HGS RESEARCH HIGHLIGHT – Saltwater Intrusion Into a Confined Island Aquifer Driven by Erosion, Changing Recharge, Sea-Level Rise, and Coastal Flooding
Stanic, S., LeRoux, N. K., Paldor, A., Mohammed, A. A., Michael, H. A., & Kurylyk, B. L. (2024). Saltwater Intrusion Into a Confined Island Aquifer Driven by Erosion, Changing Recharge, Sea‐Level Rise, and Coastal Flooding. In Water Resources Research (Vol. 60, Issue 1). American Geophysical Union (AGU). https://doi.org/10.1029/2023wr036394
“The calibrated [HydroGeoSphere] model was used to simulate the impacts of climate change including sea-level rise (SLR), storm surge overtopping, changing aquifer recharge, and erosion.”
Fig. 1: Maps of study site: (a) Prince Edward Island (PEI), Canada, with the location of Lennox Island noted by black dot; (b) Lennox Island and nearby barrier island Hog Island in Malpeque Bay.
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Looking at a new study published by Sofija Stanic, Nicole LeRoux, Anner Paldor, Aaron Mohammed, Holly Michael & Dr. Barrett Kurylyk, researchers have delved into the intricate dynamics of island aquifers under the influence of climate change stressors.
This research sheds light on the complex interactions between storm surges, reduced recharge, high erosion rates, and sea-level rise on the hydrological balance of Prince Edward Island. At the heart of the investigation lies the utilization of HydroGeoSphere (HGS), Aquanty’s sophisticated modelling platform known for its ability to simulate coupled surface water-groundwater interactions with unparalleled accuracy. By leveraging the advanced capabilities of HGS, the researchers were able to test impact that climate change and future trends in coastal hydrology will have on the islands groundwater quality and the movement on the saltwater wedge underlying PEI.
A key advantage of HGS is its versatility, offering a comprehensive toolkit for modelling a wide range of hydrological processes. From simulating storm surge scenarios to analyzing the impacts of changing recharge rates and erosion dynamics, HGS provided researchers with the flexibility to explore different scenarios in depth.
Plain Language Summary:
Due to their limited resources and adaptive capacity, small islands are highly vulnerable to climate change impacts, including saltwater intrusion. Freshwater needs on small islands are often sourced from small aquifers that are in delicate balance between conditions in the ocean, atmosphere, and land. In this study, we investigate the movement of saltwater into the freshwater aquifer of a small island that provides drinking water resources for an Indigenous First Nation. We consider climatic changes in the ocean (sea-level rise (SLR), storm surges, and related coastal erosion) and atmosphere (changes to net precipitation) and associated impacts to the island's fresh groundwater resources. We use field data paired with a mathematical model and demonstrate that the pressurized conditions of the layered island aquifer make it more resilient to SLR than unconfined aquifers in sandy islands are. However, the aquifer's freshwater volume is susceptible to coastal erosion and reduced precipitation, particularly when these happen at the same time. Results point to coastal erosion as a potential widespread driver of freshwater loss along eroding portions of the global coastline.
“Given the storm surge overtopping scenarios described later, this capacity to simulate coupled surface and subsurface flow and transport was the primary reason for selecting [HydroGeoSphere]. ”
Fig. 2: (a) Conceptual diagram of the chosen cross-section on Lennox Island (see transect A-Aʹ on Figure 1b) with a representation of climate change perturbations (changing recharge or P-ET, storm surge flooding, erosion, and sea-level rise). (b) HydroGeoSphere two-dimensional model domain and mesh with boundary conditions. The island domain dimensions changed for the erosion scenarios.
Abstract:
Aquifers on small islands are at risk of salinization due to low elevations and limited adaptive capacity, and present risks will be exacerbated by climate change. Most studies addressing small-island saltwater intrusion (SWI) have focused on homogeneous sandy islands and one or two hydraulic disturbances. We herein investigate SWI dynamics in a layered, confined island aquifer in response to multiple environmental perturbations related to climate change, with two considered in tandem. Our field and modeling work is based on an island aquifer that provides the drinking water supply for an Indigenous community in Atlantic Canada. Observation well data and electrical resistivity profiles were used to calibrate a numerical model (HydroGeoSphere) of coupled groundwater flow and salt transport. The calibrated model was used to simulate the impacts of climate change including sea-level rise (SLR), storm surge overtopping, changing aquifer recharge, and erosion. Simulated aquifer conditions were resilient to surges because the confining layer prevented deeper saltwater leaching. However, reduced recharge and erosion resulted in saltwater wedge migration of 170 and 110 m, respectively when considered individually, and up to 295 m (i.e., into the wellfield) when considered together. Despite the confining conditions, SLR resulted in wedge migration up to 55 m as the confining pressures were not sufficient to resist wedge movement. This is the first study to harness an integrated, surface-subsurface hydrologic model to assess effects of coastal erosion and other hydroclimatic stressors on island aquifers, highlighting that climate change can drive extensive salinization of critical groundwater resources.