Originally presented earlier today at the AGU 2021 Fall Meeting in the “Upgoer Five” Session, this video was inspired by the XKCD comic and book in which scientific concepts are described using only the 1000 most-common words in the English language. I participated in the session last year and had so much fun, I thought I would try it again with my coral reef research.
Unfortunately, ”ocean” and ”sea” were not on the list, so I had to go with ”big blue wet thing” instead. Want to give it a try yourself? Here is a handy tool which checks your writing to see if it meets the list of 1000 most common words: https://splasho.com/upgoer5/ It’s harder than it looks!
Here is a summary of my video:
Some small but beautiful lands in the middle of the big blue wet thing were built by tiny animals that turn into rock when they die. Although these lands might seem perfect and calm most of the time, they are actually in big trouble. The big water is going up and up and up, and the little lands could be completely under it before our kids grow old. However, they are also in trouble right now — waves can hit the little lands and make them go under the water too, even if just for a short while. These waves can hurt people and make the drinking water not-drink-able. It is hard to guess if the waves will cause trouble because they break in different ways than we are used to when they hit the rocks built by animals. The waves become longer and weirder as they move across the rocks, and can hit the land with more power than we would expect. It is even harder to guess what the waves will do because every small land made of rocks built by animals is different, and there are so many of them all around the world. To keep everyone safe, we showed a computer lots of made-up waves so that it could learn how waves look when they hit different sorts of rocks and land. The computer can then make good guesses about what real waves would do if they hit real rocks and land. If the computer thinks that the waves will cause trouble, we can warn people to go somewhere safer until the waves stop. In this way, we hope to keep everyone’s feet dry until long after our kids are old.
You can find more about this stuff in bigger words here:
1. Pearson, S.G., Storlazzi, C.D., van Dongeren, A.R., Tissier, M.F.S., & Reniers, A.J.H.M. (2017). A Bayesian‐based system to assess wave‐driven flooding hazards on coral reef‐lined coasts. Journal of Geophysical Research: Oceans, 122(12), 10099-10117. https://doi.org/10.1002/2017JC013204
In the past few weeks, Vancouver and the BC Lower Mainland have suffered not just one but three record-breaking rainstorms, a succession of ”atmospheric rivers” that dumped several hundred millimetres of rain. Highways washed out and disappeared, and numerous communities were flooded. This resulted in an enormous quantity of sediment reaching the sea via the Fraser and other local rivers. But where exactly does the sediment that’s already in the sea around Vancouver go? How has that changed in the past few hundred years since Europeans colonized the area? To get to the bottom of this, we enlisted Carlijn Meijers.
Last week, Carlijn successfully defended her thesis, ”Sediment transport pathways in Burrard Inlet”. To answer these questions, she created a detailed hydrodynamic and sediment transport model of Burrard Inlet and Georgia Strait in D-Flow FM. She then used the SedTRAILS model that we have developed to visualize sediment transport pathways.
From these models, Carlijn showed that sediment transport is largely controlled by flow through the First and Second Narrows (where the Lion’s Gate and Ironworker’s Memorial bridges cross). As the tide comes in, the water shoots through these narrow passages at speeds of up to 2 m/s and comes out the far side as a jet, spiraling off into eddies. The tide then goes out and the same happens in reverse, with water shooting out the opposite side.
Due to the sheltered nature of the inlet, waves have only a minor role in sediment transport. However, given the intensity of the tides and the great depths of Burrard Inlet (especially the Indian Arm fjord to the north), most sediment liberated by erosion tends to get carried away from shore and is essentially lost from the coastal sediment budget.
Another key point of her project was to investigate how land use changes and other human effects (e.g., damming rivers, port construction) have changed Burrard Inlet. Using the model, Carlijn showed that these changes to the inlet have shrunken its tidal prism, influencing the currents and sediment transport patterns.
These changes are especially evident when we compare satellite photos from the present day with the oldest available images from the 1940s.
Carlijn wrote an excellent report and capped it all off with one of the best master’s thesis defenses that I’ve seen in a long while. She also handled the cultural context of the project with great respect, interest, and sensitivity. If anyone reading this is looking to recruit a new engineer/researcher with heaps of potential, I cannot recommend Carlijn enough.
