1% Annual Chance Flood: See Base Flood; sometimes referred to as a “100-year flood.”
Base Flood: Base Flood is the regulatory standard under the National Flood Insurance Program for a flood having a one percent chance of being equaled or exceeded in any given year. It is also referred to as the "100-year flood." The base flood is the national standard used by the NFIP and all Federal agencies for the purposes of requiring the purchase of flood insurance and regulating new development. Base Flood Elevations (BFEs) are typically shown on Flood Insurance Rate Maps (FIRMs).
Breach: A break in a levee. The most frequent form of levee failure is a breach. A levee breach is when part of the levee actually breaks away, leaving a large opening for water to flood the land protected by the levee. A breach can be a sudden or gradual failure that is caused either by surface erosion or by a subsurface failure of the levee.
Crest Elevation: The highest river stage passing any given location.
Federally authorized levee: A levee designed and built by the Army Corps of Engineers or authorized to be part of the Army Corps of Engineers federal program, but locally operated and maintained in accordance with standards established by the Corps.
Flood: A temporary and general condition of partial or complete inundation of two acres of dry land or two or more properties.
Floodplain: Any normally dry land area that is susceptible to inundation by any natural source, such as a stream, during floods.
Floodwalls: Concrete and steel walls, built atop a levee, or in place of a levee, often where space is insufficient for a levee’s broad base.
Freeboard: At a given time, the vertical distance between the water level and the top of the structure. Freeboard can also refer to the additional height or elevation of a structure, such as a levee or floodwall above the design water elevation to provide a buffer for uncertainty. Many levees have been designed and built to a standard equal to the 1% annual chance flood plus three feet of freeboard.
Inspection of Completed Works (ICW): A Corps of Engineers program that ensures that non-federal owners of federally-built critical infrastructure, such as levees, perform essential maintenance in accordance with the project operation and maintenance manuals. Compliance inspections are performed regularly to identify maintenance deficiencies and operational problems and discuss corrective actions. When necessary, the Corps provides technical assistance before, during and after each flood emergency. Through these compliance inspections, the Corps ensures that the project will operate and function as designed.
Levee: An embankment, including floodwalls, whose primary purpose is to provide hurricane, storm, and flood reduction relating to seasonal high water, storm surges, precipitation, and other weather events, and that normally is subject to water loading for only a few days during a year. The base is commonly 10 times as wide as the height.
Local responsibility: The responsibilities of the local levee owner or Corps project sponsor are broad and may include: levee safety; land use planning and development; building codes; and operations, maintenance, repair, rehabilitation and replacement of the levee. Certifying the levee data submitted to the Federal Emergency Management Agency (FEMA) for accreditation of the levee under the National Flood Insurance Program (NFIP) is also the responsibility of the local levee owner or sponsor.
National Flood Insurance Program (NFIP): A federal program conducted by the Federal Emergency Management Agency (FEMA), enabling property owners in participating communities to purchase insurance protection against losses from flooding. The insurance is designed to provide an insurance alternative to disaster assistance to reduce the costs of repairing damage to buildings and their contents caused by floods. Participation in the NFIP is based on an agreement between local communities and the Federal Government that states if a community will adopt and enforce a floodplain management ordinance to reduce future flood risks and enforce a floodplain management ordinance to reduce future flood risks to new construction in Special Flood Hazard Areas, the Federal Government will make flood insurance available within a community as a financial protection against flood losses.
Non-federal levee: Designed, built, and managed by a non-federal entity.
Nonstructural Approaches (see also Structural Approaches): Nonstructural approaches to flood proofing are intended to reduce damage from encroaching floodwater by altering the property; these include acquiring and/or relocating a building, preparing emergency measures, such as sandbagging, and flood proofing structures.
O&M / Operations and Maintenance: The routine procedures that ensure optimal performance of levee systems.
Overtopping: Water levels exceed the crest elevation of a levee and flow into leveed areas.
Overtopping breach: A breach whose cause is known to be a result of overtopping; the levee has been compromised after overtopping and must be repaired to function prior to the next event.
Periodic Inspections: As conducted by the Levee Safety Program, a rigorous inspection that occurs every five years, which verifies proper operation and maintenance of the levee system, evaluates its structural stability, compares constructed criteria to current criteria, identifies features to monitor over time, and improves the ability to communicate the overall condition of the levee.
Rehabilitation: As related to floods, rehabilitation refers to any action or series of actions focused on the repair of an active flood control work such as a levee or floodwall to return the levee or flood control structure to its pre-flood/pre-storm level.
Rehabilitation and Inspection Program (RIP): A program established by the Army Corps of Engineers that provides for inspections of constructed federal and non-federal projects damaged by floods and storms. Financial assistance for levee rehabilitation is limited to repairs or restoration to the project’s pre-disaster condition and level of protection. An initial eligibility inspection must be performed by USACE and subsequent maintenance inspections are required.
Risk: The probability for an adverse outcome. Risk = (Frequency of an event) x (Probability of occurrence) x (Consequences).
Routine Inspections: As conducted by the Levee Safety Program, an annual visual inspection of a levee system that verifies proper operations and maintenance procedures.
Special Flood Hazard Area (SFHA): As defined by the National Flood Insurance Program (NFIP), the land area covered by the floodwaters of the base flood on NFIP maps. The SFHA is the area where the NFIP's floodplain management regulations must be enforced and the area where the mandatory purchase of flood insurance applies.
Sponsor: A non-federal entity having responsibility for operating and maintaining a levee system. Sponsors who maintain levee systems to acceptable standards set by the Army Corps of Engineers may be eligible for emergency flood control and rehabilitation assistance through the Rehabilitation & Inspection Program (RIP).
Structural Approaches (see also Nonstructural Approaches): Structural approaches to flood proofing are intended to prevent flooding by altering the flow of floodwater; these include constructing levees or dams, or modifying a waterway’s channel.