Flood hazard assessment in a polje: the case of Mucille (Classical Karst Region, NE Italy).

The Mucille karst depression is one of the few examples of polje on the Italian side of the Classical Karst Region, a shared area between Italy and Slovenia. The polje is subject to frequent flooding, becoming more problematic since 2000, as swallow holes more frequently have affected housing and recreational areas, leading the population to believe that their ability in draining the area had stopped functioning. Climate changes play an important role as there has been an intensification in extreme events (30-day cumulative precipitation of more than 350 mm) within the considered time-period 1919–2020. The necessity to provide answers to the inhabitants required in-depth studies such as hydrogeological investigations, discharge measurements and Electrical Resistivity Tomography (ERT) acquisitions. Over the 3 years of monitoring (2017–2020), two flood events reached the Selz settlement. In total, four events have been analysed to build a hydrogeological model of the area in order to properly estimate its recharge and regression curve, and to define the functionalities of the swallow holes. The defined model allowed a better knowledge and a greater awareness in proposing the proper mitigation measures able to increase the drainage capacity of the area avoiding always more frequent future floodings.