All in all, this was a fascinating project and one very close to my heart — I was born in the Vancouver area and was excited to see how the SedTRAILS model could be used in my original backyard. Let’s keep the Delft-Vancouvercollaborations going!
Ebb-tidal deltas are notoriously unpredictable. Battered about by waves and tides, their ever-shifting sands can be a royal pain in the arse for everyone from coastal residents to pirates. I have spent most of the past five years trying to identify the pathways that sand takes across these deltas as part of my PhD. However, the holy grail of ebb-tidal delta research is to take that one step further and make accurate morphodynamic predictions of their evolution on timescales of decades.
This past year, Denzel Harlequin took up the challenge, and I am pleased as punch to announce that last week he successfully defended his master’s thesis, ”Morphodynamic Modelling of the Ameland Ebb-Tidal Delta”. This is a really tricky problem to solve because of the complexity of the processes that need to be simulated.
What’s cool about Denzel’s work is that brings us closer to good morphodynamic predictions than we were before. Furthermore, where the predictions deviate from reality, he illuminates the areas where we still need to make improvements — specifically, our representation of wave-driven transports. Denzel also shows how the location of a sand nourishment can have major knock-on effects on the evolution of the ebb-tidal delta.
Denzel is a very talented modeller and I am delighted that he has joined us as a new colleague in the Applied Morphodynamics department at Deltares. I look forward to many more great collaborations to come!
We forgave Bagnold everything for the way he wrote about dunes. “The grooves and the corrugated sand resemble the hollow of the roof of a dog’s mouth.” That was the real Bagnold, a man who would put his inquiring hand into the jaws of a dog. – Michael Ondaatje, The English Patient
Ralph Bagnold, widely considered one of the godfathers of sediment transport, was a soldier in the British army who spent much of the Second World War scouting around in the Libyan desert. In the process, he learned much about the dynamics of sand dunes, and formed the basis for many theories that are still in use today for explaining how sediment is blown around by wind or water.
This week I am proud of our very own up-and-coming Bagnold, Charlotte Uphues, who successfully defended her thesis, Coastal Aeolian Sediment Transport in an Active Bed Surface Layer, on Thursday. Charlotte did a fantastic job of designing and carrying out her own super cool field experiments, using tracer sediment to estimate aeolian (wind-blown) sediment transport on a beach here in Holland. As the dunes of the Netherlands are a key component to Dutch coastal defenses against flooding, it is essential that we understand better how they evolve by improving our abilities to predict aeolian transport.
I would elaborate a bit more about her findings, but Charlotte will be submitting her thesis for publication in a journal soon, so it will remain under wraps for now. Stay tuned, I don’t think we’ve heard the last from Charlotte!
Ebb-tidal deltas are gigantic piles of sand that form at the seaward mouth of tidal inlets. They are constantly on the move, shifting shape and size in response to the waves and tides. Where exactly is that sand going? This is a question I have been struggling with for the past 5 years during my PhD, and we have recently made great strides in part due to the efforts of Paula Lambregts.
Yesterday, Paula Lambregts successfully defended her master’s thesis, “Sediment bypassing at Ameland inlet“. I had the great honour of co-supervising Paula’s research throughout the last ten or so months, and I am enormously proud of her. Her project encompassed a range of approaches, including bathymetric analysis and numerical modelling, to solve the mystery of the sediment pathways.
First, Paula’s detective work led her to examine detailed measurements of the seabed bathymetry at Ameland Inlet in the Netherlands, taken over the past fifteen years. These measurements give snapshots of the underwater delta landscape. By comparing the bathymetry from different months or years, we can track the delta’s evolution. In the image below, we see four snapshots of the ebb-tidal delta before and after the construction of a sand nourishment (i.e., the large pile of sand that appears in panel B). This nourishment was a large-scale pilot test to determine if creating sand deposits like this is a viable strategy for strengthening the coast of nearby islands.
