Can 3D-Printed Corals Help Us Prevent Flooding?

Coral reefs around the world are dying; that much is clear from the headlines we see in the news that grow increasingly distressed with each passing year. This is an ecological catastrophe, but are we also losing another key benefit of reefs? Coral reefs provide a form of natural protection against wave-driven flooding on tropical coastlines. This is partly because the physical form of the reef (often a big rocky shelf) serves as a sort of natural breakwater, but is also due to the frictional effects of the corals themselves.

Many species of coral have complex shapes that disrupt the flow of water across reefs, generating turbulence and dissipating energy. This has the effect of reducing the height of waves as they travel across the reef towards the shore. However, these effects are incredibly complex and poorly understood, so we usually just simplify them in our predictive models by considering a reef to be more “hydraulically rough” than a sandy beach, for example. But we need to do better: these models are used to forecast flooding and estimate the impact of future climate change on vulnerable coasts.

How can we improve this? In coastal engineering, we often conduct experiments in the laboratory to test our theories and understand the chaos of natural systems in more controlled settings. What if we could make a scale model of a coral reef and measure exactly how waves are dissipated?

I am extremely proud to announce the graduation of Paul van Wiechen, one of the Master’s students whom I have had the pleasure of supervising. Yesterday, he defended his thesis, “Wave dissipation on a complex coral reef: An experimental study“, where he built a tiny coral reef in the TU Delft wave flume (a 30-m long bathtub with a wave-making paddle at one end) using hundreds of 3D-printed coral models.

Paul’s thesis, “Wave dissipation on a complex coral reef: An experimental study“.

It was one of the coolest projects I have ever seen, and his research provides us with valuable measurements that give us a deeper understanding of the vital role that corals play in protecting our coasts.

He also did all of this in the middle of a global pandemic, and somehow managed to stay completely on schedule. We are very lucky, because Paul will be joining the Coastal Engineering department here at TU Delft to start a PhD on dune erosion this fall. We are all glad to have him on the team and eager to see what his research unveils next!

Clustering Coral Reefs for Coastal Flood Forecasting

Many of the world’s idyllic tropical coasts are facing threats on multiple fronts.  Rising seas threaten the very habitability of many low-lying islands, and the coral reefs that often defend these coasts from wave attack are dying, too.  Compounding this problem is the sheer number and variety of these islands: there are thousands of islands, and the coral reefs surrounding them come in all shapes and sizes.  Located around the globe, these islands are each exposed to a unique wave climate and range of sea level conditions. This variability in reef characteristics and hydrodynamic forcing makes it a big challenge to forecast how waves will respond when they approach the shore, something that is quite tricky even at the best of times.  Under these circumstances, how can we protect vulnerable coastal communities on coral reef coasts from wave-driven flooding?

This is the problem that our fantastic former student, Fred Scott (now at Baird & Associates in Canada), tackled in his paper, Hydro-Morphological Characterization of Coral Reefs for Wave Runup Prediction, recently published in Frontiers in Marine Science.  Working in partnership with Deltares and the US Geological Survey for his master’s thesis, Fred came up with a new methodology for forecasting how waves transform in response to variations in the shape and size of coral reefs.

(A) This is a typical fringing coral reef cross-section, showing waves approaching from the right, with the shore on the left. (B) Fred came up with a number of algorithms for classifying and organizing the massive dataset of coral reef cross-sections. (C) The measurements used in our study are from sites around the globe. (D) This is what 30,000 reef cross-sections look like when you try to plot them all on top of one another- clearly we need to whittle those down a bit… [Source: Scott et al, 2020]
In our previous research on this topic, we tried to predict flooding on coral reef-lined coasts using a very simplified coral reef shape.  This was fine as a first guess, but most reefs are bumpy and jagged and bear little resemblance to the unnaturally straight lines in my model. We couldn’t help it though: there just wasn’t enough data available when I started my thesis four years ago, so we did the best we could with the information we had at the time. On the bright side, using a single simple reef shape meant that we could easily run our computer simulations hundreds of thousands of times to represent a wide range of wave and relative sea level conditions.

