Sand: Ardrossan, Scotland

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:

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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!

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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!

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Majestic highland cows in Pollock County Park, Glasgow.  Note their beautiful red sandstone facades.

Sources:

Jardine, W. G. (1986). The geological and geomorphological setting of the estuary and Firth of Clyde. Proceedings of the Royal Society of Edinburgh, Section B: Biological Sciences, 90, 25-41.

Sand: Xerokambos Beach

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.

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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!

Sand: Archipel Glenans

Ga je naar het strand? Mag ik
als je terug komt het zand
uit je schoenen voor
de bodem van mijn aquarium?

Are you going to the beach?
when you come back, may I have the sand
from your shoes for
the bottom of my aquarium?

– K. Schippers

I have had that Dutch poem on a postcard on my bedroom wall for a few years now, but it unexpectedly came to life a few weeks ago.  I mentioned to some friends that I was taking pictures of sand from different beaches with a microscope and wanted to expand my collection.  My colleague Silke enthusiastically responded- she had just returned from a holiday in France and still had sand in her shoes!  “Should I bring it to the office tomorrow?” she asked.  How could I say no?

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Her holidays had taken her to the beautiful Glenans Archipelago off the coast of Brittany, not too far from where I am living right now in Brest. Unlike a lot of the sand I have looked at so far (which was mainly quartz), this beach appears to be quite shelly.  The islands are famous for their maerl beds, a sort of coral algae rich in limestone.  That may account for some of the interesting shapes and colours we see, but if you look closely, it seems there are also some threads and bits of lint from Silke’s socks!  It might not be a scientifically valid sample, but I’ll take it!

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Sand: Dunkirk Beach

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.

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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:

  1. 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].
  2. 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.
  3. 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?
  4. 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.
  5. 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, environnement15(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. Geomorphology81(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 Conservation22(3), 457-474.

 

Sand: Nourishment at Ameland

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:

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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!

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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!

Sand: Tracer Sediment

I have spent many months holed up in the laboratory counting green grains of sand. Last year we dumped over 1 ton of fluorescent, magnetic tracer sand into the North Sea, where the waves and tides then scattered them along the coast. We then spent the following weeks circling around on a boat to try and find it all again. We scooped up over 200 samples of sand from the seabed, then brought them back to the lab for analysis. We used a super strong magnet and blue UV light to separate the tracer (bright green) from the normal sand (looks grey or purple under UV light). This part is REALLY boring because most samples don’t have any tracer but we still have to look hard for it . But then we get to look at all the sand under a fancy microscope, which is my new favourite toy! Under the UV light, the tracer reminds me of little green constellations of stars in a purple night sky.

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The tracers glow bright green under ultraviolet lights.  On the top left we have a jar of normal beach sand sitting next to a jar of tracer.  The distinction becomes clear once we place them under UV illumination (top right). This is especially important when we analyze samples taken from the seabed, where there may be only a few grains of tracer (bottom left). The fluorescent properties of the tracer help it stand out from normal sand (bottom right), which lets us count the individual grains.

Fortunately, we can use computers to count the individual grains and tell us their size.  With this information, we can estimate how the size of a sand grain determines how far and fast it will travel.  This is important for planning sand nourishments to protect the coast.

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If we can figure out where the green tracer did (or didn’t) go, that will tell us how normal sand moves around on the Dutch coast. And this will hopefully keep our feet dry here in Delft for a long time to come!

Sand: Sword Beach, France

Some really cool sand that my friend Claudia brought back from France. I especially like the purple shell fragments. This image is magnified 40x from the actual size. If anyone else goes to the beach on holiday, please bring me back some sand!

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Sword Beach is located on the coast of Normandy in northern France, and is also where the British landed on D-Day in World War II.

An Ode to the LISST

This is a poem about the Laser In-Situ Scattering and Transmissometry or LISST instrument, which we use for measuring sand and mud floating through the water.  I wrote it in response to a challenge to rap about what we learned during a workshop on estuaries last summer.  I had some fun with it so I thought I’d share…

And now a poem about the LISST
It is a great solution
To measure stuff that’s floating
And its grain size distribution

When processing your measurements
You must beware the floc!
Since if you don’t account for it
You’re in for quite a shock

If there seems like too much mud
We should have some suspicion
Before all else, we have to check
The optical transmission

“We have an awful lot of sand!”
Is this hallucination?
First thing’s first: we should have checked
Our background concentration

We sometimes see before our eyes
Large particles appearin’
When gradients of salt are high
It is the fault of Schlieren

So from the depths of Ameland,
A lesson that does matter:
When working with a fancy LISST
Don’t blindly trust your data!

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The mighty LISST: a Laser In-Situ Scattering and Transmissometry instrument, which shines a small laser through the water.  When the beam hits a particle floating by, it scatters and makes a unique pattern of light and shadow, depending on how large the particle is.  We can then interpret these patterns to estimate the size of the sand or mud that are floating through the water.