Groundwater flow modelling of Al-Jizzi aquifer, Oman

The northern Al Batinah plain in Sultanate of Oman contains substantial groundwater resources that have been widely used by generations for their irrigation, industrial and domestic water supply purposes. Ground water aquifers in the region are fed by infrequent and minimal rainfall of an average of 100 mm per year, and which are over abstracted and facing water depletion. A constant water deficit caused by excessive pumping in the region has caused the water quality to deteriorate owing to seawater intrusion. Several farms have been deserted and many others are currently at risk. Sana & Shibli (2003) studied the salinity intrusion in Al-Jizzi aquifer (located in Al-Batinah region) using MODFLOW. A coarse grid (average cell sizes of about 520m x 620m) was employed. In the present study a refined grid (average cell sizes: 33.4 m × 42.8 m) is used which is further refined at the pumping wells to improve the model precision. Also, the conceptual model has been improved considering the bore-log data in the vicinity of the coast. Calibration of the two-layer steady-state conceptual model was carried out using the observed head in the monitoring wells for the year 2000. The model domain was covering nine observation and 22 pumping wells which were spread in five different zones of the model. Field data in the form of the observed water head was available and hydrogeological data which was available from the previous studies was used for calibration of the model. Geo-hydrological parameters like hydraulic conductivity and vertical anisotropy were by manually calibrating in steady state condition. Further, the model was calibrated and validated in the transient condition for the year 2001-2017.
The model showed good agreement of the calculated head with the observed water head in the study area (difference between the observed and calculated head was less than 2m). A global sensitivity analysis carried out for the hydraulic conductivity for both the layers affecting the water heads to estimate the uncertainties for this model parameter on the numerical results. Predicted water levels provide an indication of the magnitude of the change in water levels that can be expected to occur if the predicted recharge and abstraction rates are implemented. The calibrated model was used to predict two different scenarios of incremental pumping and reduced pumping by 10 – 30 % and 5 - 10% of the pumping rates used in the year 2017. The model predicted an average fall of 2.0 m in groundwater table in the study area within the next 22 years (year 2040) if groundwater abstraction continues at the present rate. If the pumping is reduced by 10 %, it could help to reclaim the water level. The study results could be useful for decision makers and practicing engineers for better management of groundwater resources in the arid regions.