Tag Archives: Arnside

Tidal bore in Arnside

Does that warning sign above (that I showed as a teaser in yesterday’s post on wave watching in and around Arnside) make you as curious as it made me?

Usually, water rises for approximately 6 hours until high tide is reached, and then falls again for another approximately 6 hours until low tide is reached. A tidal bore, however, is an incoming tide that behaves differently from what we typically see. In a tidal bore, rather than slowly rising, the leading edge of the tide comes as one wave shortly before high tide, so the tide raises extremely quickly. (SO OF COURSE I HAD TO SEE IT!!!!!!!!)

Because this can get very dangerous if you don’t expect this to happen, there are warning signs everywhere around Arnside, and a WWII air raid siren is sounded twice before the bore arrives (that’s what you will hear when you play the video below!)

There is a lot of conflicting information out there on when to expect the bore. Why is predicting of the arrival time of the bore so difficult? While tidal forcing by the moon, the sun, and tons of other things is known very accurately, a tidal bore more than a “normal” tide is influenced by other factors, especially the wind, and the shape of the estuary and thus changes in friction (which changes constantly, see yesterday’s post).

And not only don’t we know exactly when the bore will arrive relative to predicted high water times, there is a lot of conflicting information out there on when the siren in Arnside is sounded relative to the bore. To be safe, I had to take the most conservative approach to make sure we didn’t miss it. Luckily, Astrid and Felipe were willing to wait with me for a looong time to see the Arnside tidal bore, even though none of them was really keen on it! Always important to have patient friends ;-)

Anyway, once the tidal bore arrives, it is super spectacular (I think!). We weren’t there on one of the recommended days — high tide was only 8.4 meters and locals tell you to not bother for anything below 10 meters — but I still thought it was so impressive! The video below shows it at 8 times its actual speed to give you a quick first impression:


And here are the most interesting 3 minutes of the bore when it passes right in front of us. So cool how there is actually a wave trough right before the leading edge of the bore!

And once the front has passed, this is far from over! Once the front has passed, the calm waters of the estuary are replaced by a strong current running upstream relative to the river’s original direction of flow, now quickly raising water levels all throughout the estuary. And not only that: Also very interesting flow pattern, some of which are shown in the video below.

After the front had passed and we were walking back into town, we met a couple of very excited people who had absolutely no idea what just had happened and who were all “I HAVE NEVER SEEN ANYTHING LIKE THIS! WHAT WAS THIS???”. Remember, this is what the estuary looks like before the bore arrives: lots of mud, very little water. Hardly any waves. So having the bore come in — when you’ve been waiting for it for 90 minutes, but probably even more so when you aren’t expecting anything at all — is really really impressive. And it makes you realize that they aren’t kidding when they tell you about extreme danger due to fast rising tides… Imagine water filling up all the channels at that speed — you’d be cut off from shore extremely quickly, and then separated from the shore by really strong currents. So it’s an amazing spectacle to watch, but one that one should definitely not underestimate!

Wave watching in and around Arnside

Arnside is a beautiful little town on the banks of the river Kent, and Astrid and I went on a nice hike along the shores of the estuary a little while ago.

The difference between high water and low water is quite impressive here, and we started our hike right after high tide to make sure we wouldn’t be cut off by an incoming tide. Which was definitely the safest thing to do, but also made for pretty muddy shoes…

There is a ton of amazing wave watching to be done in the Kent river bed. For example the waves being diffracted around these rocks.

Or this diffraction at a “slit” between the rocks.

And the whole landscape is just gorgeous!

Very intriguing to me: A foam stripe that seems to be coming out of nowhere. Or, better, that we can’t see the cause of just yet. It’s coming from somewhere downstream (to the left).

But where is it coming from? From somewhere behind that headland. Let’s go inquire!

A little further down the coast line, we see that the foam stripe ends on a sandbank.

And coming closer still, we see that the foam is created by waves breaking on that sandbank and a second one a little further offshore. It gets collected where the bank brakes the water surface, and is then just driven downwind, but stays together, forming the stripe.

This is a closer look of the waves breaking on the sand banks.

And speaking of sand banks: There is some cool wave action in between the sand banks, too! Waves are driven in by the wind through the channel from the left. This is  a clearly visible wave field with larger wavelengths and heights than the rest of the small basin, where waves are only created locally once the wind reaches the water surface. See how on the left edge of the basin the water is sheltered from the wind by the higher edge of the sand bank?

Again, what a pretty landscape!

I really like the contrast of the lush green grassy areas and then the sandy muddy tidal river in the background.

Walking a little further, we now see a large muddy area. When we were walking here, a local told us that when he was a kid, all this area was also grass land and it only became sandy and muddy a couple of decades ago. Fascinating how the landscape changes!

But even on timescales of hours the landscape changes, and all the sandbanks and channels move with each incoming and outgoing tide.

It’s so beautiful here!

Our walk took us away from the water and up a little hill, but that gave us the opportunity to look at the channels from a different perspective.

And even the whole estuary. Do you see the rail bridge below? That’s the one we saw in the very first picture of this post.

Back in Arnside, we are approaching low tide. Which means that we have lots of freshly exposed mud with new ripples in it, as well as still water running off it. Below you see a really cool turbidity current coming out of the channel with the seagull, going into the larger reservoir. See how it carries mud with it and how the channel is meandering and clearly changing right in that moment?

Another picture, just moments later, and already has the shape of the channel changed!

Or the edges of this little basin that get exposed little by little as the tide goes out.

And then there is of course more wave watching to be done. See how this wave changes direction as it runs around the little headland?

Soooooo pretty!

And thanks to two kids playing in the water, we get even more waves where they threw a ball into the little basin.

And those waves spread over time…

Checking in with the seagull and the turbidity current again. See how much dissolved mud is being washed out all the time?

And as you might have guessed in a tidal river like river Kent — there is even more to see. Which is why we came back a couple of days later to see what all the warning signs were about…

I’ll tell you about that tomorrow!