Effects of sea-level rise on fresh groundwater resources in coastal dune areas – a case-study in the Netherlands

Worldwide, sandy coastal dune systems form a substantial part of the global shoreline. Global assessments show that approximately one-third of the world’s ice-free coastline consists of sandy beaches, many of which host coastal dune systems with fresh groundwater lenses that are crucial for drinking water supply and ecosystem functioning. These fresh groundwater resources are increasingly exposed to saltwater intrusion driven by intensified human water use, land subsidence, and sea-level rise and changes in recharge. These processes make them highly relevant case studies for integrated water resources management in coastal aquifers.

In this study, we quantify the response of fresh groundwater lenses in coastal dune systems to sea-level rise and human pressures, using the Netherlands as a well-monitored and modelled example. We apply a high-resolution 3D variable-density groundwater flow and salt transport model (iMOD-WQ which is similar to SEAWAT), calibrated against observed hydraulic heads and salinity distributions, to simulate present and future conditions. Scenario simulations include sea-level rise of 0.5 m and 1.0 m by 2100, and an extreme scenario of 3.0 m by 2150, combined with land subsidence, climate-induced changes in recharge, and ongoing groundwater extractions for domestic use.

The simulations explicitly resolve key seawater intrusion processes such as lateral saline groundwater intrusion, saline upconing under extraction wells, shifts in groundwater divides, and storm-driven saline inundation. Results indicate that under moderate sea-level rise scenarios, fresh groundwater lenses in dune systems remain relatively in a relative sense, largely due to sufficient recharge from managed aquifer recharge (MAR) practices that maintain hydraulic gradients. However, absolute freshwater volumes decline gradually, and localized risks of salinization increase near production wells. Under the extreme sea-level rise scenario of 3.0 m by 2150, several low-lying dune systems show pronounced freshwater volume losses and increased vulnerability to saltwater intrusion.

Our results demonstrate that coastal dune aquifers can be resilient to sea-level rise when supported by integrated management strategies, but also reveal clear thresholds beyond which freshwater availability rapidly deteriorates. We illustrate that high-resolution modelling can inform sustainable management of coastal aquifers worldwide under a changing climate with increasing human pressures.