Flood Risk Management Program


Frequently Asked Questions

Typical Questions a Flood Risk Manager Receives
 When  should USACE provide information to the local community for submission to FEMA  for map changes?

During Design, USACE should provide to the non-Federal sponsor information necessary for the submission of a Conditional Letter of Map Revision (CLOMR) to FEMA for any modifications proposed in the floodway that are regulated by the local government as part of their participation in the National Flood Insurance Program. More information can be found at https://www.fema.gov/media-library/assets/documents/1343.


 How do you explain the 1% annual chance of  flooding (100 year event)?

The 1% annual chance exceedance flood sometimes referred to as the 100-year flood, or base flood, has a 1% chance of occurring in any given year. It is not a safety standard, and it has been set as the level that flood insurance is not required if the 1% annual chance flood can be excluded from the floodplain. Although a 1% annual chance flood sounds remote, keep in mind that over the life of an average 30-year mortgage, a home located within the 1% flood zone (A or V zone) has a 26% chance of being inundated by the size flood. This same home has less than a 1% chance of fire damage during the same period. What is more significant is the house in a 10-year flood area is almost certain to see a 10-year flood (96% chance) in the same 30-year mortgage cycle. In many areas the difference in flood heights between a 10% and a 1% event is less than one foot.

Flood Frequency Chart

Flood frequency

Chance of flooding
in any given year

Percent chance of flooding
during 30-year mortgage


10 out of 100 (10%)



2 out of 100 (2%)



1 out of 100 (1%)



0.2 out of 100 (0.2%)



 What is residual risk?

Residual risk is the flood risk that remains after all efforts to reduce the risk are completed. Residual risk is the exposure to loss remaining after other known risks have been countered, factored in or eliminated.


 What is the Universe of Levees?

The Universe of Levees is a shown in the chart below. It shows where USACE has an interest and what is left.

Universe of Levees


 What is the table for buying  down risk?

Major General Don Riley, a previous USACE director of Civil Works, wrote a paper called Improving Public Safety — From Federal Protection to Shared Risk Reduction (2/26/2008), which first discussed the USACE vision of buying down risk and shared responsibility. The table below is the latest version of the chart. It has been modified over time.

Table for Buying Down Risk


 The local community wants to  improve its flood control system, part is Federal, and part is not. They are  willing to pay for all the upgrades. What authorities does it need to be aware of?

If the portion of the system they wish to improve is the federal portion, with their funds, they will need to proceed and ask permission through the 408 process. Such modifications must be approved by the Chief of Engineers. The authorities and procedures for major changes to an existing authorized project are outlined in: the 17 November 2008 Clarification Guidance on the Policy and Procedural guidance for the Approval of Modifications and Alterations of USACE Project; ER1165-2-119, dated 20 September 1982, Modifications to Completed Projects; and 33 USC 408, Taking Possession of, Use of or Injury to Harbor and River Improvements.

If the portion of the project does not have a tie-in or any effect on the existing authorized project, then the non-Federal partner may proceed through the normal permitting process.

If the non-Federal partner wants to proceed with a project that may have an impact on the Federal project even though they are not touching the Federal project, then the 408 process must be followed.

If there is an ongoing or proposed study to consider alternative solutions, the non-Federal partner must follow the 408 process and must also submit the necessary package for proposed credit (Section 104 of WRDA 1986 or Section 2003 of WRDA 2007), which must be submitted at the same time for approval by the Secretary of the Army for Civil Works. This is to allow the non-Federal sponsor credit for work completed ahead of Federal authorization and funding of the construction project.

To initiate a new study based on additional protection required from an existing project, an initial study can be performed under Section 216 of the Flood Control Act of 1970. The procedure is outlined in ER 1165-2-119, Modifications of Completed Projects, dated 20 September 1982. They may also follow the process to initiate a new study, starting with a Reconnaissance Report (ER 1110-2-100, Planning Guidance Notebook).


 When  the local community official or levee district asks the question: Who can certify my levee?

The decision to submit an accreditation package to FEMA for the National Flood Insurance Program (NFIP) is the responsibility of the local community.  There are two conditions when USACE will budget for and conduct these evaluations for the NFIP when requested by the community: (1) USACE operates or maintains the levee system (such as the Mississippi River & Tributaries levees) or (2) USACE has an active levee design/construction project underway. 

USACE may perform this evaluation using funds provided by non-Federal sponsors, provided that it can be demonstrated that USACE is uniquely equipped to do so and that such services are not reasonably and quickly available through ordinary business channels (Thomas Amendment). USACE Process For The National Flood Insurance Program (NFIP) Levee System Evaluation, EC 1110-2-6067 (pdf, 1.54 MB), provides a more complete answer.

 USACE already inspected my  levee: why do I have to go through the certification process?

Inspection of a levee, as related to USACE's Levee Safety Program, is a visual inspection conducted to verify that the levee system is being properly operated and maintained. The result of these inspections does not equate to a “levee certification” or “NFIP levee system evaluation.” Other criteria for a NFIP levee system evaluation, not covered by a USACE levee inspection, include levee height determination, seepage analysis, embankment stability analysis, settlement analysis, and interior drainage.

The purpose of these levee evaluations is to determine how FEMA will map the floodplain behind the levee for flood insurance purposes as part of the NFIP. Since the local community is responsible for administering the requirements of the NFIP and maintaining the levee, providing the documentation to meet 44 CFR 65.10 is a local project/system sponsor responsibility. In some cases, USACE Levee Safety Program activities will help inform and support the local’s efforts.


 What does it mean if you are  placed in the "inactive" status for PL 84-99?

In the event that a project enters into the "inactive" status because of an unacceptable routine inspection rating, all deficiencies will need to be corrected and the project must receive at least a "minimally acceptable" inspection rating before the project's status can be changed to "active." When the project is placed in the “inactive” status, the project becomes ineligible for PL 84-99 rehabilitation assistance if it is damaged in a flood or storm event. 

Regardless of status, the project will remain eligible to receive flood fighting assistance to protect life and property in the event state and local resources are overwhelmed during times of emergency (ER 500-1-1).


 Does PL 84-99 cover coastal  systems, i.e. hurricane or shore protection projects?
The Rehabilitation and Inspection Program provides for the emergency repair or rehabilitation of Federally authorized and constructed hurricane or shore protection projects (HSPP).  USACE may rehabilitate Federally authorized and constructed HSPP structures substantially eroded/damaged or destroyed by wind, wave, or water action of anything other than ordinary nature.  Emergency repair and rehabilitation of HSPPs under the authority of PL 84-99 will be limited to that necessary to allow for adequate functioning of the project, or restoration to pre-storm condition, whichever is less (ER 500-1-1).