Emirates Journal for Engineering Research, 10 (1), 57-67 (2005) (Regular Paper)
SPATIAL AND TEMPORAL TRENDS IN GROUNDWATER RESOURCES IN BAHRAIN, 1992-2002 W. K. Zubari Desert and Arid Zones Sciences Program, College of Graduate Studies, Arabian Gulf University, P.O. Box: 26671, Bahrain, E-mail:
[email protected] (Received February 2005 and accepted June 2005)
ﺗﻌﺘﺒﺮ اﻟﻤﻴﺎﻩ اﻟﺠﻮﻓﻴﺔ ﻟﻤﻜﻤﻦ اﻟﺪﻣﺎم اﻟﻤﺎﺋﻲ اﻟﻤﺼﺪر اﻟﻄﺒﻴﻌﻲ اﻟﻮﺣﻴﺪ ﻟﻠﻤﻴﺎﻩ اﻟﻌﺬﺑﺔ ﻟﺘﻠﺒﻴﺔ اﻟﻄﻠﺐ اﻟﻤﺘﺰاﻳﺪ ﻋﻠﻰ اﻟﻤﻴﺎﻩ ﻓﻲ وﻟﻘﺪ أدى اﻻﺳﺘﻐﻼل اﻟﻤﺘﻮاﺻﻞ وﻟﻔﺘﺮات ﻃﻮﻳﻠﺔ ﻟﻬﺬا اﻟﺨﺰان اﻟﻤﺎﺋﻲ إﻟﻰ اﻧﺨﻔﺎض ﻣﺴﺘﻤﺮ ﻟﻤﺴﺘﻮﻳﺎﺗﻪ.ﻣﻤﻠﻜﺔ اﻟﺒﺤﺮﻳﻦ ﻣﺆدﻳًﺎ،اﻟﻤﺎﻟﺤﺔ اﻟﻤﺤﻴﻄﺔ ﺑﻪ-اﻟﻤﺎﺋﻴﺔ واﻧﻘﻼب اﻻﻧﺤﺪارات اﻟﻬﻴﺪروﻟﻴﻜﻴﺔ ﺑﻴﻦ ﻣﻴﺎهﻪ اﻟﻌﺬﺑﺔ ﻧﺴﺒﻴًﺎ واﻟﻤﻴﺎﻩ اﻟﻤﺎﻟﺤﺔ وﺷﺒﻪ ﺗﻢ اﻟﻘﻴﺎم ﺑﻤﺴﺢ ﻟﻠﻤﺴﺘﻮﻳﺎت اﻟﻤﺎﺋﻴﺔ واﻟﻤﻠﺤﻴﺔ ﻟﻤﻴﺎﻩ اﻟﺨﺰان، وﻓﻲ هﺬﻩ اﻟﺪراﺳﺔ.إﻟﻰ ﻏﺰوهﺎ ﻟﻪ وﺗﺪهﻮر ﻧﻮﻋﻴﺔ ﻣﻴﺎهﻪ وﻟﻘﺪ ﺑﻴﻨﺖ اﻟﺘﺤﺎﻟﻴﻞ اﻟﻤﻜﺎﻧﻴﺔ. ﻟﺘﺤﺮي ﻋﻤﻠﻴﺔ اﻟﺘﺪهﻮر اﻟﻤﺎﺋﻲ ﺑﻪ2002-2001 اﻟﻤﺎﺋﻲ ﻋﻠﻰ ﻣﺴﺘﻮى اﻟﻤﻤﻠﻜﺔ ﻓﻲ اﻟﻔﺘﺮة ﻟﻤﺘﻐﻴﺮات اﻟﺤﺎﻟﺔ إﻟﻰ أن أﻏﻠﺒﻴﺔ اﻟﺴﻄﺢ اﻟﺒﻴﺰوﻣﺘﺮي ﻟﻠﺨﺰان ﻓﻲ اﻟﺒﺤﺮﻳﻦ ﻗﺪ اﻧﺤﺪر إﻟﻰ ﻣﺴﺘﻮﻳﺎت أﺳﻔﻞ ﻣﺴﺘﻮى ﺳﻄﺢ وﺑﺄن اﻟﻤﻴﺎﻩ اﻟﺘﻲ ﺗﻐﺬي ﺧﺰان اﻟﺪﻣﺎم ﻣﻦ اﻟﺠﺎﻧﺐ اﻟﺸﺮﻗﻲ ﻟﻠﻤﻠﻜﺔ اﻟﻌﺮﺑﻴﺔ اﻟﺴﻌﻮدﻳﺔ ﺗﺘﺄﺛﺮ ﻧﻮﻋﻴﺘﻬﺎ ﺑﺸﻜﻞ آﺒﻴﺮ،اﻟﺒﺤﺮ ﻣﺼﺪرهﺎ اﻟﺮﺋﻴﺴﻲ ﻣﻴﺎﻩ اﻟﺒﺤﺮ واﻟﻤﻴﺎﻩ ﺷﺒﻪ اﻟﻤﺎﻟﺤﺔ اﻟﻮاﻗﻌﺔ أﺳﻔﻞ اﻟﺨﺰان،ﺑﺴﺒﺐ اﺧﺘﻼﻃﻬﺎ ﺑﻤﻴﺎﻩ ذات ﻣﻠﻮﺣﺔ ﻋﺎﻟﻴﺔ ﺗﻢ ﺗﻘﺼﻲ اﻟﺘﻐﻴﺮات اﻟﺰﻣﺎﻧﻴﺔ، وﺑﺎﻻﻋﺘﻤﺎد ﻋﻠﻰ اﻟﺒﻴﺎﻧﺎت اﻟﻤﺘﻮﻓﺮة ﻣﻦ اﻟﺪراﺳﺎت اﻟﺴﺎﺑﻘﺔ، إﺿﺎﻓﺔ ﻟﺬﻟﻚ.