Combining historical documentary evidence and modern technological modelling techniques, Thomas Kjeldsen and Ioanna Stamataki will reconstruct the flow conditions during flash flood events
South West England has historically experienced severe and destructive flash floods. Notable examples include the Lynmouth flood of 15 August 1952, where 228 mm of rain fell in twelve hours, killing thirty-five people; the 10 July 1968 flood in the Chew Valley; and the 16 August 2004 flood in Boscastle where 200 mm of rain fell in five hours destroying several buildings and sweeping away cars and bridges. By their very definition, flash floods are localised short-in-duration phenomena, and the existing river gauging network rarely records the details of these events. Consequently, the only evidence left after an event is secondary in nature, such as flood marks left on buildings and bridges, photographic evidence, post-event surveys and newspaper reports. These events are of great importance to local communities, and there is considerable interest in the local history of these dramatic events.
The research proposed in this project will develop and test a new framework for reconstructing historical flash flood events. With an initial focus on an event on the River Chew in Somerset that occurred on 10 July 1968, we hope to test the framework on other flash flood events in the region. New data related to the River Chew event will be compiled, including witness accounts, site surveys, photographic and written evidence, newspaper articles, river flow and rainfall data. These disparate data sources will be combined into a hydraulic engineering river model to reconstruct and validate the flow conditions during the event, including an uncertainty assessment. The new insight into the hydraulic aspects of extreme flash flood events will potentially help better understand the flood risk exposure of communities across South West England. How to design more effective mitigation strategies in the future is vital, especially considering the anticipated increase in the frequency and magnitude of these types of events under a warming climate and the current increased pressures on our infrastructure.