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Bermuda Coastal Erosion Bermuda Coastal Erosion Vulnerability Assessment Vulnerability Assessment (Carried out for the Government of Bermuda) (Carried out for the Government of Bermuda) June 2006 by Dr. David A.Y. Smith, Managing Director, Smith Warner International Ltd. Presented at the 2nd Annual GIS Conference: Technological Applications for Coastal Protection Presentation Outline Presentation Outline
Project background Project background
Study objectives and methodology Study objectives and methodology
Key Findings Key Findings
Conclusions Conclusions
Development Guidelines. Development Guidelines.
Bermuda is a densely Bermuda is a densely populated, well populated, well developed island. It developed island. It’s s geology (loosely geology (loosely consolidated sandstone) consolidated sandstone) makes it susceptible to makes it susceptible to shoreline erosion; shoreline erosion;
This means that any This means that any coastal development coastal development (both existing and future) (both existing and future) places significant places significant pressure on its 180 miles pressure on its 180 miles of coastline; of coastline; Project Background Project Background Project Background Project Background
Shoreline protection and Shoreline protection and development have development have become important issues, become important issues,
Balance of shoreline Balance of shoreline protection & natural protection & natural appearance of the coast. appearance of the coast.
Bermuda Development Bermuda Development Plan Review Plan Review Study Study objectives objectives and methodology and methodology
To synthesize the data that already exists in Bermuda about coastal erosion;
To determine which coastal areas in Bermuda are prone to erosion and which structures and landforms are most at risk; and
To make recommendations of best practices for coastal development and conservation. Study Study objectives and objectives and methodology methodology
Review and analysis of existing information & data gaps;
Field investigations (initial data- gathering tour and a ground- truthing field visit).
Inventory of the shoreline types, shoreline structures, forms of erosion, lithology. Study Study objectives and objectives and methodology methodology
Hurricane & Storm Analysis
Day to Day Wave Analysis
Coastal Processes Modeling
Geological Analysis
Vulnerability Assessment Findings Findings – Data Gaps Data Gaps
Bathymetry Bathymetry – South Coast South Coast
Beach Profile data Beach Profile data Findings Findings - Main Shoreline Types Main Shoreline Types Sandy shorelines Flat rocky coastline Low cliffs High cliffs Findings Findings - Forms of Erosion Forms of Erosion Dune erosion Cliff erosion/spalling Horizontal/arch formation Bio-erosion 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 Water depth contours shown in gray (m) Wave Height SWAN Results INVESTIGATION DETAILS BERMUDA Daily Wave Climate (80th percentile Waves) Maximum from All Directions Day Day-to to-day wave exposure day wave exposure 0 45 90 135 180 225 270 315 0% 4% 8% 12% 16% >0 - 0.5 >0.5 - 1.5 >1.5 - 3 >3 - 6 >6 - 10 >10 Distribution of Offshore Daily Wave Heights at Bermuda Wave Height (m) Sediment Transport Sediment Transport Tuckers Town Elbow Beach Horseshoe Bay Grape Bay Astwood Pink Beach Mermaid Beach 0.96 1.09 0.14 3.70 3.83 0.13 Warwick Long Bay 2.50 2.92 0.42 Surf Side 4.10 5.06 0.96 1.76 1.98 0.22 2.16 2.33 0.17 4.47 7.44 2.98 1.82 1.95 0.13 2.31 2.59 0.28 2.60 2.89 0.29 Sam Halls Annual Alongshore Sediment Transport x10,000 cubic metres per year Positive (Southwest) Negative (Northeast) Net 0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 84 88 92 96 100 Water depth contours shown in gray (m) Wave Height Squared SWAN Results INVESTIGATION DETAILS BERMUDA 150 yr Hurricane Event Maximum from All Directions Extreme Wave Energy Exposure Extreme Wave Energy Exposure Beach Response to Hurricanes Beach Response to Hurricanes Change in Profile after 12 hour simulation -6 -4 -2 0 2 4 6 350 370 390 410 430 Distance (m) -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 Seabed Elevation (m) Bathymetry, t = 0 Bathymetry, t = 12 Difference (m) Geology Geology SWAN Results 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3 Water depth contours shown in gray (m) Static Storm Surge (m) INVESTIGATION DETAILS BERMUDA 150 yr Hurricane Event STATIC STORM SURGE Maximum from All Directions Storm Surge Wave Run Wave Run-up & Inundation up & Inundation Mean Sea Level Static Storm Surge Shoreline Slope 1 Inundation Wave Run-up v v Run-up is a function of shoreline type. (Beach, Rocky, Cliff etc.) These have been calculated and tabulated for each shoreline division Conclusions Conclusions
Storm waves are the main agent of erosion Storm waves are the main agent of erosion – less less apparent yet potentially significant are the biological apparent yet potentially significant are the biological agents (marine borers and agents (marine borers and Casuarina Casuarina).).
