A few weeks ago, I shared some sand that my dad brought back from the Butt of Lewis. On that same trip, he and my mom went to visit the island of Barra, where her family originated from before emigrating to eastern Canada in the 1770s.
Halfway through their holiday, I received an excited text message from my dad: “Tell me – the whole island seems like grey granite, so where does the white sand come from? (In fact all the west side beaches are white sand.) Is it coral?”
Eager for a distraction from my work, I did a quick lit review. The consensus seems that indeed, the white sand on the beaches has almost nothing to do with the gneiss found on the rest of the island. In essence, it seems as though most of the original sand was bulldozed there by glaciers during the last ice age or brought there by meltwater as they retreated. Then over the course of the past few thousand years, shell fragments have accumulated and overwhelmed the native glacial sand, making up 7.5% to 82.9% of the total sand. This results in the beautiful white beaches that you see today (Jehu & Craig, 1924; Goodenough & Merritt, 2007).
This might be my favourite sample of sand that I have analyzed yet- it is incredibly shelly, and every photo reveals beautiful new shapes and patterns. I think I will just let the sand speak for itself:
When you zoom out, it doesn’t look like much……but zooming in reveals all sorts of interesting shell fragments with different structures and colours.
I particularly love the piece in the middle of this photo: it almost looks like a piece of glazed pottery.
I’m really quite curious as to what the red and white fragment in the upper left quadrant is. It looks like a piece of octopus tentacle, although I know it can’t be!Purple is my favourite colour, so I love the shade of the fragment in the lower left corner. It actually looks a lot like the coralline algae we saw in my photographs of sand from Archipel Glenans. I wonder if something similar is present offshore of Barra… The cylindrical fragment on the right side makes me think of a Roman column.
This one might be favourite- I zoomed in to 40x magnification to take a closer look. The patterns of the white bubbles are beautiful- I am very curious whether that is a shell fragment or actually some sort of igneous rock left over from Scotland’s volcanic days…
I love the iridescence of the shell at mid-right, and the vivid pink streak in the top left quadrant. So many cool shapes and colours!
I hope you enjoyed those as much as I did. I just wish I knew more about ecology so that I had a better idea of what we were actually seeing here!
When I started this blog, I wanted to focus mainly on things related to coastal science and engineering, but for a moment I’d like to post something more personal. A few of my close friends and colleagues have had a tough week, but has also been an eventful one on the world stage.
The violence and political turmoil following the killing of Qassem Suleimani last week has been awful and frightening, but on Wednesday things took an unexpected turn for the worse. A civilian airplane carrying 176 people crashed, apparently shot down not long after it took off. It later emerged that 63 of those passengers were Canadian, and the majority of those on board were en route to Canada.
It wouldn’t matter where they were from or where they were going, it would still be an immense tragedy and terrible waste of human lives. But this one really hit me hard because as I read through the stories of all the victims, I was struck by a simple fact: a significant proportion of the 63 were science and engineering grad students or recent graduates, just like me. They were all just coming back to school after visiting their families for the holidays, just like I did last week. Just like most of my friends here.
One of my closest friends from home is an Iranian-Canadian engineer, and many of my TAs at the University of Waterloo were Iranian. I can’t help but think of them, and of all my friends and colleagues when I read about the people who were on that plane. Bright people with lives and stories, minding their own business, just going back to school or work.
2020 is not off to the greatest start so far, but we have to hope it can get better, and we have to do our best to make it so, even in our own small way. As my mom says, “never give up a chance to be kind”. Let’s start with that.
I recently paid a visit to my grandmother in Glasgow, Scotland. She is 94 1/2 years old and is still a delight to be with. Since she is living in a retirement home now and doesn’t get out much these days, I rented a car and we went for a drive together down the coast to Troon:
On our way back to Glasgow I pulled over the car in Ardrossan and grabbed a handful of sand from the beach there:
Sand from the beach at Ardrossan, Scotland. It appears to be fine, well-rounded quartz sand. Note the beautiful red tint of the grains.
