TABLE 7.1 Flood Hazard Module Use Levels in FEMA’s HAZUS-MH

HAZUS Level

Base Elevation

Estimates of Flood Hazard

Loss Estimates

Inland

Coastal

Hydrology

Hydraulics

Wave Model

Inventory

Damage Function

1. Default databases

Any available NED

USGS regression

Default resistance equation

Default 1-D wave model

Census track data

Default damage curves

2. User-modified data

User supplied

User-supplied Qp at river reach

Default resistance equation

Default 1-D wave model

Modify inventory

Modify parameters

3. Expert-supplied data

User supplied

Hydrologic model output at reaches

Hydraulic model output (predefined BFE surface grid)

Modify wave parameters

Detailed building or facility types

Community-based damage functions

NOTES: 1-D = one-dimensional; NED = National Elevation Dataset.

to simple hydrologic, hydraulic, and wave models, which are suitable only for preliminary analyses, HAZUS-MH allows the user to supply model output, building inventory data, and localized building and facility level damage curves. The higher levels of HAZUS require disciplinary expertise, as well as significant expertise in database management and operations.

HAZUS is used by federal, state, and local governments to estimate potential flood damage. For example, it formed the basis for damage information developed as part of the risk and reliability sections of the recently completed Interagency Performance Evaluation Task Force (IPET, 2008) report on risks in the New Orleans area following Hurricane Katrina. The availability of HAZUS, combined with information already gathered as part of floodplain mapping, places FEMA’s floodplain mapping program in a position to develop effective hazard-consequence flood maps.


Finding. The mapped location of buildings inside or outside an SFHA does not adequately convey a sense of flood hazard. Flood risk can be assessed and communicated more effectively in terms of the relative elevations of the structures and facilities in the flood hazard area.

CONCLUSIONS

The principal product created by FEMA’s Map Modernization Program is digital flood maps to replace paper flood maps. In some cases, this conversion was made using updated or new hydraulic, hydrologic, and topographic data. These maps represent an improvement in the quality of flood hazard information provided to the public. Where paper maps have merely been converted to digital representations, the value added has been minimal, and these maps will have to be updated to communicate flood hazard more accurately. This task must be accomplished to fully meet the objectives of the FEMA Map Modernization Program.

New technologies offer FEMA the opportunity to vastly improve the accuracy and thus the utility of digital maps. Current procedures for producing riverine and coastal maps can be improved, and these improvements are economically and socially justified. Improving the accuracy of flood maps by using higher-quality topographic data as well as updated hydrology and hydraulics enables communities to more accurately portray flood hazard and mitigate the risk to existing structures. Coastal flood mapping has revealed hazards beyond simply inundation—buildings can be damaged by wave action and by erosion of their foundations. Refining current coastal flood zone definitions to correspond more closely to actual flood damage during coastal flood events could lead to more accurate and consistent insurance ratings and thus to a better sense of flood hazard.

FEMA’s RiskMap goals open the door to the possibility of significantly improving the communication of risk to those in the most hazardous areas as well as those responsible for mitigating the risk. New technologies will enable FEMA to portray information about the flood hazard and flood risk through multiple means and to tailor the information to meet the specific



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