اﻟﻤﺎﺋﻲ وﻟﻘﺪ أﺷﺎرت اﻟﺘﺤﺎﻟﻴﻞ اﻟﺰﻣﺎﻧﻴﺔ ﻟﻬﺬﻩ اﻟﻔﺘﺮة إﻟﻰ ﺣﺪوث هﺒﻮط،2002-1992 ﻟﻤﺘﻐﻴﺮات اﻟﺤﺎﻟﺔ ﺑﺨﺰان اﻟﺪﻣﺎم ﻟﻠﻔﺘﺮة وأن ﻣﺴﺘﻮى اﻟﻤﻠﻮﺣﺔ ﺑﻤﻴﺎﻩ اﻟﺨﺰان ﻓﻲ ﻋﻤﻮم ﻣﻨﺎﻃﻖ اﻟﺒﺤﺮﻳﻦ ﻗﺪ ازداد ﺑﻨﺴﺒﺔ،ﻋﺎم وﻣﺴﺘﻤﺮ ﻓﻲ اﻟﻤﺴﺘﻮﻳﺎت اﻟﻤﺎﺋﻴﺔ وأن ﻋﻤﻠﻴﺔ ﺗﺪهﻮر ﻧﻮﻋﻴﺔ اﻟﻤﻴﺎﻩ اﻟﺠﻮﻓﻴﺔ ﻗﺪ أﺻﺒﺤﺖ أآﺜﺮ اﻧﺘﺸﺎرا ﺧﻼل ﻓﺘﺮة اﻟﺘﻘﻴﻴﻢ هﺬﻩ ﻋﻦ اﻟﻔﺘﺮات،%30 ودﻟﻠﺖ اﻟﺘﺤﺎﻟﻴﻞ اﻟﻤﻜﺎﻧﻴﺔ واﻟﺰﻣﺎﻧﻴﺔ اﻟﺘﻲ أﺟﺮﻳﺖ ﻓﻲ هﺬﻩ اﻟﺪراﺳﺔ ﻋﻠﻰ أن ﻣﺨﻄﻄﺎت وﺟﻬﻮد اﻹدارة اﻟﻤﺎﺋﻴﺔ.اﻟﺴﺎﺑﻘﺔ اﻟﺘﻲ ﺗﻢ اﺗﺨﺎذهﺎ ﻓﻲ اﻟﻌﺸﺮ ﺳﻨﻮات اﻟﻤﺎﺿﻴﺔ ﺑﻮاﺳﻄﺔ ﺳﻠﻄﺎت اﻟﻤﻴﺎﻩ ﻓﻲ اﻟﻤﻤﻠﻜﺔ ﺑﻬﺪف اﻟﺴﻴﻄﺮة ﻋﻠﻰ ﺗﺪهﻮر ﻧﻮﻋﻴﺔ وﺑﺄﻧﻪ إذا ﻟﻢ، ﻟﻢ ﺗﻜﻦ ﻓﻌﺎﻟﺔ ﻓﻲ ﺗﺤﺴﻴﻦ ﺣﺎﻟﺔ اﻟﻤﻴﺎﻩ اﻟﺠﻮﻓﻴﺔ، وﺗﺮآﺰت ﻋﻠﻰ ﺟﺎﻧﺐ ﺗﻌﻈﻴﻢ اﻟﻤﻴﺎﻩ اﻟﻤﺘﺎﺣﺔ،اﻟﻤﻴﺎﻩ اﻟﺠﻮﻓﻴﺔ ﻳﺘﻢ ﺗﺨﻔﻴﺾ ﻣﺴﺘﻮﻳﺎت ﺳﺤﺐ اﻟﻤﻴﺎﻩ اﻟﺠﻮﻓﻴﺔ إﻟﻰ ﻣﺴﺘﻮﻳﺎت ﻣﻘﺎرﺑﺔ ﻟﻤﻌﺪل ﺗﻐﺬﻳﺘﻬﺎ ﻓﺈن ﻧﻮﻋﻴﺔ هﺬﻩ اﻟﻤﻴﺎﻩ ﺳﺘﺴﺘﻤﺮ ﻓﻲ وﻹﺣﺪاث ﺗﺨﻔﻴﺾ هﺎم وﻣﺆﺛﺮ ﻓﻲ ﻣﻌﺪﻻت ﺳﺤﺐ.اﻟﺘﺪهﻮر ﻣﺆدﻳﺔ ﻓﻲ اﻟﻨﻬﺎﻳﺔ إﻟﻰ ﺧﺴﺎرة هﺬا اﻟﻤﻮرد اﻟﻤﺎﺋﻲ ﺑﺎﻟﻜﺎﻣﻞ ﻓﺈﻧﻪ ﻳﻘﺘﺮح أن ﻳﺘﻢ اﻟﺘﻮﺟﻪ ﻧﺤﻮ اﻟﺘﺪﺧﻼت واﻹﺟﺮاءات اﻹدارﻳﺔ ذات اﻟﻌﻼﻗﺔ ﺑﺠﺎﻧﺐ إدارة،اﻟﻤﻴﺎﻩ اﻟﺠﻮﻓﻴﺔ ﺑﺎﻟﻤﻤﻠﻜﺔ . ﻣﺜﻞ ﺗﻄﺒﻴﻖ اﻟﺤﺎﻓﺰ اﻻﻗﺘﺼﺎدي ﺑﻔﺮض ﺗﻌﺮﻓﺔ ﻋﻠﻰ اﻟﻜﻤﻴﺎت اﻟﻤﺴﺤﻮﺑﺔ ﻣﻦ اﻟﻤﻴﺎﻩ اﻟﺠﻮﻓﻴﺔ،اﻟﻄﻠﺐ In Bahrain, groundwater in the Dammam aquifer is the only natural source of fresh water to meet the country's increasing water demands. Prolonged over-exploitation of the aquifer has led to continuous water level decline, reversal of hydraulic gradients between the relatively freshwater aquifer and adjacent brackish- and saline- water bodies, and their encroachment and salinization of the aquifer. In this study, a countrywide potentiometry and salinity survey has been conducted in the year 2001/2002 to investigate the aquifer deterioration process. Spatial analysis of the aquifer state variables indicated that most of the potentiometric surface of the Dammam aquifer has declined to below sea level, and the quality of the aquifer recharge water, received from eastern Saudi Arabia, has been significantly influenced by inland mixing with higher concentration waters, mainly seawater and underlying brackish water. Furthermore, temporal changes in the aquifer's state variables over the period 1992-2002 are examined using salinity and potentiometry data from a previous survey. Temporal analysis indicated a general water level decline, and that the salinity in most of the aquifer areas has exhibited an increase by about 30%, and the deterioration process has become more widespread over the assessment period. Analysis of the spatial and temporal changes of the Dammam aquifer indicated that management schemes and efforts undertaken in the last 10 years by the water authorities have not been effective in modifying the aquifer's conditions, and that unless the current levels of abstraction from the aquifer are brought back closer to the level of renewable recharge, groundwater quality would be completely ruined. In order to have significant reduction in groundwater abstraction rates, it is suggested that a shift towards demand-side interventions is made, such as employing the economic incentive of groundwater pricing.
