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- Historic monuments threatened by coastal hazards at Boca do Rio, Algarve, PortugalPublication . Carrasco, A. Rita; Ferreira, Óscar; Matias, Ana; Dias, J. A.The coastal stretch of Boca do Rio, western Algarve, Portugal, is experiencing shoreline retreat. Roman ruins are located along the beach section of the coast, and a 17th-century fort is positioned over the cliff section. Both historic monuments are being destroyed by erosion but need to be protected due to their heritage status. Aerial photograph analysis was used to define the evolution of the coast for the period 1945–2001. Shoreline retreat of 0.3 m/year was measured for the sandy coast and 14 mass movements in the cliff face were identified. Considering the rate and style of shoreline evolution, several types of management scenario were evaluated, with the favored measures being the removal of the Roman ruins to a museum and the relocation of the fort inland.
- Thresholds for storm impacts on an exposed sandy coastal area in southern PortugalPublication . Almeida, L. P.; Vousdoukas, Michalis; Ferreira, Óscar; Rodrigues, B.; Matias, AnaStorms are one of the most important phenomena responsible for coastal erosion. Their destructive power presents major challenges for coastal management, and knowledge of their characteristics and associated consequences is therefore of paramount importance. In this study, thresholds for storm impacts are defined for a sandy coast in southern Portugal (Faro beach, Ria Formosa) using two different approaches: i) hydrodynamic conditions associated with historical storm impacts (i.e., infrastructural damage); and (ii) computed maximum wave run-up values (RHIGH) compared with beach morphology. Damage thresholds are defined as limits above which the action of a storm exceeds beach front response capability and starts to act directly on human infrastructures. According to method (i), four different thresholds were defined. For individual storms directed from the SW the threshold is a significant wave height of 4.7 m with a storm duration of 2 days, and for storms directed from the SE is a significant wave height of 6 m with a storm duration of at least 2 days. Regarding storm groups, for those directed from the SW the threshold is 2 storms lasting at least 2 days each with significant wave heights greater than 3.5 m, whilst for those directed from the SE the threshold is 3 short storms (lasting 1 day each) with significant wave height over 3.9 m. The return period for the SW storm group threshold is just 1.7 years. For method (ii), beach morphological parameters (DHIGH — highest elevation of the frontal dune; DLOW — elevation of the dune base; and tanβf — foreshore slope) were determined for five chosen cross-shore profiles along the study area, and RHIGH computed for different hydrodynamic conditions. Results were validated through field observations of storm impacts. The lowest thresholds for overwash are along the central part of the study area where a dune crest is absent due to human occupation. The highest thresholds for overwash are on those profiles where a frontal dune is well developed or a foredune ridge is present (western and eastern parts of the study area). This study presents a methodological strategy to compute realistic thresholds for storm impacts along Faro beach based on historical datasets of hydrodynamics and storm impacts information. The approach could be implemented in other coastal areas to provide a comprehensive assessment of the storm impact, requiring only simple information like offshore storm hydrodynamics characteristics, beach morphology and reports of coastal infrastructure damage.
- 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).
- Natural and human-induced coastal dynamics at a back-barrier beachPublication . Carrasco, A. Rita; Ferreira, Óscar; Matias, Ana; Freire, PaulaThis study contributes to the understanding of very low-energy fetch-limited environments by reporting the evolution of a back-barrier beach (Ancão Peninsula, southern Portugal). It considers two timescales: a large-scale evolution for the past 60 years based on aerial photograph analysis, and a small-scale beach evolution based on monthly topographic surveys performed during three years of monitoring. Each timescale revealed a different rate of evolution, the first reporting a modified beach response-type (from human activities), and the second reporting a natural beach response-type. Human activities caused significant changes in the back-barrier shore, whereas changes under natural forcing were much smaller, were less influential on the area's evolution, and were not sufficient to counteract or mask the consequences of human activities. The findings of the study should contribute to a better understanding about the large- and small- scale changes in other back-barriers characterised by similar very low-energy conditions.
- Determination of thresholds for storm impactsPublication . Ferreira, Óscar; Almeida, L.P.; Rodrigues, B.; Matias, AnaStorms are responsible for important erosion, coastal retreat and damage when infrastructures are placed within their acting area. The characterisation of storm parameters and associated thresholds for erosion and damage are therefore of fundamental importance for coastal management purposes. This work presents ways of determining thresholds for important morphological changes (including erosion), overwash occurrence and damage associate to storm occurrence. These methods were tested and applied to Ancão Peninsula (South Portugal) and the results shown. The use of these approaches will enable coastal managers to have a quantitative knowledge of consequences associated to each particular storm and to act accordingly, for instance defining set-back lines, designing nourishments or implementing evacuation plans.
- Management measures for ancient settlements threatened by coastal hazards at Boca do Rio, Algarve, PortugalPublication . Carrasco, Ana Rita; Ferreira, Óscar; Matias, Ana; Dias, João AlveirinhoCoastal areas are dynamic by nature, with physical changes occurring over various time scales. When these changes manifest themselves as a landward movement of the shoreline occurring on human time scales, the quantification of erosion rates becomes important (Moore and Griggs, 2002). The evolution of coastal retreat results from several relationships between external and local processes, with many variables potentially affecting the rate and manner of retreat. Currently, the Portuguese coastal zone is strongly affected by coastal erosion in association with an important sedimentary deficiency, which was initiated around the beginning of the 20th century, and became strongly enhanced after the 1930s-1940s (Dias and Neal, 1992). At present, shoreline retreat rates reach the order of a few meters per year in some parts of the Portuguese coastline (Dias and Neal, 1992). A decrease in fluvial sediment transport and a continuing rise in sea level are two of the main causes of coastal erosion not only in Portugal, but also in other parts of the world. Over shorter timescales, storms are also able to cause coastal retreat. Such retreat is only reversible on a human scale (years to decades) if sediment starvation is naturally or artificially stopped (e.g., by beach nourishment or dune building) (Carter, 1988). Changes in storm patterns and incident wave climates may result in beach realignments and higher rates of foreshore change.
- 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.
- Coastal storm risk assessment in Europe: examples from 9 study sitesPublication . Ferreira, Óscar; Ciavola, P.; Armaroli, C.; Balouin, Y.; Benavente, J.; Del Río, L.; Deserti, M.; Esteves, L. S.; Furmanczyk, K.; Haerens, P.; Matias, Ana; Perini, L.; Taborda, R.; Terefenko, P.; Trifo, E.To assess coastal storm risks thi paper compares existing hazards, associated risks, coastal management plans, and civil protection schemes from nine European countries.