Extracting quantitative data from non-conventional information for the hydraulic reconstruction of past urban flood events. A case study

The description of the floods which have occurred in the past and an assessment of the adverse impacts they have entailed are among the duties required by the European Flood Directive. Indeed, to understand the consequences of a future flood on a city that in the past has already been affected by other flood events, it is very useful to reconstruct the hydraulic effects produced by those events. Such a task is particularly difficult for cases which occurred many years ago. For past events, it is often easier to have conventional hydrological data (for example, the hyetographs of the event) than conventional hydraulic data (recordings of flow rates, water depths, etc.). It is also difficult to obtain the topography valid for the period in which the event occurred. The greater the distance in time the greater the difficulty in gathering these data. In this paper we present a criterion for making a flow of information, using various non-conventional sources of information (such as amateur videos, photographs, traditional topographic surveys, news reports, etc.). In particular, it is shown how the data thus obtained can be used together in order to reconstruct numerically the hydraulic dynamics of a flood event in an urban area with a complete hydrodynamic model, which requires a particularly accurate computational domain. All these issues will be presented and discussed with reference to the numerical reconstruction of the flood event that occurred 23 years ago (1996) in the city of Crotone (Calabria, Italy).