Tag Archives: flooding

Below Sea Level does not mean Below the Sea.

This post represents my own views and is not intended to represent the views of my employer, present or past.

I’ve been umm-ing and ah-ing for a couple of months now about whether to write this blog, but I think I have finally had enough. You see, in Hull, we are at risk of flooding from the sea, or more specifically, the Humber Estuary. This risk emerges when low pressure out in the North Sea, caused by the storms, which can be common in the winter, effectively suck up the sea causing it to raise a little. High winds whip up waves, and these add a little more height to the water. All of this has the potential to raise the level of the sea, for a few hours, by up to a couple of metres. On December 5th 2013, a storm surge (as these events are called) raised the water level in the Humber by 1.7 metres.

The added complexity to this are the tides. The difference in the water level between low and high tide at Hull, according to the Associated British Ports (ABP) is between 3.5 m for a neap tide, and 6.9 m for a spring tide – this staggers the level we have determined to be 0 m, or sea level. This means the risk of flooding is all a matter of timing. If, on December 5th 2013, the storm passed by a few hours earlier or later the surge would have aligned with the low tide, and the additional 1.7 m would have barely been noticed by anyone. However, it was timed with a high spring tide, resulting in record water levels in the Humber and caused flooding in Hull and around the Estuary.

Coastal flooding

Graphic showing how coastal, or tidal, flooding forms. This was the type of flooding which occurred around the Humber in 2013. Thanks to NERC for producing these great resources. 

When we design and build flood defences on the coast we don’t build them to just hold back tidal levels of the water, but also to defend against enhanced water levels produced by storm surges. Since 2013, the defences around Hull have been updated and a repeat of the event would result in little or no flooding in the city – I don’t know the exact level of the defence, but we can say that it is able to contain sea levels of at least 1.7 m higher than the highest natural tidal level.

A big issue facing Hull is sea level rise. Sea level has been rising since the end of last ice age, and is set to continue in the future. On top of this, the climate change caused by our industry is accelerating this. Our best estimates for the Humber area, assuming that as a species we continue increasing our influence on the climate, suggest the sea level will be around 1 m higher in 100 years than they are today – this will increase the risk of flooding and we need to ensure that the public understand this and that we continue to invest in improving the standards of our defences to keep pace.

On the first point, talking to residents of Hull about the risk of flooding from the Estuary provokes two responses. (1) There is a lack of appreciation of the risk from the Estuary, and when I start to talk about the 2013 flooding, people tend to share with me their experiences of the 2007 flooding (a surface flooding event). (2) People tend to feel that there is no point in doing anything as “Hull will be underwater in 100 years”. This latter point is what I want to discuss here, it’s a common perception and leads to a kind of apathy where people become disengaged with flood risk and actions to mitigate for it, but it is wrong.

It is a deeply held belief that goes beyond even the city – in 2015, Dr Hugh Ellis, the now Head of the Town and Country Planning Association (TCPA), made the claim that the city would be underwater in 100 years –

“We need to think about moving populations and we need to make new communities. We need to be thinking, does Hull have a future?” (Source – Daily Telegraph)

Ok, he was trying to make a valid point, one that sea level rise is going to increase the risk of flooding for coastal cities, but I don’t think bold, and inaccurate statements, like this are helpful, and they only result in residents of the areas becoming disengaged – why do anything about the problem if it is futile?

But where does this idea come from? Why are people convinced Hull will be underwater in 100 years? Why do people think it will become the “Venice of the North”? Well, look at the map below –

surging seas

Screenshot from Climate Central’s Surging Seas Risk Zone Map – this shows the Humber Region, UK, with a 1 m sea level applied.

This is map of ‘risk’ taken for the Humber area. For areas outside of the US, the Risk Map has been produced using a map of land heights obtained from space by the Shuttle Radar Topography Mission, which mapped the entire globe at resolutions between 30 m and 90 m. The areas shaded in blue are all those ‘below sea level’ – normally 0 m, but in the map above I’ve set it at 1 m to represent the predicted sea level in 100 years time. Hull isn’t labelled on that map, but it basically the large blue area between North Ferriby and Hedon – very clearly ‘under water’.

But the method is problematic, it’s too simple. An average measurement of land heights over a 30 m area is fantastic when considering it is for the whole planet, however for determining flood risk it’s a bit rubbish. It smooths the land surface, removing obstacles, like wall, roads and buildings, and crucially, flood defences. The method also ignores ‘hydraulic connectivity’*, basically meaning that for water to flood an area it has to have a source of water and a route for it to get there – flood defences work by removing this hydraulic connectivity and this is why today the Humber region, and much of Holland, is close to or below sea level, but not under the sea.

