The evolution of the Tagus river’s main channel (Santarém, Portugal)‎ through cartographic analysis

Abstract EN

The River Tagus has, over the centuries, fascinated men who, in turn, left behind records of their observations.

These made available the analysis of written and cartographic records allowing study the behavior of the Tagus from 1784 until 1992.

The aims of this study was to enrich the knowledge of the behaviour of the River Tagus, in the Almeirim-Alpiarça-Santarém triangle, far back to times where there was no reading registration, trying to improve in this way the estimates for large return periods, like high magnitude floods.

To reach such a goal, a flood frequency analysis was performed through statistical methods by using a series of continuous data as well as historical and paleohydrological information.

Based on the results and data, a Flood Risk Map and a Flood Magnitude Scale were produced.

Also, from the comparison of all the available maps it was possible to verify the most significant changes the Tagus’ channels have undergone over time and try to associate these changes to known events and floods.

In short, this study showed that, one way or another, all the above can be associated to natural or anthropic processes (influence of floods or of dams building from the 1950’s on) being the latter responsible for most of the changes of the Tagus’s main channel