Abstract
Abstract Steady-state three-dimensional model using the PMWIN MODFLOW was developed to simulate sub-regional groundwater flow during the predevelopment period in response to natural stresses within Al Kufrah area. In order to simulate the interactions among aquifer behavior in response to groundwater pumpage and contaminant transport during the postdevelopment period. The entire simulated thickness of 300 meters was modeled as three hydraulically connected horizontal layers. Each layer consists of 181 rows and 181 columns with grid spacing of 500 m by 500 m which covers an area of 8100 km2. General Head Boundary (GHB) was assigned to the southern and eastern-northeastern nodes to simulate groundwater inflow and outflow within the simulated area. Evapotranspiration from the upper layer was fixed to the model upper layer only. The hydraulic conductivity, the vertical conductance and the boundary conditions were adjusted by trial and error procedures until satisfactory matching between the observed and the simulated hydraulic head configurations in each layer were achieved. The model-calculated hydraulic heads were statistically tested against the measured pre-development hydraulic heads in 32 observation wells. They gave a root mean square error (RMSE) of 1.0854 m over the observed hydraulic heads that ranges from 364.5m to 396.4m for layer 1, and RMSE error of 1.1914m over a range of 34.16m between the lowest and the highest observed head in layer 3. This indicates the ability of the model to simulate the pre-development stage with confidence. Model water budget shows that, the primary source of groundwater recharge entered from the southern boundary (2.56x104 m3/day). Groundwater naturally discharges through the eastern-northeastern boundary (2.29x104 m3/day) and due to evapotranspiration at the low land areas (2.63x103 m3/day). The net vertical exchanges between layers 1 and 2 and between layers 2 and 3 are 5.43x102 m3/day and 6.5x102 m3/day respectively.