In this talk, I present two ways to reduce the computational cost of flood numerical models. The first feature is the subscale parametrization thanks to porosity modeling. It has first been introduced by V. Guinot in th 2000s and is still at the core of LEMON’s scientific production. It allows reducing the cost of simulation thanks to coarser meshes, while the subscale informationis captured with pre-computations on the domain topography. The second part of the talk will be dedicated to large CFL models to handle heterogeneous meshes with explicit time-schemes. The main idea is to consider hydraulic information not only on the neighbouring cells of any flux interface, but to gather it from a pre-defined dependence domain thanks to a convolution process. This provides much larger time steps (hence a reduced computational cost) without any mesh modification or accuracy loss. These two features are part of the team SW2D-LEMON, developed at Inria and Université Montpellier.