The following blog post was contributed by WISE CDT student Ioanna Stamataki from the University of Bath who spent six weeks in University College London (UCL) undertaking her experimental work.
The last six weeks have been a bit of a blur – so intense and full of new experiences and knowledge that sometimes I am wondering if it actually happened. During my time in UCL, I was based in CEGE, the Department of Civil, Environmental and Geomatic Engineering at UCL, but I was using the shared Civil and Mechanical Engineering fluids laboratory based in Mechanical Engineering.
The experiment I conducted was an experiment to represent a simplified case of the Boscastle 2004 flash flood, where 200mm of rainfall accumulated in 5 hours and even though there were no casualties it caused severe damages. As very limited data exist in general from flash floods, a practical approach to initially generate flash floods, both numerically and experimentally, is by representing with a dam break failure. This guarantees the main characteristic features: rapidity of onset and rate of rise in level.
Thus, inside the impressive 20-meter long UCL’s flume, we replicated a dam break experiment on a sloped channel. An elevated box reservoir was built at the upstream end of the flume, separating the reservoir and the floodplain. The tank’s rotating gate was quickly released and the water was discharged on the six-meter long slope that had a 1/20 inclination. Downstream of the slope, different settlement complexities – representative of different urban textures – were tested, and impact forces, velocities and pressures on the buildings were measured. Important parts of the experiment were to capture the shape of the flood wave front before impact, understand the effect of parameters such as roughness and slope in order to obtain an overall appreciation of the dynamics of the flood propagation and the flow regime’s characteristics.
The first week when I arrived in the lab the main structure was already installed in the flume and we were setting up the instrumentation and making small improvements in the structure itself. Most of the time during those first few days I felt (and probably looked as well) lost and confused as everyone seemed to know what they were doing and what had to be done next. Funnily enough when my supervisor Dr Jun Zang came to visit a few weeks later she said the exact same thing- although this time I was in the technician’s side knowing my way around the lab and knowing what had to be done with very minimal communication (interesting what a difference a few days/weeks can make).
The next two weeks passed with finalising the experimental set-up as there were some issues with the connections in the slope that caused the wave to break before reaching the buildings, which would have resulted in a lack of repeatability of our experiment. But this was analysed, assessed and fixed after numerous attempts.
With the set-up ready, the following weeks were full of experiments. I conducted 2 sets of experiments with different initial water depths in the reservoir and different settlement complexities downstream. I measured the water level along the slope and around the buildings, the velocity of the front, the loads and pressures acting on the buildings, and monitored the filling up and release of the water in the reservoir. After this, in order to assess the effects of roughness and understand further the flow regime, fake grass (that looked more like a green carpet) was laid across the slope and some main small sets of experiments were repeated resulting to some interesting differences in the results.
I feel very lucky to have had this opportunity. I managed to obtain a very nice and complete set of data, which motivated me for the months to follow – it will all be data analysis for now but I am looking forward visualising it all. It is important to remember that experimental work is an amazing experience and the learning curve is steep. In a laboratory a lot of unexpected things can go wrong and remembering this is an important lesson. With that in mind, when planning experiments, taking into account twice the expected time is a good tip. I’m definitely looking forward to work in labs again in the future!
I would like to take this opportunity to thank the Department of Civil, Environmental and Geomatic Engineering at UCL and more specifically Dr Eugeny Buldakov not only for this opportunity but for his advice and involvement and of course Dr Dimitris Stagonas and the all the technicians, specifically Leslie Ansdell and Keith Harvey, for their irreplaceable help and know-how. Finally I would also like to thank my supervisor Dr Jun Zang for giving me the opportunity to meet and work with this amazing team.