Like a Bathtub. Leaks in one diversion tunnel led to draining of hydroelectric reservoir.

As efforts begin to repair the damage to the recently completed 202-meter-tall Campos Novos Dam in southern Brazil that caused an uncontrolled release of water from its reservoir, officials continue to search for a cause of the incident.

Late last month, two of three gates on a diversion tunnel built to divert the flow of the Canoas River failed. The 650 million cu m of water from the half-filled reservoir flowed downstream into the reservoir for another recently built dam.

“We don’t know the actual cause of the leakage,” says José Ayres de Campos, engineering director for Construções e Comércio Camargo Corrêa S.A., Sao Paulo, Brazil, the engineering, procurement and construction contractor for the 880-MW hydroelectric project. “We are concerned that it is not just a single cause creating this leak but perhaps several different things.”

Ayres says cracks in the reservoir face of the dam don’t indicate major structural flaws. Camargo Corrêa officials late last month told local media that the cracks resulted from compaction of rocks at the base of the dam together with the increased rigidity of the concrete.

Both the contractor and the Inter-American Development Bank knew the existence of the cracks before the leak, says Robert Montgomery, a specialist with the IDB Private Sector Dept.

Two diversion tunnels were built to divert the river for construction. Leakage in the longer one began days after the work on the dam itself was finished last October. On June 20, the water’s pressure damaged two of the tunnel’s three steel gates and the reservoir began to drain.

Camargo Corrêa has begun working to restore access to the tunnels and initiated fill-in of the cracks on the dam, Ayres says. The company has presented a preliminary report to the consortium that owns the concession, Enercan. According to the contractor, independent consultants will examine the analysis before a plan of action is taken.

The $523.9-million project was slated to go on-line this month but the problems may push completion into early next year, Ayres says.