Hidroituango’s Collapsed ‘GAD’ Diversion Tunnel Closed Permanently, Bringing Huge Relief
EPM announced this morning (May 4) that — following years of efforts – engineers have finally achieved permanent closure of a problematic auxiliary diversion tunnel (“GAD” in Spanish initials) that collapsed in 2018 and subsequently threatened to destroy the US$5 billion “Hidroituango” hydroelectric project here in Antioquia.
“This is a milestone for the stability of the project and mitigation of risks for the communities located downstream of the future hydroelectric generation plant,” according to EPM.
“With concrete plugs 23 meters long and 14 meters high, the GAD is permanently closed.”
Along with continuing reconstruction progress inside the dam’s machine room, EPM is now confident of “starting to generate energy with the first two [power] units in the second half of 2022,” added EPM general manager Jorge Andrés Carrillo.
According to EPM, “closing the GAD was not an easy task, since it was naturally clogged [with rubble and Cauca River water], with the risk that it could unblock naturally at any time.”
So, during December 2019, the 300-ton blockage gates for each section of the GAD were lowered, which allowed for partial plugging. However, “despite this barrier, at least eight cubic meters per second of water continued to pass through a discharge system installed in the upper part of the gates, a considerable quantity that did not allow safe access for machinery and personnel” to enable permanent closure, according to EPM.
“To circumvent the situation, a maneuver called bypass was developed, which consisted of installing a piping system that allowed the water that entered through the GAD to be diverted to an intermediate discharge [tunnel] and, from there, to the spillway basin to rejoin the channel leading to the Cauca River.
“At the beginning of 2022, once this part of the GAD was dry, the auxiliary gates (right and left) were accessed to build the two concrete plugs — 23 meters long and 14 meters high,” a job that took 600 workers and engineers four months to complete, according to EPM.
The GAD initially was constructed to divert the waters of the Cauca River while two other diversion tunnels were deliberately plugged in order to enable the required GAD to take-over the diversion job.
“In March 2018, when the process of pre-plugging the right tunnel began, the flow of the Cauca River continued to flow only through the auxiliary diversion tunnel, GAD,” according to EPM.
“This auxiliary tunnel was designed and built for temporary use. It was planned to operate only from September 2017 to July 2018, when it was planned to start filling the reservoir [behind the dam]. Afterward, it would be closed permanently.
“Its operation was interrupted as of April 28, 2018 when it became clogged and then reopened naturally on several occasions, which caused sudden flooding downstream and the destruction of the two closure gates that were already installed at that point.”
As a result, EPM rushed to close the GAD with temporary measures — and accelerated completion of the dam along with the dam’s engineered spillway, enabling the Cauca River to flow over the spillway — until reconstruction of the machine room will allow that water to flow through the power turbines, as originally intended.
