Rapid Mapping of Urban Development from Historic Ordnance Survey Maps: an Application for Pluvial Flood Risk in Worcester

Between 2004 and 2008 the city of Worcester, UK experienced a number of pluvial flood events. The causes of this kind of flooding are the topic of ongoing research. This paper describes a study that aimed to investigate the urban development of Worcester over time in relation to the location of recorded pluvial flood incidents. A novel rapid mapping methods has been developed to derive urban development over five time periods between 1886 and 1995 from scanned Ordnance Survey historical maps. The technique compared well with manual digitization results with k-hat values ranging from 0.67 to 0.87 for the land use maps created for different time periods. The technique performed least well for the oldest map series, due to misclassification of the abundant symbols and annotation. The method will be particularly beneficial for investigation of town/city development in time over large areas. The resulting map of urban development in Worcester (scale 1:20,000) shows that almost half of the recorded pluvial flood incidents occurred in areas built up between 1956 and 1975, which contradicts local belief that an outdated (Victorian) drainage system causes most of the problems. The quality of the post World War II developments is more likely to be a source for concern.