Numerical Modelling Elements as Contribution to Knowledge of the Geohydraulic Model of Sulphurous Groundwater of the Dao River Basin, In Portugal

Abstract

The Dão River is a tributary river on the right bank of the Mondego River, which is the longest river located exclusively in Portuguese territory. The Dão River Basin, which covers an overall area of 1378 km2 and forms an almost ellipsoidal shape contained within a 62 km by 22 km rectangle, is situated in the Central Iberian Zone, the lithology of which consists essentially of elements of a granitic massif dating back to the Hercynian period. The downstream area features schistous rocks (Schist-Greywacke Complex) dating back to the pre- Ordovician period, which are understood to serve as a barrier to the flows that percolate in the granitic massif. Within the Dão River hydrographic basin, the sulphurous groundwater occurs in an upstream to downstream direction, with the following names: Caldas da Cavaca, Sezures, Termas de Alcafache, Caldas de Sangemil and Granjal. The sulphurous groundwaters are special because they have applications in thermalism, contributing to the area of public health and tourism, and can also be used while hot for geothermal installations, both in the environmental heating of buildings and the heating of their water supply. They may even be used in electricity production, if collected at temperatures higher than 80°C. Thus, knowledge of the geohydraulic model of this kind of groundwater is an absolute necessity, in order to make the hydrogeological prospection and collection of this kind of resource more efficient. In an effort to gain the greatest possible knowledge of the geohydraulic model of that groundwater, various studies were carried out to that effect, including geomorphologic, geological, hydrogeological, geochemical and isotopic studies, as well as others, namely numeric models based on finite element software. Thus, in addition to showing the basic elements of some of the aspects used in gaining knowledge of the geohydraulic model of the sulphurous groundwater of the Dão River Basin, this article also presents in particular the contributions obtained from the use of finite elements.