Saq Aquifer, Saudi Arabia, 2008

INVESTIGATIONS FOR UPDATING THE GROUNDWATER MATHEMATICAL MODEL(S) OF THE SAQ AND OVERLYING AQUIFERS

MAIN REPORT

VOLUME 1

Abunayyan Trading Corporation BRGM Geosciences for a sustainable Earth

RabiI 1429 H March 2008 G

Investigations for Updating the Groundwater Mathematical Model(s) of the Saq and Overlying Aquifers

Volume 1 Main Report

NoteThe present document is part of the Draft Final Report of the study entitled Investigations for updating the groundwater mathematical model(s) of the Saq and overlying aquifers. The Draft Final Report is composed of the following thirteen (13) volumes:

Volume 1 Volume 2 Volume 3 Volume 4 Volume 5 Volume 6 Volume 7 Volume 8 Volume 9 Volume 10 Volume 11 Volume 12 Volume 13

Main Report Groundwater Management Groundwater Mathematical Modelling Data Management Domestic & Industrial Water Demand Irrigation Water Abstraction Hydrology and Groundwater Recharge Groundwater Quality Hydrogeology Water Point Inventory Pumping Tests Geophysical Logging Geology

Executive Summary The present document is Volume 1 out of 13.

Ministry of Water and Electricity Kingdom of Saudi Arabia

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Contents1 2 Introduction.......................................................................................................................... 1 Main findings........................................................................................................................ 2

2.1 GEOLOGICAL MODELLING ......................................................................................................................... 2 2.1.1 Methodology........................................................................................................................... 2 2.1.2 Horizons modelled.................................................................................................................. 3 2.1.3 Model contribution to the understanding of the structure........................................................ 4 2.1.4 Conclusions............................................................................................................................ 5 2.2 FIELD INVESTIGATIONS ............................................................................................................................. 8 2.2.1 Water-point inventory ............................................................................................................. 8 2.2.2 Pumping tests....................................................................................................................... 15 2.2.3 Geophysical logging ............................................................................................................. 17 2.3 HYDROGEOLOGY ................................................................................................................................... 20 2.3.1 History of groundwater use in Saq study area...................................................................... 20 2.3.2 Main hydrogeological units ................................................................................................... 20 2.3.3 Aquifer exploitation and water salinity .................................................................................. 21 2.3.4 Groundwater Levels in the Saq aquifer ................................................................................ 24 2.3.5 Groundwater Levels in the Kahfah aquifer ........................................................................... 28 2.3.6 Groundwater Levels in the Quwarah-Sarah aquifer ............................................................. 28 2.3.7 Piezometry of the Tawil aquifer ............................................................................................ 28 2.3.8 Groundwater levels in the Jauf, Jubah and Berwath aquifers............................................... 29 2.3.9 Groundwater levels in the Khuff aquifer................................................................................ 29 2.3.10 Piezometry of the STQ aquifer system ................................................................................. 30 2.4 GROUNDWATER QUALITY ........................................................................................................................ 32 2.4.1 Comparison between the data collected during the SAQ-1 and SAQ-2 projects.................. 32 2.4.2 Salinity distribution ............................................................................................................... 32 2.4.3 Chemical facies .................................................................................................................... 34 2.4.4 Distribution of the magnesium versus chloride ratio ............................................................. 34 2.4.5 Compliance of water quality with WHO guidelines ............................................................... 34 2.4.6 Possible impact of agriculture on water resource quality...................................................... 35 2.5 GROUNDWATER RECHARGE .................................................................................................................... 38 2.6 IRRIGATION-WATER ABSTRACTION ........................................................................................................... 40 2.7 DOMESTIC AND INDUSTRIAL GROUNDWATER USE....................................................................................... 44 2.7.1 Population ............................................................................................................................ 44 2.7.2 Industry................................................................................................................................. 45 2.7.3 Public groundwater supply in the study area ........................................................................ 45 2.7.4 Present domestic-water demand.......................................................................................... 46 2.7.5 Present industrial-water demand.......................................................................................... 47 2.7.6 Forecasting future domestic and industrial water demand ................................................... 48 2.7.7 Recommendations ............................................................................................................... 49 2.8 GROUNDWATER MATHEMATICAL MODELLING ............................................................................................. 50 2.8.1 Scope of work....................................................................................................................... 50 2.8.2 Conceptual groundwater model............................................................................................ 50 2.8.3 Groundwater model design and calibration .......................................................................... 50 2.8.4 Main results of the model calibration .................................................................................... 51 2.8.5 Impact of groundwater abstraction on leakage between aquifers and aquitards .................. 56 2.8.6 Conclusions.......................................................................................................................... 58

33.1 3.2 3.3 3.4

Present status of water resources................................................................................... 60BALANCE BETWEEN ABSTRACTIONS AND GROUNDWATER RECHARGE........................................................... 60 INFLUENCE OF THE WATER-TABLE DECLINE ON WATER-SUPPLY WELLS ......................................................... 64 EXISTING GROUNDWATER RESERVE......................................................................................................... 67 IMPACT OF ABSTRACTION ON GROUNDWATER QUALITY ............................................................................... 68

44.1 4.2 4.3 4.4

Constraints on groundwater use ..................................................................................... 70AQUIFER EXPLOITABILITY........................................................................................................................ 70 DECLINING GROUNDWATER LEVELS ......................................................................................................... 70 WATER QUALITY PROBLEMS.................................................................................................................... 72 PRESENCE OF RADIOELEMENTS .............................................................................................................. 74


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Strategies in groundwater management ......................................................................... 78

5.1 POSSIBLE LINES OF ACTION .................................................................................................................... 78 5.1.1 Quantitative aspects ............................................................................................................. 78 5.1.2 Qualitative aspects ............................................................................................................... 78 5.2 SHORT-TERM VERSUS LONG-TERM APPROACH .......................................................................................... 79 5.2.1 Short- to medium-term approach.......................................................................................... 79 5.2.2 Long-term approach ............................................................................................................. 79 5.3 MODELLING SCENARIOS......................................................................................................................... 80 5.3.1 Scope of predictive modelling scenarios .............................................................................. 80 5.3.2 Main results of the predictive scenarios................................................................................ 81 5.3.3 Simulation of reasonable groundwater exploitation conditions........................................... 88

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Conclusions and Recommendations .............................................................................. 92

6.1 CONCLUSIONS ...................................................................................................................................... 92 6.1.1 On the water use .................................................................................................................. 92 6.1.2 On the aquifers..................................................................................................................... 92 6.1.3 On the water levels............................................................................................................... 93 6.1.4 On the groundwater quality .................................................................................................. 93 6.1.5 On the exploitable reserves.................................................................................................. 95 6.1.6 On future trends ................................................................................................................... 95 6.2 RECOMMENDATIONS .............................................................................................................................. 98 6.2.1 To enhance the life-time of water supply infrastructures ...................................................... 98 6.2.2 To achieve reductions in groundwater abstractions ............................................................. 98 6.2.3 To improve the quality of available water ........................................................................... 100

Annex 1: Legal instruments to ensure a sustainable use of groundwater resources in France Annex 2: Plates


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List of figuresFigure 1. Geological map of the Saq study area (BRGM, 2005) ................................................. 2 Figure 2. Structure of the top of basement, view from the southeast (colour zone = 1,000 m) ... 3 Figure 3. Completed 3D geological model ................................................................................... 4 Figure 4. North-south cross-section along the 40E meridian (longitude of Sakakah) ................ 6 Figure 5. Location map of the inventoried water points ............................................................... 9 Figure 6. Location map of the inventoried MoWE wells ............................................................. 10 Figure 7. Location map of the inventoried observation wells ..................................................... 14 Figure 8. Location of the geophysically logged wells ................................................................. 18 Figure 9. Example of lithological interpretation .......................................................................... 19 Figure 10. Evolution of the volume of groundwater abstractions in the Saq study area............ 20 Figure 11. Evolution of the volume of groundwater abstractions per aquifer............................. 22 Figure 12. Depth of top of the Saq aquifer and location of wells tapping the aquifer ................ 23 Figure 13. Groundwater-head contour map for the year 2005 Saq aquifer ............................ 26 Figure 14. Piezometric series of the Al Mukharim well (1-Q-210-S / BU9210).......................... 27 Figure 15. Piezometric series at Rawd al Uyun (1-Q-136-S / BU9136)..................................... 27 Figure 16. Distribution of groundwater salinity within the Saq study area ................................. 33 Figure 17. TDS versus well depth within the Saq study area .................................................... 34 Figure 18. Location of water samples with radioisotopes exceeding WHO guidelines within the Saq study area....................................................................................................... 36 Figure 19. Schematic cross-section through the sedimentary cover of the Arabian Shield showing the different types of rainfall recharge and other components of the underground flow pattern. ............................................................................................ 39 Figure 20. Crop identification from satellite images ................................................................... 41 Figure 21. Crop-area variations derived from remote sensing and interpolation....................... 41 Figure 22. Irrigated area per region derived from remote sensing and interpolation................. 42 Figure 23. Irrigation water abstraction per crop type over the Saq study area from 1971 to2003 .......................................................................................................................... 42 Figure 24. Irrigation water abstraction per region over the Saq study area from 1971-2003 .... 42 Figure 25. Time variation of the irrigation-water abstraction in Mm3/a per region within the Saq study area ............................................................................................................. 43 Figure 26. 3D grid of the groundwater mathematical model ...................................................... 51 Figure 27. East-west cross section at the latitude of the Dead Sea .......................................... 52 Figure 28. Natural groundwater-head distribution and streamlines simulated in the Saq aquifer .......................................................................................................................... 52


