City Island is a little island off the coast of the Bronx in New York City. The shorefront area has a rich nautical history and is a recreational community with beaches, boating, fishing, and more than 30 restaurants. It’s a small island restricted by the fact that there’s only one land transportation access on and off the island.

The aging water main served as the sole water supply to the island and was a risk to businesses, residents, and vacation goers due to a lack of adequate capacity and resilience. Our team devised an innovative approach for installing the water main by using horizontal directional drilling (HDD) through hard rock underneath Eastchester Bay, which included:

• directional drilling the water main in a curved arc in two planes
• 4,000 linear feet of 20-inch primary water main installed by directional drilling
• 115 feet below the water waterline of Eastchester Bay
• 75 feet below the mudline of Eastchester Bay

The project came about as a result of the much-anticipated replacement of the City Island Bridge—the only bridge that connects City Island with the Bronx. The bridge opened on July 4, 1901, and served as a major access point for vehicles, cyclists, and pedestrians. A temporary bridge was erected in 2015.

Social, Economic, and Sustainable Development Considerations

The existing water main was failing and placing a watermain on the new bridge would be unattractive for visitors entering this scenic shore front area. The new directionally drilled dual water mains did not disturb the island’s water service and provided additional capacity and redundancy. The methods designed also minimized the disturbance of the natural waterway and the surrounding ecosystem.

Improved Water Capacity and Infrastructure Resilience

In conjunction with the New York City (NYC) Department of Design and Construction (DDC) and NYC Department of Environmental Protection (DEP), we increased the size of the main, resulting in greater potential waterflow.

The tight space requirements were addressed by drilling a compound curve for the new water main alignment to feed the island. Two redundant 20-inch water mains were horizontally directionally drilled. If one watermain breaks, the city has a second supply source, which helps with resilience for the island.

The new directionally drilled dual water mains did not disturb the island’s water service and provided additional capacity and redundancy. The methods designed also minimized the disturbance of the natural waterway and the surrounding ecosystem." Patrick Ronan and Emilio Barcelona

Challenges and Opportunities

The biggest challenges associated with this project included interconnection with existing water pipes, avoiding interference with utilities, deep water borings and bathymetric surveys, selecting staging areas with minimum wetland impacts, and installing the sub-aqueous water mains using trenchless technology.

Directional drilled compound curve is a method that has not been used before in New York City for watermains. This project demonstrates that there is potential for tunneling under waterways throughout the city in extremely tight launch and landing point conditions in the future.

We received an American Council of Engineering Companies (ACEC) New York Engineering Excellence Diamond Award for project design and innovation. The use of the compound curve minimized impacts and hit the targets needed to reach the project’s goals.