Geographical Information System Modeling of Groundwater Potentiality in the Northeastern Part of the United Arab Emirates

Transcription

1 Geographical Information System Modeling of Groundwater Potentiality in the ortheastern Part of the United Arab Emirates Z.S. RIZK Institute of Environment and Water, Ajman University of Science & Technology, P.O.Box: 346, Ajman, United Arab Emirates. A.S. ALSHARHA Faculty of Science, United Arab Emirates University, P.O.Box: 17551, Al Ain, United Arab Emirates. ABSTRACT: Digitized grid maps on the hydrogeology, groundwater chemistry and quality, soil classification, geologic structures and drainage lines, were used along with the ArcView GIS 3.2 package to construct an analytical GIS groundwater-potential model for the area, in the eastern part of al Sharjah Emirate, United Arab Emirates. Cross-correlation of model output zoned maps was performed to identify areas of high groundwater potential for domestic and agricultural purposes. Results of the GIS model indicate that the eastern strip of the eastern Sharjah Emirate ( region) has the highest groundwater potential. The strip is located close to the recharge area in the orthern Oman Mountains and is dominated by intersections of the Dibba zone, Hatta zone and Wadi Ham structural trends, which seem to control groundwater-flow velocity and recharge rate. The strip is also characterized by fresh (total dissolved solids < 1,500 mg/l), soft (total hardness < 80 mg/l) groundwater suitable for domestic uses. Results also show that the northern and southern central parts of the study area are favorable for agriculture because both areas have cultivable soil types (Calciorthids, Torrifluvents and Torripsaments-2) and shallow groundwater (< 45 m deep) of appropriate quality (total dissolved solids < 3,000 mg/l and sodium adsorption ratio < 10). Because the eastern strip and channels of major wadis in the study area have several water wells used mainly for domestic and agricultural purposes, it is proposed to minimize or even prohibit urban and industrial activities in the upstream side of these wells and assign it as a groundwater protection zone in order to secure and maintain the present supply of good-quality groundwater. ITRODUCTIO The proximity to the orthern Oman Mountains in the UAE and availability of reasonable groundwater resources have made the area of eastern Sharjah Emirates, a favorable site for intensive agricultural activities since early 1970s. The wide application of mechanical submersible pumps in numerous water wells has led to acute aquifer depletion due to excessive groundwater discharge compared with the limited natural recharge. This unbalanced situation has resulted in a sharp decline of groundwater levels, increase of groundwater salinity, drying up of shallow wells and deterioration of groundwater quality. The Ministry of Agriculture and Fisheries recognizing these problems, conducted intensive field surveys using geophysical, hydrogeological and hydrogeochemical techniques to assess groundwater resources in the northern United Arab Emirates. In this regard, the Ministry of Agriculture and Fisheries cooperated with international agencies such as the International Water Consultants (IWACO, 1986) and Japan International Cooperation Agency (JICA, 1996). The surveys were concluded in 1995, and the authors have found it necessary to extend and continue field investigations and make use of recent Geographic Information System (GIS) techniques for evaluation of groundwater resources in the eastern part of Sharjah Emirate ( area). For this purpose, previous data and results of the present field measurements and laboratory analyses have been integrated to develop a comprehensive GIS model for the groundwater resources in the study area. The present study employs the available geophysical data, hydrogeologic measurements, results of hydrochemical analyses of groundwater samples and soil classification, along with the ESRI GIS package for identification of major geologic Desertification in the Third Millennium. Edited by A.S. Alsharhan, W.W. Wood, A.S. Goudie, A. Fowler and E.M Swetz & Zeitlinger Publishers, Lisse, The etherlands, ISB , p

