An integrated framework to model salinity intrusion in coastal unconfined aquifers considering intrinsic vulnerability factors, driving forces, and land subsidence

Abstract

Salinity intrusion is a common contamination process that affects coastal aquifers. It has been widely studied and continues to attract research attention. Advances typically apply partial frameworks to analyze factors that contribute to salinity intrusion. Such frameworks frequently overlook their interaction and occasionally oversimplify the aquifer dynamics. Studied factors include geology, geometry and hydraulics, tides, waves, sea-level rise and overexploitation, and rarely consider land subsidence. This study provides a unifying framework that integrates influencing factors including land subsidence. It explores the factor’s relevancy based on latest literature, data requirements, common assumptions, frequently used algorithms, and challenges to integrate factors and driving forces. It also synthesizes key stages to model salinity intrusion. Discussing each stage to feature advancements and knowledge gaps. Critical findings include homogeneous and heterogeneous geology that are evenly considered with advances currently towards the investigation of high heterogeneities. The latter increases dispersion and reduces the horizontal solute transport.43% of studies featuring seashore slopes found that flat slopes can enhance salinity intrusion up to 30%. In some studies, different factors have been coupled, for example, waves and tides; sea-level rise and tides; and sea-level rise and land surface inundation. By coupling land surface inundation and the upper saline plume, some studies found an increase in salinity concentration. 36% of studies coupled them with shoreline slope and three considered high heterogeneities. The interaction modifies the solute distribution and salinity concentration. In addition, it is evident that land subsidence of 1.5 and 2 mm/year can enhance the salinity intrusion when considering the relative rise of the sea level, and it can affect properties such as porosity and permeability. Our research group is currently working on applying this framework to integrate factors and driving forces, identify their relevance and to consider land subsidence impact on the aquifer’s structure. This framework facilitates the accurate modelling of salinity intrusion, advising the detailed analysis of each proposed stage to better represent and solve a targeted problem.