Search

ABSTRACT Santos, M.I.; Oliveira, F.S.B.F., and Trigo-Teixeira, A., 2018. Characterization of Maritime Storms and Analysis of their Effect on the Beaches South of the Mondego River (Portugal). In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 266–270. Coconut Creek (Florida), ISSN 0749-0208. In the study of coastal processes and coastal dynamics, the analysis of the storms impact is one of the most discussed topics in terms of management and defense of the coastal sector. The Portuguese west coast is exposed to the energetic wave climate that characterizes the North Atlantic, thus requiring permanent care as regards the efficient coastline management and planning. Indeed, the risk associated with erosion and flooding of vulnerable areas is a constant concern, making it imperative to predict the impact of these events and the response of the beach-dune systems. This study focuses on maritime storms and on the morphological response of the beach to these short-term events. The two main objectives are to characterize the storms regime in the coastal stretch between the Mondego and the Lis rivers' inlets based on the wave time series (hindcast) from the period 1952–2010, and to evaluate the impact of the storms duration on erosive events, using a short-term morphodynamic numerical model, LITPROF. This model is used for the analysis of the effect of storms on the beach morphology and thus, for comparing the erosive effect of events with the same relative storm power and different duration. The statistical analysis of the wave climate time series showed a coastal storms regime with high inter-annual and intra-annual variability in number, duration and relative storm power of events, characterized by a strong seasonality, with an average duration and relative storm power of 3 days and 2654 m2.h, respectively. The most frequent events are simultaneously in the classes [1–2[ days and [800–1600[ m2.h (36% of occurrences). The numerical model, applied to several scenarios, predicted the dominance of the duration factor for storms with similar relative storm power, leading to the conclusion that longer duration storms always generate larger erosive effects (and higher transport rates) in the cross-shore profile, when compared with storms of shorter duration. [ABSTRACT FROM AUTHOR]

ABSTRACT Bastos, A.P.; Ponte Lira, C.; Calvão, J.; Catalão, J.; Andrade, C.; Pereira, A.J.; Taborda, R.; Rato, D.; Pinho, P., and Correia, O., 2018. UAV Derived Information Applied to the Morphological Study of Slow-changing Dune Systems. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 226–230. Coconut Creek (Florida), ISSN 0749-0208. São João da Caparica (Portugal) slow-growing dune system was investigated using field-based GPS and UAV surveying methods. Here, vegetation may preclude straightforward extraction of ground surface data from DSM and low sedimentation rates demand high accuracy. The approach used comprised acquisition of UAV-derived DSM and RGB orthomosaics at flight-heights of 30 and 60 m. Results were compared with DTM derived from traditional RTK-GPS ground surveys. Two methods (M1 and M2) where used to convert UAV-derived DSM into a DTM, both departing from supervised classification of land cover. In M1, vegetation areas are removed from the original DSM, which is then re-interpolated. M2 redefines elevation of pixels corresponding to vegetation by subtracting a mean height parameter defined for each vegetation class. It was found that DTM derived from UAV and RTK-GPS data exhibit errors in the same order of magnitude, regardless of the higher resolution of the former. M2 yielded the best compromise when considering deviations in both profile and surface analysis. M2 is strongly dependent on vegetation classification and on parametrization of the vertical correction affecting each vegetation class. UAV methodology presents the best cost-benefit ratio relative to traditional RTK-GPS surveys, providing additional image information (RGB orthomosaic) synchronous of the topographic data. [ABSTRACT FROM AUTHOR]

Fernández-Fernández, S.; Silva, P.A.; Ferreira, C.; Ribeiro, A.S.; Abreu, T.; Romão, S.; Baptista, P.; Fontán-Bouzas, A.; Dias, J.M..; Coelho, C., and Bernardes, C. 2018. Assessment of Dredging/Dumping Scenarios for Figueira da Foz Coastal Region (W Portugal). In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 1266–1270. Coconut Creek (Florida), ISSN 0749-0208. Figueira da Foz coastal region (W Portugal), that comprises sandy beaches and the Mondego estuary-inlet, is exposed to the high energetic wave climate of the North Atlantic Ocean, which induces important local morphological changes. These changes entail shoaling problems as the formation of a submerse sandbar at the inlet which can block navigation towards local harbor. Therefore, coastal dredging is a non-structural temporal solution for this problem. Nevertheless, dredging activities have an impact on local hydrodynamic processes that should be known beforehand. The aim of this study is to clarify this issue using modeling tools dedicated to help stakeholders in decision making process. For that purpose, Delft3D-WAVE module propagates the most representative regional wave conditions under four dredging scenarios including the respective dump areas. Additionally, Delft3D-FLOW module simulates tidal flows along spring and neap tides. The hydrodynamic parameters, significant wave height, orbital velocity, wave-induced currents, tidal current velocity and total sediment transport are analyzed in comparison with numerical solutions obtained in reference scenario (no dredging and no dumping). The results highlight changes in these hydrodynamic parameters in dredging and dumping areas as well as in surrounded areas. Different scenarios draw a similar change pattern for different parameters, namely a reduction of flow velocity intensity within dredged areas and their increase in adjacent areas. Furthermore, hydrodynamic alterations intensify in response to the increase in significant wave height and wave direction considered. These findings are the basis for understanding the influence of dredging and dumping operations on the hydrodynamic of this coast. [ABSTRACT FROM AUTHOR]

