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