ABU DHABI // One of the biggest changes to the emirate in the coming years will be completely unseen and, if all goes well, completely unnoticed.
Abu Dhabi Executive Council's multibillion-dirham plan for infrastructure development includes an upgrade of the city's overloaded sewerage system, and its expansion into new urban areas.
A Dh5.7 billion overhaul of the network has been under construction since 2009 to meet projected population growth and ease the burden on an already strained system that dates to the 1970s.
The new sewers will triple the capacity for Abu Dhabi's main urban centre, from 580,000 to 1.7 million cubic metres per day.
The work is in line with the Strategic Tunnel Enhancement (Step) project.
"The announcement is showing support for what we're doing, that they are pleased with progress and they are pleased with the way the [Step] programme is moving forward," said Alan Thomson, the managing director at Abu Dhabi Sewerage Service Company.
"The projected growth of Abu Dhabi under the 2030 plan envisages a dramatic growth in population. The tunnel was designed to accommodate a future growth of population and industry."
The network will cover a large part of the emirate's urban centres and replace 35 existing wastewater pumping stations with a single station in Al Wathba, which is currently under construction.
Contractors have completed 30-kilometre-deep tunnel sewers for Step. These are among the world's longest gravity-driven wastewater tunnels.
Tunnel excavation for the 41km-deep sewer network that runs under the city's surface will be completed in July.
So far, half of the excavated tunnels have been lined with high-density polyethylene to increase durability and longevity.
Preparation work for the pumping station construction began in October.
The upgrade includes an additional 41km of link sewers that will connect the existing system to the Step system. Link sewers are 15 to 20 metres deep and up to three meters in diameter.
The main tunnels are 24 to 80 metres deep and typically four to five and a half metres in diameter. They will take the main flow from the island out to the treatment plant.
Drilling is primarily through gypsum and mudstone.
Precautions have been taken to limit any disturbance to the public, so people are unaware of the drilling going on below the city.
"You wouldn't notice," Mr Thomson said. "They really minimise disturbance because all the work is underground.
"Locations are chosen because they have specifically low impact on the public. They tend to be off the street, they tend to be perhaps in a central reservation where they are not obstructing any traffic flow."
Current sewer networks are overloaded.
"We didn't have adequate capacity for Abu Dhabi's population at the time. We had to do something to resolve that," Mr Thomson said.
The strained system is managed by pumping waste from overloaded areas to less loaded areas at certain times of day.
"The system is very severely overloaded and it's very limiting of what we can do. At present we are operating with over-pumping to try to serve the sewerage from one side of the island to the other."
Four contractors are working on the project.
When complete, the sewers will have a lifespan of 80 years.
Plans are under way to increase connectivity of treated water systems to new urban areas.
Outlying urban areas that will have updated sewerage systems include Al Nahdha, Al Jadeedeh, Al Wathba, Bani Yas, Khalifa City B, Al Falah, Al Heeleyeh, Al Mua'zzaz, Al Shawamekh and Al Mafraq.
This article has been corrected since it was published. The diameter of the main tunnels is four to five and a half metres, not 16. Also, the lifespan of a sewer is 80 years.