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Peter’s Take: What Arlington Should Do to Prepare For More Flooding

Peter’s Take is a weekly opinion column. The views and opinions expressed in this column are those of the author and do not necessarily reflect the views of

Last week, reported on a flood warning from Arlington’s Department of Environmental Services (DES).

A DES stormwater outreach specialist alerted Arlington residents how stormwater runoff can harm County waterways:

  • Erosion: High water volume erodes stream banks, compromising trails and trees along our stream-valley parks
  • Pollutants: Stormwater washes pollutants like nutrients (nitrogen and phosphorus), sediment, bacteria, pet waste and trash into our streams, causing poor water quality
  • Temperature: During the summer months, stormwater heats up as it flows over hot pavement, which then increases the temperature of the stream water by as much as 10 degrees Fahrenheit, causing stress or death to aquatic organisms

Last week’s story linked to a County website containing useful recommendations to help Arlington residents prepare for more storms and flooding.

Arlington County government needs to follow its own advice.

Arlington talks the talk about global climate change, but fails to walk the walk locally

Arlington County government has passed a climate change resolution criticizing President Trump for withdrawing the United States from the Paris Climate Change Agreement:

“Arlington County supports the principles of the Paris Agreement and will continue to stand with cities, counties and other public and private sector partners throughout the world to advance action in accordance with the goals outlined in the Paris Agreement.”

But having fired this rhetorical salvo, County government has failed to follow it up locally–choosing not to exercise its municipal powers to take corrective actions that would reduce growing environmental threats in Arlington:

Slow the dramatic increase in impervious surfaces

Arlington’s Flood Frequency Analysis for Four Mile Run at USGS Gaging Station 1652500 has not been updated since 2004. But even 15 years ago, this analysis concluded (at p. 17):

“[H]ow urbanized a watershed is or how developed a watershed is can be characterized by the degree of imperviousness found in the watershed…. [A] more urbanized watershed will have a greater percentage of area covered by impervious structures, i.e., roadways, rooftops, sidewalks, parking lots, etc. The effects of these impervious areas create higher peak flows and lower base flows in the watershed tributaries. These effects are most evident in the higher frequency rain/flood events….”

Flooding is exacerbated by the conversion of previously permeable surfaces into impervious and semi-pervious surfaces. Last year, Arlington County staff reported that 45% of Arlington is now covered by impervious surfaces.

From 2001 to around 2014 (a 13-year period), Arlington increased impervious surfaces by 2%. From 2014 to 2018, Arlington increased impervious surfaces by 3% in just 4 short years.

Arlington’s development activity is now adding nearly 9 acres of impervious surface area per year–adding the equivalent of the Pentagon’s footprint (roughly 29 acres) every 3 to 4 years.

Move more aggressively to protect our mature tree canopy

Mature trees provide significant stormwater volume- and rate-control benefits through soil storage, interception, and evapotranspiration. A tree with a 25-foot diameter canopy and its associated soil can manage 1-inch of rainfall flowing from 2,400 square feet of impervious surface.

Interception and evapotranspiration also decrease runoff volume, with larger trees providing exponentially greater benefit than smaller trees. See more details here and here.

Update Arlington’s Stormwater Master Plan

Arlington’s 2014 Stormwater Master Plan must be updated and refocused to address these threats:

  • Global climate change
  • Rapid local overdevelopment

Severe rainstorms are now much more common. To adapt, Arlington should enact a plan similar to Westchester County’s (NY) Flooding and Land Use Planning guide. See more details here.


In a recent press release, County government proclaimed, “Every day is Earth Day in Arlington.” It also stated that “few communities can boast Arlington’s ceaseless commitment to sustainability.” Sadly, “Every day is New Pavement Day in Arlington” is a rival slogan with too many County government adherents.

Arlington County government must now take action:

  • Slow the rate of increase in impervious surfaces
  • Preserve and increase our mature tree canopy
  • Reduce and better control stormwater runoff

Peter Rousselot previously served as Chair of the Fiscal Affairs Advisory Commission (FAAC) to the Arlington County Board and as Co-Chair of the Advisory Council on Instruction (ACI) to the Arlington School Board. He is also a former Chair of the Arlington County Democratic Committee (ACDC) and a former member of the Central Committee of the Democratic Party of Virginia (DPVA). He currently serves as a board member of the Together Virginia PAC-a political action committee dedicated to identifying, helping and advising Democratic candidates in rural Virginia.

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