The hydrogeology of the northwestern bajada region of the Sultanate of Oman
Item Type Thesis-Reproduction (electronic); text
Authors Aubel, James William.
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Link to Item http://hdl.handle.net/10150/191877 THE HYDROGEOLOGY OF THE
NORTHWESTERN BAJADA REGION OF THE
SULTANATE OF OMAN
by
James William Aubel
A Thesis Submitted to the Faculty of the
DEPARTMENT OF HYDROLOGY
In Partial Fulfillment of the Requirements For the Degree of
MASTER OF SCIENCE
In the Graduate College
THE UNIVERSITY OF ARIZONA
1985 STATEMENT BY AUTHOR
This thesis has been submitted in partial fulfillment of requirements for an advanced degree at the University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.
Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgement of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his/her judgement the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.
SIGNED: laALS2--
APPROVAL BY THESIS DIRECTOR
his thesis has been approved on the date shown below:
EUGENE S. SIMPSON Date Professor of Hydrology and Water Resources ACKNOWLEDGEMENTS
I wish to express my gratitude to the following persons who assisted in completing the required field work: Margaret Chapman,
Peter Quinlan, and Zahir Al Adawy. Special thanks goes to Abdullah
Mohammed Salim Al Barwany for his many months of hard work and dedication to collecting field data. Bill Spong was of valued assistance in supervising the drilling and in the compilation of data. Mike Foley was very helpful in spending many hours editing and proof reading the final manuscript. I also wish to thank His Majesty Sultan Qaboos
Bin Said, Sultan of Oman, for having financed the work which led indirectly to this thesis. TABLE OF CONTENTS Page
LIST OF ILLUSTRATIONS vi
LIST OF TABLES viii
ABSTRACT ix
1. INTRODUCTION 1 Purpose and Scope 3 Location and Geographic Setting 5 Physiography, Topography and Geology 5 Cultural Features and Natural Resources 10 Climate 12 Methods of Investigation 12 Previous Investigations 16 Accessibility and Operating Conditions 17 Hydrologic Data Point Identification System 18 Romanization of Arabic 20
2. GEOLOGY 21 Stratigraphie Sequence in the Northwestern Bajada 23 General Geology 23 Geomorphology 30
3. HYDROGEOLOGY 32 Pre-Tertiary System 32 Hawasina Complex-Permian to Middle Cretaceous 32 Aruma Group-Upper Cretaceous 33 Tertiary System 34 Hadhramaut Group-Paleocene to Middle Eocene 34 Fars Group-Oligocene to Pliocene 36 Taqa Formation-Oligocene to Lower Miocene 37 Undifferentiated Clastics and Evaporites-Middle Oligocene to Pliocene 39 Quaternary System 41 Surficial Deposits-Pleistocene to Recent 41 Summary of Hydrogeologic Conditions 44
iv TABLE OF CONTENTS--Vontinued
Page
4, HYDROLOGY AND WATER RESOURCES 47 Fars Group/Quaternary Aquifer 47 Source 48 Occurrence 48 Hydraulic Properties 50 Water Table and Ground-Water Movement 56 Recharge and Discharge of Ground Water. , 64 Storage of Ground Water 70 Chemical Quality of Water 73 Water Use 80
5. CONCLUSIONS AND RECOMMENDATIONS 83
Governing Conditions of the Aquifer 83 Potential of Ground Water Supply 85 Additional Exploration Drilling 86 Artificial Recharge 88 Improvement of the Water Budget 91 Water Resources Planning and Management 93 APPENDIX A: THE ROLE OF THE AFLAJ IN OMANI ECONOMY 95 APPENDIX B: INVENTORY OF WELLS, BORINGS, AFLAJ, AND SEISMIC UPHOLES IN THE STUDY AREA 106
APPENDIX C: RESULTS OF THE PAWR EXPLORATION DRILLING 121
APPENDIX D: REPRESENTATIVE GRAPHS OF THE AQUIFER TESTS 124 REFERENCES 130 LIST OF ILLUSTRATIONS
Figure Page
1. General Map of Oman and the Location of the Study Area 2
2. Detailed Geographic and Cultural Map of the Study Area 6
3. Map of the Geographic Zones of Oman and the Study Area 7 4. Map of the Major Surface Drainage Patterns of the Northwestern Bajada 9
5. Map of the Drainage Catchment Area of the Northwestern Bajada 13 6. Map Showing the Locations and Type of the Hydrologic Data Sites 15
7. Numbering System of Hydrologic Data Points 19 8. Regional Geology and Main Physical Features of Northern Oman and Vicinity 26
9. Detailed Geologic Map of the Study Area 27 10. Generalized Fence Diagram of the Study Area 29 11. Diagrammatic Sketch of the Movement of Water in the Study Area 49
12. Isopachous Map of the Saturated Thickness of the Fars Aquifer 51 13. Map Showing the Depth to Water in the Study Area 52
14. Generalized Flow Net Showing the Direction of Ground-Water Movement in the Study Area 58
15. Equipotential Map of the Study Area for the Winter of 1982-83 59
vi vii
16. Equipotential Map of the Study Area for the Summer of 1983 60
17. Generalized Hydrologic Cycle of the Fars Aquifer 66
18. Isosalinity Map in Micromhos/cm3 of the Ground Water in the Fars Aquifer 72
19. Plot of Stiff Diagrams on a Map of the Study Area 77 20. Chemical Analyses of the Ground Water in the Fars Aquifer Plotted on a Trilinear (Piper) Diagram 79 21. Map Showing the Proposed Exploration Drilling Sites In the Study Area 87
22. Generalized Cross-Section of a Typical Falaj in the Bajada 97 23. Plan View of a Typical Falaj in the Bajada 98
24. Chronologie Order in Constructing a Falaj and Its Relationship to the Water Table 100
25. The Various Engineering and Construction Details of the Aflaj in Oman 101 LIST OF TABLES
Table Page
1. Stratigraphie Correlation Between Oman and the Arabian-Persian Gulf 22
2. General Stratigraphie Column for the Study Area 24
3. Hydrogeologic Characteristics of the Major Geologic Units of the Study Area 45
4. Summary of the Transmissivity Values Calculated for the Study Area 55
5. Tabulation of the Ground Water Flow Calculations for the Winter 1982-83 Equipotential Map (Figure 15) 61
6. Tabulation of the Ground Water Flow Calculations for the Summer 1983 Equipotential Map (Figure 16) 62
7. Summary of the Total Ground Water Flow Calculated from the Equipotential Maps of Figures 15 and 16 64
8. Summary of Total Average Annual Volume of Rainfall and the Percentage which Enters the Study Area as Ground-Water Flow 67
9. Chemical Analyses of Water from Wells in the Study Area 74
10. Major Chemical Ratios of Sea Water, River Water and Fars Aquifer Water 78
11. Tabulation of Annual Abstraction of Ground Water by Aflaj in the Study Area 81
12. Proposed Exploration Drilling Sites and their Priorities 89
viii ABSTRACT
The Northwestern Bajada of the Sultanate of Oman is an arid region which relies solely on ground water. Present abstraction, which accounts for about 70 percent of the fresh water entering the aquifer system, is almost entirely by aflaj (qanats) located near the mountain front.
The results of 38 exploration boreholes drilled at 30 sites from 1982 to 1983 were analyzed along with field reconnaissance data.
P110-Pleistocene sediments comprise the aquifer system which is highly heterogeneous with lithologies ranging from marine carbonates to well-sorted continental alluvium. Transmissivities range from 10 m2/d to over 2,000 m2/d.
Ground-water quality is controlled by recharge, and conduc- tivities range from less than 1,000 to over 100,000 micromhos.
The predominant water type is sodium chloride, owing to the mainly marine deposition of the aquifer sediments. Fresh ground water occurs as shoe-string aquifers paralleling the active wadi channels which traverse the bajada. Intrusion of poor quality water will limit ground-water development.
ix CHAPTER 1
INTRODUCTION
The northern interior region of Oman comprises a large
area between the desert foreland and the Northern Oman Mountains
(Figure 1). This area, or piedmont slope, consists of two geomorphologic parts: (1) an upper part, a pediment, which is an eroded bedrock surface with a thin veneer of alluvium; and (2) a lower part of aggradational origin which is a bajada (Thornbury,
1969; Gary, et. al., 1974; Wilkinson, 1977). A bajada consists of a series of coalescing alluvial fans which form a broad, undulating and gently sloping detrital surface. In Oman, most of the deposition probably occurred from the Late Miocene to early Pleistocene.
Following the Pleistocene deposition, the bajada has been undergoing erosion causing the development several terrace levels on the older bajada surface.
The northwestern region of the interior bajada is characterized by thicker detrital deposits and relatively large reserves of ground water. This region has a good potential for water resources development and was selected as the study area. There are no specific place names for this area; it is locally referred to as "the desert".
For lack of a better name, therefore, the study area will be referred to as the Northwestern Bajada, or simply, the bajada.
1 IRAN ARABIAN GULF
....M...... • erg......
.11•111•1 •
SAUDI ARABIA
I ...0 HAIMA 00' •01
.0'.0 ARABIAN .0 .0 SEA .0 .0 .0
0 80 180 320 KM 1 I i I 0 50 100 200 MI
Figure 1 , General Map of Oman and the Location of the Study Area. Purpose and Scope
Knowledge of the water resources of a region is essential to the proper planning of a development program. With this aim the Omani Government assigned to their Public Authority for Water
Resources (PAWR) the task of evaluating the hydrologic potential of the country. To accomplish this goal the PAWR divided Oman into regions which were appraised predominantly by reconnaissance and exploration drilling. As each study was completed a report was submitted to the Water Resources Council. The appraisals were intended to be initial documentations of the water resources of an area and provide general guidelines for ground-water exploitation and planning. Specific areas that showed potential for water use and development were identified for future evaluation.
From 1982 to 1984 the author was assigned by the PAWR to appraise the Northwestern Bajada region. This thesis represents a further analysis of the data collected during, and after, that appraisal. Information from the test drilling was evaluated to determine the hydraulic properties of the aquifer, the thickness and lateral extent of the aquifer, and the amount of ground water in storage in the Northwestern Bajada. Water-table elevations were plotted and an equipotential map constructed to determine the amount of ground-water flow through the aquifer. In addition, maps were constructed to show the water quality, depth to water, and saturated thickness. 4
The late Miocene to Recent sediments in Oman are only tenta- tively studied and mapped because they are not significant to petroleum prospects; however, they are hydrologically important because they constitute some of the aquifers in Oman, including the study area.
An understanding of the deposition and occurrence of these sediments is helpful for a hydrogeologic appraisal. The author conducted field mapping of these sediments, held discussions with petroleum geologists in Oman, and researched the literature available for the geology of the Arabian-Persian Gulf region where the time/facies equivalent deposits had been studied in greater detail. Unless otherwise referenced, the geologic maps and cross-sections included in this thesis are original with the author.
The present water use in the bajada is estimated from data the author collected. The potential for additional water resources development is discussed, as well as recommendations for further exploration drilling and field work. The traditional falaj l system of ground water abstraction is an important consideration of water resources use and future development in Oman. Appendix A discusses the future of the falaj in terms of the hydrology and economics of Oman.
1Falaj (pl. Aflaj) is the Omani Arabic word for a water conveyance system. There are two types: (1) the commonly known Qanat method which taps ground water via subterranean tunnels from wells; and (2) a surface canal which conveys water from a stream or spring and is referred to as a ‘Ghayl Falaj'. 5
Location and Geographic Setting
The Northwestern Bajada forms most of what is known as the Dhahira demographic region of Oman. The study area is bounded to the east and northeast by the first limestone ridge of the Northern
Oman Mountains; the Oman-United Arab Emirates (UAE) border on the west; the lat 24° 00 , N parallel to the north; in the south, approxi- mately by the FahudLekhwair oil pipeline road between Lekhwair and Wadi Aswad; and along the southeast by Wadi Aswad and Jabel
(mountain) Aswad, which roughly follows the Tanaam-Natih road.
Figure 2 is a detailed map of the study area. The region is about
60 km (40 mi) wide in the north to over 130 km (80 mi) wide along the southern extent and approximately 170 km (100 mi) from north to south. The total area is about 15,600 km2 (6,000 mi 2 ).
The Northwestern Bajada is classified within three geographic zones; (1) the Northern Wadi Region, (2) the Sand Region, and (3) part of the Northern Inner Pedimentand Wadi Region (Figure 3).
physiography, Topography and Geology
The study area consists of gravel and sand alluvial plains and coalescing alluvial fans. Wadi channels slightly incise the plains and fans. Their courses apparently change during some floods so that areas of bare sand and gravel that spread and rejoin are easily seen on air photos and LANDSAT images. In general, the area is characterized as a broad, gently sloping plain that varies in 6 7
Ras E. 58 ° Musancam IRAN
STUDY AREA VI
VII
aon
VIII •••
0 so n 00 200 km
Border of the natural regions F-171 Sand region Boraer of the natural regions tuncertainl FIFI Central wadi region Nortnern and eastern coastal II region NEI Southern wadi region Northern Coastal terrace Southern inner Peaiment and wadi region Eastern outer pediment and wadi region Southern mountain region
Northern mountain region Southern outer pediment ana wadi El region Nortnern inner pediment and wadi region Southern coastal region Nortnern wadi region --- International boundaries
Figure 3. Map of the Geographic Zones of Oman and the Study Area. 8 elevation from over 400 m (1,200 ft) near the mountain front to about 200 m (600 ft) on the western edge, and less than 150 m
(500 ft) in the far south.
Limestone bedrock hills project through the alluvium near the mountains and to the north and southeast of the area. The major bedrock exposure in the study area is the anticline of Jabel
Hafit in the north, with an elevation of 1,240 m (4,070 ft). Sand dunes, standing over 100 m (300 ft) above the gravel plain, cover most of the western boundary of the study area.
Surface drainage patterns cross the bajada in two major directions (Figure 4). The northern area drains west to south- west across the Oman-UAE border, and is part of the Arabian-Persian
Gulf drainage system. The central to southeastern area drains in a southerly direction and terminates in the Arabian desert, or
Rub al Khali (Empty Quarter), and in a large sabkha (playa) located in Oman and called Umm as Samim. No permanent lakes or perennial streams exist in the study area.
Geologically, the bajada consists predominantly of Pliocene to Recent age sediments. The deposits are mainly marine carbonates, detritalcarbonates,andcontinentalalluvium; representing anear-shore environment of successive transgressions and regressions. The deposits grade upwards into a continental facies characterized by large alluvial fans which cover most of the bajada surface.
Bedrock exposures are mainly limestones of Paleocene to Eocene 9
Figure 4 • Map of the Major Surface Drainage Patterns of the North- western Bajada. 10
age, and were probably emplaced during Late Miocene orogenic movements.
Structurally the bajada is the far eastern edge of a marine shelf
which extends from the Precambrian Arabo-Nubian land mass in western
Saudi Arabia and terminates at the present day Oman Mountains which
represent an Oceanic trough that was uplifted in the Late Cretaceous-
Early Tertiary. (Morton, 1975; Tschopp, 1967).
Cultural Features and Natural Resources
The study area is occupied by two culturally different groups of people. The bajada proper is inhabited by several large bedouin (nomadic) tribes who lead a pastoral life of herding goats and sheep. The region along the mountain front is occupied by villagers who have an agrarian society supported by the aflaj system of irriga- tion. There is no official census for the area. The author estimates that about 7,000 to 9,000 persons live in the region. The majority live in, or near, the oases along the mountain front; probably less than 2,000 bedouin live on the bajada proper.
Administratively, Oman is divided into 41 wilayats (states) each governed by a wali (governor). The study area is part of the three wilayats: Ibri, Dhank, and Buraimi. The last named has a sub-wilayat office in Sunaynah, located within the study area.
All field work required the permission of the respective wall.
