GROUNDWATER RESOURCES AND DEVELOPMENT IN THE CENTRAL REGION OF THE ARABIAN GULF J.G. PIKE

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1 Hydrogeology in the Service of Man, Mémoires of the 18th Congress of the International Association of Hydrogeologists, Cambridge, GROUNDWATER RESOURCES AND DEVELOPMENT IN THE CENTRAL REGION OF THE ARABIAN GULF J.G. PIKE Land and Water Development Division, Food and Agriculture Organization of the United Nations, Regional Office for Asia and the Pacific, Bangkok, THAILAND. ABSTRACT The oil-producing states of the southern littoral of the Arabian Gulf all face an increasing problem in providing water supplies to meet the unprecedented growth in economic activity derived almost entirely from their very substantial oil production revenues during the past decade. Groundwater has been exploited at an increasing rate well in excess of the safe yield of the aquifer system. The impact of this continuing over-abstraction of groundwater is now reflected in the salinization of arable soil and declining agricultural productivity; a decrease of natural spring flow rates into the Gulf thereby affecting fisheries; and an increasing reliance upon highcost distilled seawater to meet the rising demands for potable water. While the present state of development could not have been achieved without recourse to distilled seawater as a major source of water, distillation plants have a limited life and are highly vulnerable to accidental interruption, with the added disadvantage that the primary energy source is normally gas associated with oil production. Any reduction in this activity for economic or political reasons causes a shortfall in energy for distillation. The need for careful conservation and efficient use of groundwater resources is therefore of vital importance since they constitute the only natural water resource in a highly developed and important area of the world. INTRODUCTION There are two fundamental aspects to the question of water development in Arabia. Firstly, there is the scarcity of groundwater resources caused by the historic lack of capital to tap underground water resources; secondly essentially in the long-term there is the absolute scarcity of water in an area where rainfall is minimal and where the heavy demand on the aquifer exceeds the rate of recharge. The oil-producing states of the southern littoral region of the Arabian Gulf - Saudi Arabia, Kuwait, Bahrain, Qatar and the United Arab Emirates all face an increasing problem in water supply to meet the unprecedented growth in economic activity derived almost entirely from their very substantial oil production revenues accrued over the past decade. Growth rates in all sectors of the economy have been phenomenal. Forecasts for water and power to meet projected domestic, industrial

2 and agricultural demands have often been exceeded in the short term. In a number of main centres, daily per capita consumption of potable water is litres which, even allowing for typical distribution losses of about 30 per cent, is nevertheless double that normally found in European countries. Similarly, to meet the demand for fresh agricultural produce by large urban communities, a considerable expansion has taken place in irrigated agriculture based upon groundwater, but with little improvement in cultivation practices. The indigenous population of the Southern Gulf littoral is less than a million with a background in trading, fishing, pearling and nomadism. The high economic growth rate over the past two decades has been made possible only by the high migration rate of technically skilled and manual workers from other Arab countries, Pakistan, India and Europe. The overall population growth rate is estimated to have been between 8 and 10 per cent per annum over the past decade. While groundwater continues to be exploited at an increasing rate mainly for agricultural purposes to meet the growing demand for fresh produce and abstraction is now nearly everywhere well in excess of the safe aquifer yield, the very large expansion in domestic and commercial demand associated with the rapid development of large urban centres has been met mainly by seawater distillation. With adequate energy' and capital resources, there is no constraint at present to the production of high-cost distilled seawater to meet domestic and commercial demand which has been developed well beyond the safe yield of any natural water resources in the region. HYDROLOGY Geological Setting The Arabian Gulf littoral forms an exposed part of the Arabian Shelf