Modeling of Seawater Intrusion into Salalah Coastal Plain Aquifer, Sultanate of Oman

Salalah Coastal Aquifer is the vital natural water resource for agriculture, domestic and commercial use for the city. A lack of balance between the recharge and abstraction rates caused seawater intrusion in the wells in the vicinity of the coastal side of Salalah Plain. In this MODFLOW and MT3DMS were implemented for Salalah Coastal Plain aquifer covering about 640 km2 representing around 83% of the total area of the plain. The groundwater modeling was carried out using MODFLOW. The model was calibrated and validated at steady state and transient state using data from 2000 to 2019. It was used to define the aquifer properties such as hydraulic conductivity, specific yield, and vertical anisotropy. MODFLOW results were mapped to MT3DMS in order to simulate solute transport at transient state. The longitudinal dispersivity and porosity of the aquifer were calibrated and validated. Across the three aquifer layers, the hydraulic conductivity was found between 10 m/day to 100 m/day, vertical anisotropy was found to be 4 and the specific yield was found between 0.01 to 0.1. The predictive modeling indicated an average of 1.5 m drop in hydraulic head across the whole study area by 2040, while the seawater intrusion effect was expected to increase at the coastal side with potential extension to the central area of the Salalah plain. The study concluded that the generated model can be used as a prediction tool to study the aquifer behavior under different climate change scenarios, as a part of the integrated water resources management for Salalah city.