On May 31, 1889, a catastrophic failure of the South Fork Dam on the Little Conemaugh River, approximately 14 miles upstream of Johnstown, PA, resulted in one of the worst natural catastrophes in the history of the United States, creating the largest loss of life from a natural disaster not caused by a hurricane or earthquake.

Intense heavy rains fell across the area in the day preceding the failure, and the poorly maintained earthen dam rapidly weakened and subsequently failed during the afternoon hours. This sudden failure sent a torrent of water down a steep canyon, into the heart of Johnstown. It was reported that the flood wave produced a wall of water 35 feet high and a half mile wide, moving rapidly down the narrow valley at 40 miles an hour! Historical reports indicate that there were a couple hours of warning given; but few people heeded the calls to move to higher ground. The flood and subsequent fires killed 2,209 people, destroyed 1,600 homes and produced $17 million in damages (1989 dollars). 

Flooding was also widespread across the state from this weather event. Major flooding was reported along the West Branch of the Susquehanna River. The prosperous lumber town of Williamsport reported that 75 percent of the town was under water during the peak of the flooding. Major flooding was also reported in Tyrone, Lewistown and Huntingdon, with a significant loss of life and property damage reported in the region.
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This flood event led the way for a series of river gages to be installed across the region in order to improve upon flood warnings.

 

Johnstown Flood Museum History

Main Street in Johnstown

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The winter of 1935-36 was cold and snowy across Pennsylvania. By the middle of March, a deep snow pack remained over parts of the state, along with frozen ground. A warmer and wetter weather pattern brought several strong rain storms systems to the area beginning the week before the floods. This set the stage for major river and ice jam flooding, with the entire state affected. Pittsburgh reported major flooding on the Allegheny and Monongahela Rivers and associated tributaries. 

An amazing total of close to 100,000 buildings were flooded with damages estimated at $250 million. Flooding in downtown Pittsburgh reached record levels, 15 feet deep in spots, with fires and gas explosions reported. Major flooding was also reported in Johnstown, where damages exceeded the great flood of 1889. During the middle of the flood, rumors circulated that a dam upstream of the city was going to fail, and this sent citizens in a rush to get to higher ground, fearing a repeat of 1889. Fortunately those rumors were false, but nonetheless, damage was extensive. In all, 67 deaths were reported in Pittsburgh and 22 in Johnstown. Flooding was not confined to just the southwest portion of the state. The Wilkes-Barre area also reported major flooding along the Susquehanna River. This flooding pushed downstream, affecting Bloomsburg and Harrisburg, where 4-15 feet of water flooded Harrisburg. In central Pennsylvania, major flooding occurred along the Juniata River, where bridges and homes were swept away near Huntingdon. By the end of the event, the death toll stood at 107. This flood led the way for a series of flood control projects to be approved for future construction.

Flooding in Pittsburgh on 3/18/1936

Cameron and Market Streets in Harrisburg

The remnants from Hurricane Agnes brought torrential rainfall and major flooding to the Pennsylvania. The hurricane, which made landfall in the Florida panhandle on June 19, slowly made its way north, before stalling out over the mid-Atlantic region for several days. As the storm system sat, barely moving, it unleashed drenching rain across the state. Widespread rainfall totals of 7 inches fell on June 21-22, with localized totals over 12 inches reported. Rainfall reported in York was 13.50 inches in 24 hours, where the city was essentially cut in two by the raging Codorus Creek. This was more than enough rainfall to bring record flooding to all the major rivers basins in the state. 

By the end of the event, Harrisburg reported over 15 inches of rain. At Harrisburg, the Susquehanna River reported a record crest of 33.27 feet, well above the 17.0 foot flood stage! During the height of the flooding, nearly half of Harrisburg was under water, including the governor’s mansion. Upstream of Harrisburg, the flooding was catastrophic. Danville was under 5 feet of water during the height of the flood. The Wilkes-Barre area suffered major damage when a Dike failed, and 100,000 residents were forced to evacuate. The Susquehanna River there crested almost 19 feet above flood stage, and 8 feet above the previous flood of record. With the levees overtopped, 25,000 homes were flooded and 17 deaths were reported. The Schuylkill River set record highs and brought major flooding to Pottstown and Norristown. Western Pennsylvania also reported major flooding, though not quite as severe as the 1936 floods. Several dams and flood control projects had been completed since the 1936 flooding which helped to temper the flooding. The final fatality count in Pennsylvania from this flood event was 48, with almost $3 billion in damages.

 
President Richard Nixon views flood damage near Harrisburg on June 24, 1972. (Charles Tasnadi, AP)
 

Market Street, Downtown Wilkes-Barre. Source unknown.

A series of major winter storms brought record snow packs to much of the state for the first half of January. The Blizzard of 1996 alone brought as much as 40 inches of snow on January 7-8. Beginning on January 19, the weather patterns took a dramatic shift away from winter and straight into an extreme version of the dreaded January Thaw. Before this happened, in addition to the deep, high liquid water content in the snow pack, many rivers and streams were solidly frozen. On the 19th, as much as 3 inches of rain fall, temperatures roses into the 50s and lower 60s, and winds were strong and gusty. This created the perfect, and unfortunate, combination for a rapid melting of snow. The snow melt, combined with the heavy rainfall, quickly brought large volumes of water into the rivers and streams, many of which were frozen. 

