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Water resources

The countries of the Arabian Peninsula have similar physiographic, social, and economic characteristics, including extremely arid climates, sparse natural vegetation, and fragile soil conditions. The natural water resources consist of limited quantities of run-off resulting from floods, groundwater in the alluvial aquifers, and extensive groundwater reserves in the deep sedimentary aquifers. The supplementary non-conventional sources include desalination of sea and brackish water, and renovated waste water. Water availability is governed by rainfall distribution in time and space, in relation to run-off generation, as well as topographic and geological features that influence water movement and storage.

The peninsula is largely desert with the exception of the coastal strips and mountain ranges. The climate is characterized by long, hot, dry summers and short, cool winters for the interior regions, and hot, somewhat more humid, summers and mild winters for coastal regions. Hydrometeorological parameters exhibit great variation: seasonal temperatures may range from -5° to 46°C in the north, central, and eastern parts of the peninsula. The coastal areas and mountainous highlands have lower and less extreme temperatures, ranging from 5° to 35°C. Humidity is generally low in the interior, ranging from 10 to 30 per cent, while in the coastal areas it may range between 60 and 95 per cent. The low percentage of cloudy days and the high solar radiation over the region result in high evaporation rates. The total annual potential evaporation ranges from 2,500 mm in the coastal areas to more than 4,500 mm inland.

The Arabian Peninsula generally has scanty and irregular rainfall. The average annual rainfall ranges from 70 to 130 mm, except in the mountain ranges of southwestern Saudi Arabia, Yemen, and southern Oman, where rainfall may reach more than 500 mm. Average rainfall has little meaning, however, since many desert areas receive no rainfall for months or years owing to extremely random storm patterns. Rainfall throughout the area is generally governed by regional Mediterranean and Indian subcontinental aircirculation patterns. Cyclonic lifting associated with the eastward passage of depressions from the Mediterranean region causes winter rainfall in the months of November and April over the northern and eastern parts of the peninsula. Spring rainfall sometimes occurs over the central and south-western parts of Saudi Arabia, Yemen, and Oman. The Indian subcontinent monsoons influence the weather over the southern region of the peninsula, resulting in summer rainfall that occurs mostly over the southern parts of Saudi Arabia, Oman, the United Arab Emirates, and most of Yemen. All these circulation patterns are modified by local topographic relief and distance from the sea. In general, rainfall amount decreases sharply with distance from the sea and in a northerly direction. The steep relief of the mountain ranges in the Asir High-lands in south-western Saudi Arabia, the Sarat Mountains in western Yemen, and the Hajar and Dhofar mountains in the southern regions of Oman that run parallel to the Red Sea and the Gulf, usually causes orographic rainfall that frequently leads to flash flooding, particularly in the summer months. Most rainfall in these areas is of high intensity and short duration, producing a large volume of surface run-off that gathers in wadis and stream beds that are normally dry. Run-off is then utilized directly for irrigation, and/or is impounded behind dams and later released for flood-plain irrigation and for increasing recharge to the alluvial aquifers beneath the wadi channel.

The main topographic features of the Arabian Peninsula are the western, southwestern, and south-eastern mountain ridges, as well as the central plateau. The mountain ridges divide numerous moderate-sized drainage basins that empty towards the Red Sea, Arabian Sea, and the Gulf of Oman, as well as larger basins that drain towards the central plateau and, in some cases, continue eastward towards the Gulf. Generally, the coastal drainage basins have steep reliefs and narrow coastal plains compared with the mild slope and large catchment area of the inland region. Steep slopes and well-defined topographic features control the availability of surface run-off as well as the modes of groundwater recharge. The remainder of the peninsula is characterized by low relief and poor drainage.

The other major features that influence the availability of groundwater resources are the peninsula's igneous and metamorphic basement rock known as the "Arabian Shield," and the sequences of sedimentary layers known as the "Arabian Shelf," shown in figures 1 and 2. The shield, which covers one-third of the peninsula, consists of an outcrop of hard rock that begins in the western part of Saudi Arabia and extends from the Gulf of Aqaba in the north to the Gulf of Aden in the south. The shield has limited groundwater stores in the alluvial deposits of wadi channels, and weathered joints and fracture zones.

