“Annually, 31 centimeters of land subsidence are reported in Tehran Province. Over 3 billion cubic meters of water are extracted from groundwater sources in the capital every year,” ISNA also quoted Ahad Vazifeh as saying.
Land subsidence is defined as a gradual settling, or sudden sinking of the earth's surface owing to subsurface movement of earth materials.
Its main causes are aquifer-system compaction, drainage of organic soils, underground mining, hydro-compaction, gas and oil extraction as well as earthquake.
Vazifeh noted that projects are underway in Tehran to help overcome the critical impacts of land subsidence.
The projects, most of which are developing very slowly, include the construction of water treatment plants, sealing of unauthorized wells, and substitution of groundwater with treated wastewater for farming and industrial purposes.
“With the launch of the seventh water treatment plant in southeast Tehran in 2019 and the sixth treatment plant in the west in 2020, about 200 wells have so far been be closed,” he added.
There are 10,000 illegal wells in Tehran Province, 10% of which belong to industries.
Another main reason of land subsidence in Iran is the injudicious groundwater extraction that has been causing serious concerns among conservationists, economic experts and academicians.
“The disturbing trend of land subsidence in Iran has overstepped the global norm of 4 mm per annum. More than 200 mm of land subsidence annually is indeed critical,” he said.
Although reversing land subsidence is almost impossible, slowing its progress is doable, provided the government and people cooperate.
Farming Systems
The reformation of water consumption and farming systems are key to addressing the worsening problems.
Surface water streams can be controlled through dam construction so that it can help vegetation in drier lands and replenish groundwater reserves.
Besides land subsidence, groundwater overdraft may lead to the destruction of vegetation, increasing the possibility of dust storms, holes in the plains and higher salt content in groundwater.
Curbing the spread of land subsidence is of primary importance. When the ground surface moves lower, the entire city sinks with it, which in turn affects the stability of buildings and the functionality of infrastructure.
Hassan Razavi, director of Tehran Regional Water Company, said it is planned to replace 300 million cubic meters of groundwater with treated wastewater in Tehran in two years and 500 mcm will be replaced in six years.
Currently, seven wastewater treatment plants are operating in Tehran, producing 45,000 cubic meters of sewage per day.
The output, which complies with environmental norms, goes to south Tehran for farming and is suitable for green spaces and industrial use.
Tehran Municipality uses groundwater for green spaces and its overuse over the past many decades has resulted in the rapid decline in groundwater levels.
Referring to the memorandum of understanding signed with Tehran Municipality to use wastewater instead of groundwater, Razavi said, “Tehran Municipality withdraws 230 million cubic meters of water from aquifers per year, of which 200 mcm will be replaced by treated sewage in the next five years."