BRIDGE – Cabot Institute for the Environment blog

Flooding in the UK: Understanding the past and preparing for the future

Posted on October 25, 2019April 3, 2023 by janet.crompton

On the 16th of October 2019, Ivan Haigh Associate Professor in Coastal Oceanography at the University of Southampton – gave a presentation on the “characteristics and drivers of compound flooding events around the UK coast” at the BRIDGE research seminar in the School of Geographical Sciences. He began by outlining the seriousness of flood risk in the UK – it is the second highest civil emergency risk factor as defined by the Cabinet Office – before moving on to the first section of the talk on his work with the Environment Agency on its Thames Estuary 2100 plan (TE2100)[1].

Thames Estuary 2100 plan: 5-year review

The construction of a Thames barrier was proposed after severe flooding in London in 1953, and it eventually became operational 30 years later in 1983. Annually, the Thames barrier removes around £2bn of flood damage risk from London and is crucial to the future prosperity of the city in a changing environment.

The Thames Barrier in its closed formation. Image source: Thames Estuary 2100 Plan (2012)

Flood defences in the Thames estuary were assessed in the TE2100 plan, which takes an innovative “adaptive pathways management approach” to the future of these flood defences over the coming century. This approach means that a range of flood defence options are devised and the choice of which ones to implement is based upon the current environmental data and the latest models of future scenarios, in particular predictions of future sea level rise.

For this method to be effective, accurate observations of recent sea level changes must be made in order to determine which management pathway to implement and to see if these measurements fit with the predictions of future sea level rise used in the plan. This work is carried out in reviews of the plan at five-year intervals, and it was this work that Ivan and his colleagues were involved with.

There is significant monthly and annual variability in the local tide gauge records that measure changes in sea level, and this can make it difficult to assess whether there is any long-term trend in the record. Using statistical analysis of the tide gauge data, the team was able to filter 91% of the variability that was due to short term changes in atmospheric pressure and winds to reveal a trend of approximately 1.5 mm per year of sea level rise, in line with the predictions of the model that is incorporated into the TE2100 plan.

Compound flood events around the UK Coast

In the second half of his presentation, Ivan went on to discuss a recent paper he was involved with studying compound flood events around the UK (Hendry et al. 2019)[2]. A compound flood occurs when a storm surge, caused by low atmospheric pressure allowing the sea surface to rise locally, combines with river flooding caused by a large rainfall event. These can be the most damaging natural disasters in the UK, and from historical data sets stretching back 50 years at 33 tide gauges and 326 river stations, the team were able to determine the frequency of compound floods across the UK.

Along the west coast, there were between 3 and 6 compound flooding events per decade, whereas on the east coast, there were between 0 and 1 per decade. This difference between east and west is driven by the different weather patterns that lead to these events. On the west coast it is the same type of low-pressure system that causes coastal storm surges and high rainfall. However, on the east coast different weather patterns are responsible for high rainfall and storm surges, meaning it is very unlikely they could occur at the same time.

Number of compound flood events per decade at each of the 326 river stations in the study. Triangle symbols implies rover mouth on West coast, circles East coast and squares South coast. Image Source: Hendry et al. 2019 [2]

There is also significant variability along the west coast of the UK as well, and the team investigated whether the characteristics of the river catchments could impact the possibility of these compound flooding events occurring. They found that smaller river catchments, and steeper terrain within the catchments, increased the probability of these compound flooding events occurring as water from rainfall was delivered to the coast more quickly. From the improved understanding of the weather patterns behind compound flooding events that this work provides, the quality and timeliness of flood warnings could be improved.

From the question and answer session we heard that current flood risk assessments do not always include the potential for compound flood events, meaning flood risk could be underestimated along the west coast of the UK. We also heard that Ivan will be working with researchers in the hydrology group here at the University of Bristol to further the analysis of the impact of river catchment characteristics on the likelihood of compound flooding events, and then extending this analysis to Europe, North America and Asia.

References

[1] Environment Agency (2012), “Thames Estuary 2100 Plan”.
[2] Alistair Hendry, Ivan D. Haigh, Robert J. Nicholls, Hugo Winter, Robert Neal, Thomas Wahl, Amélie Joly-Laugel, and Stephen E. Darby, (2019). “Assessing the characteristics and drivers of compound flooding events around the UK coast”, Hydrology and Earth System Science, 23, 3117-3139.

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This blog was written by Cabot Institute member Tom Mitcham. He is a PhD student in the School of Geographical Sciences at the University of Bristol and is studying the ice dynamics of Antarctic ice shelves and their tributary glaciers.