When I showed my dad this photo, he pointed out that the pink sand grains resembled the red sandstones found in houses and buildings all across Glasgow, the city where he grew up. When I looked into it further, it seems that many of the sandstone bricks used in facades across the city indeed came from Ayrshire, where this beach was located. This is backed up by a geological map of the Firth of Clyde, which shows our little beach comfortably inside the red sandstone zone. A delightful convergence of sediment and architecture!
The Kelvingrove Gallery, one of my favourite places in Glasgow. If you ever find yourself in Glasgow I highly recommend it- it’s free! Note the beautiful red sandstone facade.
That’s one of my favourite things about this field- there always seems to be new and interesting connections back to other things that I love!
Majestic highland cows in Pollock County Park, Glasgow. Note their beautiful red sandstone facades.
This week our sand comes from the delightfully-named Butt of Lewis, the northernmost point of the Isle of Lewis. Lewis is part of the Outer Hebrides, an archipelago off the west coast of Scotland. My parents visited there this summer as part of a trip to Barra, a neighbouring island and the ancestral home of my mom’s family. My dad brought back a little bag of sand from the beach at Ness:
The most important question here is obviously not about the sand though, but rather, why they called this place the “Butt of Lewis”. After half an hour of creative and persistent googling, I couldn’t find anything, though. My guess is just that it’s because it’s at the very back end of the island. But also quite windy?
Live, from the windy Butt of Lewis… [Source: BBC Weather]
This week, we have sand from the beach at Le Vourc’h near Porspoder in Brittany, France. I just returned from a two-month research visit to IFREMER in Brest, and while I was out there I was fortunate enough to rent a car and tour the countryside.
The beach appears to be mostly white quartz sand, but this sample had a single mysterious black grain, sticking out of the picture like the monolith in 2001: A Space Odyssey.
Sand from Porspoder Beach in Brittany, France
When I visited in November, the rocks surrounding this beach were being absolutely pulverized by massive waves, and this was only during a “minor” storm.
Nothing like watching >4 m waves smash against rocks for half an hour to remind yourself that you are a puny human who is lucky to be alive in the face of natural forces that care not one iota about our well being.
My friend Claudia responded with great zeal to my call for sand from different beaches around the world. In addition to her samples from Sword Beach and Dunkirk, she also brought back sand from her holiday to the Greek island of Crete. The sand from Xerokambos Beach is interesting compared to those two French beaches, since it is much more diverse- there are many different colours and likely different mineral origins for the sand grains that we see there.
That being said, when I see pictures of how lovely Crete looks, I have the feeling that I would not be too focused on the finer details of local sand composition if I went on holiday there!
It was Christmas 2016, and I felt like I had bitten off more than I could chew. I’m not talking about turkey, though. Four months into my PhD, I was feeling completely overwhelmed and starting to wonder what I had gotten myself into.
The goal of my project is to identify the pathways that sand takes as it moves in and around the Wadden Islands in the northern part of the Netherlands. Since the Dutch coast has a chronic erosion problem, accurately accounting for the whereabouts of their sand is a matter of national security. Right now, the Dutch deal with a deficit in their coastal sediment budget by adding more sand or “nourishing” wherever there is a shortfall.
Knowing when, where, and how much sand to add is especially challenging around these islands. Here, the persistent push and pull of the tide competes with the chaotic brutality of the waves to move sediment in complex patterns. These patterns are hard to predict with our usual box of tools, so we planned to throw everything we had at the problem: state-of-the-art field measurements, sophisticated computer models, reams of historical data, and a support team of experts from across the Netherlands. As PhD students go, I felt [and still feel!] pretty darn lucky to be a part of such a large and well-conceived project.
The Spaghetti Problem
However, as I started reading more and more about my topic, my initial enthusiasm began to wane. I was floored by just how much research had already been done on what I had thought was a fairly specific niche. The Dutch have been scrutinizing their coast for centuries, and to my inexperienced eyes, it seemed like they had already thought of everything.
There was another problem: at the end of almosteverystudyaboutsedimentpathways, there seems to be a diagram summarizing all the paths with lots of curvy arrows flying all over the place. This veritable plate of spaghetti makes for a nice conceptual drawing, but how can you statistically compare two plates of spaghetti with one another? A “past spaghetti” and a “future spaghetti”, to help understand potential responses to climate change? A “Dutch spaghetti” and an “American spaghetti”, to make my findings more general and useful for other places? If I was going to get anywhere with my PhD, I needed a spaghetti system.
