| Popis: |
This paper addresses the sustainable abstraction rate and depth, and the corresponding salinity, in a coastal aquifer as a result of abstraction from beach wells, which is applied on the coastal Nile Delta aquifer as a case study. The field measurements were conducted at West Port Said (WP site) Egypt, and included site visits, topographic survey, drilling of exploratory wells with depths ranging from 60 m to 500 m, pumping tests, water sampling and chemical analysis to identify the physical settings, geological, hydrogeological, and environmental characteristics of the study area and the surroundings. A conceptual model was developed for abstraction from WP site, with the aquifer, comprising five water-bearing layers spreading over three sub-aquifers separated by two clay confining layers. It also includes a surface coastal lake. Consequently, a numerical model was developed and validated to simulate drawdown and salinity at abstraction rates from 50,000 m3/d to 500,000 m3/d over a period of 50 years, which resulted in drawdowns of 9–84.2 m, and salinity levels range from 39,835 to 40,272 mg/L for abstraction rates of 50,000 m3/d and 500,000 m3/d, respectively. The model also included simulation of oil concentration at abstraction wells because of accidental oil spill in the sea. To generalize the conclusions for abstraction over the entire Nile Delta coastal aquifer, the numerical model developed for WP site is used to simulate abstraction at any site within the coastal aquifer with different settings, including presence or absence of coastal lake and clay confining units. It also addressed the impact of improved salinity of the coastal lake on the abstraction, mainly for salinity. Among all these scenarios at 50 year and abstraction rate of 500,000 m3/d, it was found that drawdown varies from lowest value of 54 m to highest value of 86.65 m, as well as salinity varies from lowest value of 38,629 mg/L to highest value of 41,878 mg/L. This leads to identify abstraction depth, salinity, drawdown and the daily maximum recommended sustainable abstraction rate from the subject coastal aquifer, when compared to the daily abstraction as per Egyptian government plan 2050, it was found that the Nile Delta aquifer could serve 50 % of the demand. |
