PhD contract: Interactions between Riparian Vegetation and River Flows: Implications for Energy Dissipation and the Development of Nature-Based Solutions (M/F)

Job Description

Thesis Subject

At the CNRS, on the Futuroscope site, the PPRIME Institute, in collaboration with the LEHNA Laboratory, is recruiting a PhD student as part of the 80|PRIME project to work on Interactions between Riparian Vegetation and River Flows.

1- CONTEXT:
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Riverine ecosystems are increasingly affected by bank erosion, a phenomenon intensified by human activities and climate change. In light of the limitations of conventional grey infrastructure, nature-based solutions (NbS), and in particular riparian revegetation, are emerging as sustainable and effective alternatives for mitigating erosion, reducing flow energy and preserving biodiversity.
Riparian vegetation plays a key role in modulating flows by reducing velocities, altering turbulence and promoting energy dissipation. These effects depend strongly on the morphological and biomechanical traits of plants, particularly their flexibility, which determines both their resistance to hydrodynamic stresses and their capacity to influence flow dynamics.
However, the mechanisms linking plant flexibility, deformation, turbulence and energy dissipation remain poorly understood, especially in fluvial systems, and are rarely incorporated in a realistic manner into hydraulic models.

2- THESIS TOPIC:
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This PhD aims to understand, quantify and model the interactions between riparian vegetation and river flows, in order to provide a robust scientific basis for the design of nature-based solutions.
The project addresses three major challenges:
1.The lack of robust quantitative relationships between the morphobiomechanical traits of riparian plants and the hydrodynamic forces exerted by the flow.
2.The limited understanding of the mechanisms of turbulence and energy dissipation induced by vegetation.
3.The difficulty in translating experimental results into predictive models and operational applications of NbS.

3- OBJECTIFS
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The overall objective is to understand and model the interactions between riparian vegetation and flow in watercourses, in order to provide tools to aid the design of nature-based solutions to limit erosion and preserve biodiversity. To this end, this project, known as VEG-IFS aims to understand, quantify and model the combined effect of the flexibility and morphology of riparian plants on hydrodynamic forces, turbulence and energy dissipation in river flows. The objectives are:
-To understand the physical mechanisms affecting riparian plants (forces, stresses, breakage, uprooting);
-To assess how vegetation modifies flow (reduction in velocity, mitigation of erosion);
-To provide information on the interactions between plants and flow, with a view to implementing nature-based solutions (such as riverbank vegetation) for improved watercourse management.
The innovative nature of the project lies in an explicitly interdisciplinary fluid-structure-ecology coupling approach; the combined use of living plants and biomechanically calibrated models; and an energy analysis of turbulence, which has rarely been applied to flexible aquatic vegetation.
The risk involved stems from the biological variability of plants and the complexity of fluid-structure interaction, but it is essential to move beyond current simplistic approaches.

4- ORGANISATION
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The thesis is based on an interdisciplinary fluid–structure–ecology approach, structured around three complementary strands:

-Work-package 1 – Morpho-biomechanical characterisation
Objective: to establish a robust database of morpho-biomechanical traits governing flow–vegetation interactions. Detailed measurements of morphological traits (height, density, architecture) and biomechanical traits (stiffness, flexibility, breaking thresholds) will be carried out on several contrasting riparian species. This involves two tasks:
Task 1.1 – Species selection and morphological description (Selection of riparian species contrasting in terms of morphology and flexibility. Measurement of functional traits: height, density, leaf area, stem architecture)
Task 1.2 – Biomechanical characterisation (Bending and tensile tests to determine stiffness, elastic moduli and breaking thresholds. Analysis of intra- and inter-specific variability)

-Work-package 2 – Hydraulic experiments
Objective: to measure hydrodynamic forces, plant deformation and the structure of turbulence. Experiments in a hydraulic flume will be used to measure velocity and turbulence fields (ADV, PIV), hydrodynamic forces (drag, lift) and plant deformation under different flow conditions. Calibrated models and living plants will be used in a complementary manner. Two tasks have been identified:
Task 2.1 – Setting up the hydraulic flume experiments
Task 2.2 – Hydrodynamic and mechanical measurements.

-Work-package 3 – Analysis and modelling
Objective: to link plant traits, turbulence and energy dissipation through simplified models. The experimental data will inform an energy analysis of turbulence and dissipation and the development of simplified physical and numerical models incorporating plant flexibility. Two tasks will be carried out:
Task 3.1 – Analysis of turbulence and dissipation (Spectral and energy analysis of velocity fluctuations. Quantification of vegetation-induced energy dissipation.)
Task 3.2 – Development of predictive models (Derivation of relationships linking flexibility, morphology and energy dissipation. Integration of these relationships into simplified hydraulic models.)
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* Candidates must hold a Master's degree or an engineering degree in one of the following fields or related disciplines:
- hydraulics, fluid mechanics,
- ecology, ecohydraulics, environmental sciences.

* The successful candidate must possess the following skills:
- an interest in experimentation and/or modelling,
- a basic understanding of fluid mechanics and data processing,
- scientific curiosity, the ability to work independently, and an appreciation for interdisciplinary work,
- strong scientific communication skills (in French and/or English).

Your Work Environment

-The PhD is part of the VEG-IFS project, fundining by MITI action of CNRS, and will be jointly supervised by the Institut Pprime (Poitiers), specialising in experimental hydrodynamics, fluid–structure interactions and metrology, and the Laboratoire d'Écologie des Hydrosystèmes Naturels et Anthropisés (LEHNA, Lyon), internationally recognised for its research in aquatic ecology and riparian vegetation.

-Doctoral School: enrolment at the University of Poitiers Doctoral School (MIMME).

-The doctoral researcher will be primarily based at the Institut Pprime, Université de Poitiers (pprime.fr), Futuroscope Campus, with regular research stays (a cumulative 3 to 6 months) at LEHNA.

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

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