A comparison of travel-time based catchment transport models, with application to numerical experiments

•Four different travel time based models for solute transport are analyzed.•The time invariant formulation of the travel time distribution is generally inappropriate.•The equivalent steady state approach provides a useful and effective correction to the time invariant models.•The best performance is provided by the time variant formulations of transport.•Transport prediction may become difficult when in presence of significant evapotranspiration.

SummaryIn this paper we analyze the performance of four different models of solute transport in catchments. The models employ the concept of travel time distribution. A recapitulation and critical analysis of the models and their basic assumptions is performed first, emphasizing their limitations and potential problems arising in their application. Then, detailed numerical experiments are used as a benchmark for the calibration and the assessment of the models' capabilities to simulate transport. The scope of the exercise is to test the performance of the models and their limitations in the ideal case in which the catchment system and all the hydrological variables (flow, concentration, storage, etc.) are perfectly known at any level of detail. The performance of the models and their limitations is presented and discussed. The results suggest that a time invariant formulation of the travel time distribution is usually inappropriate and not much effective in predicting transport. The performance of all models generally decreases when in presence of evapotranspiration.