Lisbon's great drainage tunnel, which will help prevent flooding in the city, has been excavated. The “Oli” tunneling machine, which left Campolide a year and a half ago, has reached Santa Apolónia, after crossing the city's underground, passing under places like Avenida da Liberdade and Almirante Reis.
The first major tunnel in Lisbon's General Drainage Plan (PGDL) has been completed. Excavation began in Campolide in December 2023, ran through the city's underground, passing under Avenida da Liberdade and Avenida Almirante Reis, and has now ended in Santa Apolónia. The moment was marked on Tuesday, July 22, at a ceremony attended by Carlos Moedas, Mayor of Lisbon. “Today is a very happy day for Lisbon”said the mayor. “I confess my emotion not only as mayor but also as a hydraulic engineer.”
The drainage tunnel between Campolide and Santa Apolónia is the first of two tunnels to be built in Lisbon to control flooding. With a length of 4.4 kilometers, a diameter of 5.5 meters and an average depth of 30-40 meters, this first tunnel is the largest and should be operational in the winter of next year, José Silva Ferreira, coordinator of Lisbon's General Drainage Plan, told reporters. “There won't be floods in Alcântara, there won't be floods in downtown Lisbon. Why is that? Because we prevent too much water from entering the low-lying areas”, he added.
The tunnel will not only capture rainwater in Campolide, but along the entire route, namely Avenida da Liberdade, Santa Marta and Avenida Almirante Reis, preventing it from reaching the lower parts of the city and causing flooding. “The project is dimensioned so that we can contain the rains that come once every 100 years.”
July 22 was a good day for Silva Ferreira. “It's a great joy and a sense of accomplishment. It's a dream that began almost 15 years ago. I've been fighting for 15 years and we've succeeded”, he told journalists. “Everything isn't ready, but the main part is, which is the excavation of this larger tunnel, which, just kidding, is a five-kilometer tunnel. Now we're going to remove the machine and take it to Beato, to start the second tunnel at the beginning of 2026. From January to April."
From Santa Apolónia to Beato
The machine Silva Ferreira is referring to is the H2OLisboa tunneling machine - or “Oli” - which arrived in the Portuguese capital from China in September 2022. When assembled, it resembles a train with several carriages and is around 130 meters long. Between Campolide and Santa Apolónia, he worked practically every day, with teams on board who ate and slept underground, ensuring that the work progressed continuously.
The tunneling machine excavated the subsoil with a giant drill, extracted the earth outside and installed large concrete rings, which gave the tunnel its shape and structure. It advanced between “six to eight rings a day” - each 1.80 meters wide - which allowed daily progress of around 10 to 14 meters, Silva Ferreira explains. He adds another curiosity: “The total amount of earth we removed from the excavation was around half a million cubic meters. That's about 13 times the volume of the Town Hall building.”
In August, the machine will leave Santa Apolónia and be transported to Beato. It is in this smaller yard that it will be reassembled to drill a new tunnel: a smaller one, just one kilometer long, between Beato and Chelas. “Why don't we do the tunnel from Chelas to Beato? Because taking the machine up there would be very complicated”, says Silva Ferreira. Transportation will take place at night along Avenida Infante D. Henrique.
The biggest challenge will be dealing with the weight of the tunneling machine: “The drill bit alone, the head you see there, weighs 70 tons. The body, which is where the motors and the main part of the mechanism are, is 410 tons. The rest is relatively simple; they look like containers”, explains the engineer. “All the preparation and assembly in Beato will take two or three months. The estimate is to start digging in January. But it's even possible that we'll get ahead of ourselves.”
Work to continue in Santa Apolónia
While the second tunnel will go ahead in Beato, the first will have to be completed in Santa Apolónia. The part of the tunnel in charge of Oli is done, but the work will continue with the joining of the tunnel excavated by the tunnel boring machine to the final section, built on the surface through an open cut. This last section opens into a large mouth facing the Tagus, created to slow down the flow of water before it reaches the river, avoiding disturbances to river navigation, as Silva Ferreira explains. “These tunnels are designed to transport rainwater that may occur once every 100 years. They have the capacity for that: 175 public meters per second”, he explains. While the tunnel itself is 5.5 meters in diameter, next to the Tagus it widens to a channel 30 meters wide. “What for? So that the water calms down and goes at a lower speed than the flood or the ebb, that is, 2 meters per second.”, on reaching the river. “In other words, it won't bother the ships that are here.”
The drainage tunnel will pass very close to the Lisbon Metro tunnel, which will force the temporary closure of the Blue Line between Terreiro do Paço and Santa Apolónia for a few months. “We're going to cross over the Metro tunnel and we're going to have to reinforce the inside of that tunnel”, Silva Ferreira said. This intervention should begin in September and last “seven to eight months”, and was not originally planned. “We realized that the soils around the Metro tunnel were not as good as we thought”he said.
