Kaushalendra Singh –
Oman is in the world’s arid belt that depends on groundwater and its limited rainfall for most of its water supplies.
The demand for water continues to rise, with desalinated water making up rest of the supply.
Thus it always remains a challenge to explore new groundwater resources.
According to official sources, a national water resources conservation plan is in place to further rationalise and improve water consumption practices and explore for new groundwater reserves.
Hydro geologists are of the view that groundwater occurs in the alluvial deposits in the beds of natural water course called ‘wadis’, where it is exploited by wells and aflaj, the traditional irrigation system of Oman.
Recharge of the alluvium occurs directly from floods, from rainfall and by transfer from hard rock aquifers.
In the northern mountains of Oman, the Samayil Ophiolites form locally an important aquifer system, feed aflaj and stores large quantities of water.
The water is released slowly into the wadi alluvium and thus maintains supplies to wells and aflaj in small alluvial basins.
These rocks yield locally significant quantities of good quality water.
Other significant sources of groundwater in the Northern Oman mountains are the limestone and dolomites of the Hajar Super Group.
In Dakhiliyah Governorate the limited aquifer storage and the infrequent rainfall events combine to make the water resources unreliable, especially in the upper reaches of the wadis.
Traditional water development has been based on aflaj though in recent years wells have become more important.
Al Massarat Aquifer is a large groundwater resource in Al Dhahirah Governorate, which has been potentially developed for municipal water supplies and support of agriculture in the Al Dhahirah Governorate.
“In the Najd, Rakhyout and on the Jabals of Salalah, aquifers in the Umm er Radhuma geological formations are the most important sources of groundwater for potable and agricultural use.
In the Najd and Jabal areas these aquifers have prominence. The confined aquifer of the Umm er Radhuma is artesian in nature at some places in Najd.
Near the south facing escarpment of the Dhofar mountains, in Rakhyout, Salalah and Mirbat-Sadah areas, Cretaceous sediments abut Tertiary Hadhramaut Group.
Near the edge of the escarpment where the groundwater table slopes steeply southwards, the UER aquifer can be unsaturated.
In these places the underlying Cretaceous Formations are an important source of water.
In their paper presented at MRMWR Hydrogeological Seminar, Aysha Mohammed al Khatiri and Ahmed Said al Barwani, have stated that rainfall is the main source of water in Oman; the average annual rainfall is 100 mm, varying from less than 50 mm in the internal desert regions to over 350 mm in the mountain areas.
“In the north of Oman, rainfall occurs during the winter (November-April), and during the summer rain occurs as thunderstorms.
Whilst in the south it occurs as results of the monsoon, which is a seasonal summer storms (June-September) and named locally as Khareef.
It provides a source of natural recharge to a number of aquifers including those in the interior and coastal plains.
In the interior and coastal plains despite, recharge from the mountains, aquifers can become stressed in some areas,” the paper stated.
The water resouces of the Sultanate occurs in two ways, either groundwater which is represented by wells and Daudi aflaj (Qanats) or surface water which is represented by the Ghaily aflaj, springs and few perenial wadis.
The flow in the wadis through runoff of short duration on few events during the year depends on rainfall, hydrological and hydrogeological characteristics of a given catchment.
According to hydro geologists, the runoff is considered to be a major source of natural recharge of the aquifers.
The flow in wadis occurs as flash flood and these are important in recharging the shallow aquifers.