There are 19 villages in the study region; all located near the mountains. The original location of the villages was dependent on the feasibility of a falaj. The major villages are, 11
from north to south; Hafit, Qabil, Sunaynah, and Tanaam. The largest
village, Sunaynah, has an estimated population of less than 1,500.
Except for the oil camp of Lekhwair, there are no villages on the
bajada proper in Oman (Figure 2). In the UAE, next to the Oman-UAE
border which forms the western edge of the study area, are the
towns of Al Wigan and Medasis. These towns were built by the UAE government for their bedouin but also are used by the bedouin of
Oman for obtaining supplies, and drinking water from desalinization
plants.
There is only one paved road in the study area, connecting
the towns of Hafit, Sunaynah and Tanaam, which roughly follows
the eastern edge of the bajada. A graded road traverses the south- eastern and southern boundary of the study area, and connects Tanaam and Lekhwair. A paved road in UAE, which becomes a graded road
in Oman, follows the Oman-UAE border along the western edge of the study area.
The discovery of oil in Oman has produced jobs for the people of the bajada, and has started to change their lifestlyes.
During the next decade rapid growth in roads, towns, agriculture and, of course, water use is expected. Presently, ground water is underutilized on the bajada proper; practically all water use takes place along the mountain pediment where abstraction of ground water is almost entirely by aflaj. 12
Climate
Oman is classified as arid to semi-arid. The Northwestern
Bajada is arid, receiving less than 100 mm (4 in) average annual precipitation. Precipitation is mainly controlled orograhically, and the catchment area above the bajada (Figure 5) recieves an estimated 120 to 180 mm (5 to 7 in) annual precipitation. Rainfall occurs predominantly in the winter and early spring (February to
May), but brief storms can occur in the summer and fall (June to
September). Rainfall is usually distributed erratically across the bajada by convective storms; however, large frontal systems can cause precipitaion over the entire northern part of the country.
These storms usually occur during the winter. Additionally, tropical cyclones of heavy and extensive rains approach the Arabian coast about once in three years (Pedgley, 1970). The author experienced a cyclonic storm on the bajada in May, 1981; this storm event exceeded
150 mm (6 in) locally (personal communication with personnel of
Geophysical Services Inc.). The winters of 1981-82 and 1982-83 were exceptionally wet years following a drought of seven to ten years. A discussion of the precipitation and the resulting recharge will be presented in Chapter 4.
Methods of Investigation
This study was part of an on-going field reconnaissance and exploration drilling program that the author conducted for
PAWR in the interior of Oman. Field work involved up to four 1 3 14
Omani nationals employed as Hydrologic Field Technicians and one
American hydrologist besides the author.
The investigation comprised four phases. The first phase was a reconnaissance of the existing ground-water use in the area and basic hydrogeologic mapping. This involved approximately 12 man-months of inventorying representative wells (dug or drilled), aflaj, and seismic upholes recently drilled for oil exploration.
A total of 106 hydrologic data points were inventoried and tabulated
(Figure 6 and Appendix B). Preliminary hydrogeologic maps were constructed at a scale of 1:250,000 to use in the planning process.
The second phase involved the determination of the requirements for an exploration drilling program. It included the selection of drilling sites, estimating proposed well depths, anticipating problems in drilling and site access, obtaining government approval to drill at the specific sites, and deciding on which drilling methods and equipment would be required. A drilling contract proposal was then written and submitted for government tender. For this study, all drilling was accomplished using top-head drive rotary rigs with air/foam and down-the-hole hammer capabilities.
After the contract was awarded, the third phase involved the actual on-site supervision of the drilling and subsequent well design and testing. Geophysical borehole studies were conducted on selected test wells. All drilling and testing information was recorded on standardized forms and filed under the PAWR hydrologic 15
co o o 0 o 0 c N) N L) ;13 N < o 10 rig! 4 . 6 Cr.4 I 0 o sa- :27 N) g3-6 a0-6 o • o (D
• Cr44›.. o
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rs4 16 data point numbering system (Appendix C). The original program was continually revised using the on-going drilling results. The exploration drilling was accomplished during two field seasons.
The first season was from November 1982 to May 1983 when 30 boreholes were drilled at 22 sites. The second season, from October 1983 to April 1984, completed eight boreholes at eight sites. In total,
38 boreholes were drilled at 30 sites over a drilling period of
14 months. The author supervised the first season of drilling and the second season was completed following general guidelines written by the author.
The last phase of the study involved report writing. A preliminary report, based on the results of the reconnaissance and exploration drilling, was written by the author and presented to the Omani Water Resources Council as part of a larger report on the hydrology of Oman (Doyel, et. al., 1984).
Previous Investigations
Prior to the author's work in this area there were no known studies, published or otherwise, concerning the water resources of the Northwestern Bajada. Investigations had been conducted at several villages located along the northeastern edge of the bajada
(University of Durham, 1974; Watson Hawksley, 1981). The ground water availibility for the oil camp operations along the southern region of the study area had been tentatively investigated (unpublished
Petroleum Development of Oman (PDO) reports). These studies, however, 17
had not addressed the regional hydrology of the bajada; it was
not realized that sufficient quantities of fresh ground water existed
for localized development of the region.
Accessibility and Operating Conditions
Access to the Northwestern Bajada is via paved roads from
the capital city of Muscat, to the east about 320 km (200 mi),
or from Buraimi, 25 km (15 mi) to the north (Figure 1). There are graded roads servicing the oil camps along the eastern and southern edges of the study area. The bajada proper is criss-crossed by
a maze of tracks of varying permanence, and traversing the study
area requires a four-wheel-drive vehicle. A good compass and reserves
of fuel and water were necessary for field work. Navigation by
the 'lay of the land' was difficult owing to the uniformity of
the topography and natural vegetation. More than several months
were required for field staff to become familiar with the area.
Locating field sites was accomplished using LANDSAT imagery
and topographic maps, both at a scale of 1:250,000, and oil exploration
seismic-line maps at a scale of 1:100,000. The seismic-line maps
and the LANDSAT imagery were the most useful for field work. The
seismic companies had installed permanent markers at known locations
and elevations. The bearings and elevations of the PAWR exploration
wells were found in relation to these markers without which it
would not have been possible. 18
The extremely high summer temperatures, maximums of over
50°C (120°F), made field work tiring and interfered with equipment such as conductivity meters, geophysical equipment and general machinery.
All field personnel were assigned vehicles equipped with single-side-band HF radios that were compatible with the PAWR national radio network. The radios were used to report drilling activities and request equipment and supplies; theywereanessentialcommunication link between the field and the office.
Hydrologic Data Point Identification System
This study uses an identification system that was developed by the PAWR. The system is based on the Universal Transverse Mercator
(UTM) Grid, Zone 40, Clarke 1880 Spheroid. The UTM grid is printed on the available maps for Oman and is convenient for locating any data point in the country.
The following example is illustrated in Figure 7. A data point with the PAWR alpha-numeric identifier DA478450AA has the
UTM GRID coordinates of E04485 N25740. The correlation is as follows:
D. 47 84 50 AA Within Oman each 100 km square
has a unique two letter identifier: i.e. E04 N25 = DA.
DA 1E 84 50 AA The first two numbers denote the 10 km
square within the 100 km square: i.e. E044135 N256_40 = 46.
DA 46 a 50 AA The second pair of numbers denote the
1 km square within the 10 km square: i.e. E04465 N256410=84. 19
r- CnJ
cJ
co r- Tr-
r—
rf) •cr E
lt) O Ts- 0
ri)
0
re)
CD
r•- rn 20
DA 46 84 aa AA The last two numbers denote the 100 m
square within the 1 km square: i.e. E04481N2564Q_= 50.
DA 46 84 50 AA The first letter identifies the data
point within the 100 m square. Succeeding letters of the
alphabet are used to distinguish additional data points
but no attempt is made to locate sites in relation to each
other: i.e. A = the first point.
DA 46 84 50 AA The last letter indicates the type of
data point: i.e. A = well, dug or drilled; B = talai;
C= oil well; D = seismic uphole; E = spring.
Although the numbering system may seem confusing at first, it is simple if one remembers the basic rule of 'read right up'.
That is, the Easting, or abscissa, is read first, then the Northing, or ordinate is read.
Romanization Of Arabic
The transliterated Arabic words used in this thesis are not in strict accordance with the standard BGN/PCGN 1956 system.
This is because many of the place names and terms were taken from maps and reports for which the original Arabic was unavailable and the transliteration system used was not known. It is believed by the author that the Arabic words presented in this thesis are sufficiently straightforward in pronunciation and do not require further elaboration. CHAPTER 2
GEOLOGY
There have been numerous regional geologic studies of Oman and the Arabian-Persian Gulf and the reader is referred to the literature (see, for example, Baker and Henson, 1952; James and
Wynd, 1965; Powers, et. al., 1966; Kassler, 1973; Falcon, 1974; Glennie, et. al., 1974; Kent, 1978). The late Tertiary to Recent age deposits of Oman, however, have been practically ignored because they are non-petroliferous. These sediments are important to the hydrology of the bajada because they constitute the major aquifer.
The few publications concerning these sediments are in disagreement as to their depositional age (Morton, 1959; Glennie, 1970; Beydoun,
1980). Whether the deposits which comprise the upper few hundred meters of the bajada are Quaternary, late Tertiary, or a Plio-
Pleistocene transition is presently debated. The question is further complicated by the recent adoption of a new stratigraphie nomenclature for Oman, which divides the Plio-Pleistocene sediments on the basis of the Tertiary/Quaternary time line (Table 1). This division cannot be identified in the field. The majority of the bajada sediments are detrital carbonates; it is uncertain whether the depositional environment was marine or lacustrine. Based upon the PAWR test drilling results, geologic mapping and literature research, the
21 22
Table 1: Stratigraphie Correlation Between Oman and the Arabian-Persian Gulf
11ME STRITICRIPAIC UNITS IRAN KUWAIT . UNITED ARAB S. IRAQ a_ SAUDI ARABIA a I NTERIOR QATAR j _ COASTAL ill1 EMIRATES . 1=1 EASTERN • 0 ,..,. le *sill CC IX O M AN 9 uCC PERIOD EPOCI 0 77 CC ICE STAGE CD 14 FOr-eue.enc.445, n FCF-AkesT cwis. 1---ogrv.P•ect FoRav.)..eac4As - > - ur SYSTEM SERIES DNS Ft...,favo,i-LoNG For4.A.•,N- -Loi•AS Fol.lrv..4,c7Ini-tS Him- RECEDE n_ BAKHTYARI HAMMAR *SC.47...p.c-Nos.s._ CALABRIA' = SURFACE DEPOSITS SURFACE DEPOSITS c.., jny PLEISTOCENE nn DczP1=0,75k cc AGHA JARI HOFUF *Snell C.1 DIBDIBBA will) noing sails ;MIL SAND ENO PLIOCENE acC DIBDIBBA pilisaitiu c") M1SHAN SION! DESIST "LORIN Sim) SILT cc Cull CCI) "C"-t-k`311C-5 oX Avvb DOT al = Ar- GACHSARAN LOWER FARS LOWER FARS DAM LOWER FARS LOWER FARS . EvA,7aneares` MIOCENE -______, -_—_--.-- <:r 7- BuROICALtAm CHAR .._ CHAR HADHRUKH -, cc „ ,,., ASMARI 1 ›. ZAHRA ...,. uubl,....t,(1. AwiltuguN .cc ------ISMAILI EOUIV • - umum r*------__------DAMMAM DAMMAM DAMMAM DAMMAM DAMMAM 1-- Detmr-P.•4.&_ / Amto.u.e..._ = = EOCE L61 iPRES11% RUS RUS RUS RUS RUS a „....7.,_ cri M 50- ,== - UPPER •cr SPARMICIAlt •C-- - Stratigraphie Seauence In The Northwestern Balada The stratigraphie nomenclature of Oman was recently formalized (PDO, 1983), and differs from the Arabian-Persian Gulf region. Table 1 shows the Upper Cretaceous to Recent stratigraphic correlation between Oman and the Arabian-Persian Gulf region. It can be seen from Table 1 that the time and facies equivalent deposits of the Miocene to Recent have been extensively delineated in Iran, Iraq, Kuwait and Saudi Arabia. Research of the literature concerning studies in these countries has been useful in attempting to understand the stratigraphy of the study area. Table 2 is a generalized strati- graphic column illustrating the lithology of the formations of interest to this study and is a useful reference to the following discussion on the geology of the bajada. General Geology The Northwestern Bajada occurs at the transition between the broad, gently dipping Arabian marine foreland shelf and the geanticlinal Oman Mountains. A brief review of the late Cretaceous to Recent geology of the study area is useful to understanding the hydrogeology. Late Cretaceous uplift emplaced nappes composed of radiolarites and ophiolites and formed the Oman Mountains (Glennie, et. al., 1974). After emplacement, the Oman Mountains were relatively stable and were the site of shallow marine carbonate deposition 24 25 during the late Cretaceous to early Tertiary (Murris, 1980). Major Tertiary transgressions along the flanks of the Oman Mountains occurred in the Paleocene, Oligocene, Miocene and late Pliocene, depositing the Hadhramaut group and the Fars group sediments (Table 2). Uplift in post-Oligocene and pre-Miocene was the last major folding to take place in Oman, except for differential uplift during the Miocene to Pliocene (Tschopp, 1967; Morton, 1975). Deposition on the bajada during post-Oligocene was influenced by the exposed Oman Mountains, producing an apron of conglomeratic carbonates. The gravel sized clasts are composed mainly of weathered radiolarites and sandstones. These Miocene to P110-Pleistocene detrital carbonates represent a near shore environment that was undergoing eustatic and orogenic changes. Sedimentation is characterized by interfingered marine and continental elastics with discontinuous evaporites. The elastics grade upwards into a predominantly continental facies until the last major transgression- regression which occurred in the late Pliocene to early Pleistocene. Deposition in the Pleistocene was influenced by the interglacial pluvials and is believed to have formed large alluvial fans which now stand as dissected terrraces on the bajada plain (Beydoun, 1980). Figure 8 is a map showing the regional geology of northern Oman, including the study area. Figure 9 is a geologic map of the Northwestern Bajada constructed from field work data collected by the author, and using LANDSAT imagery at a scale of 1:250,000. 