Have you ever seen yellow links of boom surrounding work areas within the Potomac River or in the various streams within our Project? Some passer-bys assume it is absorbent material commonly used to surround and remove oil spills, as seen occasionally on the nightly news. We do have plenty of absorbent boom on hand in case of a fuel or oil spill, but the yellow boom typically seen on our site is actually called a turbidity barrier or floating turbidity curtain.

Figure 1. Floating Turbidity Curtain

The turbidity barrier is designed to restrict the flow of silt-laden runoff from a disturbed area, to keep it contained to a confined area, and to allow the silt and sediment to settle before being carried into the adjacent watercourses. The Project has used turbidity barriers for various applications in the Potomac River , Cameron Run, Hoofs Run, Smoots Cove, and Oxon Cove, as well as various wetland creation and stream restoration mitigation sites in the region.

Typically, land disturbance is contained by silt fence or reinforced super silt fence (pictured below), which traps and treats the silt-laden water before leaving the disturbed area. Turbidity barriers are similar in concept to silt fence and work effectively where silt fence is impractical or impossible to install.

Figure 2. Super Silt Fence

What you can see on the surface is only one component of this ingenious system utilized to protect the environment. The yellow boom is filled with foam and is the flotation component. It is typically yellow but can also be black or even orange to increase visibility for boater safety. Suspended from the flotation boom is a vertical canvas that hangs to the bottom of the river or stream. This forms the "curtain" component and actually retains the sediment-laden water for settlement of silt to the stream bottom. As water depths vary from area to area, turbidity barriers must be custom made or adjusted to fit a given application. Lengths also vary from task to task. We have 100 feet of curtain across Hoofs Run to extend an existing box culvert under I-95 (see photo below) but have used several hundred feet along the Jones Point Park shoreline to construct the new bulkhead (see Figure 4).

Figure 3. Picture of Hooffs Run curtain

The length of the curtain is easily modified by adding or removing sections of curtain. Each boom "link" represents a section of curtain. It is also important to firmly secure the endpoints to a fixed and sturdy object as the force of flowing water can be enormous.

Figure 4. Picture of Jones Point Park curtain

The pictures above illustrate ideal usages of turbidity barriers for work along streams and rivers including box culvert extensions, pipe installation, grading along the shoreline, bulkhead or revetment construction, utility work, and other disturbances alongside of waterways. Another ideal use is within large bodies of water. We use turbidity barriers within the Potomac to protect the river environment from turbidity associated with pile pulling, for example, during sensitive times of the year for fish and underwater grasses.

Figure 5. Pile pulling and floating turbidity curtain
for a foundation in the Potomac River

Through careful research we have found that pressure waves associated with driving larger piles to support bridges over waterways may have the potential to harm fish, so we have developed methods to test pressure waves and implement proactive measures to ensure the protection of fish. One method is to use turbidity curtains as a "fish fence" to keep fish from swimming through areas near pile driving which may be harmful to fish.

Figure 6. Floating turbidity curtain associated with pile driving in Cameron Run

Though originally thought by some to be questionable due to strong currents and tidal cycles, the use of turbidity curtains across the Woodrow Wilson Bridge Project has proven to be an effective and versatile tool to minimize environmental impact in constructing one of the largest transportation projects in the nation surrounded by sensitive environmental resources.

A portion of this information has been provided the WWB Project Environmental Team. The balance of the information has been provided by Aer-Flo Canvas Products, Inc. http://www.aerflo.com .