Hurricane Agnes and the Susquehanna, tropical storm response

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The mighty Susquehanna meanders along the Appalachian Plateau, carrying water from the New York and Pennsylvania Highlands hundreds of miles to the Chesapeake Bay. The waterway has long proved a valuable resource for population centers that have sprung up along its shores, such as Binghamton, NY, and Harrisburg and Wilkes-Barre, Pennsylvania.

But in June 1972, a prolonged and punishing torrent of rain pushed the usually benevolent river to unprecedented heights. A catastrophic flood ensued – worse than any before or since – caused by an unlikely source: a messy tropical storm named Agnes.

Agnes wreaked havoc from Florida to New York, killing 128 people and causing $3.1 billion in damage. It was the most expensive tropical system in U.S. history at the timea record that would stand for more than a decade.

No region has been harder hit than the Susquehanna River Basin. But the devastation has paved the way for flood mitigation and response efforts that withstood their first test just over a decade ago.

On June 14, 1972, the first tropical depression of the Atlantic hurricane season developed in the northwest Caribbean Sea. The depression quickly strengthened and was declared Tropical Storm Agnes the following day.

The storm steadily strengthened as it crept north across the eastern Gulf of Mexico, becoming a low-end hurricane on June 18. Agnes was not exceptionally strong, but she was exceptionally large – 1,150 miles in diameter. The National Hurricane Center declared it “one of the largest hurricanes on record in June.”

The storm’s atypical size helped extract huge amounts of moisture from the Gulf of Mexico, dropping nearly nine inches of rain on landfall in the Florida Panhandle.

Agnes weakened into a depression as it crossed the southeast, reaching the Carolinas on 21 June. Around the same time, a cold front developed near the Great Lakes and drew in some of the moisture from Agnes. Rain fell in the mid-Atlantic, where soils were already saturated after a wet spring, preparing the ground for the flood disaster to come.

The depression moved over the Outer Banks of North Carolina into the Atlantic, where it intensified into a tropical storm. But instead of continuing east toward the sea, Agnes reversed course and headed inland, unleashing a multi-day deluge from Virginia to New York.

“The storm got sucked into the jet stream, stalled and crashed over Pennsylvania,” said David Nicosia, the meteorologist in charge of the National Weather Service’s Binghamton office.

The storm dropped 7 to 15 inches of rain from northern Virginia to southern New York, with locally higher amounts.

Extraordinary flooding occurred throughout this area, with some of the worst concentrated along the Susquehanna River and its tributaries.

Flooding on the Susquehanna River

The Susquehanna had already been flooded. In one particularly destructive event in March 1936, the river rose 20 to 30 feet. Nearly 28% of Harrisburg was under four to 15 feet of water.

“The 1936 flood led to the Flood Control Act of 1936,” said Michael Bilder, hurricane program manager for the Federal Emergency Management Agency’s Mid-Atlantic region. “This was the first time the federal government recognized that it had a role to play in national flood control.

Yet the levees and flood walls built after that 1936 flood were no match for Agnes.

The tropical storm caused record-breaking river crests – up to 15 supply above flood level — well beyond the levels imagined by the architects of flood control.

Levees were quickly overtaken in dozens of towns and villages as the river flexed and expanded into its former floodplain, disregarding development along its banks. The floods were certainly not as severe as they might have been without the 1936 flood defences, Bilder said, but they were exceptional nonetheless.

“Nearly 50,000 homes were destroyed or suffered major damage, and another 65,000 homes suffered minor damage,” Bilder said. “There has been extensive damage to critical infrastructure, in particular bridges, roads and railways. … At least 43 million tons of debris had to be removed.

Of the $3.1 billion in damage caused by Agnes, more than $2 billion occurred in the Susquehanna River Basin.

Agnes motivated substantial flood response and mitigation efforts.

Prior to the storm, “federal emergency management was not particularly well organized,” MaryAnn E. Tierney, FEMA’s Mid-Atlantic Region Administrator, said in an email. “The enormity of the disaster ultimately convinced lawmakers and federal officials to begin serious discussions about creating the organization that would eventually be called the Federal Emergency Management Agency.”

Agnes further led to a reassessment of flood control strategies. Tierney said levees were raised in Wyoming’s vulnerable valley in northeastern Pennsylvania, and properties in floodplains were removed or raised. Dykes up to 41 feet were built in the low areas of the valley.

Tierney too noted that subsequent legislation resulted in a drastic increase in the proportion of households with flood insurance.

The work done after Agnès will prove invaluable in the face of the deluge of modern times.

In September 2011, Tropical Storm Lee crawled north from the Gulf of Mexico. Its waterlogged remnants dropped more than 10 inches of rain across a mid-Atlantic and northeast swath, mirroring Agnes’ pattern.

The twisty Susquehanna responded in the same way. The river approached and in some cases exceeded 1972 levels, but levees and flood walls protected communities.

Wilkes-Barre, Pennsylvania, devastated by Agnes, this time was spared.

“During Lee, the Susquehanna peaked at 42.66 feet at Wilkes-Barre – nearly two feet higher than the record set during Agnes,” Tierney said. “The levee system performed as designed and, according to the Luzerne County Flood Protection Authority, it is estimated to have averted approximately $5 billion in property damage.”

Flooding prompts evacuations in Pennsylvania and New York as Tropical Storm Lee hits northeast

Lee’s impacts were lower than Agnes’s despite similar rainfall. He killed 12, while his inflation-adjusted cost was about a third of Agnes’.

When asked if the area was ready for another Lee or Agnes, Tierney replied that she would “never be so proud” to answer in the affirmative.

Although the threats posed by the wayward Susquehanna have been mitigated, last year the remnants of Hurricane Ida brought disastrous flash flooding to parts of the northeast. It was a clear signal that extreme events, intensified by climate change, will continue to redefine what is possible in the region.

More Washington Post retrospective articles on Hurricane Agnes

Hurricane Agnes: Looking Back After 40 Years (from 2012, focused on the Washington, DC area)

Agnes’s Wrath (from 1999, also DC-area focused)

Agnes: 3-day flood, 20-year wake (from 1992, concentrated on Potomac River)

The flood that transformed Occoquan (from 1992)

Useful resource: Hurricane Agnes 50th Anniversary Website federal, state and local government agencies in Virginia, Maryland, New York and Pennsylvania

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