26 156°E I .58 ° E STRAIT OF HORMUZ I Ru'isE sohd geofoqy a l- Desert Jib51 Tertiary Sabkha III Upper cretaceous Semail Kineous ri Dune sand Ea Upper cretaceous. Hawasina ri7 desert platform Mesozosc-Permfan limestone 111 Wadi sediments 01 Precambrian STUDY AREA 1 Musandam 5 Hamra' al-Duriri' 9 J Fand 2 J Akhdhar 6 J Sutra 10 (rat al.MilhI Salt 3 Sayh Han& 7 Haushi Hutt Swell 11Clirat Kibn-t domes 4 J Kaye.. 8 J SaLikh Figure 8. Regional Geology and Main Physical Features of Northern Oman and Vicinity. Figure 9. Geologic Map of the Study Area Qa1 QUATERNARY ALLUVIUM alluvial gravel, sand and silt restricted to channels and flood plains of present-day wadis. The percentage of reworked older elastics increases with distance from the mountain front. Qe EOLIAN SAND predominately comprises the large dune fields which cover the western part of the study area. Are believed to have formed during the Pleistocene but also includes Holocene sands. Plio-Pleistocene deposits of alluvial fans, silt, clay, and PP lacustrine and marine elastics and carbonates. The exact age is not known but has been divided into three sub-units based upon desert varnish, lithology and stratigraphie relationship, as follows: QAlluvial sand, gravel and silt forming terraces and fans F -1 adjacent to and higher than the flood plains of present-day wadi drainage. In many cases the unit consists of reworked PQ2 and PQ 1 deposits. PQ2 Alluvium, detrital marine or lacustrine and deflation lag (serir) deposits with a desert varnish coating that is less than PQ 1 . Western region is comprised predominately of reworked Mio-Pliocene desert platform sediments. Alluvium heavily coated with desert varnish which shows PQ, up almost black on the LANDSAT imagery and in the field. The unit forms large, heavily dissected fans and terraces, which stand up to 50 m above the present wadi drainage. It also forms long sinuous terraces which represent exhumed wadi channels. T1 FARS GROUP is comprised of two parts, a lower part called the F Taqa formation and an upper part called ‘undifferentiated elastics and evaporites/. A section of the upper part is included in the PlioPleistocene unit. F] TAQA FORMATION of the Fars group, composed of marly limestones, F clays, claystones and gypsiferous evaporites in the upper part. It is erratically exposed in the study area. T HADHRAMAUT GROUP, marine carbonates, many buff-colored limestones H which form the almost continous ridge along the eastern boundary of the study area. COMPLEX, thin-bedded limestones, turbidites, sandstones K H HAWASINA I and cherts. 27 t-. • • • C o o o C o o o 0 Lzar i•reTlaal, oTazou-a0 oTcrzosairi 10 to 28 The elastic surface deposits of the bajada are differentiated into four units based upon (1) the extent of desert varnish, and hence the reflectance on the LANDSAT imagery, (2) the location of the deposits, and (3) the altitude above the present drainage. Except for the present day wadi alluvium, the exact age of the surface deposits is unknown. The oldest unit is conjectured to be Plio-Pleisto- cene. The two overlying units are depositionally younger but consist mainly of older reworked sediments, some possibly of Pliocene age. The near subsurface geology of the bajada is not as uniform as it appears from the surface. Late Tertiary orogenic uplift emplaced the almost continuous ridge of lower Tertiary carbonates, which constitutes the eastern boundary of the bajada; uplift also formed large anticlines underneath the bajada surface. Jabel Hafit, at the northern boundary of the study area, is an exposed anticline resulting from this movement. Subsurface structures equally as large exist, but are not readily apparent from the bajada surface topography (personal communication with Gulf Oil personnel). The subsurface anticlines cause a local thinning of the overlying elastics. The resulting decrease in saturated thickness and generally poorer water quality was confirmed during the exploration drilling. Figure 10 is a generalized fence diagram of the study area that was constructed using information from oil wells, seismic upholes and PAWR exploration wells. The occurrence of evaporites are not readily apparent from the surface geology but several deposits were located during the 29 X 0 o 2 in— o 1 . ; Sd31311 30 test drilling and geologic field mapping. The evaporites occur erratically as thin, discontinuous lenses. The Plio-Pleistocene coast of the bajada was probably similar to the present Arabian-Persian Gulf coast: a convoluted shoreline with discontinuous supratidal zones, or coastal sabkhas. The formation of deltaic deposits are not common in arid or semi-arid environments because streams are not perennial and long-shore currents quickly remove and redistribute the small deltas which form during ephemeral wadi flows (Glennie, 1970). This may account for the general uniformity of the detrital marine sediments on the bajada. Geomorphology The bajada is characterized as a relatively featureless, undulating plain of braided wadi systems and serir (deflation lag deposits) gently sloping to the west and southwest, terminating at the edge of the Rub al Khali sand seas. From the late Pleistocene to Recent, the bajada has been undergoing continental deposition and erosion depending upon the paleo-climatic conditions. The geomorphologic shape of the present bajada was probably formed during the Pleistocene when the Arabian- Persian Gulf sea level was about 100 m (300 ft) lower than at present. This lowering of the base level contributed to dissection of the Plio-Pleistocene alluvial fans, and terraces now stand as much as 50 m (150 ft) above the bajada plain. Deflation has also accounted 31 for the erosion, and some authors believe that this was /more important than fluviatile processes (Beydoun, 1980). Exhumed wadi channels have been studied in the eastern part of northern Oman (Glennie, 1970; Beydoun, 1980). Their age is debated to be of either Plio-Pleistocene or late Pleistocene. Similar features, which are mapped as the oldest detrital unit (Figure 9), occur near Wadi Dhank in the central part of the study area. These have not been previously mentioned in the literature. PAWR exploration drilling indicates that the paleo-drainage from Wadi Dhank was probably in the direction of these exhumed channels. Test wells CA983201AA and CA971540AA were of higher yields and better quality than well CA887807AA, which is located 10 to 15 km (6 to 10 mi) closer to the present Wadi Dhank channel. It is conjectured that ground water flow is following the more transmissive buried channels associated with the paleo-drainage pattern. The large sand dunes which cover the western edge of the study area are stable and were probably formed during the Pleistocene interglacials (Glennie, 1970). The dunes are predominantly self type; stellate and complex barchan types are found further to the west. In the southwestern corner of the study area the dunes form a rectangular pattern which is believed (Glennie, 1970) to be caused by insufficient wind velocities to shape a self dune pattern. Deflation hollows in the dune complexes expose the underlying gravels of the bajada surface. CHAPTER 3 HYDROGEOLOGY The aquifer potential of the major rock units which comprise the bajada are known from other areas of Oman and the Arabian-Persian Gulf region. In the study area, there are differences in the water bearing characteristics of these formations that have not been previously published; these are presented in this chapter. Also included is a brief geologic description of each major formation or group; these were compiled from a number of publications and unpublished oil company reports. pre-Tertiary System Sediments of Pre-Tertiary age are of minor importance to the hydrology of the study area, and are only mentioned because they underlie the bajada and occur as outcrops adjacent to the study area. Hawasina Complex-Permian to Middle Cretaceous The deposits of the Hawasina complex vary from shallow marine limestones to limestone turbidites, sandstones and cherts, ranging in age from the Late Permian to the Middle Cretaceous. Their occurrence in the study area is limited to a small outcrop just north of Ibri on the far eastern edge of the bajada. The 32 33 Hawasina is in angular unconformable contact with the overlying Hadhramaut group of Early Tertiary age (Glennie, et. al., 1973). The Hawasina complex is important because it constitutes most of the mountains adjacent to the bajada and was the source rock for most of the detrital deposits of the late Tertiary Fars group. These detrital deposits, which consist of weathered cherts, sandstones and limestones, have moderate to good permeabilities. The ground-water potential of the competent Hawasina complex is poor, and it is not an aquifer in the bajada. Aruma Group-Upper Cretaceous The Aruma group gradates from globerinal shales to marls, limestones and dolomites. It is dated as Late Cretaceous, specifically from Late Santonian to Maestrichtian in age. The basal contact is disconformable with the Middle Cretaceous age Wasia formation and is overlain disconformably by the Paleocene to Eocene age Umm er Radhuma formation of the Hadhramaut group. Parts, or all, of the Aruma group underly the entire bajada region but crops out only in the Fahud and Dhank areas, adjacent to the southeastern and eastern boundaries of the study area. The Aruma group is considered an aquiclude in relation to the overlying Tertiary rocks. 34 Tertiary System Deposits of Tertiary age comprise the major area of interest on the bajada, and are divided into two groups: (1) the Hadhramaut group of Paleocene to Middle Eocene age; and (2) the Fars group of Oligocene to Pliocene age. The Hadhramaut group is of lesser importance because no potable water has been found in these rocks in the study area. A brief description of the Hadhramaut group is included because it underlies the bajada, and comprises the ridge which forms the eastern boundary of the study area. Hadhramaut Group-Paleocene to Middle Eocene The Hadhramaut group was named by Wetzel and Morton in 1948 after exposures seen in the Hadhramaut region of southern Arabia (Peoples Democratic Republic of Yemen); it comprised all Tertiary deposits of Paleocene to Middle Eocene age (Beydoun, 1966). The original description of the Hadhramaut group included four formations, from base to top: the Umm er Radhuma; Jeza; Rus; and Habshiya. These formations were recognized predominantly in southern Arabia. In Oman, the Hadhramaut group name was adapted (PDO, 1983) to refer to the four Paleocene to Middle Eocene formations of, from base to top: (1) the Umm er Radhuma, with a basal Shammar member; (2) the Rus; and (3) the Dammam, which incorporates a facies change to the (4) Andhur formation in southern Oman (Dhofar province). 35 The basal Umm er Radhuma formation rests disconformably on the Upper Cretaceous Aruma group and the top Dammam, or Andhur, formation is overlain disconformably by the Oligocene to Pliocene Fars group (Morton, 1959). The Hadhramaut group underlies all of the study area, and forms an almost continuous ridge along the eastern boundary of the bajada. Jabel Hafit, in the north, consists predominantly of upper Hadhramaut group sediments. The center of the Paleocene-Eocene basin is assumed to be in the vicinity of Suneinah, located in the north-central part of the bajada (Tschopp, 1967). Oil exploration logs indicate the thickness varies from approximately 370m (1,200 ft) in the southeast, to 1,700 m (5,600 ft) near Suneinah, and 720 m (2,400 ft) along the western edge of the study area. Outcrops do not represent the entire sequence of the Hadhramaut group due to depositional and erosional factors. Exposures range from less than 100 m (300 ft) in the southeast to about 200 m (700 ft) in the northeast, near Dhank and Jabel Hafit. The Hadhramaut group represents transgressive Paleocene to lower Eocene marine carbonates and shales of the Umm er Radhuma formation, followed by regressive lower Eocene shallow marine marls and evaporites of the Rus formation. A lesser transgression during lower to middle Eocene deposited marine carbonates of the Dammam formation. 36 Potable ground water supplies are not known to occur in this group in the study area. The highest salinities recorded for the Umm er Radhuma aquifer in Oman, over 100,000 mg/1 in total dissolved solids (TDS), are at the Lekhwair oil field in the far southwestern region of the study area (PDO unpublished reports). In other parts of Oman, particularly the southern Dhofar region, however, the Hadhramaut Group can be a good aquifer (PAWR exploration drilling; PDO unpublished reports). The Umm er Radhuma and Dammam formations are the best potential aquifers, and the intervening Rus formation is usually of poor quality water owing to marls and evaporites. Water quality appears to be determined by two factors:(1) the distance to a recharge source, and (2) the hydraulic connection between the carbonate deposits and the evaporites. Recharge to the Hadhramaut group underlying the bajada is assumed to occur directly at the outcrop exposures on the eastern edge of the basin; minor recharge is assumed to occur as leakage from the overlying clays and shales of the Fars group. Potable ground water may occur in the Hadhramaut group on the eastern edge of the bajada; however, this has not been confirmed by test drilling. Fars Group-Oligocene to Pliocene The term Fars sediments was first applied by Pilgrim in 1908 to describe a thick sequence of predominantly marine sediments of mainly Miocene age exposed in the Fars Province of Iran. In 1965 James and Wynd elevated the term to group status and defined it to include Upper Oligocene to Pliocene deposits of limestones, 37 marls, shales, evaporites and conglomeratic carbonates of shallow marine to lacustrine origin (Setudehnia, 1972). In Iran, the Fars group comprises four formations and two members; the type localities are in southwest Iran. The underlying,or adjacent, Oligocene to Lower Miocene age Asmari formation is not considered part of the Fars group (James and Wynd, 1965). Oman stratigraphie nomenclature includes the time and facies equivalent of the Asmari formation, the Taqa formation, in the Fars group (Tables 1 and 2). Except for the Taqa formation, however, the Fars group is not divided and the remaining deposits are simply referred to as undifferentiated elastics and evaporites (PDO, 1983). In Oman, the Fars group is dated as Oligocene through Pliocene. The basal contact is disconformable with the underlying Hadhramaut group, and the upper contact is disconformable to gradational with the overlying, and adjacent, Quaternary surficial deposits. This study is concerned mainly with the upper part of the Fars group, the undifferentiated elastics and evaporites of Late Miocene to Pliocene age. Taca Formation-Oligocene To Lower Miocene. The Taqa formation was first described in 1956 by Dhofar Cities Service geologists, and the type locality is in the Dhofar province of southern Oman ( Beydoun , 1966). In northern Oman the term Asmari formation or Lower Fars was used to denote the time and facies equivalent of 38 the Taqa formation; these terms have been dropped from usage (PDO, 1983). The Taqa formation is dated as Oligocene to Lower Miocene. The formation is underlain disconformably by the Dammman formation and overlain conformably, or by lateral gradation, with the undifferentiated elastics of the Fars group. The Taqa formation underlies the study area, outcrops along the southern and southwestern edge of the region, and occurs as small bedrock exposures near the mountain front. The center of the Oligocene basin was probably in the western Dubai, UAE region (Tschopp, 1967). The greatest thickness of the Taqa formation is along the northwest boundary of the bajada where thicknesses of about 660 m (2,200 ft) are reported from oil exploration wells. Elsewhere in the area, the thickness ranges from about 200 m (700ft) in the south, to about 400 m (1,000 ft) in the south-central region, to less than 100 m (300 ft) in the north. These reported thicknesses are greater than the actual thicknesses because the oil companies consider the Fars group as a single unit and do not differentiate the Taqa formation from the elastics. The Taqa formation represents a post-Oligocene transgression, characterized as chalky and reefal limestones to massive and well- bedded limestones with some marls, clays and shales in the basal and upper parts. The lower Fars group, including the Taqa formation, is less productive and contains poorer quality water than the overlying 39 undifferentiated elastics. Locally, wells drilled in the Taqa formation along the southwestern boundary of the study area may be artesian. Salinities ranging from about 10,000 mg/1 to over 50,000 mg/1 in TDS are found in wells along the southern part of the study area. The Taqa formation is not considered a viable aquifer in the study area. Undifferentiated Clastics and Evanorites-Middle OliRocene to Pliocene. The upper Fars group, the