Water quality declining in Salalah plain aquifer

Muscat, Dec 4 – Salalah’s plain aquifer is facing a serious deterioration in water quality and is threatened by salinity pollution due to sea water intrusion, a study has found. It is facing vegetation cover deterioration due to overgrazing that leads to the reduction in plain aquifer water recharged by mist catching in Khareef (autumn), according to a study conducted by Dr Mahaad Shammas, Assistant Professor at Civil & Environmental Engineering, College of Engineering, Dhofar University.
Such conditions will have economic, tourist and social implications for Dhofar, says the study.
Dr Mahaad said the plain aquifer is considered the only source of fresh water that meets the growing demand in Salalah. The aquifer water is pumped through more than 1,500 production wells.
Groundwater extraction reached 68 million m3 in 2009 and is expected to increase 3 per cent annually to reach 74 million m3 by 2020.
The study has estimated the annual subsurface recharge flowing from Jabal Al Qara to 50 million m3 per year. Safe yield extraction is expected to increase 17-21 per cent between 2009 and 2020.
Accordingly, the estimated safe production reaches about 51 million m3 as pumping rate is unsustainable and groundwater quality is obviously deteriorating in many parts of Salalah Plain.
The groundwater sustainable management at Salalah plain aquifer has been studied in order to ensure proper use of water resources, preserve it from over-exploitation and prevent reduction of groundwater levels and seawater intrusion.
Overgrazing at the mountains of Dhofar has led to reduction of forest and pasture cover by an average of 5 per cent annually, says the study.
Six scenarios have been recommended for each condition. They include relocating Garziz and keeping animal research farms far from the fresh water aquifer, suspending the pumping for producing fodder for four months in a year, making changes in agriculture/ irrigation systems and establishing a desalination plant: first and fourth options together, and first and third options together.
The study has found 60-80 per cent of the total annual natural recharge occurs through horizontal precipitation due to trees collecting mist during Khareef.
The depletion of vegetation due to overgrazing results in reduction of water recharging the aquifer since trees intercept thick mist during rains in Dhofar, catching it and supplying Salalah plain aquifer with groundwater feeding.
The researcher says the additional source of water through horizontal precipitation is expected to cause underground water flow reduction since mist contributes to the total underground water flow by 80 per cent annually.
This ecosystem is facing pressure from camels feeding on tree branches.
It is essential to minimise this overgrazing and implement reforestation programmes for pastures.
The mathematical models show an increase in the total dissolved solid materials in all groundwater wells of the plain aquifer. This means the aquifer groundwater quality is endangered by salinity.
The increasing annual deficit indicates the unstable conditions of the aquifer.
Fresh water flowing towards the sea is also decreasing, which leads to seawater intrusion. Sea water extended inside for more than 2 km between 1993 and 2009.
The study shows none of the procedures (options one to four) would be able to improve the conditions alone. Consequently, options should be incorporated in order to achieve balance and stop deterioration.
Simulation indicates the fourth option (first and fourth combined) is most effective for improving water levels during the prediction period and the sixth option (first and third combined) for improving salinity conditions.
The study recommends the sixth option because it is better for the sustainable management of the aquifer than the fifth option.
Dr Mahaad said the most effective choice for aquifer groundwater level improvement is the fifth scenario, while the sixth is the best for improving aquifer groundwater salinity conditions until 2020.
Aquifer salinity is expected to increase due to excessive extraction of water to supply high demand and loss of balance between annual recharging and extraction rates. Higher salinity rates will lead to abandonment of farming activities.
The main recommendations of the study focuses on the importance of securing a quick reduction in extraction from the aquifer to ensure Salalah aquifer’s groundwater sustainability.
The government authorities, says the study, should devise a system for measuring the amount of water pumped from each well. Amounts of water consumed for each farm should be determined. Consumption exceeding the limit should be subject to fees/ penalties.
Dr Mahaad has been working in the environment field for more than 25 years. His study also focuses on the importance of a long-term tree transplantation programme for rehabilitating degraded forests.

YAHYA AL SALMANI