20
DELTARES, JANUARY 2014
A
pproximately 30 per cent of marine
coasts are reef coasts. The species-rich
and productive coral reefs are tourist
attractions in many tropical locations,
and so they generate considerable
indirect revenue. But coral does more
than this. Throughout the world, approximately
500
million people benefit from healthy coral in one
way or another. The very existence of approximately
30
million people depends on coral. Most of these
people live on low-lying coral islands or atolls. Reef
destruction here not only leads to more coastal
erosion, it can also affect freshwater supplies in the
ground. When that happens, all the local inhabitants
can do is emigrate.
Expensive measures
Coral also protects the coast by damping waves and
currents. All this means that coral can represent a
value of no less than one million euros per square
kilometre annually, simply because expensive, man-
made coastal protection is not needed. So there are
good reasons to protect the coral. Even so, this natural
breakwater is faring badly.
It is only when the coral has gone that it becomes
clear how fast the coast can erode, requiring expensive
measures such as sand replenishment and sea defences.
In time
It recently became possible to determine the
importance of particular stretches of coral for coasts by
using Deltares computer models to calculate the impact
that these often unpredictable structures have on waves
and currents. In this way, the role that a coral reef plays
in coastal protection can be mapped out for any given
stretch of coast. Ap van Dongeren, a coastal expert with
Deltares, explains how everything started a number
of years ago. At that time, researchers from Stanford
University in the United States were able to access
Delft3D as part of the open-source agreement between
Deltares and the American Navy. Stanford used the
Delft3D to model complex circulation patterns in the
reef surrounding Hawaii. The doctorate student working
on that project, Ryan Lowe, moved on to become a
professor in Australia, where he conducted field trials
on the Ningaloo reef, demonstrating how important
long waves are. Ap van Dongeren was involved in the
subsequent validation of the XBeach model using those
data, and supplementary scale trials were conducted at
Deltares. This resulted in important insights about the
currents that distribute sediments, nutrients and larvae
on and around the reef.
Coral restoration
There are benefits for both sides: the new data
make it possible to measure how much coral reefs
mitigate wave energy and how this contributes to
coastal protection. The process knowledge is also
very important for the health of the coral itself. Victor
Langenberg, an ecologist and coral expert: ‘Coral
reefs establish their own foundations and there is
a delicate balance between their growth and the
physical conditions that allow them to survive in a
highly dynamic coastal environment. Integrating this
physical and ecological knowledge makes it possible
to deliver customised consultancy, not only to coastal
managers but also to dredging companies and
hydraulic engineers, allowing the coral to be protected
as well as possible and, where necessary, restored.’
For more information:
ap.vandongeren@deltares.nl
THE CONCEALED
STRENGTH OF CORAL
The global tourist appeal of coral is well known. People are less aware that coral
has an important role to play in coastal protection and freshwater supplies.
Recently, an approach was developed that allows us to calculate how valuable
that role is: it can be as much as one million euros per square kilometre
annually. This should be kept in mind before coral disappears completely as a
result of climate change, sewage discharges or harbour construction. Coral is
disappearing extremely quickly.
BY MARCEL MARCHAND
PHOTO: ISTOCKPHOTO
DELTARES, JANUARY 2014