Design of two retention basins along the torrent Liera on the Gares Valley (Dolomites, North East Italy) after the storm Vaia

A storm called Vaia affected the North East Italy and South West of Austria at the end of October 2018. On the Gares Valley (Canale d' Agordo, North East Italian Alps), the abundant runoff triggered several in-channel debris flows that transported hundreds of thousands of cubic meters of sediments on the valley bottom. Some control works for retaining the sediment volume have then been built in the most threatened sites. Herein we show the design of two retention basins that should protect both the Liera torrent and the main road parallel to it. We computed the debris-flow volume to be retained both using an empirical law and simulated solid-liquid hydrographs corresponding to a return period of 300 years. The estimate of the debris-flow volume in the empirical law depends on the basin area upstream of the deposition zone, whereas, in the solid-liquid hydrographs, it depends on the area of the basin closed at the initiation area, as well as on the design rainfall.