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Total annual surface runoff is only about 4 million m3 and there are no rivers, perennial streams or lakes (Table 2). There are also no dams. Bahrain receives groundwater by lateral under-flow from the Damman aquifer, which forms only a part of the extensive regional aquifer system (the Eastern Arabian Aquifer). This aquifer extends from central Saudi Arabia, where its main recharge area is located at about 300 meters above sea level, to eastern Saudi Arabia and Bahrain, which are considered the discharge areas. The rate of groundwater inflow has been estimated at about 112 million m3/year under steady-state conditions (before 1965) and this figure is considered to be the safe groundwater yield in Bahrain. But groundwater reserves suffer from severe degradation, in terms of both quality and quantity, as a result of over-extraction and seawater intrusion.
Over-utilization of the Dammam aquifer, the principal aquifer in Bahrain, by the agricultural and domestic sectors has led to its salinization through water coming from adjacent brackish and saline water bodies (particularly from the underlying saline aquifer of Umm er Radhuma). A hydrochemical study identified the locations of the sources of aquifer salinization and delineated their areas of influence. The investigation indicates that the quality of aquifer water quality has been significantly modified as groundwater flows from the northwestern parts of Bahrain, where the aquifer receives its water by lateral underflow from eastern Saudi Arabia, to the southern and southeastern parts. Four types of salinization of the aquifer have been identified:
- Brackish water up-flow from the underlying brackish water zones in north-central, western, and eastern regions;
- Seawater intrusion in the eastern region;
- Intrusion of sabkha water (saline water from saline areas) in the southwestern region;
- Irrigation return flow in a local area in the western region.
Four alternatives for the management of groundwater quality are under discussion by the water authorities in Bahrain. Priority areas have been proposed based on the type and extent of each salinization source, in addition to groundwater use in that area. Simulation modelling could be used to evaluate the effectiveness of the proposed management options in controlling the degradation of water quality in the Dammam aquifer (Zubari, 1999).
Since it has become the policy to curb the abstraction of groundwater resources in the Damman aquifer and to improve its quality, further development of water sources will undoubtedly involve desalination, either by a thermal process or reverse osmosis. The choice will depend on site-specific conditions and economy or cost. The first multi-stage flash (MSF) seawater desalination plant was introduced in Bahrain in 1976. The use of reverse-osmosis (RO) desalination for saline groundwater on Bahrain Island began in 1984-1986. One of the world’s largest RO plants for the treatment of saline groundwater, located 25 km south of the capital of Bahrain at Ras Abu-Jarjur, was commissioned in 1984. The plant has an installed capacity of 45 500 m3/day and its source of raw water is the highly saline brackish groundwater in the Umm er Radhuma formation. The RO plant was designed to meet the domestic water demand of Manama city, taking into account its advantages over an MSF plant, such as short construction time, lower energy cost, ease of operation and maintenance (UNU, 1995). In 2002, the total installed gross desalination capacity (design capacity) in Bahrain was 500 259 m3/day (Wangnick Consulting, 2002).
The reuse of treated wastewater for agriculture and landscape irrigation started in 1985. The main wastewater treatment plant in Bahrain is the Tubli Water Pollution Control Centre (Tubli WPCC) which is currently (2005) producing about 160 000 m3/day of secondary treated effluent and around 60 674 m3/day receives tertiary treatment. There are also eleven minor wastewater treatment plants with a total designed capacity of about 9 720 m3/day. Treated sewage effluent is expected to reach 200 000 m3/day or 73 million m3 per year by 2010 (Al-Noaimi, 2005). The additional amount treated, if properly used for irrigation, could significantly reduce water extraction, reserving the limited freshwater resources for potable supply and other priority uses. In Bahrain the cost of tertiary treated effluent is about US$0.317/m3, while the cost of desalinated water is about US$0.794/m3 (FAO/WHO, 2001).