An efficient tool for hydraulic hazard analysis in alpine valleys.

Coping with the problem of hydraulic risk evaluation in mountain regions requires the development of mathematical tools for efficiently solving De Saint-Venant equations. Flood propagation in mountain areas usually takes place within a setting characterized by constantly changing slope, recurring and abrupt cross-section changes: as a consequence, transcritical flow regimes can occur, even with shock formation. All these aspects require ad hoc numerical methods. Although rather effective shock-capturing algorithms are nowadays available to solve one-dimensional De Saint-Venant equations, their application to real cases is still considerably hindered by the need to have closely spaced cross-sections (and associated hydraulic and geometric quantities) in order to provide a sufficiently accurate topography reconstruction which would be too much expensive to acquire by conventional field survey procedures. Over the last decades, many algorithms for automatic extraction of drainage networks from Digital Elevation Models have been proposed in the literature and have been used almost exclusively for space-distributed hydrological and environmental applications. In this contribution we investigate the possibility of using these kinds of algorithms to provide the topographic information needed to solve one-dimensional shallow water equations for flood propagation in mountain regions.