What is a flood plain?

A flood plain is an area of relatively level land – usually bordering a lake, stream, or river – that gets inundated with water from time to time.

The flood plain includes:

• The floodway, the border area of land that normally gets inundated during annual or 10-year floods; and

• The floodway fringe, which may get inundated during a "100-year" or "500-year" flood.

Flood plains typically support rich, diverse ecosystems – often called “riparian” zones or systems – that can contain 100 or even 1,000 times as many species as a river.

Soils in a flood plain usually are rich in nutrients from past floods and other accumulated organic matter. When it floods, these areas support thriving populations of microscopic organisms that, in turn, support a host of larger opportunistic species, especially birds.

While the production of nutrients peaks and falls away quickly, this surge of new growth endures for some time. It also makes flood plains particularly valuable for agriculture.

Historically, many towns, homes and other buildings have been built in the flood plain because:

• It's were water is most available.
• Flood plain land is fertile, making it attractive for farming.
• Nearby rivers represent cheap sources of transportation and railroads were often built next to waterways.
• Flatter land is easier to develop than hilly areas.

However, the same features that made flood plains attractive places for development also make them susceptible to flooding. To reduce costs, the federal government has developed incentives and new risk management and communication tools to minimize flood damages and maximize public awareness about flood risks. You can learn more at Floodsmart.gov.

 

What is flood plain management?

Flood plain management is the operation of a community program that includes corrective and preventative measures designed to reduce flood damage. These measures take a variety of forms and generally include requirements for:

• Zoning
• Subdivision or building
• Special-purpose flood plain ordinances

A community’s agreement to adopt and enforce flood plain management ordinances, particularly those addressing new construction, is an important element in making flood insurance available to home and business owners. Since standard homeowners insurance doesn't cover flooding associated with storms and heavy rains for homeowners, renters, and business owners, Congress created the National Flood Insurance Program (NFIP) as a way for property owners to financially protect themselves. The program is administered by the Federal Emergency Management Agency .

Currently, over 20,100 communities across the nation voluntarily adopt and enforce local flood plain management ordinances. These ordinances provide building standards for new and existing development designed to reduce losses from floods.

 

Flood plain management in Washington state

In Washington the state coordinating agency for flood plain management is the Department of Ecology (Ecology). Ecology works with the Federal Emergency Management Agency (FEMA) and local governments to address statewide flood hazard challenges. Ecology provides grants and technical assistance to local communities to reduce losses to life and property and protect the environmental functions of flood hazard areas or flood plains.

Ecology also assists FEMA and the Washington State Military Department's Emergency Management Division by:

• Evaluating community floodplain management programs.

• Reviewing local flood plain ordinances.

• Participating in statewide flood hazard mitigation planning.

 

Ecology's Floodplain Management team is made up of:

• A statewide National Flood Insurance Program (NFIP) coordinator.
• A mapping specialist in Olympia who works with FEMA and communities on amending and updating flood maps and related issues.
• Flood plain specialists in Ecology's regional offices in Bellevue, Olympia and Spokane.

 

Chehalis Flood 2007

 

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