Ferreira, C.; Silva, P.A.; Fernández-Fernández, S.; Baptista, P.; Abreu, T.; Romão, S.; Fontán-Bouzas, A.; Bertin, X., and Garrido, C. 2018. Wave Climate Definition on Modeling Morphological Changes in Figueira da Foz Coastal System (W Portugal). In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp.1256–1260. Coconut Creek (Florida), ISSN 0749-0208. Field surveys at Figueira da Foz coastal system, a jettied river-mouth located to the W of Portugal, show a high impact of storm events on the morphological evolution of the ebb-tidal delta, with formation of a submerged sandbar and the quick infill of dredged areas. Non-stormy wave conditions produce minor morphological changes. The morphodynamic modeling of this system is being done to support coastal management. The methodology uses Delft3D modeling system that was previously calibrated for this coastal region. Modeling scenarios are set by considering two initial bathymetric situations, i.e., with or without an excavation site resulting from dredging operation. In order to investigate the relations between the computational efficiency and the time series of the input wave data, some tests were performed including a month with a total of 70% of storms and other with 10%, approximately. For each period it was studied the whole month period and only the storms. Numerical results disclose similar patterns of morphological evolution for both complete and storm periods simulated. Nevertheless, the omission of lower wave energy conditions slightly covers up the volume of sediment accretion in the area. This volume of sediment accretion masking effect is higher in the dredging case study, since dredged area acts as a sink of sediment. The results demonstrated that morphodynamic simulations should include the whole set of waves recorded to achieve more accurate estimations of sediment transport rates and corresponding sediment balance. [ABSTRACT FROM AUTHOR]

Plecha, S., Picado, A., Chambel-Leitão, P., Dias, J.M., Vaz, N., 2014. Study of suspended sediment dynamics in a temperate coastal lagoon: Ria de Aveiro (Portugal). In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 604-609, ISSN 0749-0208. Suspended sediment concentrations are simulated at Ria de Aveiro, a lagoon located in a temperate climate area in the northwest of Portugal. The fine-grained suspended sediment concentration is analyzed using the numerical model MOHID () and spatial maps of instantaneous and maximum concentration and also temporal variability at specified locations are analyzed in order to characterize the influence of the tide and sea level conditions in the suspended sediment concentrations within the lagoon. The highest suspended sediment concentrations were found in upstream areas during ebb conditions due to the river's proximity, while the minimum concentrations were observed near the inlet due to the presence of marine water poor in suspended sediments. When a 0.42 m sea-level rise (an estimate of conditions in 2100) is modelled, a decrease in suspended sediment concentration is observed for the overall study area, as result of an increase in the tidal prism. [ABSTRACT FROM AUTHOR]

Araújo, M.A.V.C., Di Bona, S., Trigo-Teixeira, A., 2014. Impact of detached breakwaters on shoreline evolution: a case study on the Portuguese west coast. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 041-046, ISSN 0749-0208. The Portuguese West Coast is facing severe erosion problems that threaten both the population andthe immediate seaside properties. Some locations, such as the Vagueira region, are especially vulnerable. In an attempt to reverse the present erosional trend, a coastal defense scheme involving two detached breakwaters was introduced in a phased manner. In this work, the impact of those two detached breakwaters on the down-drift coast is investigated. The study area extends from south of the Costa Nova village southwards to Mira. The shoreline evolution is predicted, for various decades, using the GENESIS model. The present time shoreline position, from which future situations are predicted, was obtained using LIDAR data acquired in 2011. Two different future scenarios are investigated: the 'do-nothing' scenario, which assumes that no further engineering interventions will be performed on the coast; and the 'detached breakwaters protected' scenario, with the first breakwater introduced in 2011 and the second in 2026. Depending on sediment supply, two types of simulations are carried out: calibrated simulations, which assume that the amount of sediments in the future will be equal to those in the present situation; and extreme simulations, which assume an acute shortage in sediment supply. Results show that if no further interventions are executed at the Vagueira region, the entire coastal stretch will continue to erode, which could lead to extreme consequences in some locations, depending on sediment supply. If two detached breakwaters are introduced at different intervals, a new accreting trend is predicted at the Vagueira region, reversing the present erosional phase. However, the erosional trend will continue southwards, unless a 3rd detached breakwater is introduced in Mira. [ABSTRACT FROM AUTHOR]

