Infrastructure Mexico City's sinking is worsening

Published 21 January 2011

Scientists are alarmed by the extent to which Mexico City has sunk; over the last 100 years, parts of the city have sunk as much as forty-two feet — and sections of the city sink as much as eight inches a year; the sinking has caused the city’s sewage system to back up resulting in dangerous floods; the sinking is the result of water being pumped from the aquifer directly below the city more quickly than it is being replenished; Mexico City is built in the middle of Lake Texcoco, which has been drained

Mexico City, the worlds’ third largest city with 18.7 million people, is sinking far more than experts had originally predicted.

In the last 100 years, parts of Mexico City have sunk as much as forty-two feet. This sinking has caused considerable damage to buildings, roads, and critical infrastructure.

In some places the sinking is so extreme that sewage lines have become slanted – resulting in the lines running backward. As a result, waste water can no longer naturally flow out of the city and must be pumped out. With uneven balconies and disjointed foundations in buildings across the city, the damage is readily apparent.

The notion that Mexico City is sinking is not new, but the extent to which it is sinking is causing alarm among experts.

Experts from the National Autonomous University of Mexico (UNAM) say the city’s fissures “are generating alarm among the population and even cause significant damage to buildings and (affecting provision of) public services.”

The city was originally built in the middle of Lake Texcoco on a series of islands. As the city expanded, a series of artificial islands were created along with a network of canals on which roads were built. Eventually the lake was drained and the city continued to expand using the dry lake bed as a foundation.

Pumping water from the aquifer directly below the city is actually causing the city to sink.

Roughly 70 percent of the city’s water supply comes from the aquifer below the city, the last vestige of Lake Texcoco. The rate at which water is being pumped is exceeding the rate at which it can be replaced, weakening the city’s foundation, which has essentially become a mud-like lakebed.

According to engineers, to prevent the city from sinking further it must stop pumping water from the aquifers or replenish its supply. This will help stabilize the foundation, but it will not raise it. “You can’t raise the city again,” said hydraulic engineer Ramón Domínguez. “The only hope is to stop it from sinking further.” Mexico City is sinking about eight inches a year and construction crews are scrambling to save the city from flooding, the most imminent danger posed by sinking. Ariel Flores, water-reuse manager for the National Water Commission, warns of the potential dangers, saying, “[Flooding] would paralyze the economy of the entire country. It would be a total disaster. Imagine the Congress, the stock exchange, the country’s biggest airport, everything under water.” In February of 2010, 4,000 homes were flooded with raw waste when the Remdios River, a sewage canal, backed up and broke its dike. The river backed up because the city has sunk so far that it must pump its waste water over the low lying Sierra de Guadalupe Mountains. To prevent future floods the city has installed five more pumps to expel waste water and is currently working against the clock to build a major drainage tunnel and dredge sewage canals. Mexico City is also strengthening key landmarks by adding pylons beneath them, filling in holes under commuter train lines, and strengthening churches in the historic center. Mexico City mayor Marcelo Ebrard, said the primary goal is “to reduce the risk of flooding as much as we can in our city.” “With luck, we’ll be in time,” he says.