Mapping the Zone: Improving Flood Map Accuracy

FIGURE 5.3 Current FEMA coastal mapping procedures used in Mississippi and Louisiana. In these studies, two-dimensional surge (ADCIRC) and wave (SWAN for Mississippi and STeady State spectral wave [STWAVE] for Louisiana) models are used to calculate the 1 percent annual chance stillwater elevation, and CHAMP/WHAFIS is used to calculate overland wave crest and post-storm topography. The 1 percent annual chance SWEL and the wave crest are then combined to calculate the BFE. NOTE: FIRM = Flood Insurance Rate Map.

TABLE 5.1 Elements of FEMA’s Current Coastal Flood Mapping Process

Empirical and Probabilistic Input Data	Coupled Surge and Wave Models for SWEL Calculation	Wave Crest and BFE Calculation
Hurricane data Probabilistic hurricane wind model data Hurricane ensemble and return period data Bathymetric data Pre- and post-storm topographic data	2-D storm surge model 2-D wave model	CHAMP/WHAFIS erosion and wave calculations along one-dimensional (1-D) transects Post-storm topographic data to verify CHAMP/WHAFIS results

Table of Contents

Front Matter R1-R14

Summary 1-6

1 Introduction 7-12

2 Flood Mapping and Flood Insurance 13-24

3 Elevation and Height Data 25-40

4 Inland Flooding 41-66

5 Coastal Flooding 67-78

6 Benefits and Costs of Accurate Flood Mapping 79-88

7 Mapping and Risk Communication: Moving to the Future 89-100

References 101-104

Appendixes 105-106

Appendix A: Methods for Estimating Base Flood Elevations in Approximate Studies 107-108

Appendix B: Biographical Sketches of Committee Members 109-112

Appendix C: Glossary 113-120

Appendix D: Acronyms and Abbreviations 121-122