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Figure 29. Simulated groundwater-head distribution and streamlines in the Saq aquifer for 2005 ............................................................................................................................. 54 Figure 30. Simulated groundwater-head decline in the Saq aquifer from 1960 to 2005............ 54 Figure 31. Simulated groundwater-head distribution and streamlines in the Tawil-Sharawra aquifer for 2005 ............................................................................................................ 55 Figure 32. Simulated groundwater-head decline in the Tawil-Sharawra aquifer from 1960 to 2005 ............................................................................................................................. 55 Figure 33. Time variation of vertical leakage between aquifers and aquitards (Vertical leakage and abstraction in Mm3/a) .............................................................................. 57 Figure 34. Groundwater abstractions in the Saq study area for different uses.......................... 60 Figure 35. Renewable groundwater resource in the Saq study area compared to the groundwater abstraction .............................................................................................. 60 Figure 36. Location of wells used for irrigation with tapped aquifer ........................................... 62 Figure 37. Simulated groundwater-head depletion in the Saq aquifer and location of watersupply wells (decline in metres from 1960 to 2005)..................................................... 63 Figure 38. Location of wells used for domestic water supply with tapped aquifer ..................... 65 Figure 39. Simulated groundwater-head decline between 1960 and 2005 in inventoried water-supply wells........................................................................................................ 66 Figure 40. Evolution of groundwater head in two observation wells in the Qassim region........ 71 Figure 41. Evolution of groundwater head in two observation wells in the Tabuk region .......... 71 Figure 42. Evolution of groundwater head in two observation wells in the Al Jawf region ........ 71 Figure 43. Occurrence of samples with a boron content exceeding WHO guidelines............... 73 Figure 44. Total radium content of Saq groundwater vs. water-level decline over the period 1960 2005 (Qassim and Hail regions) ..................................................................... 76 Figure 45. Simulated decline in the Saq aquifer from 2005 to 2055 (Scenario 2) ..................... 81 Figure 46. Piezometric evolutions in the Saq aquifer simulated in Al Qassim area (Scenario 2).................................................................................................................. 82 Figure 47. Simulated decline in the Tawil aquifer from 2005 to 2055 (Scenario 2) ................... 82 Figure 48. Optimized abstraction vs cut-off depth in the aquifer system taken as a whole (Scenario 4).................................................................................................................. 83 Figure 49. Optimized abstraction vs cut-off depth in the Saq aquifer and Al Qassim province (Scenario 4).................................................................................................................. 84 Figure 50. Zoning of the Saq aquifer for the siting of new domestic well fields (Scenario 5) .... 85 Figure 51. Zoning of the Tawil aquifer for the siting of new domestic well fields (Scenario 5) .. 85 Figure 52. Simulated drawdown in the Saq aquifer from 2005 to 2055 with current pumping rates and new well-fields in Saudi Arabia and Jordan (Scenario 3 - Simulation 1) .... 86 Figure 53. Global abstraction per crop from 1971 to 2005 and projection up to 2020 (Scenario 8-4) .............................................................................................................. 87 Figure 54. Reduction of the 2055 Saq simulated drawdown with Scenario 8-4 (MOA plan) ..... 87


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Figure 55. Irrigated areas within the Saq study area and limits of the most affected areas ...... 88 Figure 56. Qassim central area Baseline scenario and agricultural abstraction reduced by 50% .............................................................................................................................. 89 Figure 57. Qassim central area Baseline scenario and reduced agricultural abstraction scenarios...................................................................................................................... 90 Figure 1: French aquifers classified as ZRE in 2003, i.e. requiring lower abstraction volumes and a better management of the different uses (French Ministry for the Ecology and the Sustainable Development).............................................................. 108

List of tablesTable 1. Number of water points inventoried per province ............................................................... 11 Table 2. Main uses of the inventoried water points ........................................................................... 11 Table 3. Types of inventoried water points ......................................................................................... 11 Table 4. Classification of the inventoried water points according to tapped aquifer and static water level ................................................................................................................................ 12 Table 5. Inventoried well-depth statistics per aquifer ........................................................................ 13 Table 6. Aquifers monitored by the MoWE observation wells ......................................................... 13 Table 7. Results of the pumping test campaign ................................................................................. 16 Table 8. Evolution of groundwater abstraction for different aquifer units in the Saq study area ........................................................................................................................................... 22 Table 9. Species contents versus WHO guidelines and recommendations .................................. 35 Table 10. Public groundwater abstraction in the study area and comparison with other uses ... 46 Table 11. Present domestic water demand in the study area .......................................................... 47 Table 12. Present industrial-water demand in the study area ......................................................... 47 Table 13. Future domestic- and industrial-water demand in the Saq study area ......................... 48 Table 14. Present-day groundwater abstraction per Province......................................................... 61 Table 15. Immediate reduction required in agricultural groundwater demand to ensure a reasonable use of groundwater resources.......................................................................... 91


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List of platesPlate 1. Location map of the Saq study area ........................................................................... 112 Plate 2. Geological map of the Saq study area........................................................................ 113 Plate 3. Lithostratigraphical and hydrogeological units of the Saq study area ........................ 114 Plate 4. Aquifers tapped by inventoried wells .......................................................................... 115 Plate 5. Observation wells used for model calibration of the Northern and Western areas..... 116 Plate 6. Observation wells used for model calibration of the Qassim area.............................. 117 Plate 7. Simulated depth of the groundwater table in the Saq aquifer in 2005 in Qassim central area ................................................................................................................ 118 Plate 8. Simulated depth of the groundwater table in the Saq aquifer in 2030 in Qassim central area in the case of constant agricultural pumping at 2005 rates ................... 119 Plate 9. Simulated depth of the groundwater table in the Saq aquifer in 2055 in Qassim central area in the case of constant agricultural pumping at 2005 rates ................... 120 Plate 10. Simulated depth of the groundwater table in the Saq aquifer in 2005 in Tabuk area121 Plate 11. Simulated depth of the groundwater table in the Saq aquifer in 2030 in Tabuk area in the case of constant agricultural pumping at 2005 rates ....................................... 122 Plate 12. Simulated depth of the groundwater table in the Saq aquifer in 2055 in Tabuk area in the case of constant agricultural pumping at 2005 rates ....................................... 123 Plate 13. Simulated depth of the groundwater table in the Tawil aquifer in 2005 in Busayta area ............................................................................................................................ 124 Plate 14. Simulated depth of the groundwater table in the Tawil aquifer in 2030 in Busayta area (most probable scenario) ................................................................................... 125 Plate 15. Simulated depth of the groundwater table in the Tawil aquifer in 2055 in Busayta area (most probable scenario) ................................................................................... 126


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List of AbbreviationsAquifer Aquiclude A formation, group of formations, or part of a formation that is water bearing. The term aquiclude is used to designate a layer with such a low permeability that the underlying aquifer is completely sealed off. Such conditions do not occur in the Project area. Therefore, in this report the terms major aquitard and weak aquitard are used to describe the different confining layers. The term aquitard is used in hydrogeology to describe a layer with low or very low permeability. Digital Elevation Model Geo-Information System Global Positioning System metres above sea level Groundwater modelling software developed by BRGM. metres below ground level

Aquitard DEM GIS GPS m.a.s.l. MARTHE mbgl

MODFLOW Groundwater modelling software developed by USGS. MoWE MoA Ministry of Water and Electricity Ministry of Agriculture


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1 INTRODUCTIONThe groundwater resources of the Saq study area (Plate 1) are intensively exploited for drinking-water supply and irrigation (see Volumes 5 and 6 of the report); today, groundwater abstraction by far exceeds groundwater recharge (see Volume 7 of the report). However, the wells tapping the various aquifers of the region are unevenly distributed. As a result, water levels of some aquifers have dropped sharply over the past three decades in parts of the Saq study area, but show little or no decline elsewhere. A locally observed decline in water level is in itself not a measure for the degree of overexploitation of an aquifer, nor is the absence of a declining trend in another area a sign of sustainability of the groundwater reserves. Due to its very large lateral and vertical extent, the multi-layer aquifer system of the Saq study area is slow to react to any stresses imposed on it. Considering the complexity of the water balance of this multi-layer aquifer system, the degree of interaction between the various aquifers, and the relative importance of de-storage of water contained in aquifers and aquitards, it is understood that long-term predictions concerning the evolution of the aquifer system can most accurately be made by a groundwater mathematical model covering the full extent of the aquifer system. The construction and calibration of such a multi-layer aquifer model was therefore one of the main objectives of this project. Such a groundwater mathematical model can simulate realistically how the multi-layer aquifer system will react under different water-resource management scenarios, provided the model faithfully reproduces the system geometry and uses accurate data sets for its calibration. For this reason, the construction of the model was preceded by two main tasks: the construction of a 3D-geological model and the execution of a major field survey to accurately assess the present status of the water resources and to update the existing knowledge on the aquifer system. The present report is composed of 13 volumes. Volumes 4 to 13 each describe one of the tasks related to data collection and interpretation. Volumes 2 and 3 describe the construction of the groundwater mathematical model and the results of the various management scenarios simulated with the model. Volume 1 summarizes the main findings of the different project tasks and presents key data for a reflection on water-resources management within the Saq study area.


