Sunday night storm wreaks more havoc in county

Conditions at Lake Needwood dam are improving, officials say

Wednesday, July 5, 2006

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by Janel Davis, Warren Parish and Liza Gutierrez

Staff Writers

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The rains came swiftly Sunday evening, this time bringing heavy winds that smacked Aspen Hill the hardest, toppling trees and causing power outages.

‘‘There was a good amount of damage in the Aspen Hill area,” county Fire and Rescue Services spokeswoman Dorcus ‘‘Dee” Howard Richards said. ‘‘Some of those affected were already attempting to recover from last week’s evacuation efforts.”

And that has left many residents wondering whether summer rains will continue to force them to leave their homes.

Work continues on the Lake Needwood Dam as county officials prepare to determine long-term solutions to maintain the structure.

The reservoir reached a peak of 23 feet above normal levels around June 27, said Mike Riley, park development chief for the Maryland-National Capital Park and Planning Commission.

It dropped to 10 feet above normal by Monday, he said.

‘‘The effects of last night’s rainfall are insignificant,” Riley said on Monday.

All conditions at the dam are improving, he said at press time Monday afternoon. It is still leaking, but at a much slower rate, he added.

After a few days of heavy rain early last week, the earthen dam that separates the lake from Rock Creek began leaking in several places.

That, coupled with the lake swelling to almost two dozen feet above its normal level, sparked the county to evacuate hundreds of families in the Aspen Hill area in the early-morning hours of June 28. Later that day residents in Kensington and Bethesda were asked to evacuate.

Tensions eased on Thursday when levels in the nine monitoring wells located on the face of the dam, on the downstream slope, began dropping that evening.

‘‘[That] gave us the final comfort level that the dam was stable,” Riley said.

County officials lifted the area evacuation by 10 that night.

Before a solution is determined, considerable engineering studies and review by the appropriate agencies must be completed, Riley said. Historical records must be reviewed and various forms of testing need to be done, he added.

‘‘That’s going to take several weeks,” he said. ‘‘Right now no one knows what the fix is.”

Hurricane Agnes in 1972 was the only event that ever produced water levels higher than those on June 27, Riley said. No leakage was reported at the dam during Hurricane Isabel in 2003, he said. The dam was built in 1965.

Agnes showered less than two inches of precipitation in the Rockville area, and Isabel dropped almost 11 inches, according to reports from the National Oceanic and Atmospheric Administration

A dam is designed and built to hold reservoir elevations expected for its area, said Mike Stello, a geotechnical engineer with the U.S. Army Corps of Engineers.

‘‘All dams leak,” he said. ‘‘As long as the leak is controlled, it’s not a problem.”

If future storms cause an increase in reservoir levels similar to last week, Stello said, the Needwood Dam might experience the same seepage conditions.

‘‘The engineers on site have determined that dam is still structurally sound,” said Chuck Gates, spokesman for the Maryland Department of the Environment. ‘‘At this point we’re not concerned with the prospect of other storms.”

The next phase for the county is to study the dam, determine what caused the seepage, and design measures to handle it in the future, Stello said.

At some point toward the middle of last week, several small holes appeared in the Lake Needwood dam and water began to trickle out. Concerned about wave of floodwater breaking through to the Twinbrook and Aspen Hill communities downstream, county officials began evacuating residents.

A convoy of earthmovers carted sandbags and gravel to the damaged area on June 28. Workers covered the trouble spots with the material, trying to add more weight in the hopes it would inhibit additional leakage.

‘‘The good news is that [the leaking water] is clear, meaning it isn’t washing soil away from the dam,” Riley said. ‘‘The bad news is that it’s not decreasing, either.”

The leaks could either have been the result of water running through native rocks along the side of the dam or a channel that developed beneath the dam soil itself, he said.

Evidence of the high water was easy to spot, as an overflow area normally used for parking and other park buildings were flooded with brown water.

Concerned residents should call the county’s emergency help line at 240-777-2600.