The ever increasing importance of long waves due to accelerated climate change and the impact on vital functions such as coastal stability and port operations.

1. ©
Marco
Pluijm
18/02/2017
Waves
during
the
2015-­‐16
El
Niño
“were
exceptional
and
among
the
largest
ever
recorded.”
Credit:
David
Hubbard
Reason why a moderate El Nino resulted in
unprecedented erosion of the Pacific coastline
Marco Pluijm M.Sc.
Senior Expert Ports and Coasts
Reference is made to the excellent article “Last year's El Nino resulted in
unprecedented erosion of the Pacific coastline: study”, published by the University of
California on Phys.org on February 14th
, and quoting:
“Last winter's El Niño might have felt weak to residents of Southern California, but it
was in fact one of the most powerful climate events of the past 145 years.”
“If such severe El Niño events become more common in the future as some studies
suggest they might, the California coast—home to more than 25 million people—may
become increasingly vulnerable to coastal hazards. And that's independent of
projected sea level rise.”
"Wave conditions and coastal response were unprecedented for many locations
during the winter of 2015-16," said lead author Patrick Barnard, a geologist with the
USGS. "The winter wave energy equaled or exceeded measured historical
maximums along the West Coast, corresponding to extreme beach erosion across
the region." Unquote
This is highly interesting and valuable information. First of all because it supports the
picture we see all around the world these days. The picture of accelerated climate
change and related effects, often demonstrating it’s effect as a kind of surprise, still.

2. ©
Marco
Pluijm
18/02/2017
A very significant example is the increase in frequency of occurrence and duration of
long wave energy, including bound long waves and/or infra gravity waves. The type
of waves usually barely visible and often hard to record properly due to their
characteristics. Wave buoys and tidal gauges don’t pick them up. Pressure sensors
do, but their activity will only become recordable and visible once the sampling
frequency has been set up properly. Reason why adequate data about these hard to
see and detect long waves are usually very scarce.
The direct way of getting confronted with their actual presence and characteristics is
by their physical impacts. Once beaches are washed away under what looks like
moderate conditions. But the real driving force behind it are these long wave
phenomena.
Another way of getting confronted with their presence, is for instance when a ship is
properly moored in a port and still moves a meter or more back and forth, every 5 or
7 minutes, each time heaving about 20 centimeters too. Which is an absolute
nuisance for efficient handling of containers.
The number of affected ports around the globe is increasing rapidly, following the
climate change induced increase in long wave activity. Port authorities try to mitigate
for at least the horizontal movement by means of dynamic mooring control in some
cases. Still without reducing the even so obstructive vertical movements.
One of the things we learn from the article referred to, is that the same long wave
phenomena have a huge impact on coastline stability as well. Which of course was
known, but the hidden danger is in the fact that in a case like this, where the surface
weather seems to point into a moderate El Nino season, the actual wave attacks on
the coast are severe. Caused by the long wave phenomena and energy rather than
by the much shorter wind waves themselves.
Consequently, in case someone wants to control either one of these two impact
phenomena, it’s the long waves that need to be dealt with rather than the short
waves. Which waves still may look spectacular, but are not the driving force behind
what’s happening. The long waves are the real challenging ones.
Which all together means switching and moving on to a different type of coastal
protection, port layout and breakwater concepts and solutions.
In terms of coastal protection this will mean making better use of existing or to re-
instate natural coastal features such as sand banks, sand waves, submerged
barriers, etc. In order to create a much wider energy dissipation zone rather than
keep on focusing on just the traditional breakerline and run up zones.
In terms of improving the operational performance in the affected ports, changing the
breakwater concept is about the only option. While in case of new to build ports, the
use of traditional single breakwaters should be avoided and replaced by either a
sequential breakwater or a combination with a broad crested, levee type of spilling
breakwater. Due to the long wave character, moving around the layout appears not
to be a real differentiator. The whole water level keeps on going up and down with
the same order of magnitude of say 20 centimeters (West Africa), every cycle.
This all being so, implementation however still might be a somewhat hard nut to
crack. The affected ports are not always keen to acknowledge that they have been
bitten by this nasty climate change bug and try to ride it out with temporary mitigating
measures. With very limited actual effectiveness. Often having their clients pay for it,

3. ©
Marco
Pluijm
18/02/2017
stuck in the middle where it comes down to who’s actually responsible for something
which wasn’t really known nor understood properly at the time, say five or ten years
ago. When in addition the vessels were smaller too and less critical to operate.
For new to build ports and terminals there’s no excuse. Any new facility shall
undergo the full “accelerated-climate-change-check” and be properly planned and
designed accordingly in order to avoid any unwanted effects.
All together, developing and proposing smarter and more coastal-natural dynamic-
supportive solutions, is beneficial to all.
It’s a rather complex matter when it comes down to politics and traditions. And will
take some time to bring parties closer to one another and actually go for it. With
some local, small scale exceptions here and there.
Still the climate does what it wants to and does it much faster than most of us so far
have anticipated for.
Articles as the one referred to are good communications to keep de dialogue going.
And to stimulate writing these communications and participate in a global
conversation about what’s going on and can be done about it.
The basic principles have been identified and solutions are within reach. One of the
bottlenecks can still be the availability of adequate data, expanding monitoring and
developing adequate instrumentation and data analyses techniques.
Despite, knowing all this, implementation should start well before the impacts
become visible. Because one thing is for sure, if it’s not happening at your door step
right now, for sure it’s about to come out soon.
Ref: https://phys.org/news/2017-02-el-nino-gobbled-california-beaches.html#jCp