Fast forward three years to when Fred began his own thesis. We now had access to a mind-boggling dataset of over 30,000 measured coral reef cross-sections from locations around the world!  However, instead of too little data, we now had too much!  If we wanted to simulate a whole range of wave and sea level conditions on each of the reefs in our dataset, it might take months or even years to run our models! Fred had the daunting task of distilling that gargantuan database down to a more manageable number of reef cross-sections.

But how do we choose which cross-sections are the most useful or important to look at?  Even though every coral reef is, like a beautiful snowflake, utterly unique, surely there must be some general trends or similarities that we can identify, right?  This question lies at the heart of Fred’s research, and to answer it, he turned to many of the same powerful statistical and machine-learning techniques used by the likes of Google and Facebook to harvest your life’s secrets from the internet or power self-driving cars.  Maybe we can use some of this technology for good, after all!

The main approach that Fred used in this study was cluster analysis, a family of techniques that look for similarities or differences between entries in a dataset, and then group the entries accordingly into clusters.  The entries within one cluster should be more similar to each other than to the entries in other clusters.  In our case, this meant grouping the reefs into clusters by similar shape and size. This allowed us to increase efficiency and reduce redundancy by proceeding with 500 representative cross sections, instead of the entire database of 30,000.

These days when I’m lonely, I Zoom with 500 of my favourite coral reef profiles…

Other studies in our field have tried similar approaches (such as this Brazilian study of coral reef shape), but the innovative part of Fred’s technique was to also account for similarities in the hydrodynamic response of the waves to each reef via a second round of clustering. Wave transformation on coral reefs can be immensely complicated, so it is entirely possible that two reef profiles could look very different, but lead to the same amount of flooding in the end.  Since we are mainly concerned about the flooding (rather than a classification for ecological or geological purposes about coral reef formation and evolution), this suits us just fine!

In the end, Fred was able to distill this colossal dataset into between 50-312 representative cross sections that can forecast wave runup with a mean error of only about 10%, compared to predictions made using the actual cross sections.  This opens the door wide for a range of future applications, such as climate change impact assessments or coral reef restoration projects.  Right now, we are working on a new project that will apply Fred’s approach to the development of a simplified global early-warning system for wave-induced flooding on coral reef-fronted coasts.

Great work, Fred, and congratulations on your first publication! I am excited to see where this road takes us!


  1. Scott, F., Antolinez, J.A.A., McCall, R.C., Storlazzi, C.D., Reniers, A.J.H.M., & Pearson, S.G. (2020). Hydro-morphological characterization of coral reefs for wave-runup prediction. Frontiers in Marine Science. [Link]
  2. Scott, F. (2019). Data reduction techniques of coral reef morphology and hydrodynamics for use in wave runup prediction. [Link]. TU Delft MSc thesis in cooperation with Deltares and the US Geological Survey.
  3. Scott, F., Antolinez, J.A., McCall, R.T., Storlazzi, C.D., Reniers, A., and Pearson, S., 2020, Coral reef profiles for wave-runup prediction: U.S. Geological Survey data release [Link].

Betty the Resilient

Today we say goodbye to my Grandma, the inestimable Betty Pearson. Although its effects on my life have been quite tangible, the coronavirus remained quite abstract: something defined more by an absence of things than by a presence.  Sadly, my grandmother has joined the ranks of those taken down by this great absence.  Another absence that my family keenly feels right now is our own: her funeral this afternoon will be attended by my uncle and a few of my cousins, but my dad and the rest of my family are scattered across Canada and Europe. We cannot attend the ceremony in Scotland, since although our world has stopped for a moment, the pandemic outside just keeps on rolling.

But I hardly think that Grandma’s life should be upstaged by current events, so today I want to shine a light on this remarkable woman, the most resilient person I ever met. Grandma was a woman of incredible strength, courage, and love. Born in Scotland in 1925, she spent the better part of her teenage years in the Second World War, probably the sort of experience that makes you grow up too quickly.  After the war, she moved to Canada to start anew. 

