Podcast: Storm surges and their effect on coastal sand dunes

Damaged sand dunes

Damaged sand dunes

10 June 2014 by Sue Nelson

This week in the Planet Earth podcast, Joanna Bullard and Jonathan Millett of Loughborough University describe the work they're doing to find out how quickly sand dunes along the east coast of England recover from the erosion caused by massive storm surges - like the one that struck the UK coastline on 5 December 2013.

To assist those who find text-based content more accessible than audio, a transcript of this recording is available below.

Sue Nelson: This time in the Planet Earth podcast - how the coast recovers after the damaging effect of storms. I'm Sue Nelson and I'm on a beach in Mablethorpe, Lincolnshire, sand dunes behind me, a lovely beach ahead and the North Sea only one hundred metres or so in front of me. It's a very calm day today but only a few months ago this coastline was being battered by a succession of storms during a period of extreme weather. One storm on December 5th was particularly bad. It caused the whole of Scotland's rail network to shut down and a coastal surge along the East of England that resulted in flooding. For scientists, however, it was also an opportunity to study the effect on the coast itself, research that will also help coastal management and I'm joined by two of a team who are working here on this beach from Loughborough University. They are Professor Joanna Bullard and Dr Jon Millett.

Joanna, if we should start with you, what happened to this particular coastline in this region here after that infamous storm?

Joanna Bullard: Okay, well, in a way we were actually lucky because although it was a big storm surge and the water levels were very high, the storm wasn't quite as bad as it could have been. So, yes, it had a big effect on the coastline. So the dunes were eroded backwards by about 20 metres - so 20 metres of the sand dunes that you might sit on for your picnic in the summer were eroded and washed out to sea and it left a scarp about two metres high all the way along the coastline north of Mablethorpe.

Sue Nelson: Is there any evidence of that here now?

Joanna Bullard: Yes. What are we now? Six months on and you can still see part of the scarp. So, it's still a metre high or so in places but it is gradually starting to infill again with sand.

Sue Nelson: Now when that storm happened it was sort of an alarm call for you and you wanted to come here as soon as you could.

Joanna Bullard: We did, yes. We have long term field sites we wanted to see what had happened to them. So we came out the following day and we could see that there had been all this erosion and this scarp that had formed and so we went back to the university and we gathered our kit together and we came out and started taking measurements to see what impact the storm had actually had.

Sue Nelson: What sort of measurements are you taking? Obviously from what you were saying about the two metre ridge, you are measuring the height of sand.

Joanna Bullard: Yes we are. So, we have something called a terrestrial laser scanner, and it is basically a big box on a stand and we fire a laser around at the landscape and that helps us to record the shape of the landscape so we can capture the height and the steepness of the scarp and the bit of the beach that is missing because it's been eroded, and if you then come back a few weeks later and do another scan you can compare the two and you can see how much more has been eroded or how much materials has come back to replace what went missing.

Sue Nelson: Jon, you measure and map vegetation here. First of all, what sort of vegetation is surrounding us? To my uneducated eye - grass.

Jon Millett: Your uneducated eye is quite accurate. It is basically quite a simple vegetation type dominated by two types of grass. There's a grass called sea couch and a grass called lime grass. That pretty much dominates all of this part of the dunes and we also have a few shrubs, very, very spiny sea buckthorn and this is because it is quite harsh here the environment. They get washed over by the sea and they get battered by the wind and so there's only a few species that are able to survive in those conditions.

Sue Nelson: So when you're mapping the vegetation here, do you take a set area and take a note of exactly what is here and then continue to do it on a regular basis?

Jon Millett: We're more interested in not necessarily what the plants are but what they look like, because we're interested in how the plants function in this system rather than what they are. So we look at things like the growth form of the plant, the height of the plant and the cover of the plant, because that is what would be more important in effecting the changes in the dunes.

Sue Nelson: Because dunes play quite an important role in natural coastal defence, don't they?

