New urban area flood model: a comparison with MIKE11-quasi2d

Abstract. Recent hydrogeological events have increased both public interest and that of the Scientific Community in a more accurate study of flooding in urban areas. The present project proposes a new model which offers an optimal integration of two models, one for flood wave propagation in riverbeds and the other for flooding in urban areas.

We consider it necessary to not only treat the modelling of the outflow in riverbeds and outside riverbeds.together but to integrate them thoroughly. We simulate the propagation in riverbed of the flood event with a model solving the equations of De Saint Venant with the explicit scheme at the finite differences by McCormack. The propagation outside the riverbed is simulated using an algorithm proposed by Braschi et al. (1990).

This algorithm is based on a local discretization of the urban territory, divided in a series of "tanks" and "channels". Each tank is associated with an area of an extension related to the position of the other tanks and the quantity of buildings, modelled as insurmountable obstacles.

The model facilitates the simultaneous performance of the two simulations: at each instant, the quantitiy of water overflow, depending on the piezometric level in every section, is calculated as a function of the dimensions of the weirs (the banks), assuming it passes through the critical state. Then, it is transferred to the tanks placed in the surroundings of the overflow points. Those points are the starting nodes for the propagation of the flood because they are connected to the network of tanks in which the surrounding land has been schematised.

In this paper, we present a comparison of one of the most powerful models of inundation simulation in urban and no-urban areas. The field area is the city of Albenga (SV, Italy) and the simulated event is the inundation of the 1994 (return period of about 25 years).