To understand the actually risk posed by sea level rise requires a more complex model, one which accounts for tides, contains more detailed data, and more importantly includes flood defences. Our model (paper here behind paywall) does this, and a version of it is incorporated into Humber in a Box – with both of these we observe no flooding around the Estuary for natural tides with a 1 m sea level rise. This is because the defences are built to hold back the much higher water levels caused by storm surges.

Climate Central have been careful to refer to this shading as ‘risk’, and not direct inundation by the sea, but the use of blue and not making this explicit anywhere opens this up to mis-interpretation where ‘below sea level’ means ‘below the sea’. This is clearly happening – see this article in the Conversation, which made the BBC Sports pages, which used the app to suggest Everton’s new stadium “could end up underwater” in the future, or this article shared by the awesome Geomorphology Rules  Facebook page, suggesting that coastal cities in the US will be “drowning in water”.

Sea level rise is going to increase the risk of flooding in coastal cities but they are not going to be under water. The risk does not emerge from the tidal water levels, which will most likely be contained by present defences, or those to be built in the future. However, the risk from storm surges will increase – the likelihood of events like December 5th 2013 is set it increase, both in strength and frequency, and with 1 m extra sea level in 100 years our defences will need to be updated to cope with the enhanced levels. This will take a lot of money, a lot of effort, a lot of political will, and this requires the buy in and support of the residents of these areas. Telling them, or suggesting, that they will be required to relocate will only achieve the opposite.

Sea level rise and the related flood risk is a complex issue and we can’t keep trying to find simple answers.

*For areas within the US, the method uses much higher resolution height data, and accounts for hydraulic connectivity by shading areas differently.

Find me at #EGU17

It’s almost time to go to Vienna again for the 2017 General Assembly of the European Geoscience Union, or #EGU17. It’s promising to be another awesome week of science, schnitzel, and the collection of cold bugs from around the globe. Incredibly, it will be my fifth EGU, and I have the pleasure of being joined by a couple of first-timers from my research group – I’m looking forward to showing them the ropes.

I have two oral abstracts and a poster at this year’s meeting –

EGU2017-15699 | Orals | GM3.3/SSS3.13/TS4.6

LEMSI – The Landscape Evolution Model Sensitivity Investigation
Christopher Skinner, Tom Coulthard, Wolfgang Schwanghart, and Marco Van De Wiel
Wed, 26 Apr, 16:30–16:45, Room N1

This talk will show the results from our global sensitivity analysis of the CAESAR-Lisflood model. This has been a large piece of modelling work, and seems to have been going forever. Our computers have been busy for well over a year, so it’s great to get the results out there.

EGU2017-12624 | Posters | GM3.3/SSS3.13/TS4.6 | | Highlight

Influence of Rainfall Product on Hydrological and Sediment Outputs when Calibrating the STREAP Rainfall Generator for the CAESAR-Lisflood Landscape Evolution Model
Christopher Skinner, Nadav Peleg, and Niall Quinn
Wed, 26 Apr, 17:30–19:00, Hall X2

This poster has been selected by the session conveners as being of public interest. We’ve used a rainfall generator to produce ensembles of high spatial and temporal resolution rainfall, and used this to drive the CAESAR-Lisflood model – the results are very interesting indeed!

EGU2017-764 | Orals | EOS5

SeriousGeoGames – Geoscience Virtual Reality Experiences for Festival Settings
Christopher Skinner
Thu, 27 Apr, 10:45–11:00, Room L4/5

My final talk is something a little different, and will be summarising the SeriousGeoGames project the best I can in 12 minutes! I will show a little of Humber in a Box and Flash Flood!, and sum up their successes. For a preview, check out the brand new Flash Flood! YouTube Free60 –

 Please do come find me and say “hi”, or “Oi, your research is rubbish”, and if you have something you think I should see, let me know.

See you in Vienna!

Storm Surge Jan 13th 2017- Stay Alert This Evening.

It’s 6.45 AM as I’m writing this, listening to Radio Humberside and watching the snow fall on my garden in Barton-upon-Humber. For the past hour I’ve been following the news, updates from Twitter, and the reporting from live tidal gauges, trying to get an idea of the materialising image of this storm surge.

A storm surge occurs when low atmospheric pressure during storms causes the sea level to rise. This is because the low pressure draws up the water level. This is a basic explanation, but a 1mb reduction in atmospheric pressure will result in a 1cm increase in sea level. On top of the sea level increase caused by this, storms are usually windy and whip up significant waves, adding further level to the water.