between the stable Arabian Shield of western Saudi Arabian and the Mobile Belt of south-western Iran. The region lies within the basins of the northern Arabian Gulf and the Rub al Khali, separated by the Interior Platform of the central Gulf area. Within these basins, sedimentation was continuous, stratigraphie lacunae very few and the deposits relatively thick. Over the Interior Platform, thinner and lithologically more variable deposits accumulated and hiatuses are frequent. Pre-Cambrian rocks from the Arabian Shield of western Saudi Arabia are overlain to the east by a succession of sediments ranging from the Cambrian to the Quaternary. While erosion of the permanent land surface of the Arabian Shield provided the material, the tilting and gradual (but continuous) subsidence of the region to the north and east formed the géosynclinal trough for deposition. Deposition of the ancient sediments in the Tethys Sea may have contributed to this tilting and subsidence. However, in late Tertiary times the Arabian Shield split from Africa and moved relatively northward, forming the Red Sea and narrowing the Arabian Gulf. This late Tertiary crustal migration has created the Zagros and Oman mountains and is still continuing. The environment for the accumulation of a great thickness of sedimentary rocks was therefore predominantly shallow-water marine,

3 with frequent intercalations of very shallow brackish water, together with evaporitic periods and exposed continental conditions when erosion of previously deposited material took place (Powers e_t_ aj, 1966). In the central area, sandstones, silt and shales marked periods of greater erosional activity and transport, both from the Shield and from younger silicoclastic rocks, while limestones denote quieter, clearer water conditions in which biogenic and chemogenic accumulation took place. Anhydrite and halite are also present. The anhydrite is probably formed from both alteration of gypsum and originally formed anhydrite at depth. Gypsum and halite associated often indicate evaporative conditions in shallow lagoons usually separated from the sea, supplied from the land with freshwater, and from time to time flooded by the sea. The strata of central and eastern Saudi Arabia fall naturally into eight major divisions, ranging from early Palaeozoic sandstones overlain by successive carbonate rocks and sandstones, and finally by upper Cretaceous to Eocene carbonate rocks and Miocene and Pliocene clastic rocks. From a hydrogeological point of view, it is only the last two divisions (constituting the Tertiary era) that are of interest (Figure 1). Aquifer Systems The extensive aquifer systems contained within the Tertiary sedimentary formations of eastern Arabia have been the subject of wide-ranging studies and investigations over the past decade (Burdon and Otkun, 1968; Burdon, 1973; Beaumont 1979; Bakiewicz et al. 1982). In , the Food and Agriculture Organization of the United Nations (FAO) undertook a detailed survey and evaluation of available data on the groundwater resources of the entire Arabian peninsula, with the principal objective of defining the extent of the shared groundwater resources between the different states of the peninsula (FAO, 1980). The main aquifer systems of importance to the eastern coast of Saudi Arabia, Bahrain, Qatar and the United Arab Emirates are those of the Umm er Radhuma formation and the overlying younger formations of the Rus, Dammam and Neogene. In this coastal region the salinity of groundwater in the Umm er Radhuma and the underlying Aruma aquifer increases rapidly from values of 4,000 mg/1 to 30,000 mg/1 in a north-eastward direction. However, within the same region, bodies of fresh groundwater of recent meteoric origin have formed within the upper formations of the Rus, Dammam and Neogene, in the Dammam area of Saudi Arabia, to a minor extent of Bahrain Island, in northern Qatar and in the Liwa area of Abu Dhabi. These bodies of fresh groundwater were formerly considered typical freshwater lenses floating on deeper saline water, but detailed investigations in Qatar have shown that, because of vertical and horizontal variations in lithology and geological structure, this description is not always an entirely accurate one (FAO, 1981). The hydrogeological model of the main aquifer system has been accurately described by Italconsult (1969 and reproduced in Beaumont, 1979) who divided the basin into depleting or recharging aquifers, and non-depleting or recharge rejecting aquifers. The piezometric data for the entire depleting aquifer complex show essentially two distinct sets of piezometry. The first set is for

