Tucked deep within the rugged mountains of Antioquia, Colombia, the Ituango Hydropower Project is a feat of modern engineering – not just for its scale or energy potential, but for the extraordinary underwater rehabilitation works that have taken place far from public view. Following an unexpected crisis during construction, the rehabilitation of Ituango wasn’t just a patch job; it was a masterclass in subsea engineering, precision design, and adaptive construction under the most demanding of conditions.
in April 2018, a landslide blocked one of the diversion tunnels, initiating a chain of emergency responses that significantly impacted the partially constructed dam. Among the downstream consequences were the unplanned flooding of the machine house, structural damage to intake components, and months of interrupted construction. As part of a wide-ranging rehabilitation initiative, DCN Diving, a Dutch underwater construction specialist, was tasked with the underwater isolation of the dam’s intake structures – a critical component for future operation.
This article examines the rehabilitation phase, focusing on the underwater engineering and operational decisions that enabled safe and efficient repair of submerged structures, without the need to dewater the reservoir (in this particular case dewatering was not an option because all diversion tunnels were blocked, and the water could not be regulated anymore. The surplus water from the river went over the spillway). Through advanced technology and detailed planning, the project highlights how underwater construction can provide strategic solutions to large-scale infrastructure challenges.
Engineering challenges
Following the 2018 incident, Colombian authorities and contractors began assessing the extent of the damage across multiple submerged components. The intake structures, in particular, presented both operational and technical challenges. These components were located more than 60 metres below the reservoir surface, and their rehabilitation required work in an environment of high hydrostatic pressure, zero visibility, and significant logistical complexity.
DCN Diving, known for its capabilities in complex underwater operations, was selected to carry out the intervention. Their mandate was to inspect and seal (isolate), key sections of the intake system, including embedded sealing surfaces and intake gate components.
According to Arjan Bol, Commercial Director Hydropower at DCN, the uniqueness of the Ituango project was twofold: “The Isolation work had to be done underwater in a confined space enviroment, with limited visibility and large heavy loads. That’s not unusual for us – we do it quite often – but in this case, the project carried significant political weight. There was a lot of scrutiny.”
Creating a dry workspace underwater
Central to the rehabilitation strategy was the need to create isolated, dry workspaces underwater. The solution came in the form of custom-designed mechanical plugs, which allowed divers to seal off and dewater the full sections of the intake system. Each plug consisted of a steel ring permanently installed on the intake structure, and a removable cap that could be attached and detached as required. The subsea installation of additional reinforcement rings and rock injections assured the stability of the dewatered intake tunnel.
This design ensured that future maintenance could be carried out without repeating the entire sealing operation. For future maintenance,the plugs can be used again, in combination with a Saturation Diving System (SAT) allowing the reservoir to remain operational, and avoid the need for lowering water levels – a process that is time-consuming, expensive, and environmentally disruptive.
The plugs were designed and fabricated to match the specific geometries of the intake tunnels, a process guided by 3D sonar scans and digital modelling. This digital data allowed for detailed pre-installation planning and real-time adjustment of components during execution.
Underwater construction techniques
Working at depths of over 60 metres required saturation diving techniques. Divers lived in pressurized environments aboard the diving barge and were transported to the worksite via the diving bell. This allowed them to spend extended periods underwater without the need for repeated decompression cycles, which would have slowed down operations significantly.
Visibility at depth was extremely limited, often approaching zero due to turbidity. In these conditions, divers relied on tactile feedback,practical diver friendly engineering, and detailed prior planning. Physical guides and modular frame systems were installed to provide divers with orientation and structure, ensuring safe navigation and task completion.
DCN also employed remotely operated vehicles (ROVs) to assist with inspections and visual/sonar confirmation of completed work. The combination of human and robotic systems enabled a high degree of accuracy and minimized the need for rework.
Material and structural repairs
The rehabilitation/Isolation scope included the removal and reinstallation of trash racks, concrete repairs, installation of three mechanical bulkheads consisting of aforementioned plugs & rings, installation of reinforcement rings, rock grout injection, and pumping of ultra high strength grout. Surface installed pumps, mixing units and hoses were used to pump the mixture into the annular space between the plug ring and the existing tunnel wall, in such creating a pressure and watertight seal.
Closed system concrete methods were employed to pour ultra high strength grout underwater without segregation. These methods are crucial in deep-water construction, as they ensure structural consistency despite hydrostatic pressure and reduced curing times.
All materials used were subject to rigorous quality assurance checks before and after installation, with dimensional verification supported by 3D scans and sonar imaging.
Environmental and operational considerations
One of the major benefits of DCN’s standard approach on hydropower dams is the avoidance of reservoir dewatering or lowering of the water level. In this particular case lowering the water level was not possible due to blockages of the diversion tunnels. Dewatering or lowering the water level introduces risks including sediment disturbance, negative impacts on local ecosystems, and potential delays reduction of power generation. By conducting all work in situ, DCN was able to minimize disruption and maintain the dam’s strategic timeline.
The company also emphasized sustainability. “Our equipment consumes a lot of energy, but we aim to run the systems on green power from the dam,” Bol said. “In this case however, electricity was supplied from normal sources due to the fact that the dam was not operational. We also have backup generators, but we rarely use them.”
This approach not only reduces carbon emissions but demonstrates how large infrastructure repairs can align with broader environmental goals.
As part of the project’s long-term strategy, DCN established a local office in Colombia and trained regional personnel to support ongoing operations. This local presence facilitated smoother logistics and enhanced communication with the client and Colombian stakeholders.
“The team there is doing fantastic work,” Bol noted. “We’re trying to show what’s possible underwater – both to attract new business and to highlight smarter alternatives to traditional methods.”
This focus on knowledge sharing and capacity building is central to DCN’s operations across Latin America, where the demand for resilient water infrastructure continues to grow.
Conclusion
While the Ituango incident initially disrupted Colombia’s energy ambitions, the subsequent rehabilitation has become a model for how critical infrastructure can be repaired and modernized under water, without incurring the costs of complete shutdowns or environmental compromise.
DCN’s work on the project has drawn attention from hydropower operators across Latin America, many of whom are managing ageing assets in difficult environments. As Bol emphasized, “We’re continuing to grow in the hydropower and underwater engineering sectors. With our new talent and international presence, we’re ready to tackle even more complex and innovative projects.”
In this way, Ituango represents more than a repaired dam; it stands as a case study in how underwater engineering can support national infrastructure resilience, while setting new benchmarks for safety, sustainability, and efficiency. It represents a significant milestone in the region as much as it was the first of its kind, allowing the plant to be commissioned, which otherwise would not have been possible.
Life inside the dive system
The conditions at Ituango required not only skill, but endurance. DCN’s divers worked in saturation chambers, living under pressure for up to 28 days. They were transported to the work zone via the diving bell, and conducted multiple hour-long shifts while submerged. Divers used hydraulic tools, manipulated steel components, and placed concrete by touch. “Our divers often worked by feel,” Bol explained. “Every weld, every seal had to be precise – even if they couldn’t see it.”
With visibility close to zero, all operations were supported by detailed planning and digital modeling. Modular guides ensured safety and orientation. All activities were closely monitored from the surface, using ROVs and sonar to validate positioning.
Such techniques have applications far beyond Ituango. They are increasingly used in offshore wind, oil and gas decommissioning, and complex port infrastructure rehabilitation.
