A review and evaluation of catchment transit time modeling

Transit time is a fundamental catchment descriptor that reveals information about storage, flow pathways and source of water in a single characteristic. Given the importance of transit time, little guidance exists for the application of transit time modeling in complex catchment systems. This paper presents an evaluation and review of the transit time literature in the context of catchments and water transit time estimation. It is motivated by new and emerging interests in transit time estimation in catchment hydrology and the need to distinguish approaches and assumptions in groundwater applications from catchment applications. The review is focused on lumped parameter transit time modeling for water draining catchments and provides a critical analysis of unresolved issues when applied at the catchment-scale. These issues include: (1) input characterization, (2) recharge estimation, (3) data record length problems, (4) stream sampling issues, (5) selection of transit time distributions, and (6) model evaluation. The intent is to promote new advances in catchment hydrology by clarifying and formalizing the assumptions, limitations, and methodologies in applying transit time models to catchments.