The Texcoco Marvel

"How Aztec engineers tamed an environmental nightmare gives a lesson for today"

In August, 2022, I described here on The Great Change how we had attempted to recreate an ancient indigenous farming method in the highlands of middle Tennessee.

This week I donned my tall boots and waded back into our constructed wetland to restore and rebuild the chinampas. Rob Wheeler, for more than 20 years the Global Ecovillage Network representative to the UN Headquarters in New York, brought along loppers, machete and a portable saber saw to assist me. During my nearly three years pandemic absence, the wetlands had taken on a life of their own and become a swampy thicket of fallen branches, bent-over bamboo, and nettles. One could be forgiven for not seeing beneath all that to what it will eventually become—the most productive food system, on a calorie per square foot basis, ever devised by humans.

Among the engineering wonders deconstructed by the Spanish conquistadors in the 16th and 17th centuries were the vast systems of chinampas that sustained a dense metropolitan population in the high central valley of México. Their aquatic earthworks consisted of alternating narrow islands and canals, initially formed by willow fences and composted fill from the kitchen wastes, lake mud, rubbish and sewage of the lakeside villages, planted with fruit and nut trees to line and hold the banks and gardens of corn, beans and vegetables. Freshwater fish were trapped by fences in the canals where they ate mosquito larvae and grew fat on falling fruit until they could be netted and brought to market. 

A 2014 study of the chinampas in the 70-square-mile Lake Chalco-Xochimilco found they were built between the mid-15th and early 16th centuries at the peak of the Aztec Triple Alliance. In a ten-square mile study area, 23,094 relic beds and 400 mounds were digitized for mapping. The long, narrow beds averaged 3.75 meters wide and had an average length of 49.4 meters, with a land-to-water ratio of 1.07:1. In addition, there were many small lakeside homes and villages, large wharves comprised of multiple mounds and platforms, open pools, and wide canals. 

According to the researchers, chinampas allowed frost and flood protection, nutrient recovery, and irrigation by splash or scoop techniques from canoe-bound farmers during droughts (the standard tool was a lacrosse-stick-like ladle called a zoquimatl). Normal capillarity flows from the lake through the island eliminated the need for irrigation in dry cycles. Large amounts of algae (known as tecuitlatl) were collected from the surface of the Lake and used to make high-protein bread and cheese-type foods. This algae is still grown in Mexico for fertilizer.

Last month I described how the new president of México should learn from that history and re-establish these systems by restoring the indigenous ecology of the high valleys. I used images drawn by Dall-E to reimagine that near-future steam-punk utopia.

Chinampas are a permaculture technique I would always teach in my two-week permaculture design courses, and I thought that the images drawn from old Mexican textbooks that I put up in PowerPoints were pretty good. But then, last week, Tomas Pueyo published his own history of that ecosystem design to his blog, Uncharted Territories, and I was humbled. Here is one image, recreated with A.I., of how the Aztec Capitol may have looked to a chimay at the arrival of Hernan Cortés. 

From Thomas Kole: The Mexica created fertile plots of farmland by staking out pieces of the shallow lake and filling them with dirt and rubble. These chinampas were used to grow maize, beans, squash, peppers, fruit and nut trees and flowers. This is what allowed the city to grow, both in area and in population.

 In my post last month, I wrote:

The Conquistadors could not fathom the island city of Tenochtitlan when, on November, 8, 1519, they crossed the Ixtapalapa causeway over Lake Texcoco and beheld the spectacle of its glimmering central pyramid, broad white boulevards, and flowered verges. It was the most beautiful city any of them had ever beheld. Cortés and his men marched across the causeway until they were met by the Aztec Emperor, Moctezuma II, who greeted them, descending his royal litter to offer gifts. Moctezuma was immediately taken prisoner and ransomed for gold and silver. Once the ransom was paid, he was executed.

Six months later the Aztecs rose up and threw out Cortés, but it was too late. While the Spanish army spent 1520 exiled to Tlaxcala, General Smallpox ravaged and decimated the city, reducing its mighty army to bleeding pustules.

The system of chinampas was impressive but perhaps even more impressive, and described by Pueyo, was an engineering feat of the 16th century Aztecs that rivals anything in either the ancient or modern world. The high valley of Central Mexico is surrounded by volcanoes and mountains. The water from all these mountains flows to the center, where it can’t escape because ancient lava flows blocked the exits. So instead, the water accumulated in vast lakes, which lay down rich sediments of volcanic mineral soils. Whether for defensive reasons or because aquaculture was a pillar of their food supply, the Aztec capitol was built on islands in the largest lake, but there was a public health problem.

The inland sea was salty. It was toxic to irrigation and freshwater fish. It must have been a nightmare breeding ground for mosquitoes and smelly algal blooms. So what did the Aztecs do? Pueyo answers:

The Aztecs built a levee (“Dike of Nezahualcoyotl” on the map) to split the lake in half. The lower altitude part would accumulate all the salty water, while the upper part would accumulate the fresher water from the mountains. And which of these halves is at a higher altitude? The one where Tenochtitlan lies. This dike meant the city was surrounded by freshwater instead of saltwater, which allowed easy irrigation on the islands and surroundings, and hence agriculture.

Moreover, they closed the cycle of pollution from their city by turning all their sewage and kitchen wastes to compost and then building chinampas that extended out into the freshwater lake. Fruit trees planted on the island perimeters sent down roots that replaced the decaying wicker bulwarks that separated the new land from the lake, holding the islands in place permanently.

