Montgomery County officials are draining Lake Needwood to repair the dam that was damaged by the recent rainstorms.
The decision follows a recommendation to do so by the Maryland Department of the Environment.
“The No. 1 concern is repairing the damage to the dam,” said Chuck Gates, an agency spokesman. The dam owners “need to start assessing and figuring out how to fix it [and] they’ll need to drain [the lake] a little bit.”
The torrential rain increased the water level of the lake — which opened in the mid-1960s — to 23 feet above normal. The surge breached the earthen dam and prompted the evacuation of thousands of residents in neighborhoods south of the lake and connecting Rock Creek for nearly two days.
County officials say the dam is no longer leaking. But state officials say the dam remains unsafe because of uncertainty about what caused the leaks and whether the high water will affect the dam’s stability in the future.
“We want to assure the public that they are in no imminent danger,” said Mary Bradford, director of parks for the Maryland-National Capital Park and Planning Commission. “Any risks that exist are significantly reduced as we continue to lower water levels and lessen pressure on the dam.”
Mr. Gates said the state recommendation calls for the commission to hire an engineering firm to assess the situation and create a plan to repair the damage.
He also said the commission has agreed to drain the lake to 81/2 feet below normal to see whether it needs more draining to make repairs.
“There’s a possibility that we’ll have to completely empty the lake,” Mr. Gates said. But “as of now that’s just an option.”
Crews have opened two of three gates at the lake to help control the drainage into Rock Creek.
Officials said yesterday the lake’s level was at 18 inches to 2 feet above normal and it was draining at a rate of about 1 foot per day.
Marion Joyce, a spokeswoman for the commission and the Montgomery County Planning Board, said once the lake is at a desired level, it will take engineers “a couple months” to learn what caused the seepage in the dam and another couple of months to fix the problem.
The drainage also likely will affect wildlife — including fish species such as bass, catfish, pike and trout — in the lake.
Ms. Joyce said the fish would be moved to other nearby ponds and reservoirs if necessary.
“If it does have to be drawn down enough so we need to remove the fish, that will be many people, many boats, many agencies involved in that transfer,” she said.