A combined mixing model for high-frequency concentration-discharge relationships

Streamflow is the major factor influencing the evolution of solute concentration in river water and different modelling approaches exist to characterize the dependency of concentration to discharge: the simplest are based on measurable quantities (stream discharge and stream water concentration) but do not allow for an explicit, physical, flow-path interpretation; the more complex are based on mixing assumptions with different end-members sources, but require the knowledge of (unmeasurable) flow components. We present here an approach allowing to combine the simple concentration-discharge (C-Q) models with the Mass Balance (MB) mixing approach. This combined model tested on high-frequency ionic concentration series from the ORACLE-Orgeval observatory (France), where it clearly outperforms the commonly-used models applied separately. Thanks to the temporal density of the dataset, model performances are tested at different hydrological scales.