Flood Hazard Assessment in Madeira (Portugal) – The Case Study of Machico

This study aims to carry out a proper flood risk assessment in Machico’s main watercourse and purpose at least two different flood mitigation measures to prevent major impacts over the watershed. Furthermore, the assessment addresses the need for structural-measures — i.e. detention basins — towards mitigating flood hazards under high-intensity and short-duration precipitation events. It became possible to morphometrically characterize all the watersheds using empirical equations to gather specific parameters and indexes. A proper articulation between the hydrological and the spatial analysis using geographic information systems was then carried out. According to many parameters calculated the watershed of Machico proved to assume a very large-size and to be highly prone to flash floods. The spatial analysis took into consideration the watershed’s Fill Rate using both Dutch and the Ternary Phase Diagram methods and allowed us to define criteria towards the establishment of detention basins as a valid flood mitigation measure. Finally, it was clear that the watershed corresponding to Machico’s main watercourse induces the need to further implement either a detention basin or to modify the roughness coefficient of its river channel. Moreover, the comparison between the results obtained with DROTA’s Flood Risk Report, allows us to consider this study’s outcome both satisfactory and valid.