TEHRAN — 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, geologist Mohammad Javad Bolourchi has said.

Land subsidence, a gradual settling or sudden sinking of the Earth's surface due to subsurface movement of earth materials is mainly caused by aquifer-system compaction, drainage and decomposition of organic soils, underground mining, oil and gas extraction, hydrocompaction, natural compaction, sinkholes, and thawing permafrost.

Depletion of groundwater resources and pumping water excessively out of the ground at a faster rate that is replenished over the long-term have led to land subsidence and constitute a serious threat to Tehran.

Ismail Najjar, head of National Disaster Management Organization, said on September 26 that land subsidence in Tehran is reported to be 22 centimeters per annum stating that status reports indicate that land subsidence has been slowed.

Bolourchi, who was also the former spokesman for the Geological Survey and Mineral Explorations of Iran, in response to Najjar’s comments on whether land subsidence in Tehran has declined, said that if there were satellite imagery or online GPSs in the plains around Tehran, and comparing data was possible, “we could have possibly make sure if land subsidence rate is decreasing or increasing in the area.”

“Unfortunately, for the past two years, we have had no satellite data to measure the subsidence rate, unless, the National Cartographic Center, using a GPS network in Tehran's plains, could have find out statistics which indicate a decline in the subsidence rate, he said, adding, satellite tools with such a high-tech capability is only available to Japan and the United States, and is not affordable for Iran.

He further explained that “in order to actually prevent land subsidence, having a proper knowledge of the phenomenon is a must; 30 years of excessive groundwater withdrawal have gradually contributed to the phenomenon, so reversing it will also take years meaning that if we succeed in using groundwater resources sustainably one day it would definitely take 5 to 10 years to stop land subsidence.”

Tehran plain sinks 1mm per day

Studies in the Iranian calendar years of 1388 (March 2009-March 2010), 1390 (March 2011-March 2012), and 1392 (March 2013-March 2014), indicated that the plains in southern Tehran are subsiding by an average of one millimeter a day (36 centimeters a year), Bolourchi said.

30 years of excessive groundwater withdrawal have gradually contributed to the phenomenon, so reversing it will also take years meaning that if we succeed in using groundwater resources sustainably one day it would definitely take 5 to 10 years to stop land subsidence.Islamshahr, Dodangeh, Robat Karim and Shahriar counties in Tehran plain are most affected by land subsidence.

Elsewhere in his remarks, Bolourchi noted that in the Iranian calendar year of 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.

But it is not unlikely that Varamin county is sinking lower than Tehran, since agriculture is being practiced more in Varamin plan than Tehran plain, he regretted.

Industries and urban areas have replaced agricultural lands in Tehran, and that the aquifers in plains southern Tehran are no longer capable of supplying agricultural water as they are severely depleted, so, it is likely that subsidence rate of Varamin plain would exceed Tehran plain, he explained.

Head of water affairs of Varamin county Ahad Davoudi also said on September 26 that there are 1,032 illegal and 7,170 legal wells in the region which pump some 124 million cubic meters annually, and only 70 illegal wells are closed down for good. 

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, Bolourchi stated.

“Snowfall has already turned into rainfall, which has led lower infiltration rate, in addition to numerous water wells, whether legal or illegal, depleting aquifers, which all exacerbate the subsidence.

Groundwater withdrawal not yet to be reduced

Bolourchi highlighted that intensive use of groundwater has not yet been diminished, while in 1384 (March 2005- March 2006), “we warned that subsidence is not like an earthquake which causes extensive damage once it hits, land subsidence inflict damage gradually and should be managed promptly.”

Today, the plains that are sinking or has cracked open are the result of an overuse of groundwater resources over the past 10 to 20 years, which has not produced any significant economic benefit, he lamented.

Over 90 percent of the country's water supplies is consumed in agriculture sector, which generates only 17 percent of the country's employment, he said, adding, on the other hand, only 2 percent of the water supplies is consumed in the industrial sector, while it provides some 50 percent of the country's employment. 

“This is alarming, so, water consumption in the country needs to be fully optimized and managed, and wastewater must be reused in industrial sector,” he suggested.

Underground water withdrawal banned in over 350 plains 

Unfortunately, despite not having accurate data showing subsidence in all the plains of the country, the groundwater removal in nearly 350 to 390 plains is prohibited, Bolourchi highlighted.

In other words, the water withdrawn from the plains will not be reproduced in fall and winter, so that over 300 plains are prone to subsidence, he also added.

He went on to say that for instance, Fars province having the highest record in agricultural development in recent years, also demonstrate an excessive use of groundwater, as 50 percent of the water supplies in the province is provided by the groundwater resources.

Aquifers on the verge of total depletion 

Bolourchi pointed out that it is late to revive aquifers and qanats, as most of them are compacted by land subsidence. 

If aquifers are not managed properly in the country, undoubtedly, no underground water will remain within the next few years, and many issues happens, as water resources are the most strategic source of each country, he regretted.

“Our surface water totally depends on climate change. One year we may receive above normal rainfall and the other year suffer rainfall shortages, but groundwater resources can be managed, but unfortunately no plans are being implemented to manage these sources,” he concluded.

 Groundwater-related subsidence a major threat to developing countries

Groundwater-related subsidence is the subsidence (or the sinking) of land resulting from groundwater extraction. It is a growing problem in the developing world as cities increase in population and water use, without adequate pumping regulation and enforcement. One estimate has 80 percent of serious land subsidence problems associated with the excessive extraction of groundwater, making it a growing problem throughout the world.

The arid areas of the world are requiring more and more water for growing populations and agriculture. Groundwater can be considered one of the last free resources, as anyone who can afford to drill can usually draw up merely according to their ability to pump (depending on local regulations). 

However, pumping induced draw down causes a depression of the groundwater surface around the production well. This can ultimately affect a large region by making it more difficult and expensive to pump the deeper water. Thus, the extraction of groundwater becomes a tragedy of the commons, with resulting economic externalities.

Land subsidence can be problematic as they can cause damage to buildings and infrastructure such as roads and canals, increased flood risk in low-lying areas, and lasting damage to groundwater aquifers and aquatic ecosystems.

FB/MQ/MG