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What is Floodplain Management

Floodplain management is the operation of a community program of corrective and preventative measures for reducing flood damage. These measures take a variety of forms and generally include zoning, subdivision, or building requirements, and special-purpose floodplain ordinances. Mitigation practices, such as floodproofing or retrofitting a flood prone building, are equally beneficial to reducing flood damages to the community.

Before the creation of the National Flood Insurance Program (NFIP) in 1968, floodplain management as a practice was not well established - only a few States and several hundred communities actually regulated floodplain development. For many communities, the NFIP was the community's initial exposure to land use planning and community regulations.

A community's agreement to adopt and enforce floodplain management ordinances, particularly with respect to new construction is an important element in making flood insurance available to home and businesses owners. Currently over 20,000 communities voluntarily adopt and enforce local floodplain management ordinances that provide flood loss reduction building standards for new and existing development.

Flooding is the most costly natural hazard in the US in terms of causing greater loss of life and property than all other natural hazards combined. In fact, ninety percent (90%) of all disasters are flood-related.

Floodplain management is a continuous process of making decisions about whether and how floodplain lands and waters are to be used. It encompasses the choices made by owners of floodplain homes and businesses, decisions made by officials at all levels of government, development plans made by owners of commercial floodprone land, and the judgment of farmers with pastures and fields stretching to the riverbanks. The process also focuses the attention of decision makers on the relationship between human use and the conservation of natural resources.

Louisville Metro’s Vulnerability: As a “River City”, there is a long history of flooding from the Ohio River and all of it’s tributaries. In fact, flooding threatens about 22,000 houses in Jefferson County. Flooding of the Ohio River occurs mostly during January through May. Low-lying land along the Ohio River flooded frequently and flood stage is reached an average of four times every five years. In the interior of Jefferson County, heavy rains can cause flash flooding along the local streams and large expanses of flatlands, lowlands, and former swamplands. These areas are quick to flood and slow to drain.

View Louisville’s Floodplain Management Plan.

The 100-year Flood: The 100-year flood has become the accepted national standard for regulatory purposes. It is defined as the flood event that has a one percent chance of occurring in any given year or, on the average, occurs once in a 100-year period. However, 100-year floods can and do occur more frequently.

For regulatory purposes, the floodplain is divided into two areas based on water velocity: the floodway & the flood fringe. The floodway includes the channel & the portion of the adjacent floodplain required to pass the 100-year flood without increasing flood heights. Typically, this is the most hazardous portion of the floodplain where the fastest flow of water occurs. Due to the high degree of hazard, state and local floodplain regulations require that proposed floodway developments do not block the free flow of flood water because it could dangerously increase the water's depth & velocity.

The flood fringe is the remaining portion of the floodplain, outside of the floodway, that usually contains slow-moving or standing water. Development in the fringe will not normally interfere as much with the flow of water. Therefore, floodplain regulations for the flood fringe typically allow development to occur but require protection from the flood waters through the elevation of the buildings above the 100-year flood level, floodproofing buildings so that water cannot enter the structure and watershed improvements to assure overall flood elevation does not increase. View the glossary for more flood-related definitions, acronyms, and terms.

Watershed Approach: A comprehensive and holistic approach looks at an entire watershed or floodplain as an interrelated environment and attempts to satisfy numerous needs while utilizing a long-range vision. Local communities have to look beyond the watercourse and consider the watershed in its entirety if they are to protect and conserve the resources of the streams, creeks, and rivers. While the floodplain and its resources are the centerpiece, watersheds are central to the understanding and management of resources in floodplains. Because of the cause-effect relationships inherent in the land use—watercourses can serve as an index of the health of the entire watershed. Read more about MSD’s Watershed Approach.

Hazard Mitigation: The Mitigation Division at FEMA is the organization responsible for working with communities to encourage them to adopt and enforce ordinances that meet or exceed the minimum floodplain management requirements of the NFIP.

Mitigation is the cornerstone of emergency management. It is the ongoing efforts to lessen the impact disasters have on people and property. Mitigation involves keeping homes away from floodplains, engineering bridges to withstand earthquakes, creating and enforcing effective building codes to protect property from hurricanes—and more.

In response to the unacceptable loss of life and property from recent disasters, and the prospect of even greater catastrophic loss in the future, the National Mitigation Strategy has been developed to provide a conceptual framework to reduce these losses. Hazard Mitigation involves recognizing and adaptation to natural forces and is defined as any sustained action taken to reduce and eliminate long-term risk to human life and property. Read more about local mitigation.

Download FEMA Technical Bulletins

Last Updated: February 28, 2012

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