The Challenges of the Basin of MexicoTue, 11/01/2016 - 16:52
The Basin of Mexico is an endorheic cavity, as it has no natural outlet. This immense bowl filled with lakes formed from a confluence of runoffs after the emergence of the Chichinahuatzin mountain range. It was then enclosed by mountain ranges in the north, east and west, forming an elongated depression where volcanic elevations can be observed. These clearly demonstrate a fracture within the 19th parallel that extends to the Revillagigedo Islands in the pacific. This fracture formed secondary faults that led to volcanic eruptions. During the Pliocene Epoch, tensional fissures were formed from N-NW to S-SE, giving birth to the Sierra Nevada volcanoes including Tlaloc, Telapón, Papayo and Itztaccíhualt. In parallel, the Ajusco and Sierra de las Cruces emerged to create what is now called the “Valley of Mexico,” irrigated by the water that poured from the Sierra de las Cruces, Guadalupe and Sierra Nevada. These streams formed lakes where large amounts of volcanic ash were deposited, causing new variations in the environmental characteristics of the basin.
The lake system of the basin was made up of five bodies with waters of different character. Chalco and Xochimilco are freshwater lakes, though not safe for human consumption due to the large amounts of debris they contain. Zumpango, Xaltocan and Texcoco were brackish lakes. During the rainy seasons, the surrounding mountain ranges would merge these five lakes because the basin did not have a permanent internal source that would contribute to level of the lakes.
Archeological findings in Tlapacoya provide evidence that this region had been inhabited by hunters and gatherers more than 25,000 years ago, supported by the Tepexpan Man and the Peñon Woman whose remains date back approximately 6,000 years. The consolidation of agriculture in the formative period (3000 B.C to 200 A.C) encouraged the formation of urban sprawls. After Xitle’s eruption in the 2nd century, people from Cuicuilco migrated to the northeast lakes, laying the ground for Teotihuacan, one of the most important cities of Mesoamerica. After its demise in the 7th century, its habitants spread to other areas of the lake region. By the 9th century, groups from the north arrived to the central highlands. The last to arrive was the Mexica culture, founding Mexico-Tenochtitlán in 1325 after uniting with Texcoco and Tacuba against the people of Azcapotzalco. The basin has been exploited and man-made since then because of its natural resources. People took advantage of the local flora and fauna through chinampas, a humidity crop system that reached its peak between the 14th and 16th centuries. Since fresh water was of the essence, the locals devised a series of projects, or albarradas, with the purpose of containing, regulating and draining the lakes.
Springs located at the foot of the mountain were the source for drinking water, which was transferred through open aqueducts. One of the most important Mexica hydraulic infrastructure projects was the Albarradón de Nezahualcóyotl, built between 1440 and 1503 to honor Texcoco’s king. Its main function was to separate fresh and brackish waters, starting from the Cerro de la Estrella and ending in northern Atzacoalco. This infrastructure permitted the development of the chinampa system in places where they could not be previously installed due to the water’s high mineral content. During Mexica rule, several albarradón projects were constructed as a part of a grand hydraulic control system, all of them leading to Tenochtitlán.
During the conquest of Tenochtitlan, Hernán Cortés took advantage of the lake and its water systems to siege the city for 90 days, retreating on Aug. 13, 1521 after capturing Cuauhtemoc. Cortés sought to construct his new Spanish city in Coyoacan. However, he changed his mind in favor of Tenochtitlan’s ruins to avoid an uprising. The materials of the ancient temples and natives’ homes were used to build the new city, including part of the aqueducts since Cortés did not think they were useful. By 1521, the water levels began to decrease as a result of the over-exploitation of the forests surrounding the lakes.
In 1555, the city suffered its first major flood followed by another in 1579. By 1580, a “general drain” was designed but the project did not go through in full due to elevated costs. However, after the flood of 1604, the city looked for a definitive solution, leading to the implementation of the general drainage system. Among other proposals, cosmographer Enrico Martínez proposed a tunnel running toward the north of the basin, passing through Huehuetoca, that would drift the waters of the Tula River, which connects to the Panuco River and then empties into the Gulf of Mexico.
