Lake Accotink is being drained while the dam is being evaluated

Part of the lakebed at Lake Accotink is exposed, as the water level is being lowered to facilitate a study of the dam structure.

The lake drawdown is expected to lower the water level by as much as five feet. The Park Authority urges residents to keep off the lakebed to avoid getting stuck in the mud.

The dam study is aimed at determining whether the structure is safe and strong enough to continue supporting the lake. The evaluation of the dam is expected to be completed by Thanksgiving, but water levels may to take up to two months to return to their normal levels depending on precipitation.

Because the dam is owned by the Fairfax County Park Authority, they are leading the assessment of the dam with support from the Department of Public Works and Environmental Services.

Currently, the water level has drawn down approximately 2 feet with the removal of a large amount of debris along the top of the dam, said Park Authority spokesperson Ben Boxer. This is about halfway to the target water level necessary to complete the total assessment of the dam. 

The next step is opening the sluice gates that control the flow of water from the lake into the creek below the dam. When those gates open, the Park Authority will monitor the water flow to ensure there are no negative downstream impacts on Accotink Creek.

The dam study is one of three efforts initiated by the Board of Supervisors last winter to determine whether the preservation of a smaller lake – 20 to 40 acres – is feasible.

In February 2023, DPWES determined that continual dredging to maintain Lake Accotink at its current size would be too expensive and too disruptive to adjacent communities.  

The Board of Supervisors in late 2023 created the Task Force on the Future of Lake Accotink to explore alternative options. The task force suggested that a smaller lake would “present significant environmental benefits” and “meet significant community and social goals.” 

Another effort underway is the Smaller Lake Accotink Preservation Feasibility Study.

That study is expected to identify what actions might be feasible to maintain a smaller lake 20 to 40 acres and 4 to 8 feet deep in a sustainable, equitable, and cost-effective manner.

Residents are encouraged to take a survey on the draft scope of work for that study which was developed by DPWES and Wetland Studies and Solutions Inc. The survey is open through Oct. 30.

The feasibility study will consider the best options for maintaining a smaller lake, including maintenance dredging intervals, which areas of the lake should be transformed into managed wetlands or islands, and where the dredged materials should be deposited.

Related story: Lake Accotink task force presents its findings to the BoS

Another study underway is a sedimentation analysis by the U.S. Geological Survey. That study is looking at how much sediment is coming into the lake from Accotink Creek and how much is flowing downstream from the lake.

The USGS collected sediment samples from Long Branch and Accotink Creek, conducted pebble counts, began processing data, and initiated reviews of existing data and hydraulic modeling.

They also installed a stream gage and water quality monitoring station on Accotink Creek at Old Keene Mill Road.