A Comprehensive Estuarine Hydrodynamics-Salinity Study: Impact of Morphologic Changes on Ria de Aveiro (Atlantic Coast of Portugal)

Abstract

Shallow coastal lagoons driven by tidal processes are extremely dynamic environments prone to continuous natural and anthropogenic pressures. The hydrodynamics of these systems deeply depends on the effect of local morphology on the tidal propagation, so their permanent evolution constantly changes tidal dependent processes. For this reason, the present work aims to review the main characteristics of Ria de Aveiro hydrodynamics, a shallow lagoon located at the Atlantic Coast of Portugal, evaluating its evolution over the last 30 years (between 1987 and 2020) and investigating the main morphological changes in its origin. For this purpose, a comparative analysis is performed to determine the main process, including the observed hydrodynamic changes: Deepening of the inlet channel or of the main lagoon channels. To achieve these goals, the authors explored a remarkable database including bathymetric, tide gauge, and salinity data from 1987 until the present. This analysis is completed by the exploitation of a hydrodynamical model (Delft3D), validated against field data. Several simulations were performed to analyse changes in tidal propagation along the lagoon channels (considering the main semi-diurnal constituent M2), tidal asymmetry, tidal currents, tidal prism, and salinity patterns. The results show that the general deepening of the lagoon observed between 1987 and 2020 led to important changes in the lagoon hydrodynamics, namely the increase/decrease of the M2 constituent amplitude/phase, as well as the increase of tidal currents and salt intrusion within the entire lagoon, with the changes being amplified towards the head of the main channels. Although the inlet deepening partially contributed to the modifications found, the results revealed that the deepening of the main lagoon channels had the most significant contribution to the changes observed during the last 30 years.

Coastal Floods Induced by Mean Sea Level Rise—Ecological and Socioeconomic Impacts on a Mesotidal Lagoon

“…The findings described agree with previous studies for the Ria de Aveiro [16,27,29]. However, this study is the first highlighting that the municipality of Murtosa is the most affected.…”

“…Reference [16] identified that saline intrusion has increased along the lagoon between 1987 and 2020. The greatest differences were identified in the channel's heads, especially in the S. Jacinto channel.…”

“…The greatest differences were identified in the channel's heads, especially in the S. Jacinto channel. These changes were induced by the increase in the tidal amplitude, which is currently higher inland due to lagoon deepening along the last decades, and the corresponding intensification of the tidal currents and tidal prism [16]. The main impacts resulting from the salinity changes are the flooding of agricultural fields bordering the lagoon by saltier water and changes in the natural environment of several typical species of brackish water residing in the Ria de Aveiro, which have their habitats restricted to the far end areas of the lagoon channels.…”

“…In addition, large extents of salt marshes have degraded or disappeared since the end of the nineties, decreasing the natural protection of the system against inundations [19]. Previous studies further evidence that, in the absence of coastal protection works, the magnitude of inundations may well be intensified in the future with MSL rise, further increasing socioeconomic and environmental losses [16,20]. Despite the important contributions of previous works in assessing flood hazard and risk, it remains unclear how MSL rise will affect the vertical zonation of the lagoon, through the assessment of the extent of subtidal and intertidal regions, and, consequently, its natural protection against inundations.…”

“…The Ria de Aveiro, a lagoon located on the northwest Portuguese coast (Figure 1), is an example of a coastal system threatened by the adverse impacts of rising sea levels, especially considering the increase in local tidal amplitude reported during the last decades [16,17]. In fact, some of the regions adjacent to the lagoon are, today, often flooded by salt water during the equinoctial tides as well as under storm surge events, posing a risk to residential areas and agricultural activities, among others [18].…”