undifferentiated elastics and evaporites, ranges in age from the Middle Oligocene to Pliocene (PDO, 1983). The middle Oligocene to lower Miocene deposits grade laterally into competent limestones of the Taqa formation. The time and facies equivalent of the elastics has been studied extensively in Iran and Saudi Arabia (James and Wynd, 1965; Sayari and Zotl, 1978). The study of these deposits in Oman, however, is incomplete. The sediments of interest to this study are believed to be of late Miocene through Pliocene in age, and represent the final major transgression and regression in the region. The undifferentiated elastics and evaporites comprise most of the deposits found in the upper several hundred meters of the study area. Results from the PAWR exploration drilling indicate that the thickness of these elastics varies from about 140 m (460 ft) in the south-central area, to 100 m (300 ft) along the western edge, to less than 20 m (70 ft) in the north. The thickest deposits 40 were encountered in the north-central region, near Wadi Dhank, where thicknesses exceeded 200 m (700 ft). To the south and southwest the elastics thin out completely and are replaced by marls of the Taqa formation (Figure 10). The late Miocene through Pliocene lithology is related to the depth of the sea and the distance from the exposed land mass of the Oman Mountains. The sediments consist of interfingered and adjacent deposits of alluvium, competent marine carbonates, conglomeratic marine and lacustrine carbonates, and locally occurring thin gypsiferous evaporites. The alluvium is lithologically similar to the Quaternary alluvial deposits and are not differentiated in the field. The conglomeratic carbonates are either limestone or dolomite containing up to about 80 percent clasts of ehert, sandstone, limestone and weathered ophiolite. Chert and sandstone are the dominant materials. Commonly, the sediments are only slightly indurated but some zones are well-indurated. The non-detrital marine carbonates are usually thin dolomites or limestones that are moderately hard. Drilling in the detrital carbonates was relatively fast and boreholes would usually stand open without caving when using air-foam circulation. Mud drilling was rarely required. Underlying the elastic sediments is a thick clay or claystone, which is a distinctive red-orange color. This clay horizon is a marker bed indicating the bottom of the permeable elastics and, therefore, the aquifer. The clay is more than 200 m (700 ft) thick 41 along the western part of the study area (personal communication with Gulf Oil personnel). Towards the mountains and to the north, the red-orange clay is thinner and is underlain by blue-gray clay and claystone. The Fars elastics constitute an unconfined to semi-confined aquifer system that is lithologically similar to, and hydraulically connected to, the overlying and adjacent Quaternary alluvium. The basal clays and marls are assumed to respond as a regional aquitard. Because the Fars elastics vary from well-sorted gravels to conglomeratic carbonates to competent carbonates, the hydraulic conductivities vary accordingly. Initial exploratory drilling and testing done for this study indicate that the transmissivities range from about 10 m2/d to over 2,000 m 2/d (800 to 160,000 g/d/ft). Generally, transmissivities are less than 500 m 2/d (40,000 g/d/ft). In the central region of the bajada, the aquifer is over 100 m (300 ft) thick and available drawdown to wells results in yields commonly in excess of 20 l/s (300 gpm). The aquifer properties of the Fars elastics will be discussed in more detail in Chapter 4. Quaternary System Surficial Deposits-Pleistocene to Recent No differentiation of the Quaternary has been made in Oman and it is referred to as 'surficial deposits' (PDO, 1983). 42 This includes all deposits of Pleistocene to Recent age. The basal contact, which can not easily be distinguished in the field, is disconformable to gradational with the underlying and adjacent Fars group. The sand dunes in the western and southwestern region of the bajada were probably formed during the Pleistocene glaciations, and are presently stable (Glennie, 1970). The Quaternary deposits occur mainly in: (1) the wadi channels ,- (2) along the mountain pediment, (3) as terraces and exhumed wadi channels, and (4) as large sand dunes. A mappable differentiation between the Pliocene and the Pleistocene alluvial deposits has not been done. The two units comprise the same aquifer, however, and differentiating the two is of greater geological than hydrological interest. The thickness of the assumed Quaternary alluvium ranges from several meters to over 50 m (150 ft), but is usually less than 10 m (30 ft). The sand dunes reach a maximum height of over 100 m (300 ft) above the bajada surface. The recent alluvium of the Quaternary can generally be divided into three lithologie types: (1) unconsolidated; (2) semi- consolidated; and (3) consolidated or cemented. Consolidation is the result of evaporation of interstital water in the unsaturated zone which forms a calcareous precipitate that eventually cements the alluvial material. The consolidated alluvium is referred to as calcrete, caliche, or duricrust. The occurrence and degree of cementation in the alluvial fans is erratic; generally the induration 43 decreases with depth. It is not unusual, however, to encounter well-cemented gravels down to bedrock, usually less than 30 m (100 ft). The alluvium near the mountain front consists mainly of recently eroded cherts, sandstones, limestones and ophiolite. On the bajada proper, the alluvium is predominantly reworked P110- Pleistocene elastics which are similar to, and therefore hard to distinguish from, the mountain pediment alluvial material. The grain size distribution ranges from clay to boulders and is poorly sorted. With distance from the mountain front the sorting improves as the larger grain sizes decrease. Coarse gravel and cobbles occur along the western edge of the bajada, probably due to gradient changes which took place in the Pleistocene (Glennie, 1970; Beydoun, 1980). The Quaternary surficial deposits are in hydraulic continuity with the elastics of the Fars group; however, there are hydrogeologic characteristics unique to the recent alluvium due to the occurrence of calcrete, or cementation. Interconnected fractures and solution channels in the calcrete can result locally in very high hydraulic conductivities. Yields to wells are extremely variable, ranging from less than 1 l/s (20 gpm) to over 30 1/8 (500 gpm). In many locations the cemented alluvium responds hydrologically similar to fractured crystalline rock and the yields of adjacent boreholes can differ by several magnitudes. Transmissivities determined by 44 the PAW? for the recent alluvium in other areas of Oman (DtLugosz, 1983; Aubel, 1984) ranged from less than 10 m 2/d to over 5,000 2 m2/d (800 to 400,000 g/d/ft). The majority were in the 100 m /d to 3,000 m2/d (8,000 to 240,000 g/d/ft) range. Hydraulic continuity in the alluvium is inhibited by the relatively impermeable calcrete layers. Confined or semi-confined conditions occur where a well-cemented layer overlies a more permeable zone. Flowing wells from the alluvium have not been observed on the bajada owing to the shallow hydraulic gradient. Sand dunes are commonly cited in the literature as being able to recieve, store and transmit water from direct precipitation. Because of insufficient rainfall, the dunes along the western edge of the bajada are of minor hydrologic importance. The sand dunes may indirectly increase recharge in some of the major wadi channels on the western edge of the bajada. The dunes block the wadis and thus impede the surface flow and possibly increase infiltration to the shallow water table. Summary of Hvdroizeologic Conditions Table 3 is a summary of the water bearing characteristics of the major hydrogeologic units which occur on the bajada. The only aquifer with sufficient quantities of potable water for development occurs in the Late Miocene to Pliocene undifferentiated elastics of the Fars group, and in the hydraulically connected Quaternary surficial deposits. 45 1 V • H 0 0 0 42 0 13 3. V • r-4 I C tr. 0 0 0 0 H 0 0 C .4 V V 000 1-4 q 40 .4 13 4) 0 O. 0 4. 0 Sr. 0 ..-I .-1 L V 0 H 0 C 0 C I. 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I. .0 IA VI 0 0 0 0 13 L. 0 1. 03 7 IN C') E- 00 IV 0 CI D0 A 0 l'n tr P. 0 0 ••• 111 0 +13 0 ••• 0 A 0 0 13W 130 0 0 -40 0 ..4 0 0 CV 00 0 0 0 0 43 0 13 v) • -•• in 1.. 0 cg E. 0 19 43 0 C0 II I.C1 /Pi v- 13 0 0 0 Z 0 Q_4 Q_4 0'0 Fe 04 .4-' .sJ 0 0 al 0 0 01-- 01-- o. v.> g 0 0 od .... Lil . 0 /.4 Oa O. 12.0 0. 12.0 1.1 ••• = 0 0134).0 0 0 .0 E. 10 0 Z El io 413 0 0 0 0 0 .0 .4 1.4 OS ...1 .4 .4 OS 0 00. I-. I. . 0 V S. CT 0 43 00 . 0 iii 0 .... 2 1 a I-. i.. 0 E e r.0.1.1 . .4 . 0 .4 0 0 .0 0) ...e c, t. OM 1 fa• 40 t• 0 ...... 4. .= L. A. VO 0 0 m E slTgodea TuToTJanS dnoaD saga O c) a) 49 0 quo0au C 0 9U9 O0 3 SO .112 H 04 0 0 GO 0 iii c. o) aaddû 04 euopo)sTaid ...io .1' eozooared v) .4 8 .. A. m 0 E snoop 1, AssusaTent AasTqaei, v) sqaao 46 The occurrence and movement of ground water in the bajada is dictated by the distribution of the elastics and the underlying clay deposits. The thickness of the detrital sediments is governed locally by the amount of post-depositional weathering and the shape of the underlying erosional and/or structural surface. The aquifer is generally more productive where large Plio-Pleistocene alluvial fans existed and, therefore, greater saturated thicknesses and higher transmissivities result. CHAPTER 4 HYDROLOGY AND WATER RESOURCES Except for infrequent flood flows and intermittent base flows in several of the mountain front wadis, all water in the study area occurs as ground water. All of the potable, recoverable ground water in the study area occurs in the upper Fars group/Quaternary alluvium system (Table 3) and this constitutes the only aquifer which will be considered. The less important lower Fars group, the Taqa formation, comprises the aquifer along the far southern and southwestern boundary of the study area where all ground water is non-potable. The underlying Hadhramaut group contains water of such poor quality that the group is not a viable source of ground water in the study area. Fars Groua/Quaternarv Aauifer Although the Quaternary alluvium is considered a separate aquifer in the intermontane basins of Oman, in the bajada it is in close hydraulic continuity with the underlying and adjacent Fars group deposits, and both are considered as one hydrogeologic unit. For simplicity the Northwestern Bajada aquifer system will be referred to as the Fars aquifer. The hydrogeologic differences of the two rock units was discussed in Chapter 3. '47 14 8 Source Most of the ground water that enters the Fars aquifer of the study area originates from precipitation which falls on the mountains to the east and northeast. Rainfall is received, stored, and trans- mitted as floods across the bajada. Recharge occurs in the wadi channels on the bajada and, more importantly, as ground-water underflow in the major wadis which enter the bajada from the adjacent mountain front. Ground-water flow directly from the limestone ridge which forms the eastern boundary of the bajada is assumed to be relatively insignificant when compared to underflow in the wadis. A minor source of ground water is infiltration of direct precipitation on the bajada; the sheet flow is channelled into small water courses. The movement of water into and out of the bajada is shown by the diagrammatic sketch of Figure 11. Occurrence Recoverable ground water underlies most of the study area, occurring mainly in the upper part of the Fars group/Quaternary alluvium. The aquifer overlies a thick clay or claystone unit which constitutes a leaky aquitard . The Fars aquifer varies from well-sorted gravels to competent marine carbonates to some evaporites; the hydraulic conductivities vary accordingly, as does the quantity and quality of water available to wells. Some localities require that several test wells be drilled before finding a suitable production well. 14 9 50 Commonly, the fresher and larger yields of ground water come from the elastics in, or near, the main wadi channels. Fresh ground water does not parallel the mountain pediment, but traverses the bajada as 'shoe-string' aquifers which follow the wadis originating in the mountains and extending up to 80 km (50 mi) across the bajada. The saturated thickness of the Fars aquifer ranges from several meters to over 200 m (600 ft). The average thickness throughout the central part of the bajada is about 100 m (300 ft). Fig- ure 12 is an isopachous map of the saturated thickness of the Fars aquifer in the study area. Over most of the bajada, depth to ground water is shallow to moderate, ranging from less than 3 m (10 ft) to about 30 m (100 ft). In about 80 percent of the region the depth to water is less than 15 m (50 ft). Figure 13 is a map showing the depth to water under the study area. Hydraulic Properties For the determination of a quantitative analysis of an aquifer system and to facilitate realistic projections involving development of the aquifer, certain hydraulic parameters must be known. These parameters are the hydraulic conductivity (K) and the coefficients of transmissivity (T) and storage (S). In unconfined aquifers the coefficient of storage is essentially equal to the specific yield (Sy). Knowledge of these hydraulic properties and their distribution in the aquifer system is essential in calculating the amount of ground water in storage and the future response of 51 o II I (1D to o 1.0 I, - 14) • vc. I I 1 o . 1. 141 Q. • '.112 1 / / i c., I / / / 1 1 1 I re . I I 1 / / f i r / / // / ./ % . / / - / // / n / / • / / /1 I 1 / 4:7-1/ n 0° ii ' 1 / 1 • ft. / il / / / nnn , I / I o n I / 1 / I Ill/ cv / / I j / • / I / ' / e 6,/ / / / • n ...- 0 sx'l / 1' eou œ / 0 e ,_, . (I) 4-) ,) / 0). 0 // A ,./ 0 -?+, 4b, t n‘ / I z / / '-'0. 46-4, • ..e / . / ..i . , - to 4/ ▪ • 52 o Di• 0 a) 0 (L.,; (:). wen • • ro-. 0 • a- ••eri rn ar (0%0 \O • r•-; 0 to • • ro oj • r- co CD CO • csi • 10 co CV tc)• W) I • • to• ID 241 j r- • co a Co 0 o o o • Lc> • • 0 CD 04 . CD CY) • cr, • • o O) ofn % • • t / (D 0 / • • 0 a ,/ / o • 2 / \ 1 ‘3‘) I 1-7 ...c. t- / ti . ..../. n "*%. .4-• v. r- ar . Ki / • / 0 0 • 0 co• N 4 I I°. o ,,.)PI Di in / s 0 0 w --`n is • • 6 a) 1,- f .6" a. te> // ...,(2., ' `....,... to • 0 • "Tr O cv0 • ..._ .4: • • 0 t-- -'''tn / / i I ''' '4 ',2 6 ,,>' - '''•• / • •-e,y, • • / L "In i • 6— •- . ....