Experimental design of a diversion structure of granular debris flows

Many alpine torrents convey regularly debris flows of high destructive hazard. After several granular events observed in Bruchji’s torrent near the Blatten village in the Swiss Alps, it was decided to manage the risk of similar debris flows by designing and constructing a control structure inside the torrent bed. Associated with a breach in the right bank side of the torrent, this control structure should divert part of the moderate and high debris flow events toward the original alluvial cone. Two different configurations of the control structure were tested and optimized through a series of physical tests. The basic concept of this structure is to create a local lateral contraction of the torrent section topped by a horizontal rack or by a deflector beam. A physical model at the scale of 1:20 was built and granular debris flows were simulated by four successive discrete pulses. The behavior of the structure was tested inside the linear part and inside the bend of the channel reach. The geometry and dimensions of the control structure were also optimized to divert laterally a maximum volume of debris flow materials.This paper describes the physical model experiments, presents and discusses the main test results, and proposes an optimized geometry of the control structure. The most efficient configuration consists of a unilateral contract of the channel flow section inside a channel bend and to install a deflector beam.