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W. K. Zubari
58
N W
Muharraq Isl. E
W
S
Manama
Budayaa
2895000
Mohammadiyah Isl. Nabih Saleh Isl.
Jiddah Isl.
Sitrah Isl. Hamalah
2885000
Malikiyah Ras Abu Jarjur Zallaq
Aquifer rocks limit
Ras Hayan
2875000
Wasmiyah
Explanation 2865000
UT M North, meters
Umm Naasan Isl.
Sampling site for water level
Areas where the aquifer rocks outcrop 440000
200
0
Kuwait
Sampling site with full chemical analysis Sampling site with EC/TDS analysis
2855000
Bahrain consists of an archipelago of 33 islands located in the Arabian Gulf, about midway between Saudi Arabia and Qatar (Figure 1). Like most of the Arabian Peninsula, the climate is characterized by high temperatures, erratic often scanty, rainfall of less than 80 mm/yr, and high evapotranspiration rate mounting Under such arid to more than 1800 mm/yr1. conditions, Bahrain has no surface water, and groundwater is the only natural source of freshwater supply. The country's fresh water demands, amounting to about 310 Mm3/y in 2002, are met mainly by groundwater abstraction (68.4%) and desalination plants (27.1%), and to a lesser extent (4.5%) by treated wastewater. However, heavy reliance on the Dammam aquifer, the principal aquifer in Bahrain, to meet the country's ever-increasing water demands, particularly during the last three decades, have resulted in a rapid decline in its potentiometric levels and a reversal of hydraulic gradients between the relatively freshwater aquifer and adjacent brackish- and saline-water bodies. As a direct consequence, encroachment of these waters into the aquifer has occurred, causing its salinization. The deterioration of groundwater quality has restricted the use of this resource from the invaded parts of the aquifer, which are estimated in 1992 to be more than half of the original pre-development groundwater reservoir in Bahrain2. If this trend continues, the only natural source of water in Bahrain may be lost, and might dictate expensive remedies unless proper aquifer management is considered. Past and current groundwater management measures undertaken by the water authorities in Bahrain to control and reverse the deterioration of groundwater quality generally aim at reducing groundwater abstraction in the agricultural, municipal, and the industrial sectors. These measures have concentrated mainly on the supply augmentation side, and were manifested by the construction of desalination plants, reuse of treated wastewater, and artificial recharge by storm runoff water. Demand management efforts and measures were also made, however only recently, and were represented in the domestic sector (24% of total groundwater consumption) by escalating tariff system, rationing demand, pressure control, leak detection, installation of household water saving equipment, and public awareness campaigns. In the agricultural sector (main groundwater consumer at 73%), these were manifested by subsidizing modern irrigation systems, metering groundwater wells, programs for changing crop type to less water consuming crops, and agricultural extension services. Furthermore, legislations were issued to restrict groundwater use by the industrial sector.
2905000
1. INTRODUCTION
Iran A
ra
Bahrain Saudi Arabia
bi
an
Qatar
G
km
ul
f
Oman
U. A. Emirates 450000
460000
470000
UTM E ast, m eters
Figure 1. Location of Bahrain and groundwater sampling sites
The above management measures, undertaken by the water authorities in Bahrain since the early 1980s, aim primarily at reducing groundwater abstraction from the Dammam aquifer and enhancing its storage. The overall objective is to allow the aquifer's potentiometric levels to recover and modify its water quality, thus increasing its sustainability as a usable water resource as well as a strategic reserve for the country. In this study, the spatial distribution of the Dammam aquifer state variables (potentiometry and salinity) are investigated through a countrywide potentiometry and hydrochemical survey conducted in 2001/02. Furthermore, a countrywide potentiometry and hydrochemical survey conducted in 1991/923 is used as a baseline data to evaluate the effectiveness of groundwater management efforts and schemes in terms of temporal changes in the aquifer water level and quality over the period 1992-2002. Accordingly, further measures required to control future deterioration in the groundwater quality are suggested.
