[Coral-List] Impact of beach rock on erosion

Jacqui Michel jmichel at researchplanning.com
Mon Aug 11 13:06:16 EDT 2014

Although every site is different, depending on the wave climate, direction, water depths, etc., in most cases, beach rock in the nearshore acts as a natural breakwater that SLOWS the rate of beach erosion. It's removal will surely increase the rate of erosion of the shoreline.

There is a good case study that appears similar to what you describe, where the beach eroded and the formally intertidal beach rock became subtidal in the nearshore:

G. Alexandrakis, G. Ghionis, and S. Poulos (2013) The Effect of Beach Rock Formation on the Morphological Evolution of a Beach. The Case Study of an Eastern Mediterranean Beach: Ammoudara, Greece. Journal of Coastal Research: Special Issue 69 - Proceedings, Symposium in Applied Coastal Geomorphology to Honor Miles O. Hayes: pp. 47 – 59.

Jacqueline Michel, Ph.D.
Research Planning, Inc.
1121 Park Street                P.O. Box 328
Columbia, SC 29201        Columbia, SC 29202
803-256-7322 (o)
803-513-5650 (c)

Message: 4
Date: Sat, 9 Aug 2014 14:06:19 +0500
From: Barbara Gratzer <barbaragratzer at gmail.com<mailto:barbaragratzer at gmail..com>>
Subject: [Coral-List] impact of beach rock on erosion
To: Coral-List <Coral-List at coral.aoml.noaa.gov<mailto:Coral-List at coral.aoml..noaa.gov>>
Cc: Ahmed Nazim <nazim at cms.li<mailto:nazim at cms.li>>
Message-ID: <834226FF-2FBB-4523-BA87-59F901711CD3 at gmail.com<mailto:834226FF-2FBB-4523-BA87-59F901711CD3 at gmail.com>>
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Dear Coral-Listers,

My question is not directly related to corals, however I hope there are some people out there who can share their experience, opinion and expertise.

Maldives are well known to suffer from tremendous erosion problems over the past few years. Natural reasons are natural shifts (up to several metres per year), mass bleaching events, the tsunami in 2004, who probably allocated huge sandmasses, thereby influencing under currents throughout the Atolls, and loss of natural vegetation such as sand stabilising trees.

I am working in a resort in Baa Atoll where we are trying to identify other mechanisms that influence beach erosion. Our aim is to use as natural techniques as possible to keep sand shifts to a minimum. It was suggested that beach rock, which has eroded over the past 20 years and now is about 15 - 20 metres away from the shoreline, additionally adds to beach erosion.
We assume: Since a wave brakes when the wave hight is less than half of the wave length, the waves are crashing on the beach rock rather than on the beach, thereby creating high turbulence in between the rock and the actual shoreline where waves would naturally brake. We further assume this turbulence creates larger sand shift movements. We are wondering if beach rock, once exposed, should be removed and natural walls such as coral walls should be enhanced on the crest instead.

Is there any available literature about currents near beaches, turbulences on the reef flat or impacts of exposed beach rock on currents?

I am looking forward to receiving your answers and thank you in advance!



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