الملخص الإنجليزي
Salalah Coastal Aquifer is considered as the main natural water resource that the
entire city is depending on for agriculture, domestic and commercial use. The
excessive groundwater pumping becomes a concern as seawater intrusion has been
already reported at different farms and abstraction wells mainly close to coastal side
of Salalah Plain. The main objective of this study was to setup, calibrate and validate
a model for Salalah Coastal Aquifer that can be used to assess aquifer behaviour and
seawater intrusion pattern. The study was conducted over 640 km2
of Salalah Plain
which represent around 83% of Salalah Plain total area. Injection scheme, direct
rainfall and dams were considered as sources for aquifer recharge while groundwater
abstraction occurred through agricultural, domestic and commercial uses. 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 [AS1]transient state. The longitudinal dispersivity and
porosity of the aquifer were defined through the calibration and validation of the
model. MODFLOW calibration and validation results showed good agreement
between the field observed head values and model computed values with RMSE of
0.65. 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. MT3DMS calibration and validation results showed
good agreement between the field observed TDS values and model computed values.
The sensitivity analysis indicated that hydraulic head had more sensitivity to the
hydraulic conductivity among the three calibrated parameters, while groundwater
abstraction sensitivity was the highest among all the input parameters to the system.
The calibrated values of the longitudinal dispersivity and porosity were found at the
range of 500 m to50000 m, and 0.4 respectively. The study indicated a clear impact
of seawater intrusion at coastal side of the Salalah Plain. The predictive modeling
indicated an average of 1.5 m drop in hydraulic head across the whole study area by
2040, while seawater intrusion effect was expected to increase at the coastal side
with potential extension to the central area if the Salalah plain. The study concluded
that the generated model can be used as a prediction tool to study the aquifer
behaviour at different scenarios, as part of integrated water resources management
within Salalah city.
