|Second tallest dam in Brazil,
but it doesn’t hold water.
A diversion tunnel for recently built dam in Brazil failed during the last week in June, causing an uncontrolled release of the water from the huge upstream reservoir. The failure caused no loss of life and contractors assert that the dam’s main structure is intact, but the event is raising alarms from international environmental groups and sparking concerns about additional delays in the project, which is already well behind schedule.
The 626-foot (202-meter) Campos Novos dam
see diagram) in the Santa Catarina region of southern Brazil is the world’s third tallest concrete-faced rockfill dam and the second tallest dam in Brazil. A consortium led by Brazilian construction giant Camargo Corrêa and engineering consultants Engevix is building the project.
“We don’t know the actual cause of the leakage,” said José Ayres de Campos the engineering director for Camargo Corrêa. “We are concerned that it is not just a single cause creating this leak but perhaps several different things.”
The flow of water through the tunnels pushed back the plans to plug the tunnels and complete the construction of the dam. The problems may push the completion of the 880-Megawatt hydroelectric generating station possibly into early next year, Ayres said.
The contractual schedule set forth a 54-month construction period concluding January 30, 2006. The three turbines were due to begin generating on January 31, April 30 and July 31, 2006. The delays in the project have caused the company to incur penalty fees that Ayres declined to specify on June 30.
The Campos Novos hydroelectric project is a 35-year build-and-operate concession awarded in 1998 to Enercan, a consortium made up of Brazilian power company CPFL Energia with 48.7 percent; Brazilian aluminum makers CBA with 22.7 percent; metallurgy company CNT with 20 percent and two state-run electric companies.
The original estimated cost of the project was $523.9 million. It is being financed through loans through the Inter-American Development Bank and the Brazilian state-owned National Bank for Economic and Social Development (BNDES).
Construction began in August of 2001. The river was deviated through the two diversion tunnels in October of 2003. The dam is composed of 13,000,000 cubic meters of rock material quarried on site.
Two tunnels of 2823.75 feet (860.9 meters) and 3003.82 feet (915.8 meters) in length were dug to divert the water from the river around the dam during construction. The tunnels were roughly square in shape 52.48 feet (16 meters) high and about 13.12 feet (4 meters wide).
Leakage in the longer of the two tunnels began on October ten days after construction on the dam was completed. Water flowed into the tunnel at the rate of 50 cubic meters per second until a plug was installed that limited it to one cubic meter per second, Ayers said.
Leakage resumed in the beginning of April and at a greater rate. On June 20, the pressure of the water damaged two of three steel gates installed in the tunnel and allowed the water in the reservoir to flow through the diversion tunnel.
Ayers said the steel gates were designed to withstand 180 cubic meters of head but were shoved off their bases by the force of the water through the tunnel, estimated at a rate of 4,000 cubic meters per second. The entire reservoir, which was near its 1.3 billion cubic meter capacity at the time of the incident, flowed through the tunnel within the span of days.
The water flowed 15 miles (24 kilometers) downstream where it was collected in the reservoir for the 1,450MW Machadinho hydropower project located in the Pelotas River. Due to a regional drought, the water levels there were exceptionally low and the additional inflow filled the reservoir.
Ayres said a technical team would be working over the next two weeks to determine the cause of the leak and propose a solution. The IDB, who provided a $75 million loan for the project, also sent a team to evaluate the incident and plans to issue a report as well, said Robert Montgomery, a specialist with the IDB Private Sector Department Natural Resources.
|Diversion tunnel gates failed, draining reservoir.
Environmental groups have circulated photos of the dam taken on June 24 by Friends of the Earth Brazil suggest that the tunnel failure has seriously undermined the dam’s structural integrity.
“The company has been covering up the extent of the damage, the cost and time of repairing (or rebuilding) the dam, and the potential risks to people and property downstream,” said Glenn Switkes, International Rivers Network’s Latin America Campaigns Director. The company did not disseminate any information, despite the dangers posed by the weakened structure.”
Officials with both Camargo Corrêa and the IDB say the photos depict cracks in the 98,500 cubic meters of concrete on the face of the dam but that there is no major damage to the structure itself. Moreover, the cracks are completely separate to the leakage in the diversion tunnels that caused the draining of the reservoir, Ayres said.
“There is no structural damage to the dam whatsoever,” Montgomery said.
(Photos courtesy of Courtesy of Camargo Corrêa)