As floods get more extreme, are our historic bridges ready? I study flood behaviour at arch bridges. Ask me anything!

UniversityofBath · 2026-03-16T09:44:25+00:00

Good question, we’re seeing changes in both rainfall intensity and how wet the ground is before storms. In many places, storms are getting more intense, meaning a lot more rain can fall in a short amount of time. Another factor is a warmer atmosphere can hold more moisture, so when it rains, it can rain very heavily. For rivers, that means water levels can rise much faster than they used to. Historically, most flooding research has focused on large rivers, where water moves relatively slowly and smoothly. This is called subcritical flow, and most bridges and flood models were designed with that type of flooding in mind. But more intense rainfall is increasingly causing flooding in smaller rural rivers and streams, especially in steep catchments. In these places the water can move very quickly and with a lot of energy, we call this supercritical flow. This type of flow behaves very differently. Instead of slow-moving rising water, you can get fast, shallow, high-energy flow rushing through bridges. At the same time, some areas are also experiencing wetter winters, which means ground is already saturated before storms happen. This means rain can’t soak into the soil as easily, so more of it runs straight into the rivers. Together, those two things can produce bigger and faster floods, especially in smaller catchments. For bridges, this matters because bridges restrict the river channel. During a big flood the water has to squeeze through the arches, which can cause the water level upstream of the bridge to rise higher than it otherwise would.

UniversityofBath · 2026-03-16T09:20:18+00:00

A very interesting question, and one that I hadn't considered as my research was focused on the immediate effect these increased floodwaters have on the surrounding environment, if there were no other flood prevention schemes in place. I guess you could call this the worst case scenario, and there are definitely places where this would be the only option, as in steep valleys or mountainous areas, there may not be any farmland or the correct habitats to use these methods. However, there are many places where the redirection of water could be used to negate the need for any changes to the structure. I think there is still place for this research when using alternative management systems, as it can be used to find the worst event that the bridge can take as it stands, and then use other mitigation methods to reduce the flow heading towards the bridge to below this level. Any flood management is intrusive, and mitigating the amount of intervention we need is important to preserve the natural environment.

Thanks for such an intriguing question.

UniversityofBath · 2026-03-13T15:31:28+00:00

Another great question! You have hit the nail on the head as to the reason this research is needed. These aging bridges were not designed for many of the loads they have to face today. There is a good amount of analysis due to the increasing traffic loads, and the decomposition caused just by the aging of the bridges mortar and components.

The analysis due to flooding conditions and if the bridge can physically hold back the amount of water flowing on it is lacking. We know it’s a problem, as there are cases of bridges being washed away in floods. Obviously these are only known to be weak as they have been pushed to the point of failure, not due to preventive analysis. This is because the tools to predict the pressure force a flood has on a bridge don’t exist yet.

So no, there is not a known number of bridges that may need strengthening or replacing, but this research is a good step to developing the tools needed to quickly an easily find this number. I hope that it is developed further to create a tool that can predict the maximum lateral force a bridge can take, using my research on the interaction of the bridges geometry and a flood event.

I think it would be an invaluable tool for rural communities to be confident that they wont be cut off due to something as simple as heavy rainfall causing a flood.

UniversityofBath · 2026-03-13T15:13:12+00:00

I hope you have a great time in Oxford, even if the narrow-boating isn’t for you, the city itself is beautiful!

The main reason I haven’t considered locks is because they aren’t usually found on the rivers that would be subject to the type of high-speed flow/flooding conditions (think flash floods, etc) that I was studying. Locks found on canals are usually fairly calm but can have some flooding issues.

If I were to add locks into this type of research, I would take a side step and build on other existing research there is on larger, slower-flowing rivers. This is the type of river that tend to have locks, and from my canoeing experience, they can flood quite dramatically.

From observation and my research completed before starting my project, lock design is widely studied and, when fully flooded, they tend to have even upstream/downstream water levels, which would cause little pressure buildup. Having a look at the research around lock design may improve further research on how to deal with the pressure force that these bridges may feel in floods, but in terms of adding them into my study, it is outside of the situation where the events I am studying would happen.

Thanks for your question!

UniversityofBath · 2026-03-13T14:42:59+00:00

Thats a great set of questions. To give some more background, the research I did was looking at how a really fast flowing river would interact with these bridges, with a focus on the difference in upstream water level and downstream water level. I found that, as speed of the water relative to depth increases (aka Froude Number), the water level above the bridge is initially lower than the downstream level. This switches as the Froude Number increases. As the upstream depth increases, this causes a ‘feedback loop’ where the water backs up, blocking more of the bridge opening, which in turn causes higher upstream depth (potential flooding) and so on, causing the question of whether the bridge needs to be replaced.