ç . re) cs.1 53 the aquifer to water withdrawal. Complete calculations require that the areal extent of the aquifer and the hydrologic boundaries controlling flow on the perimeter of the underground reservoir are known. The most common and reliable procedure for determining the hydraulic properties of an aquifer is to conduct an aquifer test, sometimes referred to as a pumping test. The test should be of such a magnitude and duration as to stress the aquifer system and, hence, give data as to what the limits of the system may be. The assumption that the coefficients of the aquifer are constant in time and space is basic to most formulas used to determine the parameters. In practice, coefficients differ due to changes in the natural geologic conditions and, therefore, aquifer tests should be conducted at more than one place in the aquifer system. The hydraulic parameters calculated should be interpreted with consideration of the geology. During the exploration drilling phase of this study aquifer tests were conducted at 19 of the borehole sites. Of these tests, 12 were single well tests; that is, no observation well was available and all measurements were made in the pumped well. The remaining seven tests were conducted with one observation well. Due to contractual limitations only two of the aquifer tests were conducted for more than eight hours continuously. These two tests were pumped for 214 hours continuously; only one test had an observation well. 54 The aquifer testing methodology was set by PAWR management and was not under the author's control. The general procedure limited all aquifer tests to no more than eight hours continuous pumping and two hours of recovery measurements. Using excess funds remaining at the end of the first phase of drilling, the author was able to conduct the two 24-hour aquifer tests. The personnel conducting the tests usually involved one American hydrologist who was assisted by Omani Hydrologic Field Technicians and the Asian employees of the drilling contractor. Owing to the wide variety in educational backgrounds of the personnel involved, quality control was difficult and the aquifer test data are limited. The data for only 14 of the aquifer tests were analyzed by the author. The Neuman delayed-yield, Jacob-Cooper semi-log, and Theis methods were used to determine the values of transmissivity and specilfic yield. The remaining five tests were analyzed in Oman by the on-site hydrologist, using the Jacob-Cooper semi-log method. Table 4 summarizes the transmissivities that are believed to best represent the respective test-site data. See Appendix D for representative graphs of drawdown and recovery. The transmissivities ranged from 10 m 2 /d to 2,300 m2/d (800 2 to 180,000 g/d/ft). Most of the values were less than 500 m /d (40,000 g/d/ft), and the geometric mean was 120 m2/d (10,000 g/d/ft). To calculate the specific yield an aquifer test must be conducted using at least one observation well. In thick, unconfined aquifers the delayed yield, or gravity drainage, response requires that 55 Table 4: Summary of Transmissivity Values Calculated for the Study Area. UTM LOCAL TRANSMISSIVITY NO. SITE NUMBER NUMBER TYPE* (m2/d) 1 CB616933AA CB-9 PW 30 2 CB713031AA CB-1O PW 90 3 CA362956BA CA-4 OW 40 4 CA369513BA CA-7 OW 30 5 CA845906AA CA-30 PW 70** 6 CA855906AA CA-31 PW 380** 7 CA863666AA CA-32 PW 100** 8 CA887807AA CA-33 PW 120 9 CA894705AA CA-34 PW 50 10 CA971540AA CA-40 PW 280** 11 CA983201AA CA-42 PW 400 12 DA074197BA DA-8 OW 300 13 DA139760AA DA-13 PW 10 14 DA143249BA DA-15 OW 1500 15 DA146057BA DA-17 OW 2,300 16 DA164183BA DA-19 OW 80 17 DA185367BA DA-21 OW 1,500 18 DA355039AA DA-39 PW 10 19 DA456839BA DA-53 OW 3,100** * PW: Pumping Well OW: Observation Well ** Basic test data unavailable; analyzed by various hydrologists using the Jacob-Cooper Semi-Log Method. 56 an aquifer test be conducted for a sufficient duration of pumping. The aquifer test data for the study area indicates that pumping should be at least 12 hours continuous to account for gravity drainage. Only one aquifer test at a site with an observation well, (DA146057BA), was run for an adequate time (24 hours). The specific yield calculated from this site was 0.14, which is believed to be representative of the Fars aquifer on a regional scale. The hydraulic conductivity was determined using the equation: K=T/b where: K is the hydraulic conductivity (m/d) T is the transmissivity (m 2/d) b is the saturated thickness (m) The hydraulic conductivity ranged from 0.14 m/d to 23 m/d (0.5 to 70 ft/d); the majority were less than 1 m/d (3 ft/d). Although most of the aquifer tests were not of sufficient duration and there are errors in the measuremnts, it is believed by the author that the calculated hydraulic parameters are adequate for an initial regional study. Water Table and Ground-Water Movement Standard flow net analysis assumes that ground-water flow is two-dimensional only. In many aquifer systems this assumption is valid because horizontal flow is several magnitudes larger than the vertical flow. For the study area it was not possible to complete a flow net analysis because vertical flow is anon-negligible component 57 in the Fars aquifer. A generalized flow net was constructed which indicates that ground-water flow is to the west and southwest (Fig- ure 14). Ground-water discharge was calculated by analyzing the flow between two equipotential lines: the 225 m and 200 m contours.- These two equipotentials were selected for several reasons: (1) they occurred transversely to a fairly uniform section of the aquifer, and (2) the data from the PAWR exploration drilling were concentrated in this region. Discharge calculations are based on the assumption that, in the absence of local recharge, flow between any two equi- potential lines is equal to the flow through the entire aquifer (Skibitzke and daCosta, 1962). Two equipotential maps were constructed using water table elevations for the winter of 1982-83 (Figure 15) and the summer of 1983 (Figure 16). The two maps are similar, and were drawn because the water-level data were grouped in the respective seasons. The winter monsoon caused slightly higher water levels in the summer, about 1 in (3 ft), for part of the region. Twenty one flow sections were constructed between the 200 m and 225 m equipotential lines. The measurements and calculations are presented in Tables 5 and 6. 58 o LL1 0 —J o • 59 .defAll AMMIllik -AdeallUESEIR 6- 5? Wijr. 200 NM= OP as/ awe__ • .0' , . . . . Pow t-- • me /115- n•• Aim. F. • _, • .••n••• 0 cv . o , t 04„ 60 I / (..7...... /.."7" / io / .." _ / c` , • ,t- / Ft' i C) e / œ CY:A e c‘i / / / 0 0 N A 0, do / N (.1 / I o • A 0164K/114 A I _ C4,0 / di OP 10.1.1,MILOF D - 92 40. 10..., al i . — n Emir Mil 1./ 1p CO ..• /co 00 • ,,,, I ..• 00 cJ 4.• . t al. ci to P. , .., .. •10. of /111111 4 a Li 040 • 4•01"" o .4 .1 .... > r._ I de 44. 4: .....4 u (-) cv • es* 40 PV rn .... / 1 C37 • • in CD 0 4 • • __... i • ..- opp0•10.-- -3- • ... • (3) I,- ..to • , z . #. g / cv a / ig a 2 fr t e in • CV .3- r- .." .. N r- .°. .._to • e I 40 I / - I cv / \-t ro • I 40 e # d, w e ... ./ . . 10 / ‘60 .0. c,1 1 0 • e 1- e • ul••nn• •in I - , • • n o - •IIM 10 f MED .... /# IMO 1.•• -OM C" . • =ND / cn ...." / Cc • \ (.3 OP u 112 / I— • / 0 ..1-1 co — 2 / 0 .....,, ...... , . / -..i 0 0 2 ,.., k0 ->" csbn e 0 6, . I ?,,.. t / (7..?,./., 4,Q, • "•::,,, .s s•••••.„ / CV ,(1)..., • s._ / C•13 t&) '2 ''';', -0 NI. r b0 • ••••••n• 61 Table 5: Tabulation of the Ground-Water Flow Calculations for the Winter, 1982-83, Equipotential Map (Figure 15). LENGTH GRADIENT WIDTH TEXT1 DISCHARGE (m 3/d) 3 FLOW (m2/d) 1 2 SECTION (km) (ni/km) (km) TEXT TGM 1 9.0 2.8 9.0 20 166 1,031 2 8.5 2.9 9.0 20 522 3,236 3 8.4 3.0 8.5 25 637 3,162 4 7.6 3.3 8.2 30 812 3,355 5 7.0 3.6 7.2 30 778 3,214 6 6.3 4.0 6.0 30 720 2,976 7 7.0 3.6 7.1 40 1,022 3,169 8 7.3 3.4 7.0 80 1,904 2,951 9 8.5 2.9 7.0 70 1,421 2,517 10 7.0 3.6 7.5 60 1,620 3,348 11 7.5 3.3 7.5 120 2,970 3,069 12 8.5 2.9 8.0 350 8,120 2,877 13 11.0 2.3 10.7 300 7,383 3,052 14 14.0 1.8 10.3 100 1,854 2,299 15 12.8 1.9 13.0 80 1,976 3,063 16 11.2 2.2 12.3 400 10,824 3,355 17 12.0 2.1 13.0 200 5,460 3,385 18 11.5 2.2 11.0 20 484 3,001 19 10.7 2.3 10.5 20 483 2,995 20 9.3 2.7 9.2 20 497 3,080 21 9.0 2.8 9.0 30 756 3,125 TOTAL 50,409 62,260 1 TEXT: Transmissivity is extrapolated from aquifer test data of nearby sites 2 TGM' • The geometric mean of all transmissivities is equal to 120 m2/d 3 Discharge (Q) T w dh/dl (m3/d) 62 Table 6: Tabulation of the Ground-Water Flow Calculations for the Summer, 1983, Equipotential Map (Figure 16). LENGTH GRADIENT WIDTH TEXT ' DISCHARGE (m3/d) 3 FLOW (m2/d) SECTION (km) (m/km) (km) TEXT ' TGm2 1 8.7 2.9 8.7 20 303 1,877 2 8.5 2.9 8.3 20 481 2,985 3 7.9 3.2 9.0 25 720 3,571 4 6.7 3.7 6.5 30 721 2,982 5 6.5 3.8 6.1 30 695 2,874 6 6.5 3.8 6.0 30 684 2,827 7 7.5 3.6 6.8 40 979 3,035 8 7.1 3.5 7.6 80 2,128 3,298 9 9.0 2.8 8.2 70 1,607 2,847 10 7.7 3.2 9.2 100 2,944 3,651 11 7.5 3.3 9.0 350 10,395 3,683 12 10.5 2.4 13.5 300 9,720 4,018 13 10.8 2.3 9.5 100 2,185 2,709 14 13.0 1.9 9.5 80 1,444 2,238 15 9.5 2.6 9.2 100 2,392 2,966 16 9.2 2.7 9.1 400 9,828 3,047 17 11.6 2.1 11.8 200 4,956 3,073 18 11.8 2.1 11.8 20 495 3,073 19 11.2 2.2 11.0 20 484 3,001 20 9.7 2.6 9.7 20 504 3,127 21 9.8 2.5 9.5 30 570 2,356 TOTAL 54,235 63,238 1 T . EXT' Transmissivity is extrapolated from aquifer test data of nearby sites 2 TGm : The geometric mean of all transmissivities is equal to 120 m2/d 3 Discharge (Q) = T w dh/dl (m 3/d) 63 The flow calculations were accomplished using the following equation: Q= T w dh/dl where: Q is the discharge (m3/d) T is the transmissivity (m 2/d) w the width of the flow area(km) dh/dl the hydraulic gradient(m/km) The discharge calculated for each flow section is directly proportional to the transmissivity. An accurate determination of the transmissivity for each flow section, therefore, is essential to the flow analysis. The discharge through each flow section was calculated using two values for the transmissivity: (1) a value estimated from representative aquifer tests was extrapolated to each flow section, and (2) the geometric mean of all the trans- missvities was used for each flow section (Tables 5 and 6). The total discharge calculated using the geometric mean transmissivity was about 15 percent greater than the flow found using the extrap- olated transmissivities. Considering the inherent errors in the measurements taken during the aquifer tests, and the wide range of transmissivities, an average of the two flow calculations will be used. A summary of the ground- water flow calculations is given in Table 7. 64 Table 7: Summary of the Total Ground Water Flow Calculated From the Equipotential Maps of Figures 15 and 16. METHODOLOGY GROUND-WATER FLOW WINTER SUMMER (Mm3 /YR) (Mm3/YR) 18.4EXTRAPOLATED T 19.8 GEOMETRIC MEAN T 22.7 23.1 ' AVERAGE OF BOTH 20.6 21.4 The 4 percent difference between the winter and summer ground-water flows is insignificant and the assumed ground-water flow will be the average of the two values: 21 Mm3 /YR (17,000 acre-feet (AF)/YR). To determine the quantity of potable ground water (defined here as 2,000 micromhos or less) moving through the aquifer, the water quality map (Figure 18) was superimposed on the equipotential maps (Figures 15 and 16) and the discharge of the respective flow areas, or parts thereof,calculated.The potable ground-water discharge calculated is about 8 Mm 3/YR (8,000 AF/YR) for the winter, and 9 Mm3/YR (10,000 AF/YR) for the summer, or an average of 8.5 Mm 3/YR (7,000 AF/YR). Potable ground-water flow is about 40 percent of the total flow. Abstraction of fresh ground water must be considered when calculating the ground-water flow; this is discussed in the following section. Recharge and Discharge of Ground Water Abstraction of ground water is predominantly along the mountain pediment region where aflaj and wells have been constructed. Most 65 of the aflaj have been flowing for centuries; it is assumed that the aquifer system has adjusted to this and is in a condition of steady-state. The calculated ground-water flow plus the abstractions by aflaj and wells, therefore, represents essentially all of the recharge to and discharge from the Fars aquifer. Figure 17 illustrates the ground-water budget for the Fars aquifer in the study area. The total abstraction of ground water by aflaj and wells is approximately 18.5 Mm3 /YR (15,000 AF/YR) (Table 11 and Water Use section). The calculated total ground-water flow of 21 Mm3 /YR includes the volume of irrigation water which is return flow. Assuming that most of the abstracted ground water is used for irrigation, and using 30 percent as a rough estimate for return flow, then 5.5 Mm3 /YR is recycled into the flow regime. The total annual ground-water flow entering the bajada Fars aquifer is 21 Mm3 minus the 5.5 Mm 3 return flow plus the 18.5 Mm 3 abstracted, or 34 Mm3/YR (27,500 AF/YR). Calculating the potable ground-water flow is useful for estimating the volume of water available for development. Practically all of the abstracted ground water is potable (conductivity of 2,000 micromhos or less). The volume of irrigation return flow that remains potable is assumed to be only 15 percent, about 2.7 Mm3 /YR instead of 5.5 Mm3 /YR. Therefore the annual potable ground-water flow entering the bajada is 8.5 Mm3 minus 2.7 Mm3 plus 18.5 Mm 3 , or approximately 24 Mm3 /YR (20,000 AF/YR) (Figure 17). The potable ground water is about 70 percent of the total ground-water flow 66 GROUNDWATER ABSTRACTION BY MAN /8.5 M/n 3 /RR/GAT/ON RETURN FLOW GROUNDWATER 55 Mm' GROUNDWATER (2.7 Mm3 POTABLE) OUTFLOW INFLOW ro FROM THE THE AREA STUDY AREA 34 M m3 2/.0 Mm 3 (24 Mm 3 POTABLE) (8.5 Mm 3 FARS AQUIFER POTABLE) OF THE STUDY AREA DOWNWARD LEAKAGE (QUANTITY UNKNOWN) Figure 17. Generalized Hydrologic Cycle of the Fars Aquifer. 67 entering the Fars aquifer, and only 40 percent of the ground-water flow leaving the study area. The percentage of the average annual precipitation that recharges the Fars aquifer is difficult to determine accurately because of the exstensive water use within the catchment area. The drainage catchment of the study area is shown in Figure 5. The total catchment area is about 6,500 km2 (2,500 mi 2 ) and the area above an elevation of 500 m (1,500 ft) is approximately 4,200 km2 (1,600 ml 2 ). Most of the rainfall is orographically controlled and only the area above 500 m is considered in calculating the total volume of precipi- tation. There are relatively few rain gauges in Oman, and none in the drainage catchment of the study area. Incomplete records from rain gauges in adjacent areas (Figure 5) were used to estimate the rainfall on the bajada catchment area. Average annual rainfall above 500 in is estimated to be about 150 mm to 180 mm (6 to 7 in). Table 8 is a summary of the percentage of rainfall which becomes ground-water flow in the study area. Table 8: Summary of Total Average Annual Volume of Rainfall and Percentage Which Enters the Study Area as Ground-Water Flow. ANNUAL TOTAL PERCENTAGE OF RAINFALL VOLUME GROUND-WATER FLOW 1 (mm ) (MCM) TOTAL POTABLE 150 630 5 4 180 756 4 3 (1) Based on 34 Mm3 /YR total ground-water flow and 24 Mm3/YR potable ground-water flow. 68 About 4 to 5 percent of the average annual rainfall enters the Fars aquifer of the study area; practically all of this recharge is fresh water. It is important to realize that the numerous aflaj and wells located in the intermontane basins of the bajada catchment area directly affect the percentage of rainfall which recharges the Fars aquifer. The geology of the catchment area varies from ophiolites at the highest elevations to cherts, limestones, shales and sandstones of the Hawasina complex to limestones of the Hadhramaut group. All of these rock types are low to moderately permeable and direct infiltration of rainfall is considered to be minor compared to infiltration in the wadi gravels. The wadi alluvium is generally composed of highly permeable sands and gravels and recharge can be quite dramatic. Water levels in wells near the wadi channels have been measured to rise over 5 m (15 ft) after a single flood, and aflaj flows can more than double after storm events. These effects may last several months, and indicate that recharge and ground-water flow in the wadi channels is significant. Additional, but minor, recharge probably occurs directly from the limestones bordering the eastern edge of the bajada. Evidence of this is from about a dozen small aflaj which originate from fracture springs occurring at the base of the limestone ridge. Their discharge is small, however, averaging about 7 l/s (100 gpm) compared to the aflaj which originate in the wadi channels, which average approximately 40 l/s (600 gpm). In general, ground-water 69 flow from the limestones is not extensive and wells drilled in the limestones near the mountains have low yields and poor quality. Recharge directly from the wadis during flash floods flowing across the bajada is significant, but difficult to determine quan- titatively because of insufficient data. At the time of this study there were no stream gauges on the wadis flowing into the study area and discharge measurements were made by the slope-area method. This method determines only the peak flow and not the total volume of flow. High water marks which were not measured will be washed away by subsequent larger floods and, therefore, not all of the peak flows are recorded. To determine the total volume of flow from the peak discharge, an equation developed by the USGS, called the Utah method, was used. The relationship between peak flow and total volume using this method gives a result which is slightly less than expected under the conditions in Oman (personal communication with R. Thomas, PAWR surface water hydrologist). Slope-area measurements were made by PAWR hydrologists during 1982 for three wadis in the east-central region of the