Methods of Coastal Hazards Assessment
David M. BushRisk Assessment
GEOL 4093
Island-scale mapping 1990’s
• Originally done by hand on clear plastic overlays and tracing paper
• We didn’t know at the time that it was GIS• Andy and R/V Bicycle• Elevation• Forest Cover
Island-scale mapping1990’s
Island-scale mapping1990’s
• Analog GIS• Andy--R/V Bicycle• Elevation• Forest Cover
Florida Panhandle, after Opal (1995)
Pawleys Island, SC, after Hugo (1989)
South of Cancun after Gilbert, 1988
B ZoneA ZoneV Zone
Jekyll Island flood zones
ForestNo Forest
Jekyll Island forest cover
Preliminary Risk Assessment
FLOOD ZONE VEGETATION RATING
V --- Extreme
A None or sparse High
A Dense shrub or forest Moderate
Above A None or sparse Moderate
Above A Dense shrub or forest Low
WaterLow HazardModerate HazardHigh HazardExtreme Hazard
Jekyll Island preliminary hazard assessment
Mainland Mapping
V eg e ta tion Q 3 F lood D ata S .L .O .S .H .
F in a l R isk M ap
Tracy Rice developed this using fetch instead of SLOSH
Risk RatingParameter Extreme High Moderate Low
VegetationNone, sparse,
marsh,6
Scattered shrub,
4
Dense shrub,2
Maritime forest,
1
Q-3 Flood zones
VE and undes.,8
A and AE.6
X500,2
X,1
SLOSH Category 1-3,8
Category 4, 5, and upland,0
Ranges 16-22 11-15 5-10 0-4
Geo-indicators
• Elevation• Vegetation• Tidal range• Bluff configuration• Evidence of historical storm impacts• Type of structures
• Density of structures• Site relative to stream mouth• Soil and drainage• Other surrounding features
Geoindicators AssessmentGeneral Site Parameters
Geoindicators High Risk Moderate Risk Low Risk
Elevation < 3 m 3-6 m > 6 m
Tidal Range microtidal mesotidal macrotidal
Bluff Configuration
bare face, recent slump
vegetated face, ramp
well-vegetated ramp
Erosion rate rapidly eroding eroding stable or accreting
Evidence of storms
obvious possible none
Total Indicators Of High Risk Of Moderate Risk Of Low Risk
Camden County, GA Study Sites
St. Marys, GA
Elliots Bluff, GA
Puerto Rico Coastal Hazards Maps
1. Shoreline-setting hazards (long-term problems)2. Marine hazards (short-term impacts of storms)3. Earthquake and slope hazards (ground shaking,
landslides, liquefaction)4. Riverine hazards (historical floods)5. Development hazards (high-density or dangerous
settings)6. Engineering hazards (stabilization, nourishment,
sand mining)
Methodology, conclusion
Each coastal stretch is designated a relative hazard rating based on the following:
E = Extreme—more than 4 identifiable hazards H = High—3 to 4 identifiable hazardsM = Moderate—at least 2 hazardsL = Low—1 or no hazard
Puerto Rico
Culebra
Vieques
A portion of the Carolina, PR, Coastal Hazard Map.
The portion of Coastal Hazard Map 1, San Juan.
Mitigation
• Engineering– Strengthen or move buildings– Armor the coast
• Land Use Planning– Limit or reduce development density– Can help implement new techniques such as
clustered housing– Easiest with new developments
Our Approach to Mitigation
• Coastal landform protection, restoration, augmentation
• Mostly low cost• Many things individuals can do• Environmentally sensitive• Considers geologic/oceanographic processes
PAR For the Shore
• Preserve, Augment, Restore– Dunes (frontal and interior)– Coastal barriers of all types
• Mangroves• Shoals• River mouth bars• Maritime forest
– Add new sand to island
Pandora’s Island—Mitigation on the Beach
Pandora’s Island—Mitigation back from the beach
Pandora’s Island becomes Fantasy Island
Topographic Map of Study Area
Harrison County, Mississippi
3.2 mile study area
GIS - Map Stacking ExampleLand cover fromair photo
Flood zones
Land surface slope
Katrina damagelayer
Debris Line
Total Building Destruction