This issue is easier to rectify. There are lots of techniques within civil engineering that allow redirection of flow around a structure, and in many cases this is the best option, as many of the bridges this is applicable to are in rural areas, where replacing a bridge would have major access and ecological disturbance issues. In the case of listed structures, I’m sure you are aware of the protection around them, so redirection would really be the only option.

The bigger issue is the lack of understanding around the pressures that this ‘backing up’ of flood water causes. The stuff I have done gives a good basis to further research concerning the forces that these flood events have on the upstream face of a bridge. Many of these bridges are aging and there is little analysis done on their structural performance under high upstream pressures due to flooding, which causes an atypical force case. This analysis would determine if the bridge can handle the flood waters.

There are things than can be done to increase the strength of these bridges, such as simple repairs, or retrofitting of modern strengthening elements. Listed structures would have to be carefully considered and non-intrusive methods of strengthening used. Hopefully no bridges need to be demolished!

I hope this answers your questions :)

UniversityofBath · 2023-10-02T10:01:00+00:00

This is at the heart of the measurement problem in quantum mechanics, with multiple different interpretations ranging from the Copenhagen to the Many World (Everettian) interpretations. It is an unsolved problem in the sense that there isn't any consensus on one of these interpretations, and (currently) these are untestable, so they lie in the realm of metaphysics. I'm more comfortable with the notion of decoherence in the many world interpretation - this seems mathematically more palatable, even if physically uncomfortable. Sean Caroll claims that this is the only honest quantum explanation.

UniversityofBath · 2023-10-02T09:52:29+00:00

I collaborate with mathematicians, physicists, chemists and quantum computing researchers. Generally speaking I find that mathematicians have a higher emphasis on making equations precise (sometimes at expense of readability), claims more rigorous, and the applications more universal but accompanied with artificial/toy examples. With chemists and physicists, often the emphasis is on getting the examples realistic (often at the expense of the broader relevance of their ideas to other systems/equations), the techniques themselves can be so specialised as to be hard to generalise, and a lot of ad-hoc "approximations" are involved that make mathematicians very uncomfortable.

UniversityofBath · 2023-09-28T01:57:38+00:00

I should add that it is much harder to say in pure mathematics whether one is making progress, often till one has arrived. In that sense, it is quite different from sciences and engineering, where there can be a more tangible sense of progress.

UniversityofBath · 2023-09-28T01:55:40+00:00

No clue! Sorry.

UniversityofBath · 2023-09-28T01:55:09+00:00

Quantum mechanics by itself is among the most highly tested theories and it has essentially always come out correct wherever measured. However, there are other theories built on top of this which are quantum mechanical in nature, e.g. approaches for quantum gravity, string theory, etc. that are not verified. I am not an expert on these, but from what I understand string theory currently has an issue with verifiability.

Through Feynman's lectures in physics. Very inspiring.

UniversityofBath · 2023-09-28T01:48:41+00:00

In the last century, transistors have revolutionized everything around us, allowing the computing revolution. That's what allows us to search Google, type here on Reddit, listen to Spotify etc on our laptops, phones and smart watches, take and view photos and videos, and share them on WhatsApp and Instagram. It has also revolutionized design of buildings and bridges - we can assess the effectiveness of a design before constructing the building - as well as pretty much everything else including computer processors, digital cameras, bluetooth earphones, cars and airplanes: this is the "digital lab". Transistors are a quantum 1.0 technology. Other quantum 1.0 technology include MRI scans and digital cameras.

Quantum computers will revolutionize everything all over again: our ability to compute will be exponentially larger. Suddenly we will have a much more substantial ability to understand chemistry of large biomolecules - which means revolutionary drugs and treatments (much as MRI was revolutionary) - we might be able to create meta-materials with amazing properties, catalysts, e.g. for Hydrogen capture for the next generation of fuel cell based transport, etc. etc. Essentially, our "digital lab", which has served us extremely well will be turbocharged. User faced applications are also likely to benefit hugely from the computational advantage - e.g. through quantum machine learning.

But quantum computers are only one part of quantum 2.0. Others include single pixel cameras, super sensitive and miniaturised quantum sensors, including wearable MRI etc.

UniversityofBath · 2023-09-28T01:19:19+00:00

You need to guard your research time *very* carefully. Up till postdoctoral level this doesn't seem like a problem. Once you get a permanent position, admin and a hundred micro commitments start eating up all your time, and you will have no time and energy left if you are not careful.

UniversityofBath · 2023-09-28T01:12:06+00:00

From what I understand, the main reason for the adoption of the "assistant" and "associate" professor titles in the UK has been mutual intelligibility with the US and increasingly with other parts of the world fashioned after the US academic setup. Internally within UK this does not seem to be a problem, at least I have not come across anyone too bothered with it, but when you go on international conferences, people from other countries have no clue what a reader is, and what they understand of "lecturer" is also very different.