The dependable groundwater reserves are those stored in the thick extensive sequences of sedimentary formations of the Arabian Shelf, underlying two-thirds of the peninsula, as shown in figure 2. The outcrops of these formations, where recharge may take place, are located in the western part of the peninsula. The formations slope gently, and increase in thickness, as they extend eastward under the Gulf, north-easterly into Jordan and Iraq, and south-west to Yemen. In combination with rainfall distribution, these topographic and geological features control surface and groundwater availability and use in different parts of the peninsula.

Surface Water

Run-off occurs mainly in the form of intermittent flash floods, and is governed by rainfall patterns and topographic features over the Arabian Peninsula. Intermittent surface run-off volume in the peninsula is estimated at 5.3 billion cubic metres (bcm) (Abdulrazzak 1995; Saad 1995; Bahrain Country Report 1995; Qatar Country Report 1995; UAE Country Report 1986; Yemen Country Report 1995). Run-off variation and utilization in each country of the peninsula is shown in table 2. The annual run-off volume generated in south-western Saudi Arabia and Yemen is estimated to be 1,450 million cubic metres (mom) and 1,200 mcm, respectively. The national totals for Saudi Arabia (Authman 1983; BAAC 1980) and Yemen (Mohamed 1986; Al-Fusail et al. 1991; Yemen Country Report 1995) are estimated at 2,230 mcm and 2,000 mcm, respectively. Amounts of surface water available in Oman (El-Zawahry and Ibrahim 1992) and the United Arab Emirates (Al-Asam 1992; Uqba 1992; UAE Country Report 1986) were estimated at 918 mcm and 125 mcm, respectively. The remaining countries have only negligible amounts of surface run-off.

In general, utilization of surface run-off is directed towards traditional flood irrigation, especially in the south-western region of Saudi Arabia and most of Yemen. Also, regulated and unregulated flood flow is the main source of groundwater recharge to the aquifers. Approximately 195 dams of various sizes, with a combined storage capacity of 475 mcm, have been constructed in Saudi Arabia for the purposes of flood protection and groundwater recharge. Fifty-two dams have been (or are being) constructed in Yemen, the United Arab Emirates, and Oman.

Figure 1 General Geological Map and Aquifers of the Arabian Peninsula (Source: Modified after MAW 1984)

Figure 2 Schematic Geological Section of Deep Aquifers (Source: MAW 1984)

Table 2 Water Resources in the Arabian Peninsula

Sources: Saad (1995), Abdulrazzak (1995), UAE Country Report (1986), Bahrain Country Report (1995), Qatar Country Report (1995) and Yemen Country Report (1995).

Shallow Alluvial Aquifers

Alluvial deposits along the main wadi channels and the flood plains of drainage basins make up the shallow groundwater system in the peninsula. Groundwater in the shallow aquifers is the only renewable water source for these countries. The shallow aquifers in the eastern part of the peninsula, particularly in the United Arab Emirates and Oman, are generally thicker and wider than in the west, while alluvial thickness in the inland basins is greater than in those of the coastal basins. Alluvial aquifer thicknesses generally range from 20 to 200 metres, with the exception of the coastal areas of Oman where thicknesses may reach 400 metres. The width of these alluvial aquifers may range from a few hundred metres to several kilometres. The widths of the aquifers decrease in a southerly direction for basins on both the western and eastern coasts. The coastal alluvial aquifers are subject to salt-water intrusion, especially on the Gulf, owing to extensive groundwater withdrawals. Shallow aquifer water quality is generally good, with total dissolved solids ranging from 300 ppm to 3,000 ppm. Combined reserves of the alluvial aquifers shown in table 2 are estimated at 131 bcm (Abdulrazzak 1992 and 1995; Shahin 1989; Khoury et al. 1986), with the largest reserves for the numerous basins in Saudi Arabia, estimated at 84 bcm (BAAC 1980; MAW 1984; Ukayli and Husain 1988). Groundwater from the shallow alluvials is sometimes used for domestic and irrigation purposes. However, poor groundwater quality in the downstream areas may limit its use for meeting domestic needs.

