Advancing Aquifer Monitoring: TDEM’s Application in Seawater Intrusion Detection within Heterogeneous Coastal Aquifers of the Nile Delta

Coastal aquifers are vital freshwater sources worldwide, yet they are increasingly threatened by seawater intrusion due to over-extraction and climate change. The Nile Delta aquifer, one of the largest coastal groundwater reserves in the world, is particularly vulnerable to salinization, posing significant risks to agriculture, industry, and drinking water supplies. This exacerbates land salinization, infrastructure corrosion, and stresses the local economy. This study aims to explore the efficiency of the Time Domain Electromagnetic (TDEM) method in delineating seawater intrusion within coastal aquifers. The time domain electromagnetic method was used to collect 50 data points along a 50km profile perpendicular to the shoreline towards Mansoura city. Appropriate data processing techniques were applied to increase the signal-to-noise ratio and enhance the readability of data since the area has high cultural noise. Geophysical data inversion and interpretation showed the salt-fresh water boundary. Lithological data from the monitoring well allowed for the calibration of the geophysical model to ensure better results. TDEM data closely matched well data with an average error margin of 5%, showing seawater intrusion extending more than 40 km inland with a gradient nature. Intrusion depth varied between 10 and 20 meters. This confirms TDEM's effectiveness as a fast, cost-effective tool in mapping the salt-fresh water interface in the Nile Delta aquifer. This research suggests integrating TDEM with the current monitoring network for tracking changes in aquifer parameters. This approach offers a foundation for improving groundwater management strategies.