Emirates Journal for Engineering Research, Vol. 10, No.1, 2005
Spatial and Temporal Trends in Groundwater Resources in Bahrain, 1992-2002
16000
2. MATERIAL AND METHODS
Emirates Journal for Engineering Research, Vol. 10, No.1, 2005
12000
TDS, mg/L
In Bahrain, the Water Resources Directorate (WRD), Ministry of Municipalities and Agriculture, has an established groundwater level monitoring network that consists of 21 boreholes in the Dammam aquifer (Figure 1). All of these observation wells have continuous water-level data since 1980, and are reported on a monthly basis. Annual average water level data were used for preparing the water level contour map for the year 2002 for the spatial analysis of the aquifer potentiometry. Furthermore, a previous water level contour map for the period 19923 was used for the preparation of a water-level difference map for the period 1992-2002, to enable the analysis of the temporal trends in the aquifer potentiometry. The spatial analysis of groundwater quality was made through the use of a detailed hydrochemical survey for the Dammam aquifer at 283 wells across the country. The survey was carried out in the period 2001/2002. Groundwater samples were taken from constructed piped wells covering all the Dammam aquifer utilization areas in Bahrain (Figure 1). Groundwater samples from the north-central parts of Bahrain were somewhat limited, because most productive wells in these parts have been abandoned; aquifer salinity had reached about 11,000 mg/L since late 1970s4. The sampling procedure involved collecting water samples in polyethylene bottles after pumping the sampled well for at least 5 minutes and then sampling the recovered water in clean 1.5 liter polythene bottles. This was done in an attempt to remove groundwater stored in well bore and to obtain a representative sample. Collected samples were transported directly to the laboratory for chemical analysis. Out of the total 283 water samples, 132 samples were further analyzed for major cations (Na, Ca, Mg, K) and major anions (Cl, SO4, HCO3), total alkalinity (CaCO3), total hardness (CaCO3), pH, Electrical Conductivity (EC), and Total Dissolved Solids (TDS) . The rest of the water samples (151) were only analyzed for EC, and their TDS was calculated from an established relationship between the TDS and EC measured in the 132 wells (Figure 2). Standard methods were used for the determination of the chemical characteristics of the water samples5. The pH and EC were measured using portable pH and EC meters. The total alkalinity was measured by the acidimetry method using methyl orange as indicator, while the total hardness was determined by EDTA titrimetric method using black T indicator. Na and K were determined by flame photometry. SO4 was determined using standard gravimetric method using Barium Chromate. Cl was measured by the orgenometric method against Silver Nitrate using Potassium Chromate as indicator, and HCO3 by calculation from total alkalinity. Mg was measured by calculation using the formula: Mg in mg/L = (total hardness ml titrant value-Ca hardness ml titrant value)
TDS = 622 x EC - 52.8 R2 = 0.98 8000
4000
0 0
5
10
15
EC, micromhos/cm
20
25
Figure 2. EC vs TDS relationship for Dammam aquifer hydrochemical survey, 2001/2002
x Mg atomic weight. Ca hardness used to calculate Mg was determined by EDTA titrimetric method using Murexide indicator. Finally the TDS was measured by adding the total anions and cations values of the water sample. Bahrain does not have an established regularly monitored groundwater quality network, and groundwater quality monitoring is not carried out on regular basis6. However, in the past, groundwater quality monitoring for the Dammam aquifer in Bahrain has been carried out in the form of major country-wide surveys every about 10 years. Three comprehensive groundwater hydrochemical surveys were conducted in the past. These were made in 19707, 1978/794, and 1991/923. The last hydrochemical survey (1991/92) was used with the current survey to produce the salinity difference maps for the period 1991/922001/02. Furthermore, the 1978/79 survey4, which surveyed all producing wells in Bahrain at that time (854 wells), was used for the statistical comparisons with the two other recent surveys as a base-line data for the temporal analysis. Records of groundwater abstraction from the Dammam aquifer were obtained from the WRD records. Groundwater abstraction was monitored on an annual basis since 1980.
