Storm Flood Basics: Understanding Flood Types and Warnings
Broadly speaking, a flood is a temporary overflow of water onto land that is normally dry. Any property is subject to flooding if there’s enough water rushing into an area at one time, whether the origin is natural or man-made. Causes for flooding vary greatly depending on the location, time of year and weather conditions.
While you may or may not have a flood warning, it never hurts to plan ahead. In the event of an evacuation, be prepared to bring three days’ worth of essential items from your
Evacuation Checklist.
Storm Flood Descriptions
Flooding occurs in every state and territory in the United States. Any area that receives rainfall has the threat of possible flooding. View the chart below for an understanding of the different types of floods.
| River Floods |
When water levels rise over the tops of river banks due to excessive rain, consistent rain for an extended period of time, snowmelt, ice or debris jams, or dam or levee failures. |
| Coastal Floods |
Caused by higher than average tides and worsened by heavy rainfall or onshore winds (wind blowing toward the land from the ocean). Shallow coastal flooding can often occur due to low elevation or heavy coastal development – it does not need to be caused by a tropical storm. |
| Storm Surges |
An abnormal rise in sea level that occurs during hurricanes or other tropical storms. Strong winds can push the water ashore, and can be intensified by high tides and heavy rain. |
| Flash Floods |
Caused by heavy excessive rainfall in a very short period of time (generally less than six hours). They can occur suddenly and without warning, with walls of water that can reach heights of 10 to 20 feet. They move at very fast speeds, taking out trees, buildings and even bridges. |
Understanding Flood Advisory, Flood Watch and Flood Warning
At the beginning of a flood, the U.S. National Geological Survey and the National Weather Service use surface and groundwater data to determine possible flood conditions and forecast a flood alert based on either the county, or for a particular river or stream. Our chart below outlines the differences between the four basic categories.
| Flood Advisory |
A flood advisory is issued when a specific forecasted weather event may become a nuisance. During a flood advisory, flooding is not expected to be bad enough to issue a warning but could cause significant inconveniences. Have your flood resources handy and be ready to act in case a warning is issued. |
| Flood Watch |
A flood watch is issued when conditions are likely for a specific hazardous event to occur. While a flood watch is issued when conditions are favorable for a flood, a flood may not occur. |
| Flood Warning |
A flood warning is issued when a hazardous weather event is imminent or currently happening. Once a warning is issued, complete storm preparations and leave the area if directed to do so by authorities. |
| Flash Flood Warning |
A flash flood warning is issued when a flash flood is imminent or currently happening. A flash flood is a sudden, violent flood that can only take minutes to develop, even if there is no rain in the immediate area. If you are in an area susceptible to flooding, move to higher ground immediately. Once a warning is issued, complete storm preparations and leave the area if directed to do so by authorities. |
You don’t have to be in a flood plain to be at risk for flooding. Being prepared for any crisis, including a flood, takes planning. We’ve assembled some tools and resources to assist you in planning, preparing and recovering from these types of events.
Essential Resources for Flood Preparedness
Bookmark these recommended informational sources to help prepare and recover from a flood. These are national resources and are not associated with Gallagher.