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2 MAIN FINDINGS2.1 Geological modelling

The goal of the geological modelling task was to construct a numerical geological model based on the most recent scientific concepts and field data on geology, in order to improve our understanding of the flow model for groundwater-resource assessment. Previous work included the earlier flow model of the Saq 1 project (BRGM, 1985), as well as the publications since then on the stratigraphy and structure of the northern Saudi Arabian and adjacent sedimentary basins. The progress of geological knowledge since 1980 is mainly based, for outcropping formations, on the regional geological mapping (Figure 1 and Plate 2) carried out by BRGM and DMMR (now the Saudi Geological Survey), and for the subsurface on the oil exploration carried out by Saudi Aramco in the Nafud basin as well as in Central Arabia.34 32 46

36

38

40

42

44

Wadi Sirhan graben

Al Qurayyat

Aruma Formation0 50

N

100 k ilom etre

200

30

Tawil Sandstone

Sakakah D aw m at-al-Jandal

Tabuk 28 Jubbah Baq'a

Taym a

H a'il

Qibah

HarratsAL U la 26

Saq SandstoneBuraydah U nayzah

Sajir

Ad D aw adim i 24

Figure 1. Geological map of the Saq study area (BRGM, 2005)

2.1.1

Methodology

The method for constructing the numerical geological model is based on the knowledge of basinstacking patterns, i.e. of how stratigraphic units and the main unconformity surfaces separating them are related to each other in a vertical and horizontal sense, as well as on the identification and validation of 3D-georeferenced data describing the structure of the aquifer systems from a geometric point of view. This work could be broken down into six steps. The first step delineated the horizontal and vertical extent of several groups of geometrically related geological formations (packages) separated by major unconformity surfaces or faults. This was done on the basis of chrono- and litho-stratigraphical concepts as well as of a rough conceptual model of the basin structure defining the rules of the mutual horizon relationships.Ministry of Water and Electricity Kingdom of Saudi Arabia 2



The second step was to set up a correspondence chart between lithostratigraphy and hydrostratigraphy, i.e. between geological formations and their aquifer or aquitard properties, looking for a separation or connection between the different hydrologic units. The third, most time-consuming, step was to collect the necessary 3D (x, y, z) information for defining both the shape of these horizons and the geometry of the layers throughout the project area and beyond. Such data originate from a great variety of sources, implying a major work of compilation, conversion to digital format, and georeferencing with GIS tools. The fourth step was to build several versions of the model using dedicated software (ArcGIS, GDM, EarthVision) and, through iterations, to correct and improve this model by adding new layers and new control points until the model appears geologically correct. The fifth step was the display of 3D views, cross sections, and isochoric maps. The sixth step was the calculation of the clipped output grids from the model and their export as x, y, z files toward the flow model. 2.1.2 Horizons modelled

All outcropping horizons were in priority matched to outcrops through a combination of the digital geological map compiled for this project (Plate 2) and of the digital elevation model (DEM), regardless of subsurface data. Within the stratigraphical sequence, 26 main lithological units were identified so as to separately represent all main hydrogeological units (both aquifers and aquitards), considering at the same time the different stratigraphical unconformities present within the sequence. Plate 3 presents the lithostratigraphical column with the 26 identified geological units. The constructed 3D geological model is shown in Figure 2 and Figure 3.

Figure 2. Structure of the top of basement, view from the southeast (colour zone = 1,000 m)


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Figure 3. Completed 3D geological model 2.1.3 Model contribution to the understanding of the structure

Great progress has been made by constructing the 3D model and using the 3D modeller. The first improvement was to identify properly and separately the structure of the Wadi Sirhan graben, which deeply cuts into the Nafud basin following the strike of the Basement edge from Central Arabia. This structure has been identified as mainly resulting from Hercynian uplift (several thousands of metres), followed by deep truncation especially in the northwest. During a second stage, this structure was cross-cut by the Wadi Sirhan (Azraq) Graben, which complicates our understanding of the final geological result. One of the main effects of these cumulative movements has been the rapid wedging-out of the Devonian succession and the unconformable contact of a thick Cretaceous-Tertiary succession over Early Paleozoic rocks. However, at depth on the Jordanian side, a sub-continuous series from Triassic to Tertiary persists. Due to the great depths of the basin, the existence of some of these complications (e.g. Triassic rocks) has little or no effect on the groundwater management of shallower aquifers. Looking in particular at the aquifer units, a north-south section along the 40E meridian (Figure 4) illustrates the N-S wedge shape of the succession. All Early Paleozoic aquifers are present. At great depth, the Cambro-Ordovician (Siq+Burj+Saq) appears to be very thick. In spite of changing facies (prograding delta front), the Sharawra Member (orange) is here considered as partly sandy and connected to the Tawil Formation. The Jauf Formation, the hydraulic behaviour of which is complex, forms a vertical seal to the Jubah Formation, although it is water-bearing as well. The system is capped by the Maastrichtian-to-Eocene succession. From west to east, the continuity of the aquifer systems can be disrupted by the down-thrown of faults on both sides of the graben. In particular, the Saq and Qasim aquifer systems (Plate 3) come in contact with impervious layers of the Basement and the Qusaiba shale. In the northwest,Ministry of Water and Electricity Kingdom of Saudi Arabia 4



the Paleozoic sequence is drastically truncated and the Saq aquifer becomes disconnected at the bottom of the graben. The Cretaceous-Eocene becomes the main aquifer in the graben, and faultrelated vertical connections are possible. On the eastern side, the broad Mesozoic-Cainozoic wedge opens in Central and Eastern Arabia towards the east. In Central Arabia (south of the Qassim area, in the Al Faydah and Ad Dawadimi quadrangles) the Saq and Qasim formations pinch out against basement paleo-highs. Here, the Qusaiba shale is reduced or absent. 2.1.4 Conclusions

Considering groundwater-flow patterns within the Saq study area, the following items are emphasized: - The Saq Sandstone is a huge aquifer compared to the other ones. - The Hanadir Member forms a continuous seal. - The Qasim aquifers develop good reservoir properties where the Sarah Formation is thick and connected to the Kahfah Member by erosion of the Raan Member. - The Sharawra Member and Tawil Formation will be merged, but a differential permeability should be used to account for the variable and less-permeable properties of the Sharawra Member. In the first Saq project, this member was merged with the Qusaiba Member, which is probably true at depth in the north, but not closer to the outcrop. - Differing from the first Saq project, the Jauf Formation should be considered as a semi-pervious system including some water resources, but acting as a confining unit between the Tawil and Jubah formations. - The Sakaka Sandstone (obsolete term) is now known as the Devonian Jubah Formation, which is a good reservoir. - The Berwath Formation acts as local screen or seal, the extent of which is largely assumed. Its role is completed by the effect of the Sudair Shale and of the basal Wasia Formation, both unconformably overlying the Jubah Formation sandstone. - One of the most important innovations of the flow model is a better knowledge of the basement structure, of the Pre-Unayzah unconformity (PUU), and of the Wadi Sirhan (Azraq) Graben in terms of their geometric and connecting implications.


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(m.a.s.l.)

Aquifers cross-section x=505,000 mLate Cretaceous unconformity Harrats

(Qusa iba)

Pre-Qusaiba aquifers

W. Sirhan (Azraq) graben Azraq) Pre-Hercynian, postQusaiba aquifers

(m)

Figure 4. North-south cross-section along the 40E meridian (longitude of Sakakah)

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2.22.2.1

Field investigationsWater-point inventory

The purpose of the water-point inventory was to collect basic data for the updating of our information on the status of groundwater resources within the Saq and overlying aquifers. Because these objectives relate to updating different types of hydrological information, the water-point inventory of the Saq project was the corner stone for several of the other project tasks. For example, the information gathered during the water-point inventory was used for defining the groundwater-sampling program and also, within previously identified areas, for selecting wells suitable for geophysical logging and wells amenable to test pumping. Moreover, the inventory has provided essential data on irrigation practices by the farmers, which is necessary for assessing current water-abstraction rates for irrigation. Finally, the data collected during the water-point inventory were the major source of up-to-date information on hydrogeology, hydrogeochemistry and water consumption. This, in turn, allowed identifying trends in the quantitative and qualitative aspects of the water resources of the Saq study area, through comparison with literature and historical data. A total of 5,969 water points was inventoried, covering all parts of the Saq study area where wells are present, and covering all the aquifers. With all drinking-water and groundwater monitoring wells being included in the inventory, the collected data provide a complete and comprehensive picture of the current status of groundwater resources within the study area (Figure 5 and Figure 6).

