Carina L. Lopes

Flooding assessment under sea level rise scenarios: Ria de Aveiro case study

ABSTRACT Lopes, C., Azevedo, A., Dias, J.M., 2013. Flooding assessment under sea level rise scenarios: Ria de Aveiro case study Sea level rise is an important consequence of climate change with a significant impact on society and ecosystems. The present work aims to assess the sensitivity of Ria de Aveiro marginal flooded area to the sea level rise. A previous version of the hydrodynamic model ELCIRC was improved extending its numerical grid through the inclusion of the intertidal areas and the marginal topography. The present configuration was calibrated comparing model predictions with sea surface elevation data recorded at ten stations distributed throughout the lagoon. The root mean square error and the SKILL were computed, and generally an excellent/good agreement between predicted and observed sea surface elevation data was found. Once calibrated, the model was used to simulate the lagoon flooded area under present mean sea level and under two local sea level rise scenarios (0.42 m and 0.64 m), considering mean and spring tide conditions. In average was found an increase of 22% and 35% of the lagoon flooded area, respectively, relatively to the present. Additionally, an increase of 15% and 23% was found for the tidal prism at the inlet, for sea level rise scenarios of 0.42 m and 0.64 m, respectively. Numerical results evidenced that sea level oscillations induce important changes in the lagoon flooded area as well as on the local hydrodynamics. Consequently some activities developed in the lagoon margins may be in jeopardy, i.e. the agricultural fields located at the margins of S.Jacinto channel will be inundated by saltwater, if these sea level rise projections are confirmed.

Storm surge impact in the hydrodynamics of a tidal lagoon: the case of Ria de Aveiro

ABSTRACT Picado, A., Lopes, C.L., Mendes, R., Vaz, N. and Dias, J.M., 2013. Storm surge impact in the hydrodynamics of a tidal lagoon: the case of Ria de Aveiro. Storm surges are a hazardous phenomenon, since they may flood large coastal areas, causing socio-economical and habitation losses. Thus, the study of their characteristics and effects in coastal regions is crucial to prevent their negative consequences. This work aims at assessing the storm surges impact in the hydrodynamics of a tidal lagoon located in the north-western Portuguese coast (Ria de Aveiro). Storm surge amplitudes of 0.58 m, 0.84 m and 1.17 m for 2, 10 and 100 return periods, respectively, were determined adjusting the annual maximum amplitudes to a Generalized Extreme Value (GEV) distribution. To assess the hydrodynamic changes in the Ria de Aveiro under storm surge conditions, numerical modeling simulations were carried out, considering four scenarios: a single astronomical tidal forcing (reference) and astronomical tide plus 2, 10 and 100 years return period surges. Maximum levels and velocities for the entire lagoon and the tidal prism for the main cross-sections were determined and compared with the reference scenario. Generally, the model results suggest that during storm surge events the maximum levels increase in whole domain, with the largest increase found for the 100 return period storm surge scenario (1.17 m). The most significant changes occur at the main channels head for all scenarios, revealing that these regions are the most vulnerable to marginal flooding. Also, storm surges induce higher velocities and tidal prisms in the lagoon, increasing the marginal risk of erosion, as well as the salinization of the lagoon marginal lands.

Influence of mean sea level rise on tidal dynamics of the Ria de Aveiro lagoon, Portugal

ABSTRACT Lopes, C.L., Dias, J.M., 2014. Influence of mean sea level rise on tidal dynamics of the Ria de Aveiro lagoon, 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. 574–579, ISSN 0749-0208. Global mean sea level rise is an important consequence of climate change because of its impact on coastal regions. Recent studies highlight that tidal propagation in shallow waters tends to be modified with mean sea level rise, intensifying coastal threats. This study aims to quantify changes in tidal patterns in Ria de Aveiro coastal lagoon, Portugal in response to the local mean sea level rise. To achieve this goal the hydrodynamic model ELCIRC, previously calibrated and validated for Ria de Aveiro, was applied, considering the present mean sea level and a local mean sea level rise projection of 0.42 m for the end of the 21st century, assuming no change in bed elevation. The model results for present mean sea level show that the amplitude of the main semidiurnal (M2) and diurnal (K1) constituents decrease whereas the respective phase increases towards the head of the estuary, while the M4 constituent shows an opposite pattern, due to the upstream lagoon shallowness. As consequence, the tidal distortion is higher in the lagoon upper reaches than at the lagoon mouth. Under mean sea level rise conditions, the tidal wave tends to be less distorted in the upper lagoon, given that the M2 amplitude tends to increase while the M4 amplitude tends to decrease. The results highlight that tidal current magnitude decreases toward the channels head for both scenarios, but their magnitude tends to increase with mean sea level rise. The residual currents showed a net export of materials to the ocean, which will increase with mean sea level rise.