Mmm, sediment pathways… Also, to be clear, this is not The Magical Figure That Single-handedly Changed My PhD. [Source: Flickr]By Christmas, I felt like I was in a weird purgatory between “it’s all been done before! I’ll never come up with anything original!” and “this is insurmountably complex and you’re foolish to think you’ll ever figure this out”. And just a dash of “how-did-I-get-here?” imposter syndrome, for good measure. I spent much of my holiday feeling overwhelmed and inadequate, like I couldn’t possibly live up to my own expectations, or (what I thought to be) the expectations of those around me.
But: new year, new start. On January 11th, 2017, my first day back in the Netherlands from holidays, a paper about coral reef hydrodynamics popped up in my Google Scholar alerts. At that time, I was also finishing up a paper about predicting floods on tropical islands, and I liked to keep an eye on the latest developments in that topic.
“A coupled wave-hydrodynamic model of an atoll with high friction: Mechanisms for flow, connectivity, and ecological implications“. Sounds promising, I like wave models.
In this paper, they wanted to understand how waves and ocean currents move water around Palmyra Atoll, a coral island in the middle of the Pacific. Coral reefs all around the world are in big trouble, and to help them we must first understand the physical processes governing the life and death of corals.
Palmyra Atoll, a coral island in the middle of the Pacific. Unfortunately not my PhD study site… [Source: Wikipedia]This was all very interesting stuff, though not particularly relevant to my research about flood prediction, since they seemed more focused on the ecological impact of their results. It was seemingly even less relevant to my PhD topic on Dutch sand- stay focused and stop wasting your time, Stuart! But then I turned the page and there it was:
The Magical Figure That Singlehandedly Changed My PhD…
The Magical Figure That Singlehandedly Changed My PhD, Figure 13 from Rogers et al (2017). “Connectivity between hydrodynamic zones. (a) connectivity matrix showing the probability a water parcel passing through a destination zone came from a given source zone, and (b) geographic connectivity of top 10% of pathways, where shading is relative importance as an overall source, width of line is relative strength of connection.”
Essentially, the authors had summarized the pathways that coral larvae can take around an island in a mathematically elegant way. This was pretty much identical to the goal of my PhD, if you substitute coral larvae for sand, and an idyllic Pacific island for a stormy estuary in Holland. They did it with a concept called “connectivity”, and it became immediately apparent that I had some homework to do.
So what the heck is connectivity?
So what exactly do they mean by connectivity, and how are we meant to interpret that magical diagram? Let’s start at the top. The upper panel is what we call an “adjacency matrix”, but you can think of it just like one of those mileage charts that you sometimes see in the corner of highway maps.
A mileage chart, which you can read in the same way as the adjacency matrix above. If you want to get between two points, just find the intersection between your row and column of choice. 290 miles from Birmingham to Edinburgh doesn’t sound too bad, until you encounter the menace that is Birmingham traffic… [Source: The Open University]Instead of looking at the distance between two points like in a mileage chart, the authors of the reef paper consider the likelihood of water travelling from one point to another. Darker squares show a higher chance of connection, and lighter squares, a lower chance. For instance, if we look at the first column, water is more likely to flow from the point they call “WT FR NW” to point “WT W” than it is to flow to “WT FR SW”.
The second panel shows the same information as the matrix, but this time actually showing the connections on a map – a “network diagram”. The thickness of the blue lines on the network diagram indicate how strong a connection between two points is. If all this seems rather familiar, then that’s probably because you’ve already met our network diagram’s more famous cousin, the transit map:
Harry Beck’s famous map of the London Underground. This map is a network diagram, much like the coral atoll connectivity map shown earlier. It represents the stations as nodes, and the train lines between them as links. It shows the connections symbolically, rather than at their true geographical locations, but this makes it easier for use to focus on the important things, like knowing where we need to switch train lines to get back to our hotel. [Source: Transport for London]
Cool maps. So what?
