©  Marco  Pluijm,  23/03/2017    

 

 

 

 

 

 

 

 

Ref. Hydrografische Dienst der Kust Oostende

When a coastline can no longer be a line….. Marco Pluijm M.Sc. Senior Expert Ports and Coasts The traditional approach with regard to coastal protection and safety against flooding is mainly concentrated around a very narrow zone of that coast. An approach, focused on holding the line. It is actually pretty much a 2-Dimensional activity. The coastline moves parallel to the coast, usually backwards, with very little to no ability for post-event regeneration and resilience. Rehabilitation is usually done by means of artificial nourishment.

This all works pretty well within certain limits in case of average and moderate weather and impact conditions, abundance of sand and ample availability of adequate dredging equipment. As for instance is the case in large parts of North West Europe.

Changing Climate, changing conditions It becomes quite a different story when the extreme conditions are changing in terms of frequency of occurrence, intensity and duration. Which is something that’s observed in many places around the globe these days. Indicating accelerated climate change, causing trend breaches in ambient conditions. Putting pressure on existing codes and practices, defence strategies and approaches.

In case of sediment dominated coasts with the potential consequence, that erosion will increase substantially, nourishments have to be repeated more frequent and with larger quantities than before, fixed structures can be undermined and need to be upgraded.

Different approach towards suitable solutions Imposing new terms on present and future solutions. Due to the nature of accelerated climate change and related degrees of uncertainty, also impacted by multiple parameter interaction, pressing the need for anticipating for more intense impacts than before, equal need for flexibility, capacity to withstand and respond to a variety of new conditions, some of which are unknown to date, some manifesting themselves as trend breaches, demanding for solutions with sufficient Internal back up and engineered redundancy, sustainable and with adequate capacity for natural resilience. Which is quite a list of requirements. Demanding for

©  Marco  Pluijm,  23/03/2017    

a much more holistic process and natural system based approach, rather than to proceed with traditional, engineered concepts.

The next issue then is to find the answer to the question about how to respond in the most adequate way. Adequate in terms of effectivity, efficiency, resilience and sustainability.

Adding a dimension to the challenge One of the options to deal with these challenges, is spreading the increased average and extreme weather induced energy over a wider zone, making optimal use of natural coastal features, processes and resources. Moving away from the current 2-Dimensional “hold the line” approach towards a 3-Dimesional “make better use of the system” approach. Three dimensional in terms of degrees of freedom and also in interaction between hydraulics, sediment and ecosystem. Reducing human intervention and maximising added value for the short and long term for that coastal system by making optimal use of these natural processes.

Following the principles of the Resilient by Nature approach and toolbox. Making use indeed of natural coastal features, enhancing their functionality in relation to the changing conditions, improving or re-establishing natural resilience and sustainability in the sense of making optimal use of the sediment balances en ecosystem characteristics of that coast.

An illustrative example In this respect it can be illustrative to refer to an idea which was presented a few years ago by Belgian initiators and is known under the name “Vlaamse Baaien’’ (www.vlaamsebaaien.com).

Pictured above the header of this article is an illustration, showing a hydrographic map of part of the Belgian coast.

The actual position of the Belgian coastline (shown in red) is fixated by a great deal of structures, urban- and tourist developments. The current maintenance strategy is based on periodic artificial nourishment. The actual breathing space for effective nourishment however is limited due to the landward fixation and shore parallel conditions, such as currents.

With the increase in accelerated climate change induced impact forces, this strategy will become less and less effective. A reason why the initiators are understood to have presented their plan.

The faded blue areas in the same figure refer to natural sand banks, the so-called “Vlaamse Banken”. Some of which are shore parallel, while others make an angle of about 45 degrees relative to the coast. Their average actual crest height in the area of interest varies between say minus 5 and minus 10 meters, relative to Mean Sea Level.

Without going into the specific details of that plan, attention is given here to the basis of making use of natural features, such as these sand banks, as energy dissipation tools. And where deemed a necessity, to enhance their functionality and integrating them in the overall coastal protection, by adjusting their dimensions and effective behaviour. Creating added value in a sustainable way.

Enhancing the natural system The yellow spots as shown represent those parts of the existing sand banks, which are intended to be brought up to the right level to be shallow enough to be effective with regard to extreme weather induced storm and wave impact reduction. To become an active and integral part of the impact energy dissipation zone, reducing the direct exposure on that coastline. Delivering the third dimension.

One of the main parameters in the whole development is the effective level up to what extend these shallow banks will be enhanced in order to be effective. Either in height, width or effective length.

©  Marco  Pluijm,  23/03/2017    

In such an assessment there’s always the temptation to make them high enough to emerge as nearshore islands. Which basically would move the problem offshore, without solving it. So that’s not what is being proposed here. As sated, the emphasis is on spreading energy dissipation over a wider zone by optimal making use of natural coastal features as basis.

An approach to make this work is to follow what can be learned from similar, natural features elsewhere in the world. With the potential to redevelop these banks into either fully submerged natural breakwaters, overflow barriers or offshore ridges. Each creating additional opportunities for other functionalities as well.

In it’s purest form, the redevelopment into overflow barriers seems to be the most effective and efficient approach. In similarity with what’s for instance found along parts of the Mississippi Delta. Where overflow barriers are able to encounter and withstand hurricane force impacts without too much damage and with the ability to regenerate afterwards without too much human intervention or none at all.

Towards natural system based, resilient and sustainable solutions Lessons learned, transferable towards areas like the Belgian coast and develop natural based systems on basis of the same parameters, physical processes and related dimensions. Following a holistic approach based on empiric relations, proven impact behaviour, resilience and sustainability.

Making optimal use of the natural resources available, reducing the amount and frequency of artificial nourishments and so the burden on natural resources and ecosystem.

In terms of economics, following this approach of enhancing and maintaining sandbanks into submerged or overflow barriers as proposed, is estimated to undercut the accrued costs of continued artificial nourishments.

Experience based empiric relations as referred to, are an important element in the planning and design of these solutions. One of the reasons is that the current state of the art in coastal modelling is not up to par with what is required. Especially in the wave, flow and sedimenttransport range for the near shore zone we are focussing on. Which in itself should trigger research institutes and others to speed up the development of the required knowledge bases and support tools.

All in all, by adding the third dimension, creating solutions which are not only adequate towards the future and much more effective, but also more resilient and sustainable compared to current practices.

The Belgian coast as highlighted in this article is just one example. Around the globe there are many more. And in case natural features are not as developed, in most cases there is always the opportunity to create suitable conditions along this line. The knowledge and development potential are there. And facing the challenges of today, deserve to be utilised to the max. Accelerated climate change is a given, adequate safety and flood protection an urgency and necessity which can’t wait.

For further follow up and information, email contact is easily made via pluijm64@gmail.com and we’ll get back to you as soon as possible.

References

More information about this topic and the Resilient by Nature approach can be found in for instance the following publications:

“Resilient by Nature, Revisited” https://www.linkedin.com/pulse/resilient-nature-revisited-marco-pluijm

“With the decay of the Sand Engine, time to move on to more sustainable solutions”

©  Marco  Pluijm,  23/03/2017    

https://www.linkedin.com/pulse/decay-sand-engine-time-move-more-sustainable-solutions-marco-pluijm

“Hurricane impacts as resiliency Master-Class” https://www.linkedin.com/pulse/hurricane-impacts-resiliency-master-class-marco-pluijm