Influence of climate change on the Ria de Aveiro littoral: adaptation strategies for flooding events and shoreline retreat

ABSTRACT Dias, J.M., Lopes, C.L., Coelho, C., Pereira, C., Alves, F.L., Sousa, L.P., Antunes, I.C., Fernandes, M. da L., Phillips, M.R., 2014. Influence of mean sea level rise on Ria de Aveiro littoral: adaptation strategies for flooding events and shoreline retreat. 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. 320–325, ISSN 0749-0208. Floods and shoreline retreat in coastal areas threaten many millions of people across Europe. Moreover, it is agreed that climate change can amplify the magnitude and frequency of flooding events and accelerate the shoreline retreat. The main goal of this work is to assess flood and shoreline retreat risk, and define adaptation strategies under present conditions and future climate change scenarios on the Ria de Aveiro and its littoral. The hydrodynamic model ELCIRC was implemented for the Ria de Aveiro lagoon and GENESIS (U.S. Army Corps of Engineers) and LTC (Long-Term Configuration) shoreline evolution models for the littoral stretch between Esmoriz and Mira. Numerical results in present and future scenarios were used to map the flooded lagoon extension and the shoreline evolution of this coastal stretch. Analysis showed an increase of the lagoons flooded area, relative to the present, with regions more exposed to sea level rise being lowland areas located at the margins of the lagoons deeper channels. Examination of the littoral stretch showed a slight increasing trend of shoreline retreat under predicted future climate change scenarios, thereby increasing the probability of sand spit rupture. Data from numerical predictions were integrated into Geographical Information Systems covering the coastal and lagoon study areas, and produced hazard and risk maps including the identification of regional use and activities. Structural and non-structural measures were subsequently developed in order to mitigate flood and shoreline retreat effects.

Tidal dispersion and flushing times in a multiple inlet lagoon

ABSTRACT Lencart e Silva, J. D., Lopes, C. L., Picado, A., Sousa, M. C., Dias, J. M., 2014. Tidal dispersion and flushing time in a multiple inlet lagoon. 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. 598–603, ISSN 0749-0208. The Ria Formosa is a tidal multi-inlet shallow-water coastal lagoon located in the south of Portugal, subjected to the dry Mediterranean climate. The tide controls the Rias exchange with the adjacent shelf for most of the hydrological year except for isolated torrential run-off events. Episodes of low hypoxia reported in the literature may be related to the lagoons flushing time, affecting its shellfish production valued at 20 – 50 million €y−1. Over the past decades several observational and modelling studies presented values for the capacity of the tide to renovate the water inside the Ria. However, these studies lack either the spatial resolution to yield results unaffected by numerical diffusion or analyze a very limited part of the lagoons territory. In this work, we use a very-high resolution hydrodynamic model to assess the flushing time exclusively due to tidal forcing inside the Ria Formosa. A bi-dimensional implementation of the finite-volume/finite-difference Eulerian Lagrangian hydrodynamic and transport model (ELCIRC) was used, allowing for the local refinement of the computational domain, which best suits the lagoons complex morphology. The present model configuration was validated for tidal propagation with sea surface elevation collected in 1979/80 at 11 lagoon stations. The validation results show a good agreement between predicted and observed elevations, with root mean square errors lower than 20 cm and skill values higher than 0.98. A set of experiments were carried out by releasing a conservative tracer at different stages of the tide at discrete points of the Ria, where possible environmental hazard hot-spots are located and the flushing e-folding time calculated from the tracers dilution. The results are discussed taking into account the propagation of the tide in this multi-inlet, meandering topography. Evidence is presented of topographic trapping due to the complex spatial distribution of the phase lags of the semi-diurnal tidal constituents. This evidence explains the significant increase of the flushing time from the inlets to the head of the channels, thus justifying the use of detailed spatial resolution when modelling such a complex system.

Flood risk assessment in a coastal lagoon under present and future scenarios: Ria de Aveiro case study

Floods are one of the major threats to low-lying coastal lagoons, affecting people, socio-economic activities and ecosystem services. This work proposes a methodology to assess present and future flood hazard and risk in west-boundary low-lying coastal lagoons, using the Ria de Aveiro (Portugal) as case study. A multidisciplinary approach supported on Source–Pathway–Receptor–Consequence model combined with a GIS-based multi-criteria analysis was developed and applied. This comprised the following steps: (1) definition of present and future climate scenarios associated with oceanic, fluvial and combined events, combining sea levels and river discharges for different return periods; (2) characterization of flooding pathway through hydrodynamic modelling; (3) assessment of flood hazard combining flood depth and probability from hydrodynamic simulations; (4) assessment of flood risk calculating the adverse consequences on assets exposed to flood hazard. Results highlight that endangered regions are strongly dependent on the floods origin: oceanic floods threaten settlements and economic activities located along the margins of the lagoon main channels as well as habitats in the lagoon central area; fluvial floods endanger the river’s mouth adjacent areas causing damage in restricted settlements, economic activities and farmland habitats; the combined floods also threaten the margins adjacent to the transition zones. For future scenarios, it is predicted the flood risk increase/decrease for oceanic/fluvial events, as a consequence of mean sea level rise/river discharges reduction predicted for the region. Finally, this work demonstrated the value of the methodology proposed and its potential for flood risk analysis, supporting the decision-making process underlying the flood risk management.