Development of Drawdown Time Series in A Coastal Aquifer By Complex Pumping Using Analytical Approach

The study area lies in the northeast Nile Delta along the Mediterranean coast, where growing industrial, tourism, and energy projects have sharply increased the demand for potable water. With Nile water resources limited and seawater desalination increasingly challenged by petroleum contamination, reliance on the coastal multi-layered aquifer system has become essential. This research evaluates the quantitative and qualitative impacts of groundwater extraction to ensure a sustainable supply for a planned desalination plant requiring 50,000 ± 5% m³/day of raw water over a 50-year operational life. Time series analysis, supported by analytical modelling, was applied to short- and long-term pumping data from five exploration wells and two pilot production wells. Step drawdown tests determined efficiency, specific drawdown, specific capacity, and safe yield. Constant-rate pumping tests established aquifer transmissivity (T), hydraulic conductivity (K), and storativity (S). A continuous three-month pumping test assessed long-term operational performance. These field results were used to calibrate a mathematical model simulating drawdown within both wells and the aquifer, predicting interference between overlapping cones of depression. Simulation results suggest an optimal well field configuration of ten stations, each comprising two alternating production wells (A & B) pumping 220–260 m³/hr, yielding ~5,280 m³/day per station. Station spacing of 30–55 m is recommended to evenly distribute the drawdown and minimize interference. Analytical modelling confirmed that this layout would sustainably meet project demands while maintaining aquifer drawdown below ~29 m after 50 years of operation at 52,800 m³/day. Based on salinity predictions, extracted groundwater is expected to remain between the aquifer baseline (~25,000 mg/L) and Mediterranean seawater salinity, with no significant increase observed during the pilot pumping phase.