The intervention is one of works planned to reduce the hydraulic risk in the Ema torrent basin. The project involved the construction, on the hydraulic right of the Ema torrent, of a bypass expansion tank, divided into two tanks arranged in series and separated by an overflowing threshold. The extension of the floodplain area destined to be used as an expansion box lies between the Ema torrent and the foothills marked by Casa Nova, Valle di sopra e Valle di sotto and, proceeding northwards, Casa a Ema. Thus, it covers an area of approximately 64.000 square metres and contributes, in case of flood events with return times of between 10 and 20 years, to laminate a rate by controlled overflowing. The invaded volume, which can reach a maximum of about 80.000 square meters, is returned to the torrent, after the flood event, using bottom drains located in the last tank.