Population Balance Equations (PBE) for microplastic (MP) transport in aquatic environment - applied to Scheldt Estuary. The codes and files provided here are examples of the TELEMAC (www.openTELEMAC.org) implementation of the PBE model in a 2D depth-averaged model. We utilise the one-node EQMOM to compute the settling velocity of the microplastics dynamically based on the dominant size of MP particles. 2 dimensional horizontal (depth-averaged) Scheldt Estuary model: 2DH model, has been set up for the Scheldt river/estuary and Belgian part of North Sea. The model couples TELEMAC-TOMAWAC-GAIA. The transport of two sediment fractions, sand and mud is also computed using GAIA in order to allow to account for hetero-aggregation of microplastic with the abundantly present cohesive sediment flocs in areas with significant turbidity. The model has been calibrated for water levels, flow velocity and sediment concentrations, and also waves in the coastal area. The MP size based PBE method has been used. Thereby evolution of MP sizes (therefore settling velocity) is tracked dynamically, in accounting for the source and sink terms. For further details on the PBE framework of MP transport, users are referred to the journal paper https://doi.org/10.1021/acs.est.4c02223.