FLOOD05464

• County: Statewide
• Basin: Statewide
• Title: Reducing Losses In High Risk Flood Hazard Areas: A Guidebook For Local Officials
• Date: 1/1/1985
• Prepared For: FEMA
• Prepared By: Association of State Floodplain Managers
• Floodplain - Doc Type: Educational/Technical/Reference Information

-- Steep inland floodplain areas along smaller rivers and streams, on alluvial fans,

in some riverine flood ways, and in mudflow and high gradient sheet flow areas.

Steep areas are often flash flood areas with additional damage due to the sudden

rise of the wa ter;

-- Areas behind levees or dams where the protective structure suddenly fails or the

design capacity is suddenly exceeded;

n Areas subject to inundation when an ice jam breaks.

Debris in the water. The damage potential of floodwaters may be increased hun-

dreds of times when rapidly flowing floodwaters contain substantial amounts of rock, sed-

iment, ice or other natural or man-made materials. Normal standards for f1oodproofing

and elevation may be inadequate in the following situations:

-- Alluvial fan flood waters, carrying rocks and sediment;

-- Mudflow and mudfloods carrying sediments, rocks, trees and other debris;

-- Meandering streams carrying mud and rocks;

-- Ice jam flood waters carrying ice, rock, trees, parts of structures;

-- High velocity flood waters along rivers and streams carry rocks, sediment, trees,

lumber, bridges and other debris;

-- Flood waters from dam or lcvee failure carrying trees, rocks, lumber and other

debris;

n Coastal waves and storm surges carry rocks, gravel, lumber, and other debris,

Suddenness. Areas subject to rapid inundation by floodwaters or flash floods pose

special threats to life and property because there is insufficient time for evacuation,

emergency floodproofing or other protective measures. Suddenness is a serious problem in

four areas:

n Steep rivers and streams in mountainous or hilly areas subject to suddcn rainfall

and rapid runoff;

-- Areas behind dams or levees subject to failure or overtopping;

n Barrier islands and other areas principally along the Gulf or Atlantic coasts

which may be subject to relatively rapid hurricane storm surge; and

-- Coastal areas (principally along the west coast) subject to tsunamis.

Long-term or permanent inundation. Unlike the normal riverine or coastal flood situ-

ation where flood waters rise and fall quickly, certain areas are subject to long term or

essentially permanent flooding. In such areas, structures elevated on pilings or f1ood-

proofed are often permanently unusable and must be abandoned unless they are specially

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