After seeing the coral reef connectivity diagram, I started googling and soon realized that I had been woefully ignorant of an entire mathematical discipline. Network theory represents complex systems as a series of points and the links between them. Once you’ve done that, interesting patterns start to emerge, such as the “six degrees of separation” or “small-world” phenomenon. It has been used in neurology, sociology, ecology, epidemiology, geomorphology, and basically every kind of “-ology”, except for coastal science and engineering. As far as I can tell, we seem to be the last ones to the party.
The more I read, the more excited I became, and the more vital it seemed for our field to catch up. Connectivity could help us quantify and bring order to the chaotic spaghetti churned out by our models and measurements – if we could figure out how to adapt it.
The course of my PhD was changed instantly with the discovery of that figure. Not only did connectivity provide a potentially useful tool, but it jolted me out of my funk and got me excited about my PhD again. It was an important finding for my research but not a “eureka moment” where everything was suddenly solved- far from it. It has been a long uphill slog since then, but with the help of some very clever people, I think we have almost reached our first milestone. We presented our early findings at a conference in 2017, and right now we’re in the final stages of preparing a scientific article about our ideas. That paper will then have to survive the woodchipper of peer-review, so it may still be many months before my work sees the light of day. But I remain hopeful.
Would I have stumbled upon connectivity eventually, had I not seen The Magic Figure? Probably not if I had only stuck to reading papers about coastal sediment transport. This finding has shaped my attitude towards coastal engineering research- I believe that the next advances in our field will not come from developing a new bedload equation, but from adopting new tools and techniquesfrom other disciplines. Not that we don’t need better bedload equations – I just don’t think I’m the guy to do it, and I think that we could all benefit from looking over the fence at our neighbours in other fields from time to time. As William Zinsser nicely put it:
“Think flexibly about the field you’re writing about. Its frontiers may no longer be where they were the last time you looked.”
Here is another sample brought back by my friend Claudia, from Dunkirk Beach in northern France. Dunkirk is famous from the Second World War, when the Nazis had cornered Allied troops there and forced a major evacuation across the English Channel.
This is where my inner history nerd and my inner sand nerd collided to ask an interesting question: is the sand on that beach now (and in the photograph below) the same sand that was on the beach during the famous evacuation? There’s no easy answer to that question, but as it so closely relates to the main research questions of my PhD, I can’t resist indulging in such a thought experiment. Shall we try together?
To answer this question, let’s ask ourselves a few things:
What kind of sand is on the beach?
The size of the sand grains will determine how easily it is moved around by the waves and tides. Bigger particles require more energy to move, and are thus more likely to stay where they are. In general, smaller sand grains are more likely to get picked up and transported far away*. Based on the photo above, let’s assume that most of the sand grains are about 200 μm in diameter (that’s 0.0002 m).
The sand also seems to be mainly made of clear or white-brownish grains, so we can probably make a safe guess that they are mainly made of quartz. This will come in handy later if we need to make an assumption about how dense the particles are. Most of this sand comes from large sand banks offshore, which is moved to shore by waves during large storms [1].
How do waves and tides shape the coastline here? To predict how sand moves around on a beach, we need to understand the behaviour of the water there. The tidal range on this part of the French coast is quite large, between 5-8 m [1]. That large range means that a correspondingly massive volume of water is moved back and forth past the beach twice a day, which generates powerful tidal currents. Waves here mainly come from the English Channel to the west or the North Sea to the northeast, and are generally at their strongest during occasional winter storms.
In which direction does the sand usually move? There are several possible fates for our 1940 sand: (a) staying where it is, (b) moving offshore into the English channel, (c) moving westward towards Calais, (d) moving eastward to Belgium, or (e) moving onshore to build up the sand dunes there.
At these beaches, the tidal currents moving eastward towards Belgium are slightly stronger than the ones moving westward back towards England [1]. This is eastward motion is reinforced by waves and wind-driven currents, which also tend to move eastward on average [2]. As a result, the sediment effectively takes two steps forward and one step back, gradually moving in an eastward direction (i.e. (d) rather than (c)).