To cause flooding, a significant surge needs to coincide with a high tide, usually a high spring tide like we are experiencing at the moment. If the surge coincides with the low tide, it results in nothing more than an unusually high low tide level but is not a risk. This page from the MetOffice provides a great description of them.

This combination was what drove the warnings for flooding along the East Coast of England this morning. Fortunately, the flooding feared did not occur. It is important for me to be very clear now that the main risk, and the flooding warnings for today, refer to the tide this evening – keep listening to the Environment Agency, do what they say, and keep an eye on their warnings here

From the National Oceanographic Centre we can see forecasts for storm surges at tidal gauge sites. Below are the forecasts for today for the Immingham gauge – the peak surge is forecast to be over 2m. If this was to occur with the high spring tide due at Immingham this evening, over 7.4m, it could produce water levels in excess of 9.4m which would be higher even than 2013. Thankfully, the peak of the surge is forecast to occur prior to the high tide. This has happened numerous times in the past, where large surges have coincided with low tides.

surge-forecast

This does not mean there is no risk by any measure – the water levels this evening will be higher than this morning. This forecast could turn out to have predicted the timing wrong. Surges can also have the effect of drawing in the high tide, causing it to occur slightly early as demonstrated by Horsburgh and Wilson (2007) (Paywall). The winds forecast also did not occur this morning but the could arrive during the day, adding to the waves.

Storm surges are complex, with numerous facets combining to cause the risk. This makes them difficult to forecast and can evolve and change quickly. The Environment Agency have done a superb job is warning and preparing these past few days and should be commended for this work. It is also encouraging to see the greater appreciation for tidal flooding risk from the media and the public – awareness is vital component in reducing the dangers of flooding.

Stay alert and stay safe.

Another Storm Surge? Keep your eye on the forecasts!

There are warnings emerging of a storm surge along the East Coast of England for this Friday (13th January 2017). At the time of writing these are a low risk warning, but the situation can change so keep your eyes open for updated warnings from the MetOffice and Environment Agency, such as the Flood Information Service.

If you’ve read this blog before you will know that I have performed plenty of computer model simulations of the 2013 storm surge in the Humber Estuary. Thankfully, it does not look like this Friday’s surge will result in flooding, and not on the scale of 2013, but I thought I’d share a simulation of the latest model anyway. This is a simulation of the 2013 storm surge –

There still, as ever, more work to do but it’s getting there.

OTD Humber Storm Surge – 05/12/2013

No score and three years ago the storm surge of December 5th 2013 swept along the East Coast of England, and the Humber Estuary. There was flooding in Grimsby and Hull, and the port at Immingham was also badly flooded. One of the worst affected areas of the village of South Ferriby on the South Bank of the Humber, a few miles away from my home town of Barton-upon-Humber.

Since the event, my colleagues and I have done a lot of research and work based on this event. This post will briefly highlight some of this, how you can find out out more, and what we have planned for the future.

IMG_3862

At the time I was working on a project called Dynamic Humber helping to develop the CAESAR-Lisflood model. Although the original intention was to use the model to predict long-term geomorphic trends in the Estuary, basically how we can expect the mud and sediments to move and change over time, the storm surge changed the focus to flood risk.

We published our work on this in early 2015 – see the academic paper here.

The modelling technique was developed for other areas by my colleague Jorge Ramirez, and this research can be seen here.

This research led to us using our modelling to help the Environment Agency, and this work is ongoing still. We are also seeking to further the work of simulating the sediment processes within the Estuary,and understanding how this might influence future flood risk.

IMG_3816

One of the enduring images of the event was the breach it punched in the spit-like feature at mouth, Spurn Point. For nearly two centuries Spurn has essentially been a man-made structure, and its origins, true nature, and hence its future, are largely a mystery. Read more on this here.

In Easter 2015, a PhD project was begun to try and model the future of Spurn Point, merging a model of the North Sea with our model of Humber.

Finally, SeriousGeoGames emerged as a direct consequence of this event and our modelling of it. The first application, Humber in a Box, shows a simplified version of our Humber model in an attractive, immersive, virtual reality environment. By raising the sea level we can see how flood risk in the Estuary is likely to change over time.

Humber in a Box

If you have a Cardboard-style headset, try the YouTube demo here.

I’m currently working with some talented students from SEED Software on the second iteration of Humber in a Box, called TideBox. We hope to make the application more ‘self-led’ and more generic about estuaries and tide, making more accessible.

There are likely to be lots of exciting developments in 2017 and I will bring you them as soon as I can.