This study describes the application and verification of the two-dimensional hydrodynamic model MIKE21, the simulation of flow around levee breaches and mapping of flooded areas beyond the breach points. MIKE21 model is based on numerical solution of two-dimensional depth averaged Navier-Stokes equations. The experimental data from a levee breach (laboratory scale) from the previous studies were used to assess the performance of MIKE21 in levee break simulation. The experimental setup included a tilting laboratory flume with a lateral floodplain added to the flume letting the outflow propagate outside the breach. Comparison of experimental data and MIKE21 results at several stations near the breach showed that two-dimensional depth averaged approximation is quite suitable to capture the flow pattern around the breach. Nevertheless, at some points especially in regions of highly turbulent flow or sharp water surface gradients, the flow is three-dimensional and the two-dimensional approximation may not be accurate. As a case study, the Helleh River with levee system in Bushehr province was simulated. Using MIKE21, the proper locations for emergency breaching (i.e., fuse plugs spillways) in the levee system was studied and presented in some detail. Apart from MIKE21, a one-dimensional model of the river was developed using HEC-RAS. Finally the propagation of the flood waves through the breaches is shown as maps and animations.