In 1962, after the 1955 flood of record, Congress authorized the construction of the Tocks Island Dam on the main stem of the Delaware River, just north of the Delaware Water Gap. These three floods caused a total of close to $745 million of damage in the states of New York, New Jersey and Pennsylvania. From Warren County downstream to Trenton, flooding in September of 2004, April 2005, and June 2006 caused property damage and required evacuations. Most recently, the remnants of Tropical Storm Allison caused $35 million in damages and resulted in seven deaths in Bucks and Montgomery Counties, PA in June of 2001. Although flooding of this scope and magnitude is rare, damage and loss of life have occurred from more localized flooding during lesser events. The National Weather Service has estimated repetition of this record flood event would cause $2.8 billion in damages in the Delaware River Basin in today's dollars. Extensive property damage and loss of life ensued. Hurricane Diane, which remains the wettest tropical cyclone to have hit the northeastern US, added another 10 inches of rain less than a week later. First, Hurricane Connie produced 10 inches of rain in 48 hours, putting the Delaware and surrounding rivers at flood stage. Record flooding on the Delaware River occurred in August 1955, in the aftermath of two separate hurricanes traversing the area within less than a week. When floods do occur in this section, they are caused by several factors, acting alone or in combination: flows from the upper river, high spring tides resulting from tidal fluctuations, and wind tides produced by hurricanes or storm action.ġ955 FLOOD OF RECORD AND 2004-2006 FLOODS The section of the Delaware River below Burlington, New Jersey, is tidal and significantly wider than the sections further north, and less prone to flooding. Floods can also be caused by combinations of storms, snowmelt, ice jams and tidal action.

The latter are of coastal origin and are accompanied by severe winds and possible flood-producing precipitation.

Movement of warm, moist air into contact with surrounding air of lower temperature produces the violent thunderstorms and intense precipitation of the summer months and the nor'easters of the cool months. Storms occur on their own and in combination, with the most intense precipitation resulting from a combination of both types. These storms are either of tropical origin (hurricanes) or extra-tropical, such as thunderstorms and nor'easters. Watersheds adjacent to the Delaware River, like many others throughout the nation, have been increasingly affected by flooding because people live, work, travel, and recreate in the floodplains, and because their land use activities have increased the runoff from watersheds and changed the hydraulics of the floodplain itself.įloods from a river overflowing its bank are known as 'fluvial' floods and are usually caused by storms that traverse the basin. The river's floodplain, as well as those of its tributaries, has been subject to both local and widespread damage. The Delaware River has a long history of flooding.

Philadelphia flood map