Urban flooding in Britain: an approach to comparing ancient and contemporary flood exposure

T E O’Shea,J Lewin

doi:10.1007/s11069-020-04181-8

Abstract

Using modified UK Environment Agency Flood Estimation Handbook techniques, inundation extent and likely flood hydrographs for 0.1% probability annual return periods are compared for twelve Roman town sites in the UK, both at the present day and for simulated Roman catchment conditions. Eight of the study sites appear to have suffered minimal urban flood liability as occupied in the Roman period. The exceptions were Canterbury, York, Leicester, and Chichester. It is reasonable to expect flood characteristics to have changed subsequently in response to transformations in catchment land use, urban expansion, wetland reclamation, and floodway engineering. However, modelling results suggest limited differences in flood flows attributable to such factors. Greater present-day urban damage liability essentially results from floodplain urban extension. There are also contrasts between sites: those Roman towns lying on floodplains themselves, rather than on slightly elevated terraces (Canterbury, Chichester), are dominated by groundwater regimes with attenuated flood peaks. Taken together, these results suggest some Roman awareness of the actualities of urban flood liability at the time. Site sensitivity has not been carried forward as urban expansion has flourished, especially from the nineteenth century with suburban and industrial expansion. The straightforward mapping approach here suggested should in future take account of multiple century-scale hydroclimatic changes, morphological river channel and floodplain transformations over similar time periods, and on-going improvements to inundation modelling.

Highlights

The cores of many UK urban towns and cities date back to Romano-British and Saxon times (Russo 1998)
Were Roman settlements elsewhere in Europe really sited to be consistent with flood risk?
We address different challenges: did extreme floods inundate historically developing urban areas? Were early urban developments well sited with respect to flooding? And, in the absence of records, is it possible to infer awareness of flood liability at such times? if early sites were relatively secure, does present-day flood liability reflect a change in flood frequency and magnitude resulting from historical catchment changes or changes in climate, or is increased risk a function of later incautious historical urban spread? To answer such questions, an exercise in flood modelling and flood extent mapping has been undertaken for a representative selection of twelve important Roman town sites in the UK, most of which have later developed into major towns and cities (Fig. 1 and Table 1)

Summary

Introduction

The cores of many UK urban towns and cities date back to Romano-British and Saxon times (Russo 1998). Natural Hazards (2020) 104:581–591 established at Verulanium related to a prior native settlement, and possibly at other sites; numerous civitas were established as local tribal capitals (mostly on the sites of strategically-placed Roman forts); and there were vici, small towns of which some eighty are known. Many of these declined or were abandoned in post-Roman times, but were subsequently redeveloped, with the further addition of wics (trading and industrial centres that developed into places like present-day Ipswich and Southampton) in Anglo-Saxon times. Were Roman settlements elsewhere in Europe really sited to be consistent with flood risk?

Methods

Results

Discussion

Conclusion