3. HYDROGEOLOGIC SETTING The Dammam aquifer, a confined coastal aquifer, is developed in the Tertiary limestone and dolomite members of the Dammam Formation. The Dammam aquifer in Bahrain forms only a small part of an extensive regional aquifer system, termed the Eastern Arabian Aquifer, which extends from central Saudi Arabia, where the aquifer crops out and its main recharge area is located, to the Arabian Gulf, including Bahrain, Kuwait and southern Qatar. The Dammam aquifer in Bahrain receives its water mainly by underflow from this regional aquifer, with additional, insignificant amounts by rainfall recharge, averaging about 0.5Mm3/y4. According to many researchers 3,8,4,9,
59
W. K. Zubari
the steady-state rate of underflow from eastern Saudi Arabia to Bahrain ranges between from 100-112 Mm3/y. The Dammam aquifer system in Bahrain islands, which is an anticlinal structure, consists of two aquifer zones, designated the ‘A’ and ‘B’ zones, developed in the Alat (15-25 m thick) and Khobar (40-49 m thick) limestone members of the Dammam Formation, respectively (Figure 3). In the core of the anticline, at the center of Bahrain main island, the rocks of the Dammam Formation are completely eroded (Figure 1), exposing the rocks of the underlying Rus Formation (early Eocene). The Dammam aquifer system is confined in most of Bahrain from above by the claystones of the Neogene Formation (10-60 m thick), and from the base by the shale beds of the Sharks Tooth Shale Member (8-20 m thick) of the Dammam Formation, in addition to the anhydrite and shale deposits in the upperpart located in the top of the Rus Formation. The two aquifer zones are separated by the Orange Marl Member (9-15 m thick) of the same formation. In the western part of Bahrain island, at the locality of Hamalah, the Neogene claystones and parts of the Alat limestone are eroded due to a structural high that exists at that locality, and the aquifer is unconfined (Figure 1). The ‘A’ aquifer has limited hydraulic properties, where it possesses an average transmissivity of about 350 m2/d. The ‘B’ aquifer zone, developed in highly fractured limestones and dolomites, the principal aquifer in Bahrain, where it provides more than 70% of the total groundwater abstraction. This is due to the high transmissive properties (average transmissivity is about 10,000 m2/d) of the aquifer. Due to the presence
A
of a semi-confining layer between the two zones and improper well- completion practices, in which both aquifers are tapped by most wells, little variation of water chemistry exists between the ‘A’ and ‘B’ aquifer zones4. Therefore, in this study, the two are considered together to represent the Dammam aquifer. A third aquifer zone, termed locally as ‘C’, is developed in the Rus Formation and the upper parts of the Umm Er Radhuma (UER) Formation (Paleocene to early Eocene). The Rus Formation is composed of fractured chalky dolomitic limestone, with subsidiary shale and anhydrite intercalations in its upper section. The Rus Formation in the central and eastern parts of Bahrain has undergone extensive solution of its anhydrite (Figure 3), which has led to the collapse of the overlying rocks, and more importantly, has reduced the effectiveness of its upper confining layer, which causes a relatively easier migration of its water into the Dammam aquifer in those areas10. Groundwater in the 'C' aquifer zone occurs in the form of brackish water lens (8000-15000 mg/L) in Bahrain main island, with total reserves of about 10,000 Mm3. The salinity of groundwater in the aquifer gradually increases with depth. In central Bahrain island, salinity increases from about 8000 mg/L at the water table, at about 5 m elevation above mean sea level, to about 15,000 mg/L at a depth of about 150 m below mean sea level. The brackish water lens is underlain by brine with a salinity of more than 40,000 mg/L. Due to its high salinity, utilization of groundwater from the 'C' aquifer is restricted to industrial purposes in the north-central region and to supplying desalination plants on the eastern coast of Bahrain main island; total abstraction is about 30 Mm3/y.
A'
Sitrah island
Bahrain main island
Geological Units
0 20
Neogene Formation + Recent deposits
A
40 60
meters below sea level
Alat Member
B
Orange Marl Member
C
120
Khobar Member
140
Sharks Tooth Shale M.