4 the Lower Wasia-Biyadh aquifer which maintains an extremely low gradient and high hydraulic head from its recharge area to the coastline. The second set of piezometry covers the Umm er Radhuma, Rus, Dammam and Neogene complex and shows regionally similar gradients and nearly identical artesian heads. Groundwater movement in the Wasia aquifer (known in detail only in the Riyadh to Dhahran area) confirms that groundwater flows towards the Arabian Gulf under the influence of a consistently low hydraulic head, indicative of a small aquifer underflow and possibly diffuse vertical leakage through the confining Aruma aquiclude. The Umm er Radhuma's regional peizometric surface indicates flow to the north towards the Euphrates valley, to the east towards the Gulf in central Saudi Arabia and northwards to the Gulf from the Rub al Khali region. Knowledge of transmissivity is limited to the central region where the figures are generally high, coastal values being as high as 13,800 m 2 /day. Values further inland are lower (average 5,780 m 2 /day) and it is thought that the change in transmissivity is indicative of a change from laminar to turbulent flow in the aquifer (FAO, 1980). The location of the suggested change in flow regimes corresponds to an inland continuous line of sabkhah (playas) which stretches from Iraq through Kuwait central Saudi Arabia and central Rub al Khali, from whence it swings north, running past the foothills of the Oman mountains (Figure 1). It is thought that this feature is an ancient shoreline of a major marine transgression and seawater contamination of the coastal aquifer system. The groundwater movement of the Upper Dammam-Neogene aquifer is generally identical to that of the Umm er Radhuma aquifer in both hydraulic head and gradient. The basin's hydrochemistry is influenced to a large extent by the desert's evaporative environment where much of the surface sands are composed of gypsum crystals. Sulphate-dominant waters occur generally in all aquifer-outcrop areas or recharge-zone waters, in all perched aquifers, along all wadi courses (especially along the border with Iraq) and in the basin's underflow regime as it approaches the sabkhahs. Water in the underflow regime can be either chloride or sulphate-dominated, although downstream of the sabkhah line the water becomes strongly sodium chloride dominated. The total dissolved solids content is regionally consistent throughout the basin; being in the range of as much as 3,000 mg/1 above the sabkhah line (but with anomalies between 3,000 and 6,000 mg/1 where the water is highly gypsiferous) and from 6,000 to 50,000 mg/1 (and even 100,000 mg/1 or more) below the sabkhah line. Superimposed upon this major aquifer-system are perched or 'floating' bodies of fresh grondwater of recent meteoric origin which have accumulated in certain geologically favourable areas, notably in the Dammam area, Bahrain, Qatar and western Abu Dhabi. This type of aquifer has been studied in considerable detail in Qatar by FAO (1981). The major source of usable groundwater in Qatar is derived from such a body of recent meteoric water in the northern half of the country. The carbonate facies of the Rus formation overlie the Umm er Radhuma formation in this area. There is a hydraulic continuity between these two aquifers such that they form one

5 Fig. 1 Sabkhah discharge/recharge lines (After FAO, 1980)

6 unit, although the degree of vertical permeability is, to a large extent, governed by the presence or absence of residual gypsum and zones of argillaceous deposits at the base of the Rus formation. Investigations have shown that the Rus or Upper Aquifer, normally composed of chalky limestones, has a relatively low hydraulic transmissivity with values ranging from 20 to 600 m 2 /day with isolated values of up to 2,700 m 2 /day. In contrast, the lower Umm er Radhuma aquifer exhibits a higher average transmissibility in the region of 3,000 m 2 /day. Thus, while the Umm er Radhuma aquifer normally contains water of high salinity (17 to 25,000 mg/1) under Qatar, in accordance with the general deterioration in quality in north-easterly direction, fresh modern meteoric waters have percolated through favourable areas of the overlying Rus formation to improve the quality to total dissolved solids concentrations of 1,000-2,000 mg/1. The upper part of the Umm er Radhuma aquifer in Qatar with its high transmissibility, constitutes the sole major source of groundwater in that