On the ship across the Atlantic, she met some folks who were on their way to visit some friends in Richmond Hill.  Grandma stayed in touch with them, and she was later introduced to the family whom her shipmates were staying with. She got wind that they were going bowling, and their son came to pick her up. “I thought he was alright! IMMEDIATELY! I’ll always remember. He was wearing a white v-neck sweater, and he was very kind.” This was Bun (Bernard), our Grandpa, a dashing young pilot.  By 1953, they were married, and had spent several years moving around the country as his job took him to different air bases.  It was in Alberta that my Dad appeared, and a few years later in Ontario, my Uncle Glenn.  During these years, Grandpa took many journeys across the high Arctic islands of Canada, as part of mission to map these remote northern territories.

Tragedy struck in 1961, when my Grandpa died in a helicopter crash in remote Labrador.  After that, she moved back to Scotland to raise her boys closer to her parents, first living in Largs, and then Glasgow.  In spite of such an immense personal loss, she brought up Dad and Glenn in a very loving home, something for which she will have my eternal gratitude. Under the sort of circumstances that would have easily derailed lesser souls, she persisted. Grandma went back to school to become a teacher, and eventually worked her way up to became headmistress of a school in Glasgow. In spite of the tragedy that they endured at a young age, her two boys did not just get by, they thrived, getting good educations and building successful careers for themselves. Most importantly, they built loving families of their own.  In all of these things, but especially the latter, Grandma was extremely proud of her boys.  The love and strength that she brought to the world in the face of great challenges was undoubtedly an important factor in them turning out so well.

She went from Mum to Grandma when I came along in 1989, followed shortly thereafter by my three cousins, my brother, and my sister.  Even though we grew up on the other side of the Atlantic from her, she always made the effort to get to know us and see us at least once a year, usually at Christmas.  She was always full of love and encouragement.  Also chocolate and books.

The latter was particularly important for me: at Christmas 1997, Grandma gave me a book that had been winning rave reviews in the UK, but had yet to make much of a splash in Canada.  Telling the wonderful story of a young wizard and his friends, this book proved to be a gift that would keep on giving, launching an obsession that would continue into – let’s face it – my 30s.  Harry Potter still brings me great joy, and has brought me closer to friends from around the world who share that same joy.  Thanks, Grandma.

In 2006, just before my final year of high school, I was privileged to spend the summer in Scotland, hiking in the highlands and hanging out with her in Glasgow. This was the start of getting to know her as more than just a child. She started to change in my eyes, becoming more than just the wonderful woman who appeared at Christmas to dispense excellent hugs and heaps of books.  I began to understand the incredible life she had lived, and how much that had shaped my family and my own life.

My relationship with Grandma began a new when I moved to Europe to start my master’s degree in 2014. I lost my other grandparents in 2008 and 2011, but unfortunately never really got to know them well as an adult.  I was determined to make the most of things and get to know Grandma.  Furthermore, after 2014, I was the nearest member of our immediate family, so I felt that seeing her was a small way of bringing us all closer together.  Glasgow is a cheap 1.5 hr flight from Amsterdam, so I made as many trips as I could, going once or twice a year since I moved out here.

During one of my busier semesters, I gave her a call to see if she wanted to chat.  “How about Tuesday? I have bridge club right now!” My then-90-year-old Grandma had a more exciting social life than I did, but that was pretty much par for the course – she was always the life of any party she attended.  At her local mall, the salespeople all knew her by name, famous for making her rounds with friends or the occasional grandchild in tow. Until well into her 90s, she possessed extraordinary reserves of energy, taking three flights of stairs every day to get up and down from her elevatorless apartment. I hope that I have that much get-up-and-go when I am that age. 

Grandma was also elegant and full of class, always comporting herself with the utmost dignity when we went out. In spite of this demeanour, or maybe even partly because of it, she also had another side that gleefully embraced the ridiculous.  One Christmas morning, she waltzed (in a manner of speaking) down the stairs wearing a truly ostentatious Christmas sweater and pigtailed hat, looking like some sort of ludicrous viking elf.  She then proceeded to yodel, even though, I am sad to say, yodelling was not one of her many gifts.  Whenever we visited the Kelvingrove gallery in Glasgow, I always insisted that we visit the Elvis statue.  Grandma would unfailingly oblige me, joining in on the bizarre photoshoots I would instigate with her and The King.

