Climate change impacts nourishment constraints and what to do next 16122016

© Marco Pluijm, 16/12/2016

Ref. www.zandmotor.nl

Climate Change Impacts, Nourishment Constraints and what to do next… Marco Pluijm M.Sc. Senior Expert Ports and Coasts Key Elements: Climate Change; Beach Replenishment; Offshore Barriers; “Resilient by Nature” Summary This paper is about the effect of accelerated climate change impacts on natural sandy coasts and what nature inspired measures can be taken in order to guarantee, maintain and enhance the required safety and resilience levels. And how implementation of natural features with proven extreme weather impact safety and resilience, can provide such adequate solutions. In comparison with for instance sand nourishment, which in most cases does not provide a sustainable solution at all. Differences will be explained with reasons and why other and more adequate methods have to be applied in order to be effective. For which suggestions are made. Introduction Climate change comes faster and more intense than so far anticipated for. The challenge now is to assess how to plan and implement adequate solutions to provide the required safety and resilience levels on time. One popular approach in large parts of the world is to promote coastline stability and shoreline profile management by means of artificial sand nourishment, either on the beach, foreshore or in combination. A method which can provide a certain level of relief on a local scale. And in general puts a heavy burden on the marine environment at the same time. Substantial quantities of bed material have to be extracted over and over again for what basically is an endless operation. Once is chosen for the sand nourishment approach, there is basically no way back. That coastline has become a true sand addict and will need more sand with each nourishment. While sand which is transported out of the project area and its active


zone, is usually lost from the natural system. In some cases it can be re-mined, but unusually not for a number of reasons such as environmental, operational and costs. All in all, compensating coastline retreat and providing adequate safety against flooding by means of sand nourishment is not a viable nor sustainable solution. With the exception of short term and small-scale stabilization projects, for instance in the vicinity of structures (harbor moles, breakwaters) or as support of recreational beaches. Consequently true effective solutions have to be found and implemented when dealing with climate change induced extreme weather impacts. Plan and Design Data under Pressure Accelerated and intensified climate change as we are experiencing today, comes with a number of direct related impacts, such as frequent and more intense super-storms (hurricanes), increased wave set up and storm surges as well as accelerated sea level rise. Due to the nature of these events and growing impact loads, planning and design of adequate measures becomes an increasing challenge as well. Traditionally, plan and design data are based on historic time series, trend analyses and statistical forecasting. All with their own uncertainties and bandwidth. As a consequence of which, given the number of variables involved and the way they interact, it’s basically unknown what tomorrow will bring in terms of increased weather activities and how those will impact the plan and design conditions of today. Illustrated by the sheer endless number of scenario’s and data analyses which are continuously produced in high numbers, without actually delivering data which can be used for adequate planning and design of extreme weather impact solutions. With in there, the given fact that if and when a trend breach occurs, one will only know when it happens. Simply because it’s not possible to forecast a trend breach. Given all these uncertainties and variations, in order to be effective, flexibility is key. And with less accurate data to rely upon, alternative and more holistic design approaches and solutions have to be implemented. Coastline Stability and Sea Level Rise In case of sea level rise, the equilibrium profile of a straight, closed sandy coastline will follow with the same order of magnitude and consequently demand for equal fill with the required amount of deposition. Because sea level rise comes as a relative slow process and the requited quantities seem limited, such fill is usually included in the periodic nourishment projects. This seems all workable for a straight, closed coastline. However in case of an interrupted coastline and/or the vicinity of estuaries or intertidal areas, it all becomes quite a different story. Also in terms of required quantities. Because all of the exposed estuarine or intertidal area needs to follow over its full active surface area. Draining sand from adjacent foreshores and beach zones. Due to which those are suffering from exponential sand shortages, in response to which, borrowing their deficits from their neighbors etc.


A natural process full in accordance with how for instance the dune coast of the Netherlands has developed and retreated with sea level rise over the geological time periods. Until society decided that enough is enough and further retreat is not an acceptable option any more. And has chosen for maintaining the coastline at a fixed position, primarily by means of artificial nourishment. Which for a country like the Netherlands seems a viable option due to the presence of what still looks like sufficient sand available and a dredging industry which can handle those quantities at reasonable cost level. What remains, wherever you go, are the environmental impacts and sustainability aspects related to such coast maintenance policy. Taking all this into account, in particular when related to accelerated sea level rise and increase in extreme weather impacts, adding up to numbers and quantities which cannot just be included as part of periodic nourishments. And for which another approach is needed, not only in terms of money, but in particular with regard to environmental impacts and sustainability. Nourishment Constraints In 2011 the so called “Sand Engine” or “Sand Motor” was built in The Netherlands (pictured in the heading), basically as an oversized, 21,5 million m3 sand nourishment, situated along part of a straight sandy coast, as test case against a number of criteria. First of all to test if one large quantity of sand would be more cost effective than 4 or 5 times re-nourishment with smaller quantities. Second, to test if such a large quantity, while gradually spreading out along the coast by itself, is able to (better) protect the land against the effects of accelerated sea level rise. This “Sand Engine” concept as such is not new. In the late 1970’s / early 1980’s a similar test has been done under responsibility of the same Ministry of Transport and Public Works, Rijkswaterstaat. With a quantity of 1 million m3 and similar size and shape, located just a few miles south of the current location. The conclusions at the time were, that indeed the sand re-distributes itself along the neighboring coastal stretches, but also that due to the more exposed nature and convex shape, erosion rates were higher than in the undisturbed sections. For similar reasons also the cross-shore transport, for this coast typical about 1/3 of the overall sand transport capacity, increased and consequently more sand deposited in deeper water and outside the active zone. Consequently the project was not seen as a game changer and abandoned as an idea for more effective coastline management. Until revived in 2011. Following the information as provided by the initiators till date, the initial analyses of the results of the “Sand Engine” point in the same direction. In addition it has been concluded that the expected growth of the dune front does not occur at all. Attributed by the initiators as consequence of the beach width. In this respect the contribution to enhanced safety in relation to sea level rise has not been achieved. Another element which has been observed is that the old groynes in the northern part of the area, which initially were covered by the “Sand Engine” when built, have resurfaced already, well within 5 years since completion. Which indicates a shortage in deposition of sufficient sand along that part of the coast. Hence lack of support to impact safety improvement.


