Development of a mathematical model of transport processes in open channel flow and the experimental verification of the model are described in this paper. The original numerical procedure for solving the unsteady 2D dispersion equation, based on an operator-splitting approach, has been developed and validated by comparison with an analytical solution. The model was used for the interpretation of dynamic measurements of tracer concentration after instantaneous injection in a laboratory channel containing a compound cross section. Two conditions were examined (the water flows in the deeper rectangular part of the channel only, and the flow over the entire width). Very good agreement between measurements and computational results was obtained.