Old school skills and the world of virtual reality 11042017

© Marco Pluijm, 11/04/2017

© Bruun & Gerritsen, Amsterdam 1955 /Marco Pluijm

Old school skills and the world of virtual reality Marco Pluijm M.Sc. Innovator and Seasoned Professional While preparing for one of the upcoming conferences, I came across a striking description about the limitations of coastal modeling. “The fundamental, governing physics imbedded in numerical models of coastal sediment transport are not nearly as well understood as those of the hydrodynamics. Coastal sediment transport has been an active area of fundamental research for decades and the problems relate primarily to our inability to model the complex, multi-phase, turbulent flow fields under a variety of timescales” [ref. 1] It’s all about thorough understanding of the basics of complex coastal systems and processes, actual experience, knowing what’s important and about how to translate that into effective, resilient and sustainable solutions. The approach on which for instance the groundbreaking work of Bruun and Gerritsen [ref. 2, 1955] is based in an era when computers didn’t exist and the experts had to rely on their own expertise, gut feeling and a few equations. An holistic approach on which countries like the Netherlands have been built. But also an approach which somehow seems to have diminished almost entirely in today’s world of virtual mathematical model reality instead. Which in itself probably should not be a major problem as long as the boundary conditions don’t change too much nor too sudden. However there are clear indications that, due to the effects of accelerated climate change, the boundary conditions indeed are changing more rapid and become more intense than anticipated for so far. Which turns out to be the case in many places around the globe. Reason why one can have serious doubts about the quality of today’s mathematical model dominated practice environment in this respect. And


query if indeed current knowledge and tools are still fit for purpose when confronted with the impacts of accelerated climate change. The answer to that question is that without thorough understanding of the coastal environment on experience based system and process basis, the current approach is very much likely not to be adequate at all. For instance because over the years, most if not all open water coastal research and development has been focused on what’s basically a very narrow part of the shoreline, in particular on the breakerzone. Exposed to average and moderate extreme conditions only, mimicking undisturbed continuation of regression-based design conditions. Which in large parts of the world is no longer the case, judging sudden changes in hurricane frequencies and intensities, heavy downpour and temperatures. In order to be able to deal with these changes in a safe, resilient and sustainable manner, focus may need to extend to a much wider part of the coastal zone than what so far has been the norm. Extension for reason of enhanced energy dissipation capacity in relation to increase in storm and long wave energy patterns. Impacting a substantial part of the coastal zone which is hardly covered nor incorporated at all in most current wave and sediment models [ref. 3] To bridge the gap and to be able to develop adequate knowledge and tools for what’s coming, the only sensible way forward is to go back to the basics of thorough understanding of the behaviour and performance of coastal systems and phenomena on a holistic, system and process level basis. Going back to the same approach as used by Bruun & Gerritsen in the 1950’s. Assessing key parameters, order of magnitude, interaction, trends and guidelines. Which equally implies that the current practice of mathematics driven coastal engineering and planning needs careful re-evaluation and adjustment to the changing conditions on the right level. And so does the research linked with it. Current practice in open coastal water research and development turns out to be focused on what is actually adding more subroutines to existing codes and models. With the obvious intention to extend their overall functionality. But at the same time making them also harder to manage and validate. Illustrative in this respect is for instance how a model like X-Beach (McCall, 2010). has been modified for the simulation of the behaviour of bound long waves and its impact on cross shore and overflow sediment transport capacities and gradients [ref. 4]. As a consequence of which, in order to be able to validate the adjusted code against field data, a number of internal parameter restrictions had to be applied with regard to precise those processes the addition was meant for. Which brings up the question if and up to what extend indeed mathematical models can be leading the improvement in basic understanding of the actual coastal processes and interaction themselves. Because no matter how advanced each code, routine or model might be, it still is a high level simplification of reality and therefore should not be leading in the understanding of coastal processes on a systems level as such.


Without thorough understanding of the relevant in’s and out’s, validation also becomes a serious issue. Reason why apparently these days many studies consist of a large number of basically un-validated runs in comparative qualitative mode, rather than providing quantitative results. Some even dare to say that such an approach provides deeper insight in the actual process and behaviour of coastal systems. Referring to the above, this is something where things really become tricky. Others seem to be aware of this and point in the direction of variation- and risk analyses as part of their efforts to improve the overall quality. And that’s where we are really entering another world of chaos management. Simply because a risk assessment only justifies such qualification when based on upfront thorough understanding of the whole process it is related to, including relevant variables and interactions, covering all project stages, in quantifiable mode. All together a world where coastal engineering often seems to have become almost equal to a virtual reality computer game rather than an engineering practice. Almost in full contrast with all this, and likely to be seen as leading by exception, is for instance the work of De Bakker et. al [2016, ref. 5]. A striking example of where process driven research prevails over mathematics and does deliver accordingly indeed, Which work provides new insights on key parameter level with regard to (bound)long wave induced cross shore transport in relation to sloping of the foreshore. Accelerated climate change is a given and we should not allow to be overtaken by it because of an inability to go back to the old school and learn to remaster the skills on which countries like the Netherlands are built. With the rapid changes in climate conditions, other parts of the coast become more important with regard to impact, safety and resilience. The current mathematical models are not able to deal with such extension. So back to the drawing board. Back to the basics of coastal processes on an empirical basis rather than trying to solve and manage ever more complex equations. The changing natural physical conditions will teach even the biggest skeptics the essence for a nature based approach when it comes down to understanding and providing an adequate response to its changes. References 1. Highways in the Coastal Environment, Hydraulic Engineering Circular No. 25

– Volume 2 . U.S. Department of Transportation, Federal Highway Administration, Publication No. FHWA-NHI-14-006, October 2014

2. Stability of Coastal Inlets, P. Bruun & F. Gerritsen; Amsterdam - North

Holland Publishing Company, 1955 3. When a coastline can no longer be a line, Pluijm 2017, Linkedin post

https://www.linkedin.com/pulse/when-coastline-can-longer-line-marco-pluijm 4. Two-dimensional time dependent hurricane overwash and erosion modeling

at Santa Rosa Island, R.T. McCall, J.S.M. Van Thiel de Vries, N.G. Plant, A.R. Van Dongeren, J.A. Roelvink, D.M. Thompson, A.J.H.M. Reniers, 2010


5. Cross-shore sand transport by infragravity waves as a function of beach steepness, A. T. M. de Bakker J. A. Brinkkemper, F. van der Steen,M. F. S. Tissier, and B. G. Ruessink, 2016; Research Article 10.1002/2016JF003878