Flow distribution in Besòs river is studied by means of a two dimensional numerical model and a scale model. Besòs river presents a compound channel floodway with a central sinusoidal main channel and floodplains at each side of it. Floodplains are used for wastewater treatment and for that reason covered with flexible 2m high vegetation. It is shown that good agreement of numerical model and physical model is achieved with a high resolution numerical model based on the conservative form of Saint Venant equations and finite volumes, provided variations of roughness with unit discharge is taken into account, with no need of turbulence models. Good results are achieved in predicting lateral discharge distribution and flow exchange from main channel and floodplains with the two dimensional approach, something that cannot be done with one dimensional models as exemplified with a one dimensional simulation of the same case.