TRENTON — The veritable sea of ice that amassed along the Delaware River in the Trenton area this past month is expected to dissipate soon as a warming trend firmly establishes itself across the region in the coming days.
But while some observers of the prolonged ice jam have worried that the jagged floating glacial-like mass might damage the support structures for three bridges the Delaware River Joint Toll Bridge Commission owns and operates between Trenton and Morrisville, the cold hard truth is that the ice itself never directly threatened the spans.
”In a historical sense, ice jams are far from a new phenomenon along the Delaware River,” said Joseph J. Resta, the commission’s executive director. “But the region hasn’t experienced any notable ones in recent years due to a string of relatively warm winters, so there has been some public concern about the recent heaps of ice crammed beneath our river crossings.”
Ice jams have formed in this stretch of the river for thousands of years. Indeed, there have been years when the breadth and duration of ice jams far exceeded what occurred this past month. The piers and abutments that support the commission’s three Trenton bridges have weathered through worse periods of ice for decades, even centuries. The original masonry substructures supporting the Lower Trenton (“Trenton Makes”) Bridge have been in the river for more than 207 years. The substructures supporting the Calhoun Street Bridge have been around since 1861.The ones supporting the Trenton-Morrisville (Route 1) Toll Bridge date back to 1952.The piers and abutments at these three locations are substantial enough to withstand the pressures and slow movements of ice in the river.
These substructures also are in their best overall condition in decades as a result of a recent capital initiative the commission undertook to rehabilitate and undergird the piers and abutments that support 15 of the agency’s 20 main-river bridges. This undertaking — the Substructure Repair and Scour Remediation Project — involved work spread over portions of three years, 2010 to 2012. A major facet of the work was scour remediation, namely the placement of stone and aggregate around piers to replace sediments that washed away from the river bottom due to constant river currents or storm events. Scour is the leading cause of bridge collapses in the United States — accounting for 60 percent of the nation’s highway bridge failures, according to a Federal Highway Administration report. Other project elements included debris removal, concrete and crack repairs, masonry repairs, pier and apron repairs, and reconstruction of bridge foundations.
None of this means to suggest that the commission has a false sense of security, because there is an indirect threat that ice jams pose for the commission’s bridges and service mission — flooding. This was the case when an intensive “polar vortex” of arctic cold descended upon the region earlier this year, causing a stubborn ice jam that stretched from a half-mile below the Lower Trenton Bridge to just above the Calhoun Street Bridge. The ice jam became so compacted that it eventually began to back up the river’s flow, inundating a portion of Route 29 on the river’s New Jersey side and a portion of River Road on its Pennsylvania side.
Still, the flooding from this event never reached such heights that it impeded access to the commission bridges, or caused the ice to rise so high that it might breech one of the bridge’s road decks.
There is a second kind of ice-induced flood concern for the agency. This can occur when massive ice jams hold back large pools of rising water at points far up the river. If these up-river jams suddenly break up due to a rapid thaw or runoff from heavy rains, they can cause a tidal wave effect in which a torrent of ice, water and debris races down the river where it can then smash into bridge piers or form new ice jams at each subsequent bridge crossing.
This type of flooding event last occurred in 1996 and impacted a variety of commission bridges, most notably causing serious community flooding in the area of the historic steel-truss bridge at New Hope-Lambertville.
For more information about the Commission and its various initiatives to deliver safer and more convenient travel for its customers, see: www.drjtbc.org.
