PhD opportunities

Characterization of groundwater contribution to the Loing river floods (France).

Thesis proposal

Area of expertiseGeoscience and Geoengineering
Doctoral SchoolGéosciences, Ressources Naturelles et Environnement
SupervisorM. Nicolas FLIPO
Research unitCentre de Géosciences
ContactFLIPO Nicolas
Starting dateOctober 1st 2022
Keywordsquantitative hydrogeology, coupled modeling, stream-aquifer exchanges, risk assessment, flooding
AbstractIn May-June 2016, the Loing* watershed suffered from an exceptional hydrological event which generated an estimated outlet flow of over 500 m3/s. Such an unprecedented event, especially at this time of the year, fed a flood of decennial to vicennial magnitude order at the downstream area of the Seine basin. With significant damages associated with this event** and the fear that the frequency of such phenomena would increase in the future on the Seine basin under the effect of climate change, specific actions have been implemented through the Flood Prevention Action Program (PAPI).

This work primarily aims to characterize the hydrogeological functioning of the Loing watershed, known to be quite varied and complex locally, especially due to the presence of karstic zones, marked by numerous areas of water losses and resurgences. Furthermore, this watershed is particularly prone to the flooding risk due to the groundwater table rise, as highlighted by the BRGM sensitivity map to rising water tables. In-depth research will be carried out to better characterize stream-aquifer relationships at the watershed scale, in order to specify local mechanisms from which flooding phenomena originate.

First, an analysis of the available hydrological data allowing the characterization of these processes will be carried out, to identify strategic areas to be instrumented for a better monitoring of the watershed and to refine the understanding of flood genesis mechanisms (potential contribution of groundwater to extreme events, in particular).

Second, a hydrological/hydrogeological coupled modeling of the whole Loing watershed (~ 4,000 km2) will be implemented, using the CaWaQS3.x model (Catchment Water Quality Simulator), which has recently been developed to represent karstic systems within a regional hydrosystem. The CaWaQS-model will be calibrated, using a dedicated calibration methodology developed to integrate these particularities. The methodology will be based on recent methodological developments allowing a characterization of key hydrological parameters needed to describe the functioning of the hydrological systems upstream from gauging stations. This method has been developed to ensure the consistency between the regional Seine basin CaWaQS model and the sub-model of the Loing watershed. The methodology will be based on a stochastic approach to characterize the uncertainties related to the lack of knowledge of the geometry of karst systems.

The calibrated model will then support:
• The characterization of the general functioning of (i) the aquifer system, (ii) the hydraulic relations between the different aquifer layers as well as (iii) the way they interact with the surface hydraulic network.
• The quantification of potential contributions of groundwater in the flood genesis or aggravation processes.
• The reconstruction of long-term past and future hydrological trajectories of the Loing watershed. More particularly, the role played by the aquifers in flood phenomena will be investigated.

Finally, a reflection will be conducted on how to develop warning systems jointly based on (i) observation systems, (ii) understanding of the hydrogeological functioning of valued territories prone to high risk, and (iii) the predictive abilities of the CaWaQS-Loing model. In this context, a coupling approach with the ISL-Ingénierie hydraulic model*** will be implemented to generate precise rising water table maps associated with singular hydrological events.

* First order tributary of the Seine river.
** At the scale of the Seine and Loire basins, damages have been estimated at between 800 and 1,256 M€ by the French State reinsurance company (CCR).
*** Model developed within the framework of the landmark study of the PAPI plan, carried out by the Loing watershed EPAGE.
ProfileStrong background in quantitative hydrology and hydrogeology required as well as in numerical and computer science (code development skills). Management of large data sets, GIS (Geographic Information System). Good command of English is essential. The candidate will have to demonstrate his or her mastery of the following skills: autonomy, synthesis thinking, taking initiative, relational skills, scientific rigor. Mastery of the French language, both written and spoken.

How to apply
Candidates must contact the director(s) of the thesis proposal or the contact person specified. The latter will then hold auditions and select the most suitable candidate for their project.
Content of the application :
-a CV
-a letter of motivation
-transcript of marks of Master 2 (or equivalent)
-summary of the Master 2 report (or equivalent)
-Letter of recommendation from the Master 2 internship supervisor (or equivalent)
FundingConvention CIFRE