Mechanisms, configuration typology, and vulnerability of pumping-induced seawater intrusion in heterogeneous aquifers

Abstract

Coastal aquifers are vulnerable to seawater intrusion due to excessive groundwater pumping. Most research on salinization vulnerability considers homogeneous aquifers, forming the basis of management guidance. However, geologic structure can be highly heterogeneous, with preferential flow paths and low-permeability barriers that complicate flow and salt transport processes under pumping conditions. Here we use a series of variable-density groundwater flow and salt transport models with geostatistical representations of heterogeneity to illustrate characteristics of vulnerability in heterogeneous and homogeneous aquifers. Simulations showed that in homogeneous aquifers, salinization patterns were simple and related only to the hydraulic properties. In heterogeneous aquifers, salinization rates and patterns were much more complicated, and related to pumping location and depth, aquifer geometry, and geologic connections between pumping location, landward boundaries, and saline groundwater. An intrusion configuration typology approach was developed for both homogeneous and heterogeneous aquifers. The configuration approach was applied to heterogeneous aquifers of low, medium, and high geologic continuity, and vulnerability was assessed. The probability-based assessment was able to characterize the impact of pumping locations and rates in heterogeneous aquifers, considering different types of intrusion. The results showed that groundwater vulnerability to salinization was sensitive to pumping distance to the coastline for low-continuity aquifers and to pumping depth for high-continuity aquifers. The analysis provides new insights into the relationship between land-sea geologic connections and seawater intrusion vulnerability. The configuration approach plus probability-based assessment can be a starting point for large-scale aquifer characterization and more sophisticated groundwater management, including vulnerability assessment and optimization of pumping location, depth, and rate.