Flood and Drought: The Challenges of Seasonality in the Operation of Rome’s Sewers, 1870-1900

In nineteenth-century Rome, heavy rains were common, particularly during the autumn. The average depth of rain in Rome during the period 1862-1877 was greater than, for example, London. In Rome there were, however, huge seasonal fluctuations in this value. There was a considerable difference in rain content between the wettest and the driest month of the year, and sometimes extremely heavy rains concentrated in just a few hours. These variations between dry summers and wet autumns/winters presented challenges to the Hydraulic Service of Rome. Since 1870, the city has experienced rapid urban growth accompanied by a process of renewal and building of new vital infrastructure, such as combined sewers, which were intended both to drain the city and to remove the city’s sewage. It was, however, challenging to integrate these two different tasks into a fixed infrastructure in a city with vast seasonal variations in water flow. Rome’s sewers, at times, struggled to cope with the overabundance of water during autumn and winter days with consequent flooding of the lowest parts of the city as pure water was flushed throughout the network to remove waste and sewage during the summer. The paper concludes that the engineering model underlying the construction of Rome’s combined sewers was derived from the experience of cities with a different climate, such as Paris and London, but proved less effective in the context of a Mediterranean city.