[Coral-List] Coral reefs for coastal protection: A new methodological approach and engineering case study

[Jose Borrero]

Dear Curt,

Thank you for the link and congratulations on the project.

I saw the presentation on this project at the ICRS in Hawaii a few years back, I think your co-author Boze Hancock presented it.

Indeed it reinforces the notion that reefs (of coral or whatever) play an important role in shore protection due to the wave energy and/or current dissipation that they provide.

Reef degradation that results in a net increase of wave energy hitting the shoreline is a major contributor to erosion problems in many places around the world.

We have proposed a similar approach for a beach in Mauritius, but we are still waiting for the final green light for implementation.

You can see our e-poster (from the Hawaii ICRS) here:
https://www.eposters.net/poster/design-and-assessment-of-climate-change-adaptation-and-erosion-control-measures-for-mon-choisy

One issue that frequently arises however, is the unfortunate conundrum that the wave energy dissipation afforded by a structure is directly related to its submergence. The deeper the structure, the less wave energy it blocks.

Yet, the most erosive events occur during storm conditions when water levels are high (i.e. storm surge from pressure, wind and wave set up…). So care must be taken in the design that the hydrodynamic regime is not made even more erosive during storm conditions due to compression of the surf zone and/or increased water levels shoreward of the structure. These features can be difficult to model and measure in the field.

The situation in Grenada is a bit different from our Mauritius case in that your site is on a windward shore that has a relatively consistent wind wave climate producing constantly erosive conditions that are exacerbated by the degradation of the reef (and rising sea levels?).

In our Mauritius example, we are on the leeward side of NW Mauritius and there is essentially no sediment transport 99% of the time. All of the erosion occurs when there is a water level set up inside the lagoon that drives a northward current combined with wave energy crossing the barrier reef and directly impacting the shoreline. We also have the problem in the Mauritius case that the hardened shoreline upstream of our site and the degraded reef offshore have <nearly> eliminated the supply of new sand to build the beach back up. We all know reefs/breakwaters don’t magically create sand!

As such, our Mauritius design is more focused on producing ecological and recreational enhancements as opposed to the purely ‘shore protection’ aspect.

Anyway, i’m sure we’ll see more of these examples in the coming decades as more and more beach communities face the double-whammy combined effects of degraded reef and increasing sea-levels. As designers of these projects it is really important to understand all of the factors involved in an erosion ‘problem’ and not to fall in to the ‘everything [is] a nail’ mode of problem solving!

If only we could clean up all the water and get coral to grow faster!

-jose

--
Jose C. Borrero Ph.D.
eCoast Ltd.
http://www.ecoast.co.nz

http://www.jocabo.net




On 13/02/2018, at 12:34 PM, Storlazzi, Curt <cstorlazzi at usgs.gov<mailto:cstorlazzi at usgs.gov>> wrote:

Colleagues,

Check out the new paper in the Journal of Environmental Management:


*Coral reefs for coastal protection: A new methodological approach and
engineering case study in Grenada
<https://www.sciencedirect.com/science/article/pii/S0301479718300240>*



Just published by a team at UC Santa Cruz and The Nature Conservancy, this
study measures the protective role of coral reefs in Grenville Bay,
Grenada, and evaluates one of the first uses of reef restoration as natural
infrastructure specifically designed to reduce risks to people and
property.  Highlights:


•  Coral degradation is directly linked to the severe erosion which
threatens Grenville Bay, Grenada


•  This the first time a shoreline equilibrium model used by coastal
engineers to study breakwaters is applied to coral reefs


•  The study evaluates one of the first reef-based adaptation projects
specifically designed for climate adaptation and risk reduction of coastal
communities



“We are able to apply coastal engineering tools and models to support coral
reef science and management. Ours is one of the first studies to directly
show, with evidence from the field sites and engineering models, the
impacts of coral reef loss on shorelines.” – B.G. Reguero, lead author



You can find the paper here: https://authors.elsevier.com/
sd/article/S0301479718300240


Apologies for any cross-posting.....


Curt

--
---------------------------------------------------
Curt D. Storlazzi, Ph.D.
U.S. Geological Survey
Pacific Coastal and Marine Science Center
2885 Mission Street
Santa Cruz, CA 95060
(831) 460-7521 phone
(831) 427-4748 fax

Staff web page:
https://www.usgs.gov/staff-profiles/curt-d-storlazzi
Coral Reefs:
*https://coralreefs.wr.usgs.gov/ <http://coralreefs.wr.usgs.gov/>*
Sea-level Rise and Atolls:
*https://walrus.wr.usgs.gov/climate-change/atolls/
<http://walrus.wr.usgs.gov/climate-change/atolls/>*
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