There were two solutions: “either we went outside the tunnel to secure what's inside, or we went inside to secure what's outside”. We opted for internal reinforcement. “We're going to put some rings inside the tunnel to hold up our passage. To do this, we have to stop traffic in the tunnel and remove all the infrastructure - the cables and pipes that we see when we take the subway. We have to remove them, put in some ‘ribs’, we call them, and then replace the infrastructure again, and finish the work.”
All this will mean the suspension of the Blue Line between September and April/May 2025. “It has to be announced in advance when the date will be, so that people are properly warned and know that there is alternative transportation between Santa Apolónia and Terreiro do Paço. And the City Council will certainly collaborate and help the Metro to resolve this situation.”
Much more than a tunnel
Although the construction of the tunnel is invisible, the drainage work has had an impact on various parts of the city, mainly because of three vortexes that are being built to capture the water along the route. “Of the three vortices, two are completely done - Avenida da Liberdade and Almirante Reis. We're halfway through the third, in Santa Marta”, noted Silva Ferreira.
While Oli as the great tunnel was being drilled, several men were working on the construction of the vortices, vertical structures that will calm the waters before they reach the tunnel, putting them through a kind of whirlpool. Silva Ferreira explains further: “The tunnel is down here and the collectors are up there. Now, we have to send the extra water, which would flood the lower areas of the city, into our tunnel, which is on average 20 meters deep. But the water can't fall 20 meters down, otherwise everything would burst. So we have a vortex to make the water dizzy. It reduces the energy, falls into a cushion of water and is then led into the tunnel.”
Meanwhile, in Campolide, at the largest and most important of the construction sites - the size of a soccer pitch - the connection is being made between the new tunnel and the old Alcântara Channel, through which a mixture of water from the Ribeira de Alcântara, domestic sewage and rainwater flows to the Alcântara Wastewater Treatment Plant. To prevent pollution of the Tagus, an anti-pollution basin with a capacity of 17,000 cubic meters was built in Campolide, at the beginning of the two tunnels, where the first rains will be retained. “the first rains are polluted because they wash away the sidewalks”, which are often dirty with oil from cars, explains Silva Ferreira.
"If you notice, when you go down the road, you even see a kind of soap, a white foam.“ This water is decanted and then sent for treatment at the wastewater treatment plant. If it rains a lot, the anti-pollution basin can work like a sewage treatment plant, filtering out other “floating” waste, such as “plastic, styrofoam, ladies” pads". But after a certain point, the water flows straight on: it has rained a lot, “Water is just water. It's all washed away”, says the engineer.
The PDGL beyond the tunnels
José Silva Ferreira points to the completion of all the tunnel work “by the end of 2026”, admitting that this deadline may “slipping a little to the first quarter of 2027”. In any case, the Campolide-Santa Apolónia tunnel should be operational by the winter of 2026. The second tunnel won't be operational until after that, as there are “a few problems to solve on your arrival in Chelas” due to an improvement in the project.
The completion of the two tunnels does not mean the end of Lisbon's General Drainage Plan (PGDL), which runs from 2016 to 2030 and aims to protect the city from flooding caused by extreme rainfall. “The plan still has things to do, and we'll have another three to four years to do these little things”, Silva Ferreira recalls. Nor did the plan start with these two tunnels, even though they were the main parts.
Since 2015, when José Silva Ferreira took over the coordination of the PGDL team, important retention basins have been created in Ameixoeira and at the Ajuda University Pole to contain water “at source”, It also solved the flooding that occurred relatively frequently on Calçada de Carriche or in the Rio Seco area. “We also made a microtunnel in Avenida Infante D. Henrique and solved the problem of some flooding in Avenida de Berlim and Parque das Nações”, Silva Ferreira explained. “So we've already done some small things within the city. All this is the General Drainage Plan.”
”The biggest construction project underway in Western Europe”
For Carlos Moedas, tunnels are the most important component of the PGDL and “the largest construction project underway in Western Europe” - a work that “prepares us for a future in which there will be many more difficulties with water due to climate change”. “It's an invisible work. It's often in the invisible that the most important thing lies”, said the Mayor of Lisbon. “The people of Lisbon will remember her when there are no more floods in the city.”
“I want to thank engineer Silva Ferreira. He suffered for so many years watching this work not go ahead, but the two of us made a pact that this would be it”, Moedas said at a ceremony that was attended by European Commissioner Jessica Roswall, responsible for the Environment, Water Resilience and Competitive Circular Economy, and also by the Minister for the Environment, Maria da Graça Carvalho. The mayor also thanked Carmona Rodrigues, who had been the last PSD mayor of Lisbon, serving from 2005 to 2007. “We owe this project to Professor Carmona Rodrigues, for whom I would like to give a round of applause”, said the Social Democrat President.
Although the first version of Lisbon's General Drainage Plan was launched under Carmona Rodrigues, it was under Fernando Medina (PS), Moedas' predecessor, that the plan made significant progress. Medina found financing from the European Investment Bank (EIB) for the construction of the two tunnels and launched the public tender in 2019, which was awarded in December of the following year to the Mota Engil/SPIE Batignolles Internacion consortium for 132.9 million euros. Moedas only signed the contracts and went ahead with the work.