Tom Mitcham

Read Tom’s other blog:
1. Just the tip of the iceberg: Climate research at the Bristol Glaciology Centre

Climate-driven extreme weather is threatening old bridges with collapse

Posted on August 7, 2019April 13, 2023 by janet.crompton

The recent collapse of a bridge in Grinton, North Yorkshire, raises lots of questions about how prepared we are for these sorts of risks. The bridge, which was due to be on the route of the cycling world championships in September, collapsed after a month’s worth of rain fell in just four hours, causing flash flooding.

Grinton is the latest in a series of such collapses. In 2015, first Storm Eva and then Storm Frank caused flooding which collapsed the 18th century Tadcaster bridge, also in North Yorkshire, and badly damaged the medieval-era Eamont bridge in nearby Cumbria. Floods in 2009 collapsed or severely damaged 29 bridges in Cumbria alone.

With climate change making this sort of intense rainfall more common in future, people are right to wonder whether we’ll see many more such bridge collapses. And if so – which bridges are most at risk?

In 2014 the Tour de France passed over the now-destroyed bridge near Grinton. Tim Goode/PA

We know that bridges can collapse for various reasons. Some are simply old and already crumbling. Others fall down because of defective materials or environmental processes such as flooding, corrosion or earthquakes. Bridges have even collapsed after ships crash into them.

Europe’s first major roads and bridges were built by the Romans. This infrastructure developed hugely during the industrial revolution, then much of it was rebuilt and transformed after World War II. But since then, various factors have increased the pressure on bridges and other critical structures.
For instance, when many bridges were first built, traffic mostly consisted of pedestrians, animals and carts – an insignificant load for heavy-weight bridges. Yet over the decades private cars and trucks have got bigger, heavier and faster, while the sheer number of vehicles has massively increased.

Different bridges run different risks

Engineers in many countries think that numerous bridges could have reached the end of their expected life spans (between 50-100 years). However, we do not know which bridges are most at risk. This is because there is no national database or method for identifying structures at risk. Since different types of bridges are sensitive to different failure mechanisms, having awareness of the bridge stock is the first step for an effective risk management of the assets.

Newcastle’s various bridges all have different risks. Shaun Dodds / shutterstock

In Newcastle, for example, seven bridges over the river Tyne connect the city to the town of Gateshead. These bridges vary in function (pedestrian, road and railway), material (from steel to concrete) and age (17 to 150 years old). The risk and type of failure for each bridge is therefore very different.

Intense rain will become more common

Flooding is recognised as a major threat in the UK’s National Risk Register of Civil Emergencies. And though the Met Office’s latest set of climate projections shows an increase in average rainfall in winter and a decrease in average rainfall in summer, rainfall is naturally very variable. Flooding is caused by particularly heavy rain so it is important to look at how the extremes are changing, not just the averages.

Warmer air can hold more moisture and so it is likely that we will see increases in heavy rainfall, like the rain that caused the flash floods at Grinton. High resolution climate models and observational studies also show an intensification of extreme rainfall. This all means that bridge collapse from flooding is more likely in the future.

To reduce future disasters, we need an overview of our infrastructure, including assessments of change of use, ageing and climate change. A national bridge database would enable scientists and engineers to identify and compare risks to bridges across the country, on the basis of threats from climate change.

This blog is written by Cabot Institute member Dr Maria Pregnolato, Lecturer in Civil Engineering, University of Bristol and Elizabeth Lewis, Lecturer in Computational Hydrology, Newcastle University. This article is republished from The Conversation under a Creative Commons license. Read the original article.

Science and Sunflowers

Posted on August 7, 2017April 5, 2023 by janet.crompton

Sunflowerfest is an annual three-day festival of music and art held just outside Lisburn, Northern Ireland, priding itself on its family friendly atmosphere and sprawling spectrum of creative activities. Unlike the monster festivals that are held in other parts of the UK, in Northern Ireland our festivals are small (think a few thousand people, not a few hundred-thousand) with a strong focus on local talent. The perfect place for some experimental, creative science outreach…

In 2016, I contacted the organisers and floated the idea of a science outreach stall based upon my research and others in BRIDGE and the Cabot Institute. The idea, called Living Earth, was new, reasonably grand and completely untested. The response was a very enthusiastic “yes please!”

