Two 20-inch Sub-Aqueous Water Mains to City Island

The replacement of the 114-year old City Island Bridge, which connects the Bronx with City Island and serves as the sole access point for vehicles, cyclists, and pedestrians, provided an opportunity to implement a new method of design to replace an old, failing, and non-redundant water main located along the deck of the aging bridge.

The team devised an innovative approach for installing the water main by using horizontal directional drilling through hard rock underneath Eastchester Bay. Unique project features include:

• 4000 linear feet of 20-inch primary water main installed via directional drilling
• Used a curve arc in two planes for the directional drilling
• Water mains are 115 feet below the waterline of Eastchester Bay
• Water mains are 75 feet below the mudline of Eastchester Bay

A directional drilled compound curve has never been used before in NYC. With the completion of this project, NYC has the experience with installing water mains by compound curve and the potential for tunneling under waterways throughout the city in extremely tight launch point and landing point conditions in the future.