By Mina Izadi

Land subsidence threatening the capital

March 5, 2019 - 11:57

TEHRAN - Sinkholes and fissures opening up the earth are gradually encircling Iran's capital city, threatening local infrastructure and people's homes.

The latest data harvested from Tehran’s satellite cities show that the ground is cracking open in some areas, because of water crisis that has worsened as the groundwater exploitation has increased.

The region is struggling with a three-decade-long drought and growing desertification, as is the whole country.

A 2018 report from Circle of Blue, focusing on water issues in Iran, says the water scarcity in Iran has been deteriorated as the city’s population has grown to 8.7 million. The report also names climate change, population growth, mass migration, political instability, and resource mismanagement as factors pushing the country on its track to absolute drought.

The city has increasingly relied on underground water sources as opposed to rainwater; this has made the water saltier day by day.

At the same time, a great deal of the dwindling water supply gets diverted to thirsty and traditional agriculture.

As a result, land in the area is physically slumping in on itself. The ground around Tehran, sitting 1,200 meters above sea level, has sunk an average of 20 centimeters per year, according to the latest results of an underway project in the city on the restoration of Tehran groundwater sources.

More detailed data provided by Tehran Regional Water Authority, Tehran Districts 16, 17, 18, 19 and 20, comprising the central and southern part of the capital, are more prone to land subsidence compared to the north area.

According to Hassan Razavi, head of the authority says land subsidence in the plains of Varamin, Rey, Tehran, Shahriar, and Moein-Abad respectively reaches 13cm, 25cm, 7cm, 36cm and 25 cm annually, "which is a considerable record compared to the affected areas around the world."

Based on reports published by local media, during the current fiscal (ending on March 20), five incidents in the capital, three have hit the central plain, namely Qiam Square, Molavi Street, and Khayam Street.

Sudden Incidents

The phenomenon which is a normal consequence of excessive groundwater usage and uncontrollable urban development has left the residents of the affected areas in insecurity and fear.

People are worried to be trapped in a sudden pit crater while going out and do not even feel safe while at home.

Several multiple-story buildings have so far devoured by land subsidence incidents, forcing the residents to abandon their homes. Many of others have voluntarily put their houses for sale at low prices to move as soon as possible.

Tehran Bus Company earlier announced that the sudden land settling in Molavi Street, happened earlier in January, a Bus Rapid Transit (BRT) line crossing the area inevitably did a path change in order to assure safe trips.

Proposed Reasons

The official data from the Energy Ministry show that Tehran is home to merely 2% of the country's water sources while keeping over 20% of the population. However, water consumption in the capital exceeds one billion cubic meters, one-third of which is siphoned from groundwater sources.

Environmentalists and experts have repeatedly warned that the groundwater consumption rate is way too fast to be replenished naturally.

Once abundant with water, Tehran's subsurface water was achievable through Qanats.

Qanat is a gently sloping underground channel to transport water from an aquifer or water well to surface for irrigation and drinking. This is an old system of water supply from a deep well with a series of vertical access shafts.

However, with the injudicious water use, numerous Qanats has so far dewatered and filled up with low-quality gravel and soil, comprising a heterogeneous combination and resulting in a weak and loose texture.

Age old water distribution system leaking under the city has deteriorated the issue. Municipal bodies say Tehran's water distribution network is over 65 years old with huge deficiency, causing over 40% of the flowing water to leak and drain the soil.

Kicks and steady vibrations of drilling tunnels deep in the ground for the expansion of the subway network according to urban experts is the other factor increasing the possibility of land subsidence.

Scientific Look

Despite the speculations and analyses, a more scientific look on the matter shows that there are two sorts of land subsidence, namely spot and area subsidence.

Spot subsidence is often the vicious result of urban construction. Drilling tunnels, destroying Qanats or changing their paths, planting deep foundations for skyscrapers, water pipe breakage and surface water creeping into the dewatered and blocked wills are responsible for the emergence of spot subsidence or pit craters in urban areas.

The second type of phenomenon is more of an environmental issue. The main reason behind the area subsidence is water level fall in groundwater sources and densified aquifers.

An aquifer is an underground layer of water-bearing permeable rock, rock fractures or unconsolidated materials (gravel, sand, or silt). Groundwater can be extracted using water well.

When the water in aquifers is sucked up excessively, the forming material of the area becomes denser, creating a land settling on the surface. Also becoming impermeable, it will be hard to replenish the aquifers after its water is siphoned.

While restoring an area hit by spot subsidence is more readily done through urban construction equipment and techniques, restoring a land which is damaged by area subsidence is a challenging and long-term issue, hard enough to make it almost impossible.

Existing Solutions

Rewatering aquifers stretched through the province's area is proposed as a long-term, but efficient solution to curb the growing problem.

To this end, even a project has been introduced by the Energy Ministry since 2015, titled 'replenishment of groundwater resources'.

According to reliable data, Tehran aquifer annually faces 40 million cubic meters of water. Head of the project Mostafa Dehghan says feeding the aquifers is one of the most promising ways to skip the worsening land subsidence around the metropolis.

He is of the opinion that if a part of a wastewater treatment facility (sitting in the south of Tehran Province) output is apportioned to the aquifers, it will do a lot of help.

"Currently the wastewater treatment facility produces over 280 million cubic meters of water annually, of which 50million cm would do for rewatering the ground sources," he notes.

Furthermore, huge manipulation of river paths passing through the city and construction of parks and urban development along the rivers has restricted land's water absorption capability.

"Fundamental changes in the pattern of parks currently surrounding the rivers' watershed is needed to make the rivers capable of feeding the ground waters once again."

Blockage of illegal water wells dug around the province was highlighted like the other measure strictly underway in line with the target.

"Annually over 400 illegal water wells are blocked in the area. The figure has been on an upward trajectory as of 2015. Since then, over 3,000 illegal water wells have been detected and blocked only around the city," Dehghan says.

Equipping licensed wells with smart water meters can overtly and accurately measure and control the volume of water siphoned out of the groundwater resources. 

According to Dehghan, currently, smart meters have been installed on 760 water wells.

Insider experts believe that modernizing agriculture and raising public awareness on judicious water consumption will also contribute to alleviating environmental and urban damages.

Soil stabilization through pounding the weak soil in subsidence-prone areas is also among the suggested solutions to curb the issue.

Though the proposed remedial measures are likely to do a lot of help to recover the desiccating groundwater resources, they should be practiced in long-term projects. However, twenty years of steady efforts in line with the target will most probably turn the situation back to its condition in 3 decades ago. 

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