Soil water erosion is estimated to average 1.5 t/ha/year in France, and can exceed 10 t/ha/year in some regions (Cerdan et al., 2010). It is the main threat to soil degradation, and has a major impact on the hydrosystem. Its worsening under the effect of certain anthropogenic activities, combined with climate change, makes it a major threat (Borrelli et al., 2017). Limiting runoff and soil erosion is therefore a primary objective. Erosion modelling at the scale of management entities is a valuable tool for quantifying and simulating the effect of mitigation strategies.

Soil infiltration capacity and its temporal dynamics are fundamental parameters for modelling surface runoff and, consequently, soil erosion. Runoff occurs when the infiltration capacity of the soil is exceeded, or when the soil is saturated with water. On hydromorphic plains, both types of runoff can occur at different times of the year. However, the spatial and temporal variability of soil infiltration capacity remains difficult to estimate (Miyata et al., 2010), and limits the performance of runoff and erosion models. Infiltration capacity depends on intrinsic soil properties (e.g. texture, organic matter). It also depends on their structure, which evolves to a greater or lesser extent over the course of the crop year, depending on stability and cultivation practices. It is also strongly limited by soil saturation during wet periods, particularly on hydromorphic plains.

The aim of this PhD thesis is to quantify the impact of taking into account the spatial and temporal variability of soil infiltration capacity, and soil saturation, on runoff and erosion modelling in hydromorphic plains.

Work to be undertaken

The work during the course of the PhD will be to combine field and laboratory approaches with a major data analysis phase. The stages of the work will be as follows:

• Following a review of the scientific literature, consolidate the problem, research questions and hypotheses of the thesis;
• Draw up a sampling strategy for the location of observation and measurement points;
• Measure soil properties and structural stability at each point, as well as infiltration capacity and water saturation at different times of the year;
• Map the infiltration capacity and saturation status of soils at each measurement period, using ancillary data: relief, soil parameters, remote sensing data, farming practices, etc;
• Establish temporal evolution functions for infiltration capacity and soil saturation at each sampling point;
• Derive a monthly map of infiltration capacity and soil saturation;
• Apply the Watersed runoff and erosion model (Landemaine et al., 2023) taking into account the value of infiltration capacity and soil saturation at any point in space, and compare model outputs with hydrosedimentary data from watershed monitoring.
• Publish papers in international journals and present the work at congresses/conferences.

The work will be carried out at the Louroux observatory (Indre-et-Loire), which was set up in 2012 to answer questions about the dynamics of soil erosion in lowland areas. The work carried out since then has so far focused on the historical reconstruction of erosion rates within the basin, on the study of sediments accumulated within the pond located at its outlet (Foucher et al., 2014); on the identification of the sources of the material transferred (Le Gall et al., 2016); and on the hydrosedimentary dynamics within the basin's watercourses (Grangeon et al., 2017) and at plot level (Gaillot et al., 2023). In particular, this work has shown that surface runoff from soils is the main vector of eroded particles. Erosion of the banks of watercourses and that resulting from the operation of the drainage network is secondary.

Scientific material conditions

The first part of the thesis will be carried out within the GeoHydrosystems Continental Research Unit at the University of Tours, specializing in the study of matter transfers in hydrosystems. A significant part of this first part of the thesis will be devoted to field and laboratory studies. The second part of the thesis will be based at the INRAE Orléans Info&Sols research unit, which specializes in soil science. Work will focus on data analysis, valorization and writing of the thesis.

A 3-month stay abroad is possible.

Funding of the thesis is secured, the thesis will start on october, 1st 2025.

Supervision will be provided by:

• Cécile Grosbois, thesis director, Université de Tours-GéHCO (cecile.grosbois@univ-tours.fr)
• Hocine Bourennane, thesis director, INRAE-Info&Sols (hocine.bourennane@inrae.fr)
• Sébastien Salvador-Blanes, co-supervisor, Université de Tours-GéHCO (salvador@univ-tours.fr)
• Nicolas Saby, co-supervisor, INRAE-Info&Sols (Nicolas.Saby@inrae.fr)

Required candidate profile and skills

We are looking for a student with a Master 2 or engineering degree with a specialization in soil sciences, water sciences, agronomy or equivalent. The candidate should have a strong motivation for field and laboratory work, and an appetite for data processing (statistics, geostatistics) and modeling. Training in water transfer modeling would be a plus. The candidate must be dynamic, enthusiastic and self-reliant. He or she should have good writing and communication skills.

To apply

PhD candidates are encouraged to contact the thesis supervisors for any question prior to application.

Application should be submitted at the following link before July, 8, 2025:

https://collegedoctoral-cvl.fr/as/ed/voirproposition.pl?site=CDCVL&matricule_prop=66519