An estuary forms the transition between the  ocean/sea and a river and within its boundaries  fresh and salt water mix. Fresh water intake  points may be located within the reach of salt  intrusion. In order to justify political and  managerial decisions it is thus necessary to  understand and be able to predict the process  of salt intrusion in estuaries.  For one-dimensional dynamic simulation of  the hydrodynamics and salinity intrusion the  modelling suite SOBEK is available. In the  Netherlands this software is used to evaluate  the impact of for example measures and  climate change on salinity intrusion in the  Dutch Rhine Meuse Delta (RMD). Recent  validations of SOBEK have mainly focused on  water levels and discharges, while less  attention was payed to its capability to describe  salt transport. Therefore the objective of this  research is to obtain a better understanding of  dynamic one-dimensional modelling of salt  transport and improve the governing  formulations with the newest scientific insights