Sea water irrigation could be key to cutting down UAE's water usage

ABU DHABI // Under the surface of a plot of land on Yas Island, an experiment is under way that could drastically reduce the UAE's water use.
Irrigation accounts for about 80 per cent of the water used by the UAE, with traditional irrigation - such as drip or spray systems - using 12 to 15 litres of water a day per square metre of land.
But an agricultural company says it can reduce that to zero by getting rid of freshwater irrigation for landscaping and using sea water instead.
"There's a lot of landscaping on the UAE's coastal areas," said Bart Rehbein, the managing director of Epic Green Solutions. "If you can do a significant amount of irrigation with sea water then you have an unlimited supply."
The system involves subsurface irrigation. An area of 120 square metres has been excavated 60cm deep, and lined on its base and sides with rubber. Pipes are placed on top of the liners and water flows into the system through the pipes and out of holes along their base before reaching the plants' roots.
"Other places will irrigate on the surface which makes it difficult because the water evaporates," said Mr Rehbein. "Underneath, it doesn't."
But the sea water is key to ensuring a dramatic cut in water use as experts predict the groundwater to deplete in 55 years.
"There are no water tanks nor meters in this system because it's sea water so we don't care how much we use," said Mr Rehbein. "There's a solar panel to pump the water from the sea, then there's a drain line which throws the water back in the sea, so no salt builds up."
And the closed system also means the soil around does not get contaminated by salt.
"If you spray the soil with salt, it makes the ground so sterile that you can't grow anything in it," said Mr Rehbein. "We contain that salt within the cell so there's no pollution." Every six months, the accumulated salt is flushed out.
The trials started last January using sesuvium and atriplex plants, two salt-tolerant species. "They're used in seaside areas for landscaping and they're used a lot in this area," said Mr Rehbein. "We started using freshwater and after two months we managed to completely switch to sea water."
But the plants struggled with the summer heat. "There was a lot of stress to put them under the heat but now I see things are getting back to normal and they're starting to get greener," said Mr Rehbein.
Some doubts remain about whether seawater irrigation can work in the long term. "To save water, it's a good idea," said Hoda Jaffal, an agricultural engineer at Al Yousuf Agricultural and Landscaping in Dubai. "But there are much better ways like products that can be used with the soil that are able to retain water for a long time so you don't have to irrigate every day."
She said companies should treat the water before using it for irrigation to avoid harming the plants. "Even if the plant is salt tolerant, it's harmful in the long run because when the amount of salt is too high or too low, the plant cannot absorb the nutrients it needs to grow and build new tissues," she said. "Ultimately, the plant will die."
But Epic Green is convinced of the concept. Eventually, it hopes to produce biofuels from the plants.
"We're waiting for cooler weather to plant biofuel type plants," said Mr Rehbein. "We will then watch them over the course of winter."
The project echoes work at the Masdar Institute for Science and Technology, where scientists are hoping to acquire land in Abu Dhabi to produce sustainable jet fuel from salt-tolerant plants.
cmalek@thenational.ae