Geographical data The 5,969 inventoried water points in the field database comprise 5,745 water points visited in the study area and 211 water points identified outside it. Depending on the estimate used for the total number of wells in the area, this number of 5,969 represents between about 40% (for the lower estimate) and 50% (higher estimate) of the total wells existing in the study area. Two additional water points (TB9800 and TB9801) were added to the project database from the literature. Although not found during the field inventory, they are known to exist from the MoWE archives and are of specific interest because of being associated with piezometric data gathered by MoWE. Note that among the 5,747 water points within the project area, 733 are under the responsibility of MoWE.


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36 32

38

40

42

44 32

30 300 20 Kilometres 40

28

28

LegendProvince limit Governorate or district limit Limit of Saq study area

Use of the inventoried water pointsDomestic water supply Irrigation

26

26

Observation well Others / Not known

0

50

100 Kilometres

200

36

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44

Figure 5. Location map of the inventoried water points

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36 32

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44 32

30 300 10 Kilometres 20

Legend28 28Province limit Governorate or district limit Limit of Saq study area

Use of the inventoried MoWE water pointsDomestic water supply Irrigation

26

26

Observation well Others / Not known

0

50

100 Kilometres

200

36

38

40

42

44

Figure 6. Location map of the inventoried MoWE wells

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The water-point locations have been classified according to the Province limits determined by the Ministry of Planning (see Table 1). Figure 5 shows the unequal geographical distribution of the inventoried water points over the total project area, with most of them being concentrated in the Al Qassim, Al Jawf, Tabuk and Riyadh provinces. This situation reflects the actual distribution of the wells drilled over the Saq study area. Table 1. Number of water points inventoried per province Province Al Jawf Al Madinah Al Qassim Ha'il Northern Border Riyadh Tabuk TOTAL Number 2,129 196 1,421 469 91 742 699 5,747 All wells Percentage 37.0% 3.4% 24.7% 8.2% 1.6% 12.9% 12.2% 100.0% MoWE Wells only Number Percentage 101 13.8% 10 1.4% 271 37.0% 94 12.8% 81 11.1% 77 10.5% 99 13.5% 733 100.0%

Use and nature of the water points Table 2 and Table 3 show various general statistics regarding the inventory. Table 2 breaks down the inventoried water points into their main uses: i.e. domestic water supply (including well-fields), observation wells, and irrigation, livestock and industry wells. The MoWE wells associated with irrigation correspond to municipal wells used for watering public gardens (Figure 6). If several uses are made of a single borehole, only the main one is indicated. Table 2. Main uses of the inventoried water points Well use Domestic water supply Irrigation Livestock Industry Observation well Not known TOTAL All wells Number Percentage 573 10.0% 4,972 86.5% 23 0.4% 16 0.3% 115 2.0% 48 0.8% 5,747 100.0% MoWE Wells only Number Percentage 564 76.9% 70 9.5% 0 0.0% 0 0.0% 91 12.4% 8 1.1% 733 100.0%

Table 3 presents the nature of the water points: i.e. drilled well, dug well, drilled well within a dug well (hand-dug well later deepened by drilling), open hole (non-equipped drilled well: i.e. no casing, no screen), or spring. Table 3. Types of inventoried water points Type of water point Drilled well Drilled well inside dug well Dug well Open hole Spring TOTAL All wells Number Percentage 5,704 99.3% 1 0.0% 14 0.2% 27 0.5% 1 0.0% 5,747 100.0% MoWE Wells only Number Percentage 727 99.2% 0 0.0% 5 0.7% 1 0.1% 0 0.0% 733 100.0%


11



Hydrogeological data The tapped aquifer has been identified for 5,060 (86.4%) of the water points; identification was not possible for the remaining wells due to their unknown depth and/or to the absence of a general trend for a specific water-point use within the area. It should be noted that some geological layers, generally considered as aquitards, could be tapped locally due to a spatial heterogeneity of their lithology. Saq Sandstone is by far the main aquifer tapped in the area; it accounts for almost half the inventoried wells (47.3%). However, the targeted aquifers do vary from one province to another. For example, the Saq aquifer is tapped by 90% or more of the inventoried water points in the Tabuk, Hail and Riyadh provinces, and is not tapped at all in the Northern Border and Al Jawf provinces. One particular point of concern within the Saq study area is the considerable amount of wells supposedly tapping more than one aquifer. Out of all the water points visited in the field, the static water level (SWL) is known, through measurement, estimation, or information given by the owner, for 4,728 (82.3%) of them. The SWL ranges from flowing water at the surface (artesian) to 310 m below ground level (mbgl) as in ArAr. Table 4 shows the water points classified according to their SWL, with 78% ranging between 50 and 150 mbgl. The well depth is known for 4,902 of the inventoried water points, i.e. 85.3% of those visited. Table 5, presenting the mean, minimum and maximum well depths per aquifer (along with the standard deviation), shows for example that the Berwath aquifer exploited in the far northeastern part of the study area is on average tapped by deep wells with little variation around the mean depth. Other aquifers, such as the Jubah and Tawil aquifers, show a much larger range of exploitation depth.

Table 4. Classification of the inventoried water points according to tapped aquifer and static water level Aquifer name Alluvium Basalt Secondary-Tertiary-Quaternary Sudair Khuff Unayzah Berwath Jubah Jauf Tawil Sharawra Quwarah-Sarah Kahfah Saq Saq & Alluvium Basement Not known TOTAL 200 541 18 8 2 3 5 50 422 10 11 88 866 161 2185 102 2 18 1 1 17 439 2 9 50 755 97 1493 1 4 1 1 12 1 1 2 292 2 32 349 4 15 1 1 1 14 5 48 7 Total 64 1 777 27 36 6 7 47 134 891 29 46 156 2132 42 3 330 4728


12



Table 5. Inventoried well-depth statistics per aquifer Aquifer Alluvium Basalt Secondary-Tertiary-Quaternary Sudair Khuff Unayzah Berwath Jubah Jauf Tawil Sharawra Quwarah-Sarah Kahfah Saq Saq & Alluvium Basement Not known All aquifers Number of Mean depth Minimum wells in m depth in m 63 81 6 1 28 28 974 265 15 28 184 80 50 226 30 7 189 90 9 472 350 55 334 100 147 265 40 908 364 100 29 179 95 52 241 50 171 345 30 2358 479 50 42 74 40 2 215 180 6 392 40 4896 246 6 Maximum Standard depth in m Deviation (m) 200 30 28 1451 131 470 105 700 153 400 116 600 91 1500 263 1500 309 2510 149 450 95 700 206 1100 228 2400 295 120 19 250 49 960 353 2510 258

Observation wells Of the 115 observation wells (Figure 7), 91 are MoWE wells most of which, as shown in Table 6, record the water-level fluctuations in the Saq Sandstone. Table 6. Aquifers monitored by the MoWE observation wells Aquifer Secondary-Tertiary-Quaternary Khuff Jubah Jauf Tawil Kahfah Saq TOTAL Piezometers 11 2 2 3 7 10 56 91

Inventory of the SAQ-1 Project hydroclimatological stations The 1985 Saq-1 project led by BRGM included the installation of 29 hydroclimatological stations: 9 runoff (hydrological) stations and 20 meteorological (climatological) stations. All locations given in the 1985 report were visited in the field. Of the nine hydrological stations installed during the Saq-1 project, three were either not found (probably destroyed or dismantled) or out of order. Of the remaining six, none were operated when visited in the field. Nevertheless, they could still be operational if equipped with a recorder and/or in the presence of a technical operator during flood events, whenever the measurement section has not been by-passed.