We also know that there is a regular supply of sand from offshore [2], so let’s rule out (b) for simplicity. The dunes in that area are also relatively stable [2], so let’s rule (e) out, too. If most of the sand is then either moving east (d) or staying put (a), what is the likelihood that our 1940 sand is still there?
Have humans intervened with the coast there? In 2014, the French government created the largest sand nourishment in the history of France on the beach at Dunkirk [3]. This is visible in Google Earth as the giant pile of sand near the red pin (below). If there was still 1940 sand on the beach there, it is now likely buried underneath the nourishment. Depending on where my friend collected her sand, there is a good chance that it is made up of this sand that was dredged from the nearby harbour, rather than sand that was on the beach in 1940.
I had a similar issue with my tracer study: several months after our investigation, the Dutch government placed a huge nourishment right on top of our study site. That means that even if some of our tracer sand is still out there, it is likely buried deep beneath a giant pile of sand, which means that we can’t go back there to take more samples.
What is the likelihood of sand leaving the beach?
After placing the nourishment at Dunkirk in 2014, scientists monitored how the beach changed, and found that it lost 9% of its volume in 2 years [3]. Most of this sand appeared to migrate eastward, as predicted by those other studies. If we had similar data about how much the volume of the beach has changed in the past 80 years, we could estimate the rate at which sand is leaving, and hence how likely it is to still be there. From that, we could come up with a sort of “residence time”: how long we expect sand to remain on the beach given the volumes that are coming in from offshore sandbars and leaving down the coast. That would at least give us a ballpark idea of what to expect. We could also use computer simulations to more precisely predict this transport, but that’s a lot of work for our little thought experiment!
Given all of this information, I would guess that most of the sand that was on the beach in 1940 is somewhere on its way to Belgium, or is still there but buried beneath the new nourishment. Based on the assumptions that we made about this being quartz sand about 200 μm in diameter, we can estimate that in a handful of sand (say, 250-300 mL), there will be about 5 million individual grains!** If we scale this up to an entire beach, then I think the odds are good that at least a few grains have stuck around since then.
There are lots of different ways that you could go about this, though- how would you try to tackle it? Am I missing anything important?
* This “smaller-particles are more likely to get picked up by the waves and currents” rule only works for sand grains that are all more-or-less the same size. If your sand has both large and small particles, you can also have “hiding” effects where little grains of sand hide behind big grains and are harder to move. And don’t even get me started on mud! Mud particles (usually 10-100 times smaller than sand) obey a whole other set of complicated rules that are frankly a little absurd sometimes. But these are discussions for another time…
** Even though the grains in that picture are clearly a bit irregular in shape, we can pretend that they are spheres and calculate their volume Vgrain = 4/3π(0.0002/2)3 = 3.3×10-11 m3. The volume of your hand Vhand is 300 mL = 3×10-4 m3, so we can calculate the number of grains as Vhand /Vgrain, which is about 9 million. But wait! We have to account for all the spaces in between the sand grains, since we’re not dealing with a solid block of quartz. This is usually about 40% for sand, so this is how we get our final number of about 5 million.
[1] Sabatier, F., Anthony, E. J., Héquette, A., Suanez, S., Musereau, J., Ruz, M. H., & Régnauld, H. (2009). Morphodynamics of beach/dune systems: examples from the coast of France. Géomorphologie: relief, processus, environnement, 15(1), 3-22.
[2] Anthony, E. J., Vanhee, S., & Ruz, M. H. (2006). Short-term beach–dune sand budgets on the north sea coast of France: Sand supply from shoreface to dunes, and the role of wind and fetch. Geomorphology, 81(3-4), 316-329.
[3] Spodar, A., Héquette, A., Ruz, M. H., Cartier, A., Grégoire, P., Sipka, V., & Forain, N. (2018). Evolution of a beach nourishment project using dredged sand from navigation channel, Dunkirk, northern France. Journal of Coastal Conservation, 22(3), 457-474.
Today I received the sad news that Gerbrant van Vledder, an assistant professor at TU Delft, passed away unexpectedly last week.
