Figure 1. Map of Oman.
Groundwater Management in the Sultanate of Oman (a case study)
Ahmed Al Barwani and Said Al Hattaly, Water Resources Affairs Experts,
Directorate General of Water Resources, Ministry of Regional Municipalities,
Environment and Water Resources,
P.O.Box 2575, Ruwi 112, Sultanate of Oman.(firstname.lastname@example.org)
The importance of water in the arid zone is so pervasive that, its distribution reflects
the basic social values of equity and justice. The influence of water can be seen in
fundamental process-response systems. Resources are developed in response to
environmental requirements, but the developments themselves then alter the
environment. In Oman groundwater distribution is related to geology as well as the
climate. The complex geological structure of the Oman Mountains has resulted in
equally complex and well-developed fracture systems. These fractures intercept and
store rainfall which then acts as conduits to transmit water from higher altitude and
gradually discharges to springs, or as seepage into adjacent alluvial aquifers.
Settlements and traditional agriculture is commonly located near the mountains
mainly in piedmont areas where underground infiltration galleries known as aflaj can
obtain water supplies. A strong solid structure has evolved around the aflaj which
remain in wide spread use today. This paper examines the situation of the
groundwater aquifers, current water resources management, existing water policy and
Oman is situated in the south eastern part of Arabian peninsula, surrounded by United
Arab Emirates (U.A.E) from north west, Saudi Arabia from the west, Gulf of Oman
and Arabian sea from the east and south east, Figure-1. Oman is highly dependent
upon groundwater for most of the water supply. Desalination plants have been
established to provide domestic supplies for some centres, but agriculture, which is
responsible for more than 92% of fresh water consumption, is almost entirely reliant
The early settlements patterns of Oman were strongly
affected by the hydrogeology of the region. Settlements
and traditional agriculture is commonly located near the
mountains mainly in piedmont areas where
underground infiltration galleries known as aflaj can
obtain water supplies. The aflaj intercept the
groundwater base flow from the mountains and
channeled the water down to the settlements and for
irrigation in agricultural areas..
Prior to the recent development, water use in Oman was
stable and limited by the available technology.
Settlements were well established and water resources
were in long-term equilibrium with demand. Large-scale changes in the pattern of
water resources use started after 1970. It is now clear that, in most parts of the
country, water demand has exceeded the long-term rate of natural recharge to the
system and resulted in in-equilibrium once exist (Al-Hattaly 1998).
Two distinct systems occur, winter (November to April) and summer (May to
October). The southwest monsoon influences the extreme south and southeast coast
of Oman. Generally Oman is classified as arid or, in parts, extremely arid and has
virtually no permanent, potable, surface water resources (rivers, lakes).
Mean annual temperatures are typically between 26 oC and 29 oC through the lowland
areas of the country, but maximum daily temperatures rise to above 40 oC during the
summer months. Snowcaps sometimes occur above 3,000m during winter months.
Rainfall varies from less than 50 mm in central Oman, rising to over 300 mm in the
Northern Oman Mountains and shows wide year-on-year variation.
High summer temperatures and low humidity in the interior create high evaporative
conditions with mean daily evapotranspiration exceeding 12 mm. The higher
humidity in coastal regions, such as the Al Batinah and Salalah Plains reduces mean
evapotranspiration to less than 10 mm per day. Crop water requirements vary
In general, geology of Northern Oman Mountains comprises of carbonates rocks
mainly (Mesozoic limestone and dolomites), the oldest rocks in the area belongs to
the pre-Permian basement (Autochtonous Unit A), which consists of phyllites, shales,
siltstones and meta-volcanic. Boreholes drilled into pre-Permian formations are
generally low yielding due to their impervious character (PAWR, 1985). Adjacent
nappes comprised of Hawasina nappes (deep sea sediments), Semail Nappes (ocean
crust and mantle ophiolites – i.e., gabrro, peridotite, serpentinite etc,). This complex
and fascinating geology provides a challenging framework for hydrogeologic
problems. The general geology of Oman is shown in Figure 2, which was constructed
with the aid of the geological maps compiled for the former, Ministry of Petroleum
and Minerals (BRGM, 1984, 1986, 1992), and Glennie (1975).