13



36 32

38JA9088

40

42

44 32JA0650# # JA0645

JA0596 JA5013# # # # #

30TB9097 TB9098 TB9107 TB9112 TB9108 TB9405 TB9173 TB9114 TB9553 TB9072 TB9071 TB9111 TB9152

#

JA9651# #

JA9091 JA0630

JA0578

JA5009# #

JA9089 JA9139# # # # #

JA0608

JA9625

JA0583

JA0564 JA9090 JA9143 JA0306

JA9623 JA9624

JA9627 JA9093# # # ### ## # # #

JA9011

JA9094

JA5002#

JA9146#

JA5003

TB9099

30JA0151 JA9612 JA9145#

0JA5000

6 Kilometres

12

TB9109 TB9077 TB9800

JA9092

JA9147

LegendTB9158 TB9178 TB9116 TB9070 HA9130 HA9139 BU0207 HA9056 TB9075 TB9117 HA9054 TB9162 TB9163 TB9801 TB9160 TB9159 TB9161 HA9055 HA9053 BU0205 BU0206 BU0245 BU9135 BU9210 AW9650 BU9134 BU9159 BU9204 BU9202 BU9163# #

Province limit Governorate or district limitBU9053 BU0252 BU0247 BU9164

TB9115

28

BU0260 BU0246

28#

Limit of Saq study area

Tapped aquiferNot known Sec. Tertiary Quater. Khuff Jubah Jauf#

BU1150

BU9205 BU9136 BU9203 BU9734 BU9139 BU9575 BU9087

BU9157#

26

BU9158 BU9097

AS9036 BU9094 BU9100 BU9098 BU9000

26

BU9099 BU9137 BU9065 BU9052 BU9060 BU9043 BU9187 BU9013 0 BU9014

Tawil Kahfah Saq50 100 Kilometres 200

BU9070 BU9162

36

38

40

42

44

BU9086

Figure 7. Location map of the inventoried observation wells14



Of the 20 meteorological stations installed during the Saq-1 project, none were operated when visited in the field. No instrumentation was found at eight of the sites, this having probably been destroyed or buried under sand dunes (see HC station TB201) after more than 20 years. The other 12 sites are still equipped, but the equipment suffers from aging. 2.2.2 Pumping tests

The Consortium has performed pumping tests in 11 wells. Nine of these wells tap the Saq aquifer and the two other ones concern the Tawil and Neogene formations. Two types of tests were performed: - Step-drawdown tests for the assessment of well characteristics; - Constant-discharge tests for assessing the local hydrodynamic parameters of the tested aquifer. The tested wells tap various geological formations, including the Saq, Tawil and Neogene aquifers. Nine of these wells are used for drinking-water supply to the population. Among the tested wells, one was available with an observation well. The exploitation pumps were removed by MoWE in order to allow the installation of test pumps by the Consortium. The pumping program was completed as planned, except that the duration of some constantdischarge tests had to be reduced to restore water supply to the population. Step-drawdown tests were used to determine the hydrodynamic characteristics of the wells. The data recorded during constant-discharge tests were used for assessing the local hydrodynamic parameters of the tested aquifers. Data from one additional well have also been interpreted. These data were handed over by MoWE; they are related to a well tapping the Saq aquifer along the international border with Jordan. This well is provided with two observation wells. The recorded data were then used for modelling radial flow by means of different models, such as the Jacob, Theis, Hantush-Jacob, Boulton-Streltsova, and Warren-Root approaches. The results are shown in Table 7.


15



Table 7. Results of the pumping test campaign

16



2.2.3

Geophysical logging

Twenty-five boreholes were investigated with geophysical methods. This involved the use of nine geophysical probes for measuring different parameters relative to borehole geometry, the characterization of lithology, water quality, and radioactive contamination of groundwater. The nine probes were the (1) Three-Arm Caliper/CCL, (2) Cement Bond Log probe (CBL), (3) Flowmeter probe, (4) Sidewall Density (Gamma-Gamma) probe, (5) Dual Neutron probe, (6) Electric probe, (7) Gamma Spectrometry probe, (8) Temperature/Conductivity probe, and (9) Borehole Video Camera. The 25 wells, each of which was visited with MoWE engineers before approval for logging, were selected according to one or more of the following criteria: - Geological and geographical interest, with a spatial distribution covering the project area (Figure 8); - Accessibility (most of the wells were not equipped with a pump); - Recently drilled, so that the inside of the well could be visually checked using the video camera probe; - Radiometric interest: the Gamma Spectrometry probe (also called the Spectral Gamma probe) is a specific instrument for determining the presence of radionuclides; spectral gamma can distinguish uranium-, thorium- and potassium-isotope signatures within natural radioactivity. It is well known that the Saq Sandstone contains thin shale interbeds. These thin layers show high gamma-radiation levels on the geophysical logs and thus may, to a certain degree, be responsible for radium contamination in the water. The level of contamination will depend on many factors, such as the layer's thickness, its radio-isotope concentration, the type of environment (reducing or oxidizing), etc. In some wells (e.g. the Baqa Well), the high-radiation shaly zone is located at the bottom of the well; in others (e.g. the Midhnab Well), shaly layers with high radiation levels occur at intervals throughout the intersected formation. A second source of natural radioactivity seen on the geophysical logs is the Hanadir Member (or Hanadir Shale) of the Qasim Formation. This formation is not everywhere cased in the wells. For example, the Uyun Al-Jiwa Well shows a high radiation zone of partly uncased Hanadir Shale. According to laboratory analyses, this well shows a high level of contamination. A third possible source of natural radioactivity is the silty sandstone at the base of the Kahfah Member of the Qasim Formation (previously Lower Tabuk) which shows high radiation levels, especially in the Qassim region. As shown by the spectral-gamma log, the predominant radioactive element in the rock is thorium, ahead of uranium. This could result in higher concentrations of the radium-228 isotope, derived from thorium, compared to radium-226 derived from uranium. Figure 9 shows two gamma-ray peaks. The first, around 945 m depth, correlates with a decrease in the neutron logs indicating a lower effective porosity, a decrease in density and a decrease in resistivity. The interpretation deriving from these observations is the likely presence of a clay (shale) layer. The second gamma-ray peak (or series of peaks) does not seem to correlate with any other log. Interpreting this section as a clay (shale) layer is therefore much less obvious. This example shows that: - Several logs are needed to properly interpret a log chart and; - Natural radioactivity in the Saq Sandstone may not systematically be associated with clay, but may also be linked to sandstone layers containing a degree of silt/clay.


17



32 32 32 32 32 32

Al Qurayyat Al Qurayyat Al Qurayyat Al Qurayyat Al Qurayyat Al QurayyatQU9 00 9 QU9 00 9 QU9 00 9 QU9 00 9 QU9 00 9 QU9 00 9

Ar'Ar Ar'Ar Ar'Ar Ar'Ar Ar'Ar Ar'ArAR91 42 AR91 42 AR91 42 AR91 42 AR91 42 AR91 42

QU9 04 3 QU9 04 3 QU9 QU9 04 3 JA951 3 JA951 3 JA951 3 JA951 3 JA951 3 JA951 3

30 30 30 30 30 30

QU9 55 3 QU9 55 3 QU9 55 3 QU9 55 3 QU9 55 3 QU9 55 3

Sakakah Sakakah Sakakah Sakakah Sakakah SakakahJA951 9 JA951 9 JA951 9 JA951 9 JA951 9 JA951 9

T B90 97 T B90 97 T B90 97 T B90 97 T B90 97 T B90 97

T B90 99 T B90 99 B90 99 T B90 99 TB90 99 TB90 99

T B90 98 T B90 98 T B90 98 T B90 98 T B90 98 T B90 98 T B94 02 T B94 02 T T B94 02 T B94 02 T T B94 01 T B94 01 T B94 01 T B94 01 T B91 20 T B91 20 T B91 20 T B91 20 T B91 20 T B91 20

Tabuk Tabuk Tabuk TabukT B90 72 T B90 72 T B90 72 T B90 72 T B90 72 T B90 72

T B91 15 T B91 15 T B91 15 T B91 15 T B91 15 T B91 15 T B92 47 T B92 47 T T B92 47 HA90 39 HA90 39 HA90 39 HA90 39 HA90 39 HA90 39 T B91 17 T B91 17 T B91 17 T B91 17 T B91 17 T B91 17

28 28 28 28 28 28

Baq'a Baq'a Baq'a Baq'a Baq'a Baq'aBU91 38 BU91 38 BU91 38 BU91 38 BU91 38 BU91 38 HA00 26 HA00 26 HA00 26 HA00 26 HA00 26 HA00 26

Tayma Tayma Tayma TaymaHA90 58 HA90 58 HA90 58 HA90 58 HA90 58 HA90 58

Ha'il Ha'il Ha'il Ha'il Ha'il Ha'il

Al' Ula Al' Ula Al' Ula Al' Ula Al' Ula Al' Ula

BU90 03 BU90 03 BU90 03 BU90 03 BU90 03 BU90 03 BU94 58 BU94 58 BU94 58 BU94 58 BU94 58 BU94 58

Buraydah Buraydah Buraydah Buraydah Buraydah Buraydah 26 26 26 26 26 26 Unayzah Unayzah Unayzah Unayzah Unayzah Unayzah

BU90 61 BU90 61 BU90 61 BU90 61 BU90 61 BU90 61 BU93 28 BU93 28 BU93 28 BU93 28 BU93 28 BU93 28 BU90 71 BU90 71 BU90 BU90 71

LEGENDw ell used for geophysical logging major tow n minor tow n0 0 0 0 0 0 10 0 10 0 10 0 10 0 10 0 10 0 Ki lo metre s Ki lo m etre s Ki lo m etre s Ki lo metre s Ki lo m etre s Ki lo m etre s 20 0 20 0 20 0 20 0 20 0 20 0

