Challenging Dredge Operation Over Active Utilities In New York Harbor

Abstract

Channel deepening is occurring at ports throughout the United States (US) due to the ever-increasing size of vessels calling at these ports. Specifically, completion of the new Panama Canal has resulted in a wave of dredging projects along the east coast of the US, where ports are racing to complete their capital projects to capture the additional trade volumes expected from the larger ships capable of passing through the new Panama Canal. In addition to impacts on existing port structures due to berth deepening, water mains, electric lines, gas and fuel lines in subsea utility corridors crossing navigation channels where dredging is performed may result in major challenges when these utilities are active and in close proximity to the dredged mudline. To add to the complexity, most of these utilities were generally constructed long ago when subsea construction controls were less accurate and as-built conditions were not recorded with high precision.

This paper discusses the navigation channel deepening operations undertaken over the active utility corridors crossing the main navigation channel in New York Harbor. Prior to the deepening project, the limiting water depth at the New York Harbor navigation channel was 13.7 meters (45 feet), severely constricting the new generation of container ships, which requires a minimum of 15.2 meters (50 feet) navigable water depth. The main challenges encountered during the dredging project were precisely locating the utilities in the channel, both their horizontal and vertical coordinates; locating the dredging plant and the dredge bucket in the channel where currents are strong; and cutting hard native material while using a special flat dredge bucket to minimize the risk of damage to the utilities. The importance of redundancy in sensor methods for locating the exact coordinates of the utility lines and the actual depth of digging for the dredge equipment, anomalies in utility corridor dredging where presumed controls do not seem to be functioning as expected, and the risks this imposes on the dredging project are discussed in the paper with examples.