Four Mile Run Dredge Project


3100 S. Glebe road,  22206  View Map

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As of March 1, 2023, the in-stream work (dredging and repair of stone structures along the channel) is complete.  Site restoration at Long Branch is mostly complete, although there will be some additional seeding in the park area in March.  Site restoration along Four Mile Run will take place in March (tree planting, seeding, trail re-paving).  

There will be additional replacement tree planting for trees that were too close to the floodwalls and were required to be removed.  The replacement tree planting plan and schedule will be available soon.

About the Project

The Four Mile Run Dredge Project consists of removing soil, rocks and vegetation from the open channel of Four Mile Run and Long Branch tributaries to maintain the capacity of the flood channel, which helps to reduce flood risk in neighborhoods near Long Branch and lower Four Mile Run.  The project also includes some channel infrastructure repairs and maintenance, including removal of some trees near the floodwalls.   Replacement trees will be planted in nearby suitable locations.

Four Mile Run is a nine-mile long stream with a 19.6 square mile highly urbanized watershed, including portions of Arlington and Fairfax Counties and the Cities of Alexandria and Falls Church. The lower portion from I-395 downstream to National Airport is within a hardened flood-control channel that marks a shared boundary between Arlington County and the City of Alexandria. This stretch of Four Mile Run has neighborhoods and businesses that were subjected to repeated flooding beginning in the 1940s.

In response to this flooding, Arlington County and the City of Alexandria worked with the U.S. Army Corps of Engineers (USACE) to design and build a flood-control channel in the lower portion of Four Mile Run. The Four Mile Run East and West Levee System is a USACE federally authorized and constructed flood risk management project that was first authorized in 1970, modified in 1971, and reauthorized in 1974.  The project was constructed between 1974 and 1984. Required maintenance of the flood channel includes clearing of soil, rocks, vegetation growth, and stabilizing some areas of the bank as required by the USACE annual inspection program.

The channel maintenance that will be completed during the Four Mile Run Dredge Project includes:

  • Dredging, or removing soil deposits, to preserve the capacity of the channel to convey a 100 year storm,
  • Repairing erosion damage
  • Fixing stream corridor degradation 
  • Clearing debris, trees, vegetation, and shoaling
  • Maintaining storm sewer infrastructure on the banks of the project

The channel maintenance project will include planting of replacement trees for trees that were too close to floodwalls and were required to be removed.  The replacement tree planting plan will be available soon.

Public Engagement

The project falls is a Communicate level of engagement, because it addresses maintenance of the Four Mile Run streambed that is required by the Army Corps of Engineers, will help reduce flood risk along the Long Branch Tributary and will not significantly change any facilities, program or services provided to the community. The project will disrupt access and parking to a small portion of Troy Park, but that work will be completed within a month. 

Date      Activity      Materials     
 March 24, 2021   County Board approved MOA with Alexandria   
 December 2, 2021  Presentation to Four Mile Run Joint Task Force  Presentation 
 March 19, 2022    County Board approved construction contract      
 May 17, 2022, 7 PM 

 Community Meeting 

 Presentation(PDF, 7MB)

 Meeting Video