Fossil Groundwater Aquifers

The other main source of water for the countries of the Arabian Peninsula is the non-renewable fossil groundwater stored in the sedimentary deep aquifers. The sandstone and limestone geological formations of the Arabian Shelf, shown in figures 1 and 2, store significant amounts of groundwater that are thousands of years old (Burdon 1973; Edgell 1987). The sedimentary aquifers have been classified as either primary or secondary, based on their areal extent, groundwater volume, water quality, and development potential (MAW 1984). The primary aquifers are the Saq, Tabuk, Wajid, Minjur-Druma, Wasia-Biyadh, Dammam, Um er-Radhuma, and Neogene. The latter two are carbonate aquifers while the remainder are sandstone. Secondary aquifers are the Aruma, Jauf, Khuff, Jilh, Sakaka, the upper Jurassic, the lower Cretaceous, and Buwaib. These aquifers cover two-thirds of Saudi Arabia and some of them extend into Kuwait, Bahrain, Qatar, the United Arab Emirates, Oman, and Yemen, as well as into Jordan, Syria, and Iraq.

Vast amounts of groundwater stored in the primary deep aquifers serve as a dependable source of water for the central and northern regions of Saudi Arabia, and, to a lesser extent, the other countries of the peninsula. Deep groundwater reserves for the aquifers in the peninsula are estimated at 2,175 bcm, with the major portion (1,919 bcm) located in Saudi Arabia. Recharge for all the deep aquifers is estimated at a very limited 2.7 bcm per year. This reserve represents groundwater exploitable by lowering the water level to 300 metres below the ground surface, the maximum depth currently possible with modern pumping technology.

Although water in the deep aquifers is ample in quantity, the quality varies greatly and is suitable for domestic consumption in only a few areas. Total dissolved solids range from 400 to 20,000 ppm. Good-quality water is stored in only a few aquifers: the Saq, Tabuk, and Wajid in Saudi Arabia, and the Dammam in Bahrain and Kuwait (Bahrain Country Report 1995; Kuwait Country Report 1986). Brackish water from the Minjur, Wasia, Biyadh, and Um er-Radhuma aquifers usually requires treatment in most of the countries for hardness and high temperature. Water temperatures vary between 40° and 65°C, depending on the depth of extraction. Water from these deep aquifers tends to be saturated with calcium and magnesium salts and has high concentrations of sulphate and chloride ions; it also contains relatively large quantities of hydrogen sulphide and carbon dioxide gases. The brackish water from some of these deep aquifers is usually used without treatment for agricultural purposes, and for limited domestic purposes in some locations in Saudi Arabia, Bahrain, Qatar, and the United Arab Emirates. The groundwater of most of the deep aquifers requires treatment such as cooling, aeration to remove hydrogen sulphide and carbon dioxide gases, and lime soda processing.

Desalination

Experience with desalination in many of the Gulf States, particularly Saudi Arabia and Kuwait, began as early as 1938. During the last twenty years, the countries of the Arabian Peninsula, with the exception of Yemen, have become increasingly dependent on desalination to meet their water-supply requirements. Several of the Gulf countries, however, have no option but to rely on the desalination of sea water or brackish groundwater. This is because renewable groundwater supplies are very small, and often the quality is poor owing to limited recharge magnitude and salt-water intrusion. In addition, the deep aquifers, particularly those near the coastal zones, usually contain highly saline water requiring desalination. The same conditions exist for the western coastal areas of Saudi Arabia, and southern regions of the Arabian Peninsula. Most of the deep aquifers with good water quality are located at great depths and in remote areas far from the urban centres where the water is needed.

Table 3 Desalination Capacity Installed in Arab Countries, 1963 - 1993

Source: Bushnak (1995).

Capacity installed: 63% of world total; remainder: North America 13%, Europe 5%, Asia 8 %, others 11 %.

Costs associated with the development of deep fossil groundwater sources, including drilling, casings, pumping, transportation, and treatment, may be high.

