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Jean-Philippe Marchand, Pascale Biron , Thomas Buffin-Bélanger , Marie Larocque
Groundwater-surface water exchanges within lowland headwaters translate into ecological services throughout the watersheds, such as flow and biodiversity regulation. In lowland agricultural context, decades of human intervention such as channelization have disrupted the hydrological exchange between the headwater streams and their floodplain and, in doing so, undermined the ecological services these small streams provide. The disruption of hydrological exchanges between the straightened channel and former meander bends has received little attention so far, but restoring ecological services in this type of lowland headwaters requires a thorough understanding of the nature of these hydrological exchanges. This research project explores the parameters controlling the hydrological and hydraulic interactions existing within channelized lowland headwater streams with the objective of proposing a method for assessing the restoration potential of channelized streams based on connectivity with former meanders. To do so, the spatiotemporal variability of groundwater-surface water interactions between channelized reaches and their abandoned meander bends have been investigated through a dense network of piezometers at three sites in the St. Lawrence Lowland (Quebec). Empirical data show that the mechanisms controlling hydrological exchanges between natural meandering lowland rivers, their floodplain and their hillslope also operate in lowland rivers which have been straightened, backfilled, and cultivated. Moreover, the assessment of the pre-straightening hydrogeomorphological configuration of the floodplain partly explains the complex patterns of piezometric fluctuations observed at different sites. The apex of the former meanders stands out as focal areas of hydrological connectivity both fed by flows from the hillslopes, and the surrounding historical floodplain.
Conference Presentation, SER2021
Pre-approved for CECs under SER's CERP program