©  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.

©  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,

©  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