Mangrove forests protect tropical coastlines around the world from the effects of waves, in addition to providing valuable habitat for countless species. As such, their preservation and restoration is a key element of many plans for improving coastal resilience against flooding and erosion in the face of climate change. However, you can’t *just plant* a mangrove forest anywhere – mangroves are extremely picky, dancing on the edge of the intertidal zone where they get just wet enough but never too wet for too long. They also need safe, stable shorelines for their seedlings to take root and grow stronger, without too many waves and with just the right sort of muddy conditions to make a comfortable home.
Mangroves drop their seeds (called propagules) in the water, which then float around with the currents for days to weeks until they find a suitable home. But which pathways do these mangrove seedlings take as they float along the coast? Are those the same pathways that sand and mud take? These are questions that we need to answer in order to make better decisions about mangrove restoration. To get to the bottom of this, we recruited Femke Bisschop.
Big news to start 2023: I am now an Assistant Professor in Coastal Engineering here at TU Delft! An opening appeared online last summer, and after weeks of preparing applications, several rounds of interviews and a teaching demonstration, and a lot of waiting, I finally got the good news. This has been my dream job for a long time and I can’t believe it came true.
Officially, my new portfolio will focus on “Climate-Robust Deltas”. How does sediment contribute to the strength and adaptability of our coasts and deltas against the effects of sea level rise and climate change? In my research we approach this gigantic problem by quantifying sediment pathways and connectivity for strategic placement of sediment, using a combination of numerical modelling and field measurements. In the coming years, I hope to build up a diverse team of enthusiastic, coastally curious researchers to tackle these challenges. Stay tuned for opportunities to join our group!
At the end of June, we will welcome a group of about a dozen American PhD students for our second annual IRES summer school, hosted at Deltares/TU Delft/Utrecht University and organized by the University of New Orleans and The Water Institute of the Gulf in Louisiana.
Last year we hosted 14 American PhD students for two (fully funded!) weeks in beautiful Delft. It includes D-Flow FM model training, cool field trips to sites around the Netherlands, a lab session, networking galore, guest lectures, and time for exploring the area. Last year everyone seemed to learn a lot and have a pretty good time (I sure did!). We have a great team and are excited to make it even better this year. Please share this with anyone in your network whom you know might be interested!
More details can be found in the pdf below. If you are interested you can apply here before January 27th, 2023. We will host the summer school for a third and final time in 2024, so if you are too late or ineligible this year, stay tuned for another chance next year!
Tropical cyclones or hurricanes threaten the lives of millions and cause billions of dollars in damage every year. To estimate flood risks at a particular location, scientists and engineers typically start by looking at the historical record of all previous storms there. From these records, they can statistically predict how likely a storm of a given size is (e.g., the biggest storm likely to occur there in 100 years).
There are two problems with this approach: (1) What if there isn’t much historical data in the records? This is often the case for Small Island Developing States (SIDS) and in the Global South. If you don’t have enough data points (particularly for rarer, more extreme events), your statistical estimates will be much more uncertain. (2) What if the historical record isn’t representative of the conditions we are likely to see in the present and future? This is also a big problem in light of climate change, which is expected to bring sea level rise and changes in storminess to coasts around the world.
To address these challenges, our team led by Tije Bakker came up with a new approach to estimating tropical cyclone-induced hazards like wind, waves, and storm surge in areas with limited historical data. Our findings are now published open-access in Coastal Engineering here!
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!
I love lighthouses, and am borderline obsessed with them. I have lucky lighthouse socks (I’m wearing them today), I own books about them, and in high school I made a papier-mâché lighthouse lamp. I have spent hours in the rain trying to photograph them during storms. Furthermore, they are most often found in places where the sea is at its most violent, and from a technical perspective, most interesting.
Naturally, when a bright master’s student from our lab asked if I was interested in joining his thesis committee to research the impact of breaking waves on lighthouses, I could not help but say yes. My research on coral reefs focuses mainly on the complex ways in which waves change as they break across the reef. In many ways, this is a similar process to what happens when waves hit the rocky shoals that many lighthouses are built on. This makes for a compelling intersection between my professional interests and private obsessions!