country. In the Liwa area of the United Arab Emirates, drilling has revealed the existence of shallow, low salinity waters overlying deeper, more saline waters. Elsewhere in the United Arab Emirates, groundwater is contained in the shallow Quaternary deposits of the coastal plains, which are recharged indirectly from wadi spates derived from the mountains to the east and do not fall into either of the two main aquifer systems of the northern and central areas of the southern Gulf littoral. AQUIFER DYNAMICS Recharge to groundwater in desert areas is a complex process and various methods have been employed to resolve this problem in both qualitative and quantitative terms. While some earlier investigations postulated that modern recharge was unlikely, the application of environmental isotope techniques in recent investigations has clearly shown that recharge is currently taking place. In eastern Saudi Arabia, Bakiewicz et al (1980) concluded this to be so, although the rate and conditions are highly variable with a rainfall source derived from either the Mediteranean or the Indian Ocean. However, the carbon and stable oxygen and hydrogen isotopes indicated that a large proportion of the groundwater in the system was probably recharged during a more humid and cooler climatic period, 20,000 to 30,000 years ago, and that the brines in the Umm er Radhuma near the coast may be partly of ancient marine origin. In Qatar, a detailed isotope study was undertaken (IAEA, 1977; FAO, 1981; Lloyd et al. 1981) which confirms the modern date of the 'upper lens' water and other 'pluvial' water of the Umm er Radhuma. In Qatar, observations have shown recharge to be of a weighted mean value of 15 per cent of storm rainfall and 10 per cent of annual rainfall. In Saudi Arabia, Bakiewicz et al (1982) adopted a value of 15 per cent of annual rainfall after elimination of insignificant rainfall from the record. Discharge from the basin is accomplished by evaporation from sabkhahs, spring flow (both onshore and offshore in the Gulf) and pumpage to town water supply, irrigation and industrial complexes. The natural discharge conditions are analogous to open-basin or

7 sulphate-discharging conditions and considerable layers of gypsum and anhydrite have been deposited during the Tertiary and Quaternary periods and up to the present. Evidence of similar open-basin discharge conditions is seen throughout the basin in the red-bed occurrences and in the latérite, silcrete and calcrete horizons. The sabkhah line is thus an important feature of the basin's hydrogeology, not only dividing the up-gradient recharge areas from the down-gradient discharge areas, but also serving as a major discharge point. Evaporation loss from a coastal sabkhah near Dhahran was determined by energy-balance observations (Pike, 1971). In extrapolating these observations to the entire area of the sabkhah, the loss by evaporation in the coastal zone was estimated to be of the order of 500 Mm 3 yr. More detailed energy balance studies have since led to an increase in the estimate of loss to 850 Mm 3 yr From various studies of Tertiary aquifer systems of Saudi Arabia, a water balance, taken to apply to the period of substantial abstraction, has been prepared (Beaumont, 1979; Bakiewicz et al, 1982). These data have been combined and presented in diagramatic form by Pike (1983b) as an aid to understanding the system as a whole. GROUNDWATER DEVELOPMENT From the earliest times, flowing springs from the Khobar aquifer (middle Dammam) provided irrigation water for some 7,000 hectares (ha) of date palms, alfalfa and vegetables in the coastal areas of Bahrain. From about 1924, the development of wells commenced andabstraction steadily increased to a total of 140 Mm 3 yr by 1979, of which 90 Mm 3 is utilized in the irrigation of some 1,750 ha of date palms, vegetables and fodder crops, 40.5 Mm 3 for municipal use and 7 Mm 3 for industry. A further 9.2 Mm 3 yr is pumped from the Umm er Radhuma aquifer and utilized by the oil industry. In the eastern province of Saudi Arabia, groundwater abstractions commenced with oil exploration and production in By 1979, total groundwater abstraction from both the Dammam and Umm er Radhuma aquifers amounted to 424 Mm 3 yr, of which 201 Mm 3 was utilized in irrigation in the coastal area, in Wadi Al Mi yah, Al-hasa and Harad, and the balance (amounting to 223 Mm 3 ) for domestic, municipal and industrial supply to Dhahran, Dammam, Qatif and Al-Khobar. An additonal Mm 3 yr is pumped from the Neogene aquifer in Al-hasa, Wadi Al Batin an_d Wadi