Hydrological and thermal signatures to characterize groundwater influence and improve a spatialized regional hydrological model

Groundwater flow and stream-aquifer interactions are the most fundamental processes that control the physical and biological characteristics of entire hydrographic networks during low-flow periods.

Our study focuses on these complex flows represented in a physically based, regional, and fully distributed hydrological model. We use the J2000 hydrological model, applied to the case study of the Saône river in France. This 30,000 km² watershed has a contrasted lithology, with karstic sectors, which makes it possible to study the performance of the model according to the karstification of its sub-watersheds. It is also a heavily monitored watershed with daily flow measures at 227 hydrological stations evenly distributed over the study area and 587 hourly temperature measurement stations.

J2000 model performance is estimated by calculating widely used hydrological signatures such as BFI (Base Flow Index), IGF (Interbasin Groundwater Flow), or FDC (Flow Duration Curve) characteristics. This set of signatures evaluates the performance of the model with respect to the representation of groundwater flows. In addition, we calculate thermal signatures derived from the relationship between air and water temperature (damping factor, time lag, slope). They are not used as a performance criterion but they give some more information about the spatial distribution of thermal regime and the type of groundwater contribution.

The analysis of observed and simulated hydrological signatures, and observed thermal signatures, revealed various hydrological and thermal responses (e.g. shallow and deep groundwater signature), depending of the lithology of the sub-basin. In our future work, we will couple the J2000 model with the process-based thermal model T-NET (Thermal NETwork). The work presented aims to increase the performance of the thermal regime determination, which has shown significant sensitivity to groundwater contributions.