Use of a flood-routing model to assess lateral flows in a karstic stream: implications to the hydrogeological functioning of the Grands Causses area (Tarn River, Southern France)

Abstract

The aim of this study is to assess the spatiotemporal variability of lateral flows in the streams of a large karstic basin to construct a conceptual model of karst contributions to flood generation. The lateral flows of the Tarn River, which crosses the Grands Causses karst zone in Southern France, were investigated between several gauging stations along the river. First, through analysing the lateral flows on an event time scale of 30 floods, it was possible to identify the losing and gaining reaches, highlighting a highly variable attenuation/amplification role of karsts on flood generation. Second, the diffusive wave model was used to quantify the lateral flows on an hourly time step within a flood event. The simulations show a high variability of lateral outflows and inflows within a same reach according to the hydrometeorological conditions, with in some cases an inversion of the lateral flow direction during the flood. The results highlight complex surface/groundwater exchanges during a single flood event, with high river losses despite the concurrent flow of large springs feeding the stream. This spatio-temporal variability of the karst influence on flood generation was linked to the aquifer's structure, which has improved the understanding of the hydro(geo)logical functioning of the Grands Causses massif. Finally, the new methodology proposed here opens challenging perspectives towards a framework for the analysis of surface-groundwater exchanges in karstic rivers.

Quantifying peakflow attenuation/amplification in a karst river using the diffusive wave model with lateral flow

“…For highest peakflows, lateral outflow (Figure a) is generally considered in the case of overbank flow when waters from the river flow to the flood plain, without been returned to the river during the flood (Jothityangkoon & Sivapalan, ; Moussa & Bocquillon, ), modifying the shape of the hydrograph (Rak, Kozelj, & Steinman, ; Fleischmann, Paiva, Collischonn, Sorribas, & Pontes, ). Another case favouring lateral outflow is specific to permeable basins, where river losses infiltrate and recharge the underlying aquifer (Charlier et al, ; Dvory et al, ; Sorman, Abdulrazzak, & Morel‐Seytoux, ). This is notably the case in arid/Mediterranean environment, where the importance of infiltrating floodwater for aquifer recharge has been highlighted in disconnected river‐aquifer systems (Camarasa Belmonte & Segura Beltrán, ; Dahan, Shani, Enzel, Yechieli, & Yakirevich, ; Hughes & Sami, ; Lange, ; Vázquez‐Suñé, Capino, Abarca, & Carrera, ).…”

“…When carbonate formations are highly karstified, which can be the case in chalk formations, GWs contribute to the fast‐flow component in streams (Charlier, Moussa, et al, ; Maréchal, Ladouche, & Dörfliger, ), playing a significant role in flooding, even for flash floods. In karst basins, flooding may also occur by the cessation of rainfall infiltration because of the small retention capacity of a karst massif (Fleury, Maréchal, & Ladouche, ; Maréchal et al, ), or because the infiltration capacity of the underground conduit network is exceeded (Bailly‐Comte, Jourde, & Pistre, ; Bonacci, Ljubenkov, & Roje‐Bonacci, ; Lopez‐Chicano, Calvache, Martin‐Rosales, & Gisbert, ).…”

“…Another frequent feature of flood generation in karst basins is a contrasted evolution of peakflow, that is, amplification or attenuation, in a same reach depending upon the prior aquifer saturation level (Charlier, Moussa, et al, ; Maréchal et al, ). In catchments characterized by a high storage potential in thick unsaturated zones of karst aquifers, peakflow attenuation is common (Brunet & Bouvier, ; Jourde et al, ; Ladouche, Maréchal, & Dörfliger, ), which may add to the attenuation due to flood‐wave diffusion in the channel.…”

A novel platform to evaluate the dampening of water and solute transport in an experimental channel under unsteady flow conditions

“…Both water and solute models were incorporated into the hydrological models ModSpa (Moussa, ; Moussa, Chahinian, & Bocquillon, ) and MHYDAS (Charlier et al, ; Cholet et al, ; Moussa et al, ).…”

Using Wavelet Coherence to Characterize Surface Water Infiltration into a Low‐Lying Karst Aquifer

“…In the context of karstified limestone aquifers, river bed exfiltration may constitute significant aquifer recharge (Salvador et al 2012;Smith et al 2015;Koeniger et al 2017) while the magnitude and direction of the interaction may be time variant depending on the hydrometeorological conditions (Bailly-Comte et al 2009;Charlier et al 2015b;Chapuis et al 2020). Linking (and delineating) surface water and groundwater "bodies" is a crucial aspect with regard to integrated catchment management and the protection of surface NGWA.org Groundwater waters and groundwaters, which is a priority of the European Water Framework Directive (WFD) (European Commission 2000.…”