Abstract/Summary

This thesis is concerned with the hydrology of the River Walbrook and its influence on Roman London. The Walbrook had a small catchment (4.7 km2), most of which was rural in the Roman period, and flowed to the Thames through urban Roman London. The research is based upon data abstracted from reports, plans and sections of seventy archaeological investigations in the urban Roman Walbrook Valley, supplemented by archaeological literature, maps, boreholes and modern data. A methodology specifically developed for the research is described and hydrological descriptors of the Roman Walbrook and catchment are recreated, as they would have been 2,000 years ago, for a river that has not flowed for at least 400 years. A mean base flow rate of the river in the Roman period of 87 litres/sec is derived by means of a surrogate river analysis. An analysis of geoarchaeological data using GIS (Geographic Information System) is used to re-create the pre-Roman and late Roman land surfaces and to define the course and bed slopes of the river through urban Roman London and hence its flow-full capacity. A storm flow regime is derived and used to assess flood frequency for key areas within urban Roman London for a range of 36 channel conditions. In the flat northern urban area, flooding would have occurred more than once a year and somewhat less frequently in the other areas. The effectiveness of Roman land-raising activity and river management to reduce flooding is assessed and indicates limited success until completion of the town wall in 220 CE that acted as a flood control device. The counter-intuitive siting of industry in the northern suburbs, in spite of marshy conditions and frequent flooding, is examined. The beneficial use of the Walbrook, by industry, including milling, farming and for water supply and rituals, is also discussed in the context of its hydrology.