Water desalination in the Gulf States has constituted a flexible means of alleviating water-supply shortages over the past two decades. In addition, desalination provides water of excellent quality, which in turn contributes to the well-being of society in relation to sanitation, health, and better quality of life. At the present time, two-thirds of the world's total desalination capacity is installed in the Arab countries, mainly in the Arabian Peninsula, as shown in table 3. Out of 18.8 mcm per day of desalination capacity, the countries of the Arabian Gulf account for over one-half of the production (53 per cent). Saudi Arabia alone accounts for one-quarter of world capacity in desalination. Three Arab countries Saudi Arabia, Kuwait and the United Arab Emirates - rate first, third, and fourth, respectively, in desalination capacity. The present annual designed desalination capacity of the seven countries of the peninsula has reached 2.02 bcm, compared with a worldwide capacity of 5.68 bcm (Wagnick 1992; Bushnak 1995). These capacities cover all desalination plants and include numerous units in private sector ownership for industrial or other purposes. Saudi Arabia, Kuwait, and the United Arab Emirates, in particular, rely on large-scale plants capable of producing up to 500 mcm per year.

Desalination production efficiency ranges between 70 and 85 per cent of designed plant capacity. The total regional volume of desalinized water produced in 1992 was estimated at 1,628 mcm (Al-Sufy 1992; Bushnak 1992 and 1995), as shown in table 2. Desalinated water provided 51 per cent of urban and industrial water demand in 1990. The major producers of desalinated water are Saudi Arabia (51 per cent), the United Arab Emirates (22 per cent), Kuwait (15 per cent), Qatar (5 per cent), Bahrain (4 per cent), Oman (2 per cent), and Yemen (1 per cent) (Bushnak 1992 and 1995).

The total number of desalination plants in operation as of 1992 reached 45, with 23 in Saudi Arabia, 8 in the United Arab Emirates, 6 in Kuwait, 3 in Bahrain, 2 each in Oman and Qatar, and 1 in Yemen (Al-Sufy 1992). In Saudi Arabia, 17 plants are located on the Red Sea coast and 6 on the Gulf. Three large-scale multistage flash (MSF) plants are located at Al-Jubail, Jeddah, and Al-Khobar, with annual production capacities of 394 mcm, 217 mcm, and 83 mcm, respectively.

Currently, the largest desalination centre in the world is located in Al-Jubail, in the eastern province of Saudi Arabia. One-third of the desalinated water for Saudi Arabia is produced at this plant, equivalent to 7.5 per cent of world capacity. The plant consists of 40 MSF units producing approximately one million cubic metres of desalinated water. The desalinated water is transferred through pipelines with a total capacity of 1.8 x 108 cubic metres per day. One of these pipelines runs as far as Riyadh, which is 465 km from Al-Jubail, and the other delivers water to Qasim. A considerable number of urban centres are being supplied with desalinated water through this system. Kuwait and the United Arab Emirates have a large number of desalination plants.

Cost comparisons using different desalination processes range between US$1 and US$3.5 per cubic metre for sea water, and between US$0.4 and US$1.5 per cubic metre for brackish water. A survey of water production costs indicates wide variation, depending on plant size and energy prices. Usually, costs decrease with increased plant capacity. Costs reported by the Gulf countries are usually less than for countries in the rest of the world because of minimal energy charges. For example, the cost of producing one cubic metre of water in Saudi Arabia ranges from US$0.48 to US$2.2; in the United Arab Emirates, water costs range from US$1 to US$1.45; in Qatar the range is US$1.14 to US$1.64, and in Bahrain the cost is US$0.56.

In other parts of the world, where energy costs are not subsidized, production costs are somewhat higher; for example, in Florida and the US Virgin Islands, costs range from US$2.06 to US$2.60; in Malta the cost is US$1.18, and in the Canary Islands it is US$1.62. In general, water production costs in countries of the Peninsula where desalination is used extensively are distributed as follows: 38 per cent for capital investment; 20.5 per cent for energy; 21.3 per cent for labour; 16.2 per cent for maintenance, and 4 per cent for chemicals.

Brackish groundwater desalination is being used more nowadays near major urban centres because the cost of production is less than for that of sea water. Small desalination plants for brackish groundwater are usually found inland near urban centres, especially in Saudi Arabia. Plants generally have smaller capacities of up to 2O,000 cubic metres per day, in comparison to large sea-water-desalination plants where capacities may exceed 100,000 cubic metres. Small plants are common, owing to the limited volume of extraction possible from a large number of wells. Brackish water desalination usually involves the reverse osmosis (RO) process. However, the cost of treatment is much less than for sea-water desalination, owing to low salinity, and usually ranges from US$0.3 to US$0.65 per cubic metre. The cost of water production depends on plant size and also on the concentration of certain salts, heavy metals, and organic materials. The major cost components consist of investment in well drilling and pumping, and brine-water disposal. The disposal of brine presents a major environmental constraint of brackish-water desalination. Careful consideration is usually needed to avoid contamination of groundwater sources.