As Sajir As Sajir As Sajir As Sajir As Sajir As Sajir

Ad Duw adami Ad Duw adami Ad Duw adami Ad Duw adami Ad Duw adami Ad Duw adami

boundary Saq study area 24 24 24 24 24 24 35 35 35 35 35 35 37 37 37 37 37 37 39 39 39 39 39 39 41 41 41 41 41 41 43 43 43 43 43 43 45 45 45 45 45 45

Figure 8. Location of the geophysically logged wells18



Name TB9098 Neutron [Near] DEPTH (M)0

Gamma Ray50 100

0 1500 100

500 200

1000 300 400

1500

Density bed res.25000 30000 350000

Density long spac. Density high res.2500 5000 7500 10000

Res. short Res. long1000.0

Fl. cond. (S/cm) Temp. (C)40.0 50.0 51.0

Neutron [far]50015000 20000

935 940 945 950 955 960 965 970 975 980 985 990 995 1000 1005 1010 1015 1020 1025 1030 1035 1040 1045

Figure 9. Example of lithological interpretation (for explanation see text above)


19



2.32.3.1

HydrogeologyHistory of groundwater use in Saq study area

Figure 10 presents the evolution of groundwater abstraction in the Saq study area compiled from different sources. Because of the predominant position of the region in the past and the availability of historical data, separate figures are also provided for the Qassim region. It can be seen that groundwater abstraction remained marginal till the 1960s. A rapid growth in the abstracted volume occurred in the Qassim region between 1966 and 1984, which continued between 1984 and 2005. In other regions, the growth of the abstracted groundwater volume was moderate till 1984, but then was multiplied by ten during the past 20 years. The total volume of groundwater annually abstracted in the Saq study area in 2005 (8,727 Mm3/a) equals a water column of 24 mm covering the entire Saq study area (~370,000 km). This is more than five times higher than the few mm of recharge occurring during the same period and thus is not sustainable. Considering that groundwater abstraction is concentrated in the main irrigated areas representing not more than 10% of the Saq study area, it is obvious that in these regions the ratio between groundwater abstraction and groundwater recharge is over 50:1.10000 in total Saq study area (Mm3/yr) 9000 8000 Groundwater abstraction (Mm3/yr) 7000 6000 5000 4000 3000 (BRGM, 1985) 2000 1000 0 1920 in Qassim region (Mm3/yr) (this study)

(Parsons Basil, 1968)

1930

1940

1950

1960 year (G)

1970

1980

1990

2000

2010

Figure 10. Evolution of the volume of groundwater abstractions in the Saq study area (source between brackets)

2.3.2

Main hydrogeological units

Plate 3 shows, besides the lithostratigraphical and geological logs, the main hydrogeological units. In the groundwater model, three groups can be distinguished among the 13 model layers. These groups are Aquifers, Aquitards that are locally aquifers, and Aquitards. Aquifers There are seven main aquifers or aquifer groups, from bottom to top: Saq Sandstone; Kahfah sandstone;


20



Quwarah - Sarah sandstones; Sharawra and Tawil sandstones; Jubah sandstone; Khuff limestone; Secondary (Mesozoic) -Tertiary - Quaternary (STQ) sandstone and limestone.

Aquitards that are locally aquifers Two layers act regionally as aquitards, but contain units that are locally exploited as aquifer: Jauf limestone and sandstone; Unayzah and Berwath sandstones.

Aquitards Four layers have been identified as aquitards. The term aquitard is used in hydrogeology to describe a layer with low or very low permeability. The term aquiclude is used to designate a layer with such a low permeability that the underlying aquifer is completely sealed off, but such conditions do not occur in the Saq study area. Therefore, in this report the terms major aquitard and weak aquitard are used to describe the different confining layers. The following aquitards play a role in the underground flow pattern (from bottom to top): Hanadir shale; Raan shale; Qusaiba shale; Sudair shale.

2.3.3

Aquifer exploitation and water salinity

The aquifers encountered in the Saq study area do not all have the same regional extension and, depending upon their presence, depth and also their salinity, at most locations in the Saq study area only one or at most two aquifers are exploited. Plate 4 shows the inventoried (5,060 out of nearly 6,000) wells for which the tapped aquifer was determined. From this plate it can be seen that in every region one aquifer is predominantly exploited. Due to their differences in thickness, extension, hydraulic characteristics and water quality, some aquifers have a much larger area of exploitation than others. Table 8 and Figure 11 show the abstracted groundwater volumes for the main aquifer units for 1984 (BRGM, 1985) and 2005 (this study). It can be seen that the Saq Sandstone is by far the most exploited aquifer, accounting in 2005 for almost two-thirds of all abstraction within the Saq study area. The other main aquifer is the Tawil, accounting for 10% of the abstractions. The Secondary-Tertiary-Quaternary aquifer complex accounts for nearly 16% of abstractions, but this unit combines a group of independent aquifers and not a single hydrogeological unit. Saq aquifer Figure 12 shows the extent and depth of the Saq aquifer and the location of the inventoried wells tapping the aquifer. The aquifer has extensive outcrop areas along the boundary with the Arabian Shield in the west, where it receives some recharge, albeit much less than the volumes abstracted from the aquifer. East of the outcrops the aquifer is present below almost the entire study area, except for a small area northeast of Buraydah. In the northeastern part of the study area the aquifer is too deep to be exploited.


21



Table 8. Evolution of groundwater abstraction for different aquifer units in the Saq study areaAquifer Model layer 1984 (Mm3/a) 2005 (Mm3/a) % of total in 2005

STQ Khuff Jubah Jauf Tawil Quwara Kahfah Saq Total

1 3 5 6 7 9 11 13

141 87 86 9 39 90 187 1427 2064

1388 159 12 158 876 128 298 5708 8727

15.9 1.8 0.1 1.8 10.0 1.5 3.4 65.4 100.0

6000 1984 5000 2005

groundwater abstraction (Mm3/yr)

4000

3000

2000

1000

0 Saq Kahfah Quwara Tawil Jauf Jubah Khuff STQ

Figure 11. Evolution of the volume of groundwater abstractions per aquifer A total of 2,434 wells tapping the Saq aquifer has been inventoried. Most are located on outcrops in the Qassim, Hail and AlUla regions, or in the confined parts of the aquifer in the Qassim, Hail, Tayma and Tabuk regions. In the Qassim region, many wells tap the Saq aquifer near or below 1,000 m depth, whereas in the Tabuk region few wells reach such a depth. The central part of the outcrop area, south of Tayma, is fairly unexploited as are those parts of the aquifer covered by the sand dunes of the Nafud desert. For those wells where physico-chemical parameters could be measured in the field, the electrical conductivity (EC, expressed in S/cm) is shown on Figure 12. In the Qassim region, salinity levels are high (EC >2,000 S/cm) in unconfined parts of the aquifer, especially near the main wadi channels such as Wadi Ar Rumah. High salinity levels can be explained by the dissolution of salts through percolating surface water. Salt can accumulate in wadi channels in areas where runoff waters stagnate, or in sabkhas, areas where exfiltrating groundwater exists or existed in the past.


22



32 32 32 32 32 32

Al Qurayyat Al Qurayyat Al Qurayyat Al Qurayyat Al Qurayyat Al Qurayyat Ar'Ar Ar'Ar Ar'Ar Ar'Ar Ar'Ar Ar'Ar

LEGENDmajor tow n minor tow n highw ay main road minor road Saq area

30 30 30 30 30 30

Sakaka h Sakaka h Sakaka h Sakaka h Sakaka h Sakaka h

T ab uk T ab uk T ab uk T ab uk T ab uk T ab uk

28 28 28 28 28 28T aym a T aym a T aym a T aym a T aym a T aym a Ha'i lll Ha'i Ha'i Ha'i lll Ha'i Ha'i

Baq 'a Baq 'a Baq 'a Baq 'a Baq 'a Baq 'a

Al ''''''Ul a Al Ul a Al Ul a Al Ul a Al Ul a Al Ul a

0

20

40

K il ometres

Burayd ah Burayd ah Burayd ah Burayd ah Burayd ah Burayd ah Una yza h Una yza h Una yza h Una yza h Una yza h Una yza h

26 26 26 26 electrical conductivity measured in w ells tapping Saq aquifer (S/cm) 5 000 < 2 000 - 5 000 1 500 - 2 000 1 000 - 1 500 500 - 1 000 0 - 500 w ell w /out EC measurement depth top Saq aquifer (m bgl) outcrop 0 - 1000 1000 - 2500 > 2500As Saj iiirrr As Saj As Saj As Saj iiirrr As Saj As Saj

0 0 0

10 0 10 0 10 0 Ki lo m etre s Ki lo m etre s Ki lo m etre s Ki lo m etre s Ki lo m etre s Ki lo m etre s