In Southern Oman (Dhofar) two distinct physiographic zones are recognized; a
mountain plateau dominated by Tertiary limestone bedrock and a piedmont plain
zone comprising of small alluvial fan and plain systems, which merge with coastal
beach deposits. The geology of the Dhofar mountains comprises mainly of
sedimentary carbonates (limestone) of tertiary age of Hadharamut Group. Parts of the
limestone is of Karstic nature which is highly permeable and the other part overlies
Cretaceous marine sediments of inter-bedded marl and fine grained limestone that are
non-Karstic and considerable less permeable.
Surface Water Resources
In Oman, as elsewhere in arid and semi-arid
zones, surface water flow from the mountains
watersheds is ephemeral and generally occurs as
brief periods of relatively intense flood flow
closely associated with individual storm events.
Drainage of the mountain watershed storage
following major rainfall events may cause one
or two months of surface flow at the mountain
fronts in occasional years usually feeding
Ghayli aflaj for local village water supplies.
Similar characteristics were reported by Cooke
and Warren, (1992), that the varied nature of
flow in ephemeral stream channels reflect the
full range of climatic and drainage basin
characteristics, notably type and distribution of
rainfall, infiltration capacity of surface material,
antecedent moisture conditions and local
topography. In deserts where precipitation
occurs as short, intense showers, the flash flood
is a typical result. The hydrographs of such
floods usually rise steeply, show a brief period
of peak flow, and decline relatively slowly.
The falaj system has been used in the Middle East and in North Africa for many
centuries. In addition this is similar to the qanats systems of Persia, foggaras that are
underground channels, exist in Algeria, and vestiges, perhaps based on Roman
hydraulic works, are found throughout the Mediterranean region. Three different
types of water source supply the falaj systems in Oman; First, Ayni falaj - natural
springs from alluvial and fractured bedrock sources, second, Ghayli falaj - perennial
wadi flow, and third, daudi falaj - groundwater contained in wadi gravels (beneath
both present day and former wadi courses) and possibly often fractured bedrock
layers. Each system necessitates a different configuration of falaj, however all
comprise three basic sections: (1) Water collecting sections, (2) Water transporting
sections, and (3) Water distributing sections.
Groundwater distribution in the limestone massifs is controlled both on a large scale
by the overall structure and geometry of the aquifer, and on a smaller scale by the
detailed disposition of fracture flow paths. Despite local variations in lithology and
structure, the scale of the massifs is such that overall, approximately homogeneous
groundwater flow may be assumed, thus giving rise to the spring line distributions
Al-Hattaly (1998) outlines that, fresh and brackish groundwater flow systems in
Oman tend to fall into three categories, those that are reliant on storage, those that
Figure 2. Geology of Oman
depend on recharge and, the major bedrock systems in the northern and southern
Flow systems reliant on storage includes the larger sedimentary basins where thick
sediment or limestone sequences contain large volumes of groundwater in storage,
much of which may be quite old and related to wetter climatic periods. These flow
systems are buffered by large storage and can withstand climatic cycles with little
variation in yield. The thicker aquifer sequence provides a measure of security.
Groundwater systems reliant on recharge occur in basins, which contain relatively
thin active aquifer sequences underlain by rocks markedly lower permeability. These
occur mainly in upper catchment areas and highland valleys. Here, thin veneers of
coarse, poorly sorted, but locally highly permeable wadi gravels, generally rest upon
relatively low permeability bedrock. In this setting, bedrock features provide natural
traps within which groundwater flow is constructed and may discharge to surface,
often feeding aflaj systems. It cannot be guaranteed that depletion problems can be
overcome in these flow systems by additional wells. Bedrock yields may be very low
and thin alluvial aquifer sequences possessing little storage, may not be able to
sustain supply during prolonged dry periods. They are essentially transient systems
with short response times and are relatively difficult to manage because they are also
very susceptible to development pressures and drought.
The large fractured bedrock aquifer systems, which comprise the mountains of
northern and southern Oman form complex, elevated groundwater storages. Their role
may be considered as analogous to that of header tanks in a reticulated supply system.
