hurricane impacts as resiliency master class 11112016

© Marco Pluijm, 11/11/2016

Ref. USGS

Hurricane Impacts as Resiliency Master Class Marco Pluijm M.Sc. Senior Expert Ports and Coasts Key Elements: Climate Change; Extreme Event Impacts; Adaptation; “Resilient by Nature” Summary This paper is about how the effects of extreme weather conditions, such as hurricane impacts, can teach us about how to improve coastline impact safety and resiliency by making use of natural processes and systems. Sometimes it is better not to rebuild what has been destroyed. Because what was there in the first place, didn’t perform and thereforeare no longer suitable for today’s conditions and those on the longer term. Time to step up to the next level of coastal safety and resiliency. Time to introduce suitable systems with proven impact resiliency, demonstrated elsewhere. Natural systems which hardly suffer from extreme weather impacts or even not at all. This approach is elaborated upon on the basis of examples, which can provide guidance for such next, more durable and sustainable step. Introduction When hurricanes and other extreme weather events hit an area, the consequences can be devastating and often they are indeed. In this respect, coastal zones in particular are prone to heavy impacts and extreme damages. Climate change comes at us much faster than originally anticipated for and these events appear to happen with increased frequency and intensity. Hitting more and more people around the globe.


Apart from all the damage and misery they bring, these events are also phenomena to learn from and apply that knowledge to prevent and reduce the impacts of similar, future events. Synthesis One way of looking at the effects of extreme weather impacts, is to study the coastal stretches and areas which have been hit as hard, but for some reason, suffer much less damage or no damage at all, compared to other, similar areas. Apparently due to their shapes, dimensions and other characteristics, they appear to be much less vulnerable. Research learns that there appear to exist a number of these systems with such kind of behaviour and performance. Analyses and assessments on which the Resilient by Nature approach is based. More information about Resilient by Nature can be found on www.slideshare.net/MarcoPluijm/hurricane-impact-preparedness-and-resilient-by-nature-recovery Another way of looking at dealing with extreme weather impacts on coastal stretches, is the answer to the question if and how consequential damage to such coastline and other primary flood defenses, should be fixed and repaired. And if so, how that should be done. One common, almost immediate reaction after a major storm event and damage done, is to fix that damage as soon as possible, and to restore the old situation. Which from an approach of emergency repair perspective, often is the most sensible and desirable thing to do. An example of such direct response is shown in the pictures below. Showing the breach in the barrier island, next to the Mantoloking bridge, post hurricane Sandy, 2012, and the repair afterwards, by restoring the old situation with a sand mass. Which does make perfect sense when, as in this case, roads and other primary infrastructure have to be repaired as soon as possible. Ref. USGS


As an emergency response, this is a perfect solution. But maybe, once done so, afterwards, additional works would be preferred to prevent this happening again, next time when a hurricane hits this area. Prevention by means of additional works, from which an even much larger part of this coastline can benefit. By changing the overall performance of the system on the basis of lessons learned from this event and the likes. Towards a sustainable and more resilient approach In case there is a bit more time, or once emergency repairs have been done, one could decide, for instance in case of the Mantoloking breach or any similar situation in another barrier coastline, not to fix the gap nor to restore the old situation. But, in a slightly different context, for instance replace the gap by a controlled spillway with sufficient storage behind it. Often the reason why the breach has developed the way it did, is determined by storm surge and waterlevel run-up in combination with – sometimes but not always - a slight depression in the barrier island itself. This all may seem rather trivial, but it’s not often that simple. Because of the length of the barrier island, the storm surge and wave induced run-up can and will develop to the max and from there can’t go anywhere, other than over the barrier island itself. Under these conditions rip currents will also develop, but their capacity is way less than what’s required to compensate for the accumulated set up. Which leads to full exposure of the entire, closed shoreline, to both combined phenomena. Another phenomenon is the post event surge in the aftermath of the event. Things could be very much different and less severe, if for instance at regular intervals, at least part of the combined energy can flow away in a controlled manner, via engineered spillways. This would reduce the combined set-up effects and so reduce loss of property and other assets in the areas between these spillways. Looking at the picture below, it might be worth to consider such an approach.

