Debris flow mitigation and control in the Dolomites (north-eastern Italy)

Abstract

An active debris flow seriously threatens the urbanized area of Fiames, near Cortina d’Ampezzo (Dolomites, Italy) and the National road. In September 1997, following a 25,000 m3 magnitude debris flow hat temporarily dammed the river, a retention basin with a storage capacity of about 15,000 m3, was built upstream the National road. In 2002 a warning system was installed, based on the early detecting of debris-flow-induced ground vibrations and the overcoming of a flow-stage threshold in the debris basin, linked to a traffic light in order to stop the traffic on the National road in the event of a debris flow. In the following years, after more accurated studies, more effective mitigation measures were designed. The most suitable action to reduce the risk is to control the debris deposition, because the geomorphology of the site does not allow risk mitigation measures along the flow paths. For the design of the mitigation works, the two-dimensional flow routing model FLO-2D has been used to get fundamental information such as possible runout distances, depth, velocities and impact force of the design debris flow. The magnitude of the design debris flow, based on geomorphological and historical data, has been estimated in 30,000 m3. A debris basin and debris flow barriers and breakers have been considered the most suitable mitigation measures to protect human settlements, infrastructure and supply lines from rain-induced disasters by dissipating the energy of debris flow (floods), filtering coarse solid components and deflecting the flows from the areas at risk.