They maintain pressure and exploit gravity to drive groundwater along all avenues of
primary and secondary permeability. This flow maintains highland valley aflaj
systems, feeds numerous springs and provides seepage to adjacent sediments at wide
ranging depth via manifold flow paths. The mountainous areas receives more rainfall
and recharge than the plains and are less susceptible to prolonged dry periods
although shallow, local flow system may fail, particularly in more elevated areas. Out
seepage may be considered to be relatively consistent and important source for
several adjacent alluvial systems.
Regional Groundwater Resources
Groundwater distribution is related to the geology as well as the climate. Farther north
Musandam rugged mountains rise up to 1,800 m. Musandam is slightly wetter than
most parts of the Sultanate, with an average annual rainfall of about 180 mm. Water
supplies in Musandam are drawn almost entirely from wells and boreholes in the
coastal alluvium. In some inland areas, small communities derive their domestic
supplies from rainfall collected in cisterns or birkats. Aflaj are the major water source
The alluvial fans flanking the northern Oman Mountains form important aquifers that
have been extensively developed by aflaj systems and wells. On Al Batinah, alluvium
may extend to depths of up to 600 m near the coast. The Batinah has important
reserves of groundwater that are heavily exploited for irrigated agriculture. Over
pumping has resulted in saline intrusion in traditional farming areas nearer the coast.
In Al Batinah coast area, salt water intrusion reported at some places as high
abstraction rate from the aquifer exceeds the annual recharge. In addition, variation of
the size and type of material that make up the aquifers play an important role in
determining groundwater quality at Al Batinah area. Presented conditions indicate
that fresh water discharge to the sea on the Batinah coast is largely intercepted by
pumping in the coastal zone. The lot of the salt-water wedge is located several
kilometers inland in some places and could pose a serious threat to existing municipal
In the Interior, to the west and south of the northern Oman Mountains, the geology is
dominated by a number of major wadi systems. These wadis occasionally carry large
volumes of runoff generated in the mountains, considerable distances across the plains
towards Al Wusta region and the UAE. Traditional water development was largely
based on aflaj, but in recent years many wells have also been constructed.
In the upper catchment areas of Al Dhahirah and Al Dakhliyah, thin alluvial aquifers
with small storage depend upon frequent rainfall to maintain supplies and may
become seriously depleted during dry periods. Further down basin thicker, alluvial
sequences usually provide more reliable sources of supply, although water quality
may not be as good. Investigations carried-out in early 1990’s discovered large,
untapped, groundwater resource in the Al Massarat and A’Sharqiyah Sands aquifers,
which lies under the western plains of Al Dhahirah region and under the sands of
A’Sharqiyah (Wahaybah Sands).
In the south, on the Salalah Plain, water for domestic and agricultural use is mostly
pumped from dug wells and boreholes. These supplies are supplemented by four
springs located at the foot of the jabal. The Salalah Plain is underlain by limestone,
with a thin covering of alluvium. Groundwater is found in both the alluvium and the
underlying limestone, but larger supplies are primarily related to fissured zones in the
limestone. The Salalah Plain experiences cool, wet conditions in the summer due to
the southwest monsoon. Studies have shown that the interception of monsoon mist
("occult" precipitation) by rock faces and vegetation is an important part of the water
The Najd is underlain by a sequence of limestones which are found throughout much
of central and southern Oman. These limestones contain substantial quantities of
groundwater suitable for agriculture. Further investigation is currently on-going in
this area to evaluate the resource and possible development options.
The sparsely populated Al Wusta region of central Oman covers about one quarter of
the country. Fresh groundwater is relatively uncommon and occurs as narrow lenses
under major wadis or depressions, which overlie more saline regional groundwater.
These systems are periodically recharged by runoff generated during occasional,
intense rainfall events.
Water Situation Monitoring
Monitoring is the regular measurement of indicators to observe the changes in their
values that may occur with time. Currently in Oman there are over 4,000 monitoring
stations for climate, rainfall, wadi flow, sediments, aflaj, groundwater levels and
groundwater quality (Table 1). The recent review (1998) of the national monitoring
network finds that climate, rainfall and wadi flow monitoring comply broadly with
WMO Standards, although data collection appears rather sparse in the desert regions.
For groundwater level measurements, the data show that the national average density
is about one monitoring well per 132 km2.