20 0 20 0 20 0

Ad Duwa dam iii Ad Duwa dam Ad Duwa dam Ad Duwa dam iii Ad Duwa dam Ad Duwa dam

24 24 24 24 24 24 35 35 35 35 35 35 37 37 37 37 39 39 39 39 39 39 41 41 41 41 41 41 43 43 43 43 43 43 45 45 45 45 45 45

Figure 12. Depth of top of the Saq aquifer and location of wells tapping the aquifer23



In the Tayma region the salinity of the phreatic parts of the aquifer is lower, indicating that different recharge mechanisms may prevail here. The EC is generally lower (1,000>EC>500 S/cm) in the confined parts of the Saq aquifer. In the absence of mechanisms that could explain the reduction of salt levels, the likely explanation for these low EC values is that the waters stored in the deeper part of the aquifer result from recharge that occurred under more humid climatic conditions, like those during the mid-Holocene up to 4,000 years BP. Comparatively high EC values in confined parts of the Saq aquifer, such as in the region north of Buraydah, may be the result of mixing of waters in wells tapping both Saq and Kahfah aquifers. Details of other aquifers are discussed in Volume 9 of the report. 2.3.4 Groundwater Levels in the Saq aquifer

The groundwater-head-contour or piezometric map of the Saq aquifer has been drawn based on water levels recorded in 183 wells. These wells are not equally distributed over the aquifer, as information is concentrated near towns and irrigated areas. Moreover, despite its presence below almost the entire project area, the water levels are not known where its depth is below 2,000 m. For this reason, the piezometric map was drawn using plain contour lines wherever the water-table elevation is known with a certain degree of reliability (sufficient data both in quantity and quality), but using dashed lines where this elevation is estimated or extrapolated. Within the Saq study area, two main regions can be distinguished based on the groundwater flow directions: a) the Qassim-Hail region with a natural flow direction towards the northeast, and b) the Tabuk-Tayma region where the main flow direction is northward.

a) In the Qassim-Hail region, the Saq water table culminates at an elevation above 700 m.a.s.l. north of Hail, as well as in the extreme south, east of Ad Dawadimi (Figure 13). A particular situation is encountered along Wadi ar Rimah, where the alluvial aquifer appears to be in contact with the Saq aquifer. The groundwater in the alluvial aquifer is highly mineralized and where Wadi ar Rimah crosses Saq outcrops the groundwater in the Saq aquifer also shows high conductivity, indicating downward percolation of water from the alluvial aquifer. It is likely that an inverse situation existed before the intense agricultural development occurred. Until the late 1970s, the piezometric levels in the Saq aquifer near Wadi ar Rimah were higher than the ground elevation at the bottom of the deep valley created by the wadi. Groundwater flowed from the Saq Sandstone to the alluvial aquifer and this seepage resulted in the creation of sabkhas that can be found in the vicinity of Al Badai where Saq sandstone dips below Hanadir shale. Eastward, the Saq water table rapidly becomes confined below the Hanadir shale. The main feature of the Saq water table in the Qassim area is the presence of a major depletion that stretches parallel to the outcrops and the basement border. The centre of this depletion is located north of Buraydah and the observed water-table elevation is below 500 m.a.s.l. The depletion results from the intensive pumping in the irrigated areas and water levels have dropped by more than 100 m since 1983. There is an eastward shift between the axis of the depleted zone and the centre of the main irrigated areas, which is mainly due to the natural eastward slope of the water table.


24



The main northeast flow trend is thus completely disturbed by exploitation. West of Baqa, groundwater flow seems less affected by the local irrigated areas that are less important than those around Buraydah. b) The western area of the Saq basin in Saudi Arabia hosts the largest outcrops of Saq Sandstone. The area south of Tayma represents the largest unconfined part of the Saq aquifer. The aquifer remains unconfined below the large basalt flow (Harrat) northwest of AlUla, and over a 40 km wide strip along the basement border west of Tabuk. The natural flow direction is generally northward, except in unconfined areas near the contact with the basement where it follows the dip towards the centre of the basin (Figure 13). One exception to this pattern is the AlUla region, where the AlUla valley drains the Saq aquifer in the opposite direction. Along the basement border some 100 km south of Tabuk, drainage is also directed outward from the Saq basin. This leakage is confirmed by the existence of springs in the valley draining towards the Red Sea. East of Tabuk the natural flow bends northwards in the direction of Busayta. It seems that the general water flow in the Saq aquifer in the northwestern part of the study area is directed towards the Wadi Sirhan graben, which thus forms the main natural outlet of the Saq system. In the wide-spread exposures south of Tayma and around the Nafud sand dunes, water levels in the Saq aquifer show a very low gradient: this area corresponds to a thicker (1,200 to 1,800 m) zone in the aquifer resulting in an increased transmissivity. Three depleted areas are noticeable in the western area. From south to north, AlUla is the first one. The depletion is natural because of aquifer drainage by the valley, but it has been accentuated by pumping in the past 20 years. Tayma is the second depleted area. This situation is new by comparison to the previous piezometric map drawn by BRGM in 1983. Tabuk has the largest depleted area of the western region, with a drawdown estimated at 100 m in the north of the irrigated area. In conclusion, the Saq water table is heavily affected by recent withdrawals. Compared to the 1983 situation, the historically artesian zones (mainly Tabuk and Buraydah) have disappeared giving place to large depleted areas. Even the remote areas in the north, where withdrawals are scarce, have lost a few tens of metres in water level. The only region not affected by drawdown until now is located southeast of Tayma, because of its upstream and remote position compared to the main irrigated areas. Piezometric time-series have a completely different shape depending on whether they are located in a confined or an unconfined part of the aquifer. Unconfined conditions are marked by a smooth behaviour in which seasonal fluctuations are barely visible. This is due to the storage properties of the aquifer that is not fully saturated. On the contrary, marked seasonal and shortterm fluctuations reflect confined conditions, where water levels react sharply over long distances to the variation in stress induced by pumping variations. Unconfined conditions represent about 20% of the Saq aquifer extension within the Saq study area, which is evaluated at about 377,000 km within Saudi Arabia. However, considering that the exploitability is limited by aquifer depth, this ratio is assumed to reach 50%. Therefore, about half of the piezometric series reflect unconfined conditions in this aquifer. This is the case of, for instance, Al Mukharim well (Figure 14)


25



34 32

36

38

40

42

44

46

48 32

Al Qurayyat Al Qurayyat

Water level elevation 2005 (m. amsl) Water level elevation 2005 (m. amsl)

(

measured WL measured WL measured WL measured WL measured WL measured WL estimated WL estimated WL estimated WL estimated WL estimated WL estimated WL contour line contour line contour line contour line contour line contour line probable contour line probable contour line probable contour line probable contour line probable contour line probable contour line

%

30688 688 688 688 688 688 743 743 743 743 743 743 763 763 763 763 763 763 773 773 773 773 773 773 755 755 755 755 755 755 691 691 691 691 691 691

(685 685 685 685 685 685

667 667 667 667

Sakakah Sakakah Dawmat al Jandal Dawmat al Jandal70 0 700 70 700 70 0 70

aquif er limit aquif er limit aquif er limit aquif er limit aquif er limit aquif er limit main irrigated areas main irrigated areas main irrigated areas main irrigated areas main irrigated areas main irrigated areas outcrops of Saq aquif er outcrops of Saq aquif er outcrops of Saq aquif er outcrops of Saq aquif er outcrops of Saq aquif er outcrops of Saq aquif erm. amsl = metres above mean sea level m. amsl = metres above mean sea level m. amsl = metres above mean sea level m. amsl = metres above mean sea level m. amsl = metres above mean sea level m. amsl = metres above mean sea level

30

900 90 0 90 90 0 90 90 800 0 800 0 800 0 800 800 800

28

909 909 909 909 909 % %909 914 914 914 914 914 914

676 676 676 676 676 676 695 695 695 695 695 695

%

26

0 60 0 60 0 00 600 600

N0 50 100 kilometre 200

24 34 36 38 40 42 44 46 48

Figure 13. Groundwater-head contour map for the year 2005 Saq aquifer

770 700 770 000 00 0

55 5 5 5 50 5 50 5 0 0 0 0

%

0 00 00 50 65 655 65

0 00 0 000 99 90 990

0 0 8 85 850 85 85 8 8 85

800 800 800 800 800 0

700 700 7 00 700 7 0 0

709 709 709 709 709 709 763 763 763 763 763 763 775 775 775 775 775 775 912 912 912 912 912 912

% % % %% ( 739 % 739 739 739 ( (( 678Tabuk 739 Tabuk 739 678 678 678 653 678 653 678 653 777 777 653 653 653 777 777 777 ( 777 711 711 711 711 711 711750 750 750 750 750

