PhD Oral Exam - Jean-Philippe Marchand, Geography, Urban and Environmental Studies

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

This doctoral research in Geography explores the restoration of hydrological processes in heavily modified agricultural streams of the St. Lawrence Lowlands, Québec. Over the past century, these streams have been straightened, incised, and backfilled, reducing their ecological integrity and connectivity. Chapter 2 (published article) examined residual hydrological connectivity in two straightened streams (Pot-au-Beurre and Martin) through high-resolution piezometric monitoring. Maximum correlations between stream stage and groundwater levels revealed that, despite anthropogenic alterations, lateral and vertical exchanges persist, especially near abandoned meanders, indicating a potential for natural recovery where subsurface floodplain processes remain active. Chapter 3 developed a steady-state MODFLOW model for a degraded 300 m reach of the Pot-au-Beurre. Results showed that coarse alluvial deposits and residual floodplain features act as key nodes for groundwater–surface water exchanges. The study emphasizes the central role of geomorphological context in sustaining subsurface connectivity, even within simplified channel systems. Chapter 4 documented the co-design and implementation of the pilot project Un Méandre à la fois (“One Meander at a Time”), conducted with a local farming family. This semi-passive initiative combined crop withdrawal from the historical floodplain, culvert replacement, and the delineation of a functional freedom space. Ecological and hydrological monitoring (vegetation, fauna, groundwater) assessed outcomes, while governance and social acceptability were analyzed to inform broader replication. Together, these components show that agricultural stream restoration can build upon residual hydrological processes, provided that geomorphic conditions are respected and local stakeholders are engaged through flexible and adaptive strategies.