Time of Year Restrictions Print E-mail

Summary of Time of Year Restrictions

Time-of-year-restrictions (TOYRs) are followed on the Woodrow Wilson Bridge Project (Project) to ensure that natural resources and inhabitant species are protected from construction activities with potential environmental impacts. TOYRs for this Project are established by regulatory agencies such as the Army Corps of Engineers (ACOE), the Virginia Department of Environmental Quality (VDEQ), and the Maryland Department of the Environment (MDE). Note that the following Time of Year restrictions were established by the regulatory agencies specifically for this Project and that the restrictions may be different in other jurisdictions and for other projects.

Activities governed by TOYRs include:

Dredging

Dredging is prohibited by the ACOE, MDE and VDEQ between February 15 and October 15 of every year unless conducted within a cofferdam, in order to protect fishery resources and submerged aquatic vegetation (SAV).

Dredging activities were conducted on the Potomac River from October 19, 2000 to February 2, 2001 for the Dredging Contract (BR-1). Dredging was conducted to provide access for barges across shallow portions of the Potomac to facilitate construction of the foundations of the new Woodrow Wilson Bridge. Additional dredging was completed within the allotted dredging window in 2002, 2003, and 2004 to gain additional access and to reopen the construction channel after it was partially filled with silt by Tropical Storm Isabel in 2003.


Figure 1. Dredging activities were conducted using the “clamshell method” as pictured.

Dredging was conducted mechanically and with caution to minimize disturbance of the river bottom or turbidity increases in the water, which tend to degrade water quality and damage aquatic life. Hydraulic dredging (similar to dredging with a large vacuum cleaner) was prohibited on the Project due to the increased potential to injure fish and other species.

Pile Driving

Large bridges require many piles for support. Aside from the new Woodrow Wilson Bridge, the Project is constructing over 50 bridges in total, most over water or wetlands. Pile driving is authorized year-round but larger piles require the use of techniques to reduce pressure waves emitted into the surrounding water body as the hammer strikes the pile. The Project has done extensive research to determine that pressure waves can injure fish and, even more importantly, that these effects can be minimized, if not eliminated. The ACOE requires these methods be implemented from February 15 through June 15 of each year but the Project requires their contractors to use these protective methods year-round in a proactive effort to protect the environment.

The methods include air bubble curtains surrounding the pile to absorb the pressure wave (pictured below) and “fish fence” erected at a required radius around piles during driving to keep fish away from potentially harmful pressure waves.

In-water pile driving activities have been performed extensively throughout the Project, particularly as part of the Foundations Contract (BR-2) which drove over 1000 piles as long as 210 feet from May 2001 through June 2003, and as part of the US Route 1 Advanced Bridge Contract (VA-5), from June 2003 to August 2005.


Figure 2. Pile driving activities conducted on the US Route 1 Advanced Bridge Contract (VA-5) in January of 2005. Note use of Bubble Curtain.

Hydraulic Jetting

The ACOE and MDE prohibit the hydraulic jetting of piles between February 15 and October 15, unless conducted within a cofferdam, in order to protect fishery resources and submerged aquatic vegetation (SAV). Jetting is a method to either drive or remove piles from the river bottom and includes displacing bottom material with high-pressure air or water jets.

Only minor hydraulic jetting activities have been conducted on this Project to date to remove debris from the river bottom to make way for the new bridge. These activities have been performed within the TOYR.

Temporary Causeways

Stone causeways are temporary driveways built across sensitive areas such as wetlands, streams, and mudflats to provide access to the construction of permanent bridges. Once the bridge is complete, the causeway is removed and the area is returned to the original condition. Construction of temporary causeways is prohibited from February 15 through June 15 by the ACOE to protect the many species living in these sensitive areas.

Construction of temporary causeways has been conducted on the US Route 1 Advanced Bridge Contract (VA-5) within the specified Time-of-Year restrictions, as pictured below.

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Figure 3. Temporary causeways (stone structures) in use on the US Route 1 Advanced Bridge Contract in April of 2004 to facilitate bridge construction over Cameron Run in Virginia.

Underwater Explosive Demolition

Once the new Wilson Bridge is built the old bridge will need to be removed. This may include explosive demolition, which has the potential to effect the underwater environment without the proper techniques. According to ACOE, MDE, and VDEQ TOYRs, underwater blasting is permitted without restrictions between September 16 and February 14 of any year.

All underwater blasting is prohibited from February 15 through July 1. After July 1 and until September 16, underwater blasting is allowed subject to restrictions depending on water depth (deeper water may include sensitive fish and other species). The conditions mainly include “blast design” techniques to ensure the most efficient detonations possible. The optimal scenario is to use only enough explosive to fracture and collapse the intended structure while minimizing energy released to the surrounding water body, which could affect fish and other species. This is accomplished by using the appropriate amount of explosive, by setting maximum pressure thresholds, by requiring the holes drilled to contain explosives be capped, and by requiring multiple small charges be detonated in close frequency as opposed to one large charge. Other techniques will be required including detonation of small “scare charges” to purge fish from the area before setting off the actual demolition charge.

This activity may be conducted in the future as part of the currently active bridge contracts, Bascule, Virginia Approach and Maryland Approach (BR-3A, BR-3B & BR3-C respectively).

Removal of Rubble

Removal of rubble resulting from the demolition of the existing bridge from Waters of the U.S. is prohibited between February 15 and July 1 according to the ACOE, MDE, and VDEQ. This is to avoid turbidity impacts to spawning fish. Rubble removal at other times is subject to additional restrictions.

This activity will be conducted in the future as part of the currently active bridge contracts, Bascule, Virginia Approach and Maryland Approach (BR-3A, BR-3B & BR3-C) respectively.