Table 1. National Monitoring Network
Laws and Regulations
Since 1989, the governmental laws and regulations had a very important role in
protecting Oman’s water resource either from depletion or pollution. The Sultanate
had taken several important actions regarding conservation of water resources,
through many progressive regulations in order to control the demands, abstraction and
protection of water resources. Several royal decrees were issued to declare water as a
national resource, establishment of wellfield protection zones and disposal of solid
and dangerous materials.
Development and Management
Although historical events and climatic fluctuations brought periods of prosperity or
hardship, the overall picture of Oman’s water resources use and management prior to
the beginning of the renaissance is one of stability. The technologies available (aflaj
and dug wells) limited both the quantity of water available and where it could be
obtained, as they had for centuries. Settlement patterns were thus well established and
only the area of land irrigated varied as falaj flow permitted. Hydrologically,
resources were in long-term equilibrium with the demand. Indeed, the self-regulating
nature of aflaj prevented over-use.
Large-scale changes in the pattern of water resources use started after 1970, but on an
individual scale changes had already begun. Oil exploration and then oil production
introduced new technology, which required development of new water resources. It
is this technology, which has disturbed the once, exist equilibrium. It is now clear
that, in many areas of Oman, water demand has exceeded the long-term rate of
natural recharge to the system.
The formation of Ministry of Water Resources in 1989 and merging of water
resources sector with Ministry of Regional Municipalities and Environment in 2001
has resulted to further centralization of water resource functions included assessment,
monitoring and management of water resources.
Following that formation key regulatory measures and resources protection were put
in place relating to water management and conservation. These included well
permitting, protection of wellfieds and aflaj, solid and wastewater disposal and
treatment and groundwater cleanup.
Being aware of the rapid change in water resource use and increase in demand which
has disturbed the once existed equilibrium counteract action were initiated in the
resource augmentation and substitution. These included construction of recharge
dams, re-use of treated effluent, use of brackish waters and relocation of users.
Since agricultural water use accounts for more than 92% of the total water use in the
Sultanate, it is essential that agricultural users fully participate in conservation and
management measures. An overall reduction in agricultural water use can be achieved
by a combination of measures involving:
adoption of improved irrigation techniques;
optimum use of selected irrigation techniques;
selection of crops that have lower water requirements;
movement of cropping to areas of brackish water, away from areas where the
resources are over-committed.
To be successful, these improvements will need to deliver significant economic
benefits to the farmer then water conservation will become a natural by-product of
changes induced by market forces.
Growth in urban demand can be constrained by encouraging water-conserving
appliances and better plumbing, and by rigorous loss-control programmes.
Developments of urban wastewater schemes are now taking place. These will offer a
"new" resource, namely treated wastewater. The Sultanate presently limits the use of
treated wastewater to amenity irrigation. Since wastewater reuse regulations were
introduced several years ago, a worldwide evaluation of experience in wastewater
reuse by World Health Organisation suggests that this resource could be safely be
used for a wider range of applications.
Although a very arid country, Oman is blessed with good natural fresh water
resources, which must now be carefully managed to ensure that they continue to meet
the needs of future generations. The introduction of appropriate demand management
measures in areas irrigated from wells will have to be introduced to overcome locally
serious deficits. Public awareness information campaigns should be augmented as a
preliminary action to active conservation control, of domestic, industrial and
agricultural water use.
Wastewater from municipal areas represents an important resource that should be
incorporated within resource planning. As the coverage of collection and treatment
systems expands, effluent of better quality may be used beneficially either for direct
use in agriculture or to recharge the aquifer through recharge lagoons.
Al Hattaly, (1998), Groundwater Management in Oman. International Groundwater
Conference: Groundwater sustainable solutions, Melbourne Australia 8-13 February,
Cooke and Warren, (1992), Desert Geomorphology. UCL Press London.
BRGM, (1984, 1986, 1992), Geological Mapping of Oman (Ministry of Petroleum
and Minerals, Sultanate.
Glennie K. W. (1975). The Geology of the Oman Mountains, Scientific, Scientific
MWR Report. 2000. “National Water Resources Master Plan”, Unpublished Report,
October 2000, Sultanate of Oman.
UNESCO/WMO (1982) Guidelines for Evaluation of Water Resources Assessment
Programmes based on the handbook for National Evaluation. WMO (1981) Guide to
Hydrological Practices, Publication No. 168, Geneva.