2 Z.S. RIZK and A.S. ALSHARHA structures, distinction of different hydrogeologic units, study of groundwater chemistry, assessment of groundwater quality and evaluation of groundwater potential for domestic and agricultural purposes. The study area, which is located in the eastern part of Sharjah Emirate, is a part of the central agricultural region in the UAE. It covers an area of 850 km 2 and is bounded by Longitudes 55º 50º and 56º 00 E, and Latitudes 25º 00 and 25º 23º. It extends from the orthern Oman Mountains in the east to the Fayah Mountains in the west, the northern agricultural region in the north and the Al Madam plain in the south (Figure 1). METHODS OF STUDY The fieldwork involved measurement of the depth to groundwater in the Ministry of Agriculture and Fisheries observation wells and private farm wells, for the period of ; collection of groundwater samples from about 100 wells; and the measuring of physical parameters such as water temperature, hydrogen ion concentration and electrical conductivity in μs/cm. The authors also participated in pumping test experiments in several wells, infiltration measurements and geoelectrical and well logging surveys. The laboratory work included complete chemical analyses of groundwater samples collected from government and private wells for major cations (Ca 2+, Mg 2+, a + and K + ) and anions (CO 2-3, HCO - 3, 2- SO 4 and Cl - ) in the Central Laboratories of the Ministry of Agriculture and Fisheries. The results were presented as contour maps using SURFER computer program version 5.01 surface mapping system. The office work aimed at presenting, analyzing and interpreting the results of field-measured data and laboratory analyses, in addition to the results of previous investigations. The data obtained from geophysical survey, monitoring of groundwater levels and chemical analyses of groundwater samples are presented on relevant charts and graphs. The GIS modeling was carried out using ArcView GIS 3.2 package (ESRI, 1996) with ArcView Spatial Analyst, under Windows T 4.0 platform. GEOMORPHOLOGY AD GEOLOGY The study area is mainly located within desert plains and wadi flats, extending from the foothills of the orthern Oman Mountains in the east to the Arabian Gulf in the west (Figure 2). The terrain consists of vast flood plains with minor dunes of an uneven configuration. A number of wadi channels traverse the study area from the east to the west. The largest of these are Wadi, Wadi Siji, Wadi Khadrah, Wadi Hamdah and Wadi Thiqebah. The orthern Oman Mountains occupy the eastern part of the study area and are characterised by a rugged terrain with steep slopes, ranging in elevation from 200 m to 1200 m above mean sea level. The continued down cutting has developed many stepped river terraces and formed deep channels along the wadi courses at the foothills of the mountains. Most shallow wells tap the groundwater concentrated at the non-conformity surface between the Ophiolite sequence and the overlying gravel. Evidence of groundwater storage in the Ophiolite mass itself is indicated by occasional seepage during the rainy season where the fractures and weathered zones are highly integrated (Alsharhan et al., 2001). The gravel plains are covered by terrace, alluvial fans and floodplain deposits. The alluvial fans extend from the foothills of the orthern Oman Mountains in the east to sand dunes in the west. Despite that the gravel plains originate from a series of older fans, present-day runoff from the orthern Oman Mountain has small effect on them (Alsharhan et al., 2001). These plains are predominantly composed of coarse particles covered by thin silt layers. The sediment size grades from large gravel in Wadi Khadrah at the foothills of the orthern Oman Mountains to coarse sand in Wadi Lamhah further down gradient. The limestone ridges of Jebel Mileiha and Jebel Fayah break the gentle slope of the plains. The sand dunes cover a rectangular area bounded to the east by the gravel plain, Jebel Mileiha and Jebel Al Fayah, and to the west by coastal sabkhas and the Arabian Gulf. The dune sand is composed of carbonate derived from shell fragments near the coastline or quartz from quartzbearing rocks further inland. Most of the old dunes are fixed by vegetation, composed of ancient dune materials and generally aligned in an EE-WSW direction, approximately perpendicular to the prevailing winds. The recent dunes are mobile and form a series of W-SE trending ridges. Large dunes are located in the northern part of the study area and reach an elevation of more 200 m above mean sea level. The drainage lines dissecting the study area originate in the orthern Oman Mountain in the UAE. All wadis move from the east to west and northwest converging into a single channel (Wadi Lamaha), which reaches the Arabian Gulf in the northwestern corner of the study area. The drainage lines in the mountainous areas are characterized by the trellis and rectangular patterns, whereas the 424