Day to day waves contribute minimally to the Day to day waves contribute minimally to the shoreline erosion. shoreline erosion.
No dominant trend of alongshore sediment transport. No dominant trend of alongshore sediment transport.
Erosion vulnerability dependant on geology and Erosion vulnerability dependant on geology and exposure to wave energy. exposure to wave energy.
Findings have been incorporated into the Coastal Findings have been incorporated into the Coastal Development Guidelines. Development Guidelines. Storm and Erosion Vulnerability Storm and Erosion Vulnerability Development Guidelines Development Guidelines
Consider the Bermuda image Consider the Bermuda image
Recommend appropriate shoreline Recommend appropriate shoreline protection protection
Suitable structures Suitable structures
Design considerations Design considerations
Appropriate shoreline development Appropriate shoreline development
Inundation levels & setbacks Inundation levels & setbacks
‘Community Community’ approach approach Storm surge for Category 5 Hurricane coming from the east and passing south of TCI Water depth contours shown in black (m). Static Surge (m) SWAN Modelling Results 0.7 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 Wind Speed=140knots Forward Speed=11knots Central Pressure= 924mbars Radius to Maximum Winds=20km Hurricane Attributes: CATEGORY 5 HURRICANE Coming from the East, Passing South of TCI TCI - HVA STUDY CAT 5 Hurricane 40km Another Relevant Study: Another Relevant Study: Storm Surge Mapping for Turks & Storm Surge Mapping for Turks & Caicos Islands Caicos Islands 1. Drainage pathways: light purple (and housing superimposed) 2. Sea: aquamarine 3. Low lying lands: light brown 4. Ridges: green, dark brown or deep purple. 5. A housing zone vulnerable to drainage induced flooding is ringed by a red circle. Sub Sub-Catchment Catchment (Provo, TCI) (Provo, TCI) Hazards to Consider Hazards to Consider
Hurricanes and Tropical Storms with the attendant Hurricanes and Tropical Storms with the attendant effects of wind, storm surge, and flooding effects of wind, storm surge, and flooding
Droughts Droughts
Earthquakes Earthquakes
Fire Fire
Oil spills Oil spills
Environmental Health Environmental Health
Environmental Degradation particularly sand mining; Environmental Degradation particularly sand mining;
Border Security Border Security
Accidents on land and sea, and in the air Accidents on land and sea, and in the air Vulnerability Issues Vulnerability Issues
Multi Multi-hazard exposure hazard exposure
Low Low-lying topography and coastal settlements lying topography and coastal settlements
Increasing development in sensitive areas Increasing development in sensitive areas
Destruction of natural protection Destruction of natural protection– mangroves, coral mangroves, coral reefs, beaches; inappropriate coastal structures reefs, beaches; inappropriate coastal structures
High levels of flooding on all islands High levels of flooding on all islands
Increasing population with a growing component due to Increasing population with a growing component due to uncontrolled/illegal immigration uncontrolled/illegal immigration
Inadequate awareness of risk by all sectors of the Inadequate awareness of risk by all sectors of the population population
Multi Multi-island jurisdiction island jurisdiction
Institutional capacity to handle the needs. Institutional capacity to handle the needs. Hurricanes & the USVI Hurricanes & the USVI Lenny, 1999 Lenny, 1999 Photo taken from http://stormcarib.com/reports/1999/stcroix.shtml