This document summarizes a pilot project to re-engineer coral reefs off the coast of Grenada for coastal protection. The project involved (1) modeling wave dynamics and sea level rise scenarios, (2) designing and constructing pilot submerged breakwater structures made of quarry stone and concrete blocks with relocated corals, and (3) monitoring the structures to evaluate their ability to attenuate waves and reduce coastal flooding, with the goal of demonstrating the role of coral reefs in coastal protection. Over 1,500 person-hours and $7,000 per meter were required to construct the 30-meter pilot structures, which were then monitored to evaluate lessons learned for improving coastal resilience through similar nature-based solutions.

1. Re-engineering of coral reefs for coastal
protection: a pilot experience
in the Caribbean
Borja G. Reguero, P. Kramer, B. Hancock, M. Beck, V. Agostini, R. Blyther
G. Diaz, J. Lara, G. Barajas

2. “AT THE WATER
EDGE”
Grenville Bay,
Grenada
1. Assess national and local vulnerability
2. Addressing climate and disaster risks through an
integrated approach
3. Helping communities understand and assess their social,
ecological, and economic risks and together build
solutions
4. Making informed decisions—Challenges in data
availability, access, and management
5. Developing integrated adaptation and disaster risk
reduction plans that recognize the role of nature
6. Building local, national, and regional capacity
Local community
NGO staff
Nat. Gov.
regional managers
2011-2016
The Nature Conservancy is working with partners to

3. Coastline
Evolution
(80s-12)

4. Current & sediment tranport
Mangrove Lost
Field inspection (28 Jan.) and local reporting
The Coastal Problem

5. Deeper reefs
shallower reefs
Nav. channel
Seagrass & algae
Reef rubble
sand

6. CMS
BOUSS
RANS
COASTAL MODELING & Analysis of AlternativesMETHODOLOGY
& APPROACH
2 Goals:
1. Demonstrate the role of the coral reefs in the bay system
2. Study alternatives for design

7. Long – term
changes in the
dynamics
Scenario
A1B A2 B1
SLR
estimate
0.50 0.53 0.37
• Wave climate
Reguero et al (2013)
• SLR - historical
Losada et al. (2013)
• SLR - projections
Slangen et al. (2012)
Hs
Dir EF
SLR

8. The role of the
reefs in the bay
Reguero et al (2013)
Camus et al (2011)

9. Hsu and Evans (1989); Gonzalez and Medina (2001); Hsu et al (2010)
Equilibrium planform concept

10. The Proposed solution

11. The Proposed solution

12. Effect on
wave
attenuation

13. Wave Height

14. Wave attenuation across Wave Climate ConditionsFor multiple
sea states…

15. Effect on
Run-up
(short wave
component)

16. The Pilot

17. AN HOLISTIC
APPROACH TO
RESTORATION
BLENDING ECOLOGY AND ENGINEERING

18. Preparing the baskets

19. Navigating the barge

20. Unloading a barge

21. Divers carrying and packing the baskets

22. The reef at low tide

23. Clips to connect the baskets

24. 2-tier pilot submerged breakwater structure (this one with
blocks) with corals from the nursery placed along their sides

25. A completed 3-tier pilot, placed further inshore on a seagrass bottom to examine
differences in placement, height, and performance measures with the offshore reef
structures.

26. A view from the top of one of the completed pilot at low tide

27. Grenville Reef Pilot Project
By The Numbers
• Total length of pilot submerged breakwater built: ~30 meters (100 feet).
• Number of diver community man hours for pilot: 1,500
• Quarry stone mined and placed in structures: 70 tons
• Concrete building blocks placed in structures: 2,400
• Amount of 5/8th rebar steel: 44,000 feet
• Number of welds for all gabion baskets: 41,000
• Average live coral cover currently on Grenville reef flat ~1%
• Corals relocated: ~1,250 (~ 240 of these were re-planted on
structures)
• Cost (~ $7,000 US/m). 1/3rd the cost of a traditional
breakwater

28. - Forensic analysis of erosion causes
- Surf beat (non-linear interactions can be responsible of
substantial flooding) & 3D effects
- Monitoring and learning
- Scale up in other areas
- Lessons for successful implementation
- Evaluation of protection provided by reefs globally and
regionally / Mapping Ocean Wealth -
http://oceanwealth.org
- Extend to other ecosystems
Next steps

30. EFFECT

31. Borja G. Reguero borja_reguero@tnc.org
Thank you

32. (a) (b)
(c) (d)