Simulation of heavy gas dispersion based on depth-averaged equations

Many volcanic and non-volcanic areas in Italy emit a huge amount of gas into the atmosphere. Non-volcanic sources in central Italy emit a huge amount of carbon dioxide (CO2) which has a molecular mass greater than that of air. Under stable atmospheric conditions and/or in presence of topographic depressions, its concentration can reach high values resulting fatalities to humans or animals. Several episodes of this phenomenon have been recorded in central Italy and elsewhere. Although from a theoretical point of view, gas dispersion can be fully studied by solving the complete equations system for mass, momentum and energy transport, in actual practice, simplified models able to describe specific phases or aspects of the dispersion problem have to be used. In order to simulate dispersion of a heavy gas and to assess the consequent hazard, we used the established TWODEE model, which is based on a shallow layer approach. This technique uses depth-averaged variables to describe the flow behaviour of dense gas over complex topography represents a good compromise between the complexity of CFD models and the simpler integral models. We present preliminary results for a vented CO2 release in central Italy using the TWODEE model. We find that the dispersion pattern is strongly affected by the steep terrain, and the ambient windspeed.