study area. These wadis were assumed to contribute most of the recharge to flow areas 8 through 12 of the equipotential map for the winter 1982-83 (Figure 15). The total discharge for the three wadis was about 25 Mm3 (20,000 AF) and the average ground water flow through the respective areas was 5.7 Mm 3 (4,600 AF). Based on these figures approximately 23 percent of the wadi flow was recharge. This percentage 70 is probably greater than actual because the volume of wadi flow was higher than calculated. Discharge of ground water from the Fars aquifer occurs mainly as regional ground-water flow to the west and southwest and, almost as important, as abstraction by man. Additionally, ground water is assumed to leak downward through the underlying clays and marls; this is minor except along the southwestern region of the area. Most of the regional flow out of the study area is believed to be across the western boundary where the saturated thickness is about 100 m (300 ft). Ground-water flow to the southwest occurs mainly as leakage into the adjacent marly limestones of the lower Fars group. This is conjectured because the saturated thickness of the Fars elastics thins out to several meters and there is no surface flow. Of an estimated total volume of 34 Mm3/YR (27,000 AF/YR) entering the study area as ground-water flow, about 21 Mm3 /YR (17,000 AF/YR), approximately 60 percent, leaves as regional flow to the west and southwest. Initial measurements on water use indicate that about 13 Mm3/YR (10,000 AF/YR) is consumptive use, or about 40 percent of the total flow. The data available for this study is insufficient to determine the quantity of ground water which is leakage through the underlying and adjacent clays and marls. Storage of Ground Water The volume of available ground water in storage in an unconfined aquifer is calculated by multiplying the total volume of saturated 71 material by the specific yield. Specific yield is equal to the porosity of the aquifer material minus the specific retention. For the Fars aquifer, the volume of available ground water in storage could only be roughly determined because the coverage of data points was incomplete. The specific yield calculated for the Fars aquifer is 0.14 (p.58), and the volume of saturated material was determined from the saturated thickness map (Figure 12). The total volume of available ground water is approximately 126,000 Mm 3 (102 MAF). The volume of potable ground water in storage was found by superimposing the isosalinity map (Figure 18) on the saturated thickness map (Fig- ure 12). The volume of saturated material with a conductivity of less than 2,000 micromhos was multiplied by the specific yield. The volume of available potable ground water in storage is about 26,000 Mm3 (21 MAF), or 20 percent of the total available ground-water in storage. The volume of recoverable ground water is that amount which can be recovered by wells. This is usually less than the available volume owing to the physical limitations of well design, pumping, and drainage of all the water in storage. A general assumption is that the lower one third of the aquifer can not be dewatered and the volume of recoverable ground water is two thirds of the available ground water in storage. 72 0 IL) co Elsa_ o • 00_ o w • ('J tC) N- 0 CO W) PF-°0 co Ir • • 08, co • O 4t,/ t -to Cn1 73 Chemical Quality of Water Chemical analyses of water samples were performed by the PAWR water quality laboratory on 35 samples (Table 9). Twenty-six of the analyses included the major cations and anions; sodium, potassium, calcium, magnesium, cloride, bicarbonate and sulphate. Additionally, the pH, specific conductance, alkalinity as calcium carbonate and the total carbonate were analyzed. The total dissolved solids (TDS) were not analyzed; an approximate TDS can be found by multiplying the conductivity by 0.65 to 0.75. Although the PAWR had a fully equipped water quality laboratory, they did not have a sufficiently qualified chemist. The percent error of the ionic balances of the samples analyzed from the study area ranged from about 5 percent to over 30 percent, with the majority between 10 to 25 percent. The conductivities of the analyses ranged from 900 to 28,100 micromhos. The highest conductivity measured in the study area was in a sample from a field check of test well CV996037AA, in the southwest region; the conductivity was over 100,000 micromhos. This sample was from the lower part of the Fars group, the Taqa formation. Figure 18 is an isosalinity map, in micromhos, of the Fars aquifer. The ranges used for the iso- salinity lines were based on the requirements of the people who live in the region. Ground water which is 2,000 micromhos or less is considered potable; water from 2000 to 6,000 micromhos is used for marginal agriculture and watering stock; water from 6,000 to 10,000 micromhos is used mainly for watering camels which is important 74 Table 9: Chemical Analysis of Water from Wells in the Study Area CARBONATE BICARBONATE CHLORIDE SULFATE HARDNESS CALCIUM MAGNESIUM SODIUM POTASSIUM PAWR U.T.M. DATE OF SOURCE CONDUCTANCE ALKALINITY CO3 CaCO3 Cl SO4 as CACO3 Ca mg Na NO. REF. NO. COORDINATE SAMPLE OF WATER pH (microchos) as CaCO3 (mg/1) (mg/1) (mg/1) (mg/1) (mg/1) (mg/1) (mg/1) (mg/1) (mg/1) 1. CB409621AA 03492-26061 11/02/82 Fars 7.7 9,475 223 O 223 1,937 664 811 129 119 1,755 43 2. CB446367AA 03466-26437 11/02/82 Fars 8.0 12,750 128 o 128 3,160 868 2,198 350 322 2,101 72 3. CB447470AA 03474-26440 11/02/82 Fars 7.6 15,250 124 O 124 3,955 968 2,782 397 436 2,326 101 4. CB501926AA 03512-26096 11/02/82 Fars 7.6 6,750 162 O 162 1,389 504 1,215 245 147 1,020 27 --- 5. CB515611AA 03551-26161 12/05/82 Fars 8.4 5,100 - _ - 1,318 --- 1,389 156 236 6. CB520923AA 03502-26293 11/02/82 Fars 7.5 8,950 82 O 82 2,556 423 2,035 439 228 1,378 36 7. CB523073AA 0357-26203 11/02/82 Fars 8.5 9,200 138 14 124 2,202 691 1,561 241 233 1,684 41 8. CB530620AA 03502-26360 11/02/82 Fars 7.8 7,110 98 o 98 1,794 415 1,510 321 172 1,092 29 9. CB616933AA 03663-26193 05/01/83 Fars 7.7 4,347 148 O 148 828 875 559 89 82 810 18 10. CB713031AA 03733026101 04/18/83 Fars 7.6 2,236 440 11. CB734194AA 03749-26314 05/12/83 Fars 7.9 5,858 96 O 96 1,172 1,337 539 87 78 1,380 35 12. CB942299AA 03929-26429 05/12/83 Fars 7.7 2,556 194 O 194 369 640 563 74 92 422 22 13. CA362956AA 03325-25696 10/18/82 Fars 7.5 14,800 63 O 63 4,330 2,652 2,450 555 259 2,697 58 14. CA364848AA 03344-25688 01/01/83 Fars 7.5 10,450 77 O 77 2,569 1,540 1,582 381 154 1,970 59 15. CA369513AA 03391-25653 10/31/82 Fars 7.4 28,100 82 O 82 7,675 1,680 2,738 517 352 4,818 122 16. CA387885AA 03378-25885 09/26/82 Fars 7.6 7,190 74 O 74 1,700 1,450 1,196 301 108 1,054 23 17. CA471382AA 03438-25712 09/26/82 Fars 7.8 11,450 137 O 137 2,619 2,600 1,062 212 129 1,840 37 18. CA474239AA 03443-25729 09/08/82 Fars 7.7 6,960 207 o 207 1,582 790 132 100 100 1,330 33 19. CA474279AA 03447-25779 09/16/82 Fars 7.8 8,100 195 O 195 1,975 1,651 820 142 112 2,149 38 --- 20. CA568100AA 03580-25610 08/10/82 Fars 6.9 8,010 225 o 225 1,881 822 160 102 --- 21. CA669640AA 03694-25660 08/11/82 Fars 6.6 2,560 260 O 260 471 189 36 24 --- 22. CA699207AA 03690-25927 08/11/82 Fars/Alluv. 7.3 2,840 195 O 195 266 951 160 174 75 Table 9: (continued) CARBONATE BICARBONATE CHLORIDE SULFATE HARDNESS CALCIUM MAGNESIUM SODIUM POTASSIUM PAWR U .T.M. DATE OF SOURCE CONDUCTANCE ALKALINITY CO3 CaCO3 Cl SO4 as CACO3 Ca Mg Na NO. REF. NO. COORDINATE SAMPLE OF WATER pH (mIcromhos) as CaCO3 (mg/1) (mg/1) (mg/1) (mg/1) (mg/1) (mg/1) (mg/1) (mg/1) (mg/1) 23. CA769255AA 03795-25625 08/11/82 Fars/Alluv. 6.8 3,320 229 0 229 716 777 111 122 24. CA887807AA 03870-25887 04/05/83 Fars 7.6 5,806 1,677 25. CA894705AA 03840-25975 04/10/83 Fars 7.9 950 110 26. CA983201AA 03930-25821 04/05/83 Fars 7.7 1,304 150 o 150 208 177 257 40 38 182 5 27. DA020264AA 04006-25224 10/06/82 Fars/Alluv. 8.3 1,525 141 O 141 310 265 305 56 40 186 9 28. DA074197BA 04099-25717 03/06/83 Fars 8.2 1,573 183 O 183 217 290 96 14 15 388 13 29. DA139760AA 04196-25370 02/07/83 Fars 7.7 1,408 128 o 128 243 146 272 51 30 200 7 30. DA143249BA 04134-25429 02/13/83 Fars 7.5 1,560 243 O 243 232 185 454 54 78 194 8 31. DA146057AA 04165-25407 05/09/83 Fars 7.6 1,775 169 o 169 286 270 388 64 55 230 7 32. DA164183AA 04148-25613 02/26/83 Fars 7.4 10,557 133 O 133 3,054 1,625 1,698 325 215 1,690 33 33. DA185367BA 04156-25837 03/16/83 Fars 7.6 7,033 184 O 184 1,624 1,600 1,168 148 194 34. DA355039AA 04353-25509 12/15/82 Fars /All. 7.8 925 186 o 186 113 130 202 27 33 151 6 35. DA456839AA 04463-25589 12/12/82 Fars /All. 8.1 1,600 190 o 190 260 240 330 19 68 260 9 76 for the free range grazing of camels; water above 10,000 micromhos is not used except for construction and oil well drilling purposes. Fresh water exists mainly along the active wadi channels which traverse the bajada. Paleo-drainage features also are important in the distribution of potable ground water. The occurrence of fresh water indicates that most of the recharge takes place in the wadi channels; direct infiltration on the bajada and ground water movement from the adjacent bedrock is minimal. Ground-water quality is also affected by the near surface occurrence of marls of the Taqa formation and intercalated evaporites in the elastics. The presence of these deposits results in saline ground water occurring in areas where least expected, for example, in some of the active wadis near the mountain front. For general comparison, Stiff diagrams were plotted on a map of the study area (Figure 19). The Stiff diagrams show a dramatic increase in dissolved minerals in the aquifer with increasing distance from the mountains and, more importantly, with increasing distance from the main wadi channels. Water quality along the western side of the region is generally poorer; the worst quality is in the southwestern region. Poor quality water may also occur near the mountains as seen by one Stiff diagram on the eastern side of the area. The Stiff diagrams located along the main wadi channels indicate no appreciable increase in dissolved minerals for some distance from the mountains. 77 rf) 0 V- _ 0 0 = (J) C=3 co o o o o 0 o 78 The Fars aquifer is mainly a sodium chloride water type as indicated by the trilinear plot of the analyses (Figure 20). The alkalinity as calcium carbonate ranges from 63 mg/1 to 260 mg/1 and is classified as moderately hard to very hard. Most of the water analyses had alkalinities of over 120 mg/1 of calcium carbonate. Chemical ratios of the Fars aquifer water compared to sea water and river water are shown in Table 10. Table 10: Major Chemical Ratios of Sea Water, River Water and Fars Aquifer Water (values for sea and river water from Al-Ruwaih, 1984). SEA RIVER FARS RATIO WATER WATER AQUIFER CA/MG 0.2 3.67 0.28-2.79 Na/C1 0.85 1.79 0.54-1.79 Cl/HCO3 231.7 0.50-77.52 The ratios of chemical constituents in water from the Fars aquifer indicate a mixture of sea water and fresh water. Similar ratios are found in the time/facies equivalent deposits in Kuwait (Al-Ruwaih,1984), and are interpreted to suggest that the sediments were deposited under marine conditions and the ground water has subsequently been diluted by meteoric water. This interpretation is consistent with the geologic history of the bajada, as outlined in Chapters 2 and 3. Irrigation-water use depends on the type of plants, soil, climate and the amount of water applied. Salinity, sodium and boron are important aspects of the water quality that should be considered. The PAWR did not analyze for boron and, based upon 79 t4 0 4.4 •ri 0 C. .4 0 S4 0 CZ., 0 .0 .0 0 •,1 • El L. cd 0 S. .6-1 bd (0 (0 • ,-1 0 V O ..—.. O C.. O 0 L. 0. 0 4-I a. Q) ....0 = 4-) 54 cd c... 0 O 0 -.-1 v3 .--i cd ..-1 cd L. E-4 ..-i (0 (0 0 0 CV 03 L. 0 te N-I CT. 80 water use elsewhere in Oman, boron does not cause a problem. Irriga- tion-water over 1,000 micromhos can produce salinity problems the soil, but with proper management, the problem is reduced. Omanis irrigate with water up to 2,000 micromhos without serious effects.- The sodium hazard is determined using the sodium adsorption ratio (SAR). Values of less than 10 represent a low sodium hazard. The SAR values of the Fars aquifer ranged from about 4 to over 30, with the values below 10 concentrated along the wadis. Water Use Presently, the major water use in the study area is by aflaj located along the mountain front. Abstraction of ground water by aflaj is tabulated and presented in Table 11. The measurements were made by the author as part of a national water resources monitoring program. The total yearly abstraction is approximately 16 Mm 3 (13,000 AF). Practically all aflaj water is used for irrigation of date palms in the oases. The second largest abstraction of ground water is by wells, mainly shallow dug wells located near the mountains. Estimates from field observations place well water abstraction at less than 2.5 Mm3 /YR (2,000 AF/YR). The operations at the Lekhwair oil field, in the southwest corner of the study area, use an estimated non-potable 1 Mm3/YR (800 AF/YR). The total volume of ground water abstracted in 1983 from the Fars aquifer of the study area is conservatively estimated 81 Table 11: Tabulation of Annual Abstraction of Ground Water by Aflaj in the Study Area. DISCHARGE NO. SITE NUMBER LOCATION LPS MCM/YR 1 CB749844AB Qabil 53 1.67 2 CB85029AB Hafit - Falaj Gharbi 46 1.45 3 CB851242AB Hafit - Falaj Sharqi 10 0.31 4 CB851247AB Hafit - Falaj Wasti 43 1.36 5 CB911155AB Harmuzi 28 0.88 6 CB912187AB Sunaynah 59 1.86 7 CH914138AB Rayhani 36 1.13 8 DB121678AB Al Fatah 10 0.31 9 DA199228AB Afrangi 11 0.35 10 DA199396AB Jufayf 10 0.31 11 DA199480AB Bukhabi 25 0.79 12 DA286850AB Mazim 24 0.76 13 DA286916AB Masharub 14 0.44 14 DA292077AB Ma,mur 10 0.31 15 DA370942AB Subaykhi 39 1.23 16 DA454981KB Tanlam 63 1.99 17 DA464838AB Al Qali 1 0.0005 18 DA464852AB Al Akhdar 1 0.0005 19 DA465799AB Hijar 18 0.57 TOTAL 501 15.80 82 to be at least 20 Mm3/YR (16,000 AF/YR), of which approximately 18.5 Mm3 (15,000 AF) is considered potable (2,000 micromhos or less). CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS Governing Conditions of the Aouifer As may be expected in deposits consisting predominantely of interfingered alluvium, marine carbonates and detrital carbonates, the Fars aquifer is hetereogeneous and anisotropie. Transmissivity values vary accordingly, ranging from about 10 m2/d to over 2,000 m2/d (800 to 160,000 g/d/ft). The hydraulic conductivity also varies widely from about 0.14 m/d to over 200 m/d (0.46 ft/d to 700 ft/d). The specific yield could reasonably be determined at only one of the test sites where a value of 0.14 was obtained. It is assumed that a specific yield of 14 percent is realistic for this aquifer on a regional scale, but will vary locally. By definition, transmissivity is directly proportional to saturated thickness. Given that the other hydraulic properties are constant, as saturated thickness is decreased so is the trans- missivity. In terms of ground-water development, this means that a thin saturated thickness gives a lower transmissivity and less water. The Fars aquifer of the study area varies from over 200 m (700 ft) thick in the central region to completely thinned out along the southwestern, southern and parts of the eastern margins. Along 83 84 the central western boundary, the aquifer remains a fairly uniform thickness of about 100 m (300 ft). Subsurface anticlines distributed erratically under the bajada result in localized areas of thin saturated thicknesses. The chemical quality of the ground water is the most significant governing condition of the Fars aquifer. The aquifer sediments are assumed to have been deposited mostly under marine conditions, or were submerged in sea water after deposition. The ground water, therefore, is of poor quality except where diluted by fresh water recharge. Dilution of the connate water occurs almost entirely along the main wadi channels which drain from the adjacent mountains. Buried channels in the older alluvial fans also transmit fresh ground water from the mountain front, or recharge zones. Potable (2,000 micromhos or less) ground water occurs as 'shoe-string , aquifers following channels usually only a few tens of kilometers from the mountains. The furthest extent of potable