ENVIRONMENT-MEXICO: So Far from God, So Close to…Venice?

By Emilio Godoy Reprint | | Print |

Emilio Godoy

MEXICO CITY, Aug 2 2007 (IPS) - Mexico City, one of the most populous cities in the world, could become the Venice of Latin America, although without the “gondolieri” to serenade tourists as they row them along.

Experts say the capital could be flooded by five metres of water for several weeks. The city proper has 8.7 million people, making it the 10th largest city in terms of population. However, as an “urban agglomeration”, it is the second biggest in the world, with more than 20 million people in the entire urban area.

The cause of the threatened flood is intensive pumping of groundwater in the Valley of Mexico, which has diverted the course of the main drainage system of the capital, already deteriorated because of a longterm lack of maintenance.

The head of the governmental National Water Commission (CONAGUA), José Luis Luege, told the press that over-extraction has led to underground earth movements which affect the surface and the drainage pipes.

Over-exploitation of groundwater, he said, is occurring at a rate about double the renewal rate of the Valley of Mexico aquifer, which lies under the capital and the main municipalities of the state of Mexico, with a combined population of over 20 million people.

Luege said that 59,500 cubic metres of water are extracted per second, while the aquifer’s self-renewal capacity is 31,600 cubic metres per second.

Underground displacement and sinking have caused a loss of gradient in the deep drainage system of pipes, which carries sewage and rainwater, so that this main drain system for the city is no longer operating at normal efficiency.

Furthermore, heavy rainfall in the last few weeks has pushed the drainage system to the limits of its capacity. It has been on the verge of overflowing on 15 separate occasions in recent months.

Experts say that if there is a big flood, an area of 200 to 400 square kilometres could end up under water, affecting between four and eight million people.

The old saying “Poor Mexico! So far from God and so close to the United States!” could be changed (“so close to Venice!”) to describe this situation, although a flooded Mexico City would have all the disadvantages and none of the advantages of the Italian city’s tourist attractions if its streets turned into canals as a result of a disaster.

Studies by the Institute of Engineering at the public National Autonomous University of Mexico (UNAM) and by the College of Civil Engineers (CICM) warn of the risk to the deep drainage system, 110 kilometres long, which was built from 1967 to 1976.

“At present we have a backlog accumulated on the pipe’s discharge capacity, so the risk of catastrophic flooding is already high,” reported Ramón Domínguez, a researcher at UNAM’s Institute of Engineering.

Flooding is nothing new in Mexico City.

In the 13th century, the Mexica or Aztec Indians, who dominated much of Mexico, settled on the island of Tenochtitlán, surrounded by five lakes. They built canals connecting them to other communities, without altering the courses of the rivers.

After the Spaniards conquered Tenochtitlán, they changed the waterway infrastructure built by the indigenous people, which caused enormous floods, such as that of 1555.

The city legislature identified 322 sites at risk of flooding within the federal district, which is sinking at a rate of between 10 and 40 centimetres a year.

“We need a geological risk map, clearly indicating the safest areas and those that are most at risk of flooding, and pinpointing the areas where landslips are most likely to occur, so that we can establish civil protection programmes,” the president of the Mexican Federation of Sanitary and Environmental Engineering (FEMISCA), Jorge Sánchez, told IPS.

The priority must be the areas that could flood after a normal amount of rain. “Then other areas should be looked at, depending on the amount of rainfall, and after that, civil protection programmes should be set up,” Sánchez said.

The Mexico City government and experts at the National Polytechnic Institute have already begun to draw up the risk map.

Five pumping stations with a capacity of 99 cubic metres of water per second are being built and are expected to come onstream in December. When in operation, they will permit repairs to be made to the deep drainage system.

Average annual rainfall in the capital is between 700 and 800 millimetres. The National Meteorological Service forecasts more than 60 storms between August and October in Mexico City, which will put great pressure on the deep drainage system.

Domínguez proposes measures such as reforestation, upkeep of river basins, and the removal of stone-built dams in riverbeds.

“This should be done as part of an intensive programme, as soon as possible, even if it entails heavy spending. Otherwise, within a very few years there will be floods that could affect millions of people,” he warned.

The most recent serious floods in the city occurred in 1951, when the centre of the capital was under water for three months.

Recently, crevices have appeared in the south and east of the Mexican capital. In Iztapalapa, in the south of the city, crevices 22 metres deep and 30 metres in length appeared in early July, damaging houses in the area.

A few days later, a 22-year-old man drove into a crevice. His body was recovered from a depth of 22 metres, amid mud, stones and debris, and the municipal government evacuated more than 200 people. Crevices have also appeared in another six areas of the federal capital.