FEMA works to create the most accurate FIRMs possible. Accuracy can be impacted by the quality of the underlying data, and the assumptions and approximations that must be made when conducting a coastal study. The accuracy of a coastal study depends directly on several parameters:
- The accuracy and resolution of data (i.e. topographic, bathymetric, wind, and water level data);
- The length of the historical water level and wave records;
- The incidence and severity of coastal flood events affecting the study area; and
- The number and quality of coastal flood high water marks and hydrographs (used to calibrate computer models used in the study).
In an effort to improve the accuracy and resolution of topographic and bathymetric data, FEMA and mapping partners (U.S. Army Corps of Engineers, National Oceanic and Atmospheric Administration, and others) are using Light Detection and Ranging (LiDAR) technology to gather data for many coastal studies. This topographic collection approach represents a higher level of accuracy over traditional methods.
Study accuracy also depends on:
- The resolution of the computer model grids and the ability of the grids to duplicate small-scale topographic, bathymetric, and land use features;
- The ability of the modeling schemes and algorithms to capture the physics of water flow, wave mechanics, and in some cases, erosion of dunes during the base flood; and
- The ability of statistical procedures to estimate the 1-%-annual-chance flood conditions with a high degree of confidence.
- Because of the wide variety of factors that affect study results, no single benchmark exists for assessing study accuracy.