Multi-scale functioning of the stream-aquifer interface from the river reach to the basin scale

Séminaire de Nicolas Flipo (Mines Paris Tech), lundi 4 juin 2018 à 14h, salle Forestini (OSUG-A)

Séminaire animé par Julien Némery
Auteur : Nicolas Flipo, Maître de Recherche à MINES ParisTech, Directeur du PIREN Seine

Résumé/Abstract : Coupled hydrological-hydrogeological models, emphasizing the importance of the stream–aquifer interface, are more and more used in hydrological sciences for pluridisciplinary studies aiming at investigating environmental issues. They are of peculiar interest for biogeochemists who try to assess the elimination of biogenic compounds in such interfaces. If ecohydrologists do consider biogeochemical processes in sediments, it remains a challenge to quantify the functioning of the hyporheic buffer which controls the fate of biogenic compounds. In this presentation, I first illustrate the importance of the sediment compartment for the in-river carbon fate in the Seine River downstream Paris urban area using the hydro-ecological model ProSe. Far from being negligible as usually expected for large rivers, the sediments contribute for 30% to the total respiration of the system (Vilmin et al. 2016). Those estimates rely on a well calibrated model, and especially sediment fluxes along the 220 km simulated river stretch (Vilmin et al. 2015). The hyporheic zone also plays a significant role in river metabolism and greenhouse gas emission. In a collaborative work, we also recently estimated that the production and emission towards the river of end products such as CO2 are driven and controlled by the connection status (gaining or loosing) and the frequency of flow reversal due to hydrological events (Newcomer et al. 2018). It is therefore crucial to develop tools and methodologies to assess water fluxes between surface and subsurface (Flipo et al. 2014).

At the regional scale, data from river discharge gauging stations and piezometer networks are usually used to calibrate models. One of the major challenges to estimate the low-frequency component of stream-aquifer exchanges is to define the aquifer recharge properly. An original 2-step calibration procedure based on a proper hydrograph separation is presented for the Seine basin (75 000 km2). Once the aquifer recharge is estimated, the influence of high frequency processes, such as in-river water level fluctuations due to hydrological events, on stream aquifer exchanges is illustrated on the Loire basin (120 000 km2) (Baratelli et al. 2016). To achieve a proper calibration of the conductance coefficient at regional scale, a relationship is established with the aquifer properties (Pryet et al. 2015).

Albeit the conductance model is calibrated at the regional scale based on the horizontal transmissivity of the underlying aquifer, such a simplified 1D vertical coefficient is more difficult to assess at the watershed scale, where stream bed heterogeneities exerts a major control on stream-aquifer exchanges. Following the holistic view of water fluxes within a hydrosystem, an innovative multi-scale sampling system was developed on a 46 km2-watershed. The system consists in distributed measurements of water pressure and temperature of the equivalent porous media (Mouhri et al. 2013). We also developed a 1D sampling system, which allows the identification of hydro-thermal properties of the hyporheic zone based on a Bayesian inversion procedure (Cucchi et al. 2017). This method provides a good estimate of the hyporheic zone which reduces the number of parameters to identify at the stream-aquifer interface. It is then possible to determine the 2D hydro-thermo properties with a screening approach. Finally based on nested modeling it is possible to upscale the related conductance value at the regional scale (Cousquer et al. 2017) and to perform a coupled simulation of the watershed, as illustrated for the sampled basin.

Baratelli, F., N. Flipo, and F. Moatar. 2016. Estimation of distributed stream-aquifer exchanges at the regional scale using a distributed model : sensitivity to in-stream water level fluctuations, riverbed elevation and roughness. Journal of Hydrology 542:686–703.
Cousquer, Y., A. Pryet, N. Flipo, C. Delbart, and A. Dupuy. 2017. Estimating River Conductance from Prior Information to Improve Surface-Subsurface Model Calibration. Ground Water 55:408–418.
Cucchi, K., A. Rivière, A. Baudin, A. Berrhouma, V. Durand, F. Rejiba, Y. Rubin, and N. Flipo. 2017. LOMOS-mini : a coupled system quantifying transient water and heat exchanges in streambeds. Journal of Hydrology In press.
Flipo, N., A. Mouhri, B. Labarthe, S. Biancamaria, A. Rivière, and P. Weill. 2014. Continental hydrosystem modelling  : the concept of nested stream-aquifer interfaces. Hydrology and Earth System Sciences 18:3121–3149.
Mouhri, A., N. Flipo, F. Rejiba, C. de Fouquet, L. Bodet, P. Goblet, B. Kurtulus, P. Ansart, G. Tallec, V. Durand, and A. Jost. 2013. Designing a multi-scale sampling system of stream-aquifer interfaces in a sedimentary basin. Journal of Hydrology 504:194–206.
Newcomer, M. E., S. S. Hubbard, J. H. Fleckenstein, U. Maier, C. Schmidt, M. Thullner, C. Ulrich, N. Flipo, and Y. Rubin. 2018. Influence of hydrological perturbations and riverbed sediment characteristics on hyporheic zone respiration of CO2 and N2. Journal of Geophysical Research  : Biogeosciences In press.
Pryet, A., B. Labarthe, F. Saleh, M. Akopian, and N. Flipo. 2015. Reporting of stream-aquifer flow distribution at the regional scale with a distributed process-based model. Water Resources Management 29:139–159.
Vilmin, L., N. Flipo, N. Escoffier, V. Rocher, and A. Groleau. 2016. Carbon fate in a large temperate human-impacted river system : Focus on benthic dynamics. Global Biogeochem. Cycles 30:1086–1104.
Vilmin, L., N. Flipo, C. de Fouquet, and M. Poulin. 2015. Pluri-annual sediment budget in a navigated river system : the Seine River (France). Sciences of Total Environment 502:48–59.