More than 80 per cent of desalinated water in the Gulf region is produced through MSF distillation; RO accounts for 16.1 per cent. This translates into three-quarters of the world capacity for MSF desalination, and about one-quarter of RO production. The Gulf countries share in multi-effect distillation (MED), electrodialysis (ED) and vapour compression (VC), as well as other processes, at the respective rates of 16.4 per cent, 16.6 per cent, and 5.5 per cent.

Desalination of sea and brackish water has become an essential water-supply component for many urban centres in these regions. This has compelled these countries to make substantial investments in desalination technology. The availability of financial resources from oil income, and free energy sources, has further encouraged reliance on water desalination as a primary source to meet domestic water requirements. These factors, in conjunction with natural supply limitations, make it likely that reliance on desalination will continue to increase in the future. Future projections indicate that more investments in desalination technology will be required to offset overexploitation of water resources and increased public demand.

For the countries of the Arabian Peninsula, desalination is the easiest means of meeting the ever-increasing demand for water in the region. Most of the countries are constructing and planning significant expansion of their desalination capacity to meet future water requirements, as shown in table 4. Saudi Arabia is constructing additional plants with combined capacities of 126 mcm for the major cities of Medina, Yanbu, Jeddah and Al-Jubail. Future plans call for an additional capacity of 213 mcm for the cities of Jeddah and Al-Khobar. The United Arab Emirates is also expected to increase its desalination capacity by 270 mcm in the near future for its urban centres at Abu Dhabi and Dubai. Kuwait is planning to increase its desalination capacity by 110 mcm by 1997. In Qatar, the present desalination capacity of 112 mcm at Ras Abu Fontas will be raised by 16 mcm in the near future, and an additional capacity of 88 mcm will be added to the system by the end of the twentieth century. In Bahrain, desalination capacity has reached 75 mcm in 1993 and 25 mcm of further capacity is proposed for Maharraq City, while a further 40 mcm of capacity is being studied as a part of a privatization scheme for power and water. In Oman, the present desalination capacity is 55 mcm and will be increased by 13 mcm with the construction of several smaller units by 1995. Present and future combined capacities for the countries of the peninsula are expected to reach 2.92 bcm by the year 2000. Desalinated water will constitute a main source of water for domestic requirements for most of the countries of the peninsula, particularly Kuwait, Bahrain, Qatar, and the United Arab Emirates, as shown in table 4.

Table 4 Desalination Schemes in Each Country of the Arabian Peninsula

Renovated Waste Water

Existing waste-water treatment facilities in the Arabian Peninsula face difficulties in handling the ever-increasing volumes of waste water generated by increased water consumption and urbanization. Waste-water discharge from major urban centres is polluting shallow alluvial aquifers and the coastline, and has caused urban water-tables to rise. The main emphasis to date in these countries has been on simple disposal of waste water, rather than on treating and reusing effluent, owing to the extensive capital investment required. Planning for the full utilization of treated effluent remains in the early stages, and the regional treatment capacity is sufficient to handle only 40 per cent of the domestic waste water generated. The total volume of renovated waste water used in the Arabian Peninsula is estimated as about 433 mcm, which is far less than the volumes treated. The reuse volumes are shown in table 2, which represent approximately 25 per cent of the available treated waste water.

Waste-water reuse ranges between 217 mcm in Saudi Arabia and 6 mcm in Yemen. The ratios of reuse to the domestic and industrial water requirements range from 27.7 to 30 per cent. In the region as a whole, renovated waste water meets about 2 per cent of total water demand or 14 per cent of domestic and industrial demand. In Saudi Arabia, reclaimed waste water is used for irrigation of non-cash crops, landscape irrigation, and industrial cooling. In Kuwait, Bahrain, the United Arab Emirates, and Oman it is used for municipal irrigation of landscaped areas, while in Qatar it is used to irrigate animal-food crops.

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