The SPHERA code (RSE SpA), based on the Smoothed Particle Hydrodynamics numerical method, has been validated on a scaled 3D urban flood, triggered by a dam/bulkhead collapse (i.e., dam-break flooding). The paper also reports the inter-comparisons with a 2D porous model based on the finite volume method for the shallow water equations. SPHERA provides performance comparable to state-of-the-art code, with results closer to measurements during the riskiest stage of the flood. Some improvements in SPHERA estimates are achieved through direct modeling of the moving bulkhead that triggers the flooding. A scheme for flooding damage of electrical substations has been written in SPHERA. This scheme distinguishes functional damage—due to substation out-of-service events—from material damage to substation components. Finally, SPHERA is applied to the simulation of a catastrophic flood from 3D dam-breaks at 1:1 scale. The flood interacts with a hydroelectric reservoir downstream and impacts four residential centers and two electrical substations, of which damage has been assessed. SPHERA is distributed on a public digital repository on GitHub, including the input files of this study.