AbstractThe potash mines located in the central region of Catalonia generate waste brines that are transported and discharged beneath the sea on the Catalan central coast through a pipeline facility more than 100 km long. The pipeline has variable diameters; a major part has an internal diameter of 334 mm and is mainly made up of fiberglass-reinforced polyester (GRP). A 4-km-long section was monitored for 3 months. The wastewater level in the head tank, temperature, pressure evolution, and flow rate were recorded during this period. This information enabled the achievement of the major aim of this paper, that is, the discussion of the evolution of the roughness of the pipeline and the prediction of the limit deposition velocity of the suspended solid particles transported by the flow. The values obtained for absolute roughness showed wide variability in the varied between 0.57 and 16.7 mm. The values obtained for the limit deposition velocity indicated that particles of a size greater than 150 μm would settle down inside the pipe. In addition, the effect of the removal of a waste salt stockpile hill located in the vicinity of the monitored pipeline stretch was analyzed.