GIS-assisted modelling for debris flow hazard assessment based on the events of May 1998 in the area of Sarno, Southern Italy. Part II: Velocity and Dynamic Pressure

Abstract

The velocity and dynamic pressure of debris flows are critical determinants of the impact of these natural phenomena on infrastructure. Therefore, the prediction of these parameters is critical for haz¬ard assessment and vulnerability analysis. We present here an approach to predict the velocity of de¬bris flows on the basis of the energy line concept. First, we obtained empirically- and field-based esti¬mates of debris flow peak discharge, mean velocity at peak discharge and velocity at channel bends and within the fans of ten of the debris flow events that occurred in May 1998 in the area of Sarno, Southern Italy. We used this data to calibrate regression models that enable the prediction of velocity as a function of the vertical distance between the energy line and the surface. Despite the complexity in morphology and behaviour of these flows, the statistical fits were good and the debris flow veloci¬ties can be predicted with an associated uncertainty of < 30% and < 3 m s-1. We wrote code in Visual Basic for Applications (VBA) that runs within ArcGIS ® to implement the results of these calibrations and enable the automatic production of velocity and dynamic pressure maps. The collected data and resulting empirical models constitute a realistic basis for more complex numerical modelling. In addi¬tion, the GIS-implementation constitutes a useful decision-support tool for real-time hazard mitigatio