Mitigation of groundwater level deterioration of the Nubian Sandstone aquifer in Farafra Oasis, Western Desert, Egypt

摘要

Farafra Oasis is included in the New Valley Project which started in the 1960s. This project is based exclusively on groundwater of the well-known Nubian Sandstone aquifer (NSA). The hydraulic head drawdown problem in Farafra Oasis constitutes a big problem because it threatens the availability of the only water source in the Oasis. Hydrogeologically, Farafra Oasis belongs to the huge, artesian, unrenewable fossil water Nubian from sandstone aquifer. The problem began to appear at the end of the 1990s instantaneously with increased drilling of deep water wells. Huge quantities of water (267 million m(3)) are derived from the aquifer every year. Hydraulic head depression cones are formed around the main reclamation areas where the groundwater surface lowered by 35 m below the ground surface. Numerical modeling was used to investigate the hydrodynamic impacts of the present and planned groundwater extraction on the groundwater levels besides the possible means of mitigating the continuous decrease of the groundwater levels. The aquifer simulation indicated that there is a significant head decline of the groundwater, particularly in the first productive zone. Four scenarios were applied to signify the present and future development plans for the next 20 years, i.e., year 2033. Applying the present conditions reveal that heads are more declined than now. Another 30 and 17.8 m in the first and second productive zones, respectively, are expected to be added to the present groundwater drawdowns. Groundwater is expected to decline significantly if the pumping rates are to be increased by 50 % in response to natural development of the agricultural society and continuous need to more cultivation lands. Groundwater heads are expected to be lower by about 40 m in the first productive zone and 24 m in the second productive zone. The third plan examines the impact of reducing the pumping rate by about 25 % on groundwater levels by applying recent irrigation techniques as drop and sprinkler irrigation methods instead of the presently used flood irrigation. In this case, simulated drawdowns are expected to decline, and the maximum drawdowns recorded are 19 and 10 m through the next 20 years in the first and second productive zones, respectively. To mitigate the groundwater level deterioration, the study suggests the reduction of pumping rates by about 20 % by applying the recent irrigation techniques besides reclamation of about 11,000 feddan (4620 hectare) to accommodate the increasing population and need of cultivation lands in the Oasis in the next 20 years. According to plan, the simulated groundwater levels are expected to decrease by about 20.3 and 12 m at the end of the simulation period (year 2033). This means that the rate of head decline is lowered to about 1 m/year for the first productive zone and 0.6 m/year for the second productive zone with the increase in the cultivation area by about 16 %. Therefore, the study recommends the fourth plan to manage the groundwater resource in Farafra Oasis.