Reconstructing the peak flow of historical flood events using a hydraulic model: the city of Bath, United Kingdom

Historical flood events on the River Avon in the city of Bath were reconstructed using a 1D hydraulic model. The model represents the river prior to the completion of the Bath flood defence scheme and was developed based on archived data on archival materials including historical cross sections of channel geometry, technical drawings of hydraulic structures, descriptions of floodplain extent, epigraphic markings and photographs. The model was calibrated on two historical floods for which peak flow values were available from hydrological data (March 1947 and December 1960) and the calibration was based on adjustment of Manning's n as well as the introduction of floodplains identified from historical maps and photos. Subsequently, the peak flow was assessed for a total of 16 events for which flood marks existed in the centre of the city. A composite annual maximum series of peak flow was created upstream of Bath city centre and presented a flow series consisting of data from 1866 to present day. Finally, flood frequency analysis was undertaken on the dataset, showing that the inclusion of historical floods increased the 1 in 100 year design flood by up to 30%, that is, a substantial influence.