Saltwater Intrusion Into a Confined Island Aquifer Driven by Erosion, Changing Recharge, Sea-Level Rise, and Coastal Flooding
Date
2024-01-08
Journal Title
Journal ISSN
Volume Title
Publisher
Water Resources Research
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.
Key Points
- A surface-subsurface numerical model is used to investigate climate change impacts on island groundwater resources used for water supply
- The confined aquifer is resilient to storm surges which only salinize the unpumped surficial aquifer before being flushed
- Coastal erosion and recharge reductions result in the most saltwater intrusion and can work in tandem to threaten future water supply
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.
Description
This article was originally published in Water Resources Research. The version of record is available at: https://doi.org/10.1029/2023WR036394. © 2024 The Authors.
Keywords
saltwater intrusion, layered aquifer, coastal flooding, morphodynamics, climate change
Citation
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. Water Resources Research, 60, e2023WR036394. https://doi.org/10.1029/2023WR036394