| Abstract Submission No. | ABS-2.3-0029 |
| Title of Abstract | Assessing Seawater Intrusion in Multi-Layered Coastal Aquifer of the Pennar Delta through Geophysical and Hydrochemical Investigations |
| Authors | Y. Sivaprasad*, YR Satyaji Rao, R Venkata Ramana, VS Jeyakanthan |
| Organisation | Deltaic Regional Centre, National Institute of Hydrology |
| Address | DRC, National Institute of Hydrology Kakinada, AndhraPradesh, India Pincode: 533003 E-mail: sivaprasad.gw@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | Seawater intrusion is a major concern in coastal aquifers, primarily caused by excessive groundwater extraction near the coast. To assess this issue, Vertical Electrical Soundings (VES) were carried out from the coastline to the inland areas of the Pennar delta during June 2025. Groundwater samples from shallow and deep wells were also collected near the VES sites, and hydrochemical data were correlated with resistivity data. The VES results indicate that the Pennar delta hosts a multi-layered aquifer system with three to five geoelectric layers, comprising shallow alluvial aquifers and deeper confined sand/gravel aquifers separated by clay aquitards. In the upper Pennar delta, shallow aquifers show lower resistivity (4.5¿9.5 Ωm) extending to depths of nearly 30 m, whereas in the lower delta, high resistivity (8.5¿42 Ωm) is restricted to about 10 m, reflecting distinct hydrogeological settings between the southern and northern regions. Very low resistivity (<1 Ωm) observed at some coastal sites corresponds to extremely high TDS (16,000¿33,000 mg/L), confirming severe seawater intrusion. Interpolation of 1D resistivity models into 2D cross-sections delineates freshwater¿saline water boundaries and maps the extent of intrusion. Two major intrusion zones are identified: a southern pocket at Krishnapatnam, and a northern pocket spanning around Pedapalli, Ramathirtham, Varini, Alaganipadu, and Isakapalli. Seawater intrusion is shallow (15 m) at Krishnapatnam and Isakapalli, while in the northern sites it appears at deeper levels (40 m). Seawater intrusion in the region is largely driven by excessive and unregulated groundwater withdrawal for aquaculture near the shoreline, which has severely impacted the aquifer system and facilitated the inland advancement of saline water. Mitigation requires strict regulation of deep groundwater pumping in vulnerable coastal zones. The study demonstrates that VES is an effective tool for accurately mapping the depth and extent of saline intrusion and distinguishing freshwater from saline aquifers. |
| Keywords | VES, Hydrochemistry, Pennar Delta, Seawater Intrusion |