Using tracer data to calibrate a flexible, topography driven conceptual hydrological model

Abstract

This study explores the possibility of calibrating a conceptual hydrological model to tracer (Oxygen-18) data measured in streamflow with the ultimate goal to predict discharge. The hypothesis is that (changes in) Oxygen-18 concentrations in the stream should tell something about the relative contribution of fast runoff compared to slow runoff (groundwater flow) inside the stream. A conceptual hydrological model incorporating both tracer dynamics and discharge should be able to model this. Using tracer previously measured in the Brugga catchment (South-West Germany) by people of the University of Freiburg, both lumped and FLEX-Topo inspired models are developed and calibrated to this data. Results showed that of all models considered, only a FLEX-Topo inspired model, containing a variable groundwater level that is able to occasionally (partially or wholly) submerge the wetland model structure, was able to predict a decent hydrograph when calibrating purely on tracer data. The results indicate that calibration of a FLEX-Topo inspired model to only tracer data is a real possibility, and opens the door to more sophisticated modelling attempts, for instance calibration on multiple tracers or multiple tracer sampling points.