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Why Mexico's Devastating Flood:
Since López Portillo, Governments
Haven't Given a Dam

Nov. 12, 2007 (EIRNS)—The four dams on Mexico's Grijalva River—the largest in the country, which runs from Guatemala through Chiapas and Tabasco—were able to handle almost the entirety of the enormous amount of rainfall that sent flood waters down the Grijalva River at the end of October; but the Usumacinta River (the second largest in the country, in the same area) and its tributaries have no dams at all, and thus couldn't contain the massive inundation which hit the flood plain in the state of Tabasco, along the Gulf coast of Mexico's Isthmus of Tehuantepec.

This is the summary finding that emerges from a detailed report filed by the Society of Civil Engineers of Mexico (CICM) on Nov. 6. According to the CICM study:

  1. About one meter (100 cm) fell on the states of Tabasco and Chiapas in just 3 days at the end of October. This enormous amount of precipitation was far greater than the previous big flood of 1999, where 50 cm fell in the entire month of October.

  2. Where the Grijalva and the Usumacinta unite in the coastal flood plain, just downstream from the city of Villahermosa, a "hydraulic plug" developed which caused a back-up of enormous amounts of water.

  3. Storms in the Gulf of Mexico contributed as well by raising the sea level by a full meter above normal, between the effect of tides and winds.

  4. The Grijalva basin represents 27% of the surface area subjected to the heavy rainfall. Of the four major dams on the Grijalva and its tributaries, the 3 furthest upstream (La Angostura, Chicoasen and Malpaso), were able to control 100% of the water volume reaching them without having to release any of it further downstream. The fourth dam, Penitas, was able to contain about 1/3 of the 3,000 cubic meters per second of water reaching it, but was forced to release some 2,000 cubic meters per second downstream. But the CICM calculated that this volume of water contributed only 3% of the total floodwaters that hit Tabasco.

  5. The Usumacinta and its tributaries and other rivers in the region, constitute 73% of the surface area hit by the rains. And they have no dams on them whatsoever. Thus, the devastating flood.

The CICM concludes their report with the understated recommendation that Mexico must "promote a greater investment in infrastructure projects in the entire national territory, and especially in the South-Southeast region, to prevent disasters and contribute to sustained and balanced long-term economic development."