Hybrid Coral Reef Restoration

• Hybrid coral reef restoration is a cost-effective, nature-based solution for protecting vulnerable coastal populations.
• Coral reefs help prevent flood damage to tropical coastal communities by acting as flood barriers.
• They are especially effective for dense, fast-growing populations with lower-middle incomes.
• Regionally modeled valuations show hybrid coral reef restoration reduces flood risk in Florida and Puerto Rico's 1005 kilometers of reef-lined coasts
• Up to 20% restoration of the region's coral reefs could provide greater flood reduction benefits than costs.
• Reef habitats are most effective when shallow, nearshore, and fronting vulnerable communities since reef impacts and loss are at their greatest.
• Minorities, children, the elderly, and those below the poverty line can gain more than double overall hazard risk reduction benefits by taking nature based solutions.

Introduction to Coastal Hazards

• Coastal flooding and erosion from extreme weather events affect thousands of vulnerable communities worldwide.
• Coastal hazards are expected to worsen this century due to population growth and sea-level rise from climate change.
• The United States spends 500 million per year mitigating coastal hazards.
• Billions of dollars are spent recovering from tropical cyclones.
• Developing risk reduction and adaptation strategies to reduce coastal flooding and related hazards is an urgent need.

Coral Reefs as Protection

• Coral reefs reduce coastal flooding by dissipating up to 97% of incident wave energy.
• Coral reefs offer coastal protection, including erosion control.
• Coral reef-lined tropical coasts face increased flooding due to climate change and sea-level rise.
• Coral reefs protect over 200,000 coastal residents from flooding annually.
• These populations are denser, growing faster, and composed of more people from lower-middle income groups.
• Corals provide defense benefits in the US
• A rigorous, process-based, high-resolution risk modeling system was used to quantify defense benefits.
• Existing US coral reefs avert over $1.8 billion in flood damages affecting over 18,100 people per year.

Reef Restoration as Mitigation

• Reef restoration helps reduce coastal risk and increase the resiliency of communities.

Restoration Objectives

• Restoration can rebuild habitat and populations that were lost because of storms and human disturbances.
• It can improve resilience to future disturbances.
• Restoration efforts can focus on coral species, such as replanting
• Actions can combine with structures to restore reef morphology.
• Ecological restoration involves planting to increase the number of living corals in areas with solid benthic substrate and vertical structure.
• Methods can be by collecting/rehabilitating broken fragments, propagating colonies, or transplanting coral colonies.

Structural Reef Restoration

• Development of hybrid reefs involves existing rocks/dead coral or deployment of constructed metal or concrete forms.
• Needs and approaches of coral and reef structure restoration are similar to those for oyster reef restoration.

Hybrid Reef Restoration

• It replaces the lost height and complexity of reef habitats, benefiting coral and human communities.
• Reefs have been lost due to long-term bioerosion and physical damage in Pacific/Caribbean reefs.
• Structures can be seeded by coral recruitment or outplanted with corals from elsewhere.
• Enhancement of structural complexity increases coral recruitment by 400 to 600%.
• Enhancing structural complexity promotes different functional groups, like corals and fish, in restoring degraded reefs.
• The goal is to deliver ecological and ecosystem service benefits to natural/human communities via nature-based solutions.
• Ecosystems are protected, managed, or restored to address societal and environmental problems.

Green Restoration

• Outplanting corals on the seabed increases hydrodynamic roughness.

Gray and Green Restoration

• Attaching corals to deployed structures(increasing reef height and decreases water depth) increases hydrodynamic roughness

Hydrodynamic Changes in Restoration

• Increases in hydrodynamic roughness and reduction in water depth reduce wave energy and wave-driven water levels.
• Reduction in turn, reduces wave-driven run-up and flooding

Hurricane Aftermath

• After Hurricanes Irma and Maria, the US government considered large-scale coral reef restoration to reduce risk and increase resiliency.
• Post-disaster hazard mitigation funding requires benefit-to-cost analyses (BCAs).

