High Water Mark (HWM) Data

U.S. Army Corps of Engineers
Published March 24, 2025
Updated: April 3, 2025
Flooded area with a 15 miles per hour speed limit sign.

A speed limit sign in a flooded Southeast Michigan neighborhood after record-breaking rainfall demonstrates how high water can rise during a major flood.

What is High Water Mark data?

A High Water Mark (HWM) is the visible mark left by the highest level of floodwater during a specific event. These marks are often found on natural features, such as riverbanks or trees, or on infrastructure, like roads or buildings. The data collected from these high water marks helps create a historical record of flood levels, informs flood modeling, and supports decision-making for flood mitigation and planning.

How is HWM data collected?

  • Field Surveys
  • Photographic Documentation
  • Collaboration with Other Agencies
  • Remote Sensing Technology

What is HWM data used for?

  • Flood Risk Mapping
  • Floodplain Management and Zoning
  • Infrastructure and Levee Safety
  • Post-Flood Analysis and Recovery
  • Emergency Response and Preparedness