Impact of a debris flow surge on a vertical wall oblique with respect to flow direction

Debris flows are rapid to very rapid flows, made up of a high concentrated mixture of water and sediments. These types of flow are catastrophic natural phenomena affecting mountain areas and causing several property damages and loss of lives every year. The mitigation of these phenomena is then fundamental:  check dams and longitudinal protection walls are among the main structural passive countermeasures. A crucial aspect in the definition of the design criteria for these structures is the analysis of the impact force exerted by a debris flow on them.
From a scientific point of view, the state of the art in this field is quite lacking, despite the relevance of the topic. In the case of impact of a debris surge on a vertical plane normal to the flow direction, according to Armanini and Scotton (1992), two main types of impact may occur. The first type consists of a complete deviation of the flow along the vertical obstacle, assuming a jet-like behavior (Figure 1).  The second type is characterized by the formation of a reflected wave after the impact, which propagates upstream (Figure 2). The analytical solution based on momentum and mass balances in both case is already known (see Armanini 2009 and Armanini et al. 2020) and the comparison between theoretical results and experimental data are quite satisfactory. 
Much less studied is the case of the impact of a debris flow surge on a vertical wall, arranged in an oblique direction with respect to the flow direction, as in the case of lateral protection walls. 
In order to better understand its kinematic characteristics, the phenomenon  has been studied in the Hydraulic Laboratory of the University of Trento. The phenomenon has been reproduced in a channel of variable slope, by releasing a certain volume of fluid and measuring its impact force on a gate situated at the end of the channel at different oblique orientation with respect to flow direction. Several slopes of the channel and concentration of the solid fraction have been investigated. 
When the flow crash into the gate, it is deviated in the vertical direction along the obstacle and forms initially a vertical jet, which is soon deviated in the direction parallel to the gate.
The phenomenon has been theoretically investigated both in the light of the one-dimensional theory of fluid impacts already adopted for the case of impact on a vertical wall arranged orthogonally to the flow, and using a simplified approach derived from the classical two-dimensional theory of Ippen (1951) of the deviations of supercritical currents. The comparison between the predictions of the theory and the experimental data turns out to be quite good.