Jon Millett: Yes, the dunes do and the vegetation might play a role in helping with that because the vegetation is involved in the accretion of the dunes and may also help to stabilise those dunes in some situations.

Sue Nelson: So what did you find out of the storms then and what difference had it made to the vegetation here after all those series of winter storms?

Jon Millett: Straight after when we came to look at this vegetation, the storm had stripped away the tops of a lot of the grasses here. You can see now it is quite green but when we came here all these nice green shoots were gone and we were just left with these bare roots or the old shoots that were buried in the ground. And as you can see they are recovering quite well so the grass is growing up again quite quickly. So we're trying to look at how the grass grows and what might effect how well that vegetation covers. So the ridge we're stood on now we can still see the grass is a bit barer and a bit browner, and because this was higher up it would have been more affected by the sea but it has still changed very quickly in the last few months so it is already recovering quite well.

Sue Nelson: In terms of recovery, Joanna, you tend to think of the effect of storms on a coast as eroding it, pushing it back. As you said before the sand dunes were pushed back 20 metres, but this coast is something of an anomaly isn't it because that's not generally what happens.

Joanna Bullard: That's not generally what this bit of this coast does, no. So, often we think of coastal erosion and we see cliffs falling into the sea and so on, but this stretch of the coastline, so between the Humber estuary and Mablethorpe is actually moving seawards, quite quickly, on average about two metres a year and it has been doing that for the past 150 years. Sometimes a little bit quicker and sometimes a little bit more slowly.

Sue Nelson: Is that typical of this area or does it happen around the UK, or is this a complete one off oddity?

Joanna Bullard: No, about 25 to 30% of the coast of the UK is moving seawards but because it is moving seawards we don't tend to hear every much about it because there's nothing dramatic to look at, it's just inching its way forward. But here what we've got immediately north of us, just north of the Humber is the Holderness coastline which is a rapidly eroding set of cliffs and they are retreating very quickly, but as they erode the sediment that comes out of the cliffs moves southwards and is what is causing this area of the coastline near Mablethorpe to actually move seawards. But if we go a little bit south of Mablethorpe so, I don't know, 500 metres south of where we're standing, the coast starts to erode again.

Sue Nelson: Gosh, that's amazing, that close together that that actually happens.

Joanna Bullard: It is and this time last year, well about April last year, there had been a lot of coastal defence work on the dunes at Mablethorpe and the whole lot got washed away by the storm, and over the past weeks the Environment Agency have come back to try and put that coastal defence work back in again and they stop at a very sharp line, so they are only protecting part of the coastline that is naturally eroding and they don't protect the part that is naturally moving seawards because, obviously, hopefully, the coastline will mend itself.

Sue Nelson: Now, you've been working on this site for ten years and you've got a new project that started only a couple of months ago that is being funded by the Natural Environment Research Council how is the measurements and the work that you and Jon and your team are doing here going to help with coastal management as a whole in this area.

Joanna Bullard: Well what we're hoping to find out is, if you think about the coastline moving seawards at two metres a year and if I then tell you that it has eroded 20 metres in one storm, we've effectively gone back ten years. So, what we're looking at is how long it is going to take to recover that ten years of advance and I can probably tell you now that it's not going to take ten years because there's been so much change over the past three months or four months or so, since the end of winter, that actually the coastlines are recovering much more quickly than we had expected it to.

Sue Nelson: So that's unexpected good news then?

Joanna Bullard: Yeah, absolutely, yes, for this section of the coastline. Where the eroding part is then obviously that's not quite so good, but for our area we're doing quite well and it's a natural nature reserve so it would be fantastic if it can recover and the plant diversity recovers as well.

Sue Nelson: Professor Joanna Bullard and Dr Jon Millett, thank you both for letting me see you in action researching the effects of storm surges on the coast here, on the beach in Mablethorpe, Lincolnshire. And that's the Planet Earth podcast from the Natural Environment Research Council. You can follow us on Facebook and Twitter where we will post some pictures of today's recording. I am Sue Nelson, thanks for listening.