Fully-2D and quasi-2D modeling of flooding scenarios due to embankment failure

The occurrence of river levee breaks due to high return period floods can have catastrophic effects on the environment and human lives. The study of these kinds of problems is of great importance for hydraulic hazard assessment, for the development of civil protection plans and for the organization of corrective and preventative measures to reduce flood damage. In this context, the paper presents the main results of two case studies concerning two floodable regions located in the middle reach of the Po river (Northern Italy). For the first case, numerical simulations were performed by means of a 2D finite volume MUSCL-Hancock scheme (belonging to the Surface Gradient Methods class) and also by a quasi-2D numerical model based on the subdivision of the domain in storage cells linked through weirs. Even if the flooding dynamics was not correctly described in the first hours after the breaching, the results obtained through the quasi-2D approach showed a fairly good agreement with fully-2D ones: flooded areas, maximum water depths and, above all, the discharge flowing through the breach are comparable. The satisfactory results obtained led to the adoption of a hybrid methodology that was applied to the second case study: the discharge flowing through the breach was computed by the quasi-2D approach and then adopted as the inflow boundary condition for the fully-2D modeling of the sole area prone to flooding. In this way the flooding dynamics was predicted avoiding the burdensome 2D description of the riverbed; in addition the downstream boundary condition was moved far away from the breach and the computational time significantly reduced.