After describing how the delta has evolved in the past, Paula developed hypotheses about the physics underlying this behaviour- how do waves and tides move the sand around to create the patterns we observe? To answer this question, she used a combination of computer models to estimate sand transport pathways. This allows us to “connect the dots” and explain how the sand moved from one place to another. The first component was a D-Flow FM model, which is used to simulate the hydrodynamics (waves and tides) and sediment transport (where and how much sand moves). The second component of her modelling approach was to apply SedTRAILS, a brand-new tool developed by my colleagues and I at Deltares for visualizing predicting sediment transport pathways. Using SedTRAILS, she was able to create some really cool maps that indicate where the sand goes.
Drawing on her prior expertise in geology, Paula combined those two lines of evidence (the measurements of the seabed and the modelled sediment pathways), to come up with a series of fantastic conceptual diagrams. These diagrams distill the mysterious piles of sand and complex spaghetti of the images above into a more easily understandable picture:
The work that she did is extremely valuable for coastal management, since it gives more insight into where (and where not!) to construct sand nourishments. It also brings new insights to science about how these complex systems work. Last of all, it is enormously helpful for the research that we are continuing to do at TU Delft and Deltares. In September I will continue on with the work on sediment transport pathways at tidal inlets begun during my PhD, and build on the work that Paula has carried out in her thesis project. I am extremely proud of her and hope that we can continue to collaborate in the future!
Coral reefs and the islands that they protect from flooding are in big trouble. This is arecurringthemeon thisblog, and now it’s time for the latest update. We are currently building towards the development of an early flood warning system for low-lying tropical islands fronted by coral reefs. Our previous work on this topic has focused on finding ways to do this accurately for a wide variety of coral reef shapes and sizes, as well as different wave and sea level conditions. However, it’s not enough to be accurate- to deliver timely early warnings, you also need to be fast.
That’s where the latest research of Vesna Bertoncelj comes in.
Vesna’s research provides us with new approaches for making highly accurate predictions of coastal flooding, at limited computational expense. The numerical models that we use to estimate flooding often take a long time to simulate, since they resolve many complex physical processes at high resolution in space and time. However, by paring down these models to only the most essential components for the task at hand, we can do this much faster. My colleagues at Deltares recently developed the SFINCS model, which has been successfully used to predict flooding in a fraction of the time that our standard models take. But how do we put all these different pieces together?
First, Vesna established a baseline for model performance by running a computationally intensive XBeach Non-Hydrostatic model (XB-NH+), and a much faster SFINCS model. These models provide an estimate for runup (R2%), which can be taken as a proxy for coastal flooding. In the second step, she used a lookup table (LUT) of pre-computed XBeach model output and to derive the input for the SFINCS model. The crucial task is doing this quickly and accurately, so she experimented with different interpolation techniques for deriving that input. She then compared her new approach with the standard models to find the fastest and most accurate combination.
Her research gives us a useful methodology that we can implement to speed up our early flood warning system, saving time and hopefully someday saving lives.
Vesna’s quality of work is excellent and she has a fantastic attitude towards research and collaboration. Her curiosity, professionalism, and diligence will undoubtedly serve her well in the years to come. I hope that we will have other opportunities to collaborate in the future. If anybody out there needs a bright young coastal researcher and/or modeller, hire her!
We frequently hear in the news about dying coral reefs, and also about the threats of sea level rise and climate change. But there is a key gap: what if we can hit two birds with one stone, and restore damaged ecosystems while providing vital protection against flooding? Our latest research demonstrates how coastal managers and ecologists can join forces to achieve both goals, which may help stretch limited funding further.
At TU Delft, a requirement for our PhD defense is to make ten propositions based on what we have learned during the previous years. Claims posed by my friends and colleagues deal with the nitty gritty details (“All diffusive processes can be derived from an advective one, and failing to do so yields incorrect modelling“) but also the bigger picture of how we do what we do (“The way morphological models are presented and interpreted has a lot in common with predictions of snow depth in five years on December 26th at 4pm. The knowledge in these models deserves a better presentation“).
The propositions must be both defendable and opposable, so as to stimulate an interesting debate during the defense. Some of the propositions should reflect the findings of our research, but it is also traditional to include statements that have nothing to do with it. One colleague even suggested (tongue in cheek) that the increase in the height of Dutch men over time could be explained by sea level rise. I couldn’t resist analyzing the data myself, and the results were surprisingly good:
These propositions are a chance to inject a bit of last-minute philosophizing into our Doctorates of Philosophy, and range from the wise (“No wind is favourable if a person does not know to what port (s)he is steering – Seneca“) to the downright cheeky (“This proposition is not opposable“).