Consequently the overall results in terms of enhanced protection of the land against the effects of sea level rise by means of a large scale sand nourishment, do not look promising at all when it comes to enhancing the overall profile, including the dune front, beach and foreshore and delivering sufficient material to neighboring coastal stretches. Another snag are the deeper water, convex shape increased cross-shore transports due to which substantial quantities of sand settle outside the active zone, once brought there under extreme weather conditions. Sand nourishment may be a cost effective and recreation friendly alternative for coastline management on a very local scale, but by no means provides a sustainable solution with regard to enhanced safety and resilience against sea level rise and extreme weather impacts on a larger scale. Which is an absolute requirement when dealing with these phenomena. Climate Change Impact Effective Solutions When dealing with the matter at an appropriate level and scale, adequate solutions have to be found in the implementation and application of coastal features with proven natural impact safety and resilience. Which appear to exist in various places around the world and of which the characteristics can be transferred to those areas less fortunate. Along what is known as the Resilient by Nature approach and toolbox. An approach based on what can be learned from those coastal features with proven resilience with regard to extreme climate change impacts and sea level rise. Systems which have been and are being hit over and over again by extreme weather conditions such as hurricanes and super storms, survive without too much damage or no damage at all and recover soon after the event is over. More information about the Resilient by Nature approach and toolbox can be found on http://www.slideshare.net/MarcoPluijm/hurricane-impact-preparedness-and-resilient-by-nature-recovery When dealing with sea level rise and increased extreme weather impacts on a sandy coast as mentioned earlier, an example of such a natural impact safe and resilient coastal system and what can be learned from it, are some of the barrier islands in the Mississippi Delta. About how the islands apparently mage to survive multiple hurricanes and other extreme weather events without too much damage and are able to recover soon after. Key parameters to success follow from the shape, dimensions, location relative to the shoreline and orientation of these barriers, in combination with their ability to behave like broad crested weir type of breakwaters during and after extreme weather conditions.

Ref. Pilebuck.com

Schematic of sand erosion and deposition on a barrier island resulting from overwash


All in all providing a significant reduction in wave set up and storm surge, swell and long wave refraction and therefore in coastal and downstream erosion and eliminating gradients in sediment transport capacities. Plenty of reasons why adding such systems to the affected parts of for instance the North West European coastline, can be extremely effective and actually solve the problems with extreme weather impacts, overall long terms stability of the equilibrium profile, as well as compensate for part of the sea level rise in combination with reduced wave set up and storm surge reduction. A project initiative which follows part of the Resilient by Nature approach in this respect, is known as the “Vlaamse Baaien” (“Flanders Bays”) project in Belgium. Which has some of the Resilient by Nature characteristics, based on enhancement of the characteristics of the natural offshore sand banks in order to improve climate change impact safety and resilience of the Belgian coast.

Ref. www.scilogs.be Overview Flanders Bays project

Although not quite there yet, the project is still lacking a number of key factors, with a few additions and following the Resilient by Nature approach, that project can be very successful in terms of climate change impact reduction, including the effects of sea level rise. More information about the Flanders Bays project (most of it in Dutch only), can be found on http://www.vlaamsebaaien.com/de-projecten Conclusions

• The effects of Accelerated Climate Change come faster, more frequent and with more intensity than anticipated for

• Due to which the definition of adequate design and plan conditions has

become a major challenge, also because a trend breach can’t be forecasted

• Applying a holistic systems based approach therefore is preferred over an engineered approach based on poorly defined design conditions


• Where it comes down to securing increased extreme weather impact safety

and resilience and compensation of climate change induced coastal erosion and related increased vulnerability, artificial nourishment is by no means a sustainable solution on a regional or national scale, with the potential exception of some local phenomena and interests.

• Conclusions based on the evaluation of two convex shaped artificial test case

nourishments in the Netherlands and for instance supported by the excellent paper of Mr. Kirk Moore “Will there be enough money, sand to rebuild N.J.'s beaches? “, September 2016, which is accessible on: http://www.nj.com/news/index.ssf/2016/10/will_there_be_enough_money_sand_to_rebuild_njs_bea.html

• Instead implementation of nature based coastal features with proven

adequate safety and resilience levels and characteristics is the preferred viable and sustainable option.

• The Resilient by Nature approach and toolbox provide such solutions by

means of suitable systems, performance indicators, related dimensions and sustainability demands and parameters.

• Which as an example has led to the definition of what are called “Nature

Impact Shaped Breakwaters”, broad crested weir type offshore breakwaters, built of natural materials, embedded in the overall coastal dynamics as natural entities, like natural offshore barriers

• The “Flanders Bays” project is an example of such an initiative, with the

potential to be developed into a full Resilient by Nature compliant solution. Adding it all up, the only sensible path forward tackling climate change impacts effectively and efficient is by means of implementing resilient systems, instead of keep on trying with badly engineered projects on the basis of ill-defined datasets. Request for more information or providing feedback appreciated via [email protected]

Climate change impacts nourishment constraints and what to do next 16122016

Engineering

Transcript of Climate change impacts nourishment constraints and what to do next 16122016