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Doctor with H2O'Lyon Certification :
Hossein Ghaffarian


Post-doc Researcher in Fluvial Dynamics

"Hossein Ghaffarian's thesis was co-directed, combining the approaches of two H2O'Lyon laboratories, hydrodynamics with the LMFA and physical geography with EVS, on a joint project, driftwood in rivers. Hossein Ghaffarian has thus worked in the laboratory, in the ground (Isère) and in modelling. The applications, mainly the formation of logjams and the aggravation of flood hazards, have made it possible to bring together practitioners around his conclusions, as part of a LabEx IMU project. This desire to combine different approaches can be seen in the career of Hossein Ghaffarian, who had several years of professional experience in a hydraulic engineering office before starting his thesis... "




THESIS

Study of Drifwood Dynamics in Rivers for Hazard Assessment

Abstract

Driftwood is an integral part of river corridors where it plays an important role both in river ecology and morphology. During the last decades, the amount of large wood transported in some of the European rivers has increased, notably due to modifications in the human pressure and management of riparian forest buffers along rivers.This causes an increase of potential hazards for hydraulic structures and urban areas. In this context, the aim of this thesis is to study the driftwood dynamics in rivers in order to provide elements for hazard assessment. This is carried out in two ways : (i) using in-situ streamside videography to measure the amount of wood transported by the river during floods and (ii) analyzing the dynamics of individual pieces of wood both on the field and in a well-controlled experimental environment combined with theoretical models. The present work provides several scientific and technical contributions. First by studying the link between wood discharge and flood characteristics, such as flood magnitude, hydrograph and inter-flood time, we consolidate and extend the present knowledge about the link between flow and wood discharges. Second, our studies show that when a piece of wood is recruited into the river, it is accelerated on a limited distance, which scales as the wood length in the flow direction. Once the wood piece reaches the flow velocity, it behaves as a flow tracer. In terms of technical contributions, by comparing the video monitoring technique in two different sites, we provide some recommendations that are useful for practitioners for installing new monitoring stations. This work will be part of the driftwood hazard and risk assessments, for which accurate wood dynamics quantities are required.

H2O'Lyon thesis Director

Nicolas Rivière, INSA Lyon

Thesis Co-Directors

Diego Lopez, INSA Lyon
Hervé Piegay, ENS Lyon

Doctoral School

MEGA

Laboratory

Fluid Mechanics and Acoustics Laboratory (LMFA)

Defence date

November 15th, 2019

Defence language

English

Thesis Jury Members

Jean-Philippe MATAS - Univ. Claude Bernard Lyon 1
Mario Aristide LENZI - Univ. degli Studi di Padova
Dieter RICKENMANN - Swiss Fed. Res. Inst. WSL
Laurence BERGOUGNOUX - Aix Marseille Université
Laurence DUCHESNE - CNR