the broad picture of transport, but revealed the need for refinement in this type of environments (bi-directional forcing by ebb and flood cycles).