The old river of Buenos Aires comes back to life

Beneath the Rio De La Plata, a tunnel that cleans water for 4.3 million people

“To the south of the city of Buenos Aires lies a barrio that is home to immigrants and soccer players: the neighborhood of La Boca.” So begins the legend of Elisa Brown, the young woman widowed just before her wedding when her husband-to-be died at sea, Argentine Navy captain Francisco Drummond. A few months after that terrible event, on a December afternoon, the girl pulled on her wedding dress, went to the inlet where the Rio de la Plata meets the Riachuelo River, and began walking, disappearing into the waters in search of her beloved.

Later, during the years when the ground beneath the Rio De La Plata was being excavated for tunnels, part of an innovative river purification plant system, legend had it that the “novia de arena” (the sand bride) was there alongside the workers, accompanying them in their mission and protecting the waters.

Her story is just one of many that ran alongside the construction of this incredible work, where engineering, passion, culture and folklore all combined in a mission to renew one of the most polluted bodies of water in Latin America.

Riachuelo: the gamble to clean up the Buenos Aires river

The path of the Riachuelo River is 64 kilometers (40 miles) long, through Buenos Aires and its province. The river’s source is on the west side, then it reaches the bridge La Noria, along the Avenida General Paz, where it marks the border between the province and the autonomous city, flowing into the Rio de la Plata, just between the barrio of La Boca and the city of Dock Sud.

This river’s banks have always been the site of major industries. At the same time, over the years, these same industries have been one of the main sources of the river’s pollution. Today, redeveloping the Riachuelo will mean improving the quality of life of 4.3 million people, many of whom live near its banks, about 23% of the residents of the Buenos Aires metropolitan area.

This task was entrusted to the Webuild Group, charged with building a complex purification plant for the river. The new plant pushes previous limits of engineering, blazing a trail in infrastructure, and is equipped to treat up to 2.3 million cubic meters (2.3 billion litres) of sewage daily.

The result is the construction of the Tunnel Sistema Riachuelo 3, Argentina’s largest technical undertaking in recent years, consisting in several underground tunnels. The main tunnel is 12 kilometers (7 miles) long – one of the longest of its kind in the world – and runs 20 meters (66 feet) deep under the bed of the Rio de la Plata.

The 12-kilometer hydraulic tunnel runs under the Riachuelo toward the Rio de la Plata and is used as an outfall channel for the new plant’s treated water, which is then dispersed into the river at a rate of 27 cubic meters per second (953 cubic feet per second). Thirty-four steel pipes, each one 27 meters (89 feet) high, carry out the dispersion into the Rio de Plata. The pipes reach the river bed from the main tunnel, and are located in its final 1.5 kilometer (just under one mile) stretch.

Ponte de la Mujer, Buenos Aires

TBM under the riverbed

Driving a Tunnel Boring Machine (TBM) under a river bed is no small feat, particularly under 4 bar pressure and with the “finish line” a full 12 kilometers (7 miles) away.

This is especially true when the ground being excavated is treacherous, made up of silty soils and saturated sands.

The primary challenge was digging efficiently and carefully while staying on track with the project’s slated timeframe. In February 2018, the first milestone 300 meters (984 metres) of excavation was reached; by April, a conveyor belt was activated, essential for the extraction of the excavated soil and for propelling the TBM’s path forward. Over months, work was interrupted multiple times for ground analysis; since the ground changed so constantly, the excavation processes were incredibly complex. Operations on this phase of the project nonetheless came to a close on November 22, 2019 with the installation of the final ring of vertical pipes to reach Rio de la Plata.

In the digging phase, most concerns centered on the wear and tear of the TBM excavation head. A special team of professional divers was called in to work under 4 bar pressure in the excavation chamber, checking for damage. When necessary, they would change the tools on the TBM head. These efforts became unnecessary later on, thanks to the ingenuity of the site engineers, who designed a special camera that could inspect the TBM head without the need for human intervention.

Risers: vertical tubes leading into the Rio De La Plata

One of the most innovative parts of the entire project was the design and installation of the so-called risers, the 27-meter-high (89-foot) vertical pipes connecting the tunnel to the river bed and discharging the purified water into the river.

After six years’ worth of studies to develop the idea, on September 10 of 2020, the installation of the first 34 risers began, and was successfully completed two days later. On November 2, 2020, the installation of all the pipes was completed.

The final phase of the work, where the risers were secured into the river bottom, was conducted by professional divers, who had to go by touch, due to the absolute inability to see so far underwater. This was yet another of the many complex operations the project required.

The history of a megaproject

The story of the Riachuelo redevelopment project began in 2011, when Argentina launched a tender for the construction of a water treatment plant and Webuild applied for it.

Due to the complexity of the project, the Argentine government secured financing from the World Bank; the mutual objective was to expand the sewage capacity of the metropolitan area of Buenos Aires, affecting a population of roughly 4 million people.

The project as a whole was made up of three lots, two of which were financed by the World Bank, the third by the Argentinean government. The Webuild Group-led consortium was awarded Lot 3, which entailed building the outlet tunnel underneath the Rio de la Plata riverbed.

The client company Aysa, Aguas y Saneamientos S.A., issued the order to begin work on January 14, 2015, and the entire first year focused on setting up the sites and doing preliminary work. The actual work itself began on October 22, 2015, when a system of breakwaters was built to protect the river’s shores, delimiting the area where the river’s treatment plant was to be built.

Today, six years since then, the work is at an advanced stage. Throughout this period, even during the toughest months of the Covid-19 pandemic, engineers, technicians and workers have given their best to complete a work that is not just unique but essential to the welfare of Buenos Aires and its residents. The millions of people who populate the Argentine capital are indeed the motivation behind this major work, which is designed to leave a lasting and sustainable mark on the area. Perhaps even more lasting than the footprints in the sand left behind by the “novia de arena.”