TRENTON – At least two ice jams in the Delaware River along Mercer County have caused minor flooding upstream and prompted the National Weather Service to issue a flash flood watch downstream when the jams break.

The Statehouse parking garage is already closed because of localized flooding in Trenton. State employees are asked to use the parking lot at the Sun National Bank Center or at 244 Perry St., according to the state Office of Emergency Management. Shuttle service is being provided to the Statehouse.

The Mercer County Office of Emergency Management said the Route 29 exits onto Market Street and Memorial Drive in Trenton are closed due to flooding and icing.

The New Jersey Department of Transportation said they are unsure when the ramps may reopen, depending on the flooding. Drivers are asked to visit 511nj.org for real-time traffic information.

The river gauge operated by the National Weather Service at Trenton has recorded water levels at just above 18 feet, according to Sarah Johnson, a meteorologist with the

NWS office in Mount Holly. Flood stage is 20 feet.

“It is getting close and that is because of a partial ice jam downstream in the Trenton area,” Johnson said. “Ice is restricting the flow through that area.”

An ice jam is a pileup of ice in the river that restricts the flow of water, Johnson said.

Johnson said the flooding is currently localized, but the meteorologists are still working to determine if a larger area could be affected.

“We are still getting information and trying to make a determination if it is going to go to flood stage,” Johnson said, noting that temperatures are expected to stay below freezing today and into Thursday morning.

The National Weather Service's flash flood watch includes Mercer and northwestern Burlington counties on the New Jersey side of the Delaware River and lower Bucks and Philadelphia counties on the Pennsylvania side. The watch continues through late tonight.

"Perhaps later today and more likely tomorrow, the temperatures will be above freezing and that would cause the ice jam to break," said Mitchell Gaines, a meteorologist at the NWS. "Water may lead to some pretty quick rising water around the Delaware River."

Mary Goepfert, a spokeswoman for the N.J. OEM, said it has been “well over 10 years” since the state saw an ice jam in the Delaware.

The state Department of Transportation could not immediately provide information about road closures in the area.

The city of Trenton has issued a flood warning for areas along the river including the island and Glen Afton neighborhoods, said Quareeb Bashir, the fire director and director of the city’s Office of Emergency Management.

“We are monitoring the situation,” Bashir said.

Bashir said the department has been in contact with the state Office of Emergency Management about remedies to break up the ice in an effort to avoid flooding, but was unsure exactly what could be done.

The sewer department was out in Trenton today to inspect and unclog and on-street drains.

“We are setting up from a preliminary standpoint,” Bashir said. “We are looking at our procedures to make sure they are in place if there needs to be any evacuations.”

Bashir said the largest jam starts at the Calhoun Street bridge and continues downstream. There is another partial jam farther north, he said.

The Trenton Police Department issued a warning to residents along the river to be ready to evacuate if that is deemed to be necessary.

The county Office of Emergency Management is ready to assist the city of Trenton if needed, said county spokeswoman Julie Willmot.

Willmot said residents of Hamilton, Ewing and Hopewell also have been advised that flooding is possible.

The Red Cross has been notified to assist in the event of any evacuations.

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