ground water is in Wadi Al Ayn, in the south central region, where fresh ground water can be found up to 80 km (50 mi) from the mountains. Intercalated gypsiferous evaporites occur erratically on the bajada, and cause pockets of saline ground water which can not be diluted, or flushed, by fresh water recharge. It is believed that the combination of recharge being concen- trated along the wadi channels and the inherent saline conditions of the sediments results in the occurrence of poor quality ground water over most of the region. Shallow hydraulic gradients, and 85 low ground-water velocities attribute to the slow rate of dilution of the saline water. potential of Ground-Water Supply The Fars aquifer can be thought of as a bowl shaped basin of saline water that is traversed with isolated bands of fresh water. The presence of saline ground water largely controls the location of wells and, due to an intrusion hazard of poor quality water, the rate of discharge of production wells. Another factor controlling the location of production wells is the wide range in the hydraulic conductivity and the resultant variation in well yields. It may be necessary to drill several test wells at a given site before locating a well of sufficient yield. The estimated total annual ground-water flow entering the study area is about 34 Mm3 (27,500 AF/YR), of which approximately 24 Mm3 (19,500 AF) is potable. Present abstraction of ground water along the mountain front, or upstream, region of the bajada is mainly by aflaj and some wells (approximately 18.5 Mm3 /YR (15,000 AF/YR)). Practically all of the ground water used is considered potable and is about 70 percent of the fresh water presently entering the bajada. Approximate calculations of annual ground-water flow through the central part of the study area, that is, downstream of the present water use, indicates that about 21 Mm3 (17,000 AF), of which an estimated 8.5 Mm3 (7,000 AF) is considered potable, is lost from the area. These figures include a small percentage which is irrigation 86 return flow from the mountain front region. Additionally, about 26,000 Mm3 (21 MAF) of fresh water is in available storage in the bajada Fars aquifer. Assuming that recoverable ground water storage is about two thirds of the available storage, approximately only 17,000 Mm3 (1)4 MAF) is actually available. Because of the hazard of saline ground-water intrusion to the fresh water zones, only part of the fresh water in storage can be abstracted. The quantity of ground water available for future development on the bajada can not be accurately determined with the data of this study. It should be realized that the expected increase in water use in the intermontane basins of the catchment area and along the mountain pediment will affect the quantity of ground water available on the bajada. The extent of this effect is difficult to determine because increased water use, and the resultant decline in water levels, can induce more recharge to an aquifer. In general, it is believed that the Fars aquifer system should be able to support additional ground-water development which will be sufficient for the bedouin of the region. Additional Exploration Drilling The exploration drilling completed for this study should be considered as preliminary, and provided initial identification of the areas with potential for ground-water development. Additional drilling and testing is now required to more accurately quantify the water resources of these areas. Figure 21 shows the locations 87 z • • • • • • co ct• • co 0 < > 00 co c( L) L) • • - • • • . 1 . • • .I 1 I • ••n ../ ' •••• • 0- •••••,,, . (.4(v n ,..0' • 0 • ..= . ***.,.. cr) CI D. ct Cr CO \ w CL z 4— \., 0-w_ - M • 1-- 0 cv ••%.. _I cc) TC 5.. 0 0 ti) .,-1 cs. . •••••••. • 88 of the proposed explorataion sites and Table 12 lists their priority. All first priority sites study the potable ground water regions and should have an observation well drilled. The sites which have second priority are for the purpose of completing the data coverage of the bajada Fars aquifer and will probably be single well tests. An essential part of any ground-water appraisal study, which the completed drilling program did not fully address, is aquifer testing. Most of the aquifer tests were conducted without an observation well, and for a duration insufficient to account for gravity drain- age. The delayed yield effect, and the possibly of saline intrusion, requires that aquifer tests should be pumped continuously for at least 48 hours. At some sites a week of pumping would not be excessive. The proposed exploration sites will require aquifer tests of sufficient duration and discharge to fully test the aquifer para- meters. Existing sites which will require retesting are: CA863666; CA971540; CA894705; CA983201; DA074197; DA143249; DA146057; DA450677; and DA456839. Given the operating conditions in Oman, it may be more efficient and accurate to have an aquifer testing contract separate from the exploration drilling contract. Artificial Recharge Plans to intercept the relatively large quantities of water that are lost to the desert during intermittent floods is a popular concept with water resources planners in the Middle East. It is usually thought of as an easy way to solve water shortages and greatly increase the volume of ground water available for development. Although 89 Table 12: Proposed Exploration Drilling Sites. UTM NO. SITE NUMBER 1 PRIORITY2 1 CB5498 2 2 DB0145 1 3 CA3431 2 4 CA7163 2 5 CA7355 2 6 CA9255 1 7 CA9432 2 8 CA9567 2 9 CA9888 1 10 CA9959 1 11 DA0392 1 12 DA0857 1 13 DA0967 1 14 DA2046 2 15 DA2436 1 16 DA2688 2 17 DA3388 2 18 DA4255 2 19 DV3974 1 1 Sites are located to the nearest kilometer only. 2 First (1) priority are directly related to potable ground water and second (2) priority are for general Fars aquifer data coverage. 90 inducing recharge to an aquifer by impeding flood waters and thus increasing infiltration is possible, in many cases the local hydro- geology is ignored. One of the most important hydrogeologie requirements of a recharge project is the presence of a sufficient volume of unsaturated permeable material that can store the additional water. If under natural conditions there is a substantial amount of rejected recharge then inducing additonal recharge will result in more rejected recharge. The additional rejected recharge may cause in some areas water logging and, by evaporation, increased soil salinity. If additional storage is not available, then additional recharge needs to be balanced by additional discharge from the aquifer, such as abstrac- tion by man. If the local economic and cultural conditions can not justify increased water use then artificial recharge projects may not be feasible. Another hydrogeologic condition which is often overlooked is that increased withdrawls usually cause a lowering of the water table. The resulting increase in available storage will probably increase the quantity of natural recharge to the aquifer system. In some cases, this additional recharge may be sufficient for the increased demands. Artificial recharge projects are also applied where a fresh water/salt water boundary needs to be maintained, as in the study area. On the bajada the construction of simple recharge dams may be a viable way of increasing the volume of fresh water recharge 91 to further dilute the more saline Fars formation water. From the author's personal observation many of the large floods which originate in the eastern mountains will flow across the bajada. The isosalinity map (Figure 18) shows that under natural conditions fresh water recharge is occurring along the wadi channels. Increasing the amount of this fresh water recharge should further dilute the saline ground water and extend the potable ground water plumes. Simple recharge dams could be constructed in the main wadi channels on the central part of the bajada. As can be seen in Fig- ure 13, the depth to water in the central area is greater than 10 m (30 ft) and, therefore, unsaturated permeable deposits exist for additional ground water storage. If water development projects are implemented in this area, the resulting drawdown of the water table will create additional storage capacity. Artificial recharge is only mentioned as a possible means of increasing the volume of potable ground water in the study area. Before deciding upon the feasibility of such an undertaking, additional field work and studies would be required. Improvement of the Water Budget Although the hydrologic data available for this study was adequate for a preliminary appraisal of the Fars aquifer, additional information is required to more accurately quantify the water budget. Precipitation data is incomplete in Oman and in the bajada catchment area there are no rain gauges. The establishment of rain gauges in a region where rainfall is erratically distributed requires 92 a vast network of gauges and this is difficult to maintain. Measuring the runoff at the wadis which drain to the bajada is easier and more indicative of the volume of precipitation available. Subsequent to the data collected for this study, wadi gauges have been established at most of major wadis located along the mountain front. If regular monitoring of the water levels in wells on the bajada is conducted, the changes in water levels can be correlated to the wadi flow data and the percentage of recharge determined. Additional exploration drilling will give more data points to refine the equipotential maps and, therefore, the quantity of ground-water flow through the system. As indicated in this study, most of the ground-water flow into the Fars aquifer probably occurs as underflow in the major wadis which drain the catchment area. These wadis are not large, and have cut through the relatively im- permeable many limestone bedrock. Given that the saturated thickness, areal extent of saturation, hydraulic properties of the aquifer and the hydraulic gradient in these wadi gaps could be determined by exploration drilling and geophysics, then the underflow could be calculated by constructing a flow net. Changes in the underflow could be monitored by establishing observation wells that would record gradient fluctuations. Because there is practically no water use on the bajada proper, the ground-water flow also represents the discharge from the study area. The quantity which leaks downwards through the underlying clays and manly limestones is not known. This layer is considered 93 an aquitard with unknown permeability. Drilling and packer tests would be necessary to calculate the assumed leakage from the Fars aquifer. Water Resources Planning and Management Planning and management of ground water is usually the most difficult aspect of an appraisal owing to considerations of intangible social and political effects. The quantity of potable ground water available for future development in the study area is assumed to be adequate for the less than 2,000 bedouin occupying the region. The present water use is confined mainly to the mountain front and accounts for about 70 percent of the fresh ground-water flow into the study area. The future of large scale water development on the bajada will, therefore, be greatly influenced by future water use along the mountain front. Presently the Omani government is authorizing homesteading along the mountain front region and encouraging the bedouin to move in from the desert, or bajada proper. This policy is mainly influenced by the common belief that potable ground water does not exist on the bajada in sufficient quanities to support even limited development projects. It is believed that this study has shown that sufficient supplies of fresh ground water do exist under the bajada, occurring up to 80 km (50 mi) from the mountains. Water resources development in the central bajada region has several advantages. The bedouin would prefer to stay on the 94 land to which they have tribal and historical ties, and secondly, development closer to the UAE border would reduce the dependency that the Omani bedouin have on the UAE facilities. The disadvantages of water resources development on the bajada proper is that unmanaged increased water use near the mountains could drastically affect the availability of potable ground water. Overpumping on the bajada could locally reverse the hydraulic gradient and cause intrusion of the poor quality Fars formation water. Proper management of pumping and the construction of recharge dams, however, may prevent this problem in certain areas. In general, if water development projects are tailored for the indigeneous population, overuse of the potable ground water is unlikely. APPENDIX A THE ROLE OF THE AFLAJ IN OMAN Falaj, pl. aflaj, is the Omani Arabic word for a water distri- bution system. There are two main types: (1) a system which channels water from a spring or surface flow from a wadi bed, called a ghayl falaj and (2) the commonly known Persian system which taps ground water at a mother well and conveys the water to the oasis via a tunnel, termed a qanat falaj. In Oman qanat aflaj are most common, and will be the subject of this appendix. Several publications concerning the aflaj in Oman (University of Durham, 1975; Birks and Letts, 1976; and Wilkinson, 1977) adequately cover the anthropological, historical and social aspects of Omani society as it relates to the aflaj system and the reader is referred to these for a more detailed coverage of the subject. The literature does not adequately discuss, however, that the hydrogeologic conditions in many regions of Oman (that is, aquifers with low hydraulic con- ductivities and thin saturated thicknesses) result in aflaj being the most effective means of abstracting large quantities of good quality ground water. It is argued by some expatriate planners in Oman that the aflaj is inefficient, old fashioned and should be abandoned. Those that support such an idea oversimplfy a very complex system and ignore the social, hydrologic, and economic consequences if the 95 96 aflaj were abandoned. This appendix is a brief discussion in defense of preserving the falaj system in Oman. Historically, the aflaj were built to establish an agricultural base for Omani society. The climate is too arid to support non-irrigated farming, and without mechanization irrigation of large areas was not possible. Without the aflaj, Oman would not have been inhabited to the extent that it is. The major hydrogeologic condition required for a falaj to function, is that the surface gradient must be steeper than the water table gradient. This condition usually occurs along the flanks of the Oman Mountains; where many aflaj have been constructed. The best aflaj, in terms of quality and yield, are found in the intermontane basins and the piedmont regions. In the study area, aflaj occur only along the piedmont zone. Large aflaj occur on the coastal plain, but these consist of extensive conveyance systems from the mountain flanks. Most of the aflaj in Oman are less than 10 km (6 mi), and the subterranean section is usually less than 5 km (3 mi). The basic engineering principles of aflaj are straightforward. A generalized cross section of a typical piedmont plain falaj is shown in Figure 22, and a plan view is shown in Figure 23. Aflaj abstract ground water up-gradient from a village and, therefore, are able to supply the oasis with irrigation water flowing at the surface. This is the most important attribute of aflaj, even in the mechanized world of today. 97 a- 98 mother welts feeder branches . . d • ;•4 • • WADI " • FAN . -; • runnel section with traces on surface of original PIEDMONT PLAIN excavation shahs Debris nrqs • around shafts • Underground tunnel • Main gardens cut and cover section with cleaning shafts ( *wits land (seasonally cultivated) Kmmu ii Open cemented charmer SHARrA drinking water cultivated area .• • n • •• • • • • - — n -•. n • • • • • • . • • - • • • • • ..... • • • • , • • • • • n • .... • • • • • • • • ...... • , • • - • • • • • • • •, • • • • • • • ..... • • • - •• . • • .... • • • • • • •• • • ,• • • • Figure 23. Plan View of a Typical Falaj in the Bajada. 