What did we do together when I came up to Glasgow?  Truthfully, not much, but it never mattered.  We would often sit in front of the TV together, eating fish and chips, or getting up to date on the latest gossip about so-and-so’s husband from downstairs.  Determined that running up and down hills in Norway had made me too skinny, she also passed considerable time trying to convince me to put more butter on my toast. We always tried to get out of the house too, whether it was driving down the coast to Largs for a ludicrously extravagant ice cream (her favourite), rolling around Kelvingrove park, or just going for a spin around the mall.

Her apartment in Glasgow will always be one of my Happy Places.  The view from her window, the old trinkets on her shelves, and the creak of her floorboards are immensely calming.  Last year, Grandma moved into a retirement home, and even though she slowed down a lot, she always seemed to have more sparkle in her eyes than anyone else in there.  Grandma was always supportive and full of love, and I was happy that even as her memory started to fail, she still remembered me and enjoyed our time together. 

In recent visits, she would often remark to me, with a mix of sadness and pride, “I’m a survivor”.  And she was!  She made it to 94, living a life full of love in spite of the immense challenges that she faced over the years. I will miss her immensely, but am comforted by all of the good memories and positive things, of which there are many.  I love you, Grandma.

Flood Hazards on Vulnerable Atolls

How can we predict flooding on vulnerable atolls in the Pacific?  Today, Tije Bakker defended his thesis, entitled “Compound flood hazard assessment of atoll islands based on representative scenarios for typhoons and non-typhoon conditions: A Majuro case study“. Tije is one of the master’s students that I supervise, and we are all proud of him and his work.

Majuro is an atoll island in the Marshall Islands, located in the middle of the Pacific, just north of the equator.  With 20,000 people packed into less than 10 square kilometres, it is one of the most densely-populated islands on earth.  It is also in big trouble: with an average elevation of only 3 m above sea level, Majuro faces serious risks of flooding.  They can’t “head for the hills”, because there are none. The threat of drowning under rising seas looms on the horizon, but many low-lying tropical islands like Majuro will be rendered uninhabitable not within centuries but within mere decades due to flooding by waves.

Predicting these floods and planning appropriate measures to mitigate their impact is thus a matter of life or death for people living on these islands. My previous work on this topic considered only “sunny day” floods due swell waves generated by distant storms.  Tije’s thesis took the next step and focused specifically on predicting compound floods: the combined effects of flooding due to waves and rain.   On top of that, Tije took on the much more challenging task of predicting the massive and volatile typhoons that can clobber a small island like Majuro.

The methods he developed will be very useful not just for Majuro, but also for other vulnerable islands.  Given its relevance and novelty, we hope to publish it as a paper in the coming months. Great job, Tije!

Fjords of the High Arctic

A few weeks ago, I was reading a book about glaciology recently when a sentence caught my eye.  Many advances in our understanding of how glaciers developed and transformed our world during the last ice age came from studying the Canadian landscape.  In particular:

A benchmark example [of paleo ice sheet reconstruction] was the compilation of the first Glacial Map of Canada in 1959, followed by its update in 1968, by the Geological Survey of Canada, based on painstaking aerial photograph and field mapping by its officers on a map sheet by map sheet basis after the completion of the aerial photograph coverage for the whole country in the 1950s.

This caught my eye, because I knew that my Grandpa on my Dad’s side of the family was a pilot who flew a lot of aerial surveys for the Canadian government in the late 50s.  I mentioned this to my Dad, just thinking he’d say, “gee, that’s cool”, and move on.  Apparently that triggered something in him though, because a few days later my email inbox was filled with a treasure trove of old family photos that I had never seen before.  In recent years I have also developed an interest in Arctic coastal geomorphology, so this discovery scratched a couple of itches for me.

One of the photos was taken above Alexandra Fjord on Ellesmere Island, which is insanely far north (78°N!):

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Alexandra Fjord, Ellesmere Island.  Photo copyright B.G. Pearson.

The cool thing is that when I went into Google Earth, I was able to snoop around and actually to find the same vantage point.  To my surprise, it seems like the glaciers there haven’t changed much since my grandfather was there in 1957:

Alexandra Fjord today, seen in Google Earth.

However, Dad pointed out that perhaps the glacier at the front hasn’t changed, but that the ice field behind it has shrunk.  He probably has a point there…

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So pristine!  Photo copyright B.G. Pearson.

