Watershed Improvement District

Watershed Management



Overview

What is the Lake Barcroft Watershed? The Lake Barcroft watershed [hyperlink to watershed map] consists of all the land area that drains into the lake. Our watershed includes houses, roads, parking lots, schools, parks, businesses, and other land uses.

Lake Barcroft contains two main tributaries - Holmes Run and Tripps Run - that drain approximately 5,400 and 3,700 acres of land, respectively. During a rainstorm, stormwater runs off the land and into local stormwater systems, streams, and tributaries that feed into the lake.

What is the biggest threat to lake water quality? Fortunately, there is not much industry or agricultural activity that occurs in the Lake Barcroft watershed that contribute pollution to lake tributaries and drainage systems. The biggest threat is urban stormwater runoff.

The quantity and quality of stormwater runoff that drains into our lake is most affected by the land uses and activities that take place in the watershed. For example, water flowing off the Beltway will be quite different than water flowing off forested park land and it will likely contribute more runoff and pollutants.

Since even rain that runs off land in the upper reaches of the watershed may eventually make its way into the lake, it’s important to protect all of our watershed. But watershed protection begins in your back yard.


Sources of Pollution

What are the sources of pollution in our watershed? The Cameron Run Watershed Management Plan (2007) provides a good overview of the pollution sources as well as recommendations for the County to protect and improve the watershed over the next 25 years. The plan notes that the Cameron Run watershed, which includes the Lake Barcroft watershed, has experienced environmental degradation primarily as a result of urban and suburban development and its associated stormwater runoff. The “watershed is characterized by dense development, significantly degraded instream habitat conditions, and substantially degraded biological communities”. Stream bank erosion and instability is widespread.

The amount of stormwater pollution is the result of two primary factors:
  1. Quality
  2. Quantity
Stormwater quality

When stormwater runs off the land, it picks up nutrients and pesticides from lawns; oil, metals, and trash from roads and parking lots; pet waste from parks and yards; and silt and sediment from construction sites and other areas where soil is exposed. The runoff carries all these pollutants into drainage systems, streams, and eventually Lake Barcroft unless some form of treatment is provided to reduce them.

Stormwater quantity

Many hundreds of years ago, the Lake Barcroft watershed was completely covered with trees, grasses, and other natural vegetation. Whenever it rained, the land acted as a sponge soaking up water which infiltrated the soil and recharged groundwater aquifers. As the area has become urbanized over the past decades, hardscape impermeable surfaces such as roads, driveways, roofs, and parking lots have covered and transformed the land. Now when it rains, much of the water can no longer soak into the ground. Instead it runs off. This increased amount of runoff erodes streambanks causing significant increases in sediment and nutrient loads to the lake. Have you ever noticed how chocolate brown the lake is after a storm?

We don’t often think of stormwater quantity as a “pollutant”, but a recent National Research Council Report on Urban Stormwater Management in the United States (2008) recommended that flow and related parameters like impervious cover can serve as proxies for stormwater pollutant loading.

Research has shown a direct relationship between the amount of impervious cover and the health of streams. As impervious cover rises above 10% of the total watershed area, the number and diversity of aquatic species declines. Sensitive species are lost. A second threshold appears to exist at around 25 to 30% impervious cover. As streams begin to exceed this threshold, they essentially become more like conduits or drainage ditches for conveying stormwater flows and less like healthy streams. They can no longer support a diverse stream community. “Pool and riffle structure needed to sustain fish is diminished or eliminated and the substrate can no longer provide habitat for aquatic insects, or spawning areas for fish.” Stream water quality is consistently rated as fair to poor above this threshold.

The percentage of impervious cover in the Upper Holmes Run and the Tripps Run watersheds is currently in the range of 25% to 30%, and this percentage is climbing as neighborhoods infill and roads and businesses expand. For the health of the lake and its tributaries, it’s important to try to reduce the amount of impervious cover in the watershed or to implement stormwater controls to counteract its detrimental effects.


Watershed Restoration

 The Cameron Run Watershed Management Plan (2007) noted that reducing the effects of stormwater runoff created by uncontrolled impervious surface is a critical step to take for restoring the watershed. But how do we do this?

First, watershed restoration begins in your backyard. There are many things that we can do as individual homeowners to protect the lake, including planting trees, creating a rain garden, directing gutter downspouts from impervious areas to pervious areas away from the house foundation, using permeable materials for new or replacing existing driveways and walkways, minimizing fertilizer use, and lots more.

The Lake Barcroft Environmental Quality Committee has developed a Watershed Friendly Garden Certification Program [hyperlink to document] that has a comprehensive list of things you can do at your home and in your yard do to control stormwater runoff and protect water quality.

Did you know that the storm drains on the streets in Lake Barcroft drain into the lake? Many people think that these drains go to a treatment plant, but the water flows untreated into the lake. Therefore never put anything down the storm drains that you don’t want to end up in the lake such as pet waste, leaves, grass clippings, trash, used motor oil, paint, or chemicals. Wash your car at a professional car wash facility or in your yard to keep dirt and soapy water from running into the storm drain.

The watershed area for Lake Barcroft extends far beyond the boundaries of the Lake Barcroft community. In fact our community represents only a small fraction of the watershed as a whole. Thus it is important to take an active role in Fairfax County issues that may affect lake water quality, in particular ensuring that any new development has appropriate stormwater runoff controls, minimizes impervious cover, and maintains the pre-development hydrology to the maximum extent feasible. For existing development, it is important to support the County’s efforts to retrofit stormwater best management practices, low impact development practices, and green infrastructure throughout the watershed.

For more information on stormwater management and watershed restoration approaches, visit:
Fairfax County - Stormwater
Arlington County - Stormwater
Northern Virginia Soil and Water Conservation District