On the use of the calibration-based approach for debris-flow forward-analyses
Abstract. In the present paper the problem of modeling the propagation of potential debris flows is tackled resorting to a numerical approach. In particular, numerical analyses are carried out with the RASH3D code, based on a single-phase depth-averaged continuum mechanics approach.
Since each numerical analysis requires the selection of a rheology and the setting of the rheological input parameters, a calibration-based approach, where the rheological parameters are constrained by systematic adjustment during trial-and-error back-analysis of full-scale events, has been assumed.
The back-analysis of a 1000 m3 debris flow, located at Tate's Cairn, Hong Kong, and the forward-analysis of a 10 000 m3 potential debris flow, located in the same basin have been used to investigate the transferability of back-calculated rheological parameters from one case to another. Three different rheologies have been tested: Frictional, Voellmy and Quadratic.
From obtained results it emerges that 1) the back-calculation of a past event with different rheologies can help in selecting the rheology that better reproduces the runout of the analysed event and, on the basis of that selection, can give some indication about the dynamics of the investigated flow, 2) the use of back-calculated parameters for forward purposes requires that past and potential events have similar characteristics, some of which are a function of the assumed rheology. Among tested rheologies, it is observed that the Quadratic rheology is more influenced by volume size than Frictional and Voellmy rheologies and consequently its application requires that events are also similar in volume.