Al Miyah, together with natural artesian flow of 227 Mm 3 yr from the large Al-hasa Springs (FAO, 1980). In Qatar, significant development of the upper lens aquifer commenced at the same time as oil production in 1948, but has greatly accelerated during the past five years. Originally almost all abstractions were for municipal use, but as increasing quantities of distilled seawater became available, municipal groundwater use was phased out. Agriculture now consumes 93 per cent of all groundwater abstracted in the country, amounting to 58.6 Mm 3 for the irrigation of 3,300 ha in 1979 (FAO, 1981). In the United Arab Emirates (UAE), abstraction from the Quaternary aquifers of the coastal and gravel plain areas of the Emirates now amounts to over 300 Mm 3 yr~ (FAO, 1980). From

8 a simple comparison of current recharge with these abstractions from the Tertiary aquifer system and the upper lens aquifers of coastal Saudi Arabia, Qatar and the Quaternary aquifers of the UAE, it is clear that groundwater is now being mined in certain important areas of the central Arabian Gulf although there are, nevertheless, still unexploited areas within the overall Arabian systems. In eastern Saudi Arabian and Bahrain, the total abstraction (including spring flow) amounts to 813 Mm 3 yr. Total annual combined discharge and abstraction from the Umm er Radhuma aquifer exceeded natural recharge and transfer from other aquifers by 834 Mm 3 in Similarly, the Dammam and Neogene aquifers exhibited depletion by abstraction, spring flow and sabkhah evaporation of 56 Mm 3 and 388 Mm 3 respectively. In Qatar, net abstraction and spring flow from the northern freshwater lens aquifer amounted to 62.4 Mm 3 in 1980, which is 28 Mm 3 in excess of the annual average recharge (FAO, 1981). In the United Arab Emirates, FAO (1976) estimated that the shallow aquifer system underlying the gravel plains and desert foreland between Al Ain and Ras Al Khaimah had a deficit of about 125 Mm'yr which is being met from storage. More recently, the northern Emirates are reported to be showing a deficit of 50 Mm 3 yr (Jones and Marrei; 1982). The impact of this continuing over-abstraction of groundwater upon the natural environment is interrelated and complex, but evidence of declining piezometric levels, increasing groundwater salinity, abandoned saline lands and depleting submarine spring flow is now mounting. WATER RESOURCES DEVELOPMENT The groundwater resources of the region are clearly unable to provide an adequate water resource to meet present agricultural, domestic and industrial /commercial demands. For the past two decades, recourse has therefore been made to the distillation of sea water to provide for a rapidly growing urban sector. It is estimatedthat by 1980 the installed distillation capacity in the southern Gulf littoral is some 1,600 Mm 3 yr. The capital costs of establishing these large plants are very high of the order of US$1 million/mm 3 yr. Such plants are normally established in conjunction with electric power stations and utilize waste heat to distill seawater by a multistage flash process. Primary energy is usually provided by natural gas associated with oil production and, even if this is regarded as a free good, unit production costs remain high of the order of US$1.25m 3.With gas costed at the full economic price, the unit cost is increased to US$1. 50/m 3 (Pike, 1983a). Distillation plants have a limited life of 20 years; they are highly vulnerable to accidental interruption, oil spillage in the seawater intakes, explosion and fire; and they have the disadvantage that the primary energy source is normally gas associated with oil production. Any reduction in oil production due to economic, political or market forces causes a shortfall in gas supplies used for power/distillation and industrial feedstock. The availability of cheap energy supplies for distillation of seawater has to a large extent, obscured the need for conservation of groundwater. Similarly, it has allowed for unrestricted growth of the urban