What I Learned by Counting Sand for 5 Years
As the clock is ticking on my own PhD (259 days, 13 hours, 39 minutes, and 51 seconds, but who’s counting? *eye twitches*), I started preparing some propositions of my own (obviously in a fit of procrastination on my dissertation). After nearly five years of scrutinizing sand and contemplating connectivity, my research has led me to an inescapable conclusion:
Ebb-tidal deltas are badass morphological features (BAMFs), (c.f. Phillips ).
What, pray tell, is an ebb-tidal delta, and why is it so badass? Ebb-tidal deltas are large underwater piles of sand at the mouth of estuaries and tidal inlets, deposited by outflowing tides and reshaped by waves. I spend my days studying how waves and tides move sand around on the Ameland ebb-tidal delta in the northern part of the Netherlands (see below). We need to know this in order to plan ecologically-sustainable flood protection measures for the Dutch coast. A morphological feature is just a fancy name for some part of a landscape, like a hill or a valley or a beach.
What makes a badass “badass”?
Phillips defines the archetypal badass as “individualistic, non-conformist, and able to produce disproportionate results”, and applies this concept to geomorphology (the study of how landscapes evolve, at the crossroads of geology and physical geography). Ebb-tidal deltas meet these three criteria, which makes them badass morphological features (BAMFs):
Ebb-tidal deltas are each unique (in shape, location, composition, and in terms of the environmental forces shaping them (like waves and tides)), and hence individualistic.
Ebb-tidal deltas are chaotic systems which defy accurate prediction using physics-based numerical models, and hence are non-conformist or “naughty”. This numerical naughtiness is a serious problem for coastal engineers and scientists, since a failure to accurately predict ebb-tidal delta evolution can threaten public safety and lead to costly property or infrastructure damage. They do not “play by the rules” of our existing physics-based deterministic models.
Ebb-tidal deltas are highly nonlinear systems which can greatly amplify small instabilities, and hence produce disproportionate results.
In addition to the strict definitions of Phillips, ebb-tidal deltas are also “belligerent or intimidating, ruthless, and tough”, other traits reflective of badassery [Oxford Engish Dictionary]. The Columbia River ebb-tidal delta alone is responsible for dozens shipwrecks in the past century, and Ameland ebb-tidal delta has also featured numerous wrecks throughout its history.
Quoting Thomas Pynchon, Phillips also notes that badasses are “able to work mischief on a large scale”. Ameland ebb-tidal delta covers an area of approximately 100 square kilometers, roughly the size of The Hague. Many ebb-tidal deltas around the world are even larger!
Now admittedly, ebb-tidal deltas are just big piles of sand. A big pile of sand is probably not the first thing that comes to mind when you hear the word “badass”, unless you are Ralph Bagnold or a Sarlacc. This could probably also be considered gratuitous personification or anthropomorphization.
I’m sure that many of my friends and family have been scratching their heads as to why I would sacrifice the latter half of my 20s to understand them better. A critical reader might ask, “is it possible that you have only convinced yourself that ebb-tidal deltas are cool out of self-preservation?” And the answer is yes. Yes, I have. Nonetheless, I remain steadfast in my assertion that ebb-tidal deltas exhibit major symptoms of geomorphological badassery.
Although the concept of geomorphological badassery may seem silly at first, it illuminates several important truths of our (mis)understanding of these complex bathymetric features. Ebb-tidal deltas are important to study for reasons of coastal flood protection, navigational safety, and ecological value, but we are bad at predicting how they will evolve. This is because each ebb-tidal delta is unique, making it challenging to generalize their behavior. Furthermore, their chaotic, non-conformist behavior renders many of our usual deterministic prediction techniques ineffective. Lastly, the amplifying effect of highly nonlinear physical processes means that small physical changes (e.g., the development of a tiny shoal) could have disproportionately large consequences (e.g., relocation of a channel several kilometers wide). As such, badassery provides a useful conceptual framework for describing the challenges presented by ebb-tidal deltas to coastal engineers and scientists.
