The influence of man on the hyârological regime with special reference to representative and experimental basins — L'influence de l'homme sur le régime hydrologique avec référence particulière aux études sur les bassins représentatifs et expérimentaux (Proceedings of the Helsinki Symposium, June 1980; Actes du Colloque d'Helsinki, juin 1980): IAHS-AISH Publ. no. 130.

Salinity intrusion into natural aquifers

SAIF AL BIN ALI Water Directorate,

Abstract Bahrain is an island in the middle of the Arabian Gulf. It is famous for its natural springs and submarine fresh water springs. Groundwater exists in three aquifers. Aquifer A water, used for agriculture, contains 3000-10000 TDS;aquifer B water, used for domestic purposes, contains 2000-4000 TDS; and aquifer C water, as yet not used widely due to its high H2S content, contains 10 000 TDS. Excess groundwater abstraction and improper weË drilling have resulted in sea water intrusion into some of the island's natural groundwater. The problems being faced in both agricultural and domestic fields are described, together with the proposed remedies. Intrusion d'eau salée dans les aquifères naturels Résumé. Bahrein est une île au milieu du Golfe Persique. Elle est célèbre par ses sources naturelles et ses sources d'eau douce sous marines. Les eaux souterraines existantes sont réparties entre 3 couches aquifères A, B et C. L'eau de l'aquifère A utilisée par l'agriculture contient 3000 à 10 000 TSD; l'eau de l'aquifère B utilisée pour la consommation domestique, contient de 2000 à 4000 TSD; l'eau de l'aquifère C n'a pas été jusqu'ici utilisée très largement par suite de sa teneur élevée en H2S, elle contient 10 000 TSD. Une extraction abusive des eaux souterraines et des forages conduits de façon défectueuse ont donné lieu à des intrusions d'eau de mer dans certaines des nappes naturelles de l'île. Les problèmes à résoudre à la fois dans les domaines de l'agriculture et de l'alimentation en eau des agglomérations sont décrits en même temps que les solutions que l'on propose.

INTRODUCTION Bahrain consists of 33 small islands in the Arabian Gulf near the eastern coast of which is about 25 km away. A linking Bahrain (the largest island) with Saudi Arabia is expected to start during 1980, and the expected date for completion is 1985. Due firstly to the availability of water both in the land and under the sea as sub­ marine springs, and later to the availability of petrol, Bahrain was, relatively speaking, a leading country in the Gulf during the second third of this century. Water abstrac­ tion began to increase through the introduction of drilling rigs and pumps in the early thirties.

WATER USES There are four groundwater aquifers, ranging from 20 to 700 m in depth and stretch­ ing in length from the central part of Saudi Ad Dahna Sahara to somewhere north of Qatar (Fig. 1). These aquifers are separated by layers of mud and/or bedrock with varying permeability. The upper aquifer A is called Alat, and ranges in depth from 0 to 50 m. Aquifer B is called (Figs 2 and 3) and both A and B are called Dammam. Dammam aquifer (0—110 m deep) is used for both agricultural and dom­ estic purposes. Its salinity ranges from 2000 to 10000 TDS. Aquifer C is called Rus Umm Er Radhuma (UER) and is used for industrial purposes because its water is highly saline (10 000-33 000 TDS) and has a high concentration of H2S. UER varies in depth from 80 to 350 m. A new aquifer called Alwasea, not in use yet, has a salinity about 6000 TDS and ranges in depth from 400 to 700 m. The groundwater in this aquifer is hot and the abstraction from this aquifer may affect the oil field. The water quality in general is deteriorating in the southeastern part of the country. 151 152 Sait Al Bin Ali

Up leakage inferred S complete section Limestone CD Shaiy rocks t-i&ù'd Structural crest Anhydrite Sands lÙJLlâ

i î -P Quaternary A

B

c

? m su ~Ë insm FIGURE 1. Schematic diagram of aquifer systems.

FIGURE 2. Piezometric contours of Khobar aquifer, FIGURE 3. Khobar piezometric levels and water 1953. quality, 1979. Salinity intrusion into natural aquifers 153

FIGURE 4. Rus Upper Umm Er Radhuma salinity, 1979.