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My Grandpa’s airplane on the right hand side.  Photo copyright B.G. Pearson.

Why was he actually up there, and what were they surveying?  A series of radar transponders were set up across northern Canada so that the airplanes could precisely triangulate their positions .  Based out of Ottawa, my Grandpa and his colleagues carried out many long flights between remote destinations A newspaper article from 1957 describes the tremendous undertaking that mapping the entire Canadian Arctic was, apparently the world’s most ambitious aerial survey operation at the time:

SEVEN-YEAR JOB: Rockcliffe Squadron to Complete Mapping
Monday, March 25, 1957

“Planes from the RCAF’s 408 Photo Squadron at Rockcliffe Airport will fly to within 450 miles of the North Pole this Spring to complete the geodetic survey of Canada which it started seven years ago.”

“Using the huge USAF base at Thule, Greenland, and RCAF’s own base at Resolute Bay, both well within the Arctic Circle, the planes will criss-cross approximately 400,000 square miles of Arctic wasteland to produce reference points for the accurate mapping of Canada.”

“This year’s aerial mapping mileage will bring over 3,000,000 square miles – approximately 90 percent – of Canadian territory accurately surveyed by the Air Force. When the 300 men of the squadron return to base here about July 1, they will have completed the world’s greatest aerial survey operation.”

Survey points in the Canadian Arctic from the 1950s.  My Grandpa flew some of the northernmost missions.

While the mapping operation may have been motivated by a Cold War-era push to map Canada’s north for defense purposes, the operation was also of great scientific benefit.  In addition to providing a wealth of useful data for glaciologists, the measurements also provided important insights into other fundamental geophysical questions.  For instance, the earth is not a sphere, but rather an oblate spheroid, or something like a squashed rugby ball.  But even then, gravity is weird and complicated, so the rugby ball comparison only takes you so far, and precise measurements are necessary to figure out all of the actual irregularities in Earth’s shape.

Measurements like these have many applications, including for estimating sea level rise rates.  By understanding how the Canadian Arctic is rebounding in response to deglaciation, scientists can better answer Tricky Questions About Sea Level Rise there.

One of my favourite stories from the 1957 article involved some of the corrections that were made to previous maps:

“Throughout the … programme, many positions believed to be accurate were found to be in error. In 1956, for example, Prince of Wales Island (in which the North Magnetic Pole was then located) was found to be three miles further south than was indicated on the map.”

“Although they didn’t possess any supernatural strength to move mountains, from such discoveries as this, the members of the 408 Photographic Squadron did, facetiously, claim the ability to move islands.”

I would thus like to think that all my research on islands is simply carrying on a Pearson family tradition!  My Dad (a civil engineer) also worked in the Arctic during the 1980s, constructing artificial islands in the Beaufort Sea.  That’s a story for another time, though!

Speaking of Pearson family traditions, I can see that my Grandpa also had a clear eye for photographic composition, a gift that my Dad quite strongly inherited:

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Airship on some remote runway in the far Canadian north.  Photo copyright B.G. Pearson.

Another reasons I was so delighted by these photos is because one of my favourite painters, Lawren Harris, also spent a lot of time in the Canadian Arctic. I have always felt drawn to his dramatic mountain landscapes capped with snow, and nary a tree for thousands of miles.  The mountains of the far north have a particular shape to them, which seems unique compared to most of the mountains I have seen with my own eyes.

Mount Thule, Bylot Island, by Lawren Harris, one of my favourite painters.  He had a very unique view of the same Arctic landscapes my Grandpa used to fly over.

I made it as far north as Lofoten in Norway (68°N), and have flown over parts of the Arctic on transatlantic summer flights, but have never actually set foot on those rugged and remote hills.  Something for my bucket list!

One more of Alexandra Fjord from space, because I can’t get enough of the staggering beauty of these landscapes.  [Source: Sentinel 2 L1C on July 17, 2019]

Coastally Curious and in Quarantine

Greetings from Delft on Day 10 of quarantine!  These are strange times indeed, on so many levels.  I am fortunately still safe and healthy at home in Delft.  Let’s all keep our hands washed and fingers crossed in the weeks to come, and STAY THE FRIG HOME! We’re all in this together.

