There is a freshwater deficit and growing groundwater dependence in many regions of Iraq due to population development and increased water demand for numerous uses. The water table declines due to the area's numerous deep wells drilled randomly and a constant increase in water pumping from groundwater reserves. Thus, it is vital to evaluate the water resource management. The present research examines the potential for degradation and the stressors affecting the confined aquifer of the Lower Zab watershed across the governorates of Kirkuk, Erbil, and Sulaymaniyah. Utilizing the Groundwater Modelling System (GMS V10.7) software, a numerical simulation of groundwater flow was conducted to model the basin's confined aquifer. The steady-state calibration results revealed a hydraulic conductivity (HK) ranging from 3 to 10 m/day, while the estimated recharge rate (RH) was 0.0004 m/day. The model was calibrated for each observation well in the watershed by comparing observed and simulated groundwater heads. The most sensitive parameters identified were conductance (for rivers and reservoirs), HK, and RH, with the lowest residual determined for these factors. Assessment of the model's reliability utilized the root mean square error (RMSE), mean absolute error (MAE), and mean error (ME). The estimate's standard error is 0.6259 m; its RMSE is approximately 3.531 m; its NRMS is -3.352; and its maximum and minimum residuals are 5.532 m in well number W8 and -7.254 m in well number W4, respectively. Its residual mean and absolute residual mean are -1.053 m and 2.982 m, respectively. The comparison results have a correlation coefficient of 0.99. Acknowledging the lack of prior research, the study aimed to fill this gap by developing a comprehensive model that could significantly advance knowledge and management of the area's groundwater resources. The study sought to provide crucial insights for efficient planning and sustainable groundwater development in the Lower Zab Basin by establishing a fundamental groundwater flow model.
Janabi et al. (Wed,) studied this question.