Dammam Formation
80 100
160
Rus Formation
180
Limestone (Aquifer)
200
Shale and marl (Aquitard) Anhydrite (Aquitard)
220 240
(+anhydrite & shales)
A A'
Underflow from Saudi Arabia
Umm Er Radhuma Formation
A B Dammam aquifer zones C Rus-Umm Er Radhuma aquifer
260 280 300 320
0
10
Distance, km
20
30
Figure 3. Hydrogeological cross section, Bahrain 60
Emirates Journal for Engineering Research, Vol. 10, No.1, 2005
Spatial and Temporal Trends in Groundwater Resources in Bahrain, 1992-2002
4. GROUNDWATER DEVELOPMENT AND MANAGEMNET
Emirates Journal for Engineering Research, Vol. 10, No.1, 2005
250 Abstraction, Mm3
Prior to 1925, Bahrain’s population depended entirely on the naturally flowing land and offshore springs, to meet its domestic and agricultural needs. The estimated natural springs (about 15 land and 20 offshore) discharge from the aquifer was about 95 Mm3/yr 11-13. Mechanized well drilling and abstraction was introduced to Bahrain Islands in 1925 along with oil exploration activities. The oil discovery in 1932 and the sudden increase in the country’s oil revenues in the early 1970s have resulted in a rapid population growth, urban development, industrial and agricultural expansion, and was accompanied by a dramatic increase in water demands and consumption. These demands have been met mainly by abstraction from the Dammam aquifer and hence substituted the natural springs, which experienced a significant reduction in their discharge (53 Mm3 in 195215; 14.7 Mm3 in 197913; 5 Mm3 in 19903). At present, all springs have ceased to flow14. The total abstraction rate from the aquifer was about 65 Mm3/y in the early 1950s16, increased to about 112 Mm3/y in the mid-1960s12 and reached about 138 Mm3/y in the late 1970s4. In the early 1990s, the total abstraction from the aquifer reached about 205 Mm3/y3, and in 2001 it is estimated at about 218 Mm3/y. Figure 4 displays the abstraction history from the Dammam aquifer in Bahrain. The figure also indicates the Dammam aquifer safe yield, estimated at about 110 Mm3/y (equal to the aquifer’s recharge rate received at Bahrain by lateral under-flow from the upgradient Saudi Arabia aquifers under steady-state conditions), and it also shows the observed natural springs discharge rates. Total groundwater withdrawal (abstraction + natural springs discharge) in Bahrain have exceeded the suggested safe yield of the aquifer since the early 1960s, and presently is more than twice that rate, indicating that a large proportion of the water abstracted is being taken from the aquifer’s storage. The reduction of the Dammam aquifer storage and drop in its potentiometric surface has led to a marked quality deterioration and salinization of the aquifer’s water mainly by seawater intrusion and brackish water up-flow. Realizing the deteriorating conditions of groundwater resources and their limited capacity, the general policy of Bahrain water authorities with regard to water use is to allocate groundwater exclusively for the agricultural sector and to reduce groundwater dependency for the municipal sector by constructing additional desalination plants. Furthermore, tertiary treated wastewater is to supplement groundwater used in irrigation, and to meet additional requirements for future agricultural development in the country. These supply augmentation efforts were supplemented rather recentlyby demand management schemes to further reduce water use in general and groundwater in particular.
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Wells Abstraction
200 150 Aquifer Safe Yield
100 50
Natural Springs Discharge
0 1930
1940
1950
1960 1970 Year
1980
1990
2000
Figure 4. Dammam aquifer abstraction history in Bahrain, 1920-2002.
At present, all water management schemes concentrate principally on reducing groundwater abstraction from the Dammam aquifer in the agricultural and municipal sectors, which are the main groundwater consumers, at 73% and 24%, respectively. Reduction of groundwater abstraction in the agricultural sector, currently (2001) at about 160 Mm3/y (73% of total groundwater withdrawal), is conceptualized through the gradual replacement of groundwater used for irrigation by tertiary treated wastewater through an ambitious plan that would provide eventually about 73 Mm3/y of these waters by the year 2010 17-19. The expansion of the tertiary treated facilities in Bahrain are still under planning and construction phases. Bahrain has a major wastewater treatment plant (Tubli Wastewater Treatment Plant), currently receives 160,000 m3/d (58.4 Mm3/y), but due to treatment capacity limitations only 40,000 (14.6 Mm3/y) of which is tertiary treated and are used for irrigation and landscaping. The rest receives secondary treatment and is disposed of into the sea. It is planned that by the year 2010 the plant will be gradually expanded to receive and tertiary-treat about 200,000 m3/d (73 Mm3/y), all of which all will be used for irrigation. Furthermore, at present, agricultural development program emphasizing demand management and groundwater conservation has been initiated and is being partially implemented along with the expansion in the utilization of the tertiary treated wastewater in irrigation to substitute groundwater. This program is represented by three major components aimed at reducing groundwater consumption, its efficient utilization, and minimizing groundwater wastage. These are: 1) metering of all groundwater wells; 2) groundwater pricing using an incremental tariff based on volume used; and 3) changing crop types, particularly alfalfa, to less water consuming fodder crops. The first component of the program (metering groundwater wells) has started in 1997 and was implemented successfully, and had a positive impact on groundwater abstraction levels (Figure 4).
