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- Field measurements and hydrodynamic modelling to evaluate the importance of factors controlling overwashPublication . Matias, Ana; Carrasco, A.R.; Loureiro, Carlos; Masselink, Gerd; Andriolo, Umberto; McCall, Robert; Ferreira, Oscar; Plomaritis, Theocharis; Pacheco, André; Guerreiro, MarthaOverwash hydrodynamic datasets are mixed in quality and scope, being difficult to obtain due to fieldwork experimental limitations. Nevertheless, these measurements are crucial to develop reliable models to predict overwash. Aiming to overcome such limitations, this work presents accurate fieldwork data on overwash hydrodynamics, further exploring it to model overwash on a low-lying barrier island. Fieldwork was undertaken on Barreta Island (Portugal) in December 2013, during neap tides and under energetic conditions, with significant wave height reaching 2.6 m. During approximately 4 h, more than 120 shallow overwash events were measured with a video-camera, a pressure transducer and a current-meter. This high-frequency fieldwork dataset includes runup, overwash number, depth and velocity. Fieldwork data along with information from literature were used to implement XBeach model in non-hydrostatic mode (wave-resolving). The baseline model was tested for six verification cases; and the model was able to predict overwash in five. Based in performance metrics and the verification cases, it was considered that the Barreta baseline overwash model is a reliable tool for the prediction of overwash hydrodynamics. The baseline model was then forced to simulate overwash under different hydrodynamic conditions (waves and lagoon water level) and morpho-sedimentary settings (nearshore topography and beach grain-size), within the characteristic range of values for the study area. According to the results, the order of importance of factors controlling overwash predictability in the study area are: 1st) wave height (more than wave period) can promote overwash 3–4 times more intense than the one recorded during fieldwork; 2nd) nearshore bathymetry, particularly shallow submerged bars, can promote an average decrease of about 30% in overwash; 3rd) grain-size, finer sediment produced an 11% increase in overwash due to reduced infiltration; and 4th) lagoon water level, only negligible differences were evidenced by changes in the lagoon level. This implies that for model predictions to be reliable, accurate wave forecasts are necessary and topo-bathymetric configuration needs to be monitored frequently.
- Chronology of the sedimentary processes during the postglacial sea level rise in two estuaries of the Algarve coast, Southern PortugalPublication . Boski, T.; Camacho, Sarita; Moura, Delminda; Fletcher, William; Wilamowski, A.; Veiga-Pires, C.; Correia, Victor; Loureiro, C.; Santana, PauloFour profiles of estuarine sediments obtained from boreholes drilled in the Algarve, Southern Portugal were studied in order to reconstruct the process of sediment accumulation driven by the postglacial sea level rise. In addition to the sedimentological analysis, the Foraminifera Index of Marine Influence (FIMI) permitted assessment of the nature and organization of sedimentary facies in the BelicheeGuadiana and Gilão-Almargem estuaries. The Beliche- Guadiana CM5 and Almargem G2 profiles accumulated in a sheltered environment, with the former presenting an almost continuous record of the sea level rise since ca 13 000 cal yr BP. The G1 and G3 profiles from the Gilão-Almargem area represent a more discontinuous record of the last 8000 years, which accumulated in the more dynamic environment of an outer estuary. The integration of all radiocarbon ages of dated levels, led to an estimate of sediment accumulation rates. Assuming a constant position of the sediment surface with respect to the tidal range and a negligible compaction of sediment, the sea level rose at the rate of 7 mm yr ^-1 in the period from 13 000 to 7500 cal yr BP. This process slowed down to ca 0.9 mm yr 1 from 7500 cal yr BP until the present. The marked historical change in the rate of sediment accumulation in these estuaries also occurred with the accumulation of organic matter and is, therefore, important data for global biogeochemical models of carbon. The main obstacle to obtain higher temporal resolution of the sedimentary processes was the intense anaerobic respiration of organic matter via sulphate reduction, which did not allow any accumulation of peat and, furthermore, led to erasure of the palaeontological record by acid formed from the subsequent oxidation of sulphides.
- Retrieval of nearshore bathymetry from Landsat 8 images: a tool for coastal monitoring in shallow watersPublication . Pacheco, André; Horta, João; Loureiro, Carlos; Ferreira, OscarNearshore bathymetry is likely to be the coastal variable that most limits the investigation of coastal processes and the accuracy of numerical models in coastal areas, as acquiring medium spatial resolution data in the nearshore is highly demanding and costly. As such, the ability to derive bathymetry using remote sensing techniques is a topic of increasing interest in coastalmonitoring and research. This contribution focuses on the application of the linear transform algorithm to obtain satellite-derived bathymetry (SDB) maps of the nearshore, at medium resolution (30 m), from freely available and easily accessible Landsat 8 imagery. The algorithm was tuned with available bathymetric Light Detection and Ranging (LiDAR) data for a 60-km-long nearshore stretch of a highly complex coastal system that includes barrier islands, exposed sandy beaches, and tidal inlets (Ria Formosa, Portugal). A comparison of the retrieved depths is presented, enabling the configuration of nearshore profiles and extracted isobaths to be explored and compared with traditional topographic/bathymetric techniques (e.g., high- and medium-resolution LiDAR data and survey-grade echo-sounding combined with high-precision positioning systems). The results demonstrate that the linear algorithm is efficient for retrieving bathymetry frommulti-spectral satellite data for shallowwater depths (0 to 12 m), showing amean bias of−0.2m, a median difference of −0.1 m, and a root mean square error of 0.89 m. Accuracy is shown to be depth dependent, an inherent limitation of passive optical detection systems. Accuracy further decreases in areas where turbidity is likely to be higher, such as locations adjacent to tidal inlets. The SDB maps provide reliable estimations of the shoreline position and of nearshore isobaths for different cases along the complex coastline analysed. The use of freely available satellite imagery proved to be a quick and reliable method for acquiring updated mediumresolution, high-frequency (days and weeks), low-cost bathymetric information for large areas and depths of up to 12 m in clear waters without wave breaking, allowing almost constant monitoring of the submerged beach and the shoreface.
