I’ve written a little bit before about the desert city of Gran Mendoza in Western Argentina. It is a beautiful settlement of about 1 million that has existed along the borders of political and ecological feasibility over at least the last 500 years- it has variously been at the southern edge of the Inca Empire, the eastern edge of the Chilean General Captaincy (a political subdivision under Spanish colonial rule) and the western edge of the Argentine Republic while enjoying only 7 inches of rain per year (less than half that of parched Los Angeles), much of which comes in infrequent downpours, and relying on the water from ever-shrinking glaciers. This situation has lead to the creation of a series of landscape types that are interesting from a landscape architecture perspective, including the most unique and ubiquitous street profile (building to building) I have ever seen. These enable the creation of an oasis city supported by an agricultural hinterland (as opposed to, say, mining, another common economic base in the TransAmerican West) in the middle of the desert.
[detail shot of the common street in Mendoza: the typical section is- building facade, small garden, sidewalk, stone lined irrigation and stormwater canal with generous pedestrian side, curb (with stormwater curbcut) street]
All of the landscapes of this city (like most places) are best understood through this double lens- political and ecological. And few things are more political-ecological than irrigation. The landscapes of Mendoza in particular are intimately tied up with the water irrigation network. Most of the territorial concepts of this network date back to the Huarpes people, though Mendocinos including the Huarpes have shown an interest in absorbing and adapting technology from distant imperial capitals- be it the Inca, the Spanish, or Argentina. For Mendocinos, landscapes are instruments for urbanizing the desert.
When confronted with strange and interesting places like this, I always ask “what can landscape architecture learn from this situation, and what can landscape architecture bring to the table.” With that in mind I’d like to give an account of three of the largest nodes in the hydrological network over the course of this week, starting in reverse order. That is, I’ll be swimming upstream through the hydrological network. I got to visit these over the course of a week thanks to the kindness and generosity of a team of local engineers and researchers in the area, beginning with Oscar, biochemist and facility jefe (and unbelievably kind dude) of the Campo Espejo.
[in the foreground the earthwork that serves as access road and dam, to the right is one of the lagoons, in the background is the precordillera, or Andean foothills]
[plan schematic of the Campo Espejo]
The Campo Espejo is a sewage treatment plant about the size of New York City’s Central Park. It is located to the north of the city, at the base of the Andean precordillera (you can’t call them foothills, because they are huge and craggy), and just west of the large agricultural zone it irrigates named ACRE (Restricted Area for Special Cultivation). It was built and is run by a private consortium of local construction companies, though it is owned by the municipality of Mendoza.
The project was planned in the early 90’s using concepts developed by CEPIS (Center of Sanitation Engineering) of the Pan-American/World Health Association as a response to cholera outbreaks which occurred in the early 90’s through the Andean highlands, including Mendoza. It is a variation on the facultative lagoon system, and the basic premise is to create the conditions in which the biochemical processes of lagoons can be sped up and slowed down, with some degree of human control. These types of systems are finely tuned to both their region and their site because they are very sensitive to latitude (amount of sun, heat) and require a delicate formal calculus to function well. Below in internal logic and external logic I’ll get into some of the proportions and dimensions.
[the main sewage canal with a distributor canal at the bottom and sluice gate in the center; it is separated from the lagoons by the earthwork to the left which is carrying the access road; to the left is the autochthonous vegetation of the region]
During construction nearly 5 million cubic meters of earth was moved. This particular area was chosen because of three primary factors:
1) it was downhill from the city allowing the system to be primarily gravity fed
2) the pre-existing soils in this location had high levels of saltpeter, making the soils marginal for irrigated agriculture
3) existing local topography allowed for excavation and earth-moving, while still substantial, to be minimized
The Campo Espejo treats about 1,500 liters/second of sewage (the maximum capacity is 1,700 l/s). This is about 15% of domestic and industrial sewage in Grand Mendoza, the agglomerated metro area including Mendoza proper as well as smaller adjacent municipalities such as Godoy Cruz.
Sewage is brought to the facility through an underground pipe that surfaces as a canal once within the Campo Espejo facility. It is immediately screened for floatables (not the same as floaters, which have broken up over the journey and pass through the screen) which also allows for the flow rate to be measured using Bernoulli’s Principle. The canal then carries the sewage to the lagoon system. Small sluice gates open off of the main canal and distribute the sewage into the lagoons through thirteen separate distributor canals. Each distributor canal has from 5 to 10 outlets, depending on its width, which create a sheet flow into the receiving lagoons, several meters below.
The lagoon system is made of thirteen lagoon chains, each chain consisting of three lagoons (A, B, and C). The length of the lagoon A nearest to the sewage canal is equal to the combined length of B and C lagoons. This is, quite simply, because the primary biochemical and physical processes in lagoon A take about twice as long as those of the B and C lagoons.
[looking out across one of the A lagoons to the east, algae activity is low during the winter time]
In lagoon A the primary process is to break down solids into simpler chemicals (so, poop into nitrates and phosphates, for instance). Bacteria do most of this work, drawing on the oxygen in the water, the heat and light from the sun. As they do this, they clarify the water and produce waste which falls to the bottom of the lake as sludge. The sludge in the first 10 meters of lagoon A in each chain must be dredged out every few years.