3 Geographical Information System Modeling of Groundwater Potentiality in the ortheastern Part of the United Arab Emirates wadis crossing the gravel plains have a dendritic pattern. The main geological units in the study area are the S Ophiolite sequence, allochthonous units and autochonthonous units (Figure 2). The S Ophiolite is the largest rock unit within the study area and its major outcrops are confined to the orthern Oman Mountains. The Ophiolite sequence represents a complete (20 km thick), unaltered section of the Middle Cretaceous oceanic lithosphere. The Allochthonous units overly the western edges of the S Ophiolite and consist of a lower melange made up of the S Ophiolite blocks, exotic limestones, Hayabi volcanics, Hawasina sediments, metamorphic rocks and serpentinite. The Oman Mountains were subjected to a major deformation during the Cretaceous, with the emplacement of thrust nappes from northeast to southwest onto the Arabian Peninsula margin. The flysch deposits of the Campanian Juweiza Formation were deposited in the fore deep in front of the advancing nappes (Alsharhan, 1989). The autochonthonous units, mainly composed of Maastrichtian, Palaeocene and Eocene limestone with a total thickness of 600 m, unconformably overlie the Late Cretaceous allochthonous units along their eastern and western flanks. The coarsegrained clastics of the Qahlah Formation are largely restricted to the eastern side of the mountains. The Maastrichtian-Lower Tertiary sediments were deformed during the Eocene Period when Tertiary folds of -S, W-SE and E-W trends were formed as a result of reactivation of basement faults by local salt doming or regional folding. Cycles of repeated uplift are recorded in post-miocene times by a series of elevated gravel-capped terraces on the flanks of the Oman Mountains (Alsharhan and asir, 1996). GEOPHYSICAL IVESTIGATIOS Three geophysical methods including gravity, electromagnetic and well logging, were used to delineate the different hydrogeologic units, evaluate groundwater quality, study petrophysical characteristics of hydrogeologic units and define subsurface geologic structures controlling aquifer boundaries and courses of buried wadi channels. The gravity detailing technique was used to delineate the subsurface structures affecting the study area. Results revealed the presence of the E- SW Dibba zone, EE-WSW to E-W Hatta zone and W-SE Wadi Ham fault trends (Figure 3). The Bouguer anomaly calculated with the Grant and West (1965) equations indicated a general increase in thickness of the sedimentary section from 700 m in the southeastern part of the area to 3500 m in the northwest. The time domain electromagnetic soundings acquired and processed by Japan International Cooperation Agency (1996) were re-interpreted in the present work and the results are given in terms of resistivity, thickness and total dissolved solids of each geoelectric layer (Table 1). The borehole logs used in this study area carried out by IWACO (1986) and Japan International Cooperation Agency (1996) include caliper, gamma ray, resistivity, neutron, density, sonic, temperature, conductivity and hydrochemistry. Out interpretation of these data showed that the average porosity of alluvial gravel is 35%, while the limestone porosity ranges from 20% to 40%, depending on lithology and fracturing. Slight changes in the fluid temperature were noted in association with the development of secondary porosity and inflow of groundwater from the formation into boreholes. The decrease in fluid conductivity from 2150 μs/cm to 1200 μs/cm confirmed the inflow of fresher groundwater into a borehole. The high resistivity also reflects the presence of good-quality water in the formation, while the low resistivity is attributed to development of secondary porosity. The distribution of groundwater salinity in boreholes correlates with the groundwater flow interpreted from temperature gradients and fluid conductivity. Table 1. Results of the time domain electromagnetic survey conducted by Japan International Cooperation Agency (1996). Geoelectric layer Hydrogeologic character Thickness (m) Resistivity (Ohm.m) TDS (mg/l) First and second layers Upper aquifer Third layer Middle aquiclude Fourth layer Lower aquifer