Silva, A.N., Taborda, R., Antunes, C., Catalão, J. and Duarte, J. 2013. Understanding the coastal variability at Norte beach, Portugal Norte beach stands in a coastal stretch fully exposed to the high energetic North Atlantic wave regime. The beach is located updrift of the Nazaré submarine canyon head, a sedimentary sink that captures the southward directed longshore drift. Systematic monitoring of Norte beach has been conducted by a coastal video monitoring system since 2008. A total of 31 monthly coastlines were extracted and analyzed in the period between December 2008 and May 2012. Results show a rare high seasonal coastline variability which exceeds 160 m in the southward sector (adjacent to the headland) and 70 m at the central and north sectors. These coastline variations are related with modifications in the planform beach configuration: beach oscillates between a straight (generally from June to August) and an arcuate configuration (during the remaining months of the year). Results suggest that Norte beach variability depends mainly on longshore drift gradients rather than with cross-shore sedimentary transfers. The intense wave refraction over the canyon head, associated with the westerly swell waves, generates a sedimentary convergence at the centre of the beach promoting the increase of the beach curvature, while, northern and/or short waves (more frequent in summer) tend to linearize the beach. This work contributed with valuable information about the sedimentary dynamics of the Norte beach and showed that this site is a suitable candidate to evaluate longshore drift from shoreline changes. [ABSTRACT FROM AUTHOR]

Costa, S. and Coelho, C., 2013. Northwest coast of Portugal Past - behavior and future coastal defense options Portugal's northwest coast, between Ovar and Marinha Grande presents an important sediment deficit, mainly due to rivers sediments supply reduction and harbors' constrains. The sediment transport capacity resulting from the wave's action (mainly from the northwest) is nourished with the sand of the up drift beaches, leading to the shoreline's erosion and retreat. The shoreline retreat represents conflicts with the land use and human occupation, and the protection of people and properties becomes essential. Thus, coastal interventions (seawalls and groins), try to constrain the shoreline evolution, conducting to an artificial coast and site aesthetical deterioration. This work's objective is to present an analysis of the shoreline evolution, in order to select a suitable model of coastal intervention. Thus, the current paper aimed a diagnostic based in the shoreline evolution indicators in the period between 1994-2011: a) average rate of shoreline retreat; b) number of coastal defense structures implemented; c) number of coastal emergency works and interventions; and d) number of registered events related to shoreline retreat (overtopping, dune system and coastal structures partial destruction). This analysis highlights the location of the most vulnerable areas. Furthermore, different scenarios of coastal defense interventions are discussed, having as variable the associated investment costs, which represents different strategies and impacts, namely: a) maintain the existent coastal defense structures; b) adapt the existent coastal defense structures; c) perform artificial nourishments; and d) propose new coastal defense solutions. [ABSTRACT FROM AUTHOR]

The Guadiana estuary, located in the south-western part of the Iberian Peninsula, is a narrow, bedrock-controlled estuary, characterized by a seasonal fluvial regime and mesotidal conditions. Bathymetric surveys, geophysical records (Side Scan Sonar, high-resolution seismics), surficial sediment sampling, fluvial discharge data, salinity and velocity measurements were integrated to decipher the influence of tidal currents on bedload sediment transport patterns during low fluvial discharge periods. Results evidence a landward change of dominant tidal transport direction, from ebb- to flood-current dominance. The southern (seaward) estuarine stretch shows mostly seaward-directed bedload transport patterns, related to ebb-current dominance close to the fiver mouth. Further upstream, morphological and hydrological evidences suggest a higher influence of flood currents. The estuarine stratification seems to control the observed flood-ebb asymmetry, as higher flood dominance during neap tides is related with the establishment of stratified conditions. However, the prevailing tidal pattern is not able to produce a reversal of estuarine dune asymmetry in widespread zones of the southern estuarine stretch. In contrast, intense, landward-directed sediment transport is evidenced in the northern estuarine stretch. Flood-current enhancement in the northern stretch is probably related with channel narrowing and. consequently, with channel section decrease. [ABSTRACT FROM AUTHOR]

