Understanding Flooding

What is the difference between a flood plain and a flood zone?

  • A floodplain is comprised of any land area susceptible to being inundated by floodwaters from any source.
  • A flood zone is a geographic area characterized by its risk of flooding. For example, high-risk flood zones have a 1% chance of being flooded each year. The National Flood Insurance Program (NFIP), administered by FEMA, has five zones: VE zones, A zones, AE zones, AO zones, and X zones.

Millburn Township residents are advised to check their flood zone on the FEMA website here. You may also check groundwater maps through the U.S. Geological Survey website here. View current river flood conditions through USGS here and the NWS Rahway River (at Springfield) forecast by clicking here. These links all help to paint a picture of flooding conditions in our area in general as well as when a storm is impending.

National Weather Service Alerts: Warning vs. Watch

Millburn Township residents who are signed up to receive Swift911 alerts will, from time to time, receive automatic updates from the National Weather Service on special weather situations, including but not limited to the below list. These alerts can also be found on the NWS' website at https://www.weather.gov and on their social media channels.

  • A Flash Flood Warning is issued when a flash flood is imminent or occurring. If you are in a flood prone area move immediately to high ground. A flash flood is a sudden violent flood that can take from minutes to hours to develop. It is even possible to experience a flash flood in areas not immediately receiving rain.
  • A Flood Warning is issued when the hazardous weather event is imminent or already happening. A Flood Warning is issued when flooding is imminent or occurring.
  • A Flood Watch is issued when conditions are favorable for a specific hazardous weather event to occur. A Flood Watch is issued when conditions are favorable for flooding. It does not mean flooding will occur, but it is possible.
  • A Flood Advisory is issued when a specific weather event that is forecast to occur may become a nuisance. A Flood Advisory is issued when flooding is not expected to be bad enough to issue a warning. However, it may cause significant inconvenience, and if caution is not exercised, it could lead to situations that may threaten life and/or property.