4 Z.S. RIZK and A.S. ALSHARHA 55 o 50` 55 o 55` 56 o 31 LEGED To Umm Al Quiwain To Sharjah To Ras Al Khaimah Falaj Al Mualla (asim) To Masafi 26 o 30` 10 km Observation wells used for water-level measurements Private farm wells sampled for hydrogeochemical investigations City Road A R A B I A G U L F 56 o U I T E D A R A B E M I R A T E S O M A G U L F O F O M A 45` Area OMA Al Madam Plain 55 o 45` 56 o O M A 24 o 45` o 50 o 60 o I R A 30 o To Al Ain BAHRAI A R A B I A QATAR G U L F Abu Dhabi Dubai GULF OF OMA o 50` 55 o 55` o 20 o S A U D I A R A B I A UITED ARAB EMIRATES O M A 20 o 50 o 60o Figure 1. Location maps of the United Arab Emirates, area and location of observation and farm walls sampled for chemical analysis. 426

5 Geographical Information System Modeling of Groundwater Potentiality in the ortheastern Part of the United Arab Emirates 26 o 55 o 45` 56 o 56 o 26 o A R A B I A G U L F km Ras Al Khaimah O M A 45` 45` G U L F O F O M A Umm Al Qaiwain Ru us Al Jibal Dibba 30` Dibba Zone 30` UITED ARAB EMIRATES Khor Fakkan Plain Masafi OMA orthern Jibal Al Fayah Oman Fujairah Mountains Al Madam Plain Kalba Masfut O M A 24 o 45` 55 o 45` 56 o 56 o 24 o 45` QUATERARY Aeolian Sand Coastal sabkhas Inland sabkhas Gravel deposits MESOZOIC Simsima Limestone S Ophiolite Hawasina Complex Musandam Limestone Fault Fold Fracture Figure 2. Geologic and main geomorphic features map of the super basin and surrounding area (modified from the UAE ational Atlas, 1993; and JICA, 1996). 427

6 Z.S. RIZK and A.S. ALSHARHA HYDROGEOLOGY AD HYDROGEOCHEMISTRY I. Hydrogeology The study area suffers from a strongly negative water balance caused by natural constraints and human-related activities. The natural constraint is represented by low rainfall (155 mm/yr) and an extremely high potential evapotranspiration (3700 mm/yr). The human constraint is imposed by excessive groundwater pumping versus limited natural recharge. The groundwater abstraction model in the study area is more than double the natural groundwater recharge (Japan International Cooperation Agency, 1996). The core samples obtained from eight test wells, drilled to depths between 200 and 300 m, confirmed the results of 130 transient electromagnetic soundings and indicate the presence of three hydrogeologic units in the study area: the upper aquifer, a middle aquiclude and the lower aquifer. The upper aquifer is composed of Holocene- eogene unconsolidated silt to gravel, consolidated gravel and calcareous sand with a maximum thickness of 250 m and an average thickness of 100 m. The aquifer thickness varies from 60 m at the foothills of the orthern Oman Mountains 160 m east of and south of in a W-SE trough coinciding with the Wadi Ham structural trend (Figure 4). The aquifer thickness decreases to the west (70 m in GP-6 and ), north (80 m in GWR-2) and south (70 m in GP-7). The middle aquiclude consists of impervious layers of Paleogene shale, marl, claystone and dolomite. The aquiclude has a low hydraulic conductivity of 10-5 to 10-7 cm/sec (Japan International Cooperation Agency, 1996). The maximum thickness of this layer is 300 m north of Flaj Al Mualla to a minimum thickness of 50 m, encountered in observation wells and GWR- 4 along the W-SE Wadi Ham structural line. The lower aquifer is composed of carbonates and clastics of Maastrichtian to Cenomanian age. The aquifer is poorly productive with the exception of the intersections of the major fault zones, especially along the E-SW Dibba zone and W-SE Wadi Ham trends. The conglomerate layers of well-sorted gravel interbedded with limestone and dolomite facies form the most productive section in the lower aquifer. Unfortunately, the thickness of this layer does not exceed several tens of meters. A summary of the hydraulic properties of the upper and lower aquifers within the study area is given in Table 2. Table 2. A summary of hydraulic and geoelectrical properties of the aquifers in the Sharjah Emirate (Al Dhaid area), UAE (compiled from Japan International Cooperation Agency, 1996). Hydraulic property Upper Lower aquifer aquifer Average thickness (m) Average resistivity (ohm-m) Transmissivity (m 2 /day) Storage coefficient Specific capacity (m 3 /hr/m) 3 2 Porosity (%) Static water level (m-amsl) Both the IWACO (1986) and Japan International Cooperation Agency (1996) studies indicated the presence of a fissured aquifer in the area. Despite the high transmissivity (776 m 2 /day) and storativity (0.24) of this aquifer, little is known