Breached NJ Shoreline, Post Matthew, October 2016 [Ref. USGS]

During hurricane Matthew, the breach as shown developed. It also shows the houses nearby are unaffected. The fact that the breach could develop may have saved


those properties. Off course, another explanation can be that the grounds they are built on, are just a meter or so higher. Which is understood not to be the case. Either way, it doesn’t change the approach just mentioned. One could decide to leave the gap open, stabilize it, thus reducing the pressure on this coastline for any future hurricane and extreme weather events. Some of the barrier islands in the Mississippi Delta, when hit by hurricanes, do not suffer as much as some of their neighbors. One of the reasons is that because of their principle dimensions, storm surge can’t build up as much as along a closed coastline. Another phenomenon is that due to their height, storm surge and set-up can wash over part of the island, in a controlled manner. Thus all together reducing the damage of the more populated parts of the island. One of the systems included in the Resilient by Nature approach. Applying this principle on the pictured situation may lead to a much safer and more resilient coastline compared to the current situation. And in the earlier mentioned case of the Mantoloking bridge, building a spillway under the rebuilt road, will take the pressure away form that coastal section next time the waterlevels are swept up by hurricanes and high run offs. Translating these phenomena and principles into a sustainable and more resilient situation for a longer stretch of coastline, would result in planning and construction of more controlled spillways with sufficient storage capacity behind them. Which all together can be translated into a system with natural drain and enhanced run off after the extreme event, Similar to a system which is operational already for decades in Neßmersiel, Germany. A system designed and built to keep a navigation channel open by means of diurnal, natural tidal flow. Filling and emptying a storage area (polder) behind the dikes, using that volume of water to push out the daily siltation in the channel. A slightly different reason for doing so, but the basic principles are the same as when protecting a barrier coastline by allowing for controlled over-wash and storage during extreme events. Comparison with a more traditional approach In a more traditional way, restoring such coastal damage and maintainining the coastline by means of periodic beach- and foreshore nourishment, could be considered as an option. In the Mantoloking case it was decided to enhance the safety and impact resiliency of this coastline by means of a 4 mile long sheet pile steel wall with a nourishment in front of it. Which were implemented in 2013. The first re-nourishment is understood to have been done in 2015. Restoring and maintaining a coastline by means of beach nourishment, in the end, is not a sustainable solution. No matter how much sand is brought in. It’s not a game changer and not effective with regard to sea level rise and extreme weather impacts. Beach nourishment will only be effective when the coastal system is adapted to these new conditions and only by means of support, not as a long(er) term primary solution. In areas like NW Europe, with sand, marine contractors and suitable equipment in abundance, a periodical nourishment approach might work. At least for the time being. In other regions, such as the US, it is very unlikely. As basically is already demonstrated by the Mantoloking case. The availability of suitable and sufficient


sand is understood to be an issue and so the overall availability of suitable dredging equipment. And so become the cost of these works. It’s all about these locations which are urged to scale up to more adequate solutions, due to the changing conditions, much faster than originally anticipated for. Rather than to carry on with coastline maintenance on the basis of a nourishment strategy. Only when fundamental changes in the coastal system will get implemented, for instance by means of named controlled spillways or other natural enhanced impact resiliency features, the overall safety and maintenance strategy will work. Engineered solutions shall be based much more on an experience based holistic approach rather than design codes and standards. It’s all about processes and how to make those work in favor of what has to be achieved. Conclusion Sometimes it is better not to rebuild what has been destroyed by a hurricane and other extreme weather impacts and adjust the coastline, according to the features which have developed during the event and use that capacity to take the pressure away with regard to future impacts. Preferably to be combined with lessons learned from natural systems elsewhere with better proven safety and resiliency characteristics. All in all providing enhanced safety and resiliency to badly affected areas and reduce damage costs and consequences. Continuation with periodical sand nourishment, often referred to as “Building with Nature”, is hardly ever a sustainable solution. Depending on the local circumstances, the need for stepping up to the next level of dynamic coastline maintenance will vary. For some regions that moment appears to be already on their doorstep. The Resilient by Nature approach can help to plan and develop sustainable and more resilient coastline solutions. More information about this approach can be found on : www.linkedin.com/pulse/resilient-nature-presented-mcce-confrence-october-13th-marco-pluijm Resilient by Nature Community The Resilient by Nature Community is an informal platform for exchange of information and experiences about these issues and related phenomena between people who are interested and/or involved in these matters. Dealing with coastal systems in relation to extreme weather impact, safety and more effective resiliency. With this “Resilient by Nature” community growing, more and more contributions from around the world keep on coming in. Adding to the list of solutions. Which is highly appreciated. A website is under development. More information can be obtained via email on [email protected]

hurricane impacts as resiliency master class 11112016

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