Structures: How do Dams and Levees affect my flood risk?

Living downstream from a dam or in a leveed area does not eliminate flood risk.

Learn about how flood follows risk and the different types of flooding.

My family lives behind a levee so we're protected right?

Levees reduce flooding risk but they do not prevent it. Levees are designed to hold back flood waters but floodwaters can overtop levees or other issues can cause levees to fail.

How do levees work?

This online FloodSmart Levee Simulator: helps show how levees Work and the different ways levee systems may fail.

A product from the Nebraska Silver Jackets provides information about Risk, Levee Safety, the National Flood Insurance Program and more.

Where can I learn about the risks of living behind a levee?

The American Society of Civil Engineers has a levee guide called So, You Live Behind a Levee! – ASCE to help describe the different kinds of levees as well as the different risks of living behind a levee.

Other resources include FEMA's, Living with Levees It’s a Shared Responsibility - from FEMA's Levee Resources Library.

FEMA has also prepared information related to levees and flood hazards near levee systems, as well as FEMA's approach in managing non-accredited levee systems.

What is the National Levee Database?

The U.S. Army Corps of Engineers' Levee Safety Program – has published a National Levee Database that provides information about the risk associated with different levee systems. The National Levee Database is a database of levees which were constructed by USACE or are involved in the USACE PL 84-99 program (not all levees are presented in this database).

Maintentance of flood risk infrastructure is key in maintaining the risk reduction provided by dams and levees. Living behind levees or downstream of a dam provides a unique type of risk.

Where can I learn about the risks of living downstream from a dam?

The Dam Safety Program regulates the construction, operation and maintenance of Montana's dams to protect life and property from damages due to failure. The dam safety program also provides training and outreach to dam owners and engineers and assists with emergency preparedness activities.

Living With Dams: Know Your Risks is a booklet designed to help answer questions about dams: what purposes they serve, associated risks, guidance for those living near dams, and where to find further information.

What is the National Inventory of Dams?

The National Inventory of Dams provides information about dams meeting at least one of the following criteria; High hazard classification - loss of one human life is likely if the dam fails; Significant hazard classification - possible loss of human life and likely significant property or environmental destruction; Equal or exceed 25 feet in height and exceed 15 acre-feet in storage; or Equal or exceed 50 acre-feet storage and exceed 6 feet in height. This inventory includes nearly 3,000 dams in the state of Montana. The NID is updated every two years.

The USACE National Levee Database can be used to identify areas behind levee systems in the PL84-99 program.

National Levee Database

The National Inventory of Dams consists of dams meeting at least one of the following criteria; high hazard classification - loss of one human life is likely if the dam fails; significant hazard classification - possible loss of human life and likely significant property or environmental destruction; equal or exceed 25 feet in height and exceed 15 acre-feet in storage; equal or exceed 50 acre-feet storage and exceed 6 feet in height. This inventory includes nearly 3,000 dams in the state of Montana.

CorpsMap National Inventory of Dams
 

The FEMA Flood Map Service Center is the official public source for flood hazard information produced in support of the National Flood Insurance Program (NFIP). Use the map service center to find official flood maps, access other flood hazard products, and tools to better understand flood risk.

FEMA Map Service Center