Levees / Explained / people-at-risk
How the population figure behind a levee is counted
The number on each system page is the population USACE records within the leveed area. It is not a casualty estimate and not everyone in it would be affected by any given flood.
Each system record carries a population figure for the leveed area, the land the system is built to protect. It is an estimate of who lives there, derived from census geography rather than from a flood model of a particular event.
What it is not
- It is not a forecast of how many people would be flooded. That depends on the event, the elevation of individual properties, and how a system performs.
- It is not a ranking input. A system with more people behind it is not more dangerous than one with fewer.
- It is not always published. Where USACE has not recorded a figure, this site says so rather than printing a zero.
Totals on the state and county pages are summed only across the systems that publish a figure, and each page states how many that was. A total that quietly treated missing values as zero would understate the real number while looking more complete.
The related figures
Structures in the leveed area is counted the same way. The consequence estimate in dollars is a modelled figure describing property exposure in the leveed area, not a valuation of the levee and not a prediction of loss.
Terminology follows USACE National Levee Database and FEMA published definitions. Site data refreshed 2026-09-10. Nothing on this page is a statement about a specific property.