I have in part been occupying myself with preparing online lectures for our Coastal Dynamics course. We are extremely fortunate in that most of the course was already available online due to preparations made in previous years, but the lectures I was meant to give this week on tidal inlets were not. I changed a bunch of things in the slides last year, so we had a number of student requests to record new lectures. We live in an era where online education was already becoming more and more the norm, and I think this crisis will just push that trend over the edge.

With that in mind, I decided to try my hand at narrating the slides using Kaltura, a program for doing video capture. There are a few different options out there, but that was the one that I liked best. I have actually been having a lot of fun with the lectures- it feels like I’m hosting a podcast or on the radio. “GOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOD MORNING QUARANTINE!!!!!” I suspect it wouldn’t be the most popular podcast (there are not so many of us ebb-tidal delta enthusiasts), but hopefully I can convert a few of our students in the process.

On Friday I prepared a lecture on the evolution of barrier coasts, such as the Dutch coast or much of the Eastern and Gulf of Mexico coasts of the US. I couldn’t help but share a few interesting links with the students, and I thought I’d post them here too. This is a really cool animation showing 30 years of barrier island and tidal inlet evolution on the southeastern coast of Australia, obtained via satellite imagery:

There’s also the iCoast tool developed by the US Geological Survey for training their machine learning algorithms to recognize storm damage to barrier islands from hurricanes.  It shows you to see before and after photos, and asks you to tag the changes or damage that you see, which is a great way to learn more about coastal geomorphology.  You’re also helping the USGS improve their detection algorithms- citizen science!:

And here’s another cool interactive site about barrier islands that just popped up yesterday in my twitter feed:

To keep myself sane/busy this weekend, I bought a linocut printing kit from the printing shop around the corner from my house (Indrukwekkend, which means “impressive” in Dutch- I love puns that work in more than one language!).  I had always wanted to try it out, but never made time for it.  No time like the present!    I took one of my old sketches of waves (see here for the original inspiration) and made a print of it.  By the end my desk was an unholy mess of ink, but I had a lot of fun and found the linoleum carving to be very therapeutic.  See the top of the page for the finished product!


That’s all for now. Stay sane and healthy, readers!  And be kind to one another.

Do You Know the Way to San Jose? This Sediment Does…

What pathways does sediment take as it travels through an estuary?  Yesterday, Laurie van Gijzen defended her thesis, entitled “Sediment Pathways and Connectivity in San Francisco South Bay“. Laurie is one of the master’s students that I supervise, and she has done a great job on this project.

San Francisco Bay is a massive estuary, with over six million people living nearby.  In addition to San Francisco, Silicon Valley sits on its shores.  Some of the biggest tech companies in the world like Google and Facebook have their head offices right next to the Bay.  For over 150 years, the ecological health of the bay has deteriorated, in part due to land reclamations and contaminated sediment from gold mining. The dynamics of San Francisco thus have a huge economic, social, and environmental impact.

Laurie’s work focused on calibrating and improving a sediment transport model of the bay, in order to track the pathways of fine sediment (i.e., mud).  She worked with a notoriously fickle model (DELWAQ) and succeeded in greatly improving its calibration.

Laurie’s thesis summarized into a single diagram (Figure 6.1 from her report).  She shows the dominant sediment pathways as dark arrows, and the net accumulation (import, in orange) or depletion (export, in blue).  Also indicated are the dominant physical processes responsible for sediment transport in the different parts of the bay.  The baroclinic processes mentioned here are currents resulting from density differences in seawater due to changes in salinity and temperature.

Another cool thing about her work is that Laurie was the first person to apply the coastal sediment connectivity framework that I have been developing!  She was able to use this to identify key transport pathways and critical locations in the bay. It was extremely helpful for my research, as it gives us a proof of concept that our framework is applicable to multiple sites and can tell us something useful.

Her work was also accepted for a presentation at the NCK Days conference, which was meant to be held this week in Den Helder, but was cancelled due to ongoing societal chaos. Great job, Laurie!

Sand: Clatsop Beach, Oregon

Today’s sand sample is from Clatsop Beach, Oregon, on the Pacific Northwest coast of the US.  Last summer I spent several months modelling sediment transport at the mouth of the Columbia River with the US Geological survey, and had the great privilege of making a site visit at the end of my stay.