about its distribution, thickness and mode of recharge. The natural gamma ray survey conducted by Japan International Cooperation Agency (1996) indicated the presence of 50 anomalies which coincide with vertical structures affecting this fissured aquifer. The hydrogeologic condition of this aquifer needs further investigations. The depth to groundwater in the study area ranges from 40 to 100 m below the ground surface. Several water wells in the area have gone dry as a result of heavy groundwater pumping during the last three decades. The hydraulic head maps of the upper and lower aquifers for the years 1984 and 1999 show that the groundwater level decreases from 230 m in the east () to 95 m in the west (), indicating a regional groundwater flow from the orthern Oman Mountains to the Arabian Gulf (Figure 4). Between 1984 and 1999, the groundwater level decreased in most observation wells as a result of excessive pumping for all purposes. The maximum decline was 45 m measured in within city at the center of a 20 km average diameter cone-of-depression. The average hydraulic gradient is steep (0.025) along the foothills of the orthern Oman Mountains in the east, reflecting the low hydraulic conductivity of the Ophiolite sequence, and gentle (0.005) in the western region, indicating the high hydraulic conductivity of dolomitic limestone and alluvial gravel. 428

7 Geographical Information System Modeling of Groundwater Potentiality in the ortheastern Part of the United Arab Emirates 25 ò 05 To Umm Al Quiwain To Sharjah To Al Ain Falaj Al Mualla o 50` 55 o 55` 56 o o 50` 55o 55` 12 56o II. Hydrogeochemistry To Ras Al Khaimah To Masafi During the period , a hundred water wells were sampled for chemical analysis to identify the chemical characteristics of groundwater and to evaluate its quality (Figure 1) DIBBA ZOE (asim) City Road Fault Observation wells used for water-level measurements Private farm wells sampled for hydrogeochemical investigations Approximate directions of major linear trends affecting the study area 98 W A D I H A M L I E 8 29 H A T T A Z O E Figure 3. Map illustrating the major fault trends based on interpretation of gravity data in area and major linear trends obtained from drainage lineation analysis (modified from Al Mulla, 2001) The iso-temperature contour map shows that the highest-temperature groundwater (39 C) was measured at in the center of the cone-ofdepression, where a relatively higher temperature, more saline water moving upward causes this temperature anomaly. In contrast, the groundwater samples collected from wells within the courses of Wadi and Wadi Hamdah show much lower temperatures (32 C). These wells intercept relatively cooler recharge water at it moves from the orthern Oman Mountains to the Arabian Gulf. The iso-ph contour map of the groundwater in the study area illustrates that the high ph water is obtained from the mafic and ultramafic Ophiolitic rocks along the eastern front of the study area. On the other hand, the carbonate rocks of Al Fayah Mountains in the southwestern part of the study area exert their buffering effect on the ph keeping it near neutral. The electrical conductance of the groundwater in the study area is low (<1500 μs/cm) in the east and along the courses of major wadis. The electrical conductance increases to 4500 μs/cm in the northwest and 7500 μs/cm in the southwest, the directions of groundwater flow (Figure 5a). The high groundwater salinity in the southwest is attributed to the dissolution of sabkha deposits. The concentration of cations (Ca 2+, Mg 2+ and a + ) is low along the eastern front of the study area and increases towards the west and southwest, in the direction of groundwater flow. Low cations concentration also characterizes the groundwater along the courses of major wadis because they act as conduits of low-salinity recharge water moving from the recharge zone towards the discharge area. - The HCO 3 concentration decreases from 250 mg/l in the east to about 50 mg/l in the city, as a result of exploitation of the near-surface, younger water in the shallow aquifer. Westwards, - HCO 3 value increases again as a result of dissolution of carbonate rocks in the Fayah Mountains. The iso-concentration contour maps show a steady increase in SO 2-4 and Cl - levels from the east to the west and northwest, in the direction of groundwater flow. Dissolution of Sabkhas and evaporite deposits is responsible for high SO 2-4 and Cl - contents in the groundwater of the southwestern part of the study area. High Cl - is also associated with the upconing of more-salinity water from the lower aquifer as a result of heavy groundwater pumping in and around the city. - The concentrations of nitrate ion (O 3 ) and total iron (Fe), in addition to water hardness and sodium adsorption ratio (SAR), were used as quick indicators of water quality in the study area. The World Health Organization (1984) recommended 429

