In an urban flood, interaction between surface runoff and flow into the sewer system can take place. Considering this latter interaction is necessary to understand the phenomenon of urban flooding. A laboratory Model to Study the Flood Risk (MURI) is being built, which includes one lower floor for the pipes representing the sewage network and a second floor for the flow along the streets. Before the experimental study, a numerical investigation of MURI is carried out. The main objective is to obtain the main features for a few representative scenarios of the MURI experiments and to establish an experimental protocol taking into account the capacity of the measuring devices. For this purpose, three numerical models have been successively developed: a 2D model for the second floor using Rubar20 software, a 1D model for the pipe network using Rubar3 software and a coupled 1D / 2D model to simulate both latter flows and the flow interactions between the two floors. Supercritical flow conditions partly appear on the second floor, which implies that results are uncertain because it is difficult to locate transitions accurately, particularly if the mesh is not refined. Opening the exchange structures between floors strongly changes the flow distribution and locally the water depths. One can expect that the numerical model will be a useful tool to plan the experimental runs