- Field measurements of intertidal bar evolution on a high-energy beach systemPublication . Jackson, Derek W. T.; Cooper, J. Andrew G.; O'Connor, Marianne; Guisado-Pintado, Emilia; Loureiro, C.; Anfuso, GiorgioNearshore bars play a pivotal role in coastal behaviour, helping to protect and restore beach systems particularly in post-storm conditions. Examination of bar behaviour under various forcing conditions is important to help understand the short-to medium-term evolution of sandy beach systems. This study carried out over a nine-week period examines, the behaviour of three intertidal bars along a high energy sandy beach system in northwest Ireland using high-frequency topographic surveys and detailed nearshore hydrodynamic modelling.Results show that, in general, there was onshore migration for all the bars during the study period, despite the variability observed between bars, which was driven mostly by wave dominated processes. Under the prevailing conditions migration rates of up to 1.83 mday(-1) and as low as 0.07 mday(-1) were observed. During higher wave energy events the migration rates of the bars decelerated in their onshore route, however, under lower wave energy conditions, they quickly accelerated maintaining their shoreward migration direction. Tidal influence appears to be subordinate in these conditions, being restricted to moderating the localized wave energy at low tides and in maintaining runnel configurations providing accommodation space for advancing slip faces.The study highlights the intricate behavioural patterns of intertidal bar behaviour along a high energy sandy coastline and provides new insights into the relative importance of wave and tidal forcing on bar behaviour over a relatively short time period. Copyright (C) 2016 John Wiley & Sons, Ltd.
- Hazard assessement in rock cliffs at Central Algarve (Portugal): a tool for coastal managementPublication . Nunes, M.; Ferreira, Óscar; Schaefer, M.; Clifton, J.; Baily, B.; Moura, Delminda; Loureiro, C.Coastal hazards are in the interface of human activities with natural coastal processes. The conflicts arising from this relationship require new approaches suitable for coastal management that consider the dynamic of coastal areas. A method to assess hazard in rock cliffs is presented, combining cliff evolution forcing mechanisms along with protection factors, according to a weighted factors system. This method provides a rapid evaluation of vulnerability for cliffed areas, supporting coastal management and hazard mitigation. The method was applied to the rocky cliffs of the densely populated coastal zone between Galé and Olhos de Água (Southern Portugal), where high and very high hazard values were found to be dominant. A method validation was made using the vulnerability areas and the recorded mass movements over a 45 year period in the same area.
- Palaeosurface reconstruction based on sedimentary record and in sea level evolution in the Guadiana Estuary (Southern Iberia)Publication . Loureiro, C.; Boski, T.; Albardeiro, L.; Moura, Delminda; Terefenko, P.; Camacho, Sarita; Veiga-Pires, C.The sedimentary infilling of the Guadiana estuary, in the Southern Iberian Peninsula, has been extensively studied using a variety of laboratory methods, namely geochemical and sedimentological analyses, foraminifera assemblages and palynological profiles, supported by 14C dating [1-3](...)
- Modelling of estuarine response to sea-level rise during the Holocene: Application to the Guadiana Estuary-SW IberiaPublication . Sampath, DMR; Boski, T.; Loureiro, Carlos; Sousa, Carlos A. Mendes da Silva deThis paper focuses on simulations of the morphological evolution of an estuary during sedimentary infilling that accompanied Holocene sea-level rise. The simulations were conducted using the Estuarine Sedimentation Model, which uses a behaviour-oriented approach, supported by the chronostratigraphy of the estuary's sedimentary sequence. Behaviour curves were computed to represent the relationship between the estuarine channel depth below maximum high tide and the net accretion at a given location relative to the average sedimentation rate of the estuary during the Holocene. The model was validated by comparing the observed present-day bathymetry of the Guadiana River Estuary, southeastern Portugal, with the corresponding simulated bathymetries for nine control sections across the estuary. The best fit between simulated and actual sediment surface elevations was obtained along the cross-sections in the sheltered, low-energy environments of the estuary. The accuracy of the sedimentary stratigraphy of the best-fit model was further established using 16 radiocarbon ages obtained from five boreholes in the estuary. The present approach is particularly suitable for simulating long-term morphological evolution in sheltered estuarine environments where tidally driven vertical aggradation dominates at centennial to millennium timescales. However, the accuracy of simulated sediment surface elevations and consequently the robustness of behaviour-type models based on Geographical Information System platforms can be enhanced by incorporating (i) the impacts of nearshore hydrodynamic processes and episodic flood events in highly energetic channels, and (ii) the impacts of cross-currents in meandering channel sections. (C) 2015 Elsevier B.V. All rights reserved.