In an era of rising sea levels, ambitious plans for coastal protection works are emerging around the world. One such plan is the Delta21 project, proposed by group of Dutch coastal engineers and entrepreneurs. Their goal is to improve flood protection at the mouth of the Haringvliet estuary and develop a tidal power facility, all in one integrated project.
However, the law of unintended consequences often looms large in these sorts of massive infrastructure projects, particularly for environments as complex as estuaries. After a massive flood in 1953, the Dutch constructed the Delta Works, damming most of the estuaries in the southern half of the Netherlands. Prior to that, the Afsluitdijk was constructed across the Zuiderzee in the northern part of the country. These protection works have had dramatic consequences on the physical and ecological development of the Dutch coast, and manyofmycolleagues here have devoted their careers to analyzing the impact of these interventions.
But instead of just looking back and dissecting the successes and failures of 50 or 100 years past, what if we could also use our latest diagnostic tools for predicting the potential impact of bold future interventions? If the Delta21 plan goes ahead, how will the mouth and ebb-tidal delta of the Haringvliet estuary and surrounding coastline evolve? Will existing habitats (particularly in vital intertidal areas) be preserved, disappear, or even expand?
Today, Mayra Zaldivar Piña tackled these questions head on, and successfully defended her master’s thesis, “Stability of intertidal and subtidal areas after Delta21 plan“. I had the pleasure of co-supervising Mayra’s work throughout the last eight or so months, and am very proud of her. She embarked on a challenging modelling project and showed an exemplary critical scientific attitude. I was also so impressed with the persistence and tenacity she showed in doing nearly her entire project during the pandemic. Writing your thesis is a difficult and isolating experience at the best of times, and these are not the best of times. Nonetheless, she kept at it and delivered an impressive thesis in the end!
Congratulations Mayra, and best of luck in the next steps of your career!
Three years ago, I experienced one of the highlights of my professional career so far. Alongside researchers from 3 universities, the Dutch government, and several other institutions, we carried out a 40-day field measurement campaign at Ameland Inlet in the north of the Netherlands. We deployed several frames loaded up like Christmas trees with every instrument imaginable: ADVs and ADCPs to measure waves and currents, LISSTs and OBSs to measure suspended sediment, a YSI multiprobe to measure salinity and other water quality indicators, and even a 3D sonar to track the migration of ripples along the seabed.
Four of our five frames survived the relentless ebb and flow of the tide, and even two major storms (one of which left me stranded in Germany after the wind blew down all the overhead train power lines between Berlin and Amsterdam!). In the end, we obtained enough data to keep me busy for probably 3 PhDs, if not the rest of my career. This is just as well, since that last frame was buried in the storm, and based on our understanding of the local dynamics, it will likely re-emerge in another few decades, just in time for my retirement! I look forward to sharing my other findings with you here in the next few months!
Although it used to be the norm for scientists to squirrel away their data, there is an increasing movement towards open accessibility of research data. This improves transparency and accountability in the scientific process, and opens up new opportunities for collaboration. The data we collected is now available in its entirety here on the 4TU web portal or on Rijkswaterstaat’s interactive web viewer.
However, there is a lot of data – I mean A LOT! To help researchers interpret the contents of this database, we prepared an overview paper, which was finally published in the journal of Earth System Science Data! It is also accompanied by a more detailed report, which gets into the nitty-gritty details we didn’t have room to describe in the paper. Nobody likes to read a phonebook-sized report, but it’s nice to have the information there for the few brave souls who do want to comb through our dataset.
It was all a huge team effort, as evidenced by the 20+ co-authors. My contribution to this paper focused on the processing of the LISST and YSI multiprobe data, which tell us about the size of particles floating through the water, and how salty that water is. I also designed the maps. As a kid, I loved to read and draw maps, and I think that 7-year-old Stuart would have been tickled to know that he would still be dabbling in cartography all these years later.
As the research in the rest of my PhD (and beyond!) will continue to focus on the fruits of this measurement campaign, I am very keen to work together and collaborate with other researchers who have an interest in this dataset. Please get in touch if you are interested!