History of Ria de Aveiro

The natural evolution of the coastal-lagoon system estuary was halted since 1808 by the construction of a new outlet/inlet channel. It was done on the sand spit, which is isolating it from the Atlantic Ocean. Consequently, tidal amplitudes in the lagoon started increasing from 0.13m to around 1m. The improvements began being noticed since 1936 including the construction of dredging, breakwaters and jetties. They have been growing in a cross-sectional area. It has been ensuring there is an increase in the amplitude tidal to between 2.6-2.8m. The erosion of old salt pans, salt marsh and mud flats, the deepening and widening of channels has been occurring.

The primary reason is because of the higher capacity for sediment dispersal and transport due to increasing tidal currents. The tidal prism volume is calculating for spring tides. Therefore, areas bordering lagoon and particularly agricultural fields are experiencing an increasing risk progressively because of the salt and flooding water contaminating at high water. Any plan of increasing mean sea level will be contributing to an increase in both the volume and area of the water mass and could be causing essential changes in the dynamics of the system.

Increasing sea level means of 0.1m will be corresponding 5% in the system’s capacity and contributing to the increase in the tidal propagation speed. It will be resulting in an increase in the tidal prism volume by 22% of the maximum value.

Ria de Aveiro is a very remarkable geographical feature of the Atlantic Ocean coast of northern Portugal. Besides being designed as ‘ria’, the water body is bearing no resemblance with Galician rias in north Spain to northwest Spain. The most accurate description is the ‘estuary-coastal lagoon’ system.

The system is being characterized by various branching fluvial channels that are connecting to the ocean using a single tidal channel through a linking tidal lagoon. It started and evolved rapidly during Holocene, after the stability of the sea level. It has main characteristics which include salt marshes, significant areas of intertidal mud and shallow water column. The lagoon is an excellent sediment accumulation zone supplied by marine-derived materials and influent rivers.

A significant area of the catchment area in River Vouga is underlining by granites and schist which are mostly characterized by steep slopes, steep and low permeability. The underlying geology nature and climatic conditions are characterized by uneven rainfall distribution temporal pattern. It gives the main reason why permanent rivers are varying, yet they all flow throughout the year.

Ocean tides are propagating into Ria de Aveiro using a single inlet which is located in Barra town in the northern side. The waves are observing near the channel of the mouth are semidiurnal with a daily inequality that is smaller. Additionally, it has a maximum amplitude of 3m and a minimum amplitude of 1.9m. In Barra channel, there is a reduction in the magnitude of tides and delay in the times of low or high water related to those channels. The tidal wave is propagating along the narrow channel at Barra inducing tidal currents that are strong in the up streaming channel network – read article on cool things in portugal.