- Improved estimates of extreme wave conditions in coastal areas from calibrated global reanalysesPublication . Fanti, Valeria; Ferreira, Oscar; Kümmerer, Vincent; Loureiro, CarlosThe analysis of extreme wave conditions is crucial for understanding and mitigating coastal hazards. As global wave reanalyses allow to extend the evaluation of wave conditions to periods and locations not covered by in-situ measurements, their direct use is common. However, in coastal areas, the accuracy of global reanalyses is lower, particularly for extreme waves. Here we compare two leading global wave reanalyses against 326 coastal buoys, demonstrating that both reanalyses consistently underestimate significant wave height, 50-year return period and mean wave period in most coastal locations around the world. Different calibration methods applied to improve the modelled extreme waves, resulting in a 53% reduction in the underestimation of extreme wave heights. Importantly, the 50-year return period for significant wave height is improved on average by 55%. Extreme wave statistics determined for coastal areas directly from global wave reanalyses require careful consideration, with calibration largely reducing uncertainty and improving confidence. Leading global wave reanalyses greatly underestimate extreme wave heights in coastal regions but this can be reduced with the use of individual or global calibration equations, according to an evaluation of wave height reanalyses validated against data from 326 coastal buoys.
- Prediction of overwash in alongshore variable barrier islands [Previsão da ocorrência de galgamentos em ilhas barreira com variabilidade longilitoral]Publication . Matias, Ana Catarina; Carrasco, A. Rita; Loureiro, Carlos; Almeida, S.; Ferreira, OscarOverwash prediction is very important for coastal zone management. This work intends to identify alongshore variations in storm impact and evaluate the role of sub-aerial and submerged morphologies in overwash occurrence. For this study, 24 cross-shore topo-bathymetric profiles were set on Barreta Island (Ria Formosa barrier island system, Portugal). Pre- and post-overwash surveys were made between August 2012 and April 2013. During overwash events, tidal levels and wave parameters at breaking were obtained. Overwash occurred under storm and non-storm conditions, the latter coincident with spring high-tide. Beach morphology was spatially variable, and changeable from one overwash episode to the next. Predictions of overwash occurrence were made using the Overwash Potential, defined as the difference between runup and barrier elevation. Several runup equations were tested, and the results compared to the actual observations. The selected predictor provided an accuracy of 88% for the identification of the locations where overwash occurred. This study proves that nearshore and foreshore morphologies have a major impact on the longshore distribution of overwash.
- Nearshore and foreshore influence on overwash of a barrier islandPublication . Matias, Ana; Carrasco, Ana Rita; Loureiro, C.; Almeida, Sílvia; Ferreira, ÓscarAccurate prediction of the occurrence and morphological consequences of overwash are important for coastal flood risk assessment and management. A number of morphological and oceanographic factors controlling overwash have been identified by several authors, including nearshore bathymetry. This work intends to identify alongshore variations in storm impact and evaluate the role of sub-aerial and submerged morphological variations in overwash occurrence. For this study, 24 cross-shore topo-bathymetric profiles were set on Barreta Island (Ria Formosa barrier island system, Portugal), extending from the nearshore to the lagoon level on the island backbarrier. Pre- and post-overwash surveys were made between August 2012 and April 2013. Offshore wave characteristics were obtained during overwash events including offshore significant wave height (Hs), peak period and wave direction. Wave propagation and wave parameters at breaking were obtained from SWAN model simulations. During the study period, overwash occurred both under storm conditions (e.g., Hs = 3.8 m) and non-storm conditions (e.g., Hs = 0.8 m), the latter coincident with spring high-tide. Overwash water intrusion distance across the barrier varied alongshore between 0 m (no overwash) and 40 m (reaching lagoon waters). Beach morphology was spatially variable, and changeable from one overwash episode to the next. Important morphological variations of the barrier include modification of barrier crest elevation, beach slope, and presence of swash bars in the vicinity of Ancão Inlet. Predictions of overwash occurrence were made by means of the computation of the Overwash Potential (OP), defined as the difference between the wave runup and the barrier elevation. Several runup equations were tested, and the results of obtained OP were compared to the observations of actual overwash occurrence to determine the most reliable approach. The selected predictor provided an accuracy of 88% for the identification of the locations where overwash processes occurred along the barrier. The predictions were variable alongshore due to variations in breaking waves and beach slope, which in turn are related to the existence of nearshore bars, associated with the presence of the updrift Ancão Inlet. This study proves that nearshore and foreshore morphologies have a major impact on the longshore variation of overwash distribution.