All about FLOODS

What is a Flood / Flooding?

     Flooding is the temporary condition of partial or complete inundation on normally dry land and it is the most frequent and costly of all hazards in Pennsylvania. Flooding events are generally the result of excessive precipitation. General flooding is typically experienced when precipitation occurs over a given river basin for an extended period of time. Flash flooding is usually a result of heavy localized precipitation falling in a short time period over a given location, often along mountain streams and in urban areas where much of the ground is covered by impervious surfaces. The severity of a flood event is dependent upon a combination of stream and river basin topography and physiography, hydrology, precipitation and weather patterns, present soil moisture conditions, the degree of vegetative clearing as well as the presence of impervious surfaces in and around flood prone areas (NOAA, 2009). Winter flooding can include ice jams which occur when warm temperatures and heavy rain cause snow to melt rapidly. Snow melt combined with heavy rains can cause frozen rivers to swell, which breaks the ice layer on top of a river. The ice layer often breaks into large chunks, which float downstream, piling up in narrow passages and near other obstructions such as bridges and dams. All forms of flooding can damage infrastructure (USACE, 2007).

For more see the National Geographic produced video “Floods 101“.

Learn about all Northampton County disaster declarations since August of 1955 go to our Recovery page.


or 37 square miles of the Lehigh Valley (Northampton & Lehigh counties) lies within the 1% annual chance floodplain.

Is my property in a Special Flood Hazard Area (SFHA) floodplain?


Visit the Is my property in a Floodplain page to utilize the FEMA Flood Map Service Center site to see your property rests within a SFHA. 


or 43 square miles of the Lehigh Valley (Northampton & Lehigh counties) lies within the .2% annual chance floodplain.

The Lehigh Valley and Floods

Floods are one of the most common natural hazards in the United States and are the most prevalent type of natural disaster occurring in Pennsylvania. Over 94% of the municipalities in the Commonwealth have designated flood-prone areas. Both seasonal and flash floods have been the cause of millions of dollars in annual property damages, loss of lives and disruption of economic activities [Pennsylvania Emergency Management Agency (PEMA) 2013].

Flooding is the most significant natural hazard in the Lehigh Valley. Riverine, flash, storm water and ice jam floods occur around rivers, streams and creeks found throughout the Lehigh Valley. Stormwater/urban flooding occurs in areas of ditches, storm sewers, retention ponds and other facilities constructed to store runoff. Within Lehigh and Northampton Counties, the State has designated 16 watersheds for the purposes of Stormwater management. The Lehigh Valley has ordinances in place for all 16 watersheds.

Two major rivers, the Lehigh and Delaware, are located within the Lehigh Valley, along with the tributaries of these two rivers. The Lehigh River flows through Lehigh Gap at the northern boundary of Lehigh and Northampton counties southbound to Allentown where it turns eastward. The Lehigh River essentially splits the Lehigh Valley in half. From Allentown, the Lehigh River flows eastward to its confluence with the Delaware River at Easton. Major tributary streams flowing into the Lehigh River are Coplay Creek, Little Lehigh Creek, Hokendauqua Creek, Jordan Creek, Monocacy Creek and Saucon Creek. The Delaware River flows along the eastern portion of Northampton County and eventually flows into the Atlantic Ocean. Bushkill Creek and Martins Creek flow directly into the Delaware. In Lehigh and Northampton counties, all municipalities have areas prone to flooding along streams and/or rivers.

Ice jams are common in the northeastern US, and the Lehigh Valley is not an exception. Ice jams act as a natural dam and restrict flow of a body of water and may build up to a thickness great enough to raise the water level and cause flooding. The Lehigh Valley has experienced ice jams in the past.

Flood hazard areas are identified on the FEMA Flood Insurance Rate Map (FIRM) and are identified as a Special Flood Hazard Area (SFHA). SFHAs are defined as the area that will be inundated by the flood event having a 1% chance of being equaled or exceeded in any given year. The 1% annual chance flood is also referred to as the base flood or 100-year flood. The FIRM also identifies areas of the 0.2% chance flood or 500-year floodplain. The SHFA is the area where the National Flood Insurance Program’s (NFIP) floodplain management regulations must be enforced, and the area where the mandatory purchase of flood insurance applies. A structure located within a 1% floodplain has a 26% chance of suffering flood damage during the term of a 30-year mortgage (FEMA 2018).

Locally (Lehigh and Northampton counties) based on the analysis, more than 37 square miles or about 5% of the Lehigh Valley area lies within a 1% annual chance floodplain, and about 43 square miles or about 6% lies within a 0.2% chance floodplain.

Did you know these Quick Flood Facts?

  • Floods are the #1 natural disaster in the United States.

  • Flood losses in the United States averaged $2.4 billion dollars in losses per year for the last decade.

  • Just an inch (one inch) of water can cause damage to property!

  • Everyone is at risk – due to weather systems, land development runoff or regional events.

  • Homeowners insurance DOES NOT cover flood damage!

  • Thirty percent (30%) of all flood insurance claims are filed in low-to-moderate risk areas.

  • New construction can increase flood risk, especially if it changes natural runoff paths.

  • Nearly five million (5,000,000) Americans are protected with flood insurance but millions more are unaware of their personal risk for property damage – or options for protection.         

Want to learn more about National Floodplain Insurance Program (NFIP) flood insurance and its coverages? Visit