Knowledge of the amount of nutrient input to receiving waters by their catchments is often mandatory for water managers. In this study, we estimated the export of phosphorus from a Mediterranean catchment into a downstream reservoir under the constraint of limited sampling data availability. We calibrated the physically- based catchment-scale model ZIN-Sed 2D to a regionalized flow duration curve and scarce event mean sampling data of dissolved and particulate phosphorus. The model results were further confirmed by discussion of soft data from the literature. Our modelling approach differs from commonly applied models by using a time step of less than 1 day, and a Langmuir isotherm for phosphorus sorption instead of the linear isotherm. The successful model application showed that this combination of methods is applicable under data-scarce conditions and the long-term phosphorus export from the study site is below average for this region.