Working in partnership with Oregon State University and the Washington State Department of Ecology, I assisted with a topographic survey of the beaches surrounding the Columbia.  Half the team surveyed the submerged parts of the beaches via jetski, and my group walked transects across the beach and up the dunes using backpack-mounted GPS units.

Starting at far-too-early-in-the-morning, our team split off individually, and I had an entire kilometers-long stretch of the beach to myself until almost lunch time, when we reconvened.  I love long walks on the beach and take great pleasure in that sort of solitude in nature, and it was even cooler to do that while collecting data that could help the project I was working on.  The digital computer model I had worked on all summer was now suddenly a real place where I could feel the sand between my toes.

Gold in Them Hills

The sand at this beach is interesting because of the black grains we see scattered throughout.  This sediment is made of minerals like chromite, magnetite, and garnet, which are heavier than the whitish quartz grains we see around them.  These deposits, known as “placers”, were transported to the sea from the mountains inland by the Columbia River. They form on the beach because lighter minerals like quartz are preferentially sifted out by waves and currents, leaving more of the dense particles behind.   This even includes trace amounts of gold!  Can you see any in the photograph below?

Sediment sample from Clatsop Beach, OR.  Note the black “placer” deposits of heavy minerals.  Can you see any flecks of gold?

At the end of our survey, I walked along the beach to check out a surprising object emerging from the sand: the wreck of the Peter Iredale, a sailing ship that ran aground there in 1906:

The Wreck of the Peter Iredale on Clatsop Beach.

Known as the “Graveyard of the Pacific“, the mouth of the Columbia is truly a “killer ebb-tidal delta”: huge waves and powerful currents meet violently, and have caused dozens of shipwrecks over the past few centuries.  This makes effective management of the sediment there crucial for safe navigation, keeping the shipping channel dredged clear and disposing of the sediment in environmentally-friendly, cost-effective, and useful ways.

Historical shipwrecks at the Mouth of the Columbia River, seen in the Columbia River Maritime Museum.  

Strategic placement of this dredged sediment was the focus of my time at USGS last summer, but I will delve into that more in a future post!

Sand: UBC Cliffs/Wreck Beach

Vancouver holds a special place in my heart.  I was born out there, and even though we moved away when I was very young, it has continued to re-emerge in my life.  In 2011, I moved out there after a difficult breakup and the city breathed new life back into me.  While there, I discovered a new vocation in hydraulic modelling for predicting floods, something that I am still doing to this day.  I have returned to Vancouver a number of times since then, since my brother and a surprising number of my closest friends have ended up out there.  I hope to return this September for a wedding!

Coal Harbour, Vancouver.

One of my favourite parts of Vancouver is walking its coastline.  The city was built on the edge of a large fjord, but has a variety of coastal landscapes, from towering cliffs to sandy beaches, mud flats to salt marshes, and of course a number of urbanized shorelines.

Even though I am in the Netherlands now, I am trying to keep my Vancouver connection alive through my work.  Last year, I co-supervised a fantastic group of TU Delft students who worked with Kerr Wood Leidal and the University of British Columbia (UBC) to investigate the erosion of the Point Grey cliffs, on which UBC is situated.

Eroding cliffs of Point Grey.  The University of British Columbia is at the top of the cliff, so naturally they are concerned with understanding the rate of erosion and means of slowing it.

The project was an interesting one, as the students (representing three different countries) tried to bring their lessons learned about Dutch coastal engineering to Canada.  Canadian coastal zone management is much more fragmented than in the Netherlands, where everything is more or less centrally controlled by the federal government.  The entire Dutch coastline is also incredibly well-monitored, with high resolution bathymetry taken every few years, and with countless other measurements available.  Acquiring the data necessary to perform a coastal engineering study in Vancouver required contacting dozens of different sources and dealing with numerous agencies at multiple levels of government.

Sand from Wreck Beach.  It is quite coarse and angular in shape, and the green and red tints are quite nice. Being glacial in origin, these sand grains have likely been bulldozed by ice or carried by meltwater from far and wide.  This accounts for the variety of particles we see.