The project was not completed as only the waters of the Cuautitlan River were diverted. In 1623, the Marquis of Galvez shut down the Huehuetoca tunnel but in 1627 the basin flooded again, followed by three more disasters in 1627, 1628 and 1629, which lasted until 1634. After this eternal flood, the general drainage project was restarted but with a plan to direct the flow into an opencast instead of a tunnel. The construction was concluded in 1789. Although not as severe, the floods nonetheless continued, aided by urbanization that shortened the lakes’ banks.
In the first half of 19th century there was not much progress due to the Independence War in 1810 and a long period of political instability that ended with Porfirio Díaz’s government in 1876. By the second half of the century, another alternative for general drainage was proposed by engineer Francisco de Garay. He proposed a series of connections between the lakes in the basin starting at Chalco Lake and ending at Zumpango Lake, draining the excess water in the Tula River with a tunnel running next to Tequisquiac. Unfortunately, this project was not carried out due to insufficient financial resources. In 1856 the Chalco Channel, now known as the Garay Channel, was built to connect Xochimilco with Texcoco to prevent flooding in the south. During Maximiliano of Hapbsburg’s reign, the Emperor gave the green light to Garay’s project which began construction in 1866. However, with the ending of the French invasion, the initiative was again cancelled.
During Díaz’s administration, the country finally achieved economic stability and Mexico City initiated a period of growth mainly toward the occidental region, creating new colonies along the ancient road to Tacuba. The construction of the Great Channel was revisited by opening the tunnel of Tequisquiac and completing its construction on March 17, 1900. After the Revolution in 1910, the country fell once again into chaos until the 1930s. The city began expanding into the previous lakebeds, creating a challenging situation in the city’s planning and service provision. The year 1937 sparks the construction of the second tunnel towards Tequisquiac finished by 1954. However, even with these projects the flooding was not completely suppressed.
The city continued to grow expeditiously, occupying areas that were once dedicated solely to agriculture. This increased the need for drinking water, leading to the meticulous extraction of water from the subsoil and initiating the quick sinking of the city. Through the 1940s to the 1970s, rivers that once disembogued in the basin were sealed and their ancient channels were transformed into avenues.
In the 1950s, the drainage system went through a great expansion even though the city continued to have grave problems in managing rain and waste water. The General Direction of Hydraulic Works was created in 1953 and established the “General Plan to Solve Subsidence, Flooding, and Drinking Water Supply in Mexico City.” This plan was modified as years passed until it was able to offer a definite solution to flooding and drainage. In 1975, the “Mexico City’s Deep Drainage Project” was instated and because of the constant work to drain the basin from the mid-20th century, as well as the exponential growth of the city during the ‘60s, ‘70s and ‘80s, the lakes disappeared almost entirely. Xochimilco had to be rehabilitated in 1951 by diverting the channel of Churubusco to salvage the chinampa area. Meanwhile, the Texcoco disappeared completely and artificial lakes were created for the ecological recovery of the region. Zumpango and Xaltoca were also drained entirely and replaced by countless housing units. Mexico City’s deep drainage has contributed to flood control but the problem is still present. After the overflow of the Compañía Channel in Chalco, a new tunnel had to be planned. Ecological projects to restore the lakes of Texcoco, Xochimilco and Tláhuac have also been carried out.
Mexico City and the metropolitan area are an example of bad urbanization and grave subsoil problems due to indiscriminate groundwater extraction, pollution and bad water usage. More water has to be brought from another basin to meet the needs of the city and groundwater continues to be extracted with obvious consequences. Now, the project for the New Mexico City International Airport (NAICM) intends to exploit land that once was devoted to tillage and was traditionally the lakebed. Although the project is intended to be self-sufficient, what will be the repercussions inherited by future generations?