Tehran Times – According to a study carried out by the Transport, Housing and Urban Development Research Center, some 18 densely populated provinces are vastly subsiding and consequently become increasingly vulnerable to flooding and natural incidents as well as bearing huge infrastructure damage.
Provinces with a population of over 1 million have reported annual subsidence rates up to several centimeters, while vast areas of plains across the country are highly prone to land subsidence, Ali Beitollahi, secretary of the national working group on natural disasters has said.
Provinces of Isfahan, Tehran, Kerman, Khorasan Razavi, Alborz, Fars, Yazd, Hamedan, Markazi, Chaharmahal and Bakhtiari, East Azarbaijan, Zanjan, Qom, Ardabil, Kordestan, West Azarbaijan, North Khorasan and Kermanshah reported the highest rates of subsidence, respectively, he noted.
“Excessive groundwater withdrawal is known as the main driver, as groundwater levels drop, subsidence is induced through aquifer compaction,” he also added, ISNA reported on Saturday.
Over the past decades, groundwater exploitation has increased dramatically due to permanent droughts, leading to aquifer depletion, he said, lamenting, some of the aquifers levels dropped by 100 centimeters.
“Yet contribution of groundwater withdrawal to subsidence in Iran is outpacing the world,” he further noted.
On top of that, groundwater drawdowns result in filling of vacant cavities between soil particles and highly compressible soils which diminishes the aquifers capacity and increase subsidence probability, he added.
He went on to say that, groundwater overexploitation will affect the plains, as rainwater will not penetrate into the subsurface reservoirs and cause high rates of soil erosion along with permanent inundation.
“Inefficient irrigation methods in addition to digging illegal wells are the other main causes of groundwater extraction-induced subsidence, as out of 50,000 wells pumping underground water resources in the capital, 30,000 are illegal not having a permit, therefore, the country’s ground water condition is worrisome,” he explained.
There is no supervision on of groundwater withdrawal in the aforesaid wells even on those legal ones, so this will greatly increase sinking rates and requires urgent measures, he regretted.
Beitollahi further suggested that installation of smart meter systems on water pump and wells is an efficient measure in this regard.
Referring to the land subsidence risks, namely damages to agriculture, environment and natural resources, infrastructure and settlements, he added that subsidence creates curvature in the water and wastewater, and gas pipelines and leads to the instability of power towers and in the long run, will break them down.
He further added that this phenomenon will adversely affect the city’s infrastructure while bringing huge losses.
Insisting on urgently needed policies in subsiding areas, he highlighted that Ministry of Energy must take steps toward reducing groundwater exploitation, in addition to banning well construction as well as shutting down the illegal wells in the sinking provinces.
The Ministry should also control agricultural products and prohibit cultivation of water consuming products in those provinces, and instead, introducing agricultural products which require low amount of water, he also explained.
“Modern irrigation techniques must be taught to the farmers by providing the facilities to change the ways they used to water the farms,” he suggested, adding, Ministry of Agriculture also must cooperate to implement watershed management projects in order to increase the aquifers storage capacity.
The Department of Environment is another responsible organization which must take more serious steps toward environmental assessment of land subsidence and its prevention techniques, Beitollahi concluded.
Groundwater condition worrisome
Mohammad Reza Goldansaz, a researcher in the field of water resources said that an annual amount of 50 billion cubic meters of groundwater resources are withdrawn to supply agricultural, industrial as well as drinking water in Iran.
Comparing aquifers level in past 10 years, he said, have indicated that water level reduction in most aquifers amount to less than 50 centimeters annually, however, water level in some of the major ones reduced over 50 centimeters.
Environmental official Mohammad Mojabi said in July 2018 that renewable water resources have drastically decreased to less than 100 billion cubic meters from 132 billion cubic meters over the past 50 years, demonstrating 25 percent decline.
Out of 609 aquifers in the country 309 are depleted and water withdrawal is not allowed anymore in these aquifers, he added.
Land subsidence rates
In September 2018, geologist Mohammad Javad Bolourchi said that over 300 plains in Iran are at high risk of experiencing land subsidence, and as long as there is virtually no reduction in illegal overuse of groundwater resources, curbing subsidence will coincide with depletion of aquifers.
For instance, studies indicated that the plains in Varamin county, southern Tehran are subsiding by an average of one millimeter a day (36 centimeters a year), he noted, lamenting that many aquifers in central part of the country are reported salty, which needs huge water desalination systems.
In the Iranian calendar year 1384 (March 2005-March 2006), the subsidence rate in Tehran plain has been measured at 17 centimeters a year, it has been measured 12 centimeters in Varamin county, in southern Tehran.
This is while the run-down in plains of Mashhad or Rafsanjan, which has set the record high for this phenomenon since the Iranian calendar year 1345 (March 1966-March 1967), is certainly higher, regarding the reduction in precipitation rate.