The understanding and prediction of effects of engineering schemes on estuaries can be facilitated by using mathematical models. One such mathematical model, MIKE 11, that models the transport of solute and suspended solids was recently introduced into the market by the Danish Hydraulic Institute, Denmark. MIKE 11 has been tested with recent field measurements of solute concentration, tide level and flow in the middle reaches of the Tamar Estuary. The Tamar is located in the South West of England and is partially mixed in its middle reaches. The time varying dispersion coefficient for solute transport has been estimated from vertical profile data from mid-channel. The results from the modelling exercise suggest that MIKE 11 is suitable for practical modelling of a partially mixed tidal river. There is a drawback with editing. Other qualities of the software were tested and the view of the author was given on each of these qualities.