99 Figure 24 shows the general steps in constructing a falaj and clarifies the common misconception that access shafts are wells, which they are not. Usually, aflaj have only one or two 'mother wells' and their exact location are rarely known because they have been covered for several generations. It should be noted that it is not possible to excavate more than a meter or so below the water table without the risk of drowning the workers. By skimming the top of the aquifer, however, falaj discharge is highly variable with seasonal recharge causing fluctuations in the water table. Figure 25 illustrates the various engineering details and construction techniques of the aflaj found in Oman. There are several advantages and disadvantages of aflaj as compared to conventional wells. The most significant advantage of aflaj is they supply flowing water at the oasis. Good water quality is also an important advantage of aflaj. A falaj usually taps ground water in the recharge zone of the aquifer system; therefore, the water is fresher than that derived from wells in the oasis, which are located down-gradient in the aquifer. In many cases, ground water in the vicinity of the village is too saline for irrigation, and agriculture is dependent on the fresher falaj water. In regions where the ground water is of marginal quality, there is an increasing trend to use wells for irrigation. Future problems of increased soil salinity may result from replacing the fresh falaj water with the saltier ground water found under the oasis. 100 101 CROSS SECTIONS GR A VEL CHANNEL IN ROCK- Minimum MOTHER - WELL — Obtaining water from excavation, little airspace bedrock, conglomerate junction or conglomerate Pipe flew Loosely'. - cemented -, T E A C E _conglomerate Storage et debris OBLIQUE VIEWS from charnel Pulley orrn fa' WADI MOTHER-WELL- spoil heaps frog debris lo Obtaining water from incernented wodi grovels 4m1 He / / own., • /(NO OPEN ACCESS SHAFTS UNLINED TUNNEL PRONE TO • gosimeotor..71,1 IN WADI) DAMAGE IN WADI FLOWS , rged en:ggif-o-404 Tunrxtri :::10 tko ilkkiwom Access Shoff !showing mosonory lining hstT Roofs NAM? Atil Meandering 10101 ("chortnel -with bonding fe.-n144. 00 N.* in' O.Sill A Tee. 'original channel rioNkti Key Stones on Tunnel Roof 4 Wo er f Golfer y • • 'Debris from OPEN ACCESS SHAFT channel ..---Folse Roof FIRST ACCESS SHAFT Wore, o ------war II 010,-_-,• um••••n n••,...•1 - .100,...... ••01 n• ••,.... ;IMO/44 rot, Vr•Mr•Ironmoi sord11100,0,36momm.”.....•,1 INVERTED SYPHON Direci.on • OP" Noweaum...... • Li 4, Me 011. Imo Ns • •?: I Flow 0 ; w. sing Illtraregirwews—irr-tt roi ••• moseerWL, Protecting Buttress/ wilare!„,--- -swerwieOE/Jr a . "4%4 eswe w•- •„,orj,;,110/ too w.eiseeet%Pe'i Wad F wee' 0 r." . (Longi)udina Section) HAY YAL A —DIVERSION FORT (to protect villoge from CISTERN vrodi lbws) MAIN In Flow MOSQUE (with access for n washing) ilewle411 VILLAGE QUARTER 4U:flannel for lost through. flow of times when the cistern m not needed ita40 Cement Sides (locator iinpor fed qt!: cernent) NARROW CEMENT LINED voIlyel- Dom, Di str,butories CHANNEL— Relatively efficient peler logs ond to Cordent Old clothing ovairclzg STONE LINED CHANNEL LI,,"ZufMT,- f/ , Soil ALF ALF A UNLINED CHANNEL — Maximum surface area oer volume of water. Soil often overgrown Surface Chonnel 0 Access Shell WHEAT L ANDS Figure 25. The Various Engineering and Construction Details of the Aflaj in Oman. 102 The major disadvantage of aflaj is that they are affected by seasonal variations in recharge. It is possible for wells to penetrate the entire saturated thickness of an aquifer and, therefore, well yields are relatively unaffected by short-term water-table fluctuations. In Oman during the 1970 , s, drought adversely affected the yields of many aflaj and a greater dependence on wells resulted. Another advantage of wells is that an individual can, if the hydrologic conditions permit, increase the volume of water available simply by constructing additional wells. Under the aflaj system, water rights are complicated and usually there is little excess water to distribute. It would also be economically prohibitive for an individual to build a falaj. This discussion is concerned only with the existing aflaj/oases and it is understood that new farms located away from the oases would require water wells. The lack of additional falaj water forces a reliance on wells in the oases where either agricultural expansion is taking place, or falaj discharge is strongly affected by drought. Although wells apparently represent an easy and relatively inexpensive means of obtaining a more consistent source of water, the adverse affects of ground-water mining should be considered. Mech- anized pumping on a scale not previously employed in Oman, may have a drastic effect on many aquifer systems. The inherent design of a falaj prevents ground-water mining. The aquifers in Oman are in a steady-state condition with the aflaj discharges. The importance of the aflaj has recently been diminished due to Oman's foreign 103 trade surplus from oil exports. It is now possible to import food on a large scale, and this has affected the economics of local agri- culture owing to competion from foreign agribusiness. Omani farmers now must consider new and larger capital improvements of their agri- cultural system. Because the original cost of building the aflaj has long been returned, the present users are practically using "free" water. This is the crux of the aflaj improvement and main- tenance problem. When major repairs are needed, there is a reluctance to do so because the capital return is not predictable for several reasons. First, the discharge is not constant owing to the suscep- tibility to variations in seasonal recharge. Secondly, the return on the investment is generally low because most of the water is used to irrigate date palms, which are important to Omanis but are not a high cash crop. There are, however, many secondary and intangible benefits that are derived from aflaj-fed oases and these should be considered. The average village/oasis in Oman is basically a large date grove with houses scattered among the date palms. Besides providing dates, the date palms give shade and cooling from the relentlessly hot sun. The oasis is actually a tropical micro-climate, and intercropping below the date palms is widely practiced. It can not be overstressed how important the date-grove oasis is to Omani culture and society. Presently, the major benefits of the aflaj are cultural and, therefore, difficult to assign a monetary value. It is not easy for expatriate advisors to fully understand the social benefits of the aflaj. 104 Omani officials realize that the oases should be kept intact but are unaccustomed to allocating large revenues to do so. The Omani government must decide if the intangible social and cultural benefits of the aflaj outweighs the costs of improvement. Recent efforts to prevent the aflaj system from being abandoned due to neglect is being undertaken by the Omani government, and a separate department in the Ministry of Agriculture was established to administer this program. Practically all of the aflaj were con- structed hundreds of years ago using simple materials and techniques. Presently, many aflaj deliver only a small percentage of the ground water which enters at the mother well and transmission losses of over 70 percent have been measured (University of Durham, 1975). Most of the repairs involve relining the surface channels with cement and, occasionally, sections of the tunnel are replaced with concrete pipe. The renovations rarely involve the mother well section, and if so, do not correct the inherent problem of fluctuating discharge. The aflaj program is currently understaffed and work is backlogged for months. Although it is a commendable effort, the overall program is one of reaction to damaged aflaj instead of action to preserve the aflaj through modernization. If the decision is made to preserve the aflaj, or more correctly the village/oasis which is the crucial aspect for Oman, techniques for doing so are site specific. The most difficult problem to solve will be determining the base flow that each oasis needs and relate this to the capability of the respective aflaj. This will involve 105 strong local political implications and may require government inter- vention. Efforts should be made to keep the aflaj flowing by gravity but it is doubtful if this will be possible during periods of drought when the water table is low and hence the gradient changed. The mother well could be replaced with deeper infiltration galleries and pumps that would be used when the water level is too low for gravity flow. Transmission losses can be minimized by replacing the conveyance section with pipe. If a valve is installed then the discharge can be reduced during times of low water demand and/or when discharge is high due to seasonal recharge. Presently, excess water is drained off to waste. In general, aflaj are simply a method of abstracting ground water where it is located, and conveying it to a place where it is needed. Many countries do this on a large scale; for example, the southwestern part of the U.S. It seems clear to this writer that to save the village/oasis culture, a national effort is required with a large initial capital investment. The recent trend towards constructing more wells instead of repairing existing aflaj, is only a temporary solution that will possibly lead to more problems in the future. 106 .4 H oc, I-1 >1 va rl 0 0 o) co co co co a) a) 4) a) a) a) a) a) a) a) >4>-, o4 >4 >. >4 >-1 >4 >4 >. P41 4) 4/1 U) 0 N N N N go co co >-10 .nt O co o O -... a o 0 -... a --... o tn F , 0 C-- Le% ,.... In Ln N 0 Ln 0 N I-- N 0 C-- • H t.. 4 t•-• N CV t•-• 0 •-- 0% N 0 -0 (nn co .O . •. O...... O. 1. O...... •• 04 C4 .C4 .1.1 Ch N ',. 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Z 0 H ›. a. 1--1 1--1 ›. 0 •/-1•/-1 .--3 C/5 O OAO A A A 4-) Ci) 2 ° II 2 CLI 10 V A4 .ri • • • .0-1.0-1 • • • O Ci) = a• C. C. 0 cn A. 4- C \ i rn .4- Ct C../ C../ = ED '4- CV Cn 121 APPENDIX C: RESULTS OF THE PAWR EXPLORATION DRILLING TOTAL COMPLETED STATIC WATER SATURATED SPECIFIC PAWR REF. U.T.M. COMPLETION DEPTH DEPTH COMPLETEE LEVEL THICKNESS YIELD TRANSMISSIVITY CAPACITY CHEMICAL NO. NUMBER COORDINATES DATE (m) (m) IN (m) (m) (L/sec) (m2/day) (L/sec/m) ANALYSIS REMARKS 1. CB616933AA 03663-26193 04/27/83 122 122 Detrital 30.40 91 5.0 30 0.2 See Table 9 Salinity increases marine 04/26/83 with depth 2. CB713031AA 03733-26101 04/17/83 152 152 Detrital 24.31 128 14.0 90 0.4 See Table 9 Salinity increases marine 04/17/83 with depth • 3. CB734194AA 03749-26314 04/20/83 24 18 Alluvium 3.40 17 <1.5 No test N/A See Table 9 Single well test 04/23/83 well test 4. CB942299AA 03929 - 26429 04/19/83 37 18 Alluvium 11.44 3 <0.5 No test N/A See Table 9 Single 04/25/83 5. DB009465AA 04096-26045 02/13/83 44 5 Alluvium; 2.66 3 <1.0 No test N/A None Single well test clay 03/15/83 6. CA362956AA 03325-25696 10/14/82 102 102 Detrital 3 • 45 99 4.0 40 0.2 See Table 9 Pumping well marine 10/18/82 7. CA362956BA 03325-25696 10/16/82 50 50 Sand 3.52 47 N/A 40 N/A None Observation well 10/18/82 8. CA364848AA 03344-25688 10/18/84 50 50 Sand 3.81 46 N/A N/A N/A See Table 9 No test 04/27/83 9. CA369513AA 03391-25653 10/30/82 50 50 Sand 3.70 46 4.0 30 0.2 See Table 9 Pumping well 10/30/82 10. CA708100AA 03780-25010 01/84 200 200 Marl & 10.50 48 1.0 No test N/A None Water struck at mud stone 152m, confined 11. CA845906AA 03850-25496 11/83 200 200 Detrital 6.20 140 18.0 70 N/A None Single well test marine 12. CA855906AA 03850-25596 11/83 200 200 Detrital 10.60 140 20.0 380 N/A None Single well test marine 13. CA863666AA 03836-25666 10/83 239 239 Detrital 9.6 0 170 N/A 100 N/A None Single well test marine 14. CA887807AA 03870-25887 04/01/83 152 152 Detrital 23.12 129 24.0 120 0.9 See Table 9 Single well test marine 04/02/83 15. CA894705AA 03840-25975 04/07/83 113 113 Marls 11.76 101 8.0 50 0.3 See Table 9 Single well test 04/09/83 122 APPENDIX C: RESULTS OF THE PAW!? EXPLORATION DRILLING (continued) TOTAL COMPLETED STATIC WATER SATURATED SPECIFIC PAWR REF. U.T.M. COMPLETION DEPTH DEPTH COMPLETED LEVEL THICKNESS YIELD TRANSMISSIVITY CAPACITY CHEMICAL NO. NUMBER COORDINATES DATE (m) (m) IN (m) (m) (L/sec) (m2/day) (L/sec/m) ANALYSIS REMARKS 16. CA971540AA 03914-25750 10/83 221 221 Detrital 15.10 170 N/A 280 N/A None Single well test marine 17. CA983201AA 03930-25821 03/27/83 227 159 Marls 16.68 146 24.0 4 00 1.6 See Table 9 Single well test marine 03/27/83 @ 20 hours 18. DA074197AA 04049-25717 03/03/83 84 77 Detrital 10.15 71 N/A 300 N/A None Observation well marine 02/28/83 19. DA074197BA 04049-25717 03/03/83 53 51 Detrital 11.30 42 18.0 300 1.0 See Table 9 Pumping well marine 03/05/83 20. DA139760AA 04196-25370 02/02/83 117 98 Detrital 7.67 103 4.0 10 0.1 See Table 9 Single well test marine 02/15/83 21. DA143249AA 04134-25429 12/30/82 182 152 Detrital 9.30 143 N/A 900 N/A None Observation well marine 02/14/83 22. DA143249BA 04134-25429 01/03/83 157 150 Detrital 9.70 141 20.0 900 3.1 See Table 9 Pumping well marine 02/14/83 23. DA146057AA 04165-25407 01/19/83 140 112 Detrital 8.50 129 24.0 2,300 33.3 See Table 9 Pumping well marine 01/19/83 @ 24 hours test 24. DA146057BA 04165-25407 01/23/83 83 83 Detrital 8.85 75 N/A 2,300 N/A None Observation well marine 02/10/83 25. DA164183AA 04148-25613 02/23/83 168 168 Detrital 21.20 139 2.4 80 0.5 See Table 9 Pumping well marine, clay 02/25/83 26. DA164183BA 04148-25613 02/23/83 76 75 Detrital 20.15 55 N/A 80 N/A None Observation well marine 02/26/83 27. DA185367AA 04156-25837 03/10/83 38 38 Marls 7.55 16 N/A 1,500 N/A None Observation well 03/14/83 28. DA185367BA 04156-25837 03/13/83 32 30 Marine 7.64 20 18.0 1,50 0 2.3 See Table 9 Pumping well carbonates 03/15/83 29. DA273755AA 04235-25775 03/07/83 20 20 Clay Dry Dry N/A N/A N/A None Abandoned 30. DA355039AA 04353-25509 12/08/82 61 61 Detrital 17.53 39 2.0 1 0 0.3 See Table 9 Single well test marine, clay 12/13/82 123 APPENDIX C: RESULTS OF THE PAWR EXPLORATION DRILLING (continued) TOTAL COMPLETED STATIC WATER SATURATED SPECIFIC PAWR REF. U.T.M. COMPLETION DEPTH DEPTH COMPLETED LEVEL THICKNESS YIELD TRANSMISSIVITY CAPACITY CHEMICAL (L/sec) (m2/day) ANALYSIS REMARKS NO. NUMBER COORDINATES DATE (m) (m) IN (m) (m) (L/sec/m) 4.0 35 <1.0 No test N/A None Abandoned 31. DA455878AA 04457-25588 11/25/82 78 78 Clay, sand; siltstone 11/28/82 Table 9 Pumping well 32. DA456839AA 04463-25589 12/04/82 32 30 Alluvium 5.8 24 24.0 3,100 29.3 See 12/07/82 Observation DA456839BA 04463-25589 12/06/82 31 25 Alluvium 5.7 19 N/A 3,100 N/A None well 33. 12/07/82 Abandoned 34. DA560405AA 04500-25645 11/24/82 78 39 Alluvium 5.0 34 <1.0 No test N/A None 11/27/82 No test N/A Abandoned 35. DA560405BA 04500-25645 11/24/82 61 24 Alluvium 2.7 21 <1.0 None 11/27/82 36. CV785850AA 03755-24880 01/84 140 140 Marl; 16.59 0 1.0 No test N/A None mud stone when drilled; 37. CV996037AA 03963-24907 02/84 140 140 Marl; 2.80 0 No test N/A None Dry mudstone SWL 1 week later Abandoned 38. DV188450AA 04185-24840 02/84 160 160 Clay Dry 0 N/A No test N/A None 1211 • • .8) CsJ •41.n V) • Amok "...no., CV KC CO ("I >- CT) cr V) 02 = CI' CO GI nn•I LLI CL) >. CO • ZY- 0 .7 LA) A. "0 ta..1 CC -..... CC C) 01 —o ..—. E I— —i IS) (J) _I .--1 CO WWII CV E h. CI . 0 0.. z CO ,-.1 CO Z 0, • CO = .--. C. 01 II I I O. I— = .--) cÇ CY 1- CC > .-J 02 2 CC GC LU 0 LU (...) LI- 2 V) 0 CO —J Kt- CO 0 — I 1 r I II 0 ro Of o c4 V. tt, 1, 8 o ci o 6 ci 6 ( Sie4") S NMOOMV80 1vnais38 • • 125 0 -o " o • —.." 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Ir I r o 0 o o 0 a (siapLu) NMOOMV80 127 • C, • 0 0 • II 1-4 • C • 4-, • 4-, 4-, 4, • N. o o I I • —o Cr) • • • 4— 4-, • • • — o • I I • Cr. N., C.1 C'-' • 4-, *4" C‘J 4-, 'ftftn E 4, CD CV CV CD II I! CY S.- I I III! I I I 0 61 Cr co co o ci vr to co (0 CO 0 NI CV CJ (\I . rr? (sJapw) S NMOOMV80 1V-10193 .2:1 128 •-n o • o IMO./ GM 111•11•111 n1 • • • • • • • CD • • • • 2 o o • • 0 csi en co Cr (.9 1-4 o (.4 I I I re) cu _ d ci ci (sielew ) NMOOMV80 129 :d • O 0 Q. • MI • ...... • fr) • E O c2- I N. - o i Cs.1 V 17 i • d Cr) E 1 E • • r--. 'V • 0 ...... • CN.1 •• CV K E CD ›- cr) .--. N. • cc co a en • 1.1.1 k CO .cC C\J CI' CV 0 ...._... 4? 0 •st CY • C-.) ,-, I II II 1,n, nn•.11 LLI 0 —o • f= C\Jen I- I I— co -- E (/ ) C7, C \J • 1.1.1 Cr .:1- • ct- I- L.) 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