9 and industrial sector, which in turn has stimulated the demand for locally produced agricultural products irrigated by groundwater which, as we have seen, is now being overexploited. This dependence upon distilled seawater based on cheap and abundant energy supplies therefore has not encouraged economy or efficiency of use; national per capita domestic demand for water is one of the highest in the world, at 600 litres per day. At the same time, this has encouraged the proposition that high-cost distilled water could be utilized for irrigation to expand agriculture to meet some measure of food self-sufficiency. This proposition has been examined in some detail in Qatar, where it was concluded that despite overwhelming economic arguments against it, a modest amount of distilled seawater would have to be provided to stabilize the present groundwater overdraft (FAO, 1981; Pike, 1983a). This water, in conjunction with treated sewage effluent and the safe-yield of the aquifer, would provide for a modest programme of agricultural development, even though it falls far short of the levels required to achieve self-sufficiency in food. Distillation/power plants have undoubtedly played a major role in the accelerated development of the Gulf states; indeed, without them present levels of population and economic activity could not be sustained. CONCLUSIONS The major aquifer system of eastern Arabia is now being overexploited in its middle and lower reaches as a direct consequence of phenomenal economic development of the oil-producing states situated on the Gulf coast. The environmental impact of this is difficult to measure, but is already reflected in loss of agricultural land due to salinization and poses a risk to the overall supply to Bahrain and to the marine environment. In the longer term groundwater supplies will undoubtedly decrease in both quantity and quality with serious consequences for agriculture. Distilled seawater, produced by using cheap energy to meet domestic and industrial demand, will undoubtedly become the major water resource of the region in the future. The crux of the matter is whether or not it should be used as a supplement for irrigation. At present cost, such a course would be grossly uneconomic but it may be necessary even if only to preserve existing agricultural production levels. Other suggested sources of water, such as towed icebergs, are even more costly and pose considerable practical problems. The low rainfall and the usually high temperature of clouds is a drawback to cloud-seeding, which would probably only increase rainfall by a few per cent with an equal chance of reducing rain from promising clouds. The need for the careful conservation and efficient use of groundwater resources is therefore of vital importance to continued economic progress and is a question that should become a matter of major concern to governments in the region. ACKNOWLEDGEMENT This paper is published with the permission of the Food and Agriculture Organization of the United Nations, although the views expressed are those of the author alone

10 REFERENCES Bakiewicz, W., Milne, D.M. and Noori, N.C Hydrogeology of the Umm er Radhuma aquifer, Saudi Arabia, with reference to fossil gradients. Q.J. Eng. Geol., 15, Beaumont, P., Water resources development in Saudi Arabia. Geogr. Jour., 114. Burdon, D.J., Groundwater resources of Saudi Arabia. Science Mono., No. 2, ALESCO. Burdon, D.J. and Otkun, G., Hydrogeological control of development in Saudi Arabia. XIII International Geological Congress. FAO, Preliminary appraisal of water resources of the United Arab Emirates (based on the work of M. Barber and D. Carr). Unpublished. FAO, The Water Resources of Qatar and their Development FAO Project Technical Report (based on the work of J.G. Pike and D.H. Parker), Doha. FAO, Survey and Evaluation of Available Data in Shared Water Resources in the Gulf States and the Arabian Peninsula. Published for the Secretariat of the Congress of Ministers of Agriculture of the Gulf States and the Arabian peninsula, 3 volumes, FAO, Rome. FAO, The Water Resources of Qatar and their Development. FAO Project Technical Report No. 5 (based on the work of B.L. Eccleston, J.G. Pike and I. Harhash). IAEA, Report on the Environmental Isotope Investigations in Qatar. QAT/73/007 for FAO. Jones, G.P. and Marrei, S.H., Groundwater resources in the United Arab Emirates. Middle East Water and Sewage. Lloyd, J.W., Eccleston, B.L. and Pike, J.G., The Hydrochemistry of the Groundwaters of Qatar. FAO Project Technical Note No. 14, Doha, Qatar. Pike, J.G., The evaporation of grondwater from coastal Playas in the Arabian Gulf. Jour. Hydrol. II, Pike, J.G., 1983a. The planning of water resources development in the Arabian Gulf: Qatar, A case study. Jour. Inst. Water Engrs. & Scientists, 36, Pike, J.G. 1983b. Groundwater resources development and the environment in region of the Arabian Gulf. Water Resources Development, 1 (2), Powers, R.W., Ramirez, I.F., Redmond, CD., and Elberg, E.L., Geology of the Arabian Peninsula, USGS Prof. Paper No. 5600, Washington, DC