PROBLEMS Due to early poor drilling techniques, where incorrect casings had been used and no correct depth control during penetration of aquifers had been practised, the relatively good aquifer B became contaminated by the more saline aquifer C. Further, both the increase in pumping for agricultural use and the unstudied methods of dredging and land reclamation from the sea, have accelerated the rate of saline intrusion. The Dammam aquifer, which outcrops both in central Bahrain and also on the southeastern side in the sea, has experienced a steady slow increase in salinity and salinity intrusion had been recorded in the Refinery (southeast of the Dammam aquifer outcrop). The piezometric head was also slowly falling all over Bahrain (Fig. 5, Table 1). In the late fifties a sharp drop in piezometric head in the natural land springs (from aquifer A) and high salinity intrusion were recorded in Sitra Island. It is believed that the deepening and widening of the Mina Sulman sea port channel, by the use of dynamite, had fractured the bedrock of aquifer A as groundwater seepage had been noticed in that area. Thus, the salinity increased and piezometric head in old irrigation land springs was reduced to sea level resulting in the abandonment of most of the palm gardens and the death of the trees. The salinity has also been increasing during the last few years in the southwest of the country at Zallag, where, if no control is adopted, the same fate as that of Sitra 154 Saïf Ai Bin Ali

IHr Contours on the surface of the B aquifer in feet betow Bahrain Island Datum 2^P2 Contours of saïnity in parts per million of Na CI in upper zone ot B aquifer, .16(2350) 5ite file number and salinityfin brackets) of disused welt, e16 (Î350S Site file number and satinity(inbrackets)o! Current production well Salinity includes either the range observed in available sections of the salinity cf a depth sample or a pumped sample(P)t • AS Sites of wells open to both A and B aquifers-

FIGURE 5. Structure and current salinity map of aquifer B in the Sitra Refinery area.

Island is expected. The salinity intrusions in the southeast and the southwest are mainly from sea water and from the deeper, more saline waters of aquifer C. Moreover, there is a dangerous increase in salinity in the Dammam aquifer in the central northern part of Bahrain, with the Salmabad area facing an increase due to direct contamination from aquifer C where the layer separating the two has a high permeability.

REMEDIES In 1969 the Government of Bahrain established the Water Resources Bureau (WRB) with the following tasks : (1) To control and execute well drilling. (2) To seal off unused and contaminated wells. Salinity intrusion into natural aquifers 155 TABLE 1. Values of electrical conductivity (EC) in /umhos/cm at 25°C on samples analysed by BAPCO laboratory in 1952 and 1971. Values of EC in later years are averages of the quarterly survey measurements

1952 1971 1972 1973 1974 1975 Springs Ain Adari: NaCl 1765 2 260 - - - — EC - 5 250 5 570 5 585 5 803 5 970 Ain Muhazza: NaCl 1800 14160 — — _ _ EC - 23 200 18759 23 778 24182 22111 Ain Raha: NaCl 1940 6400 — — — — EC - 11752 11980 12 392 12193 12 364 Ain Kathaira: NaCl 10 800 10 800 — — — — EC - - 17 543 18 354 17652 18142 Wells Sitra7: NaCl 4 800 24 320 — — — — EC - - — — _ _ Refinery 10: NaCl 5 062 9 800 - - - - EC - - - - — — Wasmya 6 : NaCl 2175 2 340 - — — — EC - 5 559 5 527 5 664 5 646 5 731 WS: NaCl 2 225 2 240 - — — — EC — 4 900 5 602 5 026 4 966 4 944 : NaCl 1325 1340 - — — _ (BAPCO) EC - - - - — — Al Bastan: NaCl 2110 1900 - - — — EC - - — - — —

(3) To seal off the submarine springs. (4) To search for unknown leakage areas. (5) To search for new aquifers, if any. (6) To liaise with other Government and other public bodies. The Water Supply Directorate is responsible for domestic usage. There are several possibilities for improving the deteriorating situation both for agricultural and domes­ tic uses but none have been studied in detail yet, and all are very expensive to adopt. For example: (1) Provision for the laying of a water main from Saudi Arabia along the proposed new causeway. (2) Preventing leakage by driving sheet piles into the boundary of the leakage limits within the sea. (3) Land reclamation of the leakage areas in the sea to minimize sea water intrusion. Practical ideas which could be adopted are: (1) Use of sewage-treated effluent for agricultural use. (2) Using aquifer C for treated domestic, industrial and commercial water consump­ tion. (3) Metering all water uses. (4) Desalination of sea water and/or aquifer C for domestic use. (5) Land reclamation along the Saudi—Bahrain causeway, to be used as pumping stations.

Acknowledgements. I am grateful to Mr Rashid Sulaibikh, UNESCO Representative in Bahrain, for the initiation of my invitation to contribute to this symposium; to those who studied the water deterioration in piezometric head and quality and also to those who will, I hope, prevent the further deterioration in water and maintain Bahrain as a green island in the middle of the Gulf.