In lagoon B the primary operation is to consume parasites, and to continue breaking down the solids (the most difficult and time-consuming process). Bacteria consume the salmonella and coliforms and other hideous little monsters, and algal blooms really take hold as the freed phosphorous and nitrogen is consumed. In lagoon C the bacteria begin to die off for lack of food. By the end of the lagoon chain, sewage that had 10*7/cc of escheria coli (10 to the 7th power of just one type of fecal coliform) has been almost completely cleared, and material with 200 mg/l of biochemical oxygen demand has been reduced to less than 30 mg/l.
The width of the receiving lagoon is directly proportional to its length (about 5:1). This is intended to make it so that each drop of sewage remains in lagoon A for about 20 days, 40 days for the whole lagoon chain. This 40 days is a rule of thumb based on the latitude and altitude of Mendoza, and must be modulated according to a variety of environmental factors (wind, time of year, amount of rain). The system works slower in the winter, and on cloudy days, and does better with lots of sun and wind. Effectiveness is monitored by taking readings (such as fecal coliforms, BOD, phosphorous, etc) every day from each lagoon chain. The system can be sped up or slowed down by reducing the amount allowed in to the distributor canals. This requires more work from treatment facilities elsewhere in the region.
[intakes on the eastern edge of one of the lagoons pull in surface water and allow it to flow down to the next lagoon on the right]
[discharge into the next lagoon in the chain; vegetation on the earthworks can help stabilize the mounds from erosion, but can also shelter burrowing animals, compromising the structure over time]
While the proportions of the lagoon chain and each individual lagoon are fixed, their actual dimensions are site specific and are determined as a response to existing topography and the earthmoving required, the needed amount of treatment, and the funds available for construction. While lagoon A in each chain must be the highest and lagoon C the lowest, and the lagoon chain farthest downstream on the canal must be the lowest, there is a great deal of flexibility in terms of the exact heights, lengths, and sizes. All of this creates a monumental but varied topography of massive, stepped earthworks framing lagoons of varying sizes. To the west is a large mound created from the lagoon excavation, and to the east (downhill) is a low area which used to contain small seasonal wetlands.
In a sense, the Campo Espejo has scaled up and intensified the pre-existing conditions of the site. Rather than water running through this low area seasonally and creating small lagoons and an arroyo, there are massive rectangular lagoons which feed treated water into a discharge canal on the eastern edge. At this point the water has undergone the equivalent of secondary treatment. In the province of Mendoza this means that it cannot be discharged into a river or surface body of water.
The ACRE (Restricted Cultivation Agricultural Area) is therefore a key element of the larger hydrological system, nearly 10,000 acres of finishing treatment. Only, instead of consuming energy to remove elements such as phosphorous and nitrogen that remain in the Campo Espejo discharge, it puts those to work as a rich and easy-to-distribute fertilizer through a canal system that laces the countryside to the northeast of the city. Fruit orchards, pasture, and garlic all benefit from this system. Basically anything that needs to be cooked to be eaten, or that doesn’t grow with the edible part in contact with the soil is cultivated and sold to markets in the city where it is bought, consumed, and flushed back to Campo Espejo. Most of the farms are currently owned and operated by single families working plots of just a few acres to a few hundred acres.
[discharge from the lagoon system into the collector canal, which runs to the ACRE zone]
[the recently planted garlic of a local farmer, a Bolivian immigrant who owns and works a plot of about 2 hectares]
A Cultural Landscape
There are many political aspects to this, one of the simplest being that the provincial water and sewer authority (AySM, Aguas y Sanitarias Mendocinas) is very powerful, and interesting. Many of the other aspects, such as the economic and political vulnerability of the small farmers in ACRE (many of whom are Bolivian immigrants, including the one I spoke to) are very complicated. I can’t offer much insight regarding them because they proved too difficult for me to really understand in the little bit of time I had.
However, what is clear is that the Campo Espejo is an incredible component in a larger cultural landscape that is part of the history of settlement and culture here on the edges of political and ecological feasibility. The Campo Espejo/ACRE component of the regional hydrological system works as a feedback loop, returning precious water to the city in the form of food, and utilizing the nutrients in urban sewage to produce that food. I suspect that this landscape has some things to offer the Western United States regarding agricultural production, urbanism, and landscape-making as an example of both good and bad practices. In fact, I would love to know if anyone knows of similar facilities where a facultative lagoon is paired with a canal-irrigated agricultural zone in the American West.
The experience of being in this place is overwhelming- a piece of the earth the size of Central Park that seems simultaneously massive because of the huge, still expanses of water and the monumental earthworks, and tiny, being up against the massive Andean wall on one side and surrounded by the great plains of the Argentine Pampas on the other. And yet, even as your eyes are overwhelmed, your nose brings you right back down into the muck, the visceral, stinky reality of human feces. It is a bewildering and sublime experience. Right now it remains walled off, accessible to local inhabitants only through the produce they eat and the toilets they flush.
But the aesthetic potential of this vital and incredible cultural landscape suggests it might do something else. Maybe there are additional economic symbiotic relationships or political alliances to be formed, or social and ecological roles to perform. I’m not necessarily interested in a shift from the specific and controlled to the general and open. While popular to call for, especially right now in landscape architecture, that is not usually appropriate or properly aligned with the order of things. But I can imagine there are some specific points of contact between this landscape and other cultural objects, landscapes, processes, and moments.
[the monumental earthwork resulting from the lagoon excavations; perched between the Campo Espejo to the east and the Andean precordillera to the west and offering views over the entire cultural landscape, the earthwork should be studied for its social and ecological potential, and for the different forms of engagement it might offer regarding this important cultural landscape]
**Many thanks to the engineer Miriam, to Oscar, and especially to Ezequiel, for being so generous with their knowledge and time.