The aim of the studies was to determine the works necessary to ensure navigability of the River Ebro under the Stone Bridge in Zaragoza. A detailed hydraulic modelling was made dividing the channel into 6 channels corresponding to the arches of the bridge. To do this, a model was developed that calculates the transit of a wave by means of an explicit integration of the Saint-Venant equations using the equation of conservation of quantity of motion assuming that the pressure of the water on a profile coincides with the hydrostatic pressure.