Fernández-Fernández, S.; Silva, P.A.; Ferreira, C.C., and Carracedo-García, P.E., 2020. Longshore sediment transport estimation at Areão Beach (NW Portugal) under climate change scenario. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. (Seville, Spain). Journal of Coastal Research, Special Issue No. 95, pp. 479-483. Coconut Creek (Florida), ISSN 0749-0208. The knowledge of longshore sediment transport is essential to understand coastal systems morphological evolution, and consequent erosion/accretion processes. This research is focused on Areão Beach, a groined sandy beach, located southwards of Aveiro Lagoon (NW Portugal). The high energetic wave climate and coastline orientation induce a substantial southward net sediment transport rate. Nevertheless, this transport is interrupted by coastal defense structures resulting in erosion problems downdrift. Future changes in wave and storm climate can alter current patterns of coastal erosion. This contribution aims to characterize the longshore sediment transport rate under a future wave climate scenario. The Delft3D-WAVE module propagated wave spectral data for historical and future, corresponding to climate change scenario RCP8.5. The hydrodynamic parameters (significant wave height, peak wave period and wave direction) were extracted at offshore Areão Beach and linear wave theory was applied to obtain significant wave height and wave direction at breaking point. Then, CERC empirical sediment transport formula re-evaluated in 2013 was used to estimate longshore sediment transport values. The results disclose a change in the magnitude of longshore sediment transport and an intensification of northwards transport in the future. These findings can contribute for an adequate decision-making regarding beach erosion management. [ABSTRACT FROM AUTHOR]

Fortunato, A.B. and Oliveira, A., 2007. Improving the Stability of a Morphodynamic Modeling System. Journal of Coastal Research, SI 50 (Proceedings of the 9th International Coastal Symposium), 486 – 490. Gold Coast, Australia, ISSN 0749.0208 Coastal area morphodynamic modeling systems couple modules for tidal hydrodynamics, wave propagation, sediment transport and bottom update. The non-linear coupling between these modules generates spurious oscillations and stability problems that are still poorly understood. This paper assesses and compares various methods to avoid the oscillations and improve the stability of a coastal area morphodynamic modeling system (MORSYS2D). The model is assessed with a simple case, the propagation of a sinusoidal bedform, and a complex natural system (Óbidos Lagoon, Portugal), whose exceptional dynamics enhances numerical problems in the morphodynamic models. The best results are obtained with a combination of methods: a predictor-corrector method to improve the implicitness of the solution, along-flux diffusion in the Exner equation to control oscillations, and a morphological factor below unity to reduce the Courant number. With these methods, the modeling system can be used with Courant numbers well above unity. [ABSTRACT FROM AUTHOR]

Silva, R., Coelho, C., Veloso-Gomes, F. and Taveira-Pinto, F., 2007. Dynamic numerical simulation of medium term coastal evolution of the West Coast of Portugal. Journal of Coastal Research, SI 50 (Proceedings of the 9th International Coastal Symposium), 263 – 267. Gold Coast, Australia, ISSN 0749.0208 Coastal erosion is a common problem within Europe. The main causes of this phenomenon are the generalised sea-level rise, the coastal interventions (defence and harbour structures), which cause serious perturbations in the littoral drift system, the littoral occupation and the river sediment supply reduction caused by dams, dredging and fluvial regularisation. Numerical models are helpful tools in future planning and management of coastal policies, by allowing the projection and analysis of different scenarios of medium term coastal evolution. A numerical coastline evolution model (LTC – Long Term Configuration) is being developed to support coastal zone planning and management in relation to erosion problems. The model simulates the dynamic variability of sandy beaches, where the alongshore sediment transport is controlled by waves, currents, wind, water level, sediments' sources and sinks and sediments' properties. The model also simulates different coastal interventions (groins and breakwaters, longitudinal revetments, artificial nourishments, river sediments supply). It may be applied to extensive coastal areas up to one hundred years time scale. In this paper, LTC will be used in the evaluation of the relative importance of each of the identified causes of coastal erosion at the Northwest Portuguese coast at a medium term horizon. Special attention will be given to the discussion of common coastal defence interventions influence in the littoral drift system and impact in what concerns erosion. [ABSTRACT FROM AUTHOR]