Environmental Services

Stormwater & Watershed Management

 

What is watershed management? 

A watershed is an area of land that drains to a common body of water.

Watershed management is the effort to protect streams, rivers, lakes, and estuaries by focusing on land activities in the area that drains to a water body.  Watershed management includes land use planning, regulation of development, control of water pollution, stream buffer protection and stream restoration, and outreach and education. These programs consider all sources of pollution in a watershed, including spills and leaks, factories, and stormwater runoff from urban and agricultural areas. In an urban area like Arlington, with very few industrial facilities, stormwater is the main source of pollution to local streams.  

Condition of County Streams

Streams are an important natural and recreational resource in Arlington.  However, development in Arlington has significantly impacted the nearly 30 miles of perennial streams in the County.  Most of the buildings and roads in Arlington County were built prior to regulations requiring stormwater be slowed down or treated, so runoff from these areas flows uncontrolled to County streams. This is one of the key watershed management challenges facing Arlington County and its citizens today. Existing development has much greater impact on streams than new development or redevelopment.

Given the impacts of development on streams described above, it is not surprising that a County wide stream inventory conducted in 1999 that most County streams were in fair condition, with some severely degraded stream reaches. No County streams were evaluated to be in excellent condition. The inventory found 40 locations with active streambank erosion and 70 locations where riparian buffers are in poor condition. Litter is a pervasive problem in streams because storm sewers are very efficient litter delivery systems. There is also evidence of recurring spills and leaks that adversely affect water quality.

What is Stormwater?

An impervious surface do not allow water to soak through. Streets, buildings and driveways are examples of impervious surfaces.

Stormwater is rainfall that does not soak into the ground and instead flows over the land surface to the nearest water body. In urban areas like Arlington, much of the land is covered by impervious surfaces such as streets, buildings, parking lots, and driveways. Rainwater is unable to soak into the ground and and instead runs off of the street into the County's extensive storm drain network of pipes. This network of pipes releases the water, untreated, into our local streams.

Most buildings and roads in Arlington County were built before environmental laws addressing stormwater quality and quantity (such as Chesapeake Bay Preservation Ordinance and the Stormwater Detention Ordinance) took effect.  Therefore, most stormwater in Arlington County is not controlled or treated before it flows into local streams. Existing development has much greater impact on streams than new development or redevelopment - this is one of the key environmental challenges facing Arlington County and its citizens today. However, through the County's green building programs, some Sustainable Stormwater Management techniques have been installed around the County.

Stormwater Management Challenges

Stormwater management describes programs to control stormwater runoff for the purposes of reducing downstream erosion, water quality degradation, flooding, and mitigating the adverse effects of changes in land use on the aquatic environment.   The County's Stormwater Management program seeks to to balance the following goals: 

  • Reduce the potential for stormwater threats to public health, safety, and property; 
  • Reduce the impacts of new and existing urban development on Arlington streams, the Potomac River and the Chesapeake Bay; and, 
  • Comply with State and Federal stormwater, water quality, and floodplain management regulations.

Much of Arlington's stormwater drainage network was built between 1930 and 1955 and is not adequate to balance the program's three goals.  Some of the challenges include:

• Historical Drainage Decisions.  As described above, most of the County was developed before modern stormwater and floodplain management regulations. As a result, most of the stormwater runoff in the County is not controlled to reduce volume or remove pollutants before it is discharged to local streams through the storm sewer network. In addition, in certain parts of the County, private properties and homes were built very close to streams, resulting in frequent flooding and property damage as well as channelization of streams to reduce flood risks.

• Aging Infrastructure.  More than 60 percent of the County’s 360 mile underground pipe network is over 50 years old. Concrete pipes, which comprise the majority of the system, typically last between 50 and 75 years.

• System Capacity. Like much of the mid-Atlantic region, the County’s existing stormwater drainage network was designed to handle a “10-year storm event,” meaning a storm with a 10 percent chance of occurring in any year. Larger storm events – such as the June 2006 flood, which generated flows equivalent to a 50-100 year storm event – can overwhelm the system’s capacity causing substantial property damage as excess stormwater runoff flows overland.

• New state and federal regulations to reduce pollution discharged through municipal stormwater systems into the Chesapeake Bay are putting upward cost pressures on local jurisdictions.

• Climate change.  Climate models predict that the frequency of heavy rainfall events will increase sharply as global temperatures continue rising, a trend that will highlight the existing system’s obsolescence.

Stormwater Management Strategy

The County’s stormwater management program seeks to control stormwater runoff for the purposes of reducing stream erosion, protecting water quality, reducing risks from flooding, and mitigating the adverse effects of changes in land use on the aquatic environment.   Both near term and long-term efforts must be implemented concurrently, given the legacy land use decisions that significantly constrain what can be achieved in the landscape.  

The following actions comprise the central elements of the County’s stormwater management strategy:

  • Reduce risks to public/private property from flooding
  • Maintain and replace stormwater infrastructure
  • Restore stream corridors and other water quality improvement projects
  • Add stormwater treatment facilities, such as Green Streets, to areas that currently do not have stormwater treatment
  • Require on-site stormwater controls for new development
  • Implement urban housekeeping best practices
    • Street sweeping
    • Catch basin cleaning
  • Public outreach, education, and volunteer monitoring programs

Stormwater Funding

The County Board approved a sanitary district tax in 2008 to fund stormwater system improvements.  The average Arlington homeowner pays roughly $54 in stormwater taxes per year. Between 2009 - 2014, the estimated funding level for the expanded stormwater program is $5.3 million per year, of which roughly $3 million per year goes for capital projects.  According to the proposed CIP for FY 2011 - FY 2016, the County will invest approximately $23.8 million in capital projects over this period, including approximately $5.2 million of federal cost share funding, for a net cost of $18.6 million.

This funding will pay for increased stormwater facility inspections, storm sewer system inventory and mapping, engineering plan review regulatory compliance, and a comprehensive update to the County’s Storm Water Master Plan. Capital funding will address system capacity improvements in critical locations, storm sewer maintenance and replacement, stream restoration projects, stormwater treatment retrofits to improve water quality in County streams, and initial implementation of the Four Mile Run Restoration Master Plan.

Read the Stormwater Program and Financing Action Plan that led up to this expanded stormwater program. 


Last Modified: December 04, 2013
2100 Clarendon Blvd. Arlington, VA 22201 Tel: 703-228-3000 TTY: 703-228-4611