Implementation Obstacles

• Restoration projects for hazard mitigation need to meet the same BCA criteria.
• This framework has not been assessed for natural infrastructure alternatives used for US federal hazard risk mitigation funding
• Oceanographic, hydrodynamic, ecologic, social, and economic models were combined to assess flood risk reduction benefits.

Modeling Projects

• Assessed potential reef restoration projects along >1005 km of Florida and Puerto Rico shorelines at 10-m2 resolution.
• Used multidecadal wave and coastal water-level data, high-resolution bathymetric/topographic/benthic habitat data.
• Also physics-based numerical hydrodynamic models that resolve nonlinear wave and coastal water-level processes.
• Water depths and flood zones identify at-risk people, buildings, direct/indirect economic impacts.

Theoretical Restorations

• The restoration could produce a 1.25-m reef height increase and greater hydrodynamic roughness(5 m in cross-shore direction)
• A 1m high artificial structure is put in place with .25m high corals on top.
• The study resulted in quantification of benefit-to-cost ratios by using hybrid methodology, shows role of geomorphology/community, and gives new insights into social differences between Florida/Puerto Rico

Results

• The flood zone of a 100-year coastal storm will decrease by 19.7 km^2

Flood Mitigation

• Coastal flooding reduced in regions by increased friction and wave breaking caused by an increased roughness and height by restored hybrid reefs
• People, property, economics would be protected in most locations.
• Mitigation is most effective in low-lying areas away from beachfronts

Geophysical Factors

• Restoration is effective when there is a reduction in total water level when restoration occurs.
• Restoration on narrower reef complexes is effective.
• It is more effective closer to shore.
• Restoration effectiveness on shallower water depths.
• Narrow reefs at shallow depths closer to shore effectively reduce flooding

Risks Reduced

• There would be 14,734 protected persons
• Property damages would reduce by $1.006 billion
• Economic activity would reduce by $797 million in 2023 US dollars.
• Reduced risk by 18.6% for people, 20.4% for property damage, 14.9% for economic disruption.

Reduced Flood Zone

• 1-in-100-year flood damages would occur 20% less frequently.
• Damages in Florida are $161 million(+14.2%)
• Damages in Puerto Rico are $20 million(+24.6%)
• Econ activity in Florida would be $174 million(+12.2%)
• Econ activity in Puerto Rico would be $36 million(+22.1%)
• +0.7% benefit for Floridian public
• +51.9% benefit for Puerto Rican private sector

EAB Figures

• Average EAB for undeveloped zones are .002-0.201, averages being .057 and 2.18 for developed zones
• Averages change to, $182 in Culebra,to $34 000 in undeveloped zones,
• Puerto Rico increases to $12 000
• Developed zones increase to $137 000

BCA

• Restoration costs 3 million per km to be conservative
• Benefits >$378 million a year in Florida /Puerto Rico but are 10m
• Areas are reduced due needs in adaptation
• Areas increase economic value
• Best areas for restoration cost highly, developed, located at shallow water

Hybrid Reef

• Coral + general restoration
• Costs are variable, high labor and construction needed
• .5 - 3 million, likely under 2 million per km construction fee averages
• 3 million in used dollars for an estimate.
• Maintenance is a factor
• 3% on benefits/year
• BCR 1 is "cost effective" due to new, cheaper technologies
• Coral reduction in risk is 20%

Coastal Benefit Breakdown

• Increased savings and decreased flood exposure will depend on quality model and the areas
• The most affected areas are low zones , and the study showed some areas better protected than others

Social Econ Benefit differences

• Increased people in FL
• Econ benefit is FL is at 849$,Puerto Rico is 173$

Restoration is cost-effective due to some factors such as...

• Increased social and eco benefits for FL
• Reduced risks on both land
• Decreased maintenance
• Low discount and long lifespan

Mitigation

• Restoration reduces flooding and erosion
• High values need the best restoration

Differences in Models

• Used SWAN for reduction
• Coastal damages and economic loss are reduced by using data from XBeach

Flood Risk model details

• All numbers, including socioeconomic factors, were derived from reputable sources like US and FEMA