8 Z.S. RIZK and A.S. ALSHARHA - limit for nitrate (O 3 ) in drinking water (10 mg/l as O ) is exceeded in the north-central and eastern parts of the study area due to intensive farming activities. Despite that iron is a very common element in rocks and soils of the area; low iron concentrations were measured in the analyzed groundwater because the free to semi-confined nature of the aquifers allows the oxygen to precipitate water-dissolved iron. The groundwater in eastern is soft (total hardness <100 mg/l), while the groundwater in the northern, western and southwestern parts is hard to very hard (total hardness >1500 mg/l) (Figure 5b). The sodium adsorption ratio (SAR) of the groundwater in the study area is predominantly <10, which is good for irrigation water, whereas the groundwater in the Al Fayah Mountains has sodium adsorption ratio >16, which is harmful to plants if this water were used for irrigation. The northeastern corner of the study area has sodium adsorption ratio values in excess of 13 (Figure 5c). GIS MODELIG OF GROUDWATER POTETIALITY The geographic information system is an efficient tool for studying, assessment and management of natural resources (Lang, 1998). Rofail et al. (1998) defined GIS as an organized collection of computer hardware, software, geographic data and personal design to efficiently capture, store, update, manipulate, analyze and display all forms of geographically referenced information. In the present study, the GIS technique was used to cross correlate soil suitability map, hydraulic head maps, groundwater quality maps, drainage basins and geologic structures maps, and to assess groundwater potentiality for domestic and agricultural uses in the area. I. Model Construction The present analytical model was carried out using the ArcView GIS 3.2 package (ESRI products) with ArcView Spatial Analyst. Figure 10 is the flow chart of the model. Two sets of data were included in the database prepared for the purpose of this study: field data and digitized data. The field data include well locations, groundwater levels, concentration of chemical species and water quality parameters, whereas the digitized data include maps of soil classification, drainage basins and major structural trends. Field data, including the groundwater salinity, total hardness, sodium adsorption ratio and depth to groundwater at the Ministry of Agriculture and Fisheries observation wells, was stored in database of dbf 4 format. The dbf4-formatted data was transformed into point data (vector) using a unified grid, based on the soil classification map for the study area as extended coordinates for all output maps and models. Surface interpolation (raster) of an accuracy of 50 x 50 m was assigned for each data point, which were regrouped according to selected criteria into reclassed, grid-zone maps. All maps were digitized into 50 x 50 m grid data (raster) and selected layers of grid data were superimposed according to specified criteria using the cell-based modeling technique. Finally, models were constructed, based on buffering and overlaying techniques of various interrelated zoned maps. II. Input Data The input data for the analytical GIS models of the eastern part of Sharjah Emirates ( area) are shown in (Table 3). The soil classification map shows seven soil types: Calciorthids, Torrifluvents, Torripsaments-2, Gypsiorthids, Torriorthents, wadi beds and rock outcrops (Figure 6). The Calciorthids, Torrifluvents and Torripsaments-2 soil types were considered as one group, which is suitable for agriculture according to the available soil types in UAE (Abrol et al., 1988). On the other hand, Gypsiorthids, Torriorthents, wadi beds and rock outcrops represented the second group, which was considered unsuitable for agriculture. III. Model Outputs The model outputs were obtained by overly of interrelated zoned maps for iso-salinity, total hardness, sodium adsorption ratio, depth to groundwater, soil types and major fault zones and drainage lines. Table 4 shows overlies of different layers, output figures, and range of variables and their aerial distribution. Model outputs define priority areas of high groundwater potentiality for domestic and agricultural purposes (Figure 7). 430

