US Geological
  Survey logo

Large Floods in the United States: Where They Happen and Why

By Jim E. O'Connor and John E. Costa


U.S. Geological Survey Circular 1245

Report cover


The spatial distribution of large gaged floods throughout the United States shows that the locations of most of the largest flows are related to specific combinations of regional climatology, topography, and basin size. Key factors include the general northward trend of decreasing atmospheric moisture, proximity to oceanic moisture sources such as the Pacific Ocean and the Gulf of Mexico, and orientation of topographic features relative to directions of moisture flow, with the largest flows being at locations where topographically high areas are oriented perpendicular to directions of moisture flow. Additionally, the largest flows in large river basins are primarily caused by persistent climatologic conditions such as seasonal snowfall. In contrast, the largest flows in smaller basins are most commonly the result of intense precipitation due to convective storms.



Floods-A National Hazard
Largest of the Large
Where Are the Largest Flows?
Why Are Large Flows Where They Are?
For More Information

Download the report (PDF, 7.5 MB). (Adobe PDF Reader required, version 5 or higher preferred.)

If you do not have the Adobe PDF Reader, it is available for free download from Adobe Systems Incorporated.

Users with visual disabilities can visit for conversion tools and information to help make PDF files accessible.

For more information:
Chief, Office of Surface Water
U.S. Geological Survey
Water Resources Division
12201 Sunrise Valley Drive, MS 415
Reston, VA 20192

This report may be obtained free from:
U.S. Geological Survey
Information Services
Box 25286 Federal Center
Denver, CO 80225

FirstGov button  Take Pride in America button