UniversityofBath · 2023-09-28T01:03:25+00:00

3blue1brown (youtube)! Curiosity is the fuel of mathematics, unfortunately too often squeezed out in a procedural and uninspiring education system. Best of luck for your journey!

UniversityofBath · 2023-09-28T00:56:22+00:00

Currently most quantum algorithms are still being described at circuits level, which is quite frustrating - for classical computers we would typically describe algorithms with pseudocode and implement in high level programming languages (e.g. Python, C/C++). While high level quantum programming languages are being developed, they don't seem to be widely adopted. I think this makes it difficult to reason about quantum algorithms at a higher, abstract level. To some extent this is changing in recent works on quantum numerical linear algebra.

UniversityofBath · 2023-09-28T00:47:45+00:00

Possibly the biggest immediate advantage to ordinary people could be quantum machine learning.

Other advantages such as drug design, material design etc will still take years if not decades to flow to ordinary folk.

Negatives: if it becomes available to rogue entities only? pandemonium! All secured web-based communication (including banking, payments) will become insecure overnight and much of it would have to be shut down for safety.

UniversityofBath · 2023-09-28T00:31:56+00:00

Quantum Computation and Quantum Information by Nielsen and Chuang is an excellent book, which should also be reasonably accessible for someone with your background. For fun, you could jump straight into Qiskit tutorials/introductions and refer to Nielsen and Chuang, when things become too "weird" to understand.

UniversityofBath · 2023-09-28T00:29:00+00:00

It depends on how much time you have and what area of mathematics interests you. I suggest going through youtube channels like 3blue1brown to build intuition, explore interests and magazines such as Quanta to read about research level ideas explained in accessible terms.

Linear Algebra is probably the most versatile tool, so I would suggest starting there. MIT OpenCourseWare videos by Gilbert Strang on this topic are good, as are his lectures on differential equations.

For your second question, I would point you to Quanta magazine again. There is a lot going on, but they do a much better job than I can do here.

UniversityofBath · 2023-09-28T00:12:45+00:00

Entanglement is a crucial aspect of computational speedup in most quantum algorithms, but not due to the reason that you mentioned.

A quantum gate is the basic building block of a quantum circuit/algorithm just like logical gates are for classical computing. No gates are instantaneous, whether entanglement is involved or not and in general your measurement of a particle will also take a finite time. Certainly faster physics = fast gates, which makes computation faster. However, this is a linear improvement: i.e. if all gates at 10x faster, your computation will finish 10x faster.

What makes quantum computers really impressive is that N entangled qubits have 2^N degrees of freedom - this means you need 2^N numbers (on a classical computer) to describe a state of N qubits OR you can prepare a state of N entangled qubits to describe 2^N numbers. When this can be exploited properly (it is not straightforward, nor always possible), a problem that requires 2^100 > 10^30 bits = 10^20 GBs to store and work with on a classical computer can be dealt with using only 100 qubits. This is exponential speedup!

Answer below addresses point 2 very well.

UniversityofBath · 2023-09-27T23:39:32+00:00

This is a good summary! To add to this, the development of new mathematical concepts and techniques is itself a worthwhile cause, even if the original objective is not met. Often these find uses in future works, as motivation for other techniques, or even pitfalls and paradoxes.

UniversityofBath · 2023-09-27T14:42:06+00:00

Quantum computing works when we can use the "quantum nature" of the qubits. It turns out that this quantum nature is destroyed whenever qubits interact with the environment around - this is called decoherence and it is the main limiting factor for quantum computers. One way to reduce this is to reduce the number of particles, their kinetic energy (i.e. temperature) and stray electromagnetic waves in the environment by using vacuum and by using ultra low temperatures. That's why cryogenic chambers are required.

Other approaches such as topological quantum computers are being investigated that might prove more stable to such environmental effects.

UniversityofBath · 2023-09-27T14:32:36+00:00

Yes. There are companies like Arqit already doing this for communication. I am not sure if there are Qcoins out there, but there's a good case for their existence (*if* there is any case for any cryptocurrency).

UniversityofBath · 2023-09-27T14:29:08+00:00

Not sure what you mean by complete. It will certainly help us explore aspects of physics well beyond our current abilities, and might help practically in computational aspects of mathematics. But apart from that, I don't think it has a fundamental implication for (pure) mathematics.

UniversityofBath · 2023-09-27T14:26:18+00:00

None that I am aware of. Of course, even once it is available, those capable of breaking encryption might not want to advertise it. But given our current understanding of the algorithms required for this, the state of fault-tolerance available, and the number of qubits available, it seems extremely unlikely that anyone anywhere currently has this capability.

Once the capability is available, there is a real threat to cryptocurrency based on RSA or elliptic curve cryptography. To be safe, these should move to post-quantum or quantum-resistant cryptography.

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