SIMULATION OF DIFFERENT PUMPING SCENARIOS ON THE GROUNDWATER - SEA WATER INTRUSION INTO THE TRIPOLI AQUIFER, LIBYA

Abstract

In arid and semi-arid regions; increasing groundwater salinity is one of the significant signs of groundwater quality degradation. This is a particularly serious environmental problem in coastal cities where the groundwater resources are being contaminated by sea water intrusion in coastal aquifers. In the coastal aquifer of the Tripoli region, the sea water intrusion continues to expand and the salinity of many wells has increased drastically in the last decades. The volume of groundwater being abstracted from this aquifer has exceeded the safe yield of the aquifer, causing a very significant drop in the water table, thus drying some of the wells. This issue of increased salinity in many parts of the aquifer has become a major cause of the deterioration of the aquifer structure. To address this issue, numerical modelling has been used to effectively manage groundwater resources to predict future responses, particularly in complex aquifer systems and heterogeneous formations. The ModelMuse model has been used as an indicator tool of this serious problem in the Tripoli aquifer. In this paper, three suggested pumping scenarios with varying abstraction rates for the next 80 years(from 2020 to 2100) were suggested. The impact of each scenario on groundwater level were investigated by using MODFLOW 2005 under ModelMuse software. The pumping scenarios; include: firstly, maintaining the fixed pumping rate of 70×106 m3 /yr for the study period, then increasing pumping rates due to population growth and in the third scenario, maintaining the pumping rate by using the sustainable abstraction of 19×106 m3 /yr for the period from 2020 to 2100. Results indicate that the first and second scenarios have a negative effect on the groundwater level, where these scenarios will lead to a significant decrease in the groundwater level. It is predicted that most of the wells will be dry by the year 2100 and sea water intrusion will extend to the boundary of the Tripoli aquifer in the South. However, when a sustainable quantity will be pumped from the aquifer (third scenario), a clear recovery of the aquifer will occur (increase in groundwater levels with reverse movement of the sea water from the aquifer towards the sea).

Keywords

• Groundwater level
• Pumping scenarios
• Sea water intrusion
• Sustainable abstraction
• Tripoli aquifer.