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MARBLE FALLS — LCRA plans to lower the level of Lake Marble Falls by one foot for about 14 weeks starting Sept. 6 to protect workers refurbishing the first of two hydroelectric generators inside of Starcke Dam.

Lake Marble Falls has a normal operating range of between 736.2 feet and 737 feet above mean sea level. The lake is scheduled to be lowered to a range between 735.2 feet and 736 feet on Sept. 6 and will remain at the lower range until Dec. 19.

It will take only a few hours to drop the level of the lake. The work is being timed to occur after the Labor Day holiday, a traditionally busy time on the lake.

"We understand that lowering Lake Marble Falls may cause a level of inconvenience, but protecting the safety of our workers must take precedence," said Bubba Lewis, area supervisor of Hydro Operations for LCRA. "There's just no way around this."

The two hydroelectric generation units have been operable since Starcke Dam was finished in 1951. Starcke Dam forms Lake Marble Falls, which is one of four "pass-through" lakes in the Highland Lakes system. Hydroelectric generation is typically used to pass water downstream into Lake Travis.

The renovation at Starcke Dam began in June 2005 and is scheduled to be completed in January 2008. It is part of a $73.3 million upgrade to hydroelectric facilities at all six Highland Lakes dams.

While construction continues inside the dam, workers are about to refurbish the first of the dam's two head gates. Those are the giant doors that can be closed to block water from the penstock, the tunnel that carries water through the dam. The force of that water turns the blades attached to a generator. Electricity is produced when the generator turns. The gates, which are typically opened, can be closed to allow workers to access the tunnel.

Replacement of a head gate is a complex process. First, the gate is closed to block water from the penstock. Once closed, large, specially designed metal planks called stop logs are carefully lowered into place to form a temporary gate.

The stop logs haven't been used since the dam was built more than half a century ago. Engineers have urged the lowering of the lake to reduce pressure on the stop logs as a precaution to help protect the workers inside the dam. As the lake level decreases, so does the incredible pressure placed on the stop logs by the lake water.

Next year, when workers move on to the second of the two hydroelectric generators in the dam, the lake will have to be lowered again. The date of the second lowering has not been set.