USACE Proposes Maintenance Dredging of Federal Navigation Channel Near Chelsea Street Bridge (USA)

The U.S. Army Corps of Engineers, New England District is proposing to perform maintenance dredging of the Federal navigation channel in the vicinity of the Chelsea Street Bridge in Boston and Chelsea, Mass.

The replacement of the existing Chelsea Street Bridge with a new vertical lift bridge by others will allow the Corps to modify the existing Federal navigation channel in the vicinity of the bridge. The Chelsea River navigation channel was authorized to a width of 225 feet by the River and Harbor Act of 1962, but because of the restrictions caused by the Chelsea Street Bridge, the channel was never widened to its authorized width.

“The project area is located approximately 125 feet downstream of the bridge to approximately 350 feet upstream of the bridge,” said Project Manager Mike Keegan, of the Corps’ New England District, Programs/Project Management Division. “There are two alternatives currently under consideration to widen the channel. Both alternatives are located in disturbed areas where previous vehicular or railroad bridges, and utilities were constructed.”

The first alternative would create a minimum 140-foot-wide channel in the vicinity of the new Chelsea Street Bridge. The second alternative is the creation of a minimum 175-foot-wide channel. The 175-foot-wide channel alignment is dependent on bulkhead modifications that must be designed and implemented by non-Federal interests. These bulkhead modifications must be completed before the navigation channel can be widened to 175 feet. Both alternatives would widen the channel to the channel depth of -38 feet Mean Lower Low Water (MLLW) which was authorized in the Water Resources Development Act of 1990.

Fuel tankers transiting the existing Chelsea River have less than six feet of clearance between the existing Chelsea Street bascule bridge fenders. The new vertical lift bridge that is currently under construction will eliminate any constriction of the navigation channel. The purpose of this Federal navigation project is to widen the navigation channel in the area of the Chelsea Street Bridge quickly after the new bridge is finished.

Widening the channel will potentially allow a larger class of vessels to safely enter the oil terminals upstream of the bridge which could increase the volume and reduce the transportation cost of home heating oil and various other commodities available in Massachusetts.

The project is also needed to reduce potentially hazardous navigation conditions. Dredging is expected to begin as soon as possible after completion of the new bridge, sometime in the beginning of 2012.

Approximately 34,700 cubic yards of material, which includes two feet of overdepth dredging, would be removed by mechanical means to widen the channel to 140 feet. Of this amount, approximately 5,100 cubic yards of surface material is unsuitable for ocean placement and will need to be placed into the existing Confined Aquatic Disposal (CAD) cell C12 constructed during the deepening of the Boston Harbor Navigation Improvement Project. This cell is located at the upper end of the navigation channel in the Chelsea River.

The remaining 29,600 cubic yards of material will be placed in the U.S. Environmental Protection Agency-designated Massachusetts Bay Disposal Site (MBDS) located 20 miles offshore. This active disposal site is and has been used for the placement of dredged material that has passed chemical and biological testing.

All of the dredged material will be placed in a split hull scow for transportation to either the CAD cell or the MBDS for placement. Approximately 53,000 cubic yards of material, including two feet of overdepth dredging, would need to be removed by mechanical means to widen the existing navigation channel in the Chelsea River to 175 feet. Off this amount, approximately 7,100 cubic yards is unsuitable for ocean disposal and would be disposed into CAD cell C12. The remaining 45,900 cubic yards of suitable material would be disposed at the MBDS. Dredging and disposal activities would take approximately 30 days to accomplish.

A portion of the Chelsea River located just below the Chelsea Street Bridge and through the existing bridge opening was last dredged in 2008 from a depth of –35 feet to –38 feet MLLW. The rest of the river was previously dredged between 1999 and 2000.

An Environmental Assessment for this work is being prepared. To protect the endangered right whale, whale observers will be on board the scows transiting to the MBDS from Feb. 1 to May 31 to avoid potential ship strikes. No other endangered species or their critical habitat designated as endangered or threatened pursuant to the Endangered Species Act are expected to be effected by the proposed project. The Corps is assessing the effects that the proposed project is likely to have on Essential Fish Habitat and has made a preliminary determination that there will be no significant impacts on the designated fisheries resources. Full determination will be made upon completion of the Essential Fish Habitat assessment.

The proposed work is being coordinated with the following Federal, state and local agencies: U.S. Fish and Wildlife Service, U.S. Environmental Protection Agency, the National Marine Fisheries Service, the Massachusetts Department of Environmental Protection, the Massachusetts Executive Office of Energy and Environmental Affairs, the Massachusetts Department of Marine Fisheries, the Massachusetts Division of Fisheries and Wildlife, the Massachusetts State Historic Preservation Office, the city of Chelsea Conservation Commission, and the city of Boston Conservation Commission.

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Source: usace, June 2, 2011;