Time variant travel time distributions (TTD) and Storage Selection (SAS) functions are an integrative description of flow path variability within a catchment and are tied to fundamental catchment functions of storage, mixing, and release. The TTDs and SAS functions of vegetative water use have often been overlooked and the link to TTDs of discharge is still poorly understood. Recent research showed that trees access water that is isotopically different from streamflow. Hence, it is necessary to consider this so-called ‘ecohydrological separation’ in travel time research to better understand water ages in various parts of the water cycle and to reduce the uncertainty in travel time modelling. Furthermore, the spatio-temporal pattern of tree water uptake depth and the associated isotopic composition have not been understood today. Here, we intend to tackle these open questions by combining experimental ecohydrological work and travel time modelling in a SAS framework. We will assess ecohydrological separation, isotopic fluxes in water uptake by vegetation, and the depth distribution of water uptake with a comprehensive experimental approach to understand the spatio-temporal characteristics of ecohydrological separation. Furthermore, we will include this information into travel time modelling and compare the vegetation impact on TTDs in various water cycle components (tree water uptake, evaporation, discharge) for the Weierbach catchment and three of its sub-catchments. This will move travel time modelling forward and help us to better understand hydrological catchment functions of water storage, mixing, and release.