Stephanie Moore sent me this link to a story by Dudley Althaus that recently appeared in the Houston Chronicle. Althaus documents the dire water situation in Mexico City and its outlying areas, home to about 22 million people.
To those of us in hydrogeology, Mexico City has long been known as the 'poster child' (along with parts of the Central Valley of California) for land subsidence. Much of Mexico City is built upon a lake bed; lacustrine (lake) sediments are notoriously fine-grained (small particle size - clay) and susceptible to consolidation when groundwater is pumped. This causes the land surface to subside. Parts of Mexico City have subsided as much as 30 feet (9 meters).
The photo of the cathedral isn't really a good example of land subsidence due to pumping. For one thing, they have not been pumping large quantities of groundwater for centuries. My guess is that the leaning cathedral is due to differential compaction/consolidation caused by soil properties and/or drainage issues. In other words, it's more a soil mechanics problem than a groundwater pumping one.
Back to Althaus' story.
Taps already are running dry for weeks at a time in large sections of the metroplex, especially in poorer neighborhoods. Officials warn that without extraordinary deluges in the coming weeks, extreme scarcity will stalk the area once the dry season begins in late October.
“We are on a collision course,” said Lorenzo Rosenzweig, director of a Mexico City foundation that finances water studies and other environmental programs. “The whole way we manage this watershed has to be rethought.”
The sierra-encircled basin that holds the Mexican capital was a vast lake bed when the Spaniards took it from the Aztecs nearly 500 years ago. Planners have been draining it ever since to make way for humans, treating the area's water more as a nuisance than a necessity.
That worked pretty well for a very long time. It doesn't any more.
“We've reached the end of a model,” said Arkansas-born Elena Burns, a naturalized Mexican citizen who helped coordinate a recent proposal to re-engineer Mexico City's watershed. “It's not sustainable.”
Decades of explosive population growth and poor planning have badly stressed the aquifers that supply three-quarters of the area's water. Three times as much water is sucked from the basin's aquifers as trickles back into them.
Tunnels today flush most rainfall and sewage runoff to the lowlands northeast of the city and on to the Gulf of Mexico, depriving the groundwater of replenishment. The water flowing daily out of the basin nearly equals the amount pumped into it from aquifers and the distant Cutzamala and Lerma reservoir systems, Burns said.
I did not realize that much of the basin's runoff was exported from the basin. No wonder land subsidence is so prevalent. And sewage runoff, if properly treated, would be a good source of recharge. Burns might want to consult the Orange County Water District.
In 1995, a National Research Council committee and its Mexican counterparts did a joint study, Mexico City's Water Supply: Improving the Outlook for Sustainability.
A description:
This book addresses the technical, health, regulatory, and social aspects of ground water withdrawals, water use, and water quality in the metropolitan area of Mexico City, and makes recommendations to improve the balance of water supply, water demand, and water conservation. The study came about through a nongovernmental partnership between the U.S. National Academy of Sciences' National Research Council and the Mexican Academies of Science and Engineering. The book will contain a Spanish-language translation of the complete English text.
Might be worth perusing.
One solution...
“There are just too many of us in this city. The earth can't handle so many of us.” -- diner owner Rafaela Camacho, quoted in the story
Possibly a bit “over-the-top” I found as I perused this posting my mind suddenly seizing on Shakespeare’s words in Julius Caesar … “I come to bury Caesar, not to praise him. The evil that men do lives after them; the good is oft interred with their bones.”
As I ponder these words, I find myself asking … are we asking the right questions…? Or might our questions be out of order…? Our discussions about – water – (including most of my own) most often begin emphasizing (praise) what is wrong, bad, depilating and unhealthy about some aspect of water. Might is our discussions emphasize how we bury and release what we feel we are doing wrong, badly, incorrectly, ineffectually respecting – water – and give honest praise to those things we are in these moments doing correctly, openly, honestly, effectively for – water.
Might our continuous attention to the negative impact man’s action has on water merely perpetuate exactly that..? How do we effectively “re-frame” the water discussion to draw one’s attention to our attitude about water, our honest concern about water, whether we see water as part of the “commons” or merely a commodity for sale to the highest bidder…?
At some seminar long ago, I believe it was when I was attempting to sell real estate, an instructor made a comment I have not forgotten … “what works, works, what doesn’t, doesn’t, and doing more of what doesn’t work, won’t make it work” … perhaps a bit corny but I think its validity seeps through. If we continue to emphasize and give bold headlines to the negatives about – water – how can we honestly expect anyone seeing and reading to attain a different more positive paradigm about water…?
Respectfully,
Authentically Wired
http://waterman99.wordpress.com
Posted by: PAUL F MILLER | Sunday, 06 September 2009 at 11:41 AM