GIS-based numerical modeling for the groundwater assessment: a case study in the Quaternary aquifer, Assiut Governorate, Egypt

The Quaternary aquifer in Assiut Governorate is the most important water resource necessary for irrigation and development in Assiut Governorate. The study area is located between latitudes 26° 47′–27° 37′ N and longitudes 30° 37′–31° 34′ E, covering about 2500 km2. This study is an integrated GIS-supported approach proposed to create and develop a transient three-dimensional groundwater flow model for the Quaternary aquifer in Assiut Governorate. Based on the prevailing climatic, environmental, developmental, and water demand conditions, the model was designed to investigate the most feasible groundwater management option. In this context, a great focus was given to the impact of the construction of the Assiut new barrages on the groundwater situation in the study area. According to the actual and supposed extraction rates of the Quaternary aquifer, six scenarios were suggested; however, only four of them are presented here. For the construction of rigid potentiometric isolines, the available records of water levels in more than 540 wells were used. The model was calibrated under the steady state and transient conditions using the trial and error method. The period 2007–2010 was chosen as a calibration period based on the availability and temporal distribution of the data. The simulation of the actual extraction rates (scenario 1, 767 × 106 m3/y) indicated that by 2050, the biggest drawdown is happening at the northwestern part with an average value of 8 m. In contrast, the groundwater is rising by about 6 m by 2050 in the same scenario. The simulation of the full capacity, proposed extraction rates (scenario 3, 1534 × 106 m3/y) resulted in severe changes of the hydraulic head patterns within almost all of the study area of the Quaternary aquifer during the simulation period. This scenario showed clearly a 12-m drawdown which occurs at the northeast part of the study area. Scenario 4 supposed a decrease in the water level of the River Nile by 1 m, a general increase in the groundwater level was detected by the end of the simulation. In scenario 5, the new location of the Assiut new barrage was simulated; the upstream water level has been considered the same as the old one and, however, is displaced 500 m downstream. By 2025, the impact of this scenario was observed by the increase in the hydraulic head in Assiut city by about 0.1 to 0.2 m. During the calibration process, it has been learned that there should be a groundwater recharge from the western and eastern plateau; however, this conclusion still needs further studies to confirm it.