In the end, the students looked at a number of possible solutions for slowing the coastal retreat, including sand nourishments and revetments.  One of the most intriguing concepts that they explored was the idea of a clam garden, a traditional approach from the First Nations people living on the BC coastline.   Originally intended for aquaculture, clam gardens are usually small rock walls placed along gravel beaches, behind which where clam-friendly sand or mud can accumulate.  However, this approach could have added benefits for coastal protection by attenuating waves and encouraging the deposition of sediment.  In many ways, it is not that different from the Dutch using brushwood dams to reclaim land in the Netherlands or my colleagues using similar structures to rebuild mangrove habitats.

In Canada, the involvement of First Nations in coastal planning is becoming increasingly important (as I think it should be!), and there is a lot that science and engineering can benefit from their traditional forms of knowledge and experience.  Building with nature instead of fighting against it has recently become a popular design philosophy in coastal engineering, and who better to have as allies in that task than the people who have been living with and building with nature already for centuries?

World War II-era bunker on Wreck Beach overlooking the Georgia Strait, with North Vancouver in the background.


The Delft-Vancouver connection continues: right now we have a group of five students investigating coastal protection solutions with Kerr Wood Leidal and the Tsleil-Waututh Nation.  They have already been out there for a month, and I am excited to see what they come up with!

Sunset over the Spanish Banks, just around the corner from UBC.

Tricky Questions About Sea Level Rise

Last week in our Coastal Dynamics course, we discussed the topic of sea level rise (SLR) and its impact on coastlines around the world.  A rather perceptive student asked me about an assignment question about the subtleties of regional sea level rise:

Where in the world does the melting of the Antarctic Ice Sheet have the greatest impact?

This is a good question, because it shines a light on the complex reality of sea level rise: it is not the same everywhere.  Local factors like isostatic adjustment and regional subsidence mean that certain locations can deviate significantly from the global average rate of sea level change.

Isostatic adjustment is the flexing of the earth’s crust as it rebounds from the heavy weight of ice sheets that once pressed down on it (much like the behaviour of your couch cushions after you stand up). This means that some formerly-glaciated areas like Northern Canada and Norway actually experience a local sea level fall, not a rise.  Further away from those glaciated areas, you can have the opposite effect and experience increased sea level rise due to a sort of levering effect.

However, another important principle (and a mind-blowing one to me, when I first heard it), is that of gravitational attraction: ice sheets are so massive that they actually exert a gravitational pull on the oceans, pulling water levels up towards them.  The flipside of this is that when those ice caps melt, the water near them redistributes to the other parts of the oceans further away.  This leads to the remarkable notion that us in the northern hemisphere will suffer most from the melting of Antarctica, while our southern cousins will get their feet wet primarily from the deglaciation of Greenland and mountainous ice caps in the northern hemisphere.

Contribution to sea level rise from Greenland (top panel) and the West Antarctic Ice Sheet (bottom panel).  In general, the further away from the ice sheet, the greater the increase in sea level (orange colours).  Source: Milne, et al. (2009). Identifying the causes of sea-level changeNature Geoscience2(7), 471-478.

There has recently been some interesting research on the idea of “fingerprinting” the impact of a particular glacier on sea level rise at a given location through exploratory modelling:

“The loss of mass changes Earth’s gravitational field causing the fresh meltwater and ocean water to move away towards faraway coastlines; the resulting pattern of sea-level rise is the fingerprint of melting from that particular ice sheet or glacier. For example, the latest study found that ice melt in Antarctica causes sea level to rise 52% faster in California and Florida than it does in other parts of the world, Velicogna says. Much of Earth’s middle and lower latitudes bear the brunt of rising sea levels because they’re sandwiched between Antarctica and Greenland, which are home to massive ice sheets that are shedding mass as meltwater or icebergs.” Source.

This article in the Guardian nicely illustrates the relevant concepts.  See also here and here for more details.  From these sources (and the references therein) we can see that the mechanisms contributing to sea level rise are highly location-dependent, and I barely skim the surface here.  Although these questions of “which glacier is submerging my house?” are scientifically fascinating, it shines some light on just how complicated our planet’s climate system really is.  It is scary to wonder about all of the future impacts like these that we can’t foresee or don’t yet understand…