The tran-SAS model is intended to simulate solute transport based on a catchment scale approach. Hence, it is not suited to simulating the circulation of solutes for which the chronology of inputs and outputs and the water residence time at outlet are irrelevant. The codes implemented in the tran-SAS package are meant to be easy to edit and allow users with limited programming experience to adapt the model to their specific context.
The model requires only the specification of catchment-scale fluxes like precipitation, streamflow and evapotranspiration. It is thus simpler than previous approaches that require the specification of a full hydrologic model. The use of pure SAS functions also implies that model results can be very sensitive to the choice of parameters. The example below shows that a simple preference for younger rather than older stored water may significantly affect the model results and lead to different water age distributions in the discharge.
In addition, the o(ST,t) reservoir depletion pattern can become large corresponding to very high values of the storage function, potentially leading to unstable fast decay. Therefore, the use of very pronounced age selections should be carefully considered and tested for potential numerical instabilities.
In addition, the o(ST,t) model is not suitable for the simulation of transient events since it cannot capture the dynamics of reversible processes in the system. This limitation is mainly due to the fact that the system behaves as a nonlinear and dynamical process, resulting in fast fluctuations of concentration in the discharge.