Many in our field know him for his work with SWAN, but I would like to shine a light on something else: his research on using wave models to understand how the people of the Marshall Islands have used wave diffraction around islands to navigate their boats for centuries.
Gerbrant had a strong curiosity about using modern tools to find an overlap with more traditional ways of perceiving the world around us; to listen to voices that were not often heard, and find their scientific merit. I think this was unique among engineers, and a really inspiring example. Whether you knew him or not, I encourage you to check out this fascinating article in which his Pacific adventures were featured:
Although I hadn’t spoken to him much recently, Gerbrant was very supportive during my MSc thesis, when I was researching the impact of waves on low-lying tropical coasts like those of the Marshall Islands. He showed a keen interest in my work, actually reading and giving feedback on my whole 232-page report! Given the dread with which I now confront verbose master’s student reports myself, I am especially grateful for the time he gave me. He supported my interest in Marshallese wave piloting, and with his encouragement, I eventually wrote a brief chapter in my thesis about it. I was lucky to have his experienced and critical eye on my side.
This all comes as quite a surprise. I still have a book that he lent me last year, which I haven’t given back yet…
The main protective barrier for the Netherlands against the threat of flooding from the sea is a row of colossal sand dunes and wide beaches that stretch the length of their coast. However, that barrier is not completely natural — since the Dutch coast is in a constant state of erosion, the sand in their coastal zone has to be continually replenished. This replenishment takes the form of nourishments, which are essentially just massive piles of sand placed on beaches, dunes, or just offshore. The Dutch are lucky, since the bottom of the North Sea is covered in sand for hundreds of kilometers in every direction, meaning that there is a ready supply available for this purpose.
Although we still have plenty to learn about how to construct these nourishments effectively and in an environmentally friendly way, we are starting to get the hang of it — at least for long, straight, sandy coastlines like in Holland. However, this all gets a bit trickier when we turn our attention to the Wadden Islands dotting the northern coast of the Netherlands. These little islands sit between the stormy North Sea and the shallow Wadden Sea, a large estuary whose ecological value is unmatched in the Netherlands.
The coast of these islands is punctuated by a series of inlets connecting the two seas. Chaos reigns at these inlets, where strong tidal currents pass in and out, clashing with waves and whisking sandy shoals in and out of existence in unpredictable ways. This makes the inlets treacherous for ships, but also a challenge to simulate with our computer models and design nourishments for.
How, then, are are we meant to nourish the coast of these islands? We want to keep their inhabitants (and those on the nearby mainland) safe from flooding, but also need to be careful about inadvertently disrupting the vital ecological habitat of the Wadden Sea.
To answer that question, the Dutch government initiated the Kustgenese or Coastal Genesis project. In collaboration with several Dutch universities, companies, and research institutes, they set out to better understand how these tidal inlets work, and whether it is possible to effectively nourish them. The project focuses on Ameland Inlet, which is located between the islands of Ameland and Terschelling.
My PhD project is but a very tiny piece of the very large Kustgenese pie. My goal is to figure out specifically how the size of sand grains affects the paths that they take around tidal inlets. It has been the dream job for someone who has loved playing in the sand ever since he was a little kid. As a result, it has entailed a lot of time at my computer and in the laboratory, investigating the characteristics of the sand in Ameland inlet (that’s also why I have so many pictures of sand on this blog- we have a really cool microscope!). It is very fine sand and would be absolutely perfect for squidging your toes through on a hot day — if it weren’t at the bottom of the sea, that is:
Native sediment from Ameland ebb-tidal delta
In the spirit of ‘why not?’, the Dutch government decided that the best way to test whether nourishments would be effective in this environment was to just go ahead and try one out last year. They dredged up 5 million cubic metres of sand (that’s enough to fill 3 Skydomes, for anyone reading this back home in Toronto) and placed them just outside the inlet. A few months ago, one of the Dutch government officials showed up at a meeting with a “present” for me… some sand from the nourishment!
Nourishment sediment dredged from offshore and placed on Ameland ebb-tidal delta.
Needless to say, I was very excited. At first glance, it appears quite similar to the native sediment, so that means it should behave in a similar manner. Time will tell how the nourishment evolves- we are watching very closely!
Coastally Curious 