% %628 % 628 628 628 % 628 628

707 707 707 707 707 707

770 770 770 770 770 %770 790 790 790 790 790 790 786 786 786 786 786 786

( 812 812 812 812 812 812 784 784 784 784 784 784 % Tayma %782 % Tayma 782 782 782 782 ( ( 782 % 807 781 781 807 807 781 781 781 781 807 807 807 ( ( 792 792 792 792 792 792 ( 815 815 815 815 815 837 837 837 837 837 837 ( 815 831 831 831 831 831 831 800 800 800 ( 800 800 800 843 843 ( 843 843 793 843 793 843 793 780 780 780 780 780 ( 793( %780 ( %750 750 750 852 852 852 750 750 750 852 852 749 749 749 749 749 ( 852 839 ( 839 839 839 839 839 ( 749 ( AL Ula AL(Ula

%

781 781 781 781

Jubbah Jubbah779 779 779 779 779 779 766 766 766 766 766 766

676 676 676 676 728 728 728 728 728 728

%(

((

%%

839 839 839 839 839 ( 839

743 743 743 754 743704 754 743704 754 743 754 754 754 704 704 704 704 % % 600 691 691 691 %608 600 691 691 691 608 600 608 600 713 713 713 608 600 578 508 608 600 578 508 608 713 713 713 578 508 578 508 578 508 578 508 728 700 % 728 728 728 700 728 700 728 700 493 493 493 493 493 493 601 601 601 % 601 601 601

( ( ((

637 637 637 637 637 670 670 670 670 670 670 %637 640 640 640 640 640 640 655 674 655 649 649 674 655 674 655 649 649 649 %674 668 %649 668 668 586 586 586 586 586 586 %668 508 508 508 508 508 508 612 612 612 612 612 612

0 650 650 650 650 650

750 75 75 0 750 750

( ( (( 698 698 698 698 698 698 610 610 610 610 610 610 ( ( ( 666 666 666 587 587 607 666 587 607 666 607 666 587 587 607 587 607 607 % (( 648 695 648 695 648 695 648 695 648 695 648 695 ( (( (0 50 650 650 65 0 65 65

0 50 0 850 850 850 750 7 50 750 7 750 750

700 700 700 700 700 700

741 741 741 741 741 %741

650 650 650 650 650

((

Baq'a Baq'a

28

Ha'il Ha'il

( ( ((( ( ( (( ( (

(

514 514 514 ( 514 514 514 ( ( % 619 648 619 648 619 648 619 648 619 648 ( 648 ( 619 498 498 498 498 498 498 610 610 ( (610 ( 579 579 579 579 ( 579 579 ( Buraydah Buraydah 680 680 680 % 532 680 680 680 522 522 522 522 532 ( 532 % 522 ( 599 522 618 (532(599( 618 532 599 618 532599 618 618 ( 599 618 599 612 612 ((((612 ( 551 Unayzah 612 612 638 638 638 551 (((621 612 ( 551 Unayzah 638 638 638 551 551 621 621 ( ( 619 551 621 (619 621 619 621 619 619 ( (619( 574 645 612 645 612 645 612 645 612 645 645 574 574 574 574 641 ( 641 641 641%% ( 574 641 641 644 662 644 662 644 662 644 662 644 662 644 662 613 613 % 613 613 613 % ( 613 655 655 655 655 655 655 ( 583 583 583 626 583 626 583 ( %583 626 626 626 ( 626 % % 672 672 672 672 672 673 673 673 % Sajir 673 673 673 ( 672 Sajir ( 686 686 686 ( ( 686 686 686 703 703 ( 703 703 703 ( 703 Ad Dawadimi Ad Dawadimi

(

Qibah Qibah00 0 00 0 0 00 555 55 555 555

0 0 0 0 0 0 5 50 50 50 50 50

26

0 0 0 0 0 0 500 500 500 50 50 50

24

26



Depth (m) 68 70 72 74 76 78 80 82 m 84 86 88 90 92 94 96 10/12/1983 09/12/1985 09/12/1987 08/12/1989 08/12/1991 07/12/1993 07/12/1995 06/12/1997 06/12/1999 05/12/2001 05/12/2003

Figure 14. Piezometric series of the Al Mukharim well (1-Q-210-S / BU9210)

In the confined areas of the aquifer, the influence of seasonal pumping is clearly seen in the piezometric series. This is obviously emphasized when pumping wells are located nearby. Wells in the Qassim or Tabuk depressions illustrate this phenomenon. For instance, the observation well at Rawd al Uyun (Figure 15) shows alternate drawdown and recovery linked to the rate of pumping that developed in this area during the years 1983 to 1993, and decreased afterwards. A sharp drawdown starting in December alternates with a smoother increase of the water level from April to December as the aquifer recovers after irrigation.

Depth (m) 15 20 25 30 35 40 45 50 m 55 60 65 70 75 80 85 90 95 100 10/12/1983 09/12/1987 08/12/1991 07/12/1995 06/12/1999 05/12/2003

Figure 15. Piezometric series at Rawd al Uyun (1-Q-136-S / BU9136)


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2.3.5

Groundwater Levels in the Kahfah aquifer

In the western part of the Saq study area, natural flow is towards the north, whereas in the Qassim area groundwater flow is directed towards northeast. In 1983, in places such as the Hail or Tabuk irrigated zones, the Saq water level was higher than that of the Kahfah aquifer. Today, this situation has changed and the Saq water table is everywhere at a lower elevation. In the Qassim area, the natural groundwater flow has been disturbed by intensive pumping. Observations show a depleted area with a minimum elevation at 500 m.a.s.l. below Buraydah, which is roughly the same elevation as in the Saq aquifer and could indicate that equilibrium is reached between the two aquifers. This equilibrium may be due to the fact that many wells tap both layers, thus establishing a hydraulic contact between the two layers. However, the extension of the depleted area is slightly different compared to the depletion observed in the Saq aquifer, and outside the centre of the depression the water table in the Kahfah aquifer is generally 10 to 50 m above the Saq water table. The Kahfah water table is presently down to 100 m below the 1983 water level in the centre of the depletion, but this difference decreases when moving away from the Buraydah area. Water levels are similar to those observed in 1983 southeast of Baqa. North of Hail, the present water table again appears to be lower than the 1983 levels. This pattern well reflects the distribution of irrigated areas, the highest drawdown taking place near the centre of irrigated areas. In the western part of the Saq study area, the irrigated zone near Tabuk coincides with a large depression in the water table. The water levels in the centre of the depression are below 650 m.a.s.l. Here, too, a large number of wells tap both aquifers and the influenced levels have the same shape. However, there is no equilibrium between the two aquifers. 2.3.6 Groundwater Levels in the Quwarah-Sarah aquifer

The Quwarah-Sarah aquifer is a complex system in which the aquifer properties may vary widely because of the presence of paleo-channels in the upper Zarqa and Sarah members. These units are glacial deposits unconformably overlying the Quwarah sandstone. Paleovalleys also incise the Raan shale that forms the base of the system and connects it with the underlying Kahfah and Saq formations. For this reason, the aquifer thickness is heterogeneous and holes exist at different spots, such as 40 km north of Tabuk. The formation is not found east and south of Unayzah. Under these circumstances it is very difficult to draw a piezometric map for this aquifer. An attempt is however presented, to show that the general flow direction follows the same trend as the underlying aquifers. The groundwater flow is directed northeast in the Tabuk-Tayma region and probably travels to the Wadi Sirhan graben. The gradient should be affected by the thickness variation of the reservoir. In the Qassim area, the flow is directed northeast as well. 2.3.7 Piezometry of the Tawil aquifer

More than 900 wells have been identified in the Tawil aquifer (previously known as Upper Tabuk, or TBK6), which is intensely exploited in the Busayta area west of Al Jawf, and in the Dawmat al Jandal area. Despite this important number of data, only around 35 points have been retained for the drawing of the map, because a huge number of wells are located in the same zone and provide the same data. The Tawil aquifer is present in the northern half of the study area. Large outcrops exist in the area between Tabuk and Busayta. In the northwest of the Saq study area, the flow direction in the Tawil aquifer is mainly towards Wadi Sirhan. East of longitude 40E, flow is predominantly


28



directed towards the north and northeast. Most of the groundwater flow originates from the Nafud area and much lesser flow originates from the outcrops in the west. Two different systems can be distinguished: west and east of Wadi Sirhan. West of Wadi Sirhan (Busayta area), it is clear from the observed water levels that drainage occurs along Wadi Sirhan. Water from the Tawil aquifer becomes vertically connected with geological units above it, i.e. with Mesozoic and Tertiary deposits. Towards the north, the Tawil Formation disappears and its groundwater flows in the Secondary-Tertiary-Quaternary (STQ) formations. This is confirmed by chemical parameters that show a dilution effect along the wadi, due to the mixing of fresh Tawil water with brackish Wadi Sirhan groundwater. West of Wadi Sirhan, the Tawil is a productive aquifer of good-quality water that is intensely exploited. The drawdown created by withdrawals is about 40 m in its centre. Remote areas south of Busayta are not yet affected by the depletion. Eas

Documents

Saq Aquifer, Saudi Arabia, 2008