But what of that dike? That is what drew my attention when I read the piece. Look at the map. That bridge that passes from North to South, bisecting the lake, is 25 miles long. The Aztecs did not have cranes and concrete. They had boats and baskets. And yet they made a causeway that is nearly four times longer than the Seven Mile Bridge connecting Key West to Florida, which is actually 6.79 miles long. Any of the three causeways on the map that connect the island city to the mainland are more than twice as long as Florida’s second longest — the Long Key Bridge, at 2.3 miles.

I am reminded of another engineering marvel I visited a few years ago in Dujiangyan City, Sichuan, China (都江堰). Originally constructed around 256 BC by King Zhaoxiang (秦昭襄王) of Qin, it is still in use today. During the Warring States period over 2,250 years ago, people who lived in the area of the Min River were plagued by annual flooding. The royal hydrologist Li Bing investigated the problem and discovered that the river was swelled by fast-flowing spring melt-water from the local mountains that burst the banks when it reached the slow-moving and heavily silted stretch below. One solution would have been to build a dam, but fortunately the King lacked an Army Corps Engineers to advise him. Instead all he had were Taoist priests. They said, do not fight the water, bend it. 

With tens of thousands of laborers, Zhao and Li made a levee in the middle of the river from long sausage-shaped baskets of woven bamboo filled with stones (zhulong) held in place by wooden tripods (macha). The artificial island took four years to complete and resembled a fish's mouth 鱼嘴. Next, Zhao and Li cut a deep channel to one side of the island. Remember, this was before the invention of gunpowder and normally cutting through the hard mountain granite with hand tools would have taken decades. But Li Bing invented a method of using fire and water to rapidly heat and cool the rocks, causing them to crack and allowing them to be easily removed. After only eight years, a channel 20 meters (66 ft) wide had been gouged out on the mountain side of the river.

When the spring floodwaters came, they rushed to the two sides of the fish’s mouth. The valley side led to a shallow delta of irrigated rice paddies, but the mountain side, gouged deep into bedrock, captured the cresting wave and diverted it harmlessly downriver.

Wikipedia says:

After the system was finished, no more floods occurred. The irrigation made Sichuan the most productive agricultural region in China for a time. The construction is also credited with giving the people of the region a laid-back attitude to life. By eliminating disaster and ensuring a regular and bountiful harvest, it left them with plenty of free time.

If you enjoy Sichuan cuisine, you may have Zhao and Li to thank. And, in 2000, Dujiangyan became a UNESCO World Heritage Site.

As I wrote here in 2021,

Zhao harnessed the river not by damming it, but by dividing it. He spread it, slowed it, sank it and stored it. Millions visit the Dujiangyan fish mouth still today to watch it renew by rain, gravity, and the weight of water as it irrigates over 2,000 square miles (5,300 km2) of high dry plains.

We know we are capable of this. Why then do we read in The New York Times of August 27 that desertification of half the continental United States is all but inevitable now? As a permaculturist I often teach by using a 5-minute excerpt from the 30-minute Drylands episode of The Global Gardener where Bill Mollison walks through some WPA/CCC swales in Arizona [made with horse-drawn graders] and describes how they have prospered, untended, for 60 years (now 90), reforesting the same desert landscape that in the 1930s had blown dark sandstorms into Washington DC.

Today those forested swales are refreshing the deep water desert aquifer for future generations. That is, among other things, one element of the Biden infrastructure plan. If Biden or a surrogate replacement is reelected and given a Congressional majority, a modern Climate Conservation Corps under the auspices of Deb Haaland’s Department of Interior could be once more building earthworks as great as the chinampas, fish mouth, or CCC swales. Deb Haaland’s agenda:

Action #1: Promote Climate-Resilient Lands, Waters, and Cultural Resources

Outcome: Lands, waters, and cultural resources threatened by climate change are managed, protected, and/or preserved for current and future generations 

Action #2: Advance Climate Equity

Outcome: Vulnerable communities disproportionately impacted by climate change have equitable access to opportunities, services, and resources. 

Action #3: Transition to a Resilient Clean Energy Economy

Outcome: Climate-resilient infrastructure supports current energy and mineral resource needs and future energy needs will be increasingly met through renewable and sustainable sources. 

Action #4: Support Tribal and Insular Community Resilience

Outcome: Tribes and Insular areas are provided technical and financial resources to support climate-resilient investments. 

Action #5: Empower the Next Generation of Conservation and Resilience Workers

Outcome: A new generation of Americans are empowered and equipped to bolster resilience and tackle the climate crisis.

This all depends on what happens after US voters return to the polls in November.

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#RestorationGeneration.

當人類被關在籠内，地球持續美好，所以，給我們的教訓是:
人類毫不重要，空氣，土壤，天空和流水没有你們依然美好。
所以當你們走出籠子的時候，請記得你們是地球的客人，不是主人。

When humans are locked in a cage, the earth continues to be beautiful. Therefore, the lesson for us is: Human beings are not important. The air, soil, sky and water are still beautiful without you. So, when you step out of the cage, please remember that you are guests of the Earth, not its hosts.

We have a complete solution. We can restore whales to the ocean and bison to the plains. We can recover all the great old-growth forests. We possess the knowledge and tools to rebuild savannah and wetland ecosystems. It is not too late. All of these great works are recoverable. We can have a human population sized to harmonize, not destabilize. We can have an atmosphere that heats and cools just the right amount, is easy on our lungs and sweet to our nostrils with the scent of ten thousand flowers. All of that beckons. All of that is within reach.