Towards a Fully Distributed Characterization of Water Residence and Transit Time by Coupled Hydrology-Transport Modeling

Abstract:

Water residence and transit time are crucial elements in flow pathways and catchment response characterization.

The temporal distribution of catchment transit times has been generally studied and modelled with lumped parameter approaches.

However, understanding the dominant controls in a more holistic manner requires attention to the spatially distributed catchment properties also in relation to their control on the basin response to different type of precipitation events.

A tool that looks both at the time and space distribution of water residence and transport can be useful for predicting water and solute fluxes and ultimately for better understanding the dependence of catchment transit and residence times on geomorphological and climatic factors.

To this purpose we couple a fully distributed, yet essential, process-based watershed model with a component to simulate solute transport.

Key features of the developed tool include: (a) reduced complexity spatially-distributed hydrological model; (b) spatially-distributed water age and conservative tracer concentration; (c) possibility to explicitly compute transit time distributions for different precipitation events and locations.

The presented framework is tested on the Plynlimon watershed (UK), where long-term records of hydrological variables are available. Among them, discharge and chloride concentration are used to investigate the model behavior.

We present the integrated model concept, the underlying methodologies, the results from the case study application, as well as preliminary virtual experiments that allow exploring the full statistical space of travel and residence times.