So, last year a squad of five outreachers (Alan Kennedy, Emily White and Michael Cooper of the Cabot Institute, plus Dewi Owen and Zuleika Gregory our puppeteers) arrived in blustery Northern Ireland and over the course of the festival recreated the entire history of Earth. 4.5 billion years in 3 days. With the help of punters at the festival, we built a 1.5 m diameter model of the Earth out of willow, foliage, recycled and craft materials. As the Earth was built, we recreated many of the major processes and events that shape it today, from the placement of the continents, the expansion of biomes and climate zones, the formation of the cryosphere and the destruction of the Anthropocene.

As well as this geological ‘Big Art Attack’, crafts and a puppet show entitled This Soup Tastes Funny! about the evolution of life were put on in the festival’s dedicated Kids Zone. Our puppets, Doug and Barry, had to travel back in time to the primordial soup and race through evolution in order to relive the first day of the festival. Five time periods, four puppet costume changes, asteroid impacts, crowd participation and even a song left the young audience both entertained, but also possibly very confused… That’s a lot of science to take on-board in 15 minutes!

We (and our marquee) got battered by wind, rain and the exhausting amount of activities we were juggling, including our recreational ‘time off’. However, we certainly offered something unique at the festival and left a positive impression with the organisers:

“Just to say THANK YOU to you and the crew for all the great things you did at Sunflowerfest. So appreciate everything you do and did. We would always welcome you back to do whatever you would like!” – Vanessa, Sunflowerfest Organiser

Now, I have quite an active imagination, so that last sentence was a dangerously open invitation… With 2017’s festival theme being ‘a parallel universe’, I thought something immersive on the theme of deep time would fit right in. The new plan was to build a time machine! Or in other words transform the inside of a marquee into a jungle, to show what Ireland would have been like during the hot Eocene period ~50 million years ago. As I wrote down a proposal for the festival application, this seemed like it would be reasonably straightforward compared to 2016. In hindsight, I misjudged that.

Logistically, constructing a jungle was only possible because my mum had recently had some trees in the garden felled and she also had several hedges needing cut back. A supply of logs and some waxy leafed laurel and bay that would hold their colour after cutting for the duration of the festival made a good, but somewhat bulky start. These were attached to the marquee ceiling and a heavy metal tripod to give us a central ‘tree’ and performance space to demonstrate some tectonic themed experiments. Ferns and other leafy plants were then dug up and temporarily housed in buckets to fill out the back of the tent and childhood toys added around the stall for the jungle fauna. Finally, a small speaker playing jungle sound effects was hidden up in the canopy to complete the experience.

Obviously, a hearty dose of imagination was required to convince yourself our locally sourced, temperate vegetation was an Eocene jungle, but luckily this year our stand was based entirely in the Kids Zone, where imagination is not in short supply. Ideally, I wanted to have a Superser heater in the back of the tent to raise the temperature to 35 °C, but doubted that would pass the risk assessment. We settled for having the ambient Northern Irish temperature, but luckily, we did have a few biblically heavy rain showers to give it a nice wet rainforest feel. It took three days of preparation, cutting, digging and replanting vegetation, and five hours of construction, but eventually we had the most eye-catching stand in the whole Kids Zone. It was pretty much the Eocene.

In our jungle, we had information about how Ireland has changed over the past billion years, a floating plate tectonics game and crafted fossils and jungle wildlife to decorate the stand, all of which kept us mostly run off our feet during our three-hour slots each day. Our flagship performance however, was a bicarbonate soda-vinegar erupting volcano, as ~50 million years ago Northern Ireland was at the centre of lots of volcanic activity, forming for example the Giant’s Causeway. Without a single trial run (we spent all of our preparation time building the jungle), our resident chemistry undergraduate, Oliver Feighan, carried out the experiment in front of an audience 40 strong. It was possibly the least explosive or inspiring volcano in the world. As the foam dribbled out the top of the bottle it was met with a slow and bemused round of applause. Those kids will definitely go on to be the environmental scientists of the future.

Creative outreach at big events may not always go quite to plan, it takes time and effort and you can sometimes bite off more than you can chew, but it’s a great way reframe the relevance of research in a totally different way, speak to a new audience (a very bohemian crowd, in the case of Sunflowerfest) and just do something fun. It’s not often families can experience palaeoclimate, tribal drumming circles and the Rubberbandits* all in one day. We ended up going on to run the globe building activity from 2016 at a further two events (you can see a highlight video of the almost finished piece here). Although kids and parents found 2017’s time machine a lot of fun and it looked surprisingly effective, unfortunately I don’t think I will have time or energy to ever recreate the Eocene again! However, while I may be leaving the Eocene in the past, I highly doubt this will be my last Sunflowerfest.

*Caution, likely explicit content

Blog post by Press Gang member Alan Kennedy.