Cécile Coulon
Ph.D. student
Department of Geology and Geological Engineering
Laval University

Supervised by:

Jean-Michel Lemieux (Regular member)

Research project description

Numerical groundwater modeling of the Magdalen Islands and sustainable groundwater abstraction scenarios minimizing saltwater intrusion and anticipating climate change effects

Introduction: In the Magdalen Islands (Quebec, Canada), due to the absence of sufficient surface water resources and the cost of seawater desalinization, groundwater is the only drinking water source. Due to its insular nature, this groundwater resource is vulnerable to seawater intrusion at depth. The risk of seawater intrusion is exacerbated by increased water demand and groundwater pumping during the summer and could be further enhanced in the future owing to the combined effects of climate change (sea-level rise, coastal erosion and decrease in groundwater recharge). This is also an environment undergoing vast changes, as snowfall and periods of winter freezing and declining. How can groundwater management be optimized in the Magdalen Islands, to minimize the risk of seawater intrusion while anticipating the effects of climate change?The first aim of the PhD will be to evaluate current municipal groundwater pumping scenarios: are they sustainable? These municipal pumping scenarios will then be optimized: what is the total amount of fresh groundwater that can withdrawn from the aquifer, compared to groundwater recharge rates and the depth to the saltwater-freshwater interface? Finally, we will provide recommendations for future groundwater abstraction: what standards and criteria should be considered when implementing new groundwater wells? The effects of climate change will be taken into account for each and every part of the analysis (including the decline of snowfall and of freezing periods during the winter).Study sites: The Magdalen Islands are an archipelago of about 202 km2, located in the middle of the Gulf of Saint Lawrence. Eight islands of this archipelago are inhabited, seven of which are connected by narrow sand dunes. Water is used for domestic, industrial, agricultural, commercial and institutional purposes. The archipelago’s four most populated islands each have a municipal well field and a water supply network. In total, around 40 municipal wells exploit the Magdalen Islands’ groundwater resources, which are stored in a heterogeneous and fractured sandstone aquifer.Material and methods: In coastal areas, knowledge on the extent of seawater intrusion and on the depth to the freshwater-saltwater interface is critical for groundwater management. In the Madgalen Islands, as in many other coastal regions, this data is scarce and scattered both spatially and temporally. The development of a numerical groundwater model will therefore be essential, as a first step. Once the model is calibrated, different climatic scenarios will be integrated to the simulations and multi-objective optimization will be used as a tool to address management issues.Expected results: During the PhD, each islands’ municipal well field will be optimized, in terms of the maximum amount of water that can be withdrawn provided the rate of water renewal and the depth to the saltwater-freshwater interface. Within these well fields, the spatial and temporal distribution of pumping rates for each groundwater well will be optimized. Finally, recommendations will be specified for the implementation of future groundwater wells, based on a certain amount of criteria (for example, maximum well number, minimal distance between wells, minimal distance to the coast).

Research Site Coordinates

Scientific Communications

Coulon, C., Lemieux, J.-M., Pryet, A., Bayer, P., Young, N., Molson, J., 2022. Pumping Optimization Under Uncertainty in an Island Freshwater Lens Using a Sharp‐Interface Seawater Intrusion Model. <strong>Water Resources Research</strong>, 58(8). DOI: <a href="" target="_blank">10.1029/2021WR031793</a>.

Coulon, C., Pryet, A., Lemieux, J.-M., Yrro, B.J.F., Bouchedda, A., Gloaguen, E., Comte, J.-C., Dupuis, J.C., Banton, O., 2021. A framework for parameter estimation using sharp-interface seawater intrusion models. <strong>Journal of Hydrology</strong>, 600, 126509. DOI: <a href="" target="_blank">10.1016/j.jhydrol.2021.126509</a>.

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