Part of the Bahía Blanca urban fabric extends over the floodplain of the Napostá Grande stream, a watercourse that originates in the Ventania Serrano system, south-west of the province of Buenos Aires. In this lower section, urban planning and road works contributed to the formation of sub-basins and changes to the drainage network. The aim of the work is to analyse surface drainage in an urban sub-basin where the road infrastructure extends parallel to the Napostá Grande stream. The analysis focuses on a stretch of the Camino de La Carrindanga, an avenue that structures the road traffic in the northern part of the city. To this end, an MDT (Digital Terrestrial Model) was generated from the sub-basin, the accuracy of which was improved by reliefs with VANT (unmanned air vehicle) and field measurements using GNSS equipment (Global Navigation Satellite System). Areas of flooding associated with soil microdepressions were recognised. The analysis of the profiles showed that the new profile of the ditch added to the maintenance of the sector would reduce the drawbacks of erection in the short term by facilitating draining into drainage routes. However, in the lower zone, the difference in level of less than 1 m between the drainage bottom and the watercourse and the presence of constructions cause the drainage to be redirected and the loss of direct connection to the main channel. This results in the sector becoming anguish for days after heavy rainfall.