Saltwater intrusion and land subsidence destroy northern Nile Delta archaeological sites: An assessment using hydrochemical indices, SAR satellite imagery, and analytic hierarchy process (AHP)

Abstract

Archaeological sites in deltaic regions face increasing environmental threats. This study provides the first assessment of seawater intrusion and land subsidence impacts on archaeological sites in the Nile Delta through hydrochemical investigations, InSAR techniques, and multi-criteria decision analysis of 33 sites. The results reveal that 80.7 % of groundwater samples are of the seawater (NaCl) type, with northern groundwater primarily consisting of old marine water. The Groundwater Quality Index for Seawater Intrusion shows that 54.6 % of sites have saline groundwater and 45.4 % have mixed groundwater. Hydrochemical Facies Evolution analysis indicates that 73 % of sites are north of the freshwater-seawater interface, with water tables <1 m deep. All sites show high risks of limescale accumulation and corrosive conditions. SBAS-InSAR analysis (2020-2024) detected displacement velocities between -16 and + 5 mm/year, with maximum subsidence in the northern region. The archaeological risk map was developed using the AHP, integrating water corrosion indices, water table depth, soil texture, and subsidence rates. The map classified the archaeological sites into four risk categories: 8 sites were classified as severe risk, 12 sites as high risk, 11 sites as moderate risk, and 2 sites as low risk. These findings highlight the urgent need for mitigation strategies, including groundwater level reduction and prioritized documentation of high-risk archaeological sites.

Keywords: Archaeological preservation; Archaeological risk map; Archaeological sites deterioration; Climate change; Coastal archaeology; Groundwater salinization; InSAR; MCDA; Seawater intrusion; Water corrosion indices.