FLOOD06826

• County: Statewide
• Basin: Statewide
• Title: National Economic Development Procedures Manual-Urban Flood Damage
• Date: 3/1/1988
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Educational/Technical/Reference Information

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STEP FOUR: OUTLINE AREA FLOODED

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Definition, The area flooded simply refers to the geographic extent

of flood inundation for one particular event or several magnitudes of

flooding, At a minimum, the geographic extent of three areas should be

shown: 1) the floodway, which is the natural storage area along the river

or stream; 2) the one-percent chance (one hundred year) flood;

and, 3) the SPF flood level, It may also be useful to show the limits of

the flood of record (the largest flood recorded) or the most recent major

flood, A map of the area flooded is shown in Figure V-6,

Use. The area flooded is outlined on a map primarily to let the

economist know what floodplain property needs to be surveyed, and the

degree of attention to give each area, Effort should not be wasted on

surveying areas with too little expected average aEnual damage to support

flood protection. 'Both the economist and the project planner can get a

general idea in the early stages of planning of what type of project might

be economically justified by observing the amount and type of property

subject to flooding at various frequencies.

The floodway is important to identify because the National Flood

Insurance Program mandates that participating communities completely

restrict floodway development, Floodways are subject to particularly high

velocities and subsequent danger for inhabitants, Floodway development

along Some streams can also raise water surface elevations for given

frequencies of flooding.

The one-percent flood is important because of Federal Insurance

Administration rules against development and rebuilding within that zone.

V-17