Historical changes of bottom topography and tidal amplitude in the Ria de Aveiro, Portugal–trends for future evolution

Abstract

The natural evolution of the estuary-coastal lagoon system of the Ria de Aveiro, Portugal, was halted in 1808 by the construction of a new inlet/outlet channel through the sand spit which isolates it from the Atlantic Ocean. In consequence, tidal amplitudes in the lagoon increased from 0.07-0.13 m to over 1 m. Improvements to the channel since 1936, including construction of jetties, breakwaters and dredging, have increased its cross-sectional area. This has caused a steady increase in tidal amplitude to between 2.5 and 2.8 m, the erosion of mud flats, salt marsh and old salt pans, the widening and deepening of channels, and a greater capacity for sediment transport and dispersal due to the increased tidal currents. The volume of the tidal prism calculated for spring tides is now 1.7 times that in 1951; thus areas bordering the lagoon, especially agricultural fields, are experiencing a progressively increasing risk of flooding and salt water contamination at high water. Any future increase of mean sea level will contribute to an increase of both area and volume of the water mass and could cause important changes to the dynamics of the system. An increase in mean sea level of 0.1 m will, for example, correspond to an increase of 5% in the capacity of the system and contribute to an increase in the speed of tidal propagation. The resulting increase in the volume of the tidal prism will be up to 22% of the present maximum value. KEY WORDS: Coastal lagoon · Tidal changes · Morphological evolution · Sea level rise · Ria de AveiroResale or republication not permitted without written consent of the publisher

Influence of morphological changes in a lagoon flooding extension: case study of Ria de Aveiro (Portugal)

“…Human action has been the major factor controlling the lagoon morphology (da Silva and Duck, 2001;Duck and da Silva, 2012). The most noteworthy human intervention was the creation of an artificial inlet in 1808, in response to persistent accretion of the natural inlet.…”

Effects of storminess, sand supply and the North Atlantic Oscillation on sand invasion and coastal dune accretion in western Portugal

“…(c) Road cutting exposure of early Holocene dune near Leitoes. (d) Podsolized sand dune near Ovar showing location of PT9marked with an arrow town of Aveiro from the sea until an artificial inlet was opened in 1808(da Silva and Duck, 2001). Current estimates of average annual sediment load transported by the rivers into the lagoon are 0.24 x 106 m3, some of which is currently forming an ebb-tide delta outside the inlet-outlet channel (daSilva and Duck, 2001).…”

Tidal changes in estuarine systems induced by local geomorphologic modifications

“…The evolution of the Ria de Aveiro during the 20th century has been characterized by the erosion of these intertidal areas and widening of most channels. These changes, together with other anthropogenic contributions, are believed to have modified the tidal dynamics of the system, making it more vulnerable to risks of flooding and to sea level rise (da Silva and Duck, 2001).…”