This water volume set the stage for major flooding, both from high water and ice jams from the 19th and 21st. The Susquehanna River Basin was extremely hard hit, with several tributaries reporting record flooding. The West Branch of the Susquehanna River and its tributaries reported major flooding, many caused by ice jams. On the main stem at Harrisburg, the river crested at its highest level since Agnes. Ice jam flooding across the basin was severe, including several major ice jams in proximity of Harrisburg. One jam resulted in the collapse of the Walnut Street Bridge. Downstream from that bridge, the high ice flows resulted in major damage to the Safe Harbor water power facility and the Holtwood hydroelectric facility. Further west, record breaking flooding also was observed across the Ohio River Basin. Severe flooding was reported in the Pittsburgh area when the Allegheny and Monongahela River crested within 5 hours of each other. This rare event brought major flooding to parts of downtown, including the Point State Park. By the time the flooding subsided, 19 people had perished. Flooding was reported in 57 of 67 counties in the state.


Figure River ice accumulating along Front Street in Harrisburg


Flooding in Duncannon on the Susquehanna River


Flooding in Duncannon on the Susquehanna River

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After one of the driest July's in Pennsylvania history, two powerful hurricanes moved up the eastern seaboard in quick succession in August 1955, bringing the most destructive flooding in history to a large part of eastern Pennsylvania. Hurricane Connie was the first storm to hit the region on August 12-13. The storm brought a little more than just drought busting rainfall when 6-10 inches of rain fell across the eastern portions of the state. Flooding, while not as widespread and severe as the pending storm, brought smaller rivers and streams out of their banks in Buck, Chester and Lancaster counties. Two fatalities were reported from automobiles being swept into the fast moving streams in this area. The heavy rains from Hurricane Connie were just priming the pump for the next big rain maker associated with Hurricane Diane. 

Just a few days after the flooding from Connie subsided, Hurricane Diane made landfall near Wilmington, NC, on August 17. The storm moved inland into the central Appalachian foothills before moving north into Pennsylvania on August 18. The deep tropical moisture met up with an existing area low pressure over the eastern half of the state, producing torrential rains. With soils moist from the heavy rains from Connie and streams already flowing high, flooding quickly increased in severity during the evening hours on the 18th. Rainfall estimated between 7 to 9 inches fell in a 6-hour period, with the heaviest amounts centered over the mountainous portions of northeast Pennsylvania. These small mountain creeks produced destructive flooding and led to several deadly small dam failures, such as the one at Camp Davis, Brodhead Creek, near East Stroudsburg. In a truly horrific event, 47 campers, mostly children, were huddled in a building that was rapidly flooded and dislodged, into the roaring flood waters. Hours later, only 7 of the campers were found alive. 

The deadly flooding continued downstream in Stroudsburg and East Stroudsburg, where 78 lives were lost in Monroe and Pike counties. Further north, in Wayne County, a dam failure resulted in two lives lost. The Lackawanna River experienced its worst flooding in history; downtown Scranton was under water. All of this water emptied into the Delaware River, producing severe flooding. The Portland-Columbia (New Jersey) covered bridge, then the longest wooden bridge in the country, which had withstood several major floods, collapsed after water levels rose over the bridge. The Lehigh Valley suffered major flooding, and Easton was completely underwater and cut off by the high waters. The death toll from the flooding associated with Hurricane Diane in Pennsylvania was 113, with property damage estimated to be at least $70 million.|


Flooding in Easton, PA, August 20, 1955


Flooding in Easton, PA, August 20, 1955

 

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Flash flooding is a rapid and extreme flow of high water into a normally dry area, or a rapid water level rise in a stream or creek above a predetermined flood level, beginning within six hours of the causative event (i.e., intense rainfall, dam failure, ice jam). More information...

River flooding occurs when river levels rise and overflow their banks or the edges of their main channel and inundate areas that are normally dry. More information...

At any time of year, a storm from over the ocean can bring heavy precipitation to the U.S. coasts. Whether such a storm is tropical or not, prolonged periods of heavy precipitation can cause flooding in coastal areas, as well as further inland as the storm moves on shore. More information...

A back-up of water into surrounding areas can occur when a river or stream is blocked by a build-up of ice or other debris. Debris Jam: A back-up of water into surrounding areas can occur when a river or stream is blocked by a build-up of debris. More information...

Flooding due to snowmelt most often occurs in the spring when rapidly warming temperatures quickly melt the snow. The water runs off the already saturated ground into nearby streams and rivers, causing them to rapidly rise and, in some cases, overflow their banks.More information...

A break or failure can occur with little to no warning. Most often they are caused by water overtopping the structure, excessive seepage through the surrounding ground, or a structural failure. More information...