Dredging Laid Groundwork for New York’s New Tappan Zee Bridge

By Marsha Cohen
Four years and almost $4 billion later the first span of the new Tappan Zee Bridge opened at 1:36 a.m. on Saturday morning August 26 when four lanes of the bridge heading westward opened up to traffic. The bridge officially named the Governor Mario M. Cuomo Bridge after the former three-term governor of New York State is the first major bridge to be built in the New York City area since 1964. 
The builders of the bridge Tappan Zee Constructors LLC – a consortium of Fluor Enterprises Inc. American Bridge Company Granite Construction Northeast Inc. and Traylor Bros. Inc. with design firms HDR Buckland & Taylor URS and GZA– were responsible for the design and construction of the 3.1-mile expanse that goes from two heavily populated suburbs of New York City Westchester and Rockland counties at one of the widest parts of the Hudson River. 
Dredging operations which took place in phases starting in 2013 laid the groundwork for the construction of the new bridge and the eventual demolition of the old one scheduled for next year. In total almost one million cubic yards of dredged material were removed from 139 acres of the Hudson River riverbed for the construction of the new bridge and 107 acres of dredged riverbed were armored with sand and stone up to 2 feet in depth to ensure sediment is not stirred up by vessels navigating in the Hudson. Temporary fixed platforms and trestles were constructed as well as permanent fixed platforms supported by steel piles and in‐water pile‐supported piers and the installation of 150 linear feet of steel sheet pile bulkhead. Although Weeks Marine was not part of the team that won the Design-Build construction contract to replace the bridge it won a separate contract to do the dredging work associated with the project.
In accordance with the New York State Department of Conservation permits dredging operations each year were confined to a narrow environmental window that commenced in early August and ended not later than October 31 each year. To keep within this tight timeframe demanded that dredging crews work 24 hours a day seven days a week thus ensuring that dredging would avoid the main season for spawning and fish migration particularly for the Atlantic and shortnose sturgeon which are endangered species. Throughout the project intensive water quality monitoring and sturgeon monitoring were conducted and regularly reported and dredging was adjusted as necessary to comply with regulations.
In 2013 during the first three-month phase dredging crews started operations from the main navigation channel end of the dredging footprint toward the shoreline on both the Rockland and Westchester County sides of the bridge. They deepened the river’s shallow water level in the work zones by removing sediment from the river bottom. The dredged materials were then processed and properly disposed of at offsite locations. Abiding by the environmental window stipulations dredging operations stopped in late October and resumed again in 2014 from August 1 to November 1. 

I Lift NY super crane arrived at the bridge in October 2014 and was ready for its first lift in April 2015. (Photo
courtesy of the New York State Thruway Authority.)

In particular the dredges removed some 188000 cubic yards of sand and silt south of the original bridge to create an access channel for a super-sized crane known as the “I Lift NY” crane. The crane needed to work nearshore in an area that is only 6 to 8 feet deep at low tide. The operations of the “I Lift NY” super crane with a 328-foot boom included placing the new bridge’s pile caps girders and deck segments and was a crucial piece of equipment in meeting the heavy-lifting necessary throughout the project. At a later date it will dismantle the old bridge. Weeks Marine Inc. (WMI) as subcontractor to Tappan Zee Constructors performed these dredging activities using WMI 506 and WMI 549 dredges and purpose-built environmental clamshell buckets to perform the work. The buckets release less sediment into the river than conventional equipment which further protects local aquatic life. 

The super crane which traveled 6000 miles from the West Coast through the Panama Canal reached the bridge location in October 2014. At the end of April 2015 the super crane lifted its first load – a 600-ton concrete segment of the bridge’s foundation. This was the start of the work the “I Lift NY” crane did throughout construction works. In summer 2015 dredging operations commenced on August 1 and ended on September 17 – a month earlier than planned. Again dredging activities occurred 24/7.  
As of now the completion of the new bridge is in sight: The westbound span is open to traffic and the eastbound lanes are scheduled to be ready for traffic in the spring of 2018.  

Dredging an access channel for the I Lift NY super crane was an essential element in the construction of the
bridge and went on 24/7. (Photo courtesy of the New York State Thruway Authority.)