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W. K. Zubari
However, the second component of the program (groundwater pricing) could not be implemented due to socio-economical and political constraints, and is still pending. The third component of the program (changing crop type) is still in the experimental and extension stage and also receives farmers resistant. Currently (2001), domestic consumption in Bahrain is about 143 Mm3, with about 90 Mm3/y supplied by desalination, while the rest (53 Mm3) is from groundwater abstraction, and represents about 24% of total groundwater withdrawal. Reduction of groundwater abstraction in the municipal sector is being planned through the construction of a major desalination plant and rehabilitating and upgrading the capacity of its existing three desalination plants. It is expected that desalination capacity increases to about 176 Mm3/y by the year 2010. By this expansion, it is anticipated that groundwater abstraction by the municipal sector would be reduced significantly. On the demand management side, there have been considerable efforts and major achievements in reducing and/or maintaining water consumption in general and groundwater in particular, through a wellplanned schemes in the municipal sector. Unlike the conditions in the agricultural sector, the presence of a conducive environment, represented by a metering/billing system since the early 1980s and the ability to control supply have facilitated the implementation of these schemes. These programs have started initially in 1986 and were enforced in the early 1990s, and were represented by reviewing and applying escalating tariffs system, rationing demand during peak times, pressure control, leak detection, economic incentives, advice and installation of households' water saving equipment, and public awareness campaigns20. The estimated total impact of these programs was in lowering the annual increase in municipal water demand from about 11% in the period before implementing these programs to 4% in 1994 21. Despite these continuing efforts, groundwater production for municipal purposes has continued to increase, due to the limited capacity of the country’s desalination plants and increasing municipal water requirements resulting from population growth and urban expansion. This has prompted the issuance of a prime ministerial order to maintain a ceiling for groundwater production by the municipal sector to no more than 54 Mm3/y in May 1994, until the commissioning of a new desalination plant with a capacity of about 50 Mm3/y. In April 2000, Al-Hidd desalination plant was commissioned, and groundwater production ceiling was left. Another management measure was aimed at reducing groundwater utilization by the industrial sector, currently at about 5 Mm3/y (3% of total groundwater withdrawal). Beginning from 1980, the water authorities have issued a legislative order that consisted of prohibiting the industrial sector from using the Dammam aquifer water22 and to meet its
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water demands from the underlying brackish water zones (Rus-Umm Er Radhuma aquifer; TDS = 8,000 15,000 mg/L). The objectives of this scheme are to control and decrease the abstraction rates from the Dammam aquifer by the expanding industrial sector, and to lower the potentiometric levels in the brackish water zones and decrease the vertical hydraulic gradients between the Dammam aquifer and its underlying brackish water zones in order to reduce their upward migration and salinization of the aquifer4,10. Moreover, in the early 1990s, artificial recharge was considered by the water authorities in Bahrain to augment depleting groundwater resources and to improve their deteriorating quality. Two pilot projects for rainfall collection into retention basins and its recharge into the Dammam aquifer via gravity recharge wells are being carried out and are still under investigation and evaluation. However, rainfall variability in space and time constrains the proper evaluation of the effectiveness of these schemes23. In the following section, the current potentiometry and salinity surveys were used to assess the effectiveness of the above management schemes in modifying the deteriorating groundwater resources in Bahrain in terms of spatial and temporal changes in the aquifer's state variables.
5. RESULTS AND DISCUSSION 5.1. Spatial Trend Analysis Potentiometry Average potentiometric level contour map for the Dammam aquifer for the year 2002 is displayed in Figure 5. The contour map indicates that most of the potentiometric surface of the Dammam aquifer in Bahrain is below sea level, with two major cones of depression (-2.0 m below sea level) in the western area, where intensive agricultural activities and groundwater abstraction are located. In the northcentral region, the potentiometric surface is anomalously high, reaching about +1.2 m above sea level. This high represents the areas where active brackish water up-flow from the underlying Rus Formation is taking place. The highest potentiometric surface in Bahrain is located in north and northwest (-0.4 m at north Muharraq island and -0.2 m at Umm Al-Na'asan island), where the aquifer in Bahrain receives its water by under-flow from Saudi Arabia. The results of the countrywide hydrochemical survey are statistically summarized in Table 1. The Dammam aquifer in Bahrain receives its water by lateral underflow from the equivalent aquifers in Eastern Saudi Arabia. Groundwater received at Bahrain generally has a background quality limits characterized by: TDS
