Floods are among the natural phenomena, the more frequent and deadly having provoked in Portugal, more than 537 dead, between 1966 and 2016. The study of flood risk plays a key role in decision-making of its management.
GIS is defined by its ability to manage and perform analysis on spatial information, they are the appropriate tool to process information and for the analysis of flooding risk. In
... [Show full abstract] this study, several GIS methodologies have been applied to perform the characterization of the Nabão River basin and to assess flood risk.
At the Nabão river’s catchment area scale, a risk study based on multi-criteria AHP methodology was performed considering elevation, slope, soil type, soil use and occupation as parameters. The results obtained using AHP, revealed a very high risk in 2,2% of the basin’s area and high in 15%. A major portion of the Nabão River basin presents high and very high risk in the lower regions and in populated areas with great soil sealing.
At a Tomar city scale, hydraulic simulations were carried out using HEC-RAS and HEC-GeoRAS for the 10, 25, 50 and 100 years return periods. The information obtained, depth and water speed, was used to attain the hydrodynamic hazard which, along with physical susceptibility, allowed for the calculation of total hazard.
Results allowed to conclude that, most of the city presents moderate to high flood hazard. Areas more vulnerable include, for all return periods, the right bank of the River in which much of the traditional shops, housing and some public services are settled.
