The annual land subsidence in Tehran Province is reportedly 36 centimeters, especially in its southern plains, which is the result of excessive groundwater extraction from underground aquifers, the deputy for operations at Tehran Regional Water Company said.
“Due to the decline in precipitation, persistent drought and lack of sufficient surface water resources, some farmers in the province have been digging illegal wells to withdraw water from the precious but fast-depleting groundwater resources; even the amount of water extraction from authorized wells is very high,” IRNA quoted Ahmad Ali Qorbanian as saying.
Over 3 billion cubic meters of water are extracted from groundwater sources in the capital every year. Besides land subsidence, groundwater overdraft could destroy vegetation, increase dust storms, create holes in the plains and increase salt content in groundwater.
Land subsidence is defined as a gradual settling, or sudden sinking of the earth's surface owing to subsurface movement of earth materials.
In addition to injudicious groundwater extraction, other causes of land subsidence are aquifer-system compaction, drainage of organic soils, underground mining, hydro-compaction, earthquake and gas and oil extraction.
Although reversing land subsidence is almost impossible, slowing its progress is doable and a number of measures have been taken in this regard in the past few years, but their progress is very slow.
“Preventing the activity of unauthorized wells has been one of the measures,” Qorbanian said, adding that in the past five years, over 8,000 illegal wells have been sealed in the province, helping save 275 million cubic meters of water per annum.
According to the official, the company continues to seal unauthorized wells, as there are more than 20,000 illegal wells whose water is used in the agricultural sector, for drinking and irrigation of green spaces.
Referring to the number of legal wells, Qorbanian said: “There are 13,490 authorized wells in the province, from which 1.870 billion cubic meters of water are extracted annually.”
Smart Meters
Smart meters have also been installed on the wells in recent years to prevent groundwater overdraft.
“Since the beginning of the current Iranian year [March 21], 280 wells have been equipped with smart meters and the number will increase to 800 by the end of the [current fiscal] year [March 20, 2022],” the official said.
“So far, about 3,000 smart meters have been installed on the authorized wells of the province.”
Smart wells are advanced structures with sensors and valves installed downhole to allow easy and systematic monitoring.
Equipping wells with the new system will help utility companies closely monitor water use online and prevent excessive withdrawal from authorized wells.
Other Measures
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.
According to Tehran’s water officials, plans are underway to replace 300 million cubic meters of groundwater with treated wastewater in the province 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, is piped to south Tehran for farming, watering green spaces and making industrial use.
Other helpful measures include the reformation of water consumption and farming systems for 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.
