Four Mile Run


Four Mile Run flows through residential areas as well as urban corridors in south and western Arlington.

Drainage Area

Four Mile Run is the largest stream flowing through Arlington, draining approximately two-thirds of the County.

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Drainage area of the Barcroft monitoring site. This area also encompasses the other Four Mile Run monitoring sites of Banneker, Bluemont and Glencarlyn.

Rapid Stream Assessment Technique Scale: Fair

In 2011, we assessed all the streams in the County as part of the Stormwater Master Plan Update. The assessment used the Channel Evolution Model to evaluate which sections of the streams are actively eroding to prioritize them for stream restoration. During that assessment, about 10 percent of the upper reaches of Four Mile Run were found to be in actively eroding condition, while many areas of the stream were beginning to naturally stabilize or had been artificially stabilized. In the lower reaches, more than 25 percent were in stable condition, about 20 percent were naturally stabilizing and about 6 percent were actively eroding.

About Four Mile Run

A study by the Northern Virginia Regional Commission (NVRC) examined the sources of the bacteria, showing the major sources of identifiable bacteria were urban wildlife (waterfowl and raccoons), humans and dogs. A Total Maximum Daily Load (TMDL) has been created for Four Mile Run, and a management strategy for controlling anthropogenic sources of bacteria to the stream has been created. The NVRC has more information about the Four Mile Run TMDL.

Watershed retrofit studies for Four Mile Run have also been completed.

Macroinvertebrate Monitoring Data

Since 2001, there have been two monitoring sites located on Four Mile Run.

  • Bluemont Park, south of Wilson Boulevard.
  • Banneker Park, slightly downstream of the Arlington County and City of Falls Church line.

Barcroft Park, located in south Arlington, was added and monitored for a short time in 2005. The site was reinstated in 2009 with new volunteer support.

Macroinvertebrates commonly found are:

  • Damselflies
  • Flatworms
  • Midges
  • Net-spinning caddisflies
  • Small minnow mayflies

In fall 2011 and spring 2012, we contracted a professional monitoring group to collect family/genus-level macroinvertebrate and fish data at each of our volunteer monitoring sites.

Click on one the graphs above for an enlarged version. 

Bacteria Monitoring Data

There are 10 sites on Four Mile Run that volunteers monitor for bacteria. Learn more about bacteria monitoring data.