Briefing: Impacts of Victorian engineering on a modern flood risk study

A strategic flood risk management (SFRM) study was undertaken for the heavily urbanised reaches of the River Medlock through Manchester, UK. Many of the buildings and structures on this reach date back to the Victorian era and the industrial revolution, when rapid growth of cities often focused on areas around sources of water for industrial and transportation needs. Key structures on the modelled reach include the Medlock Cloughs, a group of structures designed by Victorian engineers to actively manage water levels in the Bridgewater Canal and the Medlock. Further downstream at Potato Wharf, Giants Basin allows overflow from the canal to spill back into the river. A one-dimensional hydrodynamic model to represent the study reaches was built. Hydraulic modelling of the Medlock Cloughs and Giants Basin proved challenging for several reasons. It was not possible to verify existing survey data or to obtain new survey data because of health and safety issues. The study team was also unable to establish maintenance procedures on the structures or determine whether they now operate as intended by the Victorian engineers who built them. These obstacles were overcome by using old survey drawings, historic data and photographs in modelling the structure. The Medlock Cloughs component of the model proved crucial to obtaining accurate level and flow results for the modelled reaches, as the split in flows between the canal and river controlled the water levels upstream. The lessons learnt from this study may have application in assessing flood risk in other similar situations, and included the requirement for credible, accurate data for structures, and the importance of accurately representing, in a computational model, old structures that are no longer operating as intended.