Sewer inlets are one of the most important elements for avoiding floods in urban areas, capturing runoff and introducing into the sewer system. Traditionally the inlets have been designed by resistance criteria, without including or analysing their hydraulic efficiency. Currently CFD techniques plays an important role in order to assess more efficient inlets, minimizing the need for flume experiment and taking into account the hydraulics for their design. 2D models are good enough to represents the hydrodynamics, which is mainly 1D on the street and 2D on the surroundings of the inlet. These models cannot properly capture 3D phenomena over the inlet, the discharge through the inlet is not well represented. This work presents different techniques, based on the similarity between the hydrological infiltration models and the discharge captured by the inlet, aiming to enhance the 2D model Iber to adequately reproduce the discharges captured by the grates, even without representing the complex three-dimensional hydrodynamics around and over the inlet. The results fit well with the observed data, properly reproducing the hydraulic structures as hydraulic jumps, recirculation and cross waves.