Identifying Solutions to Changing Wave Patterns

waves
Waves during the 2015‐16 El Niño were exceptional and among the largest ever recorded. Credit: David Hubbard

By Marco Pluijm 2017-02-23 18:53:16

A recent University of California study highlighted unprecedented erosion of the U.S. Pacific coastline saying: 

“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 U.S. Geological Survey. The winter wave energy equaled or exceeded measured historical maximums along the West Coast, corresponding to extreme beach erosion across the region.

This is highly interesting and valuable information. Firstly, it supports the picture we see all around the world these days: the picture of accelerated climate change and related effects - often demonstrating the effects as a kind of surprise, still.

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. These types of waves are 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. This is the reason why adequate data about these hard to see and detect long waves are usually very scarce.

The most direct way of being clear about their presence and characteristics is through their physical impacts. Beaches can be washed away under what looks like moderate conditions, but the real driving force behind it is these long wave phenomena.

Another way they make their presence felt is for instance when a ship is properly moored in a port and still moves a meter or more back and forth, every five or seven minutes, each time heaving about 20 centimeters (eight inches). This is an absolute nuisance for efficient handling of containers.

The number of affected ports around the globe is increasing rapidly, following a 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, but this does not reduce 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. This was, of course, known, but the hidden danger lies in the fact that in a case like this, where the surface weather seems to point into a moderate El Niño 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 the case that 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. While the short waves may look spectacular, they are not the driving force behind what’s happening. The long waves are the real challenge.

This all means we need to switch to different types of coastal protection, port layout and breakwater concepts and solutions.

In terms of coastal protection, this will mean making better use of existing or reinstated natural coastal features such as sand banks, sand waves, submerged barriers, etc. This would create a much wider energy dissipation zone rather than just focusing on traditional breaker-line and run up zones. 

In terms of improving operational performance in affected ports, changing the breakwater concept is about the only option. In new 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. 

Implementing this could be challenging. 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. It often having their clients pay for it, stuck in the middle when it comes down to who’s actually responsible for something which wasn’t really known or understood properly at the time, say five or ten years ago. Back then, the vessels were smaller too and less critical to operate.

For new-to-build ports and terminals there’s no excuse. Any new facility should undergo the full “accelerated-climate-change-check” and be properly planned and designed accordingly in order to avoid any unwanted effects.

In the long run, developing and proposing smarter and more coastal-natural dynamic supportive solutions is beneficial to all.

It’s a rather complex matter which comes down to politics and traditions. It will take some time to bring parties closer to one another to move ahead with appropriate solutions.
 
The basic principles have been identified and solutions are within reach. One of the bottlenecks could still be the availability of adequate data, expanding monitoring and developing adequate instrumentation and data analyses techniques.

Still it should be remembered that the climate does what it wants to and does it much faster than most of us so far have anticipated.

Therefore, implementation should start well before the impacts become visible. One thing is for sure, if it’s not happening at your door step right now, it’s about to soon.

Articles such as the one referred to are a good way of keeping the dialogue going.

The opinions expressed herein are the author's and not necessarily those of The Maritime Executive.