On the assessment of debris-flow travel distance

Debris flows are common phenomena in mountainous, steep and prone-to-intense-erosion catchments. The hazard assessment in view of their occurrence is mainly based on the estimation of the potential inundated area. The travel distance (the entire horizontal path length) is the most important variable to easily estimate the debris-flow impact on the fan. Different methods exist to predict this variable. Among these, empirical-statistical approaches are the most immediate to apply, although they should be adopted only when conditions are similar to those on which their development was based. In this research, several literature methods to assess the travel distance are presented focusing on the empirical-statistical methods that mostly relate travel distance to the event sediment volume. The debris-flow catchments under analysis have different geological and hydrological features and the deposited volumes cover a wide interval of magnitude (volume range: 5.3∙103 - 1.0∙106 m3; Veneto and Trentino Alto Adige Regions, Italian Alps). The literature runout equations are tested through information from after-event field surveys. The research results yield a positive confirmation in using some empirical literature equations as well as a specific calibrated equation, and assessing the degree of uncertainties in the estimate according to the flow type (debris flow/flood). Technical advices close the contribution addressing the opportunity - when maps are produced for risk management and urban planning to always insert an intermediate hazard zone between „safe‟ areas and the expected bound of high-hazard areas (lowest limit of the runout path).