9 Geographical Information System Modeling of Groundwater Potentiality in the ortheastern Part of the United Arab Emirates Table 3. Input parameters of the GIS analytical model for the eastern Sharjah Emirate ( area) and their applications. Input Parameter Range Application Hydraulic head m Definition of recharge and discharge areas and direction(s) of groundwater flow. Total dissolved solids (TDS) 705-7,500 mg/l Construction of iso-salinity contour and zoned maps. Total hardness (TH) mg/l Preparation of iso-total hardness contour and zoned maps. Sodium adsorption ratio (SAR) 7-28 Construction is iso-sar contour and zoned maps. Soil classification Suitable to unsuitable Evaluation of soil types in terms of their suitability for agriculture. Structural trends and drainage -- Assessment of the impact of both parameters on the basins groundwater potentiality and recharge. Table 4. Sample outputs of the Geographical Information System (GIS) analytical model for the area and their aerial distribution. Layers Ranges Aerial distribution TDS and TH TDS < 1500 mg/l and TH < 80 mg/l The majority of the study area TDS and SAR TDS < 3000 mg/l and The majority of the study area Depth to water, TDS and SAR Depth < 45 m, TDS < 3000 mg/l and The northern and southern central parts of the study area Depth to water, TDS, SAR and soil type Depth < 45 m TDS < 3000 mg/l, and cultivable soil The northern and southern central parts of the study area TDS, fault zones, soil type TDS < 1500 mg/l, fault intersections and cultivable soil The eastern strip of the study area 55o 50` 55o 55` 56o o 50` 55o 55` 56o A B C o 50` 55o 55` 56o 5 To Umm Al Quiwain To Umm Al Quiwain To Umm Al Quiwain (asim) (asim) (asim) o 50` 55o 55` 56o 55o 50` 55o 55` 56o 55o 50` 55o 55` 56o Figure 4. Hydraulic head contour map of the upper aquifer in the area, in meters above mean sea level; A) 1985, B) 1998 and C) hydraulic-head decline between 1985 and 1998 (modified from Al Mulla, 2001). 431

10 Z.S. RIZK and A.S. ALSHARHA 55 o 50` 55o 55` 56o 55o 50` 55o 55` 56o 55 o 50` 55 o 55` 56 o A B C SAR > Brackish Water 250 Hard Water 10 (asim) (asim) (asim) Fresh Water Brackish Water 2500 Very Hard Water SAR > Soft Water Fresh Water o 50` 55 o 55` 56 o 55 o 50` 55 o 55` 56 o 55o 50` 55o 55` 56o Figure 5. Iso-electrical conductance (A), hardness (B and sodium adsorption ratio (C) of groundwater in the eastern part of Al Sharjah Emirate in January o 50` 55o 55` 56o A (asim) B 55o 50` 55o 55` 56o TDS > 3000 mg/l SAR > 10 C 55o 50` 55o 55` 56o Depth > 45 TDS > 3000 mg/l SAR > 10 Depth < 45 TDS < 3000 mg/l (asim) (asim) TDS < 3000 mg/l Depth > 45 TDS > 3000 mg/l SAR > 10 TDS > 3000 mg/l SAR > 10 TDS < 3000 mg/l Depth < 45 TDS < 3000 mg/l 55 o 50` 55 o 55` 56 o Calciorthids Rock Outcrop Torriothents Wadi Beds Gypsiorthids Torrifluvents Torripsaments-2 55o 50` 55o 55` 56o 55 o 50` 55 o 55` 56 o Figure 6. Soil classification map (A), suitability of water for agriculture (B) and shallow groundwater resources (C) in the eastern part of Al Sharjah Emirate in January

11 Geographical Information System Modeling of Groundwater Potentiality in the ortheastern Part of the United Arab Emirates 55o 50` 55o 55` 56o A B 55 o 50` 55 o 55` 56 o To Umm Al Quiwain (asim) (asim) To Masafi o 50` 55o 55` 56o o 50` 55 o 55` o Figure 7. Areas suitable for agricultural purposes A) and areas of high groundwater potentiality B) in the eastern part of Al Sharjah Emirate in January COCLUSIOS The results of the present investigations contribute to understanding the factors affecting groundwater flow, recharge and potential for domestic and agricultural purposes in the area. The fault systems affecting the study area are the E-SW Dibba zone, EE-WSW to E-W Hatta zone and W-SE Wadi Ham line. These faults and related wadi channels act as conduits for lowsalinity recharge water moving from the recharge area towards discharge area. The total domain electromagnetic survey illustrated the presence of four geoelectric layers. The upper two layers constitute the upper free to semi-confined aquifer, the third layer corresponds to the middle aquiclude and the fourth geoelectric layer represents the lower confined aquifer. The hydraulic heads in both aquifers indicate that the groundwater flows from the orthern Oman Mountain in the east towards the Arabian Gulf in the west and northwest. Excessive groundwater pumping for agricultural purposes during the last 15 years has created a 20 km diameter cone-of-depression centered at well within the Al Dhiad city. A maximum drawdown of 45 m indicates a 3-meters annual decline in groundwater level. The groundwater salinity in the area of eastern Sharjah Emirate is < 750 mg/l in the northeast, 3000 mg/l in the central area, 4500 mg/l in the northwest and > 7500 mg/l in the southwest, increasing from the east to west in the direction of groundwater flow. The World Health Organization recommended limit for nitrate (O - 3 ) in drinking water is exceeded in the north central part of the study area due to intensive farming activities. The groundwater in the eastern strip is soft (with total hardness < 80 mg/l), while the northern, western and southwestern parts have hard to very hard groundwater (total hardness >1500 mg/l). The results of GIS modeling indicate that the eastern strip of the study area has the highest groundwater potentiality for domestic and agricultural uses because it is dominated by intersections of major structural trends, which facilitate the groundwater movement and recharge. The strip is also characterized by fresh (total 433

12 Z.S. RIZK and A.S. ALSHARHA dissolved solids < 1500 mg/l), soft (total hardness <80 mg/l) groundwater suitable for domestic uses. The northern and southern central parts of the study area are favorable for agriculture because both areas have shallow (< 45 m deep) groundwater of appropriate quality (total dissolved solids < 3000 mg/l and sodium adsorption ratio < 10) and possess soil types (Calciorthids, Torrifluvents and Torripsaments-2) suitable for agriculture. The eastern strip and channels of major wadis within the study area have many groundwater production wells used for domestic and agricultural purposes. Therefore, it is recommended to minimize or even prohibit urban and industrial activities on the upstream side of these wells and assign it to a groundwater protection zone in order to maintain the present supply of good-quality groundwater. REFERECES Al Mulla, M.M. (2001). Application of geophysical, hydrogeological and GIS techniques for investigation of groundwater resources in the Al Dhaid area, UAE. Unpublished M.Sc. Thesis, Faculty of Science, UAE University, United Arab Emirates, 155p. Alsharhan, A.S.. Rizk, Z.A., airn, A.E.M., Bakhit, D.W. and Alhajari, S.A. (eds.) (2001). Hydrogeology of an Arid Region: The Arabian Gulf and Adjoining Areas. Published by Elsevier B.V., The etherlands. Alsharhan, A.S. (1989). Petroleum Geology of the United Arab Emirates. Journal of Petroleum Geology 12(3) Alsharhan, A.S. and asir, S.J.Y. (1996). Sedimentologi-cal and geochemical interpretation of a transgressive sequence: the Late Cretaceous Qahlah Formation in the western Oman Mountains, UAE. Sedimentary Geology 101, Abrol, I.P, Yadav, J.S.P and Massoud, F.I. (1988) Saltaffected soils and their management: Food and Agriculture Organization (FAO) Soils Bulletin 39, Rome, 131p. Environmental System Research Institute (ESRI) (1996). Using the ArcView spatial analyst, USA, 148p. Grant, F.S., and West, G.F. (1965). Interpretation theory in applied geophysics: McGraw Hill, ew York, 583p. International Water Consultants (IWACO) (1986). Drilling deep wells at various locations in the UAE. A study conducted by IWACO and funded by Ministry of Agriculture and Fisheries (MAF) in the UAE: The etherlands, 6, Groundwater development in the central agricultural region of the UAE, 117p. Japan International Cooperation Agency (1996) The master plan study on the groundwater resources development for agriculture in the vicinity of Al Dhaid in the UAE - A study prepared by JICA and funded by Ministry of Agriculture and Fisheries (MAF) in the UAE: Final Report. Lang, L., 1998, Managing natural resources with GIS, Environmental System Research Institute, Inc (ESRI), California. 117p. Rofail,., Zahraa, S. and Ibrahim, Y. (1998). Application of geographic information systems in natural resources management in arid zones: Water Resources Division (ACSAD/WS/R 122). The Arab Center for the Studies of Arid Zones and Dry Lands, Syria, 103p. United Arab Emirates ational Atlas (1993). Remote sensing center, UAE University, Al Ain, United Arab Emirates, 188p. World Health Organization (1984). WHO guidelines for drinking water quality: 1, Recommendations, Geneva, Switzerland, 130p. 434