Some morphological aspects and hydrological characterization of the Tagus floods in the Santarém region, Portugal

Abstract

In Portugal, few studies have been made of the historical floods of the River Tagus (the longest in the Iberian Peninsula). This fact led to the study of the Lower Tagus (Santarém region) using written historical documents, cartographic documents and hydrological data, consisting mainly of water level records. With the support of the historical documents and the analysis of all the maps, it was possible to verify that human intervention has been fundamental in the morphological changes of the Tagus’ channel. The river changed from a braided to a single channel with alternate bars. From the hydrological data, return periods for the floods were determined, using the Pearson Type 3 distribution. The selection of the most important floods, from 1855 to 1998, enabled us to build a “flood hazard scale” for this region.