Flood Risk Assessment at the Douro River Estuary

Estuaries have huge socio-economic and environmental importance. They are a shelter for many species and their natural resources are exploited by human activities. However, the intensification of flood events and the sea-level rise (SLR), caused by climate change (CC), can jeopardize its complex dynamics. This work characterizes the hydrodynamic behaviour of the Douro river estuary, located in northern Portugal, under extreme flood events. This coastal system, with high population density and strong urbanized banks, is particularly important in terms of economic activities mainly related to Port wine cellars, tourism, and navigation. A numerical model of the estuary was set up and calibrated using the OpenDA software to automatically determine the model’s parameters/coefficients values. Besides, several numerical scenarios were run considering different extreme sea levels (ESL), associated with CC conditions, and extreme flood discharges (EFD), resulting from the 50, 100, and 1000 years return period estimation. Results showed that for the same flood river discharge, a water level variation from 13 to 40 cm is expected at the estuarine mouth, depending on the CC scenario. However, the water level in the Douro estuary is mainly affected by river discharges rather than by SLR. This is a consequence of the geometric configuration of the deep and narrow estuarine channel. It was also demonstrated that the breakwaters can increase flood risk during extreme events for this estuarine region